Gradle User Manual
Version 4.5.1
Copyright © 2007-2018 Hans Dockter, Adam Murdoch
Gradle build tool source code is open and licensed under the Apache License 2.0 . Gradle user manual and
DSL references are licensed under Creative Commons Attribution-NonCommercial-ShareAlike 4.0
International License .
Table of Contents
About Gradle
Introduction
Overview
Working with existing builds
Installing Gradle
Command-Line Interface
The Gradle Wrapper
The Gradle Daemon
Dependency Management for Java Projects
Executing Multi-Project Builds
Continuous build
Composite builds
Build Environment
Troubleshooting
Embedding Gradle using the Tooling API
Build Cache
Writing Gradle build scripts
Build Script Basics
Build Init Plugin
Writing Build Scripts
Authoring Tasks
Working With Files
Using Ant from Gradle
Build Lifecycle
Logging
Authoring Multi-Project Builds
Using Gradle Plugins
Standard Gradle plugins
The Project Report Plugin
The Build Dashboard Plugin
Comparing Builds
Publishing artifacts
The Maven Plugin
The Signing Plugin
Ivy Publishing (new)
Maven Publishing (new)
The Distribution Plugin
The Announce Plugin
The Build Announcements Plugin
Dependency management
Introduction to Dependency Management
Declaring Dependencies
Declaring Repositories
Inspecting Dependencies
Managing Transitive Dependencies
Working with Dependencies
Customizing Dependency Resolution Behavior
Troubleshooting Dependency Resolution
Extending the build
Writing Custom Task Classes
Writing Custom Plugins
Gradle Plugin Development Plugin
Organizing Build Logic
Lazy Configuration
Initialization Scripts
Testing Build Logic with TestKit
Building JVM projects
Java Quickstart
The Java Plugin
The Java Library Plugin
Web Application Quickstart
The War Plugin
The Ear Plugin
The Jetty Plugin
The Application Plugin
The Java Library Distribution Plugin
Groovy Quickstart
The Groovy Plugin
The Scala Plugin
The ANTLR Plugin
The Checkstyle Plugin
The CodeNarc Plugin
The FindBugs Plugin
The JDepend Plugin
The PMD Plugin
The JaCoCo Plugin
The OSGi Plugin
The Eclipse Plugins
The IDEA Plugin
The Software model
Rule based model configuration
Software model concepts
Implementing model rules in a plugin
Building Java Libraries
Building Play applications
Building native software
Extending the software model
Glossary
Dependency Types
Repository Types
Appendix
A. Gradle Samples
B. Potential Traps
C. The Feature Lifecycle
D. Documentation licenses
List of Examples
1. Excluding tasks
2. Abbreviated camel case task name
3. Obtaining detailed help for tasks
4. Information about properties
5. Running the Wrapper task
6. The generated distribution URL
7. Providing options to Wrapper task
8. The generated distribution URL
9. Executing the build with the Wrapper batch file
10. Upgrading the Wrapper version
11. Checking the Wrapper version after upgrading
12. Customizing the Wrapper task
13. The generated distribution URL
14. Specifying the HTTP Basic Authentication credentials using system properties
15. Specifying the HTTP Basic Authentication credentials in distributionUrl
16. Configuring SHA-256 checksum verification
17. Declaring dependencies
18. Definition of an external dependency
19. Shortcut definition of an external dependency
20. Usage of Maven central repository
21. Usage of JCenter repository
22. Usage of a remote Maven repository
23. Usage of a remote Ivy directory
24. Usage of a local Ivy directory
25. Publishing to an Ivy repository
26. Publishing to a Maven repository
27. Listing the projects in a build
28. Dependencies of my-app
29. Declaring a command-line composite
30. Declaring a separate composite
31. Depending on task from included build
32. Build that does not declare group attribute
33. Declaring the substitutions for an included build
34. Depending on a single task from an included build
35. Depending on a tasks with path in all included builds
36. Setting properties with a gradle.properties file
37. Specifying system properties in gradle.properties
38. Setting a project property via gradle.properties
39. Setting a project property via environment variable
40. Changing JVM settings for Gradle client JVM
41. Changing JVM settings for forked Gradle JVMs
42. Set Java compile options for JavaCompile tasks
43. Prevent releasing outside of CI
44. Configuring an HTTP proxy using gradle.properties
45. Configuring an HTTPS proxy using gradle.properties
46. Using the tooling API
47. Configure the local cache
48. Pull from HttpBuildCache
49. Configure remote HTTP cache
50. Allow untrusted SSL certificate for HttpBuildCache
51. Recommended setup for CI push use case
52. Consistent setup for buildSrc and main build
53. Init script to configure the build cache
54. Your first build script
55. Execution of a build script
56. A task definition shortcut
57. Using Groovy in Gradle's tasks
58. Using Groovy in Gradle's tasks
59. Declaration of task that depends on other task
60. Lazy dependsOn - the other task does not exist (yet)
61. Dynamic creation of a task
62. Accessing a task via API - adding a dependency
63. Accessing a task via API - adding behaviour
64. Accessing task as a property of the build script
65. Adding extra properties to a task
66. Using AntBuilder to execute ant.loadfile target
67. Using methods to organize your build logic
68. Defining a default task
69. Different outcomes of build depending on chosen tasks
70. Accessing property of the Project object
71. Using local variables
72. Using extra properties
73. Configuring arbitrary objects
74. Configuring arbitrary objects using a script
75. Groovy JDK methods
76. Property accessors
77. Method call without parentheses
78. List and map literals
79. Closure as method parameter
80. Closure delegates
81. Defining tasks
82. Defining tasks - using strings for task names
83. Defining tasks with alternative syntax
84. Accessing tasks as properties
85. Accessing tasks via tasks collection
86. Accessing tasks by path
87. Creating a copy task
88. Configuring a task - various ways
89. Configuring a task - with closure
90. Defining a task with closure
91. Adding dependency on task from another project
92. Adding dependency using task object
93. Adding dependency using closure
94. Adding a 'must run after' task ordering
95. Adding a 'should run after' task ordering
96. Task ordering does not imply task execution
97. A 'should run after' task ordering is ignored if it introduces an ordering cycle
98. Adding a description to a task
99. Overwriting a task
100. Skipping a task using a predicate
101. Skipping tasks with StopExecutionException
102. Enabling and disabling tasks
103. Custom task class
104. Ad-hoc task
105. Ad-hoc task declaring a destroyable
106. Using runtime API with custom task type
107. Using skipWhenEmpty() via the runtime API
108. Inferred task dependency via task outputs
109. Inferred task dependency via a task argument
110. Declaring a method to add task inputs
111. Declaring a method to add a task as an input
112. Failed attempt at setting up an inferred task dependency
113. Setting up an inferred task dependency between output dir and input files
114. Setting up an inferred task dependency with files()
115. Setting up an inferred task dependency with builtBy()
116. Ignoring up-to-date checks
117. Runtime classpath normalization
118. Task rule
119. Dependency on rule based tasks
120. Adding a task finalizer
121. Task finalizer for a failing task
122. Locating files
123. Creating a file collection
124. Using a file collection
125. Implementing a file collection
126. Creating a file tree
127. Using a file tree
128. Using an archive as a file tree
129. Specifying a set of files
130. Appending a set of files
131. Copying files using the copy task
132. Specifying copy task source files and destination directory
133. Selecting the files to copy
134. Copying files using the copy() method without up-to-date check
135. Copying files using the copy() method with up-to-date check
136. Renaming files as they are copied
137. Filtering files as they are copied
138. Nested copy specs
139. Using the Sync task to copy dependencies
140. Creating a ZIP archive
141. Creation of ZIP archive
142. Configuration of archive task - custom archive name
143. Configuration of archive task - appendix & classifier
144. Activating reproducible archives
145. Using an Ant task
146. Passing nested text to an Ant task
147. Passing nested elements to an Ant task
148. Using an Ant type
149. Using a custom Ant task
150. Declaring the classpath for a custom Ant task
151. Using a custom Ant task and dependency management together
152. Importing an Ant build
153. Task that depends on Ant target
154. Adding behaviour to an Ant target
155. Ant target that depends on Gradle task
156. Renaming imported Ant targets
157. Setting an Ant property
158. Getting an Ant property
159. Setting an Ant reference
160. Getting an Ant reference
161. Fine tuning Ant logging
162. Single project build
163. Hierarchical layout
164. Flat layout
165. Lookup of elements of the project tree
166. Modification of elements of the project tree
167. Adding of test task to each project which has certain property set
168. Notifications
169. Setting of certain property to all tasks
170. Logging of start and end of each task execution
171. Using stdout to write log messages
172. Writing your own log messages
173. Writing a log message with placeholder
174. Using SLF4J to write log messages
175. Configuring standard output capture
176. Configuring standard output capture for a task
177. Customizing what Gradle logs
178. Multi-project tree - water & bluewhale projects
179. Build script of water (parent) project
180. Multi-project tree - water, bluewhale & krill projects
181. Water project build script
182. Defining common behavior of all projects and subprojects
183. Defining specific behaviour for particular project
184. Defining specific behaviour for project krill
185. Adding custom behaviour to some projects (filtered by project name)
186. Adding custom behaviour to some projects (filtered by project properties)
187. Running build from subproject
188. Evaluation and execution of projects
189. Evaluation and execution of projects
190. Running tasks by their absolute path
191. Dependencies and execution order
192. Dependencies and execution order
193. Dependencies and execution order
194. Declaring dependencies
195. Declaring dependencies
196. Cross project task dependencies
197. Configuration time dependencies
198. Configuration time dependencies - evaluationDependsOn
199. Configuration time dependencies
200. Dependencies - real life example - crossproject configuration
201. Project lib dependencies
202. Project lib dependencies
203. Fine grained control over dependencies
204. Build and Test Single Project
205. Partial Build and Test Single Project
206. Build and Test Depended On Projects
207. Build and Test Dependent Projects
208. Applying a script plugin
209. Applying a core plugin
210. Applying a community plugin
211. Applying plugins only on certain subprojects.
212. Using plugins from custom plugin repositories.
213. Plugin resolution strategy.
214. Complete Plugin Publishing Sample
215. Applying a binary plugin
216. Applying a binary plugin by type
217. Applying a plugin with the buildscript block
218. Using the Build Dashboard plugin
219. Defining an artifact using an archive task
220. Defining an artifact using a file
221. Customizing an artifact
222. Map syntax for defining an artifact using a file
223. Configuration of the upload task
224. Using the Maven plugin
225. Creating a standalone pom.
226. Upload of file to remote Maven repository
227. Upload of file via SSH
228. Customization of pom
229. Builder style customization of pom
230. Modifying auto-generated content
231. Customization of Maven installer
232. Generation of multiple poms
233. Accessing a mapping configuration
234. Using the Signing plugin
235. Sign with GnuPG
236. Configure the GnupgSignatory
237. Signing a configuration
238. Signing a configuration output
239. Signing a task
240. Signing a task output
241. Conditional signing
242. Signing a POM for deployment
243. Applying the “ivy-publish” plugin
244. Publishing a Java module to Ivy
245. Publishing additional artifact to Ivy
246. customizing the publication identity
247. Customizing the module descriptor file
248. Publishing multiple modules from a single project
249. Declaring repositories to publish to
250. Choosing a particular publication to publish
251. Publishing all publications via the “publish” lifecycle task
252. Generating the Ivy module descriptor file
253. Publishing a Java module
254. Example generated ivy.xml
255. Applying the 'maven-publish' plugin
256. Adding a MavenPublication for a Java component
257. Adding additional artifact to a MavenPublication
258. customizing the publication identity
259. Modifying the POM file
260. Publishing multiple modules from a single project
261. Declaring repositories to publish to
262. Publishing a project to a Maven repository
263. Publish a project to the Maven local repository
264. Generate a POM file without publishing
265. Using the distribution plugin
266. Adding extra distributions
267. Configuring the main distribution
268. publish main distribution
269. Applying the announce plugin
270. Configure the announce plugin
271. Using the announce plugin
272. Using the build announcements plugin
273. Using the build announcements plugin from an init script
274. Declaring a binary dependencies with a concrete version
275. Declaring a binary dependencies with a dynamic version
276. Declaring a binary dependencies with a changing version
277. Declaring multiple file dependencies
278. Declaring project dependencies
279. Declaring and using a custom configuration
280. Resolving a JavaScript artifact for a declared dependency
281. Resolving a JavaScript artifact with classifier for a declared dependency
282. Declaring JCenter repository as source for resolving dependencies
283. Declaring a custom repository by URL
284. Declaring multiple repositories
285. Declaring the JGit dependency with a custom configuration
286. Rendering the dependency report for a custom configuration
287. Declaring the JGit dependency and a conflicting dependency
288. Using the dependency insight report for a given dependency
289. Unresolved artifacts for transitive dependencies
290. Excluding transitive dependency for a particular dependency declaration
291. Excluding transitive dependency for a particular configuration
292. Enforcing a dependency version
293. Enforcing a dependency version on the configuration-level
294. Disabling transitive dependency resolution for a declared dependency
295. Disabling transitive dependency resolution on the configuration-level
296. Configuration.copy
297. Accessing declared dependencies
298. Configuration.files
299. Configuration.files with spec
300. Configuration.copy
301. Configuration.copy vs. Configuration.files
302. Forcing consistent version for a group of libraries
303. Using a custom versioning scheme
304. Blacklisting a version with a replacement
305. Changing dependency group and/or name at the resolution
306. Substituting a module with a project
307. Substituting a project with a module
308. Conditionally substituting a dependency
309. Specifying default dependencies on a configuration
310. Enabling dynamic resolve mode
311. 'Latest' version selector
312. Custom status scheme
313. Custom status scheme by module
314. Ivy component metadata rule
315. Rule source component metadata rule
316. Component selection rule
317. Component selection rule with module target
318. Component selection rule with metadata
319. Component selection rule using a rule source object
320. Declaring module replacement
321. Dynamic version cache control
322. Changing module cache control
323. Defining a custom task
324. A hello world task
325. A customizable hello world task
326. A build for a custom task
327. A custom task
328. Using a custom task in another project
329. Testing a custom task
330. Defining an incremental task action
331. Running the incremental task for the first time
332. Running the incremental task with unchanged inputs
333. Running the incremental task with updated input files
334. Running the incremental task with an input file removed
335. Running the incremental task with an output file removed
336. Running the incremental task with an input property changed
337. Creating a unit of work implementation
338. Submitting a unit of work for execution
339. Waiting for asynchronous work to complete
340. Submitting an item of work to run in a worker daemon
341. A custom plugin
342. A custom plugin extension
343. A custom plugin with configuration closure
344. Evaluating file properties lazily
345. Mapping extension properties to task properties
346. A build for a custom plugin
347. Wiring for a custom plugin
348. Using a custom plugin in another project
349. Applying a community plugin with the plugins DSL
350. Testing a custom plugin
351. Using the Java Gradle Plugin Development plugin
352. Nested DSL elements
353. Managing a collection of objects
354. Using the Java Gradle Plugin Development plugin
355. Using the gradlePlugin {} block.
356. Using inherited properties and methods
357. Using injected properties and methods
358. Configuring the project using an external build script
359. Custom buildSrc build script
360. Adding subprojects to the root buildSrc project
361. Running another build from a build
362. Declaring external dependencies for the build script
363. A build script with external dependencies
364. Ant optional dependencies
365. Using a read-only and configurable property
366. Using file and directory property
367. Implicit task dependency
368. List property
369. Using init script to perform extra configuration before projects are evaluated
370. Declaring external dependencies for an init script
371. An init script with external dependencies
372. Using plugins in init scripts
373. Declaring the TestKit dependency
374. Declaring the JUnit dependency
375. Using GradleRunner with JUnit
376. Using GradleRunner with Spock
377. Making the code under test classpath available to the tests
378. Injecting the code under test classes into test builds
379. Injecting the code under test classes into test builds for Gradle versions prior to 2.8
380. Using the Java Gradle Development plugin for generating the plugin metadata
381. Automatically injecting the code under test classes into test builds
382. Reconfiguring the classpath generation conventions of the Java Gradle Development plugin
383. Specifying a Gradle version for test execution
384. Testing cacheable tasks
385. Using the Java plugin
386. Building a Java project
387. Adding Maven repository
388. Adding dependencies
389. Customization of MANIFEST.MF
390. Adding a test system property
391. Publishing the JAR file
392. Eclipse plugin
393. Java example - complete build file
394. Multi-project build - hierarchical layout
395. Multi-project build - settings.gradle file
396. Multi-project build - common configuration
397. Multi-project build - dependencies between projects
398. Multi-project build - distribution file
399. Using the Java plugin
400. Custom Java source layout
401. Accessing a source set
402. Configuring the source directories of a source set
403. Defining a source set
404. Defining source set dependencies
405. Compiling a source set
406. Assembling a JAR for a source set
407. Generating the Javadoc for a source set
408. Running tests in a source set
409. Declaring annotation processors
410. Filtering tests in the build script
411. JUnit Categories
412. Grouping TestNG tests
413. Preserving order of TestNG tests
414. Grouping TestNG tests by instances
415. Creating a unit test report for subprojects
416. Customization of MANIFEST.MF
417. Creating a manifest object.
418. Separate MANIFEST.MF for a particular archive
419. Saving a MANIFEST.MF to disk
420. Configure Java 6 build
421. Using the Java Library plugin
422. Declaring API and implementation dependencies
423. Making the difference between API and implementation
424. Declaring API and implementation dependencies
425. Configuring the Groovy plugin to work with Java Library
426. War plugin
427. Running web application with Gretty plugin
428. Using the War plugin
429. Customization of war plugin
430. Using the Ear plugin
431. Customization of ear plugin
432. Using the application plugin
433. Configure the application main class
434. Configure default JVM settings
435. Configure custom directory for start scripts
436. Include output from other tasks in the application distribution
437. Automatically creating files for distribution
438. Using the Java library distribution plugin
439. Configure the distribution name
440. Include files in the distribution
441. Groovy plugin
442. Dependency on Groovy
443. Groovy example - complete build file
444. Using the Groovy plugin
445. Custom Groovy source layout
446. Configuration of Groovy dependency
447. Configuration of Groovy test dependency
448. Configuration of bundled Groovy dependency
449. Configuration of Groovy file dependency
450. Configure Java 6 build for Groovy
451. Using the Scala plugin
452. Custom Scala source layout
453. Declaring a Scala dependency for production code
454. Declaring a Scala dependency for test code
455. Declaring a version of the Zinc compiler to use
456. Forcing a scala-library dependency for all configurations
457. Forcing a scala-library dependency for the zinc configuration
458. Adjusting memory settings
459. Forcing all code to be compiled
460. Configure Java 6 build for Scala
461. Explicitly specify a target IntelliJ IDEA version
462. Using the ANTLR plugin
463. Declare ANTLR version
464. setting custom max heap size and extra arguments for ANTLR
465. Using the Checkstyle plugin
466. Using the config_loc property
467. Customizing the HTML report
468. Using the CodeNarc plugin
469. Using the FindBugs plugin
470. Customizing the HTML report
471. Using the JDepend plugin
472. Using the PMD plugin
473. Applying the JaCoCo plugin
474. Configuring JaCoCo plugin settings
475. Configuring test task
476. Configuring violation rules
477. Configuring test task
478. Using application plugin to generate code coverage data
479. Coverage reports generated by applicationCodeCoverageReport
480. Using the OSGi plugin
481. Configuration of OSGi MANIFEST.MF file
482. Using the Eclipse plugin
483. Using the Eclipse WTP plugin
484. Partial Overwrite for Classpath
485. Partial Overwrite for Project
486. Export Classpath Entries
487. Customizing the XML
488. Using the IDEA plugin
489. Partial Rewrite for Module
490. Partial Rewrite for Project
491. Export Dependencies
492. Customizing the XML
493. applying a rule source plugin
494. a model creation rule
495. a model mutation rule
496. creating a task
497. a managed type
498. a String property
499. a File property
500. a Long property
501. a boolean property
502. an int property
503. a managed property
504. an enumeration type property
505. a managed set
506. a scalar collection
507. strongly modelling sources sets
508. a DSL example applying a rule to every element in a scope
509. DSL configuration rule
510. Configuration run when required
511. Configuration not run when not required
512. DSL creation rule
513. DSL creation rule without initialization
514. Initialization before configuration
515. Nested DSL creation rule
516. Nested DSL configuration rule
517. DSL configuration rule for each element in a map
518. Nested DSL property configuration
519. a DSL example showing type conversions
520. a DSL rule using inputs
521. model task output
522. Using the Java software plugins
523. Creating a java library
524. Configuring a source set
525. Creating a new source set
526. The components report
527. Declaring a dependency onto a library
528. Declaring a dependency onto a project with an explicit library
529. Declaring a dependency onto a project with an implicit library
530. Declaring a dependency onto a library published to a Maven repository
531. Declaring a module dependency using shorthand notation
532. Configuring repositories for dependency resolution
533. Specifying api packages
534. Specifying api dependencies
535. Main sources
536. Client component
537. Broken client component
538. Making non-API implementation-only change
539. Recompiling the client
540. Declaring target platforms
541. Declaring binary specific sources
542. Declaring target platforms
543. Using the JUnit plugin
544. Executing the test suite
545. Executing the test suite
546. Declaring a component under test
547. Declaring local Java installations
548. Using the Play plugin
549. The components report
550. Selecting a version of the Play Framework
551. Adding dependencies to a Play application
552. A Play 2.6 project
553. Adding Guice dependency in Play 2.6 project
554. Configuring extra source sets to a Play application
555. Adding extra source sets to a Play application
556. Configuring Scala compiler options
557. Configuring routes style
558. Configuring a custom asset pipeline
559. Configuring dependencies on Play subprojects
560. Add extra files to a Play application distribution
561. Applying both the Play and IDEA plugins
562. Defining a library component
563. Defining executable components
564. Sample build
565. Dependent components report
566. Dependent components report
567. Report of components that depends on the operators component
568. Report of components that depends on the operators component, including test suites
569. Assemble components that depends on the passing/static binary of the operators component
570. Build components that depends on the passing/static binary of the operators component
571. Adding a custom check task
572. Running checks for a given binary
573. The components report
574. The 'cpp' plugin
575. C++ source set
576. The 'c' plugin
577. C source set
578. The 'assembler' plugin
579. The 'objective-c' plugin
580. The 'objective-cpp' plugin
581. Settings that apply to all binaries
582. Settings that apply to all shared libraries
583. Settings that apply to all binaries produced for the 'main' executable component
584. Settings that apply only to shared libraries produced for the 'main' library component
585. The 'windows-resources' plugin
586. Configuring the location of Windows resource sources
587. Building a resource-only dll
588. Providing a library dependency to the source set
589. Providing a library dependency to the binary
590. Declaring project dependencies
591. Creating a precompiled header file
592. Including a precompiled header file in a source file
593. Configuring a precompiled header
594. Defining build types
595. Configuring debug binaries
596. Defining platforms
597. Defining flavors
598. Targeting a component at particular platforms
599. Building all possible variants
600. Defining tool chains
601. Reconfigure tool arguments
602. Defining target platforms
603. Registering CUnit tests
604. Configuring CUnit tests
605. Running CUnit tests
606. Registering GoogleTest tests
607. an example of using a custom software model
608. Declare a custom component
609. Register a custom component
610. Declare a custom binary
611. Register a custom binary
612. Declare a custom source set
613. Register a custom source set
614. Generates documentation binaries
615. Generates tasks for text source sets
616. Register a custom source set
617. an example of using a custom software model
618. components report
619. public type and internal view declaration
620. type registration
621. public and internal data mutation
622. example build script and model report output
623. Module dependencies
624. File dependencies
625. Generated file dependencies
626. Project dependencies
627. Gradle API dependencies
628. Gradle TestKit dependencies
629. Gradle's Groovy dependencies
630. Flat repository resolver
631. Adding central Maven repository
632. Adding Bintray's JCenter Maven repository
633. Adding Google Maven repository
634. Adding the local Maven cache as a repository
635. Adding custom Maven repository
636. Adding additional Maven repositories for JAR files
637. Accessing password-protected Maven repository
638. Ivy repository
639. Ivy repository with named layout
640. Ivy repository with pattern layout
641. Ivy repository with multiple custom patterns
642. Ivy repository with Maven compatible layout
643. Ivy repository with authentication
644. Declaring a Maven and Ivy repository
645. Using the SFTP protocol for a repository
646. Declaring a S3 backed Maven and Ivy repository
647. Declaring a S3 backed Maven and Ivy repository using IAM
648. Declaring a Google Cloud Storage backed Maven and Ivy repository using default application
credentials
649. Configure repository to use only digest authentication
650. Configure repository to use preemptive authentication
B.1. Variables scope: local and script wide
B.2. Distinct configuration and execution phase
About Gradle
Introduction
We would like to introduce Gradle to you, a build system that we think is a quantum leap for build technology
in the Java (JVM) world. Gradle provides:
A very flexible general purpose build tool like Ant.
Switchable, build-by-convention frameworks a la Maven. But we never lock you in!
Very powerful support for multi-project builds.
Very powerful dependency management (based on Apache Ivy).
Full support for your existing Maven or Ivy repository infrastructure.
Support for transitive dependency management without the need for remote repositories or pom.xml and ivy.xml
files.
Ant tasks and builds as first class citizens.
Groovy build scripts.
A rich domain model for describing your build.
In Overview you will find a detailed overview of Gradle. Otherwise, the guides are waiting, have fun :)
§
About this user guide
This user guide, like Gradle itself, is under very active development. Some parts of Gradle aren’t
documented as completely as they need to be. Some of the content presented won’t be entirely clear or will
assume that you know more about Gradle than you do. We need your help to improve this user guide. You
can find out more about contributing to the documentation at the Gradle web site.
Throughout the user guide, you will find some diagrams that represent dependency relationships between
Gradle tasks. These use something analogous to the UML dependency notation, which renders an arrow
from one task to the task that the first task depends on.
Page 20 of 717
Overview
§
Features
Here is a list of some of Gradle’s features.
Declarative builds and build-by-convention
At the heart of Gradle lies a rich extensible Domain Specific Language (DSL) based on Groovy. Gradle
pushes declarative builds to the next level by providing declarative language elements that you can
assemble as you like. Those elements also provide build-by-convention support for Java, Groovy, OSGi,
Web and Scala projects. Even more, this declarative language is extensible. Add your own new language
elements or enhance the existing ones, thus providing concise, maintainable and comprehensible builds.
Language for dependency based programming
The declarative language lies on top of a general purpose task graph, which you can fully leverage in
your builds. It provides utmost flexibility to adapt Gradle to your unique needs.
Structure your build
The suppleness and richness of Gradle finally allows you to apply common design principles to your
build. For example, it is very easy to compose your build from reusable pieces of build logic. Inline stuff
where unnecessary indirections would be inappropriate. Don’t be forced to tear apart what belongs
together (e.g. in your project hierarchy). Avoid smells like shotgun changes or divergent change that turn
your build into a maintenance nightmare. At last you can create a well structured, easily maintained,
comprehensible build.
Deep API
From being a pleasure to be used embedded to its many hooks over the whole lifecycle of build
execution, Gradle allows you to monitor and customize its configuration and execution behavior to its
very core.
Gradle scales
Gradle scales very well. It significantly increases your productivity, from simple single project builds up to
huge enterprise multi-project builds. This is true for structuring the build. With the state-of-art incremental
build function, this is also true for tackling the performance pain many large enterprise builds suffer from.
Multi-project builds
Gradle’s support for multi-project build is outstanding. Project dependencies are first class citizens. We
allow you to model the project relationships in a multi-project build as they really are for your problem
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domain. Gradle follows your layout not vice versa.
Gradle provides partial builds. If you build a single subproject Gradle takes care of building all the
subprojects that subproject depends on. You can also choose to rebuild the subprojects that depend on a
particular subproject. Together with incremental builds this is a big time saver for larger builds.
Many ways to manage your dependencies
Different teams prefer different ways to manage their external dependencies. Gradle provides convenient
support for any strategy. From transitive dependency management with remote Maven and Ivy
repositories to jars or directories on the local file system.
Gradle is the first build integration tool
Ant tasks are first class citizens. Even more interesting, Ant projects are first class citizens as well.
Gradle provides a deep import for any Ant project, turning Ant targets into native Gradle tasks at runtime.
You can depend on them from Gradle, you can enhance them from Gradle, you can even declare
dependencies on Gradle tasks in your build.xml. The same integration is provided for properties, paths,
etc …
Gradle fully supports your existing Maven or Ivy repository infrastructure for publishing and retrieving
dependencies. Gradle also provides a converter for turning a Maven pom.xml into a Gradle script.
Runtime imports of Maven projects will come soon.
Ease of migration
Gradle can adapt to any structure you have. Therefore you can always develop your Gradle build in the
same branch where your production build lives and both can evolve in parallel. We usually recommend to
write tests that make sure that the produced artifacts are similar. That way migration is as less disruptive
and as reliable as possible. This is following the best-practices for refactoring by applying baby steps.
Groovy
Gradle’s build scripts are written in Groovy, not XML. But unlike other approaches this is not for simply
exposing the raw scripting power of a dynamic language. That would just lead to a very difficult to
maintain build. The whole design of Gradle is oriented towards being used as a language, not as a rigid
framework. And Groovy is our glue that allows you to tell your individual story with the abstractions
Gradle (or you) provide. Gradle provides some standard stories but they are not privileged in any form.
This is for us a major distinguishing feature compared to other declarative build systems. Our Groovy
support is not just sugar coating. The whole Gradle API is fully Groovy-ized. Adding Groovy results in an
enjoyable and productive experience.
The Gradle wrapper
The Gradle Wrapper allows you to execute Gradle builds on machines where Gradle is not installed. This
is useful for example for some continuous integration servers. It is also useful for an open source project
to keep the barrier low for building it. The wrapper is also very interesting for the enterprise. It is a zero
administration approach for the client machines. It also enforces the usage of a particular Gradle version
thus minimizing support issues.
Free and open source
Gradle is an open source project, and is licensed under the ASL.
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§
Why Groovy?
We think the advantages of an internal DSL (based on a dynamic language) over XML are tremendous when
used in build scripts . There are a couple of dynamic languages out there. Why Groovy? The answer lies in
the context Gradle is operating in. Although Gradle is a general purpose build tool at its core, its main focus
are Java projects. In such projects the team members will be very familiar with Java. We think a build should
be as transparent as possible to all team members.
In that case, you might argue why we don’t just use Java as the language for build scripts. We think this is a
valid question. It would have the highest transparency for your team and the lowest learning curve, but
because of the limitations of Java, such a build language would not be as nice, expressive and powerful as it
could be.[1] Languages like Python, Groovy or Ruby do a much better job here. We have chosen Groovy as
it offers by far the greatest transparency for Java people. Its base syntax is the same as Java’s as well as its
type system, its package structure and other things. Groovy provides much more on top of that, but with the
common foundation of Java.
For Java developers with Python or Ruby knowledge or the desire to learn them, the above arguments don’t
apply. The Gradle design is well-suited for creating another build script engine in JRuby or Jython. It just
doesn’t have the highest priority for us at the moment. We happily support any community effort to create
additional build script engines.
[1] At http://www.defmacro.org/ramblings/lisp.html you find an interesting article comparing Ant, XML, Java
and Lisp. It’s funny that the 'if Java had that syntax' syntax in this article is actually the Groovy syntax.
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Working with existing builds
Installing Gradle
§
Prerequisites
Gradle requires a Java JDK or JRE to be installed, version 7 or higher (to check, use java -version).
Gradle ships with its own Groovy library, therefore Groovy does not need to be installed. Any existing
Groovy installation is ignored by Gradle.
Gradle uses whatever JDK it finds in your path. Alternatively, you can set the JAVA_HOME environment
variable to point to the installation directory of the desired JDK.
§
Download
You can download one of the Gradle distributions from the Gradle web site.
§
Unpacking
The Gradle distribution comes packaged as a ZIP. The full distribution contains:
The Gradle binaries.
The user guide (HTML and PDF).
The DSL reference guide.
The API documentation (Javadoc).
Extensive samples, including the examples referenced in the user guide, along with some complete and
more complex builds you can use as a starting point for your own build.
The binary sources. This is for reference only. If you want to build Gradle you need to download the source
distribution or checkout the sources from the source repository. See the Gradle web site for details.
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Environment variables
§
Environment variables
For running Gradle, firstly add the environment variable GRADLE_HOME. This should point to the unpacked
files from the Gradle website. Next add GRADLE_HOME /bin to your PATH environment variable. Usually,
this is sufficient to run Gradle.
§
Running and testing your installation
You run Gradle via the gradle command. To check if Gradle is properly installed just type gradle -v. The
output shows the Gradle version and also the local environment configuration (Groovy, JVM version, OS,
etc.). The displayed Gradle version should match the distribution you have downloaded.
§
JVM options
JVM options for running Gradle can be set via environment variables. You can use either GRADLE_OPTS or JAVA_OPTS
, or both. JAVA_OPTS is by convention an environment variable shared by many Java applications. A typical
use case would be to set the HTTP proxy in JAVA_OPTS and the memory options in GRADLE_OPTS. Those
variables can also be set at the beginning of the gradle or gradlew script.
Note that it’s not currently possible to set JVM options for Gradle on the command line.
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Command-Line Interface
The command-line interface is one of the primary methods of interacting with Gradle. The following serves
as a reference of executing and customizing Gradle use of a command-line or when writing scripts or
configuring continuous integration.
Use of the Gradle Wrapper is highly encouraged. You should substitute ./gradlew or gradlew.bat for gradle
in all following examples when using the Wrapper.
Executing Gradle on the command-line conforms to the following structure. Options are allowed before and
after task names.
gradle [taskName...] [--option-name...]
If multiple tasks are specified, they should be separated with a space.
Options that accept values can be specified with or without = between the option and argument; however,
use of = is recommended.
--console=plain
Options that enable behavior have long-form options with inverses specified with --no-. The following are
opposites.
--build-cache
--no-build-cache
Many long-form options, have short option equivalents. The following are equivalent:
--help
-h
Note: Many command-line flags can be specified in gradle.properties to avoid needing to be
typed. See the configuring build environment guide for details.
The following sections describe use of the Gradle command-line interface, grouped roughly by user goal.
Some plugins also add their own command line options, for example --tests for Java test filtering.
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Executing tasks
§
Executing tasks
You can run a task and all of its dependencies.
gradle myTask
You can learn about what projects and tasks are available in the project reporting section.
§
Executing tasks in multi-project builds
In a multi-project build, subproject tasks can be executed with ":" separating subproject name and task
name. The following are equivalent when run from the root project .
gradle :mySubproject:taskName
gradle mySubproject:taskName
You can also run a task for all subprojects using the task name only. For example, this will run the "test" task
for all subprojects when invoked from the root project directory.
gradle test
When invoking Gradle from within a subproject, the project name should be omitted:
cd mySubproject
gradle taskName
Note: When executing the Gradle Wrapper from subprojects, one must reference gradlew
relatively. For example: ../gradlew taskName. The community gdub project aims to make this
more convenient.
§
Executing multiple tasks
You can also specify multiple tasks. For example, the following will execute the test and deploy tasks in
the order that they are listed on the command-line and will also execute the dependencies for each task.
gradle test deploy
§
Excluding tasks from execution
You can exclude a task from being executed using the -x or --exclude-task command-line option and
providing the name of the task to exclude.
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Figure 1. Example Task Graph
Example 1. Excluding tasks
Output of gradle dist --exclude-task test
> gradle dist --exclude-task test
:compile
compiling source
:dist
building the distribution
BUILD SUCCESSFUL in 0s
2 actionable tasks: 2 executed
You can see that the test task is not executed, even though it is a dependency of the dist task. The test
task’s dependencies such as compileTest are not executed either. Those dependencies of test that are
required by another task, such as compile, are still executed.
§
Forcing tasks to execute
You can force Gradle to execute all tasks ignoring up-to-date checks using the --rerun-tasks option:
gradle test --rerun-tasks
This will force test and all task dependencies of test to execute. It’s a little like running gradle clean test
, but without the build’s generated output being deleted.
§
Continuing the build when a failure occurs
By default, Gradle will abort execution and fail the build as soon as any task fails. This allows the build to
complete sooner, but hides other failures that would have occurred. In order to discover as many failures as
possible in a single build execution, you can use the --continue option.
gradle test --continue
When executed with --continue, Gradle will execute every task to be executed where all of the
dependencies for that task completed without failure, instead of stopping as soon as the first failure is
encountered. Each of the encountered failures will be reported at the end of the build.
If a task fails, any subsequent tasks that were depending on it will not be executed. For example, tests will
not run if there is a compilation failure in the code under test; because the test task will depend on the
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compilation task (either directly or indirectly).
§
Task name abbreviation
When you specify tasks on the command-line, you don’t have to provide the full name of the task. You only
need to provide enough of the task name to uniquely identify the task. For example, it’s likely gradle che
is enough for Gradle to identify the check task.
You can also abbreviate each word in a camel case task name. For example, you can execute task compileTest
by running gradle compTest or even gradle cT.
Example 2. Abbreviated camel case task name
Output of gradle cT
> gradle cT
:compile
compiling source
:compileTest
compiling unit tests
BUILD SUCCESSFUL in 0s
2 actionable tasks: 2 executed
You can also use these abbreviations with the -x command-line option.
§
Common tasks
The following are task conventions applied by built-in and most major Gradle plugins.
§
Computing all outputs
It is common in Gradle builds for the build task to designate assembling all outputs and running all checks.
gradle build
§
Running applications
It is common for applications to be run with the run task, which assembles the application and executes
some script or binary.
gradle run
Running all checks
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§
Running all checks
It is common for all verification tasks, including tests and linting, to be executed using the check task.
gradle check
§
Cleaning outputs
You can delete the contents of the build directory using the clean task, though doing so will cause
pre-computed outputs to be lost, causing significant additional build time for the subsequent task execution.
gradle clean
§
Project reporting
Gradle provides several built-in tasks which show particular details of your build. This can be useful for
understanding the structure and dependencies of your build, and for debugging problems.
You can get basic help about available reporting options using gradle help.
§
Listing projects
Running gradle projects gives you a list of the sub-projects of the selected project, displayed in a
hierarchy.
gradle projects
You also get a project report within build scans. Learn more about creating build scans.
§
Listing tasks
Running gradle tasks gives you a list of the main tasks of the selected project. This report shows the
default tasks for the project, if any, and a description for each task.
gradle tasks
By default, this report shows only those tasks which have been assigned to a task group. You can obtain
more information in the task listing using the --all option.
gradle tasks --all
Show task usage details
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§
Show task usage details
Running gradle help --task someTask gives you detailed information about a specific task.
Example 3. Obtaining detailed help for tasks
Output of gradle -q help --task libs
> gradle -q help --task libs
Detailed task information for libs
Paths
:api:libs
:webapp:libs
Type
Task (org.gradle.api.Task)
Description
Builds the JAR
Group
build
This information includes the full task path, the task type, possible command line options and the description
of the given task.
§
Reporting dependencies
Build scans give a full, visual report of what project and binary dependencies exist on which configurations,
transitive dependencies, and dependency version selection.
gradle myTask --scan
This will give you a link to a web-based report, where you can find dependency information like this.
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Learn more in Inspecting Dependencies.
§
Listing project dependencies
Running gradle dependencies gives you a list of the dependencies of the selected project, broken down
by configuration. For each configuration, the direct and transitive dependencies of that configuration are
shown in a tree. Below is an example of this report:
gradle dependencies
Concrete examples of build scripts and output available in the Inspecting Dependencies.
Running gradle buildEnvironment visualises the buildscript dependencies of the selected project,
similarly to how gradle dependencies visualizes the dependencies of the software being built.
gradle buildEnvironment
Running gradle
dependencyInsight gives you an insight into a particular dependency (or
dependencies) that match specified input.
gradle dependencyInsight
Since a dependency report can get large, it can be useful to restrict the report to a particular configuration.
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This is achieved with the optional --configuration parameter:
§
Listing project properties
Running gradle properties gives you a list of the properties of the selected project.
Example 4. Information about properties
Output of gradle -q api:properties
> gradle -q api:properties
-----------------------------------------------------------Project :api - The shared API for the application
------------------------------------------------------------
allprojects: [project ':api']
ant: org.gradle.api.internal.project.DefaultAntBuilder@12345
antBuilderFactory: org.gradle.api.internal.project.DefaultAntBuilderFactory@12345
artifacts: org.gradle.api.internal.artifacts.dsl.DefaultArtifactHandler_Decorated@12345
asDynamicObject: DynamicObject for project ':api'
baseClassLoaderScope: org.gradle.api.internal.initialization.DefaultClassLoaderScope@12345
buildDir: /home/user/gradle/samples/userguide/tutorial/projectReports/api/build
buildFile: /home/user/gradle/samples/userguide/tutorial/projectReports/api/build.gradle
§
Software Model reports
You can get a hierarchical view of elements for software model projects using the model task:
gradle model
Learn more about the model report in the software model documentation.
§
Command-line completion
Gradle provides bash and zsh tab completion support for tasks, options, and Gradle properties through
gradle-completion, installed separately.
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Figure 2. Gradle Completion
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Debugging options
§
Debugging options
-?, -h, --help
Shows a help message with all available CLI options.
-v, --version
Prints Gradle, Groovy, Ant, JVM, and operating system version information.
-S, --full-stacktrace
Print out the full (very verbose) stacktrace for any exceptions. See also logging options.
-s, --stacktrace
Print out the stacktrace also for user exceptions (e.g. compile error). See also logging options.
--scan
Create a build scan with fine-grained information about all aspects of your Gradle build.
-Dorg.gradle.debug=true
Debug Gradle client (non-Daemon) process. Gradle will wait for you to attach a debugger at localhost:5005
by default.
-Dorg.gradle.daemon.debug=true
Debug Gradle Daemon process.
§
Performance options
Try these options when optimizing build performance. Learn more about improving performance of Gradle
builds here.
Many of these options can be specified in gradle.properties so command-line flags are not necessary.
See the configuring build environment guide.
--build-cache, --no-build-cache
Toggles the Gradle build cache. Gradle will try to reuse outputs from previous builds. Default is off .
--configure-on-demand, --no-configure-on-demand
Toggles Configure-on-demand. Only relevant projects are configured in this build run. Default is off .
--max-workers
Sets maximum number of workers that Gradle may use. Default is number of processors .
--parallel, --no-parallel
Build projects in parallel. For limitations of this option please see the section called “Parallel project
execution”. Default is off .
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--profile
Generates a high-level performance report in the $buildDir/reports/profile directory. --scan is
preferred.
--scan
Generate a build scan with detailed performance diagnostics.
§
Gradle daemon options
You can manage the Gradle Daemon through the following command line options.
--daemon, --no-daemon
Use the Gradle Daemon to run the build. Starts the daemon if not running or existing daemon busy.
Default is on .
--foreground
Starts the Gradle Daemon in a foreground process.
--status (Standalone command)
Run gradle --status to list running and recently stopped Gradle daemons. Only displays daemons of
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the same Gradle version.
--stop (Standalone command)
Run gradle --stop to stop all Gradle Daemons of the same version.
-Dorg.gradle.daemon.idletimeout=(number of milliseconds)
Gradle Daemon will stop itself after this number of milliseconds of idle time. Default is 10800000 (3
hours).
§
Logging options
§
Setting log level
You can customize the verbosity of Gradle logging with the following options, ordered from least verbose to
most verbose. Learn more in the logging documentation.
-Dorg.gradle.logging.level=(quiet,warn,lifecycle,info,debug)
Set logging level via Gradle properties.
-q, --quiet
Log errors only.
-w, --warn
Set log level to warn.
-i, --info
Set log level to info.
-d, --debug
Log in debug mode (includes normal stacktrace).
Lifecycle is the default log level.
§
Customizing log format
You can control the use of rich output (colors and font variants) by specifying the "console" mode in the
following ways:
-Dorg.gradle.console=(auto,plain,rich,verbose)
Specify console mode via Gradle properties. Different modes described immediately below.
--console=(auto,plain,rich,verbose)
Specifies which type of console output to generate.
Set to plain to generate plain text only. This option disables all color and other rich output in the
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console output. This is the default when Gradle is not attached to a terminal.
Set to auto (the default) to enable color and other rich output in the console output when the build
process is attached to a console, or to generate plain text only when not attached to a console. This is
the default when Gradle is attached to a terminal.
Set to rich to enable color and other rich output in the console output, regardless of whether the build
process is not attached to a console. When not attached to a console, the build output will use ANSI
control characters to generate the rich output.
Set to verbose to enable color and other rich output like the rich, but output task names and outcomes
at the lifecycle log level, as is done by default in Gradle 3.5 and earlier.
§
Showing or hiding warnings
By default, Gradle won’t display all warnings (e.g. deprecation warnings). Instead, Gradle will collect them
and render a summary at the end of the build like:
Deprecated Gradle API and/or features were used in this build, making it incompatible with
You can control the verbosity of warnings on the console with the following options:
-Dorg.gradle.warning.mode=(all,none,summary)
Specify warning mode via Gradle properties. Different modes described immediately below.
--warning-mode=(all,none,summary)
Specifies how to log warnings. Default is summary.
Set to all to log all warnings.
Set to summary to suppress all warnings and log a summary at the end of the build.
Set to none to suppress all warnings, including the summary at the end of the build.
§
Rich Console
Gradle’s rich console displays extra information while builds are running.
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Features:
Logs above grouped by task that generated them
Progress bar and timer visually describe overall status
Parallel work-in-progress lines below describe what is happening now
§
Execution options
The following options affect how builds are executed, by changing what is built or how dependencies are
resolved.
--include-build
Run the build as a composite, including the specified build. See Composite Builds.
--offline
Specifies that the build should operate without accessing network resources. Learn more about options
to override dependency caching.
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--refresh-dependencies
Refresh the state of dependencies. Learn more about how to use this in the dependency management
docs.
--dry-run
Run Gradle with all task actions disabled. Use this to show which task would have executed.
§
Bootstrapping new projects
§
Creating new Gradle builds
Use the built-in gradle init task to create a new Gradle builds, with new or existing projects.
gradle init
Most of the time you’ll want to specify a project type. Available types include basic (default), java-library
, java-application, and more. See init plugin documentation for details.
gradle init --type java-library
§
Standardize and provision Gradle
The built-in gradle wrapper task generates a script, gradlew, that invokes a declared version of Gradle,
downloading it beforehand if necessary.
gradle wrapper --gradle-version=4.4
You can also specify --distribution-type=(bin|all), --gradle-distribution-url, --gradle-distributi
in addition to --gradle-version. Full details on how to use these options are documented in the Gradle
wrapper section.
§
Environment options
You can customize many aspects about where build scripts, settings, caches, and so on through the options
below. Learn more about customizing your build environment.
-b, --build-file
Specifies the build file. For example: gradle --build-file=foo.gradle. The default is build.gradle
, then build.gradle.kts, then myProjectName.gradle.
-c, --settings-file
Specifies the settings file. For example: gradle --settings-file=somewhere/else/settings.gradle
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-g, --gradle-user-home
Specifies the Gradle user home directory. The default is the .gradle directory in the user’s home
directory.
-p, --project-dir
Specifies the start directory for Gradle. Defaults to current directory.
--project-cache-dir
Specifies the project-specific cache directory. Default value is .gradle in the root project directory.
-u, --no-search-upward (deprecated)
Don’t search in parent directories for a settings.gradle file.
-D, --system-prop
Sets a system property of the JVM, for example -Dmyprop=myvalue. See the section called “System
properties”.
-I, --init-script
Specifies an initialization script. See Initialization Scripts.
-P, --project-prop
Sets a project property of the root project, for example -Pmyprop=myvalue. See the section called
“Project properties”.
-Dorg.gradle.jvmargs
Set JVM arguments.
-Dorg.gradle.java.home
Set JDK home dir.
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The Gradle Wrapper
The recommended way to execute any Gradle build is with the help of the Gradle Wrapper (in short just
“Wrapper”). The Wrapper is a script that invokes a declared version of Gradle, downloading it beforehand if
necessary. As a result, developers can get up and running with a Gradle project quickly without having to
follow manual installation processes saving your company time and money.
Figure 3. The Wrapper workflow
In a nutshell you gain the following benefits:
Standardizes a project on a given Gradle version, leading to more reliable and robust builds.
Provisioning a new Gradle version to different users and execution environment (e.g. IDEs or Continuous
Integration servers) is as simple as changing the Wrapper definition.
So how does it work? For a user there are typically three different workflows:
You set up a new Gradle project and want to add the Wrapper to it.
You want to run a project with the Wrapper that already provides it.
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You want to upgrade the Wrapper to a new version of Gradle.
The following sections explain each of these use cases in more detail.
§
Adding the Gradle Wrapper
Generating the Wrapper files requires an installed version of the Gradle runtime on your machine as
described in Installing Gradle. Thankfully, generating the initial Wrapper files is a one-time process.
Every vanilla Gradle build comes with a built-in task called wrapper. You’ll be able to find the task listed
under the group "Build Setup tasks" when listing the tasks. Executing the wrapper task generates the
necessary Wrapper files in the project directory.
Example 5. Running the Wrapper task
Output of gradle wrapper
> gradle wrapper
:wrapper
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
Note: To make the Wrapper files available to other developers and execution environments you’ll
need to check them into version control. All Wrapper files including the JAR file are very small in
size. Adding the JAR file to version control is expected. Some organizations do not allow projects to
submit binary files to version control. At the moment there are no alternative options to the
approach.
The generated Wrapper properties file, gradle/wrapper/gradle-wrapper.properties, stores the
information about the Gradle distribution.
The server hosting the Gradle distribution.
The type of Gradle distribution. By default that’s the -bin distribution containing only the runtime but no
sample code and documentation.
The Gradle version used for executing the build. By default the wrapper task picks the exact same Gradle
version that was used to generate the Wrapper files.
Example 6. The generated distribution URL
gradle/wrapper/gradle-wrapper.properties.
distributionUrl=https\://services.gradle.org/distributions/gradle-4.3.1-bin.zip
All of those aspects are configurable at the time of generating the Wrapper files with the help of the following
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command line options.
--gradle-version
The Gradle version used for downloading and executing the Wrapper.
--distribution-type
The Gradle distribution type used for the Wrapper. Available options are bin and all. The default value
is bin.
--gradle-distribution-url
The full URL pointing to Gradle distribution ZIP file. Using this option makes --gradle-version and --distributi
obsolete as the URL already contains this information. This option is extremely valuable if you want to
host the Gradle distribution inside your company’s network.
--gradle-distribution-sha256-sum
The SHA256 hash sum used for verifying the downloaded Gradle distribution.
Let’s assume the following use case to illustrate the use of the command line options. You would like to
generate the Wrapper with version 4.0 and use the -all distribution to enable your IDE to enable
code-completion and being able to navigate to the Gradle source code. Those requirements are captured by
the following command line execution:
Example 7. Providing options to Wrapper task
Output of gradle wrapper --gradle-version 4.0 --distribution-type all
> gradle wrapper --gradle-version 4.0 --distribution-type all
:wrapper
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
As a result you can find the desired information in the Wrapper properties file.
Example 8. The generated distribution URL
gradle/wrapper/gradle-wrapper.properties.
distributionUrl=https\://services.gradle.org/distributions/gradle-4.0-all.zip
Let’s have a look at the following project layout to illustrate the expected Wrapper files:
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.
build.gradle
settings.gradle
gradle
wrapper
gradle-wrapper.jar
gradle-wrapper.properties
gradlew
gradlew.bat
A Gradle project typically provides a build.gradle and a settings.gradle file. The Wrapper files live
alongside in the gradle directory and the root directory of the project. The following list explains their
purpose.
gradle-wrapper.jar
The Wrapper JAR file containing code for downloading the Gradle distribution.
gradle-wrapper.properties
A properties file responsible for configuring the Wrapper runtime behavior e.g. the Gradle version
compatible with this version.
gradlew, gradlew.bat
A shell script and a Windows batch script for executing the build with the Wrapper.
You can go ahead and execute the build with the Wrapper without having to install the Gradle runtime. If the
project you are working on does not contain those Wrapper files then you’ll need to generate them.
§
Using the Gradle Wrapper
It is recommended to always execute a build with the Wrapper to ensure a reliable, controlled and
standardized execution of the build. Using the Wrapper looks almost exactly like running the build with a
Gradle installation. Depending on the operation system you either run gradlew or gradlew.bat instead of
the gradle command. The following console output demonstrate the use of the Wrapper on a Windows
machine for a Java-based project.
Example 9. Executing the build with the Wrapper batch file
Output of gradlew.bat build
> gradlew.bat build
Downloading https://services.gradle.org/distributions/gradle-4.0-all.zip
.....................................................................................
Unzipping C:\Documents and Settings\Claudia\.gradle\wrapper\dists\gradle-4.0-all\ac27o8rbd
Set executable permissions for: C:\Documents and Settings\Claudia\.gradle\wrapper\dists\gr
BUILD SUCCESSFUL in 12s
1 actionable task: 1 executed
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In case the Gradle distribution is not available on the machine, the Wrapper will download it and store in the
local file system. Any subsequent build invocation is going to reuse the existing local distribution as long as
the distribution URL in the Gradle properties doesn’t change.
Note: The Wrapper shell script and batch file reside in the root directory of a single or multi-project
Gradle build. You will need to reference the correct path to those files in case you want to execute
the build from a subproject directory e.g. ../../gradlew tasks.
§
Upgrading the Gradle Wrapper
Projects will typically want to keep up with the times and upgrade their Gradle version to benefit from new
features and improvements. One way to upgrade the Gradle version is manually change the distributionUrl
property in the Wrapper property file. The better and recommended option is to run the wrapper task and
provide the target Gradle version as described in the section called “Adding the Gradle Wrapper”. Using the wrapper
task ensures that any optimizations made to the Wrapper shell script or batch file with that specific Gradle
version are applied to the project. As usual you’d commit the changes to the Wrapper files to version control.
Use the Gradle wrapper task to generate the wrapper, specifying a version. The default is the current
version, which you can check by executing ./gradlew --version.
Example 10. Upgrading the Wrapper version
Output of ./gradlew wrapper --gradle-version 4.2.1
> ./gradlew wrapper --gradle-version 4.2.1
BUILD SUCCESSFUL in 4s
1 actionable task: 1 executed
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Example 11. Checking the Wrapper version after upgrading
Output of ./gradlew -v
> ./gradlew -v
Downloading https://services.gradle.org/distributions/gradle-4.2.1-bin.zip
...................................................................
Unzipping /Users/claudia/.gradle/wrapper/dists/gradle-4.2.1-bin/dajvke9o8kmaxbu0kc5gcgeju/
Set executable permissions for: /Users/claudia/.gradle/wrapper/dists/gradle-4.2.1-bin/dajv
-----------------------------------------------------------Gradle 4.2.1
-----------------------------------------------------------Build time:
Revision:
2017-10-02 15:36:21 UTC
a88ebd6be7840c2e59ae4782eb0f27fbe3405ddf
Groovy:
Ant:
JVM:
OS:
2.4.12
Apache Ant(TM) version 1.9.6 compiled on June 29 2015
1.8.0_60 (Oracle Corporation 25.60-b23)
Mac OS X 10.13.1 x86_64
§
Customizing the Gradle Wrapper
Most users of Gradle are happy with the default runtime behavior of the Wrapper. However, organizational
policies, security constraints or personal preferences might require you to dive deeper into customizing the
Wrapper. Thankfully, the built-in wrapper task exposes numerous options to bend the runtime behavior to
your needs. Most configuration options are exposed by the underlying task type Wrapper.
Let’s assume you grew tired of defining the -all distribution type on the command line every time you
upgrade the Wrapper. You can save yourself some keyboard strokes by re-configuring the wrapper task.
Example 12. Customizing the Wrapper task
build.gradle
wrapper {
distributionType = Wrapper.DistributionType.ALL
}
With the configuration in place running ./gradlew wrapper --gradle-version 4.1 is enough to
produce a distributionUrl value in the Wrapper properties file that will request the -all distribution.
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Example 13. The generated distribution URL
gradle/wrapper/gradle-wrapper.properties.
distributionUrl=https\://services.gradle.org/distributions/gradle-4.1-all.zip
Check out the API documentation for more detail descriptions of the available configuration options. You can
also find various samples for configuring the Wrapper in the Gradle distribution.
§
Authenticated Gradle distribution download
The Gradle Wrapper can download Gradle distributions from servers using HTTP Basic Authentication. This
enables you to host the Gradle distribution on a private protected server. You can specify a username and
password in two different ways depending on your use case: as system properties or directly embedded in
the distributionUrl. Credentials in system properties take precedence over the ones embedded in distributionUr
.
Security Warning
HTTP Basic Authentication should only be used with HTTPS URLs and not plain HTTP ones. With
Basic Authentication, the user credentials are sent in clear text.
Using system properties can be done in the .gradle/gradle.properties file in the user’s home
directory, or by other means, see the section called “Gradle properties”.
Example 14. Specifying the HTTP Basic Authentication credentials using system properties
gradle.properties.
systemProp.gradle.wrapperUser=username
systemProp.gradle.wrapperPassword=password
Embedding credentials in the distributionUrl in the gradle/wrapper/gradle-wrapper.properties
file also works. Please note that this file is to be committed into your source control system. Shared
credentials embedded in distributionUrl should only be used in a controlled environment.
Example 15. Specifying the HTTP Basic Authentication credentials in distributionUrl
gradle/wrapper/gradle-wrapper.properties.
distributionUrl=https://username:password@somehost/path/to/gradle-distribution.zip
This can be used in conjunction with a proxy, authenticated or not. See the section called “Accessing the
web through a HTTP proxy” for more information on how to configure the Wrapper to use a proxy.
Verification of downloaded Gradle distributions
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§
Verification of downloaded Gradle distributions
The Gradle Wrapper allows for verification of the downloaded Gradle distribution via SHA-256 hash sum
comparison. This increases security against targeted attacks by preventing a man-in-the-middle attacker
from tampering with the downloaded Gradle distribution.
To enable this feature, download the .sha256 file associated with the Gradle distribution you want to verify.
§
Downloading the SHA-256 file
You can download the .sha256 file from the stable releases or release candidate and nightly releases. The
format of the file is a single line of text that is the SHA-256 hash of the corresponding zip file.
§
Configuring checksum verification
Add the downloaded hash sum to gradle-wrapper.properties using the distributionSha256Sum
property or use --gradle-distribution-sha256-sum on the command-line.
Example 16. Configuring SHA-256 checksum verification
gradle/wrapper/gradle-wrapper.properties.
distributionSha256Sum=371cb9fbebbe9880d147f59bab36d61eee122854ef8c9ee1ecf12b82368bcf10
Gradle will report a build failure in case the configured checksum does not match the checksum found on the
server for hosting the distribution. Checksum Verification is only performed if the configured Wrapper
distribution hasn’t been downloaded yet.
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The Gradle Daemon
From Wikipedia…
A daemon is a computer program that runs as a background process, rather than being under
the direct control of an interactive user.
Gradle runs on the Java Virtual Machine (JVM) and uses several supporting libraries that require a
non-trivial initialization time. As a result, it can sometimes seem a little slow to start. The solution to this
problem is the Gradle Daemon : a long-lived background process that executes your builds much more
quickly than would otherwise be the case. We accomplish this by avoiding the expensive bootstrapping
process as well as leveraging caching, by keeping data about your project in memory. Running Gradle builds
with the Daemon is no different than without. Simply configure whether you want to use it or not - everything
else is handled transparently by Gradle.
§
Why the Gradle Daemon is important for performance
The Daemon is a long-lived process, so not only are we able to avoid the cost of JVM startup for every build,
but we are able to cache information about project structure, files, tasks, and more in memory.
The reasoning is simple: improve build speed by reusing computations from previous builds. However, the
benefits are dramatic: we typically measure build times reduced by 15-75% on subsequent builds. We
recommend profiling your build by using --profile to get a sense of how much impact the Gradle Daemon
can have for you.
The Gradle Daemon is enabled by default starting with Gradle 3.0, so you don’t have to do anything to
benefit from it.
If you run CI builds in ephemeral environments (such as containers) that do not reuse any processes, use of
the Daemon will slightly decrease performance (due to caching additional information) for no benefit, and
may be disabled.
§
Running Daemon Status
To get a list of running Gradle Daemons and their statuses use the --status command.
Sample output:
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PID VERSION
28411 3.0
34247 3.0
STATUS
IDLE
BUSY
Currently, a given Gradle version can only connect to daemons of the same version. This means the status
output will only show Daemons for the version of Gradle being invoked and not for any other versions.
Future versions of Gradle will lift this constraint and will show the running Daemons for all versions of
Gradle.
§
Disabling the Daemon
The Gradle Daemon is enabled by default, and we recommend always enabling it. There are several ways to
disable the Daemon, but the most common one is to add the line
org.gradle.daemon=false
to the file «USER_HOME»/.gradle/gradle.properties, where «USER_HOME» is your home directory.
That’s typically one of the following, depending on your platform:
C:\Users\<username> (Windows Vista & 7+)
/Users/<username> (macOS)
/home/<username> (Linux)
If that file doesn’t exist, just create it using a text editor. You can find details of other ways to disable (and
enable) the Daemon in the section called “FAQ” further down. That section also contains more detailed
information on how the Daemon works.
Note that having the Daemon enabled, all your builds will take advantage of the speed boost, regardless of
the version of Gradle a particular build uses.
Continuous integration
Since Gradle 3.0, we enable Daemon by default and recommend using it for both developers'
machines and Continuous Integration servers. However, if you suspect that Daemon makes your CI
builds unstable, you can disable it to use a fresh runtime for each build since the runtime is
completely isolated from any previous builds.
§
Stopping an existing Daemon
As mentioned, the Daemon is a background process. You needn’t worry about a build up of Gradle
processes on your machine, though. Every Daemon monitors its memory usage compared to total system
memory and will stop itself if idle when available system memory is low. If you want to explicitly stop running
Daemon processes for any reason, just use the command gradle --stop.
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This will terminate all Daemon processes that were started with the same version of Gradle used to execute
the command. If you have the Java Development Kit (JDK) installed, you can easily verify that a Daemon
has stopped by running the jps command. You’ll see any running Daemons listed with the name GradleDaemon
.
§
FAQ
§
How do I disable the Gradle Daemon?
There are two recommended ways to disable the Daemon persistently for an environment:
Via environment variables: add the flag -Dorg.gradle.daemon=false to the GRADLE_OPTS environment
variable
Via properties file: add org.gradle.daemon=false to the «GRADLE_USER_HOME»/gradle.properties
file
Note: Note, «GRADLE_USER_HOME» defaults to «USER_HOME»/.gradle, where «USER_HOME» is
the home directory of the current user. This location can be configured via the -g and --gradle-user-home
command line switches, as well as by the GRADLE_USER_HOME environment variable and org.gradle.user.hom
JVM system property.
Both approaches have the same effect. Which one to use is up to personal preference. Most Gradle users
choose the second option and add the entry to the user gradle.properties file.
On Windows, this command will disable the Daemon for the current user:
(if not exist "%USERPROFILE%/.gradle" mkdir "%USERPROFILE%/.gradle") && (echo. >> "%USERPR
On UNIX-like operating systems, the following Bash shell command will disable the Daemon for the current
user:
mkdir -p ~/.gradle && echo "org.gradle.daemon=false" >> ~/.gradle/gradle.properties
Once the Daemon is disabled for a build environment in this way, a Gradle Daemon will not be started
unless explicitly requested using the --daemon option.
The --daemon and --no-daemon command line options enable and disable usage of the Daemon for
individual build invocations when using the Gradle command line interface. These command line options
have the highest precedence when considering the build environment. Typically, it is more convenient to
enable the Daemon for an environment (e.g. a user account) so that all builds use the Daemon without
requiring to remember to supply the --daemon option.
Why is there more than one Daemon process on my machine?
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§
Why is there more than one Daemon process on my machine?
There are several reasons why Gradle will create a new Daemon, instead of using one that is already
running. The basic rule is that Gradle will start a new Daemon if there are no existing idle or compatible
Daemons available. Gradle will kill any Daemon that has been idle for 3 hours or more, so you don’t have to
worry about cleaning them up manually.
idle
An idle Daemon is one that is not currently executing a build or doing other useful work.
compatible
A compatible Daemon is one that can (or can be made to) meet the requirements of the requested build
environment. The Java runtime used to execute the build is an example aspect of the build environment.
Another example is the set of JVM system properties required by the build runtime.
Some aspects of the requested build environment may not be met by an Daemon. If the Daemon is running
with a Java 7 runtime, but the requested environment calls for Java 8, then the Daemon is not compatible
and another must be started. Moreover, certain properties of a Java runtime cannot be changed once the
JVM has started. For example, it is not possible to change the memory allocation (e.g. -Xmx1024m), default
text encoding, default locale, etc of a running JVM.
The “requested build environment” is typically constructed implicitly from aspects of the build client’s (e.g.
Gradle command line client, IDE etc.) environment and explicitly via command line switches and settings.
See Build Environment for details on how to specify and control the build environment.
The following JVM system properties are effectively immutable. If the requested build environment requires
any of these properties, with a different value than a Daemon’s JVM has for this property, the Daemon is not
compatible.
file.encoding
user.language
user.country
user.variant
java.io.tmpdir
javax.net.ssl.keyStore
javax.net.ssl.keyStorePassword
javax.net.ssl.keyStoreType
javax.net.ssl.trustStore
javax.net.ssl.trustStorePassword
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javax.net.ssl.trustStoreType
com.sun.management.jmxremote
The following JVM attributes, controlled by startup arguments, are also effectively immutable. The
corresponding attributes of the requested build environment and the Daemon’s environment must match
exactly in order for a Daemon to be compatible.
The maximum heap size (i.e. the -Xmx JVM argument)
The minimum heap size (i.e. the -Xms JVM argument)
The boot classpath (i.e. the -Xbootclasspath argument)
The “assertion” status (i.e. the -ea argument)
The required Gradle version is another aspect of the requested build environment. Daemon processes are
coupled to a specific Gradle runtime. Working on multiple Gradle projects during a session that use different
Gradle versions is a common reason for having more than one running Daemon process.
§
How much memory does the Daemon use and can I give it more?
If the requested build environment does not specify a maximum heap size, the Daemon will use up to 1GB of
heap. It will use the JVM’s default minimum heap size. 1GB is more than enough for most builds. Larger
builds with hundreds of subprojects, lots of configuration, and source code may require, or perform better,
with more memory.
To increase the amount of memory the Daemon can use, specify the appropriate flags as part of the
requested build environment. Please see Build Environment for details.
§
How can I stop a Daemon?
Daemon processes will automatically terminate themselves after 3 hours of inactivity or less. If you wish to
stop a Daemon process before this, you can either kill the process via your operating system or run the gradle --stop
command. The --stop switch causes Gradle to request that all running Daemon processes, of the same
Gradle version used to run the command , terminate themselves.
§
What can go wrong with Daemon?
Considerable engineering effort has gone into making the Daemon robust, transparent and unobtrusive
during day to day development. However, Daemon processes can occasionally be corrupted or exhausted.
A Gradle build executes arbitrary code from multiple sources. While Gradle itself is designed for and heavily
tested with the Daemon, user build scripts and third party plugins can destabilize the Daemon process
through defects such as memory leaks or global state corruption.
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It is also possible to destabilize the Daemon (and build environment in general) by running builds that do not
release resources correctly. This is a particularly poignant problem when using Microsoft Windows as it is
less forgiving of programs that fail to close files after reading or writing.
Gradle actively monitors heap usage and attempts to detect when a leak is starting to exhaust the available
heap space in the daemon. When it detects a problem, the Gradle daemon will finish the currently running
build and proactively restart the daemon on the next build. This monitoring is enabled by default, but can be
disabled by setting the org.gradle.daemon.performance.enable-monitoring system property to
false.
If it is suspected that the Daemon process has become unstable, it can simply be killed. Recall that the --no-daemon
switch can be specified for a build to prevent use of the Daemon. This can be useful to diagnose whether or
not the Daemon is actually the culprit of a problem.
§
Tools & IDEs
The Gradle Tooling API (see Embedding Gradle using the Tooling API), that is used by IDEs and other tools
to integrate with Gradle, always use the Gradle Daemon to execute builds. If you are executing Gradle
builds from within you’re IDE you are using the Gradle Daemon and do not need to enable it for your
environment.
§
How does the Gradle Daemon make builds faster?
The Gradle Daemon is a long lived build process. In between builds it waits idly for the next build. This has
the obvious benefit of only requiring Gradle to be loaded into memory once for multiple builds, as opposed to
once for each build. This in itself is a significant performance optimization, but that’s not where it stops.
A significant part of the story for modern JVM performance is runtime code optimization. For example,
HotSpot (the JVM implementation provided by Oracle and used as the basis of OpenJDK) applies
optimization to code while it is running. The optimization is progressive and not instantaneous. That is, the
code is progressively optimized during execution which means that subsequent builds can be faster purely
due to this optimization process. Experiments with HotSpot have shown that it takes somewhere between 5
and 10 builds for optimization to stabilize. The difference in perceived build time between the first build and
the 10th for a Daemon can be quite dramatic.
The Daemon also allows more effective in memory caching across builds. For example, the classes needed
by the build (e.g. plugins, build scripts) can be held in memory between builds. Similarly, Gradle can
maintain in-memory caches of build data such as the hashes of task inputs and outputs, used for
incremental building.
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Dependency Management for Java Projects
This chapter introduces some of the basics of dependency management in Gradle.
§
What is dependency management?
Very roughly, dependency management is made up of two pieces. Firstly, Gradle needs to know about the
things that your project needs to build or run, in order to find them. We call these incoming files the
dependencies of the project. Secondly, Gradle needs to build and upload the things that your project
produces. We call these outgoing files the publications of the project. Let’s look at these two pieces in more
detail:
Most projects are not completely self-contained. They need files built by other projects in order to be
compiled or tested and so on. For example, in order to use Hibernate in my project, I need to include some
Hibernate jars in the classpath when I compile my source. To run my tests, I might also need to include
some additional jars in the test classpath, such as a particular JDBC driver or the Ehcache jars.
These incoming files form the dependencies of the project. Gradle allows you to tell it what the
dependencies of your project are, so that it can take care of finding these dependencies, and making them
available in your build. The dependencies might need to be downloaded from a remote Maven or Ivy
repository, or located in a local directory, or may need to be built by another project in the same multi-project
build. We call this process dependency resolution .
Note that this feature provides a major advantage over Ant. With Ant, you only have the ability to specify
absolute or relative paths to specific jars to load. With Gradle, you simply declare the “names” of your
dependencies, and other layers determine where to get those dependencies from. You can get similar
behavior from Ant by adding Apache Ivy, but Gradle does it better.
Often, the dependencies of a project will themselves have dependencies. For example, Hibernate core
requires several other libraries to be present on the classpath with it runs. So, when Gradle runs the tests for
your project, it also needs to find these dependencies and make them available. We call these transitive
dependencies .
The main purpose of most projects is to build some files that are to be used outside the project. For
example, if your project produces a Java library, you need to build a jar, and maybe a source jar and some
documentation, and publish them somewhere.
These outgoing files form the publications of the project. Gradle also takes care of this important work for
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you. You declare the publications of your project, and Gradle take care of building them and publishing them
somewhere. Exactly what “publishing” means depends on what you want to do. You might want to copy the
files to a local directory, or upload them to a remote Maven or Ivy repository. Or you might use the files in
another project in the same multi-project build. We call this process publication .
§
Declaring your dependencies
Let’s look at some dependency declarations. Here’s a basic build script:
Example 17. Declaring dependencies
build.gradle
apply plugin: 'java'
repositories {
mavenCentral()
}
dependencies {
compile group: 'org.hibernate', name: 'hibernate-core', version: '3.6.7.Final'
testCompile group: 'junit', name: 'junit', version: '4.+'
}
What’s going on here? This build script says a few things about the project. Firstly, it states that Hibernate
core 3.6.7.Final is required to compile the project’s production source. By implication, Hibernate core and its
dependencies are also required at runtime. The build script also states that any junit >= 4.0 is required to
compile the project’s tests. It also tells Gradle to look in the Maven central repository for any dependencies
that are required. The following sections go into the details.
§
Dependency configurations
A Configuration is a named set of dependencies and artifacts. There are three main purposes for a
Configuration:
Declaring Dependencies
The plugin uses configurations to make it easy for build authors to declare what other subprojects or
external artifacts are needed for various purposes during the execution of tasks defined by the plugin.
Resolving Dependencies
The plugin uses configurations to find (and possibly download) inputs to the tasks it defines.
Exposing Artifacts for Consumption
The plugin uses configurations to define what artifacts it generates for other projects to consume.
With those three purposes in mind, let’s take a look at a few of the standard configurations defined by the
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Java Library Plugin. You can find more details in the section called “The Java Library plugin configurations”.
implementation
The dependencies required to compile the production source of the project, but which are not part of the
api exposed by the project. This configuration is an example of a configuration used for Declaring
Dependencies.
runtimeClasspath
The dependencies required by the production classes at runtime. By default, this includes the
dependencies declared in the api, implementation, and runtimeOnly configurations. This
configuration is an example of a configuration used for Resolving Dependencies, and as such, users
should never declare dependencies directly in the runtimeClasspath configuration.
apiElements
The dependencies which are part of this project’s externally consumable API as well as the classes
which are defined in this project which should be consumable by other projects. This configuration is an
example of Exposing Artifacts for Consumption.
Various plugins add further standard configurations. You can also define your own custom configurations to
use in your build. Please see the section called “Defining the scope of a dependency with configurations” for
the details of defining and customizing dependency configurations.
§
External dependencies
There are various types of dependencies that you can declare. One such type is an external dependency .
This is a dependency on some files built outside the current build, and stored in a repository of some kind,
such as Maven central, or a corporate Maven or Ivy repository, or a directory in the local file system.
To define an external dependency, you add it to a dependency configuration:
Example 18. Definition of an external dependency
build.gradle
dependencies {
compile group: 'org.hibernate', name: 'hibernate-core', version: '3.6.7.Final'
}
An external dependency is identified using group, name and version attributes. Depending on which kind
of repository you are using, group and version may be optional.
The shortcut form for declaring external dependencies looks like “ group : name : version ”.
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Example 19. Shortcut definition of an external dependency
build.gradle
dependencies {
compile 'org.hibernate:hibernate-core:3.6.7.Final'
}
To find out more about defining dependencies, have a look at Declaring Dependencies.
§
Repositories
How does Gradle find the files for external dependencies? Gradle looks for them in a repository . A
repository is really just a collection of files, organized by group, name and version. Gradle understands
several different repository formats, such as Maven and Ivy, and several different ways of accessing the
repository, such as using the local file system or HTTP.
By default, Gradle does not define any repositories. You need to define at least one before you can use
external dependencies. One option is use the Maven central repository:
Example 20. Usage of Maven central repository
build.gradle
repositories {
mavenCentral()
}
Or Bintray’s JCenter:
Example 21. Usage of JCenter repository
build.gradle
repositories {
jcenter()
}
Or any other remote Maven repository:
Example 22. Usage of a remote Maven repository
build.gradle
repositories {
maven {
url "http://repo.mycompany.com/maven2"
}
}
Or a remote Ivy repository:
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Example 23. Usage of a remote Ivy directory
build.gradle
repositories {
ivy {
url "http://repo.mycompany.com/repo"
}
}
You can also have repositories on the local file system. This works for both Maven and Ivy repositories.
Example 24. Usage of a local Ivy directory
build.gradle
repositories {
ivy {
// URL can refer to a local directory
url "../local-repo"
}
}
A project can have multiple repositories. Gradle will look for a dependency in each repository in the order
they are specified, stopping at the first repository that contains the requested module.
To find out more about defining repositories, have a look at Declaring Repositories.
§
Publishing artifacts
Dependency configurations are also used to publish files.[2] We call these files publication artifacts , or
usually just artifacts .
The plugins do a pretty good job of defining the artifacts of a project, so you usually don’t need to do
anything special to tell Gradle what needs to be published. However, you do need to tell Gradle where to
publish the artifacts. You do this by attaching repositories to the uploadArchives task. Here’s an example
of publishing to a remote Ivy repository:
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Example 25. Publishing to an Ivy repository
build.gradle
uploadArchives {
repositories {
ivy {
credentials {
username "username"
password "pw"
}
url "http://repo.mycompany.com"
}
}
}
Now, when you run gradle uploadArchives, Gradle will build and upload your Jar. Gradle will also
generate and upload an ivy.xml as well.
You can also publish to Maven repositories. The syntax is slightly different. [3] Note that you also need to
apply the Maven plugin in order to publish to a Maven repository. when this is in place, Gradle will generate
and upload a pom.xml.
Example 26. Publishing to a Maven repository
build.gradle
apply plugin: 'maven'
uploadArchives {
repositories {
mavenDeployer {
repository(url: "file://localhost/tmp/myRepo/")
}
}
}
To find out more about publication, have a look at Publishing artifacts.
§
Where to next?
For all the details of dependency resolution, see Introduction to Dependency Management, and for artifact
publication see Publishing artifacts.
If you are interested in the DSL elements mentioned here, have a look at Project.configurations{},
Project.repositories{} and Project.dependencies{}.
Otherwise, continue on to some guides.
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[2] We think this is confusing, and we are gradually teasing apart the two concepts in the Gradle DSL.
[3] We are working to make the syntax consistent for resolving from and publishing to Maven repositories.
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Executing Multi-Project Builds
Only the smallest of projects has a single build file and source tree, unless it happens to be a massive,
monolithic application. It’s often much easier to digest and understand a project that has been split into
smaller, inter-dependent modules. The word “inter-dependent” is important, though, and is why you typically
want to link the modules together through a single build.
Gradle supports this scenario through multi-project builds.
§
Structure of a multi-project build
Such builds come in all shapes and sizes, but they do have some common characteristics:
A settings.gradle file in the root or master directory of the project
A build.gradle file in the root or master directory
Child directories that have their own *.gradle build files (some multi-project builds may omit child project
build scripts)
The settings.gradle file tells Gradle how the project and subprojects are structured. Fortunately, you
don’t have to read this file simply to learn what the project structure is as you can run the command gradle projects
. Here’s the output from using that command on the Java multiproject build in the Gradle samples:
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Example 27. Listing the projects in a build
Output of gradle -q projects
> gradle -q projects
-----------------------------------------------------------Root project
-----------------------------------------------------------Root
+--+--|
|
\---
project 'multiproject'
Project ':api'
Project ':services'
+--- Project ':services:shared'
\--- Project ':services:webservice'
Project ':shared'
To see a list of the tasks of a project, run gradle <project-path>:tasks
For example, try running gradle :api:tasks
This tells you that multiproject has three immediate child projects: api , services and shared . The services
project then has its own children, shared and webservice . These map to the directory structure, so it’s easy
to find them. For example, you can find webservice in <root>/services/webservice.
By default, Gradle uses the name of the directory it finds the settings.gradle as the name of the root
project. This usually doesn’t cause problems since all developers check out the same directory name when
working on a project. On Continuous Integration servers, like Jenkins, the directory name may be
auto-generated and not match the name in your VCS. For that reason, it’s recommended that you always set
the root project name to something predictable, even in single project builds. You can configure the root
project name by setting rootProject.name.
Each project will usually have its own build file, but that’s not necessarily the case. In the above example, the
services project is just a container or grouping of other subprojects. There is no build file in the
corresponding directory. However, multiproject does have one for the root project.
The root build.gradle is often used to share common configuration between the child projects, for
example by applying the same sets of plugins and dependencies to all the child projects. It can also be used
to configure individual subprojects when it is preferable to have all the configuration in one place. This
means you should always check the root build file when discovering how a particular subproject is being
configured.
Another thing to bear in mind is that the build files might not be called build.gradle. Many projects will
name the build files after the subproject names, such as api.gradle and services.gradle from the
previous example. Such an approach helps a lot in IDEs because it’s tough to work out which build.gradle
file out of twenty possibilities is the one you want to open. This little piece of magic is handled by the settings.gradle
file, but as a build user you don’t need to know the details of how it’s done. Just have a look through the child
project directories to find the files with the .gradle suffix.
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Once you know what subprojects are available, the key question for a build user is how to execute the tasks
within the project.
§
Executing a multi-project build
From a user’s perspective, multi-project builds are still collections of tasks you can run. The difference is that
you may want to control which project’s tasks get executed. You have two options here:
Change to the directory corresponding to the subproject you’re interested in and just execute gradle <task>
as normal.
Use a qualified task name from any directory, although this is usually done from the root. For example: gradle :servic
will build the webservice subproject and any subprojects it depends on.
The first approach is similar to the single-project use case, but Gradle works slightly differently in the case of
a multi-project build. The command gradle test will execute the test task in any subprojects, relative to
the current working directory, that have that task. So if you run the command from the root project directory,
you’ll run test in api , shared , services:shared and services:webservice . If you run the command from the
services project directory, you’ll only execute the task in services:shared and services:webservice .
For more control over what gets executed, use qualified names (the second approach mentioned). These
are paths just like directory paths, but use ‘:’ instead of ‘/’ or ‘\’. If the path begins with a ‘:’, then the path is
resolved relative to the root project. In other words, the leading ‘:’ represents the root project itself. All other
colons are path separators.
This approach works for any task, so if you want to know what tasks are in a particular subproject, just use
the tasks task, e.g. gradle :services:webservice:tasks .
Regardless of which technique you use to execute tasks, Gradle will take care of building any subprojects
that the target depends on. You don’t have to worry about the inter-project dependencies yourself. If you’re
interested in how this is configured, you can read about writing multi-project builds later in the user guide.
There’s one last thing to note. When you’re using the Gradle wrapper, the first approach doesn’t work well
because you have to specify the path to the wrapper script if you’re not in the project root. For example, if
you’re in the webservice subproject directory, you would have to run ../../gradlew build.
That’s all you really need to know about multi-project builds as a build user. You can now identify whether a
build is a multi-project one and you can discover its structure. And finally, you can execute tasks within
specific subprojects.
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Continuous build
Note: Continuous build is an incubating feature. This means that it is incomplete and not yet at
regular Gradle production quality. This also means that this Gradle User Guide chapter is a work in
progress.
Typically, you ask Gradle to perform a single build by way of specifying tasks that Gradle should execute.
Gradle will determine the actual set of tasks that need to be executed to satisfy the request, execute them
all, and then stop doing work until the next request. A continuous build differs in that Gradle will keep
satisfying the initial build request (until instructed to stop) by executing the build when it is detected that the
result of the previous build is now out of date. For example, if your build compiles Java source files to Java
class files, a continuous build would automatically initiate a compile when the source files change.
Continuous build is useful for many scenarios.
§
How do I start and stop a continuous build?
A continuous build can be started by supplying either the --continuous or -t switches to Gradle, along
with the list of tasks, switches and arguments that define the work to do. For example, gradle build --continuous
. This will have the same effect as running gradle build, but instead of Gradle exiting when done, it will
wait for changes to the build inputs. When a change occurs, gradle build will be automatically executed
again and the process repeats.
If Gradle is attached to an interactive input source, such as a terminal, the continuous build can be exited by
pressing CTRL-D (On Microsoft Windows, it is required to also press ENTER or RETURN after CTRL-D). If
Gradle is not attached to an interactive input source (e.g. is running as part of a script), the build process
must be terminated (e.g. using the kill command or similar). If the build is being executed via the Tooling
API, the build can be cancelled using the Tooling API’s cancellation mechanism.
§
What will cause a subsequent build?
Task file inputs
Task implementations declare their file system inputs by annotating their properties with
InputFiles and other similar annotations. Please see the section called “Up-to-date checks (AKA
Incremental Build)” for more information.
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At this time, only changes to task inputs are noticed. Gradle will start watching for changes just before the
task starts to execute. No other changes will initiate a build. For example, changes to build scripts and build
logic will not initiate build. Likewise, changes to files that are read during the configuration of the build, not
the execution, will not initiate a build. In order to incorporate such changes, the continuous build must be
restarted manually.
Consider a typical build using the Java plugin, using the conventional filesystem layout. The following
diagram visualizes the task graph for gradle build:
Figure 4. Java plugin task graph
The following key tasks of the graph use files in the corresponding directories as inputs:
compileJava
src/main/java
processResources
src/main/resources
compileTestJava
src/test/java
processTestResources
src/test/resources
Assuming that the initial build is successful (i.e. the build task and its dependencies complete without
error), changes to files in, or the addition/remove of files from, the locations listed above will initiate a new
build. If a change is made to a Java source file in src/main/java, the build will fire and all tasks will be
scheduled. Gradle’s incremental build support ensures that only the tasks that are actually affected by the
change are executed.
If the change to the main Java source causes compilation to fail, subsequent changes to the test source in src/test/ja
will not initiate a new build. As the test source depends on the main source, there is no point building until
the main source has changed, potentially fixing the compilation error. After each build, only the inputs of the
tasks that actually executed will be monitored for changes.
Continuous build is in no way coupled to compilation. It works for all types of tasks. For example, the processResources
task copies and processes the files from src/main/resources for inclusion in the built JAR. As such, a
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change to any file in this directory will also initiate a build.
§
Limitations and quirks
There are several issues to be aware with the current implementation of continuous build. These are likely to
be addressed in future Gradle releases.
§
Build cycles
Gradle starts watching for changes just before a task executes. If a task modifies its own inputs while
executing, Gradle will detect the change and trigger a new build. If every time the task executes, the inputs
are modified again, the build will be triggered again. This isn’t unique to continuous build. A task that
modifies its own inputs will never be considered up-to-date when run "normally" without continuous build.
If your build enters a build cycle like this, you can track down the task by looking at the list of files reported
changed by Gradle. After identifying the file(s) that are changed during each build, you should look for a task
that has that file as an input. In some cases, it may be obvious (e.g., a Java file is compiled with compileJava
). In other cases, you can use --info logging to find the task that is out-of-date due to the identified files.
§
Restrictions with Java 9
Due to class access restrictions related to Java 9, Gradle cannot set some operating system specific
options, which means that:
On macOS, Gradle will poll for file changes every 10 seconds instead of every 2 seconds.
On Windows, Gradle must use individual file watches (like on Linux/Mac OS), which may cause continuous
build to no longer work on very large projects.
§
Performance and stability
The JDK file watching facility relies on inefficient file system polling on macOS (see: JDK-7133447). This can
significantly delay notification of changes on large projects with many source files.
Additionally, the watching mechanism may deadlock under heavy load on macOS (see: JDK-8079620). This
will manifest as Gradle appearing not to notice file changes. If you suspect this is occurring, exit continuous
build and start again.
On Linux, OpenJDK’s implementation of the file watch service can sometimes miss file system events (see:
JDK-8145981).
Changes to symbolic links
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§
Changes to symbolic links
Creating or removing symbolic link to files will initiate a build.
Modifying the target of a symbolic link will not cause a rebuild.
Creating or removing symbolic links to directories will not cause rebuilds.
Creating new files in the target directory of a symbolic link will not cause a rebuild.
Deleting the target directory will not cause a rebuild.
§
Changes to build logic are not considered
The current implementation does not recalculate the build model on subsequent builds. This means that
changes to task configuration, or any other change to the build model, are effectively ignored.
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Composite builds
Note: Composite build is an incubating feature. While useful for many use cases, there are bugs to
be discovered, rough edges to smooth, and enhancements we plan to make. Thanks for trying it out!
§
What is a composite build?
A composite build is simply a build that includes other builds. In many ways a composite build is similar to a
Gradle multi-project build, except that instead of including single projects, complete builds are included.
Composite builds allow you to:
combine builds that are usually developed independently, for instance when trying out a bug fix in a library
that your application uses
decompose a large multi-project build into smaller, more isolated chunks that can be worked in
independently or together as needed
A build that is included in a composite build is referred to, naturally enough, as an "included build". Included
builds do not share any configuration with the composite build, or the other included builds. Each included
build is configured and executed in isolation.
Included builds interact with other builds via dependency substitution. If any build in the composite
has a dependency that can be satisfied by the included build, then that dependency will be replaced by a
project dependency on the included build.
By default, Gradle will attempt to determine the dependencies that can be substituted by an included build.
However for more flexibility, it is possible to explicitly declare these substitutions if the default ones
determined by Gradle are not correct for the composite. See the section called “Declaring the dependencies
substituted by an included build”.
As well as consuming outputs via project dependencies, a composite build can directly declare task
dependencies on included builds. Included builds are isolated, and are not able to declare task
dependencies on the composite build or on other included builds. See the section called “Depending on
tasks in an included build”.
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Defining a composite build
§
Defining a composite build
The following examples demonstrate the various ways that 2 Gradle builds that are normally developed
separately can be combined into a composite build. For these examples, the my-utils multi-project build
produces 2 different java libraries (number-utils and string-utils), and the my-app build produces
an executable using functions from those libraries.
The my-app build does not have direct dependencies on my-utils. Instead, it declares binary
dependencies on the libraries produced by my-utils.
Example 28. Dependencies of my-app
my-app/build.gradle
apply plugin: 'java'
apply plugin: 'application'
apply plugin: 'idea'
group "org.sample"
version "1.0"
mainClassName = "org.sample.myapp.Main"
dependencies {
compile "org.sample:number-utils:1.0"
compile "org.sample:string-utils:1.0"
}
repositories {
jcenter()
}
Note: The code for this example can be found at samples/compositeBuilds/basic in the ‘-all’
distribution of Gradle.
§
Defining a composite build via --include-build
The --include-build command-line argument turns the executed build into a composite, substituting
dependencies from the included build into the executed build.
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Example 29. Declaring a command-line composite
Output of gradle --include-build ../my-utils run
> gradle --include-build ../my-utils run
:processResources NO-SOURCE
:my-utils:string-utils:compileJava
:my-utils:string-utils:processResources NO-SOURCE
:my-utils:string-utils:classes
:my-utils:string-utils:jar
:my-utils:number-utils:compileJava
:my-utils:number-utils:processResources NO-SOURCE
:my-utils:number-utils:classes
:my-utils:number-utils:jar
:compileJava
:classes
:run
The answer is 42
BUILD SUCCESSFUL in 0s
2 actionable tasks: 2 executed
§
Defining a composite build via settings.gradle
It’s
possible
to
make
the
above
arrangement
persistent,
by
using
Settings.includeBuild(java.lang.Object) to declare the included build in the settings.gradle
file. The settings.gradle file can be used to add subprojects and included builds at the same time.
Included builds are added by location. See the examples below for more details.
§
Defining a separate composite build
One downside of the above approach is that it requires you to modify an existing build, rendering it less
useful as a standalone build. One way to avoid this is to define a separate composite build, whose only
purpose is to combine otherwise separate builds.
Example 30. Declaring a separate composite
settings.gradle
rootProject.name='adhoc'
includeBuild '../my-app'
includeBuild '../my-utils'
In this scenario, the 'main' build that is executed is the composite, and it doesn’t define any useful tasks to
execute itself. In order to execute the 'run' task in the 'my-app' build, the composite build must define a
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delegating task.
Example 31. Depending on task from included build
build.gradle
task run {
dependsOn gradle.includedBuild('my-app').task(':run')
}
More details tasks that depend on included build tasks below.
§
Restrictions on included builds
Most builds can be included into a composite, however there are some limitations.
Every included build:
must have a settings.gradle file.
must not itself be a composite build.
must not have a rootProject.name the same as another included build.
must not have a rootProject.name the same as a top-level project of the composite build.
must not have a rootProject.name the same as the composite build rootProject.name.
§
Interacting with a composite build
In general, interacting with a composite build is much the same as a regular multi-project build. Tasks can be
executed, tests can be run, and builds can be imported into the IDE.
§
Executing tasks
Tasks from the composite build can be executed from the command line, or from you IDE. Executing a task
will result in direct task dependencies being executed, as well as those tasks required to build dependency
artifacts from included builds.
Note: There is not (yet) any means to directly execute a task from an included build via the
command line. Included build tasks are automatically executed in order to generate required
dependency artifacts, or the including build can declare a dependency on a task from an included
build.
Importing into the IDE
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§
Importing into the IDE
One of the most useful features of composite builds is IDE integration. By applying the idea or eclipse plugin
to your build, it is possible to generate a single IDEA or Eclipse project that permits all builds in the
composite to be developed together.
In addition to these Gradle plugins, recent versions of IntelliJ IDEA and Eclipse Buildship support direct
import of a composite build.
Importing a composite build permits sources from separate Gradle builds to be easily developed together.
For every included build, each sub-project is included as an IDEA Module or Eclipse Project. Source
dependencies are configured, providing cross-build navigation and refactoring.
§
Declaring the dependencies substituted by an included build
By default, Gradle will configure each included build in order to determine the dependencies it can provide.
The algorithm for doing this is very simple: Gradle will inspect the group and name for the projects in the
included build, and substitute project dependencies for any external dependency matching ${project.group}:${proj
.
There are cases when the default substitutions determined by Gradle are not sufficient, or they are not
correct for a particular composite. For these cases it is possible to explicitly declare the substitutions for an
included build. Take for example a single-project build 'unpublished', that produces a java utility library but
does not declare a value for the group attribute:
Example 32. Build that does not declare group attribute
build.gradle
apply plugin: 'java'
When this build is included in a composite, it will attempt to substitute for the dependency module
"undefined:unpublished" ("undefined" being the default value for project.group, and 'unpublished' being
the root project name). Clearly this isn’t going to be very useful in a composite build. To use the unpublished
library unmodified in a composite build, the composing build can explicitly declare the substitutions that it
provides:
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Example 33. Declaring the substitutions for an included build
settings.gradle
rootProject.name = 'app'
includeBuild('../anonymous-library') {
dependencySubstitution {
substitute module('org.sample:number-utils') with project(':')
}
}
With this configuration, the "my-app" composite build will substitute any dependency on org.sample:number-utils
with a dependency on the root project of "unpublished".
§
Cases where included build substitutions must be declared
Many builds that use the uploadArchives task to publish artifacts will function automatically as an
included build, without declared substitutions. Here are some common cases where declared substitutions
are required:
When the archivesBaseName property is used to set the name of the published artifact.
When a configuration other than default is published: this usually means a task other than uploadArchives
is used.
When the MavenPom.addFilter() is used to publish artifacts that don’t match the project name.
When the maven-publish or ivy-publish plugins are used for publishing, and the publication
coordinates don’t match ${project.group}:${project.name}.
§
Cases where composite build substitutions won’t work
Some builds won’t function correctly when included in a composite, even when dependency substitutions are
explicitly declared. This limitation is due to the fact that a project dependency that is substituted will always
point to the default configuration of the target project. Any time that the artifacts and dependencies
specified for the default configuration of a project don’t match what is actually published to a repository, then
the composite build may exhibit different behaviour.
Here are some cases where the publish module metadata may be different from the project default
configuration:
When a configuration other than default is published.
When the maven-publish or ivy-publish plugins are used.
When the POM or ivy.xml file is tweaked as part of publication.
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Builds using these features function incorrectly when included in a composite build. We plan to improve this
in the future.
§
Depending on tasks in an included build
While included builds are isolated from one another and cannot declare direct dependencies, a composite
build is able to declare task dependencies on its included builds. The included builds are accessed using
Gradle.getIncludedBuilds() or Gradle.includedBuild(java.lang.String), and a task
reference is obtained via the IncludedBuild.task(java.lang.String) method.
Using these APIs, it is possible to declare a dependency on a task in a particular included build, or tasks with
a certain path in all or some of the included builds.
Example 34. Depending on a single task from an included build
build.gradle
task run {
dependsOn gradle.includedBuild('my-app').task(':run')
}
Example 35. Depending on a tasks with path in all included builds
build.gradle
task publishDeps {
dependsOn gradle.includedBuilds*.task(':uploadArchives')
}
§
Current limitations and future plans for composite builds
We think composite builds are pretty useful already. However, there are some things that don’t yet work the
way we’d like, and other improvements that we think will make things work even better.
Limitations of the current implementation include:
No support for included builds that have publications that don’t mirror the project default configuration. See
the section called “Cases where composite build substitutions won’t work”.
Native builds are not supported. (Binary dependencies are not yet supported for native builds).
Substituting plugins only works with the buildscript block but not with the plugins block.
Improvements we have planned for upcoming releases include:
Better detection of dependency substitution, for build that publish with custom coordinates, builds that
produce multiple components, etc. This will reduce the cases where dependency substitution needs to be
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explicitly declared for an included build.
The ability to target a task or tasks in an included build directly from the command line. We are currently
exploring syntax options for allowing this functionality, which will remove many cases where a delegating
task is required in the composite.
Making the implicit buildSrc project an included build.
Supporting composite-of-composite builds.
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Build Environment
Gradle provides multiple mechanisms for configuring behavior of Gradle itself and specific projects. The
following is a reference for using these mechanisms.
When configuring Gradle behavior you can use these methods, listed in order of highest to lowest
precedence (first one wins):
Command-line flags such as --build-cache. These have precedence over properties and environment
variables.
System properties such as systemProp.http.proxyHost=somehost.org stored in a gradle.properties
file.
Gradle properties such as org.gradle.caching=true that are typically stored in a gradle.properties
file in a project root directory or GRADLE_USER_HOME environment variable.
Environment variables such as GRADLE_OPTS sourced by the environment that executes Gradle.
Aside from configuring the build environment, you can configure a given project build using Project
properties such as -PreleaseType=final.
§
Gradle properties
Gradle provides several options that make it easy to configure the Java process that will be used to execute
your build. While it’s possible to configure these in your local environment via GRADLE_OPTS or JAVA_OPTS,
it is useful to store certain settings like JVM memory configuration and Java home location in version control
so that an entire team can work with a consistent environment.
Setting up a consistent environment for your build is as simple as placing these settings into a gradle.properties
file. The configuration is applied in following order (if an option is configured in multiple locations the last one
wins ):
gradle.properties in project root directory.
gradle.properties in GRADLE_USER_HOME directory.
system properties, e.g. when -Dgradle.user.home is set on the command line.
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The following properties can be used to configure the Gradle build environment:
org.gradle.caching=(true,false)
When set to true, Gradle will reuse task outputs from any previous build, when possible, resulting is much
faster builds. Learn more about using the build cache.
org.gradle.configureondemand=(true,false)
Enables incubating configuration on demand, where Gradle will attempt to configure only necessary
projects.
org.gradle.console=(auto,plain,rich,verbose)
Customize console output coloring or verbosity. Default depends on how Gradle is invoked. See
command-line logging for additional details.
org.gradle.daemon=(true,false)
When set to true the Gradle Daemon is used to run the build. Default is true.
org.gradle.daemon.idletimeout=(# of idle millis)
Gradle Daemon will terminate itself after specified number of idle milliseconds. Default is 10800000 (3
hours).
org.gradle.debug=(true,false)
When set to true, Gradle will run the build with remote debugging enabled, listening on port 5005. Note
that this is the equivalent of adding -agentlib:jdwp=transport=dt_socket,server=y,suspend=y,address=
to the JVM command line and will suspend the virtual machine until a debugger is attached. Default is false
.
org.gradle.java.home=(path to JDK home)
Specifies the Java home for the Gradle build process. The value can be set to either a jdk or jre
location, however, depending on what your build does, using a JDK is safer. A reasonable default is used
if the setting is unspecified.
org.gradle.jvmargs=(JVM arguments)
Specifies the JVM arguments used for the Gradle Daemon. The setting is particularly useful for
configuring JVM memory settings for build performance.
org.gradle.logging.level=(quiet,warn,lifecycle,info,debug)
When set to quiet, warn, lifecycle, info, or debug, Gradle will use this log level. The values are not case
sensitive. The lifecycle level is the default. See the section called “Choosing a log level”.
org.gradle.parallel=(true,false)
When configured, Gradle will fork up to org.gradle.workers.max JVMs to execute projects in
parallel. To learn more about parallel task execution, see the Gradle performance guide.
org.gradle.warning.mode=(all,none,summary)
When set to all, summary or none, Gradle will use different warning type display. See the section
called “Logging options” for details.
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org.gradle.workers.max=(max # of worker processes)
When configured, Gradle will use a maximum of the given number of workers. Default is number of CPU
processors. See also performance command-line options.
The following example demonstrates usage of various properties.
Example 36. Setting properties with a gradle.properties file
gradle.properties
gradlePropertiesProp=gradlePropertiesValue
sysProp=shouldBeOverWrittenBySysProp
envProjectProp=shouldBeOverWrittenByEnvProp
systemProp.system=systemValue
build.gradle
task printProps
doLast {
println
println
println
println
println
}
}
Output
of
{
commandLineProjectProp
gradlePropertiesProp
systemProjectProp
envProjectProp
System.properties['system']
gradle
-q
-PcommandLineProjectProp=commandLineProjectPropValue
-Dorg.gradle.project.systemProjectProp=systemPropertyValue printProps
> gradle -q -PcommandLineProjectProp=commandLineProjectPropValue -Dorg.gradle.project.syst
commandLineProjectPropValue
gradlePropertiesValue
systemPropertyValue
envPropertyValue
systemValue
§
System properties
Using the -D command-line option, you can pass a system property to the JVM which runs Gradle. The -D
option of the gradle command has the same effect as the -D option of the java command.
You can also set system properties in gradle.properties files with the prefix systemProp.
Example 37. Specifying system properties in gradle.properties
systemProp.gradle.wrapperUser=myuser
systemProp.gradle.wrapperPassword=mypassword
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The following system properties are available. Note that command-line options take precedence over system
properties.
gradle.wrapperUser=(myuser)
Specify user name to download Gradle distributions from servers using HTTP Basic Authentication.
Learn more in the section called “Authenticated Gradle distribution download”.
gradle.wrapperPassword=(mypassword)
Specify password for downloading a Gradle distribution using the Gradle wrapper.
gradle.user.home=(path to directory)
Specify the Gradle user home directory.
In a multi project build, “systemProp.” properties set in any project except the root will be ignored. That is,
only the root project’s gradle.properties file will be checked for properties that begin with the “systemProp.
” prefix.
§
Environment variables
The following environment variables are available for the gradle command. Note that command-line
options and system properties take precedence over environment variables.
GRADLE_OPTS
Specifies command-line arguments to use when starting the Gradle client. This can be useful for setting
the properties to use when running Gradle.
GRADLE_USER_HOME
Specifies the Gradle user home directory (which defaults to $USER_HOME/.gradle if not set).
JAVA_HOME
Specifies the JDK installation directory to use.
§
Project properties
You can add properties directly to your Project object via the -P command line option.
Gradle can also set project properties when it sees specially-named system properties or environment
variables. If the environment variable name looks like ORG_GRADLE_PROJECT _prop =somevalue, then
Gradle will set a prop property on your project object, with the value of somevalue. Gradle also supports
this for system properties, but with a different naming pattern, which looks like org.gradle.project.prop
. Both of the following will set the foo property on your Project object to "bar".
Example 38. Setting a project property via gradle.properties
org.gradle.project.foo=bar
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Example 39. Setting a project property via environment variable
ORG_GRADLE_PROJECT_foo=bar
Note: The properties file in the user’s home directory has precedence over property files in the
project directories.
This feature is very useful when you don’t have admin rights to a continuous integration server and you need
to set property values that should not be easily visible. Since you cannot use the -P option in that scenario,
nor change the system-level configuration files, the correct strategy is to change the configuration of your
continuous integration build job, adding an environment variable setting that matches an expected pattern.
This won’t be visible to normal users on the system.
You can access a project property in your build script simply by using its name as you would use a variable.
Note: If a project property is referenced but does not exist, an exception will be thrown and the build
will fail.
You should check for existence of optional project properties before you access them using the
Project.hasProperty(java.lang.String) method.
§
Configuring JVM memory
Gradle defaults to 1024 megabytes maximum heap per JVM process ( -Xmx1024m), however, that may be
too much or too little depending on the size of your project. There are many JVM options (this blog post on
Java performance tuning and this reference may be helpful).
You can adjust JVM options for Gradle in the following ways:
The JAVA_OPTS environment variable is used for the Gradle client, but not forked JVMs.
Example 40. Changing JVM settings for Gradle client JVM
JAVA_OPTS="-Xmx2g -XX:MaxPermSize=256m -XX:+HeapDumpOnOutOfMemoryError -Dfile.encoding=UTF
You need to use the org.gradle.jvmargs Gradle property to configure JVM settings for the Gradle
Daemon.
Example 41. Changing JVM settings for forked Gradle JVMs
org.gradle.jvmargs=-Xmx2g -XX:MaxPermSize=256m -XX:+HeapDumpOnOutOfMemoryError -Dfile.enco
Note: Many settings (like the Java version and maximum heap size) can only be specified when
launching a new JVM for the build process. This means that Gradle must launch a separate JVM
process to execute the build after parsing the various gradle.properties files.
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When running with the Gradle Daemon, a JVM with the correct parameters is started once and
reused for each daemon build execution. When Gradle is executed without the daemon, then a new
JVM must be launched for every build execution, unless the JVM launched by the Gradle start script
happens to have the same parameters.
Certain tasks in Gradle also fork additional JVM processes, like the test task when using
Test.setMaxParallelForks(int) for JUnit or TestNG tests. You must configure these through the
tasks themselves.
Example 42. Set Java compile options for JavaCompile tasks
apply plugin: "java"
tasks.withType(JavaCompile) {
options.compilerArgs += ["-Xdoclint:none", "-Xlint:none", "-nowarn"]
}
See other examples in the Test API documentation and test execution in the Java plugin reference.
Build scans will tell you information about the JVM that executed the build when you use the --scan option.
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Configuring a task using project properties
§
Configuring a task using project properties
It’s possible to change the behavior of a task based on project properties specified at invocation time.
Suppose you’d like to ensure release builds are only triggered by CI. A simple way to handle this is through
an isCI project property.
Example 43. Prevent releasing outside of CI
build.gradle
task performRelease {
doLast {
if (project.hasProperty("isCI")) {
println("Performing release actions")
} else {
throw new InvalidUserDataException("Cannot perform release outside of CI")
}
}
}
Output of gradle performRelease -PisCI=true --quiet
> gradle performRelease -PisCI=true --quiet
Performing release actions
§
Accessing the web through a HTTP proxy
Configuring an HTTP or HTTPS proxy (for downloading dependencies, for example) is done via standard
JVM system properties. These properties can be set directly in the build script; for example, setting the
HTTP proxy host would be done with System.setProperty('http.proxyHost', 'www.somehost.org')
. Alternatively, the properties can be specified in gradle.properties.
Example 44. Configuring an HTTP proxy using gradle.properties
systemProp.http.proxyHost=www.somehost.org
systemProp.http.proxyPort=8080
systemProp.http.proxyUser=userid
systemProp.http.proxyPassword=password
systemProp.http.nonProxyHosts=*.nonproxyrepos.com|localhost
There are separate settings for HTTPS.
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Example 45. Configuring an HTTPS proxy using gradle.properties
systemProp.https.proxyHost=www.somehost.org
systemProp.https.proxyPort=8080
systemProp.https.proxyUser=userid
systemProp.https.proxyPassword=password
systemProp.https.nonProxyHosts=*.nonproxyrepos.com|localhost
You may need to set other properties to access other networks. Here are 2 references that may be helpful:
ProxySetup.java in the Ant codebase
JDK 7 Networking Properties
§
NTLM Authentication
If your proxy requires NTLM authentication, you may need to provide the authentication domain as well as
the username and password. There are 2 ways that you can provide the domain for authenticating to a
NTLM proxy:
Set the http.proxyUser system property to a value like domain / username .
Provide the authentication domain via the http.auth.ntlm.domain system property.
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Troubleshooting
Note: This chapter is currently a work in progress.
When using Gradle (or any software package), you can run into problems. You may not understand how to
use a particular feature, or you may encounter a defect. Or, you may have a general question about Gradle.
This chapter gives some advice for troubleshooting problems and explains how to get help with your
problems.
§
Working through problems
If you are encountering problems, one of the first things to try is using the very latest release of Gradle. New
versions of Gradle are released frequently with bug fixes and new features. The problem you are having may
have been fixed in a new release.
If you are using the Gradle Daemon, try temporarily disabling the daemon (you can pass the command line
switch --no-daemon). More information about troubleshooting the daemon process is located in The
Gradle Daemon.
§
Getting help
The place to go for help with Gradle is http://forums.gradle.org. The Gradle Forums is the place where you
can report problems and ask questions of the Gradle developers and other community members.
If something’s not working for you, posting a question or problem report to the forums is the fastest way to
get help. It’s also the place to post improvement suggestions or new ideas. The development team
frequently posts news items and announces releases via the forum, making it a great way to stay up to date
with the latest Gradle developments.
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Embedding Gradle using the Tooling API
§
Introduction to the Tooling API
Gradle provides a programmatic API called the Tooling API, which you can use for embedding Gradle into
your own software. This API allows you to execute and monitor builds and to query Gradle about the details
of a build. The main audience for this API is IDE, CI server, other UI authors; however, the API is open for
anyone who needs to embed Gradle in their application.
Gradle TestKit uses the Tooling API for functional testing of your Gradle plugins.
Eclipse Buildship uses the Tooling API for importing your Gradle project and running tasks.
IntelliJ IDEA uses the Tooling API for importing your Gradle project and running tasks.
§
Tooling API Features
A fundamental characteristic of the Tooling API is that it operates in a version independent way. This means
that you can use the same API to work with builds that use different versions of Gradle, including versions
that are newer or older than the version of the Tooling API that you are using. The Tooling API is Gradle
wrapper aware and, by default, uses the same Gradle version as that used by the wrapper-powered build.
Some features that the Tooling API provides:
Query the details of a build, including the project hierarchy and the project dependencies, external
dependencies (including source and Javadoc jars), source directories and tasks of each project.
Execute a build and listen to stdout and stderr logging and progress messages (e.g. the messages shown in
the 'status bar' when you run on the command line).
Execute a specific test class or test method.
Receive interesting events as a build executes, such as project configuration, task execution or test
execution.
Cancel a build that is running.
Combine multiple separate Gradle builds into a single composite build.
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The Tooling API can download and install the appropriate Gradle version, similar to the wrapper.
The implementation is lightweight, with only a small number of dependencies. It is also a well-behaved
library, and makes no assumptions about your classloader structure or logging configuration. This makes the
API easy to embed in your application.
§
Tooling API and the Gradle Build Daemon
The Tooling API always uses the Gradle daemon. This means that subsequent calls to the Tooling API, be it
model building requests or task executing requests will be executed in the same long-living process. The
Gradle Daemon contains more details about the daemon, specifically information on situations when new
daemons are forked.
§
Quickstart
As the Tooling API is an interface for developers, the Javadoc is the main documentation for it. We provide
several samples that live in samples/toolingApi in your Gradle distribution. These samples specify all of
the required dependencies for the Tooling API with examples for querying information from Gradle builds
and executing tasks from the Tooling API.
To use the Tooling API, add the following repository and dependency declarations to your build script:
Example 46. Using the tooling API
build.gradle
repositories {
maven { url 'https://repo.gradle.org/gradle/libs-releases' }
}
dependencies {
compile "org.gradle:gradle-tooling-api:${toolingApiVersion}"
// The tooling API need an SLF4J implementation available at runtime, replace this wit
runtime 'org.slf4j:slf4j-simple:1.7.10'
}
The main entry point to the Tooling API is the GradleConnector. You can navigate from there to find code
samples and explore the available Tooling API models. You can use GradleConnector.connect() to
create a ProjectConnection. A ProjectConnection connects to a single Gradle project. Using the
connection you can execute tasks, tests and retrieve models relative to this project.
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Gradle version and Java version compatibility
§
Gradle version and Java version compatibility
§
Provider side
The current version of Tooling API supports running builds using Gradle versions 1.2 and later. However,
support for running builds with Gradle versions older than 2.6 is deprecated and will be removed in Tooling
API version 5.0.
§
Consumer side
The current version of Gradle supports running builds via Tooling API versions 2.0 and later. However,
support for running builds via Tooling API versions older than 3.0 is deprecated and will be removed in
Gradle 5.0.
You should note that not all features of the Tooling API are available for all versions of Gradle. For example,
build cancellation is only available when a build uses Gradle 2.1 and later. Refer to the documentation for
each class and method for more details.
§
Java version
The Tooling API requires Java 8 or later. Java 7 is currently still supported but will be removed in Gradle 5.0.
The Gradle version used by builds may have additional Java version requirements.
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Build Cache
Note: The build cache feature is ready to be used for Java, Groovy and Scala projects. Work
continues to make it available in more areas.
Note: The build cache feature described here is different from the Android plugin build cache.
§
Overview
The Gradle build cache is a cache mechanism that aims to save time by reusing outputs produced by other
builds. The build cache works by storing (locally or remotely) build outputs and allowing builds to fetch these
outputs from the cache when it is determined that inputs have not changed, avoiding the expensive work of
regenerating them.
A first feature using the build cache is task output caching . Essentially, task output caching leverages the
same intelligence as up-to-date checks that Gradle uses to avoid work when a previous local build has
already produced a set of task outputs. But instead of being limited to the previous build in the same
workspace, task output caching allows Gradle to reuse task outputs from any earlier build in any location on
the local machine. When using a shared build cache for task output caching this even works across
developer machines and build agents.
Apart from task output caching, we expect other features to use the build cache in the future.
Note: A complete guide is available about using the build cache. It covers the different scenarios
caching can improve, and detailed discussions of the different caveats you need to be aware of
when enabling caching for a build.
§
Enable the Build Cache
By default, the build cache is not enabled. You can enable the build cache in a couple of ways:
Run with --build-cache on the command-line
Gradle will use the build cache for this build only.
Put org.gradle.caching=true in your gradle.properties
Gradle will try to reuse outputs from previous builds for all builds, unless explicitly disabled with --no-build-cache
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.
When the build cache is enabled, it will store build outputs in the Gradle user home. For configuring this
directory or different kinds of build caches see the section called “Configure the Build Cache”.
§
Task Output Caching
Beyond incremental builds described in the section called “Up-to-date checks (AKA Incremental Build)” ,
Gradle can save time by reusing outputs from previous executions of a task by matching inputs to the task.
Task outputs can be reused between builds on one computer or even between builds running on different
computers via a build cache.
We have focused on the use case where users have an organization-wide remote build cache that is
populated regularly by continuous integration builds. Developers and other continuous integration agents
should pull cache entries from the remote build cache. We expect that developers will not be allowed to
populate the remote build cache, and all continuous integration builds populate the build cache after running
the clean task.
For your build to play well with task output caching it must work well with the incremental build feature. For
example, when running your build twice in a row all tasks with outputs should be UP-TO-DATE. You cannot
expect faster builds or correct builds when enabling task output caching when this prerequisite is not met.
Task output caching is automatically enabled when you enable the build cache, see the section called
“Enable the Build Cache”.
§
What does it look like
Let us start with a project using the Java plugin which has a few Java source files. We run the build the first
time.
$> gradle --build-cache compileJava
Build cache is an incubating feature.
Using local directory build cache for the root build (location = /home/user/.gradle/caches
:compileJava
:processResources
:classes
:jar
:assemble
BUILD SUCCESSFUL
We see the directory used by the local build cache in the output. Apart from that the build was the same as
without the build cache. Let’s clean and run the build again.
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$> gradle clean
:clean
BUILD SUCCESSFUL
$> gradle --build-cache assemble
Build cache is an incubating feature.
Using local directory build cache for the root build (location = /home/user/.gradle/caches
:compileJava FROM-CACHE
:processResources
:classes
:jar
:assemble
BUILD SUCCESSFUL
Now we see that, instead of executing the :compileJava task, the outputs of the task have been loaded
from the build cache. The other tasks have not been loaded from the build cache since they are not
cacheable. This is due to :classes and :assemble being lifecycle tasks and :processResources and :jar
being Copy-like tasks which are not cacheable since it is generally faster to execute them.
§
Cacheable tasks
Since a task describes all of its inputs and outputs, Gradle can compute a build cache key that uniquely
defines the task’s outputs based on its inputs. That build cache key is used to request previous outputs from
a build cache or push new outputs to the build cache. If the previous build is already populated by someone
else, e.g. your continuous integration server or other developers, you can avoid executing most tasks locally.
The following inputs contribute to the build cache key for a task in the same way that they do for up-to-date
checks:
The task type and its classpath
The names of the output properties
The names and values of properties annotated as described in the section called “Custom task types”
The names and values of properties added by the DSL via TaskInputs
The classpath of the Gradle distribution, buildSrc and plugins
The content of the build script when it affects execution of the task
Task types need to opt-in to task output caching using the @CacheableTask annotation. Note that @CacheableTask
is not inherited by subclasses. Custom task types are not cacheable by default.
Built-in cacheable tasks
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§
Built-in cacheable tasks
Currently, the following built-in Gradle tasks are cacheable:
Java toolchain: JavaCompile, Javadoc
Groovy toolchain: GroovyCompile, Groovydoc
Scala toolchain: ScalaCompile, ScalaDoc
Native toolchain: CppCompile, CCompile
Testing: Test
Code quality tasks: Checkstyle, CodeNarc, FindBugs, JDepend, Pmd
Jacoco: JacocoMerge, JacocoReport
Other tasks: AntlrTask ValidateTaskProperties, WriteProperties
§
Non-cacheable tasks
All other tasks are currently not cacheable, but this may change in the future for other languages (Kotlin) or
domains (native, Android, Play). Some tasks, like Copy or Jar, usually do not make sense to make
cacheable because Gradle is only copying files from one location to another. It also doesn’t make sense to
make tasks cacheable that do not produce outputs or have no task actions.
§
Declaring task inputs and outputs
It is very important that a cacheable task has a complete picture of its inputs and outputs, so that the results
from one build can be safely re-used somewhere else.
Missing task inputs can cause incorrect cache hits, where different results are treated as identical because
the same cache key is used by both executions. Missing task outputs can cause build failures if Gradle does
not completely capture all outputs for a given task. Wrongly declared task inputs can lead to cache misses
especially when containing volatile data or absolute paths. (See the section called “Task inputs and outputs”
on what should be declared as inputs and outputs.)
Note: The task path is not an input to the build cache key. This means that tasks with different task
paths can re-use each other’s outputs as long as Gradle determines that executing them yields the
same result.
In order to ensure that the inputs and outputs are properly declared use integration tests (for example using
TestKit) to check that a task produces the same outputs for identical inputs and captures all output files for
the task. We suggest adding tests to ensure that the task inputs are relocatable, i.e. that the task can be
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loaded from the cache into a different build directory (see @PathSensitive).
In order to handle volatile inputs for your tasks consider configuring input normalization.
§
Known issues with task output caching
The task output caching feature has known issues that may impact the correctness of your build when using
the build cache, and there are some caveats to keep in mind which may reduce the number of cache hits
you get between machines. These issues will be corrected as this feature becomes stable.
Note that task output caching relies on incremental build. Problems that affect incremental builds can also
affect task output caching even if the affected tasks are not cacheable. Most issues only cause problems if
your build cache is populated by non-clean builds or if caching has been enabled for unsupported tasks. For
a current list of open problems with incremental builds see these Github issues.
Note: When reporting issues with the build cache, please check if your issue is a known issue or
related to a known issue.
§
Correctness issues
These issues may affect the correctness of your build when using the build cache. Please consider these
issues carefully.
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Table 1. Correctness issues
Description
Impact
Workaround
Gradle currently tracks the major version of Java that is Only enable caching for builds that all use the
Tracking
Java
the used for compilation and test execution. If your build uses same Java implementation or manually add the
vendor several Java implementations (IBM, OpenJDK, Oracle, etc) Java vendor as an input to compilation and test
implementation that are the same major version, Gradle will treat them all as execution tasks by using the runtime api for
equivalent and re-use outputs from any implementation.
adding task inputs.
Gradle currently tracks the major version of Java (6 vs 7 vs
8) that is used for compilation and test execution. If your
Tracking
the
Java version
build expects to use several minor releases (1.8.0_102 vs Manually add the full Java version as an input to
1.8.0_25), Gradle will treat all of these as equivalent and compilation and test execution tasks by using the
re-use outputs from any minor version. In our experience, runtime api for adding task inputs.
bytecode produced by each major version is functionally
equivalent.
For tasks that fork processes (like Test), Gradle does not Declare environment variables as inputs to the
Environment
variables
are track any of the environment variables visible to the process. t a s k
w i t h
not tracked as This can allow undeclared inputs to affect the outputs of the TaskInputs.property(java.lang.String,
inputs.
task.
Changes
in
Gradle’s
file
encoding that
affect the build
script
java.lang.Object).
Gradle can produce different task output based on the file Set the UTF-8 file encoding on all tasks which
encoding used by the JVM. Gradle will use a default file allow setting the encoding. Use UTF-8 file
encoding based on the operating system if file.encoding encoding everywhere by setting file.encoding
is not explicitly set.
to UTF-8 for the Gradle JVM.
Javadoc
ignores custom Gradle’s Javadoc task does not take into account any You can add your custom options as input
command-line changes to custom command-line options.
properties or disable caching of Javadoc.
options
§
Caveats
These issues may affect the number of cache hits you get between machines.
Table 2. Caveats
Description
Impact
Overlapping
If two or more tasks share an output directory or files,
Workaround
outputs between Gradle will disable caching for these tasks when it Use separate output directories for each task.
tasks
detects an overlap.
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Using
cached
C/C++
object
files
with
absolute paths
When Gradle compiles C/C++ code, object files tend to
have absolute paths embedded inside them. This
doesn’t affect their correctness, but it can interfere with
debuggers that search for source code at those absolute
Build the project from the same absolute path on
every machine.
paths.
Gradle calculates the build cache key based on the MD5
Line endings in
build scripts files.
hash of the build script contents. If the line endings are Check if your VCS will change source file line
different between developers and the CI servers, Gradle endings and configure it to have a consistent line
will calculate different build cache keys even when all ending across all platforms.
other inputs to a task are the same.
Gradle provides ways of specifying the path sensitivity
for individual task properties (see @PathSensitive);
Absolute paths in however, it is common to need to pass absolute paths to
tools or to tests via system properties or command line If
command-line
arguments
possible,
use
relative
paths
(via
and arguments. These kinds of inputs will cause cache Project.relativePath(java.lang.Object)
system
misses because not every developer or CI server uses ). Further tooling will be provided later.
properties.
an identical absolute path to the root of a build. Tasks
like Test include system properties and JVM arguments
as inputs to the build cache key.
The JaCoCo agent relies on appending to a shared
Using
JaCoCo output file that may be left over from a different test
disables caching execution. If Gradle allowed Test tasks to be cacheable None.
of the Test task.
with the JaCoCo plugin, it could not guarantee the same
results each time.
Adding
new
actions
to
cacheable tasks
in a build file Actions added by a plugin (from buildSrc or externally)
makes that task do not have this problem because their classloader is
sensitive
to restricted to the classpath of the plugin.
Avoid adding actions to cacheable tasks in a build
file.
unrelated
changes to the
build file.
Modifying inputs
or outputs during
task execution.
Order
files
outputs.
of
input
affects
It’s possible to modify a task’s inputs or outputs during
execution in ways that change the output of a task. This
breaks incremental builds and can cause problems with
the build cache.
Use a configure task to finalize configuration for a
given task. A configure task configures another
task as part of its execution.
Some tools are sensitive to the order of its inputs and
will produce slightly different output. Gradle will usually
provide the order of files from the filesystem, which will
Provide a stable order for tools affected by order.
be different across operating systems.
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ANTLR3
produces output
with a timestamp.
When generating Java source code with ANTLR3 and
the The ANTLR Plugin, the generated sources contain a
timestamp that reduces how often Java compilation will
be cached. ANTLR2 and ANTLR4 are not affected.
If you cannot upgrade to ANLTR4 use a custom
template or remove the timestamp in a doLast
action.
§
Configure the Build Cache
You can configure the build cache by using the Settings.buildCache(org.gradle.api.Action)
block in settings.gradle.
Gradle supports a local and a remote build cache that can be configured separately. When both build
caches are enabled, Gradle tries to load build outputs from the local build cache first, and then tries the
remote build cache if no build outputs are found. If outputs are found in the remote cache, they are also
stored in the local cache, so next time they will be found locally. Gradle pushes build outputs to any build
cache that is enabled and has BuildCache.isPush() set to true.
By default, the local build cache has push enabled, and the remote build cache has push disabled.
The local build cache is pre-configured to be a DirectoryBuildCache and enabled by default. The
remote build cache can be configured by specifying the type of build cache to connect to (
BuildCacheConfiguration.remote(java.lang.Class)).
§
Built-in local build cache
The built-in local build cache, DirectoryBuildCache, uses a directory to store build cache artifacts. By
default, this directory resides in the Gradle user home directory, but its location is configurable.
Gradle will periodically clean-up the local cache directory to reduce it to a configurable target size. This
means that the local build cache directory may temporarily grow over the target size until the next clean-up is
scheduled.
For more details on the configuration options refer to the DSL documentation of DirectoryBuildCache.
Here is an example of the configuration.
Example 47. Configure the local cache
settings.gradle
buildCache {
local(DirectoryBuildCache) {
directory = new File(rootDir, 'build-cache')
targetSizeInMB = 1024
}
}
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§
Remote HTTP build cache
Gradle has built-in support for connecting to a remote build cache backend via HTTP. For more details on
what the protocol looks like see HttpBuildCache. Note that by using the following configuration the local
build cache will be used for storing build outputs while the local and the remote build cache will be used for
retrieving build outputs.
Example 48. Pull from HttpBuildCache
settings.gradle
buildCache {
remote(HttpBuildCache) {
url = 'https://example.com:8123/cache/'
}
}
You can configure the credentials the HttpBuildCache uses to access the build cache server as shown in
the following example.
Example 49. Configure remote HTTP cache
settings.gradle
buildCache {
remote(HttpBuildCache) {
url = 'http://example.com:8123/cache/'
credentials {
username = 'build-cache-user'
password = 'some-complicated-password'
}
}
}
Note: You may encounter problems with an untrusted SSL certificate when you try to use a build
cache backend with an HTTPS URL. The ideal solution is for someone to add a valid SSL certificate
to the build cache backend, but we recognize that you may not be able to do that. In that case, set
HttpBuildCache.isAllowUntrustedServer() to true:
Example 50. Allow untrusted SSL certificate for HttpBuildCache
Note: settings.gradle
buildCache {
remote(HttpBuildCache) {
url = 'https://example.com:8123/cache/'
allowUntrustedServer = true
}
}
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This is a convenient workaround, but you shouldn’t use it as a long-term solution.
§
Configuration use cases
The recommended use case for the build cache is that your continuous integration server populates the
remote build cache with clean builds while developers pull from the remote build cache and push to a local
build cache. The configuration would then look as follows.
Example 51. Recommended setup for CI push use case
settings.gradle
ext.isCiServer = System.getenv().containsKey("CI")
buildCache {
local {
enabled = !isCiServer
}
remote(HttpBuildCache) {
url = 'https://example.com:8123/cache/'
push = isCiServer
}
}
If you use a buildSrc directory, you should make sure that it uses the same build cache configuration as
the main build. This can be achieved by applying the same script to buildSrc/settings.gradle and settings.gra
as shown in the following example.
Example 52. Consistent setup for buildSrc and main build
settings.gradle
apply from: new File(settingsDir, 'gradle/buildCacheSettings.gradle')
buildSrc/settings.gradle
apply from: new File(settingsDir, '../gradle/buildCacheSettings.gradle')
gradle/buildCacheSettings.gradle
ext.isCiServer = System.getenv().containsKey("CI")
buildCache {
local {
enabled = !isCiServer
}
remote(HttpBuildCache) {
url = 'https://example.com:8123/cache/'
push = isCiServer
}
}
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It is also possible to configure the build cache from an init script, which can be used from the command line,
added to your Gradle user home or be a part of your custom Gradle distribution.
Example 53. Init script to configure the build cache
init.gradle
gradle.settingsEvaluated { settings ->
settings.buildCache {
// vvv Your custom configuration goes here
remote(HttpBuildCache) {
url = 'https://example.com:8123/cache/'
}
// ^^^ Your custom configuration goes here
}
}
§
Build cache and composite builds
Gradle’s composite build feature allows including other complete Gradle builds into another. Such included
builds will inherit the build cache configuration from the top level build, regardless of whether the included
builds define build cache configuration themselves or not.
The build cache configuration present for any included build is effectively ignored, in favour of the top level
build’s configuration. This also applies to any buildSrc projects of any included builds.
§
How to set up an HTTP build cache backend
Gradle provides a Docker image for a build cache node, which can connect with Gradle Enterprise for
centralized management. The cache node can also be used without a Gradle Enterprise installation with
restricted functionality.
§
Implement your own Build Cache
Using a different build cache backend to store build outputs (which is not covered by the built-in support for
connecting to an HTTP backend) requires implementing your own logic for connecting to your custom build
cache
backend.
To
this
end,
custom
build
cache
types
can
be
registered
via
BuildCacheConfiguration.registerBuildCacheService(java.lang.Class,
java.lang.Class). For an example of what this could look like see the Gradle Hazelcast plugin.
Gradle Enterprise includes a high-performance, easy to install and operate, shared build cache backend.
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Writing Gradle build scripts
Build Script Basics
§
Projects and tasks
Everything in Gradle sits on top of two basic concepts: projects and tasks .
Every Gradle build is made up of one or more projects . What a project represents depends on what it is that
you are doing with Gradle. For example, a project might represent a library JAR or a web application. It
might represent a distribution ZIP assembled from the JARs produced by other projects. A project does not
necessarily represent a thing to be built. It might represent a thing to be done, such as deploying your
application to staging or production environments. Don’t worry if this seems a little vague for now. Gradle’s
build-by-convention support adds a more concrete definition for what a project is.
Each project is made up of one or more tasks . A task represents some atomic piece of work which a build
performs. This might be compiling some classes, creating a JAR, generating Javadoc, or publishing some
archives to a repository.
For now, we will look at defining some simple tasks in a build with one project. Later chapters will look at
working with multiple projects and more about working with projects and tasks.
§
Hello world
You run a Gradle build using the gradle command. The gradle command looks for a file called build.gradle
in the current directory.[4] We call this build.gradle file a build script , although strictly speaking it is a
build configuration script, as we will see later. The build script defines a project and its tasks.
To try this out, create the following build script named build.gradle.
Example 54. Your first build script
build.gradle
task hello {
doLast {
println 'Hello world!'
}
}
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In a command-line shell, move to the containing directory and execute the build script with gradle -q hello
:
What does -q do?
Most of the examples in this user guide are run with the -q command-line option. This suppresses
Gradle’s log messages, so that only the output of the tasks is shown. This keeps the example output
in this user guide a little clearer. You don’t need to use this option if you don’t want to. See Logging
for more details about the command-line options which affect Gradle’s output.
Example 55. Execution of a build script
Output of gradle -q hello
> gradle -q hello
Hello world!
What’s going on here? This build script defines a single task, called hello, and adds an action to it. When
you run gradle hello, Gradle executes the hello task, which in turn executes the action you’ve
provided. The action is simply a closure containing some Groovy code to execute.
If you think this looks similar to Ant’s targets, you would be right. Gradle tasks are the equivalent to Ant
targets, but as you will see, they are much more powerful. We have used a different terminology than Ant as
we think the word task is more expressive than the word target . Unfortunately this introduces a terminology
clash with Ant, as Ant calls its commands, such as javac or copy, tasks. So when we talk about tasks, we
always mean Gradle tasks, which are the equivalent to Ant’s targets. If we talk about Ant tasks (Ant
commands), we explicitly say Ant task .
§
A shortcut task definition
Note: This functionality is deprecated and will be removed in Gradle 5.0 without replacement. Use
the
methods
and
Task.doFirst(org.gradle.api.Action)
Task.doLast(org.gradle.api.Action) to define an action instead, as demonstrated by the
rest of the examples in this chapter.
There is a shorthand way to define a task like our hello task above, which is more concise.
Example 56. A task definition shortcut
build.gradle
task hello << {
println 'Hello world!'
}
Again, this defines a task called hello with a single closure to execute. The << operator is simply an alias
for doLast.
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§
Build scripts are code
Gradle’s build scripts give you the full power of Groovy. As an appetizer, have a look at this:
Example 57. Using Groovy in Gradle's tasks
build.gradle
task upper {
doLast {
String someString = 'mY_nAmE'
println "Original: " + someString
println "Upper case: " + someString.toUpperCase()
}
}
Output of gradle -q upper
> gradle -q upper
Original: mY_nAmE
Upper case: MY_NAME
or
Example 58. Using Groovy in Gradle's tasks
build.gradle
task count {
doLast {
4.times { print "$it " }
}
}
Output of gradle -q count
> gradle -q count
0 1 2 3
§
Task dependencies
As you probably have guessed, you can declare tasks that depend on other tasks.
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Example 59. Declaration of task that depends on other task
build.gradle
task hello {
doLast {
println 'Hello world!'
}
}
task intro(dependsOn: hello) {
doLast {
println "I'm Gradle"
}
}
Output of gradle -q intro
> gradle -q intro
Hello world!
I'm Gradle
To add a dependency, the corresponding task does not need to exist.
Example 60. Lazy dependsOn - the other task does not exist (yet)
build.gradle
task taskX(dependsOn: 'taskY') {
doLast {
println 'taskX'
}
}
task taskY {
doLast {
println 'taskY'
}
}
Output of gradle -q taskX
> gradle -q taskX
taskY
taskX
The dependency of taskX to taskY is declared before taskY is defined. This is very important for
multi-project builds. Task dependencies are discussed in more detail in the section called “Adding
dependencies to a task”.
Please notice that you can’t use shortcut notation (see the section called “Shortcut notations”) when referring
to a task that is not yet defined.
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Dynamic tasks
§
Dynamic tasks
The power of Groovy can be used for more than defining what a task does. For example, you can also use it
to dynamically create tasks.
Example 61. Dynamic creation of a task
build.gradle
4.times { counter ->
task "task$counter" {
doLast {
println "I'm task number $counter"
}
}
}
Output of gradle -q task1
> gradle -q task1
I'm task number 1
§
Manipulating existing tasks
Once tasks are created they can be accessed via an API . For instance, you could use this to dynamically
add dependencies to a task, at runtime. Ant doesn’t allow anything like this.
Example 62. Accessing a task via API - adding a dependency
build.gradle
4.times { counter ->
task "task$counter" {
doLast {
println "I'm task number $counter"
}
}
}
task0.dependsOn task2, task3
Output of gradle -q task0
> gradle
I'm task
I'm task
I'm task
-q task0
number 2
number 3
number 0
Or you can add behavior to an existing task.
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Example 63. Accessing a task via API - adding behaviour
build.gradle
task hello {
doLast {
println 'Hello Earth'
}
}
hello.doFirst {
println 'Hello Venus'
}
hello.doLast {
println 'Hello Mars'
}
hello {
doLast {
println 'Hello Jupiter'
}
}
Output of gradle -q hello
> gradle -q hello
Hello Venus
Hello Earth
Hello Mars
Hello Jupiter
The calls doFirst and doLast can be executed multiple times. They add an action to the beginning or the
end of the task’s actions list. When the task executes, the actions in the action list are executed in order.
§
Shortcut notations
There is a convenient notation for accessing an existing task. Each task is available as a property of the
build script:
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Example 64. Accessing task as a property of the build script
build.gradle
task hello {
doLast {
println 'Hello world!'
}
}
hello.doLast {
println "Greetings from the $hello.name task."
}
Output of gradle -q hello
> gradle -q hello
Hello world!
Greetings from the hello task.
This enables very readable code, especially when using the tasks provided by the plugins, like the compile
task.
§
Extra task properties
You can add your own properties to a task. To add a property named myProperty, set ext.myProperty
to an initial value. From that point on, the property can be read and set like a predefined task property.
Example 65. Adding extra properties to a task
build.gradle
task myTask {
ext.myProperty = "myValue"
}
task printTaskProperties {
doLast {
println myTask.myProperty
}
}
Output of gradle -q printTaskProperties
> gradle -q printTaskProperties
myValue
Extra properties aren’t limited to tasks. You can read more about them in the section called “Extra
properties”.
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Using Ant Tasks
§
Using Ant Tasks
Ant tasks are first-class citizens in Gradle. Gradle provides excellent integration for Ant tasks by simply
relying on Groovy. Groovy is shipped with the fantastic AntBuilder. Using Ant tasks from Gradle is as
convenient and more powerful than using Ant tasks from a build.xml file. From the example below, you
can learn how to execute Ant tasks and how to access Ant properties:
Example 66. Using AntBuilder to execute ant.loadfile target
build.gradle
task loadfile {
doLast {
def files = file('../antLoadfileResources').listFiles().sort()
files.each { File file ->
if (file.isFile()) {
ant.loadfile(srcFile: file, property: file.name)
println " *** $file.name ***"
println "${ant.properties[file.name]}"
}
}
}
}
Output of gradle -q loadfile
> gradle -q loadfile
*** agile.manifesto.txt ***
Individuals and interactions over processes and tools
Working software over comprehensive documentation
Customer collaboration over contract negotiation
Responding to change over following a plan
*** gradle.manifesto.txt ***
Make the impossible possible, make the possible easy and make the easy elegant.
(inspired by Moshe Feldenkrais)
There is lots more you can do with Ant in your build scripts. You can find out more in Using Ant from Gradle.
§
Using methods
Gradle scales in how you can organize your build logic. The first level of organizing your build logic for the
example above, is extracting a method.
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Example 67. Using methods to organize your build logic
build.gradle
task checksum {
doLast {
fileList('../antLoadfileResources').each { File file ->
ant.checksum(file: file, property: "cs_$file.name")
println "$file.name Checksum: ${ant.properties["cs_$file.name"]}"
}
}
}
task loadfile {
doLast {
fileList('../antLoadfileResources').each { File file ->
ant.loadfile(srcFile: file, property: file.name)
println "I'm fond of $file.name"
}
}
}
File[] fileList(String dir) {
file(dir).listFiles({file -> file.isFile() } as FileFilter).sort()
}
Output of gradle -q loadfile
> gradle -q loadfile
I'm fond of agile.manifesto.txt
I'm fond of gradle.manifesto.txt
Later you will see that such methods can be shared among subprojects in multi-project builds. If your build
logic becomes more complex, Gradle offers you other very convenient ways to organize it. We have devoted
a whole chapter to this. See Organizing Build Logic.
§
Default tasks
Gradle allows you to define one or more default tasks that are executed if no other tasks are specified.
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Example 68. Defining a default task
build.gradle
defaultTasks 'clean', 'run'
task clean {
doLast {
println 'Default Cleaning!'
}
}
task run {
doLast {
println 'Default Running!'
}
}
task other {
doLast {
println "I'm not a default task!"
}
}
Output of gradle -q
> gradle -q
Default Cleaning!
Default Running!
This is equivalent to running gradle clean run. In a multi-project build every subproject can have its own
specific default tasks. If a subproject does not specify default tasks, the default tasks of the parent project
are used (if defined).
§
Configure by DAG
As we later describe in full detail (see Build Lifecycle), Gradle has a configuration phase and an execution
phase. After the configuration phase, Gradle knows all tasks that should be executed. Gradle offers you a
hook to make use of this information. A use-case for this would be to check if the release task is among the
tasks to be executed. Depending on this, you can assign different values to some variables.
In the following example, execution of the distribution and release tasks results in different value of
the version variable.
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Example 69. Different outcomes of build depending on chosen tasks
build.gradle
task distribution {
doLast {
println "We build the zip with version=$version"
}
}
task release(dependsOn: 'distribution') {
doLast {
println 'We release now'
}
}
gradle.taskGraph.whenReady {taskGraph ->
if (taskGraph.hasTask(release)) {
version = '1.0'
} else {
version = '1.0-SNAPSHOT'
}
}
Output of gradle -q distribution
> gradle -q distribution
We build the zip with version=1.0-SNAPSHOT
Output of gradle -q release
> gradle -q release
We build the zip with version=1.0
We release now
The important thing is that whenReady affects the release task before the release task is executed. This
works even when the release task is not the primary task (i.e., the task passed to the gradle command).
§
Where to next?
In this chapter, we have had a first look at tasks. But this is not the end of the story for tasks. If you want to
jump into more of the details, have a look at Authoring Tasks.
Otherwise, continue on to the tutorials in Java Quickstart and Dependency Management for Java Projects.
[4] There are command line switches to change this behavior. See Command-Line Interface)
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Build Init Plugin
Note: The Build Init plugin is currently incubating. Please be aware that the DSL and other
configuration may change in later Gradle versions.
The Gradle Build Init plugin can be used to bootstrap the process of creating a new Gradle build. It supports
creating brand new projects of different types as well as converting existing builds (e.g. An Apache Maven
build) to be Gradle builds.
Gradle plugins typically need to be applied to a project before they can be used (see the section called
“Using plugins”). The Build Init plugin is an automatically applied plugin, which means you do not need to
apply it explicitly. To use the plugin, simply execute the task named init where you would like to create the
Gradle build. There is no need to create a “stub” build.gradle file in order to apply the plugin.
It also leverages the wrapper task to generate the Gradle Wrapper files for the project.
§
Tasks
The plugin adds the following tasks to the project:
Table 3. Build Init plugin - tasks
Task name
Depends on
Type
Description
init
wrapper
InitBuild
Generates a Gradle project.
wrapper
-
Wrapper
Generates Gradle wrapper files.
§
What to set up
The init supports different build setup types . The type is specified by supplying a --type argument value.
For example, to create a Java library project simply execute: gradle init --type java-library.
If a --type parameter is not supplied, Gradle will attempt to infer the type from the environment. For
example, it will infer a type value of “pom” if it finds a pom.xml to convert to a Gradle build.
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If the type could not be inferred, the type “basic” will be used.
The init plugin also supports generating build scripts using either the Gradle Groovy DSL or the Gradle
Kotlin DSL. The build script DSL to use defaults to the Groovy DSL and is specified by supplying a --dsl
argument value. For example, to create a Java library project with Kotlin DSL build scripts simply execute: gradle init
.
All build setup types include the setup of the Gradle Wrapper.
Note that the migration from Maven builds only supports the Groovy DSL for generated build scripts.
§
Build init types
Note: As this plugin is currently incubating, only a few build init types are currently supported. More
types will be added in future Gradle releases.
§
“pom” (Maven conversion)
The “pom” type can be used to convert an Apache Maven build to a Gradle build. This works by converting
the POM to one or more Gradle files. It is only able to be used if there is a valid “ pom.xml” file in the
directory that the init task is invoked in or, if invoked via the “-p” command line option, in the specified
project directory. This “pom” type will be automatically inferred if such a file exists.
The Maven conversion implementation was inspired by the maven2gradle tool that was originally developed
by Gradle community members.
The conversion process has the following features:
Uses effective POM and effective settings (support for POM inheritance, dependency management,
properties)
Supports both single module and multimodule projects
Supports custom module names (that differ from directory names)
Generates general metadata - id, description and version
Applies maven, java and war plugins (as needed)
Supports packaging war projects as jars if needed
Generates dependencies (both external and inter-module)
Generates download repositories (inc. local Maven repository)
Adjusts Java compiler settings
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Supports packaging of sources and tests
Supports TestNG runner
Generates global exclusions from Maven enforcer plugin settings
§
“java-application”
The “java-application” build init type is not inferable. It must be explicitly specified.
It has the following features:
Uses the “application” plugin to produce a command-line application implemented using Java
Uses the “jcenter” dependency repository
Uses JUnit for testing
Has directories in the conventional locations for source code
Contains a sample class and unit test, if there are no existing source or test files
Alternative test framework can be specified by supplying a --test-framework argument value. To use a
different test framework, execute one of the following commands:
gradle init --type java-application --test-framework spock: Uses Spock for testing
instead of JUnit
gradle init --type java-application --test-framework testng: Uses TestNG for testing
instead of JUnit
§
“java-library”
The “java-library” build init type is not inferable. It must be explicitly specified.
It has the following features:
Uses the “java” plugin to produce a library Jar
Uses the “jcenter” dependency repository
Uses JUnit for testing
Has directories in the conventional locations for source code
Contains a sample class and unit test, if there are no existing source or test files
Alternative test framework can be specified by supplying a --test-framework argument value. To use a
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different test framework, execute one of the following commands:
gradle init --type java-library --test-framework spock: Uses Spock for testing instead of
JUnit
gradle init --type java-library --test-framework testng: Uses TestNG for testing instead
of JUnit
§
“scala-library”
The “scala-library” build init type is not inferable. It must be explicitly specified.
It has the following features:
Uses the “scala” plugin to produce a library Jar
Uses the “jcenter” dependency repository
Uses Scala 2.10
Uses ScalaTest for testing
Has directories in the conventional locations for source code
Contains a sample scala class and an associated ScalaTest test suite, if there are no existing source or test
files
Uses the Zinc Scala compiler by default
§
“groovy-library”
The “groovy-library” build init type is not inferable. It must be explicitly specified.
It has the following features:
Uses the “groovy” plugin to produce a library Jar
Uses the “jcenter” dependency repository
Uses Groovy 2.x
Uses Spock testing framework for testing
Has directories in the conventional locations for source code
Contains a sample Groovy class and an associated Spock specification, if there are no existing source or
test files
“groovy-application”
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§
“groovy-application”
The “groovy-application” build init type is not inferable. It must be explicitly specified.
It has the following features:
Uses the “groovy” plugin
Uses the “application” plugin to produce a command-line application implemented using Groovy
Uses the “jcenter” dependency repository
Uses Groovy 2.x
Uses Spock testing framework for testing
Has directories in the conventional locations for source code
Contains a sample Groovy class and an associated Spock specification, if there are no existing source or
test files
§
“basic”
The “basic” build init type is useful for creating a fresh new Gradle project. It creates a sample build.gradle
file, with comments and links to help get started.
This type is used when no type was explicitly specified, and no type could be inferred.
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Writing Build Scripts
This chapter looks at some of the details of writing a build script.
§
The Gradle build language
Gradle provides a domain specific language , or DSL, for describing builds. This build language is based on
Groovy, with some additions to make it easier to describe a build.
A build script can contain any Groovy language element.[5] Gradle assumes that each build script is encoded
using UTF-8.
§
The Project API
In the tutorial in Java Quickstart we used, for example, the apply() method. Where does this method come
from? We said earlier that the build script defines a project in Gradle. For each project in the build, Gradle
creates an object of type Project and associates this Project object with the build script. As the build
script executes, it configures this Project object:
Getting help writing build scripts
Don’t forget that your build script is simply Groovy code that drives the Gradle API. And the
Project interface is your starting point for accessing everything in the Gradle API. So, if you’re
wondering what 'tags' are available in your build script, you can start with the documentation for the Project
interface.
Any method you call in your build script which is not defined in the build script, is delegated to the Project
object.
Any property you access in your build script, which is not defined in the build script, is delegated to the Project
object.
Let’s try this out and try to access the name property of the Project object.
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Example 70. Accessing property of the Project object
build.gradle
println name
println project.name
Output of gradle -q check
> gradle -q check
projectApi
projectApi
Both println statements print out the same property. The first uses auto-delegation to the Project
object, for properties not defined in the build script. The other statement uses the project property
available to any build script, which returns the associated Project object. Only if you define a property or a
method which has the same name as a member of the Project object, would you need to use the project
property.
§
Standard project properties
The Project object provides some standard properties, which are available in your build script. The
following table lists a few of the commonly used ones.
Table 4. Project Properties
Name
Type
Default Value
project
Project
The Project instance
name
String
The name of the project directory.
path
String
The absolute path of the project.
description
String
A description for the project.
projectDir
File
The directory containing the build script.
buildDir
File
projectDir /build
group
Object
unspecified
version
Object
unspecified
ant
AntBuilder
An AntBuilder instance
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The Script API
§
The Script API
When Gradle executes a script, it compiles the script into a class which implements Script. This means
that all of the properties and methods declared by the Script interface are available in your script.
§
Declaring variables
There are two kinds of variables that can be declared in a build script: local variables and extra properties.
§
Local variables
Local variables are declared with the def keyword. They are only visible in the scope where they have been
declared. Local variables are a feature of the underlying Groovy language.
Example 71. Using local variables
build.gradle
def dest = "dest"
task copy(type: Copy) {
from "source"
into dest
}
§
Extra properties
All enhanced objects in Gradle’s domain model can hold extra user-defined properties. This includes, but is
not limited to, projects, tasks, and source sets. Extra properties can be added, read and set via the owning
object’s ext property. Alternatively, an ext block can be used to add multiple properties at once.
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Example 72. Using extra properties
build.gradle
apply plugin: "java"
ext {
springVersion = "3.1.0.RELEASE"
emailNotification = "build@master.org"
}
sourceSets.all { ext.purpose = null }
sourceSets {
main {
purpose = "production"
}
test {
purpose = "test"
}
plugin {
purpose = "production"
}
}
task printProperties {
doLast {
println springVersion
println emailNotification
sourceSets.matching { it.purpose == "production" }.each { println it.name }
}
}
Output of gradle -q printProperties
> gradle -q printProperties
3.1.0.RELEASE
build@master.org
main
plugin
In this example, an ext block adds two extra properties to the project object. Additionally, a property
named purpose is added to each source set by setting ext.purpose to null (null is a permissible
value). Once the properties have been added, they can be read and set like predefined properties.
By requiring special syntax for adding a property, Gradle can fail fast when an attempt is made to set a
(predefined or extra) property but the property is misspelled or does not exist. Extra properties can be
accessed from anywhere their owning object can be accessed, giving them a wider scope than local
variables. Extra properties on a project are visible from its subprojects.
For further details on extra properties and their API, see the ExtraPropertiesExtension class in the
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API documentation.
§
Configuring arbitrary objects
You can configure arbitrary objects in the following very readable way.
Example 73. Configuring arbitrary objects
build.gradle
task configure {
doLast {
def pos = configure(new java.text.FieldPosition(10)) {
beginIndex = 1
endIndex = 5
}
println pos.beginIndex
println pos.endIndex
}
}
Output of gradle -q configure
> gradle -q configure
1
5
§
Configuring arbitrary objects using an external script
You can also configure arbitrary objects using an external script.
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Example 74. Configuring arbitrary objects using a script
build.gradle
task configure {
doLast {
def pos = new java.text.FieldPosition(10)
// Apply the script
apply from: 'other.gradle', to: pos
println pos.beginIndex
println pos.endIndex
}
}
other.gradle
// Set properties.
beginIndex = 1
endIndex = 5
Output of gradle -q configure
> gradle -q configure
1
5
§
Some Groovy basics
The Groovy language provides plenty of features for creating DSLs, and the Gradle build language takes
advantage of these. Understanding how the build language works will help you when you write your build
script, and in particular, when you start to write custom plugins and tasks.
§
Groovy JDK
Groovy adds lots of useful methods to the standard Java classes. For example, Iterable gets an each
method, which iterates over the elements of the Iterable:
Example 75. Groovy JDK methods
build.gradle
// Iterable gets an each() method
configurations.runtime.each { File f -> println f }
Have a look at http://groovy-lang.org/gdk.html for more details.
Property accessors
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§
Property accessors
Groovy automatically converts a property reference into a call to the appropriate getter or setter method.
Example 76. Property accessors
build.gradle
// Using a getter method
println project.buildDir
println getProject().getBuildDir()
// Using a setter method
project.buildDir = 'target'
getProject().setBuildDir('target')
§
Optional parentheses on method calls
Parentheses are optional for method calls.
Example 77. Method call without parentheses
build.gradle
test.systemProperty 'some.prop', 'value'
test.systemProperty('some.prop', 'value')
§
List and map literals
Groovy provides some shortcuts for defining List and Map instances. Both kinds of literals are
straightforward, but map literals have some interesting twists.
For instance, the “apply” method (where you typically apply plugins) actually takes a map parameter.
However, when you have a line like “apply plugin:'java'”, you aren’t actually using a map literal,
you’re actually using “named parameters”, which have almost exactly the same syntax as a map literal
(without the wrapping brackets). That named parameter list gets converted to a map when the method is
called, but it doesn’t start out as a map.
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Example 78. List and map literals
build.gradle
// List literal
test.includes = ['org/gradle/api/**', 'org/gradle/internal/**']
List<String> list = new ArrayList<String>()
list.add('org/gradle/api/**')
list.add('org/gradle/internal/**')
test.includes = list
// Map literal.
Map<String, String> map = [key1:'value1', key2: 'value2']
// Groovy will coerce named arguments
// into a single map argument
apply plugin: 'java'
§
Closures as the last parameter in a method
The Gradle DSL uses closures in many places. You can find out more about closures here. When the last
parameter of a method is a closure, you can place the closure after the method call:
Example 79. Closure as method parameter
build.gradle
repositories {
println "in a closure"
}
repositories() { println "in a closure" }
repositories({ println "in a closure" })
§
Closure delegate
Each closure has a delegate object, which Groovy uses to look up variable and method references which
are not local variables or parameters of the closure. Gradle uses this for configuration closures , where the delegate
object is set to the object to be configured.
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Example 80. Closure delegates
build.gradle
dependencies {
assert delegate == project.dependencies
testCompile('junit:junit:4.12')
delegate.testCompile('junit:junit:4.12')
}
§
Default imports
To make build scripts more concise, Gradle automatically adds a set of import statements to the Gradle
scripts. This means that instead of using throw new org.gradle.api.tasks.StopExecutionException()
you can just type throw new StopExecutionException() instead.
Listed below are the imports added to each script:
Gradle default imports.
import
import
import
import
import
import
import
import
import
import
import
import
import
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org.gradle.*
org.gradle.api.*
org.gradle.api.artifacts.*
org.gradle.api.artifacts.cache.*
org.gradle.api.artifacts.component.*
org.gradle.api.artifacts.dsl.*
org.gradle.api.artifacts.ivy.*
org.gradle.api.artifacts.maven.*
org.gradle.api.artifacts.query.*
org.gradle.api.artifacts.repositories.*
org.gradle.api.artifacts.result.*
org.gradle.api.artifacts.transform.*
org.gradle.api.artifacts.type.*
org.gradle.api.attributes.*
org.gradle.api.component.*
org.gradle.api.credentials.*
org.gradle.api.distribution.*
org.gradle.api.distribution.plugins.*
org.gradle.api.dsl.*
org.gradle.api.execution.*
org.gradle.api.file.*
org.gradle.api.initialization.*
org.gradle.api.initialization.dsl.*
org.gradle.api.invocation.*
org.gradle.api.java.archives.*
org.gradle.api.logging.*
org.gradle.api.logging.configuration.*
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org.gradle.api.model.*
org.gradle.api.plugins.*
org.gradle.api.plugins.announce.*
org.gradle.api.plugins.antlr.*
org.gradle.api.plugins.buildcomparison.gradle.*
org.gradle.api.plugins.osgi.*
org.gradle.api.plugins.quality.*
org.gradle.api.plugins.scala.*
org.gradle.api.provider.*
org.gradle.api.publish.*
org.gradle.api.publish.ivy.*
org.gradle.api.publish.ivy.plugins.*
org.gradle.api.publish.ivy.tasks.*
org.gradle.api.publish.maven.*
org.gradle.api.publish.maven.plugins.*
org.gradle.api.publish.maven.tasks.*
org.gradle.api.publish.plugins.*
org.gradle.api.publish.tasks.*
org.gradle.api.reflect.*
org.gradle.api.reporting.*
org.gradle.api.reporting.components.*
org.gradle.api.reporting.dependencies.*
org.gradle.api.reporting.dependents.*
org.gradle.api.reporting.model.*
org.gradle.api.reporting.plugins.*
org.gradle.api.resources.*
org.gradle.api.specs.*
org.gradle.api.tasks.*
org.gradle.api.tasks.ant.*
org.gradle.api.tasks.application.*
org.gradle.api.tasks.bundling.*
org.gradle.api.tasks.compile.*
org.gradle.api.tasks.diagnostics.*
org.gradle.api.tasks.incremental.*
org.gradle.api.tasks.javadoc.*
org.gradle.api.tasks.scala.*
org.gradle.api.tasks.testing.*
org.gradle.api.tasks.testing.junit.*
org.gradle.api.tasks.testing.testng.*
org.gradle.api.tasks.util.*
org.gradle.api.tasks.wrapper.*
org.gradle.authentication.*
org.gradle.authentication.aws.*
org.gradle.authentication.http.*
org.gradle.buildinit.plugins.*
org.gradle.buildinit.tasks.*
org.gradle.caching.*
org.gradle.caching.configuration.*
org.gradle.caching.http.*
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org.gradle.caching.local.*
org.gradle.concurrent.*
org.gradle.external.javadoc.*
org.gradle.ide.visualstudio.*
org.gradle.ide.visualstudio.plugins.*
org.gradle.ide.visualstudio.tasks.*
org.gradle.ide.xcode.*
org.gradle.ide.xcode.plugins.*
org.gradle.ide.xcode.tasks.*
org.gradle.ivy.*
org.gradle.jvm.*
org.gradle.jvm.application.scripts.*
org.gradle.jvm.application.tasks.*
org.gradle.jvm.platform.*
org.gradle.jvm.plugins.*
org.gradle.jvm.tasks.*
org.gradle.jvm.tasks.api.*
org.gradle.jvm.test.*
org.gradle.jvm.toolchain.*
org.gradle.language.*
org.gradle.language.assembler.*
org.gradle.language.assembler.plugins.*
org.gradle.language.assembler.tasks.*
org.gradle.language.base.*
org.gradle.language.base.artifact.*
org.gradle.language.base.compile.*
org.gradle.language.base.plugins.*
org.gradle.language.base.sources.*
org.gradle.language.c.*
org.gradle.language.c.plugins.*
org.gradle.language.c.tasks.*
org.gradle.language.coffeescript.*
org.gradle.language.cpp.*
org.gradle.language.cpp.plugins.*
org.gradle.language.cpp.tasks.*
org.gradle.language.java.*
org.gradle.language.java.artifact.*
org.gradle.language.java.plugins.*
org.gradle.language.java.tasks.*
org.gradle.language.javascript.*
org.gradle.language.jvm.*
org.gradle.language.jvm.plugins.*
org.gradle.language.jvm.tasks.*
org.gradle.language.nativeplatform.*
org.gradle.language.nativeplatform.tasks.*
org.gradle.language.objectivec.*
org.gradle.language.objectivec.plugins.*
org.gradle.language.objectivec.tasks.*
org.gradle.language.objectivecpp.*
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import
org.gradle.language.objectivecpp.plugins.*
org.gradle.language.objectivecpp.tasks.*
org.gradle.language.plugins.*
org.gradle.language.rc.*
org.gradle.language.rc.plugins.*
org.gradle.language.rc.tasks.*
org.gradle.language.routes.*
org.gradle.language.scala.*
org.gradle.language.scala.plugins.*
org.gradle.language.scala.tasks.*
org.gradle.language.scala.toolchain.*
org.gradle.language.swift.*
org.gradle.language.swift.plugins.*
org.gradle.language.swift.tasks.*
org.gradle.language.twirl.*
org.gradle.maven.*
org.gradle.model.*
org.gradle.nativeplatform.*
org.gradle.nativeplatform.platform.*
org.gradle.nativeplatform.plugins.*
org.gradle.nativeplatform.tasks.*
org.gradle.nativeplatform.test.*
org.gradle.nativeplatform.test.cpp.*
org.gradle.nativeplatform.test.cpp.plugins.*
org.gradle.nativeplatform.test.cunit.*
org.gradle.nativeplatform.test.cunit.plugins.*
org.gradle.nativeplatform.test.cunit.tasks.*
org.gradle.nativeplatform.test.googletest.*
org.gradle.nativeplatform.test.googletest.plugins.*
org.gradle.nativeplatform.test.plugins.*
org.gradle.nativeplatform.test.tasks.*
org.gradle.nativeplatform.test.xctest.*
org.gradle.nativeplatform.test.xctest.plugins.*
org.gradle.nativeplatform.test.xctest.tasks.*
org.gradle.nativeplatform.toolchain.*
org.gradle.nativeplatform.toolchain.plugins.*
org.gradle.normalization.*
org.gradle.platform.base.*
org.gradle.platform.base.binary.*
org.gradle.platform.base.component.*
org.gradle.platform.base.plugins.*
org.gradle.play.*
org.gradle.play.distribution.*
org.gradle.play.platform.*
org.gradle.play.plugins.*
org.gradle.play.plugins.ide.*
org.gradle.play.tasks.*
org.gradle.play.toolchain.*
org.gradle.plugin.devel.*
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org.gradle.plugin.devel.plugins.*
org.gradle.plugin.devel.tasks.*
org.gradle.plugin.management.*
org.gradle.plugin.use.*
org.gradle.plugins.ear.*
org.gradle.plugins.ear.descriptor.*
org.gradle.plugins.ide.api.*
org.gradle.plugins.ide.eclipse.*
org.gradle.plugins.ide.idea.*
org.gradle.plugins.javascript.base.*
org.gradle.plugins.javascript.coffeescript.*
org.gradle.plugins.javascript.envjs.*
org.gradle.plugins.javascript.envjs.browser.*
org.gradle.plugins.javascript.envjs.http.*
org.gradle.plugins.javascript.envjs.http.simple.*
org.gradle.plugins.javascript.jshint.*
org.gradle.plugins.javascript.rhino.*
org.gradle.plugins.signing.*
org.gradle.plugins.signing.signatory.*
org.gradle.plugins.signing.signatory.pgp.*
org.gradle.plugins.signing.type.*
org.gradle.plugins.signing.type.pgp.*
org.gradle.process.*
org.gradle.testing.base.*
org.gradle.testing.base.plugins.*
org.gradle.testing.jacoco.plugins.*
org.gradle.testing.jacoco.tasks.*
org.gradle.testing.jacoco.tasks.rules.*
org.gradle.testkit.runner.*
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import org.gradle.vcs.*
import org.gradle.vcs.git.*
import org.gradle.workers.*
[5] Any language element except for statement labels.
Page 132 of 717
Authoring Tasks
In the introductory tutorial (Build Script Basics) you learned how to create simple tasks. You also learned
how to add additional behavior to these tasks later on, and you learned how to create dependencies
between tasks. This was all about simple tasks, but Gradle takes the concept of tasks further. Gradle
supports enhanced tasks , which are tasks that have their own properties and methods. This is really
different from what you are used to with Ant targets. Such enhanced tasks are either provided by you or built
into Gradle.
§
Task outcomes
When Gradle executes a task, it can label the task with different outcomes in the console UI and via the
Tooling API (see Embedding Gradle using the Tooling API). These labels are based on if a task has actions
to execute, if it should execute those actions, if it did execute those actions and if those actions made any
changes.
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Table 5. Details about task outcomes
Outcome
label
Description of outcome
Situations that have this outcome
Used whenever a task has actions and Gradle has determined they should be
(no label)
or EXECUTED
executed as part of a build.
Task executed its actions.
Used whenever a task has no actions and some dependencies, and any of the
dependencies are executed. See also the section called “Lifecycle tasks”.
Used when a task has outputs and inputs and they have not changed. See the
section called “Up-to-date checks (AKA Incremental Build)”.
Used when a task has actions, but the task tells Gradle it did not change its outputs.
UP-TO-DATE
Task’s
outputs
did
not
Used when a task has no actions and some dependencies, but all of the
change.
dependencies are up-to-date, skipped or from cache. See also the section called
“Lifecycle tasks”.
Used when a task has no actions and no dependencies.
Task’s outputs could be
FROM-CACHE found
from
a
previous Used when a task has outputs restored from the build cache. See Build Cache.
execution.
Used when a task has been explicitly excluded from the command-line. See the
SKIPPED
Task did not execute its
actions.
section called “Excluding tasks from execution”.
Used when a task has an onlyIf predicate return false. See the section called
“Using a predicate”.
NO-SOURCE
Task did not need to Used when a task has inputs and outputs, but no sources. For example, source files
execute its actions.
are .java files for JavaCompile.
§
Defining tasks
We have already seen how to define tasks using a keyword style in Build Script Basics. There are a few
variations on this style, which you may need to use in certain situations. For example, the keyword style
does not work in expressions.
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Example 81. Defining tasks
build.gradle
task(hello) {
doLast {
println "hello"
}
}
task(copy, type: Copy) {
from(file('srcDir'))
into(buildDir)
}
You can also use strings for the task names:
Example 82. Defining tasks - using strings for task names
build.gradle
task('hello') {
doLast {
println "hello"
}
}
task('copy', type: Copy) {
from(file('srcDir'))
into(buildDir)
}
There is an alternative syntax for defining tasks, which you may prefer to use:
Example 83. Defining tasks with alternative syntax
build.gradle
tasks.create(name: 'hello') {
doLast {
println "hello"
}
}
tasks.create(name: 'copy', type: Copy) {
from(file('srcDir'))
into(buildDir)
}
Here we add tasks to the tasks collection. Have a look at TaskContainer for more variations of the create()
method.
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Locating tasks
§
Locating tasks
You often need to locate the tasks that you have defined in the build file, for example, to configure them or
use them for dependencies. There are a number of ways of doing this. Firstly, each task is available as a
property of the project, using the task name as the property name:
Example 84. Accessing tasks as properties
build.gradle
task hello
println hello.name
println project.hello.name
Tasks are also available through the tasks collection.
Example 85. Accessing tasks via tasks collection
build.gradle
task hello
println tasks.hello.name
println tasks['hello'].name
You can access tasks from any project using the task’s path using the tasks.getByPath() method. You
can call the getByPath() method with a task name, or a relative path, or an absolute path.
Example 86. Accessing tasks by path
build.gradle
project(':projectA') {
task hello
}
task hello
println
println
println
println
tasks.getByPath('hello').path
tasks.getByPath(':hello').path
tasks.getByPath('projectA:hello').path
tasks.getByPath(':projectA:hello').path
Output of gradle -q hello
> gradle -q hello
:hello
:hello
:projectA:hello
:projectA:hello
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Have a look at TaskContainer for more options for locating tasks.
§
Configuring tasks
As an example, let’s look at the Copy task provided by Gradle. To create a Copy task for your build, you can
declare in your build script:
Example 87. Creating a copy task
build.gradle
task myCopy(type: Copy)
This creates a copy task with no default behavior. The task can be configured using its API (see Copy). The
following examples show several different ways to achieve the same configuration.
Just to be clear, realize that the name of this task is “ myCopy”, but it is of type “Copy”. You can have
multiple tasks of the same type , but with different names. You’ll find this gives you a lot of power to
implement cross-cutting concerns across all tasks of a particular type.
Example 88. Configuring a task - various ways
build.gradle
Copy myCopy = task(myCopy, type: Copy)
myCopy.from 'resources'
myCopy.into 'target'
myCopy.include('**/*.txt', '**/*.xml', '**/*.properties')
This is similar to the way we would configure objects in Java. You have to repeat the context ( myCopy) in the
configuration statement every time. This is a redundancy and not very nice to read.
There is another way of configuring a task. It also preserves the context and it is arguably the most readable.
It is usually our favorite.
Example 89. Configuring a task - with closure
build.gradle
task myCopy(type: Copy)
myCopy {
from 'resources'
into 'target'
include('**/*.txt', '**/*.xml', '**/*.properties')
}
This works for any task. Line 3 of the example is just a shortcut for the tasks.getByName() method. It is
Page 137 of 717
important to note that if you pass a closure to the getByName() method, this closure is applied to configure
the task, not when the task executes.
You can also use a configuration closure when you define a task.
Example 90. Defining a task with closure
build.gradle
task copy(type: Copy) {
from 'resources'
into 'target'
include('**/*.txt', '**/*.xml', '**/*.properties')
}
Don’t forget about the build phases
A task has both configuration and actions. When using the doLast, you are simply using a shortcut
to define an action. Code defined in the configuration section of your task will get executed during
the configuration phase of the build regardless of what task was targeted. See Build Lifecycle for
more details about the build lifecycle.
§
Adding dependencies to a task
There are several ways you can define the dependencies of a task. In the section called “Task
dependencies” you were introduced to defining dependencies using task names. Task names can refer to
tasks in the same project as the task, or to tasks in other projects. To refer to a task in another project, you
prefix the name of the task with the path of the project it belongs to. The following is an example which adds
a dependency from projectA:taskX to projectB:taskY:
Page 138 of 717
Example 91. Adding dependency on task from another project
build.gradle
project('projectA') {
task taskX(dependsOn: ':projectB:taskY') {
doLast {
println 'taskX'
}
}
}
project('projectB') {
task taskY {
doLast {
println 'taskY'
}
}
}
Output of gradle -q taskX
> gradle -q taskX
taskY
taskX
Instead of using a task name, you can define a dependency using a Task object, as shown in this example:
Example 92. Adding dependency using task object
build.gradle
task taskX {
doLast {
println 'taskX'
}
}
task taskY {
doLast {
println 'taskY'
}
}
taskX.dependsOn taskY
Output of gradle -q taskX
> gradle -q taskX
taskY
taskX
For more advanced uses, you can define a task dependency using a closure. When evaluated, the closure is
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passed the task whose dependencies are being calculated. The closure should return a single Task or
collection of Task objects, which are then treated as dependencies of the task. The following example adds
a dependency from taskX to all the tasks in the project whose name starts with lib:
Example 93. Adding dependency using closure
build.gradle
task taskX {
doLast {
println 'taskX'
}
}
taskX.dependsOn {
tasks.findAll { task -> task.name.startsWith('lib') }
}
task lib1 {
doLast {
println 'lib1'
}
}
task lib2 {
doLast {
println 'lib2'
}
}
task notALib {
doLast {
println 'notALib'
}
}
Output of gradle -q taskX
> gradle -q taskX
lib1
lib2
taskX
For more information about task dependencies, see the Task API.
§
Ordering tasks
Note: Task ordering is an incubating feature. Please be aware that this feature may change in later
Gradle versions.
Page 140 of 717
In some cases it is useful to control the order in which 2 tasks will execute, without introducing an explicit
dependency between those tasks. The primary difference between a task ordering and a task dependency
is that an ordering rule does not influence which tasks will be executed, only the order in which they will be
executed.
Task ordering can be useful in a number of scenarios:
Enforce sequential ordering of tasks: e.g. 'build' never runs before 'clean'.
Run build validations early in the build: e.g. validate I have the correct credentials before starting the work for
a release build.
Get feedback faster by running quick verification tasks before long verification tasks: e.g. unit tests should
run before integration tests.
A task that aggregates the results of all tasks of a particular type: e.g. test report task combines the outputs
of all executed test tasks.
There are two ordering rules available: “ must run after ” and “ should run after ”.
When you use the “must run after” ordering rule you specify that taskB must always run after taskA,
whenever both taskA and taskB will be run. This is expressed as taskB.mustRunAfter(taskA). The
“should run after” ordering rule is similar but less strict as it will be ignored in two situations. Firstly if using
that rule introduces an ordering cycle. Secondly when using parallel execution and all dependencies of a
task have been satisfied apart from the “should run after” task, then this task will be run regardless of
whether its “should run after” dependencies have been run or not. You should use “should run after” where
the ordering is helpful but not strictly required.
With these rules present it is still possible to execute taskA without taskB and vice-versa.
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Example 94. Adding a 'must run after' task ordering
build.gradle
task taskX {
doLast {
println 'taskX'
}
}
task taskY {
doLast {
println 'taskY'
}
}
taskY.mustRunAfter taskX
Output of gradle -q taskY taskX
> gradle -q taskY taskX
taskX
taskY
Example 95. Adding a 'should run after' task ordering
build.gradle
task taskX {
doLast {
println 'taskX'
}
}
task taskY {
doLast {
println 'taskY'
}
}
taskY.shouldRunAfter taskX
Output of gradle -q taskY taskX
> gradle -q taskY taskX
taskX
taskY
In the examples above, it is still possible to execute taskY without causing taskX to run:
Example 96. Task ordering does not imply task execution
Output of gradle -q taskY
> gradle -q taskY
taskY
Page 142 of 717
To specify a “must run after” or “should run after” ordering between 2 tasks, you use the
Task.mustRunAfter(java.lang.Object[]) and Task.shouldRunAfter(java.lang.Object[])
methods. These methods accept a task instance, a task name or any other input accepted by
Task.dependsOn(java.lang.Object[]).
Note that “B.mustRunAfter(A)” or “B.shouldRunAfter(A)” does not imply any execution dependency
between the tasks:
It is possible to execute tasks A and B independently. The ordering rule only has an effect when both tasks
are scheduled for execution.
When run with --continue, it is possible for B to execute in the event that A fails.
As mentioned before, the “should run after” ordering rule will be ignored if it introduces an ordering cycle:
Example 97. A 'should run after' task ordering is ignored if it introduces an ordering cycle
build.gradle
task taskX {
doLast {
println 'taskX'
}
}
task taskY {
doLast {
println 'taskY'
}
}
task taskZ {
doLast {
println 'taskZ'
}
}
taskX.dependsOn taskY
taskY.dependsOn taskZ
taskZ.shouldRunAfter taskX
Output of gradle -q taskX
> gradle -q taskX
taskZ
taskY
taskX
§
Adding a description to a task
You can add a description to your task. This description is displayed when executing gradle tasks.
Page 143 of 717
Example 98. Adding a description to a task
build.gradle
task copy(type: Copy) {
description 'Copies the resource directory to the target directory.'
from 'resources'
into 'target'
include('**/*.txt', '**/*.xml', '**/*.properties')
}
§
Replacing tasks
Sometimes you want to replace a task. For example, if you want to exchange a task added by the Java
plugin with a custom task of a different type. You can achieve this with:
Example 99. Overwriting a task
build.gradle
task copy(type: Copy)
task copy(overwrite: true) {
doLast {
println('I am the new one.')
}
}
Output of gradle -q copy
> gradle -q copy
I am the new one.
This will replace a task of type Copy with the task you’ve defined, because it uses the same name. When
you define the new task, you have to set the overwrite property to true. Otherwise Gradle throws an
exception, saying that a task with that name already exists.
§
Skipping tasks
Gradle offers multiple ways to skip the execution of a task.
Using a predicate
Page 144 of 717
§
Using a predicate
You can use the onlyIf() method to attach a predicate to a task. The task’s actions are only executed if
the predicate evaluates to true. You implement the predicate as a closure. The closure is passed the task as
a parameter, and should return true if the task should execute and false if the task should be skipped. The
predicate is evaluated just before the task is due to be executed.
Example 100. Skipping a task using a predicate
build.gradle
task hello {
doLast {
println 'hello world'
}
}
hello.onlyIf { !project.hasProperty('skipHello') }
Output of gradle hello -PskipHello
> gradle hello -PskipHello
:hello SKIPPED
BUILD SUCCESSFUL in 0s
§
Using StopExecutionException
If the logic for skipping a task can’t be expressed with a predicate, you can use the
StopExecutionException. If this exception is thrown by an action, the further execution of this action as
well as the execution of any following action of this task is skipped. The build continues with executing the
next task.
Page 145 of 717
Example 101. Skipping tasks with StopExecutionException
build.gradle
task compile {
doLast {
println 'We are doing the compile.'
}
}
compile.doFirst {
// Here you would put arbitrary conditions in real life.
// But this is used in an integration test so we want defined behavior.
if (true) { throw new StopExecutionException() }
}
task myTask(dependsOn: 'compile') {
doLast {
println 'I am not affected'
}
}
Output of gradle -q myTask
> gradle -q myTask
I am not affected
This feature is helpful if you work with tasks provided by Gradle. It allows you to add conditional execution of
the built-in actions of such a task.[6]
§
Enabling and disabling tasks
Every task has an enabled flag which defaults to true. Setting it to false prevents the execution of any of
the task’s actions. A disabled task will be labelled SKIPPED.
Example 102. Enabling and disabling tasks
build.gradle
task disableMe {
doLast {
println 'This should not be printed if the task is disabled.'
}
}
disableMe.enabled = false
Output of gradle disableMe
> gradle disableMe
:disableMe SKIPPED
BUILD SUCCESSFUL in 0s
Page 146 of 717
Up-to-date checks (AKA Incremental Build)
§
Up-to-date checks (AKA Incremental Build)
An important part of any build tool is the ability to avoid doing work that has already been done. Consider the
process of compilation. Once your source files have been compiled, there should be no need to recompile
them unless something has changed that affects the output, such as the modification of a source file or the
removal of an output file. And compilation can take a significant amount of time, so skipping the step when
it’s not needed saves a lot of time.
Gradle supports this behavior out of the box through a feature it calls incremental build. You have almost
certainly already seen it in action: it’s active nearly every time the UP-TO-DATE text appears next to the
name of a task when you run a build. Task outcomes are described in the section called “Task outcomes”.
How does incremental build work? And what does it take to make use of it in your own tasks? Let’s take a
look.
§
Task inputs and outputs
In the most common case, a task takes some inputs and generates some outputs. If we use the compilation
example from earlier, we can see that the source files are the inputs and, in the case of Java, the generated
class files are the outputs. Other inputs might include things like whether debug information should be
included.
Figure 5. Example task inputs and outputs
An important characteristic of an input is that it affects one or more outputs, as you can see from the
previous figure. Different bytecode is generated depending on the content of the source files and the
minimum version of the Java runtime you want to run the code on. That makes them task inputs. But
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whether compilation has 500MB or 600MB of maximum memory available, determined by the memoryMaximumSize
property, has no impact on what bytecode gets generated. In Gradle terminology, memoryMaximumSize is
just an internal task property.
As part of incremental build, Gradle tests whether any of the task inputs or outputs have changed since the
last build. If they haven’t, Gradle can consider the task up to date and therefore skip executing its actions.
Also note that incremental build won’t work unless a task has at least one task output, although tasks usually
have at least one input as well.
What this means for build authors is simple: you need to tell Gradle which task properties are inputs and
which are outputs. If a task property affects the output, be sure to register it as an input, otherwise the task
will be considered up to date when it’s not. Conversely, don’t register properties as inputs if they don’t affect
the output, otherwise the task will potentially execute when it doesn’t need to. Also be careful of
non-deterministic tasks that may generate different output for exactly the same inputs: these should not be
configured for incremental build as the up-to-date checks won’t work.
Let’s now look at how you can register task properties as inputs and outputs.
§
Custom task types
If you’re implementing a custom task as a class, then it takes just two steps to make it work with incremental
build:
1. Create typed properties (via getter methods) for each of your task inputs and outputs
2. Add the appropriate annotation to each of those properties
Note: Annotations must be placed on getters or on Groovy properties. Annotations placed on
setters, or on a Java field without a corresponding annotated getter are ignored.
Gradle supports three main categories of inputs and outputs:
Simple values
Things like strings and numbers. More generally, a simple value can have any type that implements Serializable
.
Filesystem types
These consist of the standard File class but also derivatives of Gradle’s FileCollection type and
anything else that can be passed to either the Project.file(java.lang.Object) method - for single
file/directory properties - or the Project.files(java.lang.Object[]) method.
Nested values
Custom types that don’t conform to the other two categories but have their own properties that are inputs or
outputs. In effect, the task inputs or outputs are nested inside these custom types.
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As an example, imagine you have a task that processes templates of varying types, such as FreeMarker,
Velocity, Moustache, etc. It takes template source files and combines them with some model data to
generate populated versions of the template files.
This task will have three inputs and one output:
Template source files
Model data
Template engine
Where the output files are written
When you’re writing a custom task class, it’s easy to register properties as inputs or outputs via annotations.
To demonstrate, here is a skeleton task implementation with some suitable inputs and outputs, along with
their annotations:
Example 103. Custom task class
buildSrc/src/main/java/org/example/ProcessTemplates.java
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package org.example;
import
import
import
import
import
java.io.File;
java.util.HashMap;
org.gradle.api.*;
org.gradle.api.file.*;
org.gradle.api.tasks.*;
public class ProcessTemplates extends DefaultTask {
private TemplateEngineType templateEngine;
private FileCollection sourceFiles;
private TemplateData templateData;
private File outputDir;
@Input
public TemplateEngineType getTemplateEngine() {
return this.templateEngine;
}
@InputFiles
public FileCollection getSourceFiles() {
return this.sourceFiles;
}
@Nested
public TemplateData getTemplateData() {
return this.templateData;
}
@OutputDirectory
public File getOutputDir() { return this.outputDir; }
// + setter methods for the above - assume we’ve defined them
@TaskAction
public void processTemplates() {
// ...
}
}
buildSrc/src/main/java/org/example/TemplateData.java
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package org.example;
import java.util.HashMap;
import java.util.Map;
import org.gradle.api.tasks.Input;
public class TemplateData {
private String name;
private Map<String, String> variables;
public TemplateData(String name, Map<String, String> variables) {
this.name = name;
this.variables = new HashMap<>(variables);
}
@Input
public String getName() { return this.name; }
@Input
public Map<String, String> getVariables() {
return this.variables;
}
}
Output of gradle processTemplates
> gradle processTemplates
:processTemplates
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
Output of gradle processTemplates
> gradle processTemplates
:processTemplates UP-TO-DATE
BUILD SUCCESSFUL in 0s
1 actionable task: 1 up-to-date
There’s plenty to talk about in this example, so let’s work through each of the input and output properties in
turn:
templateEngine
Represents which engine to use when processing the source templates, e.g. FreeMarker, Velocity, etc. You
could implement this as a string, but in this case we have gone for a custom enum as it provides greater type
information and safety. Since enums implement Serializable automatically, we can treat this as a simple
value and use the @Input annotation, just as we would with a String property.
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sourceFiles
The source templates that the task will be processing. Single files and collections of files need their own
special annotations. In this case, we’re dealing with a collection of input files and so we use the @InputFiles
annotation. You’ll see more file-oriented annotations in a table later.
templateData
For this example, we’re using a custom class to represent the model data. However, it does not implement Serializabl
, so we can’t use the @Input annotation. That’s not a problem as the properties within TemplateData - a
string and a hash map with serializable type parameters - are serializable and can be annotated with @Input
. We use @Nested on templateData to let Gradle know that this is a value with nested input properties.
outputDir
The directory where the generated files go. As with input files, there are several annotations for output files
and directories. A property representing a single directory requires @OutputDirectory. You’ll learn about
the others soon.
These annotated properties mean that Gradle will skip the task if none of the source files, template engine,
model data or generated files have changed since the previous time Gradle executed the task. This will often
save a significant amount of time. You can learn how Gradle detects changes later.
This example is particularly interesting because it works with collections of source files. What happens if only
one source file changes? Does the task process all the source files again or just the modified one? That
depends on the task implementation. If the latter, then the task itself is incremental, but that’s a different
feature to the one we’re discussing here. Gradle does help task implementers with this via its incremental
task inputs feature.
Now that you have seen some of the input and output annotations in practice, let’s take a look at all the
annotations available to you and when you should use them. The table below lists the available annotations
and the corresponding property type you can use with each one.
Table 6. Incremental build property type annotations
Annotation
Expected property
type
Description
@Input
Any serializable type
A simple input value
@InputFile
File*
A single input file (not directory)
@InputDirectory
File*
A single input directory (not file)
@InputFiles
Iterable<File>*
An iterable of input files and directories
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An iterable of input files and directories that represent a Java classpath. This
allows the task to ignore irrelevant changes to the property, such as different
names for the same files. It is similar to annotating the property @PathSensitive(RELATIVE)
but it will ignore the names of JAR files directly added to the classpath, and it
will consider changes in the order of the files as a change in the classpath.
@Classpath
Iterable<File>*
Gradle will inspect the contents of jar files on the classpath and ignore changes
that do not affect the semantics of the classpath (such as file dates and entry
order). See also the section called “Using the classpath annotations”.
Note: The @Classpath annotation was introduced in Gradle 3.2. To
stay compatible with earlier Gradle versions, classpath properties
should also be annotated with @InputFiles.
An iterable of input files and directories that represent a Java compile
classpath. This allows the task to ignore irrelevant changes that do not affect
the API of the classes in classpath. See also the section called “Using the
classpath annotations”.
The following kinds of changes to the classpath will be ignored:
Changes to the path of jar or top level directories.
Changes to timestamps and the order of entries in Jars.
Changes to resources and Jar manifests, including adding or removing
resources.
Changes to private class elements, such as private fields, methods and inner
@CompileClasspath Iterable<File>*
classes.
Changes to code, such as method bodies, static initializers and field initializers
(except for constants).
Changes to debug information, for example when a change to a comment
affects the line numbers in class debug information.
Changes to directories, including directory entries in Jars.
Note: The @CompileClasspath annotation was introduced in Gradle
3.4. To stay compatible with Gradle 3.3 and 3.2, compile classpath
properties should also be annotated with @Classpath. For
compatibility with Gradle versions before 3.2 the property should also
be annotated with @InputFiles.
File*
A single output file (not directory)
@OutputDirectory File*
A single output directory (not file)
@OutputFile
Map<String, File>
@OutputFiles
An iterable of output files (no directories). The task outputs can only be cached
** or Iterable<File>
if a Map is provided.
*
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Map<String, File>
An iterable of output directories (no files). The task outputs can only be cached
@OutputDirectories** or Iterable<File>
if a Map is provided.
*
@Destroys
@LocalState
File or Iterable<File>
Specifies one or more files that are removed by this task. Note that a task can
*
define either inputs/outputs or destroyables, but not both.
File or Iterable<File>
Specifies one or more files that represent the local state of the task. These files
*
are removed when the task is loaded from cache.
A custom type that may not implement Serializable but does have at least
@Nested
Any custom type
one field or property marked with one of the annotations in this table. It could
even be another @Nested.
Indicates that the property is neither an input nor an output. It simply affects the
@Console
Any type
console output of the task in some way, such as increasing or decreasing the
verbosity of the task.
@Internal
Any type
Indicates that the property is used internally but is neither an input nor an
output.
*
In fact, File can be any type accepted by Project.file(java.lang.Object) and Iterable<File>
can be any type accepted by Project.files(java.lang.Object[]). This includes instances of Callable
, such as closures, allowing for lazy evaluation of the property values. Be aware that the types FileCollection
and FileTree are Iterable<File>s.
**
Similar to the above, File can be any type accepted by Project.file(java.lang.Object). The Map
itself can be wrapped in Callables, such as closures.
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Table 7. Additional annotations used to further qualifying property type annotations
Annotation
Description
Used with @InputFiles or @InputDirectory to tell Gradle to skip the task if the corresponding files or
directory are empty, along with all other input files declared with this annotation. Tasks that have been
@SkipWhenEmpty
skipped due to all of their input files that were declared with this annotation being empty will result in a
distinct “no source” outcome. For example, NO-SOURCE will be emitted in the console output.
@Optional
Used with any of the property type annotations listed in the Optional API documentation. This annotation
disables validation checks on the corresponding property. See the section on validation for more details.
Used with any input file property to tell Gradle to only consider the given part of the file paths as important.
@PathSensitiveFor example, if a property is annotated with @PathSensitive(PathSensitivity.NAME_ONLY), then
moving the files around without changing their contents will not make the task out-of-date.
Annotations are inherited from all parent types including implemented interfaces. Property type annotations
override any other property type annotation declared in a parent type. This way an @InputFile property
can be turned into an @InputDirectory property in a child task type.
Annotations on a property declared in a type override similar annotations declared by the superclass and in
any implemented interfaces. Superclass annotations take precedence over annotations declared in
implemented interfaces.
The Console and Internal annotations in the table are special cases as they don’t declare either task
inputs or task outputs. So why use them? It’s so that you can take advantage of the Java Gradle Plugin
Development plugin to help you develop and publish your own plugins. This plugin checks whether any
properties of your custom task classes lack an incremental build annotation. This protects you from
forgetting to add an appropriate annotation during development.
§
Using the classpath annotations
Besides @InputFiles, for JVM-related tasks Gradle understands the concept of classpath inputs. Both
runtime and compile classpaths are treated differently when Gradle is looking for changes.
As opposed to input properties annotated with @InputFiles, for classpath properties the order of the
entries in the file collection matter. On the other hand, the names and paths of the directories and jar files on
the classpath itself are ignored. Timestamps and the order of class files and resources inside jar files on a
classpath are ignored, too, thus recreating a jar file with different file dates will not make the task out of date.
Runtime classpaths are marked with @Classpath, and they offer further customization via classpath
normalization.
Input properties annotated with @CompileClasspath are considered Java compile classpaths. Additionally
to the aforementioned general classpath rules, compile classpaths ignore changes to everything but class
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files. Gradle uses the same class analysis described in the section called “Compile avoidance” to further
filter changes that don’t affect the class' ABIs. This means that changes which only touch the implementation
of classes do not make the task out of date.
§
Nested inputs
When analyzing @Nested task properties for declared input and output sub-properties Gradle uses the type
of the actual value. Hence it can discover all sub-properties declared by a runtime sub-type.
When adding @Nested to an iterable, each element is treated as a separate nested input.
This allows richer modeling and extensibility for tasks, as e.g. shown by CompileOptions.getCompilerArgumentPro
.
For example, to declare annotation processor arguments, it is possible to do the following:
class MyAnnotationProcessor implements CompilerArgumentProvider {
@InputFile
@PathSensitivite(NONE)
File inputFile
@OutputFile
File outputFile
MyAnnotationProcessor(File inputFile, File outputFile) {
this.inputFile = inputFile
this.outputFile = outputFile
}
@Override
List<String> asArguments() {
[
"-AinputFile=${inputFile.absolutePath}",
"-AoutputFile=${outputFile.absolutePath}"
]
}
}
compileJava.options.compilerArgumentProviders << new MyAnnotationProcessor(inputFile, outp
This models an annotation processor which requires an input file and generates an output file.
The approach works for Java compiler arguments, since CompileOptions.getCompilerArgumentProviders()
is an Iterable annotated with @Nested. In the same way, this kind of modelling is available to custom
tasks.
Runtime API
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§
Runtime API
Custom task classes are an easy way to bring your own build logic into the arena of incremental build, but
you don’t always have that option. That’s why Gradle also provides an alternative API that can be used with
any tasks, which we look at next.
When you don’t have access to the source for a custom task class, there is no way to add any of the
annotations we covered in the previous section. Fortunately, Gradle provides a runtime API for scenarios
just like that. It can also be used for ad-hoc tasks, as you’ll see next.
§
Using it for ad-hoc tasks
This runtime API is provided through a couple of aptly named properties that are available on every Gradle
task:
Task.getInputs() of type TaskInputs
Task.getOutputs() of type TaskOutputs
Task.getDestroyables() of type TaskDestroyables
These objects have methods that allow you to specify files, directories and values which constitute the task’s
inputs and outputs. In fact, the runtime API has almost feature parity with the annotations. All it lacks is
validation of whether declared files are actually files and declared directories are directories. Nor will it create
output directories if they don’t exist. But that’s it.
Let’s take the template processing example from before and see how it would look as an ad-hoc task that
uses the runtime API:
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Example 104. Ad-hoc task
build.gradle
task processTemplatesAdHoc {
inputs.property("engine", TemplateEngineType.FREEMARKER)
inputs.files(fileTree("src/templates"))
inputs.property("templateData.name", "docs")
inputs.property("templateData.variables", [year: 2013])
outputs.dir("$buildDir/genOutput2")
doLast {
// Process the templates here
}
}
Output of gradle processTemplatesAdHoc
> gradle processTemplatesAdHoc
:processTemplatesAdHoc
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
As before, there’s much to talk about. To begin with, you should really write a custom task class for this as
it’s a non-trivial implementation that has several configuration options. In this case, there are no task
properties to store the root source folder, the location of the output directory or any of the other settings.
That’s deliberate to highlight the fact that the runtime API doesn’t require the task to have any state. In terms
of incremental build, the above ad-hoc task will behave the same as the custom task class.
All the input and output definitions are done through the methods on inputs and outputs, such as property()
, files(), and dir(). Gradle performs up-to-date checks on the argument values to determine whether
the task needs to run again or not. Each method corresponds to one of the incremental build annotations, for
example inputs.property() maps to @Input and outputs.dir() maps to @OutputDirectory. The
only difference is that the file(), files(), dir() and dirs() methods don’t validate the type of file
object at the given path (file or directory), unlike the annotations.
The files that a task removes can be specified through destroyables.register().
Example 105. Ad-hoc task declaring a destroyable
build.gradle
task removeTempDir {
destroyables.register("$projectDir/tmpDir")
doLast {
delete("$projectDir/tmpDir")
}
}
One notable difference between the runtime API and the annotations is the lack of a method that
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corresponds directly to @Nested. That’s why the example uses two property() declarations for the
template data, one for each TemplateData property. You should utilize the same technique when using the
runtime API with nested values. Any given task can either declare destroyables or inputs/outputs, but cannot
declare both.
§
Using it for custom task types
Another type of example involves adding input and output definitions to instances of a custom task class that
lacks the requisite annotations. For example, imagine that the ProcessTemplates task is provided by a
plugin and that it’s missing the incremental build annotations. In order to make up for that deficiency, you can
use the runtime API:
Example 106. Using runtime API with custom task type
build.gradle
task processTemplatesRuntime(type: ProcessTemplatesNoAnnotations) {
templateEngine = TemplateEngineType.FREEMARKER
sourceFiles = fileTree("src/templates")
templateData = new TemplateData("test", [year: 2014])
outputDir = file("$buildDir/genOutput3")
inputs.property("engine",templateEngine)
inputs.files(sourceFiles)
inputs.property("templateData.name", templateData.name)
inputs.property("templateData.variables", templateData.variables)
outputs.dir(outputDir)
}
Output of gradle processTemplatesRuntime
> gradle processTemplatesRuntime
:processTemplatesRuntime
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
Output of gradle processTemplatesRuntime
> gradle processTemplatesRuntime
:processTemplatesRuntime UP-TO-DATE
BUILD SUCCESSFUL in 0s
1 actionable task: 1 up-to-date
As you can see, we can both configure the tasks properties and use those properties as arguments to the
incremental build runtime API. Using the runtime API like this is a little like using doLast() and doFirst()
to attach extra actions to a task, except in this case we’re attaching information about inputs and outputs.
Note that if the task type is already using the incremental build annotations, the runtime API will add inputs
and outputs rather than replace them.
Fine-grained configuration
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§
Fine-grained configuration
The runtime API methods only allow you to declare your inputs and outputs in themselves. However, the
file-oriented ones return a builder - of type TaskInputFilePropertyBuilder - that lets you provide
additional information about those inputs and outputs.
You can learn about all the options provided by the builder in its API documentation, but we’ll show you a
simple example here to give you an idea of what you can do.
Let’s say we don’t want to run the processTemplates task if there are no source files, regardless of
whether it’s a clean build or not. After all, if there are no source files, there’s nothing for the task to do. The
builder allows us to configure this like so:
Example 107. Using skipWhenEmpty() via the runtime API
build.gradle
task processTemplatesRuntimeConf(type: ProcessTemplatesNoAnnotations) {
// ...
sourceFiles = fileTree("src/templates") {
include "**/*.fm"
}
inputs.files(sourceFiles).skipWhenEmpty()
// ...
}
Output of gradle clean processTemplatesRuntimeConf
> gradle clean processTemplatesRuntimeConf
:processTemplatesRuntimeConf NO-SOURCE
BUILD SUCCESSFUL in 0s
1 actionable task: 1 up-to-date
The TaskInputs.files() method returns a builder that has a skipWhenEmpty() method. Invoking this
method is equivalent to annotating to the property with @SkipWhenEmpty.
Prior to Gradle 3.0, you had to use the TaskInputs.source() and TaskInputs.sourceDir()
methods to get the same behavior as with skipWhenEmpty(). These methods are now deprecated and
should not be used with Gradle 3.0 and above.
Now that you have seen both the annotations and the runtime API, you may be wondering which API you
should be using. Our recommendation is to use the annotations wherever possible, and it’s sometimes worth
creating a custom task class just so that you can make use of them. The runtime API is more for situations in
which you can’t use the annotations.
Important beneficial side effects
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§
Important beneficial side effects
Once you declare a task’s formal inputs and outputs, Gradle can then infer things about those properties.
For example, if an input of one task is set to the output of another, that means the first task depends on the
second, right? Gradle knows this and can act upon it.
We’ll look at this feature next and also some other features that come from Gradle knowing things about
inputs and outputs.
§
Inferred task dependencies
Consider an archive task that packages the output of the processTemplates task. A build author will see
that the archive task obviously requires processTemplates to run first and so may add an explicit dependsOn
. However, if you define the archive task like so:
Example 108. Inferred task dependency via task outputs
build.gradle
task packageFiles(type: Zip) {
from processTemplates.outputs
}
Output of gradle clean packageFiles
> gradle clean packageFiles
:processTemplates
:packageFiles
BUILD SUCCESSFUL in 0s
3 actionable tasks: 2 executed, 1 up-to-date
Gradle will automatically make packageFiles depend on processTemplates. It can do this because it’s
aware that one of the inputs of packageFiles requires the output of the processTemplates task. We call this
an inferred task dependency.
The above example can also be written as
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Example 109. Inferred task dependency via a task argument
build.gradle
task packageFiles2(type: Zip) {
from processTemplates
}
Output of gradle clean packageFiles2
> gradle clean packageFiles2
:processTemplates
:packageFiles2
BUILD SUCCESSFUL in 0s
3 actionable tasks: 2 executed, 1 up-to-date
This is because the from() method can accept a task object as an argument. Behind the scenes, from()
uses the project.files() method to wrap the argument, which in turn exposes the task’s formal outputs
as a file collection. In other words, it’s a special case!
§
Input and output validation
The incremental build annotations provide enough information for Gradle to perform some basic validation
on the annotated properties. In particular, it does the following for each property before the task executes:
@InputFile - verifies that the property has a value and that the path corresponds to a file (not a directory)
that exists.
@InputDirectory - same as for @InputFile, except the path must correspond to a directory.
@OutputDirectory - verifies that the path doesn’t match a file and also creates the directory if it doesn’t
already exist.
Such validation improves the robustness of the build, allowing you to identify issues related to inputs and
outputs quickly.
You will occasionally want to disable some of this validation, specifically when an input file may validly not
exist. That’s why Gradle provides the @Optional annotation: you use it to tell Gradle that a particular input
is optional and therefore the build should not fail if the corresponding file or directory doesn’t exist.
§
Continuous build
Another benefit of defining task inputs and outputs is continuous build. Since Gradle knows what files a task
depends on, it can automatically run a task again if any of its inputs change. By activating continuous build
when you run Gradle - through the --continuous or -t options - you will put Gradle into a state in which it
continually checks for changes and executes the requested tasks when it encounters such changes.
You can find out more about this feature in Continuous build.
Task parallelism
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§
Task parallelism
One last benefit of defining task inputs and outputs is that Gradle can use this information to make decisions
about how to run tasks when the "--parallel" option is used. For instance, Gradle will inspect the outputs of
tasks when selecting the next task to run and will avoid concurrent execution of tasks that write to the same
output directory. Similarly, Gradle will use the information about what files a task destroys (e.g. specified by
the Destroys annotation) and avoid running a task that removes a set of files while another task is running
that consumes or creates those same files (and vice versa). It can also determine that a task that creates a
set of files has already run and that a task that consumes those files has yet to run and will avoid running a
task that removes those files in between. By providing task input and output information in this way, Gradle
can infer creation/consumption/destruction relationships between tasks and can ensure that task execution
does not violate those relationships.
§
How does it work?
Before a task is executed for the first time, Gradle takes a snapshot of the inputs. This snapshot contains the
paths of input files and a hash of the contents of each file. Gradle then executes the task. If the task
completes successfully, Gradle takes a snapshot of the outputs. This snapshot contains the set of output
files and a hash of the contents of each file. Gradle persists both snapshots for the next time the task is
executed.
Each time after that, before the task is executed, Gradle takes a new snapshot of the inputs and outputs. If
the new snapshots are the same as the previous snapshots, Gradle assumes that the outputs are up to date
and skips the task. If they are not the same, Gradle executes the task. Gradle persists both snapshots for
the next time the task is executed.
Gradle also considers the code of the task as part of the inputs to the task. When a task, its actions, or its
dependencies change between executions, Gradle considers the task as out-of-date.
Gradle understands if a file property (e.g. one holding a Java classpath) is order-sensitive. When comparing
the snapshot of such a property, even a change in the order of the files will result in the task becoming
out-of-date.
Note that if a task has an output directory specified, any files added to that directory since the last time it was
executed are ignored and will NOT cause the task to be out of date. This is so unrelated tasks may share an
output directory without interfering with each other. If this is not the behaviour you want for some reason,
consider using TaskOutputs.upToDateWhen(groovy.lang.Closure)
The inputs for the task are also used to calculate the build cache key used to load task outputs when
enabled. For more details see the section called “Task Output Caching”.
Advanced techniques
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§
Advanced techniques
Everything you’ve seen so far in this section will cover most of the use cases you’ll encounter, but there are
some scenarios that need special treatment. We’ll present a few of those next with the appropriate solutions.
§
Adding your own cached input/output methods
Have you ever wondered how the from() method of the Copy task works? It’s not annotated with @InputFiles
and yet any files passed to it are treated as formal inputs of the task. What’s happening?
The implementation is quite simple and you can use the same technique for your own tasks to improve their
APIs. Write your methods so that they add files directly to the appropriate annotated property. As an
example, here’s how to add a sources() method to the custom ProcessTemplates class we introduced
earlier:
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Example 110. Declaring a method to add task inputs
buildSrc/src/main/java/org/example/ProcessTemplates.java
public class ProcessTemplates extends DefaultTask {
// ...
private FileCollection sourceFiles = getProject().files();
@SkipWhenEmpty
@InputFiles
@PathSensitive(PathSensitivity.NONE)
public FileCollection getSourceFiles() {
return this.sourceFiles;
}
public void sources(FileCollection sourceFiles) {
this.sourceFiles = this.sourceFiles.plus(sourceFiles);
}
// ...
}
build.gradle
task processTemplates(type: ProcessTemplates) {
templateEngine = TemplateEngineType.FREEMARKER
templateData = new TemplateData("test", [year: 2012])
outputDir = file("$buildDir/genOutput")
sources fileTree("src/templates")
}
Output of gradle processTemplates
> gradle processTemplates
:processTemplates
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
In other words, as long as you add values and files to formal task inputs and outputs during the configuration
phase, they will be treated as such regardless from where in the build you add them.
If we want to support tasks as arguments as well and treat their outputs as the inputs, we can use the project.files()
method like so:
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Example 111. Declaring a method to add a task as an input
buildSrc/src/main/java/org/example/ProcessTemplates.java
// ...
public void sources(Task inputTask) {
this.sourceFiles = this.sourceFiles.plus(getProject().files(inputTask));
}
// ...
build.gradle
task copyTemplates(type: Copy) {
into "$buildDir/tmp"
from "src/templates"
}
task processTemplates2(type: ProcessTemplates) {
// ...
sources copyTemplates
}
Output of gradle processTemplates2
> gradle processTemplates2
:copyTemplates
:processTemplates2
BUILD SUCCESSFUL in 0s
2 actionable tasks: 2 executed
This technique can make your custom task easier to use and result in cleaner build files. As an added
benefit, our use of getProject().files() means that our custom method can set up an inferred task
dependency.
One last thing to note: if you are developing a task that takes collections of source files as inputs, like this
example, consider using the built-in SourceTask. It will save you having to implement some of the plumbing
that we put into ProcessTemplates.
§
Linking an @OutputDirectory to an @InputFiles
When you want to link the output of one task to the input of another, the types often match and a simple
property assignment will provide that link. For example, a File output property can be assigned to a File
input.
Unfortunately, this approach breaks down when you want the files in a task’s @OutputDirectory (of type File
) to become the source for another task’s @InputFiles property (of type FileCollection). Since the
two have different types, property assignment won’t work.
As an example, imagine you want to use the output of a Java compilation task - via the destinationDir
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property - as the input of a custom task that instruments a set of files containing Java bytecode. This custom
task, which we’ll call Instrument, has a classFiles property annotated with @InputFiles. You might
initially try to configure the task like so:
Example 112. Failed attempt at setting up an inferred task dependency
build.gradle
apply plugin: "java"
task badInstrumentClasses(type: Instrument) {
classFiles = fileTree(compileJava.destinationDir)
destinationDir = file("$buildDir/instrumented")
}
Output of gradle clean badInstrumentClasses
> gradle clean badInstrumentClasses
:clean UP-TO-DATE
:badInstrumentClasses NO-SOURCE
BUILD SUCCESSFUL in 0s
1 actionable task: 1 up-to-date
There’s nothing obviously wrong with this code, but you can see from the console output that the compilation
task is missing. In this case you would need to add an explicit task dependency between instrumentClasses
and compileJava via dependsOn. The use of fileTree() means that Gradle can’t infer the task
dependency itself.
One solution is to use the TaskOutputs.files property, as demonstrated by the following example:
Example 113. Setting up an inferred task dependency between output dir and input files
build.gradle
task instrumentClasses(type: Instrument) {
classFiles = compileJava.outputs.files
destinationDir = file("$buildDir/instrumented")
}
Output of gradle clean instrumentClasses
> gradle clean instrumentClasses
:clean UP-TO-DATE
:compileJava
:instrumentClasses
BUILD SUCCESSFUL in 0s
3 actionable tasks: 2 executed, 1 up-to-date
Alternatively, you can get Gradle to access the appropriate property itself by using the project.files()
method in place of project.fileTree():
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Example 114. Setting up an inferred task dependency with files()
build.gradle
task instrumentClasses2(type: Instrument) {
classFiles = files(compileJava)
destinationDir = file("$buildDir/instrumented")
}
Output of gradle clean instrumentClasses2
> gradle clean instrumentClasses2
:clean UP-TO-DATE
:compileJava
:instrumentClasses2
BUILD SUCCESSFUL in 0s
3 actionable tasks: 2 executed, 1 up-to-date
Remember that files() can take tasks as arguments, whereas fileTree() cannot.
The downside of this approach is that all file outputs of the source task become the input files of the target - instrumentC
in this case. That’s fine as long as the source task only has a single file-based output, like the JavaCompile
task. But if you have to link just one output property among several, then you need to explicitly tell Gradle
which task generates the input files using the builtBy method:
Example 115. Setting up an inferred task dependency with builtBy()
build.gradle
task instrumentClassesBuiltBy(type: Instrument) {
classFiles = fileTree(compileJava.destinationDir) {
builtBy compileJava
}
destinationDir = file("$buildDir/instrumented")
}
Output of gradle clean instrumentClassesBuiltBy
> gradle clean instrumentClassesBuiltBy
:clean UP-TO-DATE
:compileJava
:instrumentClassesBuiltBy
BUILD SUCCESSFUL in 0s
3 actionable tasks: 2 executed, 1 up-to-date
You can of course just add an explicit task dependency via dependsOn, but the above approach provides
more semantic meaning, explaining why compileJava has to run beforehand.
Providing custom up-to-date logic
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§
Providing custom up-to-date logic
Gradle automatically handles up-to-date checks for output files and directories, but what if the task output is
something else entirely? Perhaps it’s an update to a web service or a database table. Gradle has no way of
knowing how to check whether the task is up to date in such cases.
That’s where the upToDateWhen() method on TaskOutputs comes in. This takes a predicate function
that is used to determine whether a task is up to date or not. One use case is to disable up-to-date checks
completely for a task, like so:
Example 116. Ignoring up-to-date checks
build.gradle
task alwaysInstrumentClasses(type: Instrument) {
classFiles = files(compileJava)
destinationDir = file("$buildDir/instrumented")
outputs.upToDateWhen { false }
}
Output of gradle clean alwaysInstrumentClasses
> gradle clean alwaysInstrumentClasses
:compileJava
:alwaysInstrumentClasses
BUILD SUCCESSFUL in 0s
3 actionable tasks: 2 executed, 1 up-to-date
Output of gradle alwaysInstrumentClasses
> gradle alwaysInstrumentClasses
:compileJava UP-TO-DATE
:alwaysInstrumentClasses
BUILD SUCCESSFUL in 0s
2 actionable tasks: 1 executed, 1 up-to-date
The { false } closure ensures that copyResources will always perform the copy, irrespective of
whether there is no change in the inputs or outputs.
You can of course put more complex logic into the closure. You could check whether a particular record in a
database table exists or has changed for example. Just be aware that up-to-date checks should save you
time. Don’t add checks that cost as much or more time than the standard execution of the task. In fact, if a
task ends up running frequently anyway, because it’s rarely up to date, then it may not be worth having an
up-to-date check at all. Remember that your checks will always run if the task is in the execution task graph.
One common mistake is to use upToDateWhen() instead of Task.onlyIf(). If you want to skip a task on
the basis of some condition unrelated to the task inputs and outputs, then you should use onlyIf(). For
example, in cases where you want to skip a task when a particular property is set or not set.
Configure input normalization
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§
Configure input normalization
For up to date checks and the build cache Gradle needs to determine if two task input properties have the
same value. In order to do so, Gradle first normalizes both inputs and then compares the result. For
example, for a compile classpath, Gradle extracts the ABI signature from the classes on the classpath and
then compares signatures between the last Gradle run and the current Gradle run as described in the
section called “Compile avoidance”.
It is possible to customize Gradle’s built-in strategy for runtime classpath normalization. All inputs annotated
with @Classpath are considered to be runtime classpaths.
Let’s say you want to add a file build-info.properties to all your produced jar files which contains
information about the build, e.g. the timestamp when the build started or some ID to identify the CI job that
published the artifact. This file is only for auditing purposes, and has no effect on the outcome of running
tests. Nonetheless, this file is part of the runtime classpath for the test task and changes on every build
invocation. Therefore, the test would be never up-to-date or pulled from the build cache. In order to benefit
from incremental builds again, you are able tell Gradle to ignore this file on the runtime classpath at the
project level by using Project.normalization(org.gradle.api.Action):
Example 117. Runtime classpath normalization
build.gradle
normalization {
runtimeClasspath {
ignore 'build-info.properties'
}
}
The effect of this configuration would be that changes to build-info.properties would be ignored for
up-to-date checks and build cache key calculations. Note that this will not change the runtime behavior of the
test task - i.e. any test is still able to load build-info.properties and the runtime classpath is still the
same as before.
§
Stale task outputs
When the Gradle version changes, Gradle detects that outputs from tasks that ran with older versions of
Gradle need to be removed to ensure that the newest version of the tasks are starting from a known clean
state.
Note: Automatic clean-up of stale output directories has only been implemented for the output of
source sets (Java/Groovy/Scala compilation).
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Task rules
§
Task rules
Sometimes you want to have a task whose behavior depends on a large or infinite number value range of
parameters. A very nice and expressive way to provide such tasks are task rules:
Example 118. Task rule
build.gradle
tasks.addRule("Pattern: ping<ID>") { String taskName ->
if (taskName.startsWith("ping")) {
task(taskName) {
doLast {
println "Pinging: " + (taskName - 'ping')
}
}
}
}
Output of gradle -q pingServer1
> gradle -q pingServer1
Pinging: Server1
The String parameter is used as a description for the rule, which is shown with gradle tasks.
Rules are not only used when calling tasks from the command line. You can also create dependsOn
relations on rule based tasks:
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Example 119. Dependency on rule based tasks
build.gradle
tasks.addRule("Pattern: ping<ID>") { String taskName ->
if (taskName.startsWith("ping")) {
task(taskName) {
doLast {
println "Pinging: " + (taskName - 'ping')
}
}
}
}
task groupPing {
dependsOn pingServer1, pingServer2
}
Output of gradle -q groupPing
> gradle -q groupPing
Pinging: Server1
Pinging: Server2
If you run “gradle -q tasks” you won’t find a task named “pingServer1” or “pingServer2”, but this
script is executing logic based on the request to run those tasks.
§
Finalizer tasks
Note: Finalizers tasks are an incubating feature (see the section called “Incubating”).
Finalizer tasks are automatically added to the task graph when the finalized task is scheduled to run.
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Example 120. Adding a task finalizer
build.gradle
task taskX {
doLast {
println 'taskX'
}
}
task taskY {
doLast {
println 'taskY'
}
}
taskX.finalizedBy taskY
Output of gradle -q taskX
> gradle -q taskX
taskX
taskY
Finalizer tasks will be executed even if the finalized task fails.
Example 121. Task finalizer for a failing task
build.gradle
task taskX {
doLast {
println 'taskX'
throw new RuntimeException()
}
}
task taskY {
doLast {
println 'taskY'
}
}
taskX.finalizedBy taskY
Output of gradle -q taskX
> gradle -q taskX
taskX
taskY
On the other hand, finalizer tasks are not executed if the finalized task didn’t do any work, for example if it is
considered up to date or if a dependent task fails.
Finalizer tasks are useful in situations where the build creates a resource that has to be cleaned up
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regardless of the build failing or succeeding. An example of such a resource is a web container that is
started before an integration test task and which should be always shut down, even if some of the tests fail.
To specify a finalizer task you use the Task.finalizedBy(java.lang.Object[]) method. This
method
accepts
a
task
instance,
a
task
name,
or
any
other
input
accepted
by
Task.dependsOn(java.lang.Object[]).
§
Lifecycle tasks
Lifecycle tasks are tasks that do not do work themselves. They typically do not have any task actions.
Lifecycle tasks can represent several concepts:
a work-flow step (e.g., run all checks with check)
a buildable thing (e.g., create a debug 32-bit executable for native components with debug32MainExecutable
)
a convenience task to execute many of the same logical tasks (e.g., run all compilation tasks with compileAll
)
Many Gradle plug-ins define their own lifecycle tasks to make it convenient to do specific things. When
developing your own plugins, you should consider using your own lifecycle tasks or hooking into some of the
tasks already provided by Gradle. See the Java plugin the section called “Tasks” for an example.
Unless a lifecycle task has actions, its outcome is determined by its dependencies. If any of the task’s
dependencies are executed, the lifecycle task will be considered executed. If all of the task’s dependencies
are up-to-date, skipped or from cache, the lifecycle task will be considered up-to-date.
§
Summary
If you are coming from Ant, an enhanced Gradle task like Copy seems like a cross between an Ant target
and an Ant task. Although Ant’s tasks and targets are really different entities, Gradle combines these notions
into a single entity. Simple Gradle tasks are like Ant’s targets, but enhanced Gradle tasks also include
aspects of Ant tasks. All of Gradle’s tasks share a common API and you can create dependencies between
them. These tasks are much easier to configure than an Ant task. They make full use of the type system,
and are more expressive and easier to maintain.
[6] You might be wondering why there is neither an import for the StopExecutionException nor do we
access it via its fully qualified name. The reason is, that Gradle adds a set of default imports to your script
(see the section called “Default imports”).
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Working With Files
Most builds work with files. Gradle adds some concepts and APIs to help you achieve this.
§
Locating files
You can locate a file relative to the project directory using the Project.file(java.lang.Object)
method.
Example 122. Locating files
build.gradle
// Using a relative path
File configFile = file('src/config.xml')
// Using an absolute path
configFile = file(configFile.absolutePath)
// Using a File object with a relative path
configFile = file(new File('src/config.xml'))
// Using a java.nio.file.Path object with a relative path
configFile = file(Paths.get('src', 'config.xml'))
// Using an absolute java.nio.file.Path object
configFile = file(Paths.get(System.getProperty('user.home')).resolve('global-config.xml'))
You can pass any object to the file() method, and it will attempt to convert the value to an absolute File
object. Usually, you would pass it a String, File or Path instance. If this path is an absolute path, it is
used to construct a File instance. Otherwise, a File instance is constructed by prepending the project
directory path to the supplied path. The file() method also understands URLs, such as file:/some/path.xml
.
Using this method is a useful way to convert some user provided value into an absolute File. It is
preferable to using new File(somePath), as file() always evaluates the supplied path relative to the
project directory, which is fixed, rather than the current working directory, which can change depending on
how the user runs Gradle.
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File collections
§
File collections
A file collection is simply a set of files. It is represented by the FileCollection interface. Many objects in
the Gradle API implement this interface. For example, dependency configurations implement FileCollection
.
One way to obtain a FileCollection instance is to use the Project.files(java.lang.Object[])
method. You can pass this method any number of objects, which are then converted into a set of File
objects. The files() method accepts any type of object as its parameters. These are evaluated relative to
the project directory, as per the file() method, described in the section called “Locating files”. You can
also pass collections, iterables, maps and arrays to the files() method. These are flattened and the
contents converted to File instances.
Example 123. Creating a file collection
build.gradle
FileCollection collection = files('src/file1.txt',
new File('src/file2.txt'),
['src/file3.txt', 'src/file4.txt'],
Paths.get('src', 'file5.txt'))
A file collection is iterable, and can be converted to a number of other types using the as operator. You can
also add 2 file collections together using the + operator, or subtract one file collection from another using the operator. Here are some examples of what you can do with a file collection.
Example 124. Using a file collection
build.gradle
// Iterate over the files in the collection
collection.each { File file ->
println file.name
}
// Convert the collection to various types
Set set = collection.files
Set set2 = collection as Set
List list = collection as List
String path = collection.asPath
File file = collection.singleFile
File file2 = collection as File
// Add and subtract collections
def union = collection + files('src/file3.txt')
def different = collection - files('src/file3.txt')
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You can also pass the files() method a closure or a Callable instance. This is called when the contents
of the collection are queried, and its return value is converted to a set of File instances. The return value
can be an object of any of the types supported by the files() method. This is a simple way to 'implement'
the FileCollection interface.
Example 125. Implementing a file collection
build.gradle
task list {
doLast {
File srcDir
// Create a file collection using a closure
collection = files { srcDir.listFiles() }
srcDir = file('src')
println "Contents of $srcDir.name"
collection.collect { relativePath(it) }.sort().each { println it }
srcDir = file('src2')
println "Contents of $srcDir.name"
collection.collect { relativePath(it) }.sort().each { println it }
}
}
Output of gradle -q list
> gradle -q list
Contents of src
src/dir1
src/file1.txt
Contents of src2
src2/dir1
src2/dir2
Some other types of things you can pass to files():
FileCollection
These are flattened and the contents included in the file collection.
Task
The output files of the task are included in the file collection.
TaskOutputs
The output files of the TaskOutputs are included in the file collection.
It is important to note that the content of a file collection is evaluated lazily, when it is needed. This means
you can, for example, create a FileCollection that represents files which will be created in the future by,
say, some task.
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File trees
§
File trees
A file tree is a collection of files arranged in a hierarchy. For example, a file tree might represent a directory
tree or the contents of a ZIP file. It is represented by the FileTree interface. The FileTree interface
extends FileCollection, so you can treat a file tree exactly the same way as you would a file collection.
Several objects in Gradle implement the FileTree interface, such as source sets.
One way to obtain a FileTree instance is to use the Project.fileTree(java.util.Map) method.
This creates a FileTree defined with a base directory, and optionally some Ant-style include and exclude
patterns.
Example 126. Creating a file tree
build.gradle
// Create a file tree with a base directory
FileTree tree = fileTree(dir: 'src/main')
// Add include and exclude patterns to the tree
tree.include '**/*.java'
tree.exclude '**/Abstract*'
// Create a tree using path
tree = fileTree('src').include('**/*.java')
// Create a tree using closure
tree = fileTree('src') {
include '**/*.java'
}
// Create a tree using a map
tree = fileTree(dir: 'src', include: '**/*.java')
tree = fileTree(dir: 'src', includes: ['**/*.java', '**/*.xml'])
tree = fileTree(dir: 'src', include: '**/*.java', exclude: '**/*test*/**')
You use a file tree in the same way you use a file collection. You can also visit the contents of the tree, and
select a sub-tree using Ant-style patterns:
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Example 127. Using a file tree
build.gradle
// Iterate over the contents of a tree
tree.each {File file ->
println file
}
// Filter a tree
FileTree filtered = tree.matching {
include 'org/gradle/api/**'
}
// Add trees together
FileTree sum = tree + fileTree(dir: 'src/test')
// Visit the elements of the tree
tree.visit {element ->
println "$element.relativePath => $element.file"
}
Note: By default, the FileTree instance fileTree() returns will apply some Ant-style default
exclude patterns for convenience. For the complete default exclusion list, see Default Excludes.
§
Using the contents of an archive as a file tree
You can use the contents of an archive, such as a ZIP or TAR file, as a file tree. You do this using the
Project.zipTree(java.lang.Object) and Project.tarTree(java.lang.Object) methods.
These methods return a FileTree instance which you can use like any other file tree or file collection. For
example, you can use it to expand the archive by copying the contents, or to merge some archives into
another.
Example 128. Using an archive as a file tree
build.gradle
// Create a ZIP file tree using path
FileTree zip = zipTree('someFile.zip')
// Create a TAR file tree using path
FileTree tar = tarTree('someFile.tar')
//tar tree attempts to guess the compression based on the file extension
//however if you must specify the compression explicitly you can:
FileTree someTar = tarTree(resources.gzip('someTar.ext'))
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Specifying a set of input files
§
Specifying a set of input files
Many objects in Gradle have properties which accept a set of input files. For example, the JavaCompile
task has a source property, which defines the source files to compile. You can set the value of this property
using any of the types supported by the files() method, which was shown above. This means you can set the
property using, for example, a File, String, collection, FileCollection or even a closure. Here are
some examples:
Example 129. Specifying a set of files
build.gradle
task compile(type: JavaCompile)
// Use a File object to specify the source directory
compile {
source = file('src/main/java')
}
// Use a String path to specify the source directory
compile {
source = 'src/main/java'
}
// Use a collection to specify multiple source directories
compile {
source = ['src/main/java', '../shared/java']
}
// Use a FileCollection (or FileTree in this case) to specify the source files
compile {
source = fileTree(dir: 'src/main/java').matching { include 'org/gradle/api/**' }
}
// Using a closure to specify the source files.
compile {
source = {
// Use the contents of each zip file in the src dir
file('src').listFiles().findAll {it.name.endsWith('.zip')}.collect { zipTree(it) }
}
}
Usually, there is a method with the same name as the property, which appends to the set of files. Again, this
method accepts any of the types supported by the files() method.
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Example 130. Appending a set of files
build.gradle
compile {
// Add some source directories use String paths
source 'src/main/java', 'src/main/groovy'
// Add a source directory using a File object
source file('../shared/java')
// Add some source directories using a closure
source { file('src/test/').listFiles() }
}
§
Copying files
You can use the Copy task to copy files. The copy task is very flexible, and allows you to, for example, filter
the contents of the files as they are copied, and map to the file names.
To use the Copy task, you must provide a set of source files to copy, and a destination directory to copy the
files to. You may also specify how to transform the files as they are copied. You do all this using a copy spec
. A copy spec is represented by the CopySpec interface. The Copy task implements this interface. You
specify the source files using the CopySpec.from(java.lang.Object[]) method. To specify the
destination directory, use the CopySpec.into(java.lang.Object) method.
Example 131. Copying files using the copy task
build.gradle
task copyTask(type: Copy) {
from 'src/main/webapp'
into 'build/explodedWar'
}
The from() method accepts any of the arguments that the files() method does. When an argument resolves
to a directory, everything under that directory (but not the directory itself) is recursively copied into the
destination directory. When an argument resolves to a file, that file is copied into the destination directory.
When an argument resolves to a non-existing file, that argument is ignored. If the argument is a task, the
output files (i.e. the files the task creates) of the task are copied and the task is automatically added as a
dependency of the Copy task. The into() accepts any of the arguments that the file() method does. Here
is another example:
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Example 132. Specifying copy task source files and destination directory
build.gradle
task anotherCopyTask(type: Copy) {
// Copy everything under src/main/webapp
from 'src/main/webapp'
// Copy a single file
from 'src/staging/index.html'
// Copy the output of a task
from copyTask
// Copy the output of a task using Task outputs explicitly.
from copyTaskWithPatterns.outputs
// Copy the contents of a Zip file
from zipTree('src/main/assets.zip')
// Determine the destination directory later
into { getDestDir() }
}
You can select the files to copy using Ant-style include or exclude patterns, or using a closure:
Example 133. Selecting the files to copy
build.gradle
task copyTaskWithPatterns(type: Copy) {
from 'src/main/webapp'
into 'build/explodedWar'
include '**/*.html'
include '**/*.jsp'
exclude { details -> details.file.name.endsWith('.html') &&
details.file.text.contains('staging') }
}
You can also use the Project.copy(org.gradle.api.Action) method to copy files. It works the
same way as the task with some major limitations though. First, the copy() is not incremental (see the
section called “Up-to-date checks (AKA Incremental Build)”).
Example 134. Copying files using the copy() method without up-to-date check
build.gradle
task copyMethod {
doLast {
copy {
from 'src/main/webapp'
into 'build/explodedWar'
include '**/*.html'
include '**/*.jsp'
}
}
}
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Secondly, the copy() method cannot honor task dependencies when a task is used as a copy source (i.e.
as an argument to from()) because it’s a method and not a task. As such, if you are using the copy()
method as part of a task action, you must explicitly declare all inputs and outputs in order to get the correct
behavior.
Example 135. Copying files using the copy() method with up-to-date check
build.gradle
task copyMethodWithExplicitDependencies{
// up-to-date check for inputs, plus add copyTask as dependency
inputs.files copyTask
outputs.dir 'some-dir' // up-to-date check for outputs
doLast{
copy {
// Copy the output of copyTask
from copyTask
into 'some-dir'
}
}
}
It is preferable to use the Copy task wherever possible, as it supports incremental building and task
dependency inference without any extra effort on your part. The copy() method can be used to copy files
as part of a task’s implementation. That is, the copy method is intended to be used by custom tasks (see
Writing Custom Task Classes) that need to copy files as part of their function. In such a scenario, the custom
task should sufficiently declare the inputs/outputs relevant to the copy action.
§
Renaming files
Example 136. Renaming files as they are copied
build.gradle
task rename(type: Copy) {
from 'src/main/webapp'
into 'build/explodedWar'
// Use a closure to map the file name
rename { String fileName ->
fileName.replace('-staging-', '')
}
// Use a regular expression to map the file name
rename '(.+)-staging-(.+)', '$1$2'
rename(/(.+)-staging-(.+)/, '$1$2')
}
Filtering files
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§
Filtering files
Example 137. Filtering files as they are copied
build.gradle
import org.apache.tools.ant.filters.FixCrLfFilter
import org.apache.tools.ant.filters.ReplaceTokens
task filter(type: Copy) {
from 'src/main/webapp'
into 'build/explodedWar'
// Substitute property tokens in files
expand(copyright: '2009', version: '2.3.1')
expand(project.properties)
// Use some of the filters provided by Ant
filter(FixCrLfFilter)
filter(ReplaceTokens, tokens: [copyright: '2009', version: '2.3.1'])
// Use a closure to filter each line
filter { String line ->
"[$line]"
}
// Use a closure to remove lines
filter { String line ->
line.startsWith('-') ? null : line
}
filteringCharset = 'UTF-8'
}
When you use the ReplaceTokens class with the “filter” operation, the result is a template engine that
replaces tokens of the form “@tokenName@” (the Apache Ant-style token) with a set of given values. The
“expand” operation does the same thing except it treats the source files as Groovy templates in which tokens
take the form “${tokenName}”. Be aware that you may need to escape parts of your source files when using
this option, for example if it contains literal “$” or “<%” strings.
It’s a good practice to specify the charset when reading and writing the file, using the filteringCharset
property. If not specified, the JVM default charset is used, which might not match with the actual charset of
the files to filter, and might be different from one machine to another.
§
Using the CopySpec class
Copy specs form a hierarchy. A copy spec inherits its destination path, include patterns, exclude patterns,
copy actions, name mappings and filters.
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Example 138. Nested copy specs
build.gradle
task nestedSpecs(type: Copy) {
into 'build/explodedWar'
exclude '**/*staging*'
from('src/dist') {
include '**/*.html'
}
into('libs') {
from configurations.runtime
}
}
§
Using the Sync task
The Sync task extends the Copy task. When it executes, it copies the source files into the destination
directory, and then removes any files from the destination directory which it did not copy. This can be useful
for doing things such as installing your application, creating an exploded copy of your archives, or
maintaining a copy of the project’s dependencies.
Here is an example which maintains a copy of the project’s runtime dependencies in the build/libs
directory.
Example 139. Using the Sync task to copy dependencies
build.gradle
task libs(type: Sync) {
from configurations.runtime
into "$buildDir/libs"
}
§
Creating archives
A project can have as many JAR archives as you want. You can also add WAR, ZIP and TAR archives to
your project. Archives are created using the various archive tasks: Zip, Tar, Jar, War, and Ear. They all
work the same way, so let’s look at how you create a ZIP file.
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Example 140. Creating a ZIP archive
build.gradle
apply plugin: 'java'
task zip(type: Zip) {
from 'src/dist'
into('libs') {
from configurations.runtime
}
}
Why are you using the Java plugin?
The Java plugin adds a number of default values for the archive tasks. You can use the archive
tasks without using the Java plugin, if you like. You will need to provide values for some additional
properties.
The archive tasks all work exactly the same way as the Copy task, and implement the same CopySpec
interface. As with the Copy task, you specify the input files using the from() method, and can optionally
specify where they end up in the archive using the into() method. You can filter the contents of file,
rename files, and all the other things you can do with a copy spec.
§
Archive naming
The format of projectName - version . type is used for generated archive file names. For example:
Example 141. Creation of ZIP archive
build.gradle
apply plugin: 'java'
version = 1.0
task myZip(type: Zip) {
from 'somedir'
}
println myZip.archiveName
println relativePath(myZip.destinationDir)
println relativePath(myZip.archivePath)
Output of gradle -q myZip
> gradle -q myZip
zipProject-1.0.zip
build/distributions
build/distributions/zipProject-1.0.zip
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This adds a Zip archive task with the name myZip which produces ZIP file zipProject-1.0.zip. It is
important to distinguish between the name of the archive task and the name of the archive generated by the
archive task. The default name for archives can be changed with the archivesBaseName project property.
The name of the archive can also be changed at any time later on.
There are a number of properties which you can set on an archive task. These are listed below in Table 8.
You can, for example, change the name of the archive:
Example 142. Configuration of archive task - custom archive name
build.gradle
apply plugin: 'java'
version = 1.0
task myZip(type: Zip) {
from 'somedir'
baseName = 'customName'
}
println myZip.archiveName
Output of gradle -q myZip
> gradle -q myZip
customName-1.0.zip
You can further customize the archive names:
Example 143. Configuration of archive task - appendix & classifier
build.gradle
apply plugin: 'java'
archivesBaseName = 'gradle'
version = 1.0
task myZip(type: Zip) {
appendix = 'wrapper'
classifier = 'src'
from 'somedir'
}
println myZip.archiveName
Output of gradle -q myZip
> gradle -q myZip
gradle-wrapper-1.0-src.zip
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Table 8. Archive tasks - naming properties
Property name
Type
archiveName
String
Default value
baseName - appendix - version - classifier . extension
If any of these properties is empty the trailing - is not added to the name.
archivePath
File
destinationDir File
destinationDir / archiveName
Description
The base file name of
the generated archive
The absolute path of
the generated archive.
The
directory
to
Depends on the archive type. JARs and WARs go into project.buildDir /libraries
generate the archive
. ZIPs and TARs go into project.buildDir /distributions.
into
The
baseName
String project.name
base
name
portion of the archive
file name.
The appendix portion
appendix
String null
of the archive file
name.
version
String project.version
classifier
String null
The version portion of
the archive file name.
The classifier portion
of the archive file
name,
extension
String
Depends on the archive type, and for TAR files, the compression type as The extension of the
well: zip, jar, war, tar, tgz or tbz2.
archive file name.
§
Sharing content between multiple archives
You can use the Project.copySpec(org.gradle.api.Action) method to share content between
archives.
§
Reproducible archives
Sometimes it can be desirable to recreate archives in a byte for byte way on different machines. You want to
be sure that building an artifact from source code produces the same result, byte for byte, no matter when
and where it is built. This is necessary for projects like reproducible-builds.org.
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Reproducing the same archive byte for byte poses some challenges since the order of the files in an archive
is influenced by the underlying filesystem. Each time a zip, tar, jar, war or ear is built from source, the order
of the files inside the archive may change. Files that only have a different timestamp also causes archives to
be slightly different between builds. All AbstractArchiveTask (e.g. Jar, Zip) tasks shipped with Gradle
include incubating support producing reproducible archives.
For example, to make a Zip task reproducible you need to set Zip.isReproducibleFileOrder() to true
and Zip.isPreserveFileTimestamps() to false. In order to make all archive tasks in your build
reproducible, consider adding the following configuration to your build file:
Example 144. Activating reproducible archives
build.gradle
tasks.withType(AbstractArchiveTask) {
preserveFileTimestamps = false
reproducibleFileOrder = true
}
Often you will want to publish an archive, so that it is usable from another project. This process is described
in Publishing artifacts
§
Properties files
Properties files are used in many places during Java development. Gradle makes it easy to create properties
files as a normal part of the build. You can use the WriteProperties task to create properties files.
The WriteProperties task also fixes a well-known problem with Properties.store() that can reduce
the usefulness of incremental builds (see the section called “Up-to-date checks (AKA Incremental Build)” ).
The standard Java way to write a properties file produces a unique file every time, even when the same
properties and values are used, because it includes a timestamp in the comments. Gradle’s WriteProperties
task generates exactly the same output byte-for-byte if none of the properties have changed. This is
achieved by a few tweaks to how a properties file is generated:
no timestamp comment is added to the output
the line separator is system independent, but can be configured explicitly (it defaults to '\n')
the properties are sorted alphabetically
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Using Ant from Gradle
Gradle provides excellent integration with Ant. You can use individual Ant tasks or entire Ant builds in your
Gradle builds. In fact, you will find that it’s far easier and more powerful using Ant tasks in a Gradle build
script, than it is to use Ant’s XML format. You could even use Gradle simply as a powerful Ant task scripting
tool.
Ant can be divided into two layers. The first layer is the Ant language. It provides the syntax for the build.xml
file, the handling of the targets, special constructs like macrodefs, and so on. In other words, everything
except the Ant tasks and types. Gradle understands this language, and allows you to import your Ant build.xml
directly into a Gradle project. You can then use the targets of your Ant build as if they were Gradle tasks.
The second layer of Ant is its wealth of Ant tasks and types, like javac, copy or jar. For this layer Gradle
provides integration simply by relying on Groovy, and the fantastic AntBuilder.
Finally, since build scripts are Groovy scripts, you can always execute an Ant build as an external process.
Your build script may contain statements like: "ant clean compile".execute().[7]
You can use Gradle’s Ant integration as a path for migrating your build from Ant to Gradle. For example, you
could start by importing your existing Ant build. Then you could move your dependency declarations from the
Ant script to your build file. Finally, you could move your tasks across to your build file, or replace them with
some of Gradle’s plugins. This process can be done in parts over time, and you can have a working Gradle
build during the entire process.
§
Using Ant tasks and types in your build
In your build script, a property called ant is provided by Gradle. This is a reference to an AntBuilder
instance. This AntBuilder is used to access Ant tasks, types and properties from your build script. There
is a very simple mapping from Ant’s build.xml format to Groovy, which is explained below.
You execute an Ant task by calling a method on the AntBuilder instance. You use the task name as the
method name. For example, you execute the Ant echo task by calling the ant.echo() method. The
attributes of the Ant task are passed as Map parameters to the method. Below is an example of the echo
task. Notice that we can also mix Groovy code and the Ant task markup. This can be extremely powerful.
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Example 145. Using an Ant task
build.gradle
task hello {
doLast {
String greeting = 'hello from Ant'
ant.echo(message: greeting)
}
}
Output of gradle hello
> gradle hello
:hello
[ant:echo] hello from Ant
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
You pass nested text to an Ant task by passing it as a parameter of the task method call. In this example, we
pass the message for the echo task as nested text:
Example 146. Passing nested text to an Ant task
build.gradle
task hello {
doLast {
ant.echo('hello from Ant')
}
}
Output of gradle hello
> gradle hello
:hello
[ant:echo] hello from Ant
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
You pass nested elements to an Ant task inside a closure. Nested elements are defined in the same way as
tasks, by calling a method with the same name as the element we want to define.
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Example 147. Passing nested elements to an Ant task
build.gradle
task zip {
doLast {
ant.zip(destfile: 'archive.zip') {
fileset(dir: 'src') {
include(name: '**.xml')
exclude(name: '**.java')
}
}
}
}
You can access Ant types in the same way that you access tasks, using the name of the type as the method
name. The method call returns the Ant data type, which you can then use directly in your build script. In the
following example, we create an Ant path object, then iterate over the contents of it.
Example 148. Using an Ant type
build.gradle
task list {
doLast {
def path = ant.path {
fileset(dir: 'libs', includes: '*.jar')
}
path.list().each {
println it
}
}
}
More information about AntBuilder can be found in 'Groovy in Action' 8.4 or at the Groovy Wiki
§
Using custom Ant tasks in your build
To make custom tasks available in your build, you can use the taskdef (usually easier) or typedef Ant
task, just as you would in a build.xml file. You can then refer to the custom Ant task as you would a
built-in Ant task.
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Example 149. Using a custom Ant task
build.gradle
task check {
doLast {
ant.taskdef(resource: 'checkstyletask.properties') {
classpath {
fileset(dir: 'libs', includes: '*.jar')
}
}
ant.checkstyle(config: 'checkstyle.xml') {
fileset(dir: 'src')
}
}
}
You can use Gradle’s dependency management to assemble the classpath to use for the custom tasks. To
do this, you need to define a custom configuration for the classpath, then add some dependencies to the
configuration. This is described in more detail in the section called “Declaring dependencies”.
Example 150. Declaring the classpath for a custom Ant task
build.gradle
configurations {
pmd
}
dependencies {
pmd group: 'pmd', name: 'pmd', version: '4.2.5'
}
To use the classpath configuration, use the asPath property of the custom configuration.
Example 151. Using a custom Ant task and dependency management together
build.gradle
task check {
doLast {
ant.taskdef(name: 'pmd',
classname: 'net.sourceforge.pmd.ant.PMDTask',
classpath: configurations.pmd.asPath)
ant.pmd(shortFilenames: 'true',
failonruleviolation: 'true',
rulesetfiles: file('pmd-rules.xml').toURI().toString()) {
formatter(type: 'text', toConsole: 'true')
fileset(dir: 'src')
}
}
}
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§
Importing an Ant build
You can use the ant.importBuild() method to import an Ant build into your Gradle project. When you
import an Ant build, each Ant target is treated as a Gradle task. This means you can manipulate and execute
the Ant targets in exactly the same way as Gradle tasks.
Example 152. Importing an Ant build
build.gradle
ant.importBuild 'build.xml'
build.xml
<project>
<target name="hello">
<echo>Hello, from Ant</echo>
</target>
</project>
Output of gradle hello
> gradle hello
:hello
[ant:echo] Hello, from Ant
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
You can add a task which depends on an Ant target:
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Example 153. Task that depends on Ant target
build.gradle
ant.importBuild 'build.xml'
task intro(dependsOn: hello) {
doLast {
println 'Hello, from Gradle'
}
}
Output of gradle intro
> gradle intro
:hello
[ant:echo] Hello, from Ant
:intro
Hello, from Gradle
BUILD SUCCESSFUL in 0s
2 actionable tasks: 2 executed
Or, you can add behaviour to an Ant target:
Example 154. Adding behaviour to an Ant target
build.gradle
ant.importBuild 'build.xml'
hello {
doLast {
println 'Hello, from Gradle'
}
}
Output of gradle hello
> gradle hello
:hello
[ant:echo] Hello, from Ant
Hello, from Gradle
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
It is also possible for an Ant target to depend on a Gradle task:
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Example 155. Ant target that depends on Gradle task
build.gradle
ant.importBuild 'build.xml'
task intro {
doLast {
println 'Hello, from Gradle'
}
}
build.xml
<project>
<target name="hello" depends="intro">
<echo>Hello, from Ant</echo>
</target>
</project>
Output of gradle hello
> gradle hello
:intro
Hello, from Gradle
:hello
[ant:echo] Hello, from Ant
BUILD SUCCESSFUL in 0s
2 actionable tasks: 2 executed
Sometimes it may be necessary to “rename” the task generated for an Ant target to avoid a naming collision
with existing Gradle tasks. To do this, use the AntBuilder.importBuild(java.lang.Object,
org.gradle.api.Transformer) method.
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Example 156. Renaming imported Ant targets
build.gradle
ant.importBuild('build.xml') { antTargetName ->
'a-' + antTargetName
}
build.xml
<project>
<target name="hello">
<echo>Hello, from Ant</echo>
</target>
</project>
Output of gradle a-hello
> gradle a-hello
:a-hello
[ant:echo] Hello, from Ant
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
Note that while the second argument to this method should be a Transformer, when programming in
Groovy we can simply use a closure instead of an anonymous inner class (or similar) due to Groovy’s
support for automatically coercing closures to single-abstract-method types.
§
Ant properties and references
There are several ways to set an Ant property, so that the property can be used by Ant tasks. You can set
the property directly on the AntBuilder instance. The Ant properties are also available as a Map which you
can change. You can also use the Ant property task. Below are some examples of how to do this.
Example 157. Setting an Ant property
build.gradle
ant.buildDir = buildDir
ant.properties.buildDir = buildDir
ant.properties['buildDir'] = buildDir
ant.property(name: 'buildDir', location: buildDir)
build.xml
<echo>buildDir = ${buildDir}</echo>
Many Ant tasks set properties when they execute. There are several ways to get the value of these
properties. You can get the property directly from the AntBuilder instance. The Ant properties are also
available as a Map. Below are some examples.
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Example 158. Getting an Ant property
build.xml
<property name="antProp" value="a property defined in an Ant build"/>
build.gradle
println ant.antProp
println ant.properties.antProp
println ant.properties['antProp']
There are several ways to set an Ant reference:
Example 159. Setting an Ant reference
build.gradle
ant.path(id: 'classpath', location: 'libs')
ant.references.classpath = ant.path(location: 'libs')
ant.references['classpath'] = ant.path(location: 'libs')
build.xml
<path refid="classpath"/>
There are several ways to get an Ant reference:
Example 160. Getting an Ant reference
build.xml
<path id="antPath" location="libs"/>
build.gradle
println ant.references.antPath
println ant.references['antPath']
§
Ant logging
Gradle maps Ant message priorities to Gradle log levels so that messages logged from Ant appear in the
Gradle output. By default, these are mapped as follows:
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Table 9. Ant message priority mapping
Ant Message Priority
Gradle Log Level
VERBOSE
DEBUG
DEBUG
DEBUG
INFO
INFO
WARN
WARN
ERROR
ERROR
§
Fine tuning Ant logging
The default mapping of Ant message priority to Gradle log level can sometimes be problematic. For
example, there is no message priority that maps directly to the LIFECYCLE log level, which is the default for
Gradle. Many Ant tasks log messages at the INFO priority, which means to expose those messages from
Gradle, a build would have to be run with the log level set to INFO, potentially logging much more output
than is desired.
Conversely, if an Ant task logs messages at too high of a level, to suppress those messages would require
the build to be run at a higher log level, such as QUIET. However, this could result in other, desirable output
being suppressed.
To help with this, Gradle allows the user to fine tune the Ant logging and control the mapping of message
priority to Gradle log level. This is done by setting the priority that should map to the default Gradle LIFECYCLE
log level using the AntBuilder.setLifecycleLogLevel(java.lang.String) method. When this
value is set, any Ant message logged at the configured priority or above will be logged at least at LIFECYCLE
. Any Ant message logged below this priority will be logged at most at INFO.
For example, the following changes the mapping such that Ant INFO priority messages are exposed at the LIFECYCLE
log level.
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Example 161. Fine tuning Ant logging
build.gradle
ant.lifecycleLogLevel = "INFO"
task hello {
doLast {
ant.echo(level: "info", message: "hello from info priority!")
}
}
Output of gradle hello
> gradle hello
:hello
[ant:echo] hello from info priority!
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
On the other hand, if the lifecycleLogLevel was set to ERROR , Ant messages logged at the WARN
priority would no longer be logged at the WARN log level. They would now be logged at the INFO level and
would be suppressed by default.
§
API
The Ant integration is provided by AntBuilder.
[7] In Groovy you can execute Strings. To learn more about executing external processes with Groovy have
a look in 'Groovy in Action' 9.3.2 or at the Groovy wiki
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Build Lifecycle
We said earlier that the core of Gradle is a language for dependency based programming. In Gradle terms
this means that you can define tasks and dependencies between tasks. Gradle guarantees that these tasks
are executed in the order of their dependencies, and that each task is executed only once. These tasks form
a Directed Acyclic Graph. There are build tools that build up such a dependency graph as they execute their
tasks. Gradle builds the complete dependency graph before any task is executed. This lies at the heart of
Gradle and makes many things possible which would not be possible otherwise.
Your build scripts configure this dependency graph. Therefore they are strictly speaking build configuration
scripts .
§
Build phases
A Gradle build has three distinct phases.
Initialization
Gradle supports single and multi-project builds. During the initialization phase, Gradle determines which
projects are going to take part in the build, and creates a Project instance for each of these projects.
Configuration
During this phase the project objects are configured. The build scripts of all projects which are part of the
build are executed. Gradle 1.4 introduced an incubating opt-in feature called configuration on demand . In
this mode, Gradle configures only relevant projects (see the section called “Configuration on demand”).
Execution
Gradle determines the subset of the tasks, created and configured during the configuration phase, to be
executed. The subset is determined by the task name arguments passed to the gradle command and
the current directory. Gradle then executes each of the selected tasks.
§
Settings file
Beside the build script files, Gradle defines a settings file. The settings file is determined by Gradle via a
naming convention. The default name for this file is settings.gradle. Later in this chapter we explain
how Gradle looks for a settings file.
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The settings file is executed during the initialization phase. A multiproject build must have a settings.gradle
file in the root project of the multiproject hierarchy. It is required because the settings file defines which
projects are taking part in the multi-project build (see Authoring Multi-Project Builds). For a single-project
build, a settings file is optional. Besides defining the included projects, you might need it to add libraries to
your build script classpath (see Organizing Build Logic). Let’s first do some introspection with a single project
build:
Example 162. Single project build
settings.gradle
println 'This is executed during the initialization phase.'
build.gradle
println 'This is executed during the configuration phase.'
task configured {
println 'This is also executed during the configuration phase.'
}
task test {
doLast {
println 'This is executed during the execution phase.'
}
}
task testBoth {
doFirst {
println 'This is executed first during the execution phase.'
}
doLast {
println 'This is executed last during the execution phase.'
}
println 'This is executed during the configuration phase as well.'
}
Output of gradle test testBoth
> gradle test testBoth
This is executed during the initialization phase.
This is executed during the configuration phase.
This is also executed during the configuration phase.
This is executed during the configuration phase as well.
:test
This is executed during the execution phase.
:testBoth
This is executed first during the execution phase.
This is executed last during the execution phase.
BUILD SUCCESSFUL in 0s
2 actionable tasks: 2 executed
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For a build script, the property access and method calls are delegated to a project object. Similarly property
access and method calls within the settings file is delegated to a settings object. Look at the Settings
class in the API documentation for more information.
§
Multi-project builds
A multi-project build is a build where you build more than one project during a single execution of Gradle.
You have to declare the projects taking part in the multiproject build in the settings file. There is much more
to say about multi-project builds in the chapter dedicated to this topic (see Authoring Multi-Project Builds).
§
Project locations
Multi-project builds are always represented by a tree with a single root. Each element in the tree represents
a project. A project has a path which denotes the position of the project in the multi-project build tree. In most
cases the project path is consistent with the physical location of the project in the file system. However, this
behavior is configurable. The project tree is created in the settings.gradle file. By default it is assumed
that the location of the settings file is also the location of the root project. But you can redefine the location of
the root project in the settings file.
§
Building the tree
In the settings file you can use a set of methods to build the project tree. Hierarchical and flat physical
layouts get special support.
§
Hierarchical layouts
Example 163. Hierarchical layout
settings.gradle
include 'project1', 'project2:child', 'project3:child1'
The include method takes project paths as arguments. The project path is assumed to be equal to the
relative physical file system path. For example, a path 'services:api' is mapped by default to a folder
'services/api' (relative from the project root). You only need to specify the leaves of the tree. This means that
the inclusion of the path 'services:hotels:api' will result in creating 3 projects: 'services', 'services:hotels' and
'services:hotels:api'. More examples of how to work with the project path can be found in the DSL
documentation of Settings.include(java.lang.String[]).
Flat layouts
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§
Flat layouts
Example 164. Flat layout
settings.gradle
includeFlat 'project3', 'project4'
The includeFlat method takes directory names as an argument. These directories need to exist as
siblings of the root project directory. The location of these directories are considered as child projects of the
root project in the multi-project tree.
§
Modifying elements of the project tree
The multi-project tree created in the settings file is made up of so called project descriptors . You can modify
these descriptors in the settings file at any time. To access a descriptor you can do:
Example 165. Lookup of elements of the project tree
settings.gradle
println rootProject.name
println project(':projectA').name
Using this descriptor you can change the name, project directory and build file of a project.
Example 166. Modification of elements of the project tree
settings.gradle
rootProject.name = 'main'
project(':projectA').projectDir = new File(settingsDir, '../my-project-a')
project(':projectA').buildFileName = 'projectA.gradle'
Look at the ProjectDescriptor class in the API documentation for more information.
§
Initialization
How does Gradle know whether to do a single or multiproject build? If you trigger a multiproject build from a
directory with a settings file, things are easy. But Gradle also allows you to execute the build from within any
subproject taking part in the build.[8] If you execute Gradle from within a project with no settings.gradle
file, Gradle looks for a settings.gradle file in the following way:
It looks in a directory called master which has the same nesting level as the current dir.
If not found yet, it searches parent directories.
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If not found yet, the build is executed as a single project build.
If a settings.gradle file is found, Gradle checks if the current project is part of the multiproject hierarchy
defined in the found settings.gradle file. If not, the build is executed as a single project build. Otherwise
a multiproject build is executed.
What is the purpose of this behavior? Gradle needs to determine whether the project you are in is a
subproject of a multiproject build or not. Of course, if it is a subproject, only the subproject and its dependent
projects are built, but Gradle needs to create the build configuration for the whole multiproject build (see
Authoring Multi-Project Builds). You can use the -u command line option to tell Gradle not to look in the
parent hierarchy for a settings.gradle file. The current project is then always built as a single project
build. If the current project contains a settings.gradle file, the -u option has no meaning. Such a build
is always executed as:
a single project build, if the settings.gradle file does not define a multiproject hierarchy
a multiproject build, if the settings.gradle file does define a multiproject hierarchy.
The automatic search for a settings.gradle file only works for multi-project builds with a physical
hierarchical or flat layout. For a flat layout you must additionally follow the naming convention described
above (“master”). Gradle supports arbitrary physical layouts for a multiproject build, but for such arbitrary
layouts you need to execute the build from the directory where the settings file is located. For information on
how to run partial builds from the root see the section called “Running tasks by their absolute path”.
Gradle creates a Project object for every project taking part in the build. For a multi-project build these are
the projects specified in the Settings object (plus the root project). Each project object has by default a name
equal to the name of its top level directory, and every project except the root project has a parent project.
Any project may have child projects.
§
Configuration and execution of a single project build
For a single project build, the workflow of the after initialization phases are pretty simple. The build script is
executed against the project object that was created during the initialization phase. Then Gradle looks for
tasks with names equal to those passed as command line arguments. If these task names exist, they are
executed as a separate build in the order you have passed them. The configuration and execution for
multi-project builds is discussed in Authoring Multi-Project Builds.
§
Responding to the lifecycle in the build script
Your build script can receive notifications as the build progresses through its lifecycle. These notifications
generally take two forms: You can either implement a particular listener interface, or you can provide a
closure to execute when the notification is fired. The examples below use closures. For details on how to use
the listener interfaces, refer to the API documentation.
Project evaluation
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§
Project evaluation
You can receive a notification immediately before and after a project is evaluated. This can be used to do
things like performing additional configuration once all the definitions in a build script have been applied, or
for some custom logging or profiling.
Below is an example which adds a test task to each project which has a hasTests property value of true.
Example 167. Adding of test task to each project which has certain property set
build.gradle
allprojects {
afterEvaluate { project ->
if (project.hasTests) {
println "Adding test task to $project"
project.task('test') {
doLast {
println "Running tests for $project"
}
}
}
}
}
projectA.gradle
hasTests = true
Output of gradle -q test
> gradle -q test
Adding test task to project ':projectA'
Running tests for project ':projectA'
This example uses method Project.afterEvaluate() to add a closure which is executed after the
project is evaluated.
It is also possible to receive notifications when any project is evaluated. This example performs some
custom logging of project evaluation. Notice that the afterProject notification is received regardless of
whether the project evaluates successfully or fails with an exception.
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Example 168. Notifications
build.gradle
gradle.afterProject {project, projectState ->
if (projectState.failure) {
println "Evaluation of $project FAILED"
} else {
println "Evaluation of $project succeeded"
}
}
Output of gradle -q test
> gradle -q test
Evaluation of root project 'buildProjectEvaluateEvents' succeeded
Evaluation of project ':projectA' succeeded
Evaluation of project ':projectB' FAILED
You can also add a ProjectEvaluationListener to the Gradle to receive these events.
§
Task creation
You can receive a notification immediately after a task is added to a project. This can be used to set some
default values or add behaviour before the task is made available in the build file.
The following example sets the srcDir property of each task as it is created.
Example 169. Setting of certain property to all tasks
build.gradle
tasks.whenTaskAdded { task ->
task.ext.srcDir = 'src/main/java'
}
task a
println "source dir is $a.srcDir"
Output of gradle -q a
> gradle -q a
source dir is src/main/java
You can also add an Action to a TaskContainer to receive these events.
Task execution graph ready
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§
Task execution graph ready
You can receive a notification immediately after the task execution graph has been populated. We have
seen this already in the section called “Configure by DAG”.
You can also add a TaskExecutionGraphListener to the TaskExecutionGraph to receive these
events.
§
Task execution
You can receive a notification immediately before and after any task is executed.
The following example logs the start and end of each task execution. Notice that the afterTask notification
is received regardless of whether the task completes successfully or fails with an exception.
Example 170. Logging of start and end of each task execution
build.gradle
task ok
task broken(dependsOn: ok) {
doLast {
throw new RuntimeException('broken')
}
}
gradle.taskGraph.beforeTask { Task task ->
println "executing $task ..."
}
gradle.taskGraph.afterTask { Task task, TaskState state ->
if (state.failure) {
println "FAILED"
}
else {
println "done"
}
}
Output of gradle -q broken
> gradle -q broken
executing task ':ok' ...
done
executing task ':broken' ...
FAILED
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You can also use a TaskExecutionListener to the TaskExecutionGraph to receive these events.
[8] Gradle supports partial multiproject builds (see Authoring Multi-Project Builds).
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Logging
The log is the main 'UI' of a build tool. If it is too verbose, real warnings and problems are easily hidden by
this. On the other hand you need relevant information for figuring out if things have gone wrong. Gradle
defines 6 log levels, as shown in Table 10. There are two Gradle-specific log levels, in addition to the ones
you might normally see. Those levels are QUIET and LIFECYCLE . The latter is the default, and is used to
report build progress.
Table 10. Log levels
Level
Used for
ERROR
Error messages
QUIET
Important information messages
WARNING
Warning messages
LIFECYCLE
Progress information messages
INFO
Information messages
DEBUG
Debug messages
Note: The rich components of the console (build status and work in progress area) are displayed
regardless of the log level used. Before Gradle 4.0 those rich components were only displayed at
log level LIFECYCLE or below.
§
Choosing a log level
You can use the command line switches shown in Table 11 to choose different log levels. You can also
configure the log level using gradle.properties, see the section called “Gradle properties”. In Table 12 you
find the command line switches which affect stacktrace logging.
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Table 11. Log level command-line options
Option
Outputs Log Levels
no logging options
LIFECYCLE and higher
-q or --quiet
QUIET and higher
-w or --warn
WARN and higher
-i or --info
INFO and higher
-d or --debug
DEBUG and higher (that is, all log messages)
Table 12. Stacktrace command-line options
Option
Meaning
No stacktraces are printed to the console in case of a build error (e.g. a compile error). Only in case of
No stacktrace options internal exceptions will stacktraces be printed. If the DEBUG log level is chosen, truncated stacktraces
are always printed.
Truncated stacktraces are printed. We recommend this over full stacktraces. Groovy full stacktraces
-s or --stacktrace
are extremely verbose (Due to the underlying dynamic invocation mechanisms. Yet they usually do not
contain relevant information for what has gone wrong in your code.) This option renders stacktraces for
deprecation warnings.
-S or --full-stacktrace
The full stacktraces are printed out. This option renders stacktraces for deprecation warnings.
§
Writing your own log messages
A simple option for logging in your build file is to write messages to standard output. Gradle redirects
anything written to standard output to its logging system at the QUIET log level.
Example 171. Using stdout to write log messages
build.gradle
println 'A message which is logged at QUIET level'
Gradle also provides a logger property to a build script, which is an instance of Logger. This interface
extends the SLF4J Logger interface and adds a few Gradle specific methods to it. Below is an example of
how this is used in the build script:
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Example 172. Writing your own log messages
build.gradle
logger.quiet('An info log message which is always logged.')
logger.error('An error log message.')
logger.warn('A warning log message.')
logger.lifecycle('A lifecycle info log message.')
logger.info('An info log message.')
logger.debug('A debug log message.')
logger.trace('A trace log message.')
Use the typical SLF4J pattern to replace a placeholder with an actual value as part of the log message.
Example 173. Writing a log message with placeholder
build.gradle
logger.info('A {} log message', 'info')
You can also hook into Gradle’s logging system from within other classes used in the build (classes from the buildSrc
directory for example). Simply use an SLF4J logger. You can use this logger the same way as you use the
provided logger in the build script.
Example 174. Using SLF4J to write log messages
build.gradle
import org.slf4j.Logger
import org.slf4j.LoggerFactory
Logger slf4jLogger = LoggerFactory.getLogger('some-logger')
slf4jLogger.info('An info log message logged using SLF4j')
§
Logging from external tools and libraries
Internally, Gradle uses Ant and Ivy. Both have their own logging system. Gradle redirects their logging output
into the Gradle logging system. There is a 1:1 mapping from the Ant/Ivy log levels to the Gradle log levels,
except the Ant/Ivy TRACE log level, which is mapped to Gradle DEBUG log level. This means the default
Gradle log level will not show any Ant/Ivy output unless it is an error or a warning.
There are many tools out there which still use standard output for logging. By default, Gradle redirects
standard output to the QUIET log level and standard error to the ERROR level. This behavior is configurable.
The project object provides a LoggingManager, which allows you to change the log levels that standard
out or error are redirected to when your build script is evaluated.
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Example 175. Configuring standard output capture
build.gradle
logging.captureStandardOutput LogLevel.INFO
println 'A message which is logged at INFO level'
To change the log level for standard out or error during task execution, tasks also provide a
LoggingManager.
Example 176. Configuring standard output capture for a task
build.gradle
task logInfo {
logging.captureStandardOutput LogLevel.INFO
doFirst {
println 'A task message which is logged at INFO level'
}
}
Gradle also provides integration with the Java Util Logging, Jakarta Commons Logging and Log4j logging
toolkits. Any log messages which your build classes write using these logging toolkits will be redirected to
Gradle’s logging system.
§
Changing what Gradle logs
You can replace much of Gradle’s logging UI with your own. You might do this, for example, if you want to
customize the UI in some way - to log more or less information, or to change the formatting. You replace the
logging using the Gradle.useLogger(java.lang.Object) method. This is accessible from a build
script, or an init script, or via the embedding API. Note that this completely disables Gradle’s default output.
Below is an example init script which changes how task execution and build completion is logged.
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Example 177. Customizing what Gradle logs
init.gradle
useLogger(new CustomEventLogger())
class CustomEventLogger extends BuildAdapter implements TaskExecutionListener {
public void beforeExecute(Task task) {
println "[$task.name]"
}
public void afterExecute(Task task, TaskState state) {
println()
}
public void buildFinished(BuildResult result) {
println 'build completed'
if (result.failure != null) {
result.failure.printStackTrace()
}
}
}
Output of gradle -I init.gradle build
> gradle -I init.gradle build
[compile]
compiling source
[testCompile]
compiling test source
[test]
running unit tests
[build]
build completed
3 actionable tasks: 3 executed
Your logger can implement any of the listener interfaces listed below. When you register a logger, only the
logging for the interfaces that it implements is replaced. Logging for the other interfaces is left untouched.
You can find out more about the listener interfaces in the section called “Responding to the lifecycle in the
build script”.
BuildListener
ProjectEvaluationListener
TaskExecutionGraphListener
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TaskExecutionListener
TaskActionListener
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Authoring Multi-Project Builds
The powerful support for multi-project builds is one of Gradle’s unique selling points. This topic is also the
most intellectually challenging.
A multi-project build in gradle consists of one root project, and one or more subprojects that may also have
subprojects.
§
Cross project configuration
While each subproject could configure itself in complete isolation of the other subprojects, it is common that
subprojects share common traits. It is then usually preferable to share configurations among projects, so the
same configuration affects several subprojects.
Let’s start with a very simple multi-project build. Gradle is a general purpose build tool at its core, so the
projects don’t have to be Java projects. Our first examples are about marine life.
§
Configuration and execution
the section called “Build phases” describes the phases of every Gradle build. Let’s zoom into the
configuration and execution phases of a multi-project build. Configuration here means executing the build.gradle
file of a project, which implies e.g. downloading all plugins that were declared using ‘ apply plugin’. By
default, the configuration of all projects happens before any task is executed. This means that when a single
task, from a single project is requested, all projects of multi-project build are configured first. The reason
every project needs to be configured is to support the flexibility of accessing and changing any part of the
Gradle project model.
§
Configuration on demand
The Configuration injection feature and access to the complete project model are possible because every
project is configured before the execution phase. Yet, this approach may not be the most efficient in a very
large multi-project build. There are Gradle builds with a hierarchy of hundreds of subprojects. The
configuration time of huge multi-project builds may become noticeable. Scalability is an important
requirement for Gradle. Hence, starting from version 1.4 a new incubating 'configuration on demand' mode is
introduced.
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Configuration on demand mode attempts to configure only projects that are relevant for requested tasks, i.e.
it only executes the build.gradle file of projects that are participating in the build. This way, the
configuration time of a large multi-project build can be reduced. In the long term, this mode will become the
default mode, possibly the only mode for Gradle build execution. The configuration on demand feature is
incubating so not every build is guaranteed to work correctly. The feature should work very well for
multi-project builds that have decoupled projects (the section called “Decoupled Projects”). In “configuration
on demand” mode, projects are configured as follows:
The root project is always configured. This way the typical common configuration is supported (allprojects or
subprojects script blocks).
The project in the directory where the build is executed is also configured, but only when Gradle is executed
without any tasks. This way the default tasks behave correctly when projects are configured on demand.
The standard project dependencies are supported and makes relevant projects configured. If project A has a
compile dependency on project B then building A causes configuration of both projects.
The task dependencies declared via task path are supported and cause relevant projects to be configured.
Example: someTask.dependsOn(":someOtherProject:someOtherTask")
A task requested via task path from the command line (or Tooling API) causes the relevant project to be
configured. For example, building 'projectA:projectB:someTask' causes configuration of projectB.
Eager to try out this new feature? To configure on demand with every build run see the section called
“Gradle properties”. To configure on demand just for a given build, see the section called “Performance
options”.
§
Defining common behavior
Let’s look at some examples with the following project tree. This is a multi-project build with a root project
named water and a subproject named bluewhale.
Example 178. Multi-project tree - water & bluewhale projects
Build layout
water/
build.gradle
settings.gradle
bluewhale/
Note: The code for this example can be found at samples/userguide/multiproject/firstExample/water
in the ‘-all’ distribution of Gradle.
settings.gradle
include 'bluewhale'
And where is the build script for the bluewhale project? In Gradle build scripts are optional. Obviously for a
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single project build, a project without a build script doesn’t make much sense. For multiproject builds the
situation is different. Let’s look at the build script for the water project and execute it:
Example 179. Build script of water (parent) project
build.gradle
Closure cl = { task -> println "I'm $task.project.name" }
task('hello').doLast(cl)
project(':bluewhale') {
task('hello').doLast(cl)
}
Output of gradle -q hello
> gradle -q hello
I'm water
I'm bluewhale
Gradle allows you to access any project of the multi-project build from any build script. The Project API
provides a method called project(), which takes a path as an argument and returns the Project object for
this path. The capability to configure a project build from any build script we call cross project configuration .
Gradle implements this via configuration injection .
We are not that happy with the build script of the water project. It is inconvenient to add the task explicitly
for every project. We can do better. Let’s first add another project called krill to our multi-project build.
Example 180. Multi-project tree - water, bluewhale & krill projects
Build layout
water/
build.gradle
settings.gradle
bluewhale/
krill/
Note: The code for this example can be found at samples/userguide/multiproject/addKrill/water
in the ‘-all’ distribution of Gradle.
settings.gradle
include 'bluewhale', 'krill'
Now we rewrite the water build script and boil it down to a single line.
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Example 181. Water project build script
build.gradle
allprojects {
task hello {
doLast { task ->
println "I'm $task.project.name"
}
}
}
Output of gradle -q hello
> gradle -q hello
I'm water
I'm bluewhale
I'm krill
Is this cool or is this cool? And how does this work? The Project API provides a property allprojects
which returns a list with the current project and all its subprojects underneath it. If you call allprojects
with a closure, the statements of the closure are delegated to the projects associated with allprojects.
You could also do an iteration via allprojects.each, but that would be more verbose.
Other build systems use inheritance as the primary means for defining common behavior. We also offer
inheritance for projects as you will see later. But Gradle uses configuration injection as the usual way of
defining common behavior. We think it provides a very powerful and flexible way of configuring multiproject
builds.
Another possibility for sharing configuration is to use a common external script. See the section called
“Configuring the project using an external build script” for more information.
§
Subproject configuration
The Project API also provides a property for accessing the subprojects only.
Defining common behavior
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§
Defining common behavior
Example 182. Defining common behavior of all projects and subprojects
build.gradle
allprojects {
task hello {
doLast { task ->
println "I'm $task.project.name"
}
}
}
subprojects {
hello {
doLast {
println "- I depend on water"
}
}
}
Output of gradle -q hello
> gradle -q hello
I'm water
I'm bluewhale
- I depend on water
I'm krill
- I depend on water
You may notice that there are two code snippets referencing the “hello” task. The first one, which uses the
“task” keyword, constructs the task and provides it’s base configuration. The second piece doesn’t use the “ task
” keyword, as it is further configuring the existing “hello” task. You may only construct a task once in a
project, but you may add any number of code blocks providing additional configuration.
§
Adding specific behavior
You can add specific behavior on top of the common behavior. Usually we put the project specific behavior
in the build script of the project where we want to apply this specific behavior. But as we have already seen,
we don’t have to do it this way. We could add project specific behavior for the bluewhale project like this:
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Example 183. Defining specific behaviour for particular project
build.gradle
allprojects {
task hello {
doLast { task ->
println "I'm $task.project.name"
}
}
}
subprojects {
hello {
doLast {
println "- I depend on water"
}
}
}
project(':bluewhale').hello {
doLast {
println "- I'm the largest animal that has ever lived on this planet."
}
}
Output of gradle -q hello
> gradle -q hello
I'm water
I'm bluewhale
- I depend on water
- I'm the largest animal that has ever lived on this planet.
I'm krill
- I depend on water
As we have said, we usually prefer to put project specific behavior into the build script of this project. Let’s
refactor and also add some project specific behavior to the krill project.
Example 184. Defining specific behaviour for project krill
Build layout
water/
build.gradle
settings.gradle
bluewhale/
build.gradle
krill/
build.gradle
Note: The code for this example can be found at samples/userguide/multiproject/spreadSpecifics/wa
in the ‘-all’ distribution of Gradle.
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settings.gradle
include 'bluewhale', 'krill'
bluewhale/build.gradle
hello.doLast {
println "- I'm the largest animal that has ever lived on this planet."
}
krill/build.gradle
hello.doLast {
println "- The weight of my species in summer is twice as heavy as all human beings."
}
build.gradle
allprojects {
task hello {
doLast { task ->
println "I'm $task.project.name"
}
}
}
subprojects {
hello {
doLast {
println "- I depend on water"
}
}
}
Output of gradle -q hello
> gradle -q hello
I'm water
I'm bluewhale
- I depend on water
- I'm the largest animal that has ever lived on this planet.
I'm krill
- I depend on water
- The weight of my species in summer is twice as heavy as all human beings.
§
Project filtering
To show more of the power of configuration injection, let’s add another project called tropicalFish and
add more behavior to the build via the build script of the water project.
Filtering by name
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§
Filtering by name
Example 185. Adding custom behaviour to some projects (filtered by project name)
Build layout
water/
build.gradle
settings.gradle
bluewhale/
build.gradle
krill/
build.gradle
tropicalFish/
Note: The code for this example can be found at samples/userguide/multiproject/addTropical/water
in the ‘-all’ distribution of Gradle.
settings.gradle
include 'bluewhale', 'krill', 'tropicalFish'
build.gradle
allprojects {
task hello {
doLast { task ->
println "I'm $task.project.name"
}
}
}
subprojects {
hello {
doLast {
println "- I depend on water"
}
}
}
configure(subprojects.findAll {it.name != 'tropicalFish'}) {
hello {
doLast {
println '- I love to spend time in the arctic waters.'
}
}
}
Output of gradle -q hello
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> gradle -q hello
I'm water
I'm bluewhale
- I depend on water
- I love to spend time in the
- I'm the largest animal that
I'm krill
- I depend on water
- I love to spend time in the
- The weight of my species in
I'm tropicalFish
- I depend on water
arctic waters.
has ever lived on this planet.
arctic waters.
summer is twice as heavy as all human beings.
The configure() method takes a list as an argument and applies the configuration to the projects in this
list.
§
Filtering by properties
Using the project name for filtering is one option. Using extra project properties is another. (See the section
called “Extra properties” for more information on extra properties.)
Example 186. Adding custom behaviour to some projects (filtered by project properties)
Build layout
water/
build.gradle
settings.gradle
bluewhale/
build.gradle
krill/
build.gradle
tropicalFish/
build.gradle
Note: The code for this example can be found at samples/userguide/multiproject/tropicalWithProper
in the ‘-all’ distribution of Gradle.
settings.gradle
include 'bluewhale', 'krill', 'tropicalFish'
bluewhale/build.gradle
ext.arctic = true
hello.doLast {
println "- I'm the largest animal that has ever lived on this planet."
}
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krill/build.gradle
ext.arctic = true
hello.doLast {
println "- The weight of my species in summer is twice as heavy as all human beings."
}
tropicalFish/build.gradle
ext.arctic = false
build.gradle
allprojects {
task hello {
doLast { task ->
println "I'm $task.project.name"
}
}
}
subprojects {
hello {
doLast {println "- I depend on water"}
afterEvaluate { Project project ->
if (project.arctic) { doLast {
println '- I love to spend time in the arctic waters.' }
}
}
}
}
Output of gradle -q hello
> gradle -q hello
I'm water
I'm bluewhale
- I depend on water
- I'm the largest animal that
- I love to spend time in the
I'm krill
- I depend on water
- The weight of my species in
- I love to spend time in the
I'm tropicalFish
- I depend on water
has ever lived on this planet.
arctic waters.
summer is twice as heavy as all human beings.
arctic waters.
In the build file of the water project we use an afterEvaluate notification. This means that the closure
we are passing gets evaluated after the build scripts of the subproject are evaluated. As the property arctic
is set in those build scripts, we have to do it this way. You will find more on this topic in the section called
“Dependencies - Which dependencies?”
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Execution rules for multi-project builds
§
Execution rules for multi-project builds
When we executed the hello task from the root project dir, things behaved in an intuitive way. All the hello
tasks of the different projects were executed. Let’s switch to the bluewhale dir and see what happens if we
execute Gradle from there.
Example 187. Running build from subproject
Output of gradle -q hello
> gradle -q hello
I'm bluewhale
- I depend on water
- I'm the largest animal that has ever lived on this planet.
- I love to spend time in the arctic waters.
The basic rule behind Gradle’s behavior is simple. Gradle looks down the hierarchy, starting with the current
dir , for tasks with the name hello and executes them. One thing is very important to note. Gradle always
evaluates every project of the multi-project build and creates all existing task objects. Then, according to the
task name arguments and the current dir, Gradle filters the tasks which should be executed. Because of
Gradle’s cross project configuration every project has to be evaluated before any task gets executed. We
will have a closer look at this in the next section. Let’s now have our last marine example. Let’s add a task to
bluewhale and krill.
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Example 188. Evaluation and execution of projects
bluewhale/build.gradle
ext.arctic = true
hello {
doLast {
println "- I'm the largest animal that has ever lived on this planet."
}
}
task distanceToIceberg {
doLast {
println '20 nautical miles'
}
}
krill/build.gradle
ext.arctic = true
hello {
doLast {
println "- The weight of my species in summer is twice as heavy as all human being
}
}
task distanceToIceberg {
doLast {
println '5 nautical miles'
}
}
Output of gradle -q distanceToIceberg
> gradle -q distanceToIceberg
20 nautical miles
5 nautical miles
Here’s the output without the -q option:
Example 189. Evaluation and execution of projects
Output of gradle distanceToIceberg
> gradle distanceToIceberg
:bluewhale:distanceToIceberg
20 nautical miles
:krill:distanceToIceberg
5 nautical miles
BUILD SUCCESSFUL in 0s
2 actionable tasks: 2 executed
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The build is executed from the water project. Neither water nor tropicalFish have a task with the
name distanceToIceberg. Gradle does not care. The simple rule mentioned already above is: Execute
all tasks down the hierarchy which have this name. Only complain if there is no such task!
§
Running tasks by their absolute path
As we have seen, you can run a multi-project build by entering any subproject dir and execute the build from
there. All matching task names of the project hierarchy starting with the current dir are executed. But Gradle
also offers to execute tasks by their absolute path (see also the section called “Project and task paths”):
Example 190. Running tasks by their absolute path
Output of gradle -q :hello :krill:hello hello
> gradle -q :hello :krill:hello hello
I'm water
I'm krill
- I depend on water
- The weight of my species in summer is twice as heavy as all human beings.
- I love to spend time in the arctic waters.
I'm tropicalFish
- I depend on water
The build is executed from the tropicalFish project. We execute the hello tasks of the water, the krill
and the tropicalFish project. The first two tasks are specified by their absolute path, the last task is
executed using the name matching mechanism described above.
§
Project and task paths
A project path has the following pattern: It starts with an optional colon, which denotes the root project. The
root project is the only project in a path that is not specified by its name. The rest of a project path is a
colon-separated sequence of project names, where the next project is a subproject of the previous project.
The path of a task is simply its project path plus the task name, like “ :bluewhale:hello”. Within a project
you can address a task of the same project just by its name. This is interpreted as a relative path.
§
Dependencies - Which dependencies?
The examples from the last section were special, as the projects had no Execution Dependencies . They had
only Configuration Dependencies . The following sections illustrate the differences between these two types
of dependencies.
Execution dependencies
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§
Execution dependencies
§
Dependencies and execution order
Example 191. Dependencies and execution order
Build layout
messages/
build.gradle
settings.gradle
consumer/
build.gradle
producer/
build.gradle
Note: The code for this example can be found at samples/userguide/multiproject/dependencies/first
in the ‘-all’ distribution of Gradle.
build.gradle
ext.producerMessage = null
settings.gradle
include 'consumer', 'producer'
consumer/build.gradle
task action {
doLast {
println("Consuming message: ${rootProject.producerMessage}")
}
}
producer/build.gradle
task action {
doLast {
println "Producing message:"
rootProject.producerMessage = 'Watch the order of execution.'
}
}
Output of gradle -q action
> gradle -q action
Consuming message: null
Producing message:
This didn’t quite do what we want. If nothing else is defined, Gradle executes the task in alphanumeric order.
Therefore, Gradle will execute “:consumer:action” before “:producer:action”. Let’s try to solve this
with a hack and rename the producer project to “aProducer”.
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Example 192. Dependencies and execution order
Build layout
messages/
build.gradle
settings.gradle
aProducer/
build.gradle
consumer/
build.gradle
build.gradle
ext.producerMessage = null
settings.gradle
include 'consumer', 'aProducer'
aProducer/build.gradle
task action {
doLast {
println "Producing message:"
rootProject.producerMessage = 'Watch the order of execution.'
}
}
consumer/build.gradle
task action {
doLast {
println("Consuming message: ${rootProject.producerMessage}")
}
}
Output of gradle -q action
> gradle -q action
Producing message:
Consuming message: Watch the order of execution.
We can show where this hack doesn’t work if we now switch to the consumer dir and execute the build.
Example 193. Dependencies and execution order
Output of gradle -q action
> gradle -q action
Consuming message: null
The problem is that the two “action” tasks are unrelated. If you execute the build from the “ messages”
project Gradle executes them both because they have the same name and they are down the hierarchy. In
the last example only one “action” task was down the hierarchy and therefore it was the only task that was
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executed. We need something better than this hack.
§
Declaring dependencies
Example 194. Declaring dependencies
Build layout
messages/
build.gradle
settings.gradle
consumer/
build.gradle
producer/
build.gradle
Note: The code for this example can be found at samples/userguide/multiproject/dependencies/messa
in the ‘-all’ distribution of Gradle.
build.gradle
ext.producerMessage = null
settings.gradle
include 'consumer', 'producer'
consumer/build.gradle
task action(dependsOn: ":producer:action") {
doLast {
println("Consuming message: ${rootProject.producerMessage}")
}
}
producer/build.gradle
task action {
doLast {
println "Producing message:"
rootProject.producerMessage = 'Watch the order of execution.'
}
}
Output of gradle -q action
> gradle -q action
Producing message:
Consuming message: Watch the order of execution.
Running this from the consumer directory gives:
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Example 195. Declaring dependencies
Output of gradle -q action
> gradle -q action
Producing message:
Consuming message: Watch the order of execution.
This is now working better because we have declared that the “ action” task in the “consumer” project has
an execution dependency on the “action” task in the “producer” project.
§
The nature of cross project task dependencies
Of course, task dependencies across different projects are not limited to tasks with the same name. Let’s
change the naming of our tasks and execute the build.
Example 196. Cross project task dependencies
consumer/build.gradle
task consume(dependsOn: ':producer:produce') {
doLast {
println("Consuming message: ${rootProject.producerMessage}")
}
}
producer/build.gradle
task produce {
doLast {
println "Producing message:"
rootProject.producerMessage = 'Watch the order of execution.'
}
}
Output of gradle -q consume
> gradle -q consume
Producing message:
Consuming message: Watch the order of execution.
§
Configuration time dependencies
Let’s see one more example with our producer-consumer build before we enter Java land. We add a
property to the “producer” project and create a configuration time dependency from “consumer” to “producer
”.
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Example 197. Configuration time dependencies
consumer/build.gradle
def message = rootProject.producerMessage
task consume {
doLast {
println("Consuming message: " + message)
}
}
producer/build.gradle
rootProject.producerMessage = 'Watch the order of evaluation.'
Output of gradle -q consume
> gradle -q consume
Consuming message: null
The default evaluation order of projects is alphanumeric (for the same nesting level). Therefore the “ consumer
” project is evaluated before the “producer” project and the “producerMessage” value is set after it is
read by the “consumer” project. Gradle offers a solution for this.
Example 198. Configuration time dependencies - evaluationDependsOn
consumer/build.gradle
evaluationDependsOn(':producer')
def message = rootProject.producerMessage
task consume {
doLast {
println("Consuming message: " + message)
}
}
Output of gradle -q consume
> gradle -q consume
Consuming message: Watch the order of evaluation.
The use of the “evaluationDependsOn” command results in the evaluation of the “producer” project
before the “consumer” project is evaluated. This example is a bit contrived to show the mechanism. In this
case there would be an easier solution by reading the key property at execution time.
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Example 199. Configuration time dependencies
consumer/build.gradle
task consume {
doLast {
println("Consuming message: ${rootProject.producerMessage}")
}
}
Output of gradle -q consume
> gradle -q consume
Consuming message: Watch the order of evaluation.
Configuration dependencies are very different from execution dependencies. Configuration dependencies
are between projects whereas execution dependencies are always resolved to task dependencies. Also note
that all projects are always configured, even when you start the build from a subproject. The default
configuration order is top down, which is usually what is needed.
To change the default configuration order to “bottom up”, use the “evaluationDependsOnChildren()”
method instead.
On the same nesting level the configuration order depends on the alphanumeric position. The most common
use case is to have multi-project builds that share a common lifecycle (e.g. all projects use the Java plugin).
If you declare with dependsOn an execution dependency between different projects, the default behavior of
this method is to also create a configuration dependency between the two projects. Therefore it is likely that
you don’t have to define configuration dependencies explicitly.
§
Real life examples
Gradle’s multi-project features are driven by real life use cases. One good example consists of two web
application projects and a parent project that creates a distribution including the two web applications. [9] For
the example we use only one build script and do cross project configuration .
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Example 200. Dependencies - real life example - crossproject configuration
Build layout
webDist/
settings.gradle
build.gradle
date/
src/main/java/
org/gradle/sample/
DateServlet.java
hello/
src/main/java/
org/gradle/sample/
HelloServlet.java
Note: The code for this example can be found at samples/userguide/multiproject/dependencies/webDi
in the ‘-all’ distribution of Gradle.
settings.gradle
include 'date', 'hello'
build.gradle
allprojects {
apply plugin: 'java'
group = 'org.gradle.sample'
version = '1.0'
}
subprojects {
apply plugin: 'war'
repositories {
mavenCentral()
}
dependencies {
compile "javax.servlet:servlet-api:2.5"
}
}
task explodedDist(type: Copy) {
into "$buildDir/explodedDist"
subprojects {
from tasks.withType(War)
}
}
We have an interesting set of dependencies. Obviously the date and hello projects have a configuration
dependency on webDist, as all the build logic for the webapp projects is injected by webDist. The
execution dependency is in the other direction, as webDist depends on the build artifacts of date and hello
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. There is even a third dependency. webDist has a configuration dependency on date and hello
because it needs to know the archivePath. But it asks for this information at execution time . Therefore we
have no circular dependency.
Such dependency patterns are daily bread in the problem space of multi-project builds. If a build system
does not support these patterns, you either can’t solve your problem or you need to do ugly hacks which are
hard to maintain and massively impair your productivity as a build master.
§
Project lib dependencies
What if one project needs the jar produced by another project in its compile path, and not just the jar but also
the transitive dependencies of this jar? Obviously this is a very common use case for Java multi-project
builds. As already mentioned in the section called “Project dependencies” , Gradle offers project lib
dependencies for this.
Example 201. Project lib dependencies
Build layout
java/
settings.gradle
build.gradle
api/
src/main/java/
org/gradle/sample/
api/
Person.java
apiImpl/
PersonImpl.java
services/personService/
src/
main/java/
org/gradle/sample/services/
PersonService.java
test/java/
org/gradle/sample/services/
PersonServiceTest.java
shared/
src/main/java/
org/gradle/sample/shared/
Helper.java
Note: The code for this example can be found at samples/userguide/multiproject/dependencies/java
in the ‘-all’ distribution of Gradle.
We have the projects “shared”, “api” and “personService”. The “personService” project has a lib
dependency on the other two projects. The “api” project has a lib dependency on the “shared” project. “services
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” is also a project, but we use it just as a container. It has no build script and gets nothing injected by another
build script. We use the : separator to define a project path. Consult the DSL documentation of
Settings.include(java.lang.String[]) for more information about defining project paths.
Example 202. Project lib dependencies
settings.gradle
include 'api', 'shared', 'services:personService'
build.gradle
subprojects {
apply plugin: 'java'
group = 'org.gradle.sample'
version = '1.0'
repositories {
mavenCentral()
}
dependencies {
testCompile "junit:junit:4.12"
}
}
project(':api') {
dependencies {
compile project(':shared')
}
}
project(':services:personService') {
dependencies {
compile project(':shared'), project(':api')
}
}
All the build logic is in the “build.gradle” file of the root project.[10] A “ lib ” dependency is a special form of
an execution dependency. It causes the other project to be built first and adds the jar with the classes of the
other project to the classpath. It also adds the dependencies of the other project to the classpath. So you
can enter the “api” directory and trigger a “gradle compile”. First the “shared” project is built and then
the “api” project is built. Project dependencies enable partial multi-project builds.
If you come from Maven land you might be perfectly happy with this. If you come from Ivy land, you might
expect some more fine grained control. Gradle offers this to you:
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Example 203. Fine grained control over dependencies
build.gradle
subprojects {
apply plugin: 'java'
group = 'org.gradle.sample'
version = '1.0'
}
project(':api') {
configurations {
spi
}
dependencies {
compile project(':shared')
}
task spiJar(type: Jar) {
baseName = 'api-spi'
from sourceSets.main.output
include('org/gradle/sample/api/**')
}
artifacts {
spi spiJar
}
}
project(':services:personService') {
dependencies {
compile project(':shared')
compile project(path: ':api', configuration: 'spi')
testCompile "junit:junit:4.12", project(':api')
}
}
The Java plugin adds per default a jar to your project libraries which contains all the classes. In this example
we create an additional library containing only the interfaces of the “api” project. We assign this library to a
new dependency configuration . For the person service we declare that the project should be compiled only
against the “api” interfaces but tested with all classes from “api”.
§
Disabling the build of dependency projects
Sometimes you don’t want depended on projects to be built when doing a partial build. To disable the build
of the depended on projects you can run Gradle with the -a option.
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Parallel project execution
§
Parallel project execution
With more and more CPU cores available on developer desktops and CI servers, it is important that Gradle
is able to fully utilise these processing resources. More specifically, parallel execution attempts to:
Reduce total build time for a multi-project build where execution is IO bound or otherwise does not consume
all available CPU resources.
Provide faster feedback for execution of small projects without awaiting completion of other projects.
Although Gradle already offers parallel test execution via Test.setMaxParallelForks(int) the feature
described in this section is parallel execution at a project level. Parallel execution is an incubating feature.
Please use it and let us know how it works for you.
Parallel project execution allows the separate projects in a decoupled multi-project build to be executed in
parallel (see also: the section called “Decoupled Projects”). While parallel execution does not strictly require
decoupling at configuration time, the long-term goal is to provide a powerful set of features that will be
available for fully decoupled projects. Such features include:
the section called “Configuration on demand”.
Configuration of projects in parallel.
Re-use of configuration for unchanged projects.
Project-level up-to-date checks.
Using pre-built artifacts in the place of building dependent projects.
How does parallel execution work? First, you need to tell Gradle to use parallel mode. You can use the --parallel
command line argument or configure your build environment (the section called “Gradle properties”). Unless
you provide a specific number of parallel threads, Gradle attempts to choose the right number based on
available CPU cores. Every parallel worker exclusively owns a given project while executing a task. Task
dependencies are fully supported and parallel workers will start executing upstream tasks first. Bear in mind
that the alphabetical ordering of decoupled tasks, as can be seen during sequential execution, is not
guaranteed in parallel mode. In other words, in parallel mode tasks will run as soon as their dependencies
complete and a task worker is available to run them , which may be earlier than they would start during a
sequential build. You should make sure that task dependencies and task inputs/outputs are declared
correctly to avoid ordering issues.
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Decoupled Projects
§
Decoupled Projects
Gradle allows any project to access any other project during both the configuration and execution phases.
While this provides a great deal of power and flexibility to the build author, it also limits the flexibility that
Gradle has when building those projects. For instance, this effectively prevents Gradle from correctly
building multiple projects in parallel, configuring only a subset of projects, or from substituting a pre-built
artifact in place of a project dependency.
Two projects are said to be decoupled if they do not directly access each other’s project model. Decoupled
projects may only interact in terms of declared dependencies: project dependencies (the section called
“Project dependencies”) and/or task dependencies (the section called “Task dependencies”). Any other form
of project interaction (i.e. by modifying another project object or by reading a value from another project
object) causes the projects to be coupled. The consequence of coupling during the configuration phase is
that if gradle is invoked with the 'configuration on demand' option, the result of the build can be flawed in
several ways. The consequence of coupling during execution phase is that if gradle is invoked with the
parallel option, one project task runs too late to influence a task of a project building in parallel. Gradle does
not attempt to detect coupling and warn the user, as there are too many possibilities to introduce coupling.
A very common way for projects to be coupled is by using configuration injection (the section called “Cross
project configuration”). It may not be immediately apparent, but using key Gradle features like the allprojects
and subprojects keywords automatically cause your projects to be coupled. This is because these
keywords are used in a build.gradle file, which defines a project. Often this is a “root project” that does
nothing more than define common configuration, but as far as Gradle is concerned this root project is still a
fully-fledged project, and by using allprojects that project is effectively coupled to all other projects.
Coupling of the root project to subprojects does not impact 'configuration on demand', but using the allprojects
and subprojects in any subproject’s build.gradle file will have an impact.
This means that using any form of shared build script logic or configuration injection ( allprojects, subprojects
, etc.) will cause your projects to be coupled. As we extend the concept of project decoupling and provide
features that take advantage of decoupled projects, we will also introduce new features to help you to solve
common use cases (like configuration injection) without causing your projects to be coupled.
In order to make good use of cross project configuration without running into issues for parallel and
'configuration on demand' options, follow these recommendations:
Avoid a subproject’s build.gradle referencing other subprojects; preferring cross configuration from the
root project.
Avoid changing the configuration of other projects at execution time.
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Multi-Project Building and Testing
§
Multi-Project Building and Testing
The build task of the Java plugin is typically used to compile, test, and perform code style checks (if the
CodeQuality plugin is used) of a single project. In multi-project builds you may often want to do all of these
tasks across a range of projects. The buildNeeded and buildDependents tasks can help with this.
Look at Example 202. In this example, the “:services:personservice” project depends on both the “:api
” and “:shared” projects. The “:api” project also depends on the “:shared” project.
Assume you are working on a single project, the “ :api” project. You have been making changes, but have
not built the entire project since performing a clean. You want to build any necessary supporting jars, but
only perform code quality and unit tests on the project you have changed. The build task does this.
Example 204. Build and Test Single Project
Output of gradle :api:build
> gradle :api:build
:shared:compileJava
:shared:processResources
:shared:classes
:shared:jar
:api:compileJava
:api:processResources
:api:classes
:api:jar
:api:assemble
:api:compileTestJava
:api:processTestResources
:api:testClasses
:api:test
:api:check
:api:build
BUILD SUCCESSFUL in 0s
9 actionable tasks: 9 executed
While you are working in a typical development cycle repeatedly building and testing changes to the “ :api”
project (knowing that you are only changing files in this one project), you may not want to even suffer the
expense of building “:shared:compile” to see what has changed in the “:shared” project. Adding the “-a
” option will cause Gradle to use cached jars to resolve any project lib dependencies and not try to re-build
the depended on projects.
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Example 205. Partial Build and Test Single Project
Output of gradle -a :api:build
> gradle -a :api:build
:api:compileJava
:api:processResources
:api:classes
:api:jar
:api:assemble
:api:compileTestJava
:api:processTestResources
:api:testClasses
:api:test
:api:check
:api:build
BUILD SUCCESSFUL in 0s
6 actionable tasks: 6 executed
If you have just gotten the latest version of source from your version control system which included changes
in other projects that “:api” depends on, you might want to not only build all the projects you depend on, but
test them as well. The buildNeeded task also tests all the projects from the project lib dependencies of the
testRuntime configuration.
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Example 206. Build and Test Depended On Projects
Output of gradle :api:buildNeeded
> gradle :api:buildNeeded
:shared:compileJava
:shared:processResources
:shared:classes
:shared:jar
:api:compileJava
:api:processResources
:api:classes
:api:jar
:api:assemble
:api:compileTestJava
:api:processTestResources
:api:testClasses
:api:test
:api:check
:api:build
:shared:assemble
:shared:compileTestJava
:shared:processTestResources
:shared:testClasses
:shared:test
:shared:check
:shared:build
:shared:buildNeeded
:api:buildNeeded
BUILD SUCCESSFUL in 0s
12 actionable tasks: 12 executed
You also might want to refactor some part of the “ :api” project that is used in other projects. If you make
these types of changes, it is not sufficient to test just the “ :api” project, you also need to test all projects
that depend on the “:api” project. The buildDependents task also tests all the projects that have a
project lib dependency (in the testRuntime configuration) on the specified project.
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Example 207. Build and Test Dependent Projects
Output of gradle :api:buildDependents
> gradle :api:buildDependents
:shared:compileJava
:shared:processResources
:shared:classes
:shared:jar
:api:compileJava
:api:processResources
:api:classes
:api:jar
:api:assemble
:api:compileTestJava
:api:processTestResources
:api:testClasses
:api:test
:api:check
:api:build
:services:personService:compileJava
:services:personService:processResources
:services:personService:classes
:services:personService:jar
:services:personService:assemble
:services:personService:compileTestJava
:services:personService:processTestResources
:services:personService:testClasses
:services:personService:test
:services:personService:check
:services:personService:build
:services:personService:buildDependents
:api:buildDependents
BUILD SUCCESSFUL in 0s
17 actionable tasks: 17 executed
Finally, you may want to build and test everything in all projects. Any task you run in the root project folder
will cause that same named task to be run on all the children. So you can just run “ gradle build” to build
and test all projects.
§
Multi Project and buildSrc
the section called “Build sources in the buildSrc project” tells us that we can place build logic to be
compiled and tested in the special buildSrc directory. In a multi project build, there can only be one buildSrc
directory which must be located in the root directory.
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Property and method inheritance
§
Property and method inheritance
Properties and methods declared in a project are inherited to all its subprojects. This is an alternative to
configuration injection. But we think that the model of inheritance does not reflect the problem space of
multi-project builds very well. In a future edition of this user guide we might write more about this.
Method inheritance might be interesting to use as Gradle’s Configuration Injection does not support methods
yet (but will in a future release).
You might be wondering why we have implemented a feature we obviously don’t like that much. One reason
is that it is offered by other tools and we want to have the check mark in a feature comparison :). And we like
to offer our users a choice.
§
Summary
Writing this chapter was pretty exhausting and reading it might have a similar effect. Our final message for
this chapter is that multi-project builds with Gradle are usually not difficult. There are five elements you need
to remember: allprojects, subprojects, evaluationDependsOn, evaluationDependsOnChildren
and project lib dependencies.[11] With those elements, and keeping in mind that Gradle has a distinct
configuration and execution phase, you already have a lot of flexibility. But when you enter steep territory
Gradle does not become an obstacle and usually accompanies and carries you to the top of the mountain.
[9] The real use case we had, was using http://lucene.apache.org/solr, where you need a separate war for
each index you are accessing. That was one reason why we have created a distribution of webapps. The
Resin servlet container allows us, to let such a distribution point to a base installation of the servlet
container.
[10] We do this here, as it makes the layout a bit easier. We usually put the project specific stuff into the
build script of the respective projects.
[11] So we are well in the range of the 7 plus 2 Rule :)
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Using Gradle Plugins
Gradle at its core intentionally provides very little for real world automation. All of the useful features, like the
ability to compile Java code, are added by plugins . Plugins add new tasks (e.g. JavaCompile), domain
objects (e.g. SourceSet), conventions (e.g. Java source is located at src/main/java) as well as
extending core objects and objects from other plugins.
In this chapter we discuss how to use plugins and the terminology and concepts surrounding plugins.
§
What plugins do
Applying a plugin to a project allows the plugin to extend the project’s capabilities. It can do things such as:
Extend the Gradle model (e.g. add new DSL elements that can be configured)
Configure the project according to conventions (e.g. add new tasks or configure sensible defaults)
Apply specific configuration (e.g. add organizational repositories or enforce standards)
By applying plugins, rather than adding logic to the project build script, we can reap a number of benefits.
Applying plugins:
Promotes reuse and reduces the overhead of maintaining similar logic across multiple projects
Allows a higher degree of modularization, enhancing comprehensibility and organization
Encapsulates imperative logic and allows build scripts to be as declarative as possible
§
Types of plugins
There are two general types of plugins in Gradle, script plugins and binary plugins. Script plugins are
additional build scripts that further configure the build and usually implement a declarative approach to
manipulating the build. They are typically used within a build although they can be externalized and
accessed from a remote location. Binary plugins are classes that implement the Plugin interface and adopt
a programmatic approach to manipulating the build. Binary plugins can reside within a build script, within the
project hierarchy or externally in a plugin jar.
A plugin often starts out as a script plugin (because they are easy to write) and then, as the code becomes
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more valuable, it’s migrated to a binary plugin that can be easily tested and shared between multiple projects
or organizations.
§
Using plugins
To use the build logic encapsulated in a plugin, Gradle needs to perform two steps. First, it needs to resolve
the plugin, and then it needs to apply the plugin to the target, usually a Project.
Resolving a plugin means finding the correct version of the jar which contains a given plugin and adding it
the script classpath. Once a plugin is resolved, its API can be used in a build script. Script plugins are
self-resolving in that they are resolved from the specific file path or URL provided when applying them. Core
binary plugins provided as part of the Gradle distribution are automatically resolved.
Applying a plugin means actually executing the plugin’s Plugin.apply(T) on the Project you want to
enhance with the plugin. Applying plugins is idempotent . That is, you can safely apply any plugin multiple
times without side effects.
The most common use case for using a plugin is to both resolve the plugin and apply it to the current project.
Since this is such a common use case, it’s recommended that build authors use the plugins DSL to both
resolve and apply plugins in one step. The feature is technically still incubating, but it works well, and should
be used by most users.
§
Script plugins
Example 208. Applying a script plugin
build.gradle
apply from: 'other.gradle'
Script plugins are automatically resolved and can be applied from a script on the local filesystem or at a
remote location. Filesystem locations are relative to the project directory, while remote script locations are
specified with an HTTP URL. Multiple script plugins (of either form) can be applied to a given target.
§
Binary plugins
You apply plugins by their plugin id , which is a globally unique identifier, or name, for plugins. Core Gradle
plugins are special in that they provide short names, such as 'java' for the core JavaPlugin. All other
binary plugins must use the fully qualified form of the plugin id (e.g. com.github.foo.bar), although
some legacy plugins may still utilize a short, unqualified form. Where you put the plugin id depends on
whether you are using the plugins DSL or the buildscript block.
Locations of binary plugins
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§
Locations of binary plugins
A plugin is simply any class that implements the Plugin interface. Gradle provides the core plugins (e.g. JavaPlugin
) as part of its distribution which means they are automatically resolved. However, non-core binary plugins
need to be resolved before they can be applied. This can be achieved in a number of ways:
Including the plugin from the plugin portal or a custom repository using the plugins DSL (see the section
called “Applying plugins with the plugins DSL”).
Including the plugin from an external jar defined as a buildscript dependency (see the section called
“Applying plugins with the buildscript block”).
Defining the plugin as a source file under the buildSrc directory in the project (see the section called “Build
sources in the buildSrc project”).
Defining the plugin as an inline class declaration inside a build script.
For more on defining your own plugins, see Writing Custom Plugins.
§
Applying plugins with the plugins DSL
Note: The plugins DSL is currently incubating. Please be aware that the DSL and other
configuration may change in later Gradle versions.
The new plugins DSL provides a succinct and convenient way to declare plugin dependencies. It works with
the Gradle plugin portal to provide easy access to both core and community plugins. The plugins DSL block
configures an instance of PluginDependenciesSpec.
To apply a core plugin, the short name can be used:
Example 209. Applying a core plugin
build.gradle
plugins {
id 'java'
}
To apply a community plugin from the portal, the fully qualified plugin id must be used:
Example 210. Applying a community plugin
build.gradle
plugins {
id 'com.jfrog.bintray' version '0.4.1'
}
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See PluginDependenciesSpec for more information on using the Plugin DSL.
§
Limitations of the plugins DSL
This way of adding plugins to a project is much more than a more convenient syntax. The plugins DSL is
processed in a way which allows Gradle to determine the plugins in use very early and very quickly. This
allows Gradle to do smart things such as:
Optimize the loading and reuse of plugin classes.
Allow different plugins to use different versions of dependencies.
Provide editors detailed information about the potential properties and values in the buildscript for editing
assistance.
This requires that plugins be specified in a way that Gradle can easily and quickly extract, before executing
the rest of the build script. It also requires that the definition of plugins to use be somewhat static.
There are some key differences between the new plugin mechanism and the “traditional” apply() method
mechanism. There are also some constraints, some of which are temporary limitations while the mechanism
is still being developed and some are inherent to the new approach.
§
Constrained Syntax
The new plugins {} block does not support arbitrary Groovy code. It is constrained, in order to be
idempotent (produce the same result every time) and side effect free (safe for Gradle to execute at any
time).
The form is:
plugins {
id «plugin id» version «plugin version» [apply «false»]
}
Where «plugin version» and «plugin id» must be constant, literal, strings and the apply statement
with a boolean can be used to disable the default behavior of applying the plugin immediately (e.g. you
want to apply it only in subprojects). No other statements are allowed; their presence will cause a
compilation error.
The plugins {} block must also be a top level statement in the buildscript. It cannot be nested inside
another construct (e.g. an if-statement or for-loop).
§
Can only be used in build scripts
The plugins {} block can currently only be used in a project’s build script. It cannot be used in script
plugins, the settings.gradle file or init scripts.
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Future versions of Gradle will remove this restriction.
If the restrictions of the new syntax are prohibitive, the recommended approach is to apply plugins using the
buildscript {} block.
§
Applying plugins to subprojects
If you have a multi-project build, you probably want to apply plugins to some or all of the subprojects in your
build, but not to the root or master project. The default behavior of the plugins {} block is to
immediately resolve and apply the plugins. But, you can use the apply false syntax to tell Gradle not
to apply the plugin to the current project and then use apply plugin: «plugin id» in the subprojects
block:
Example 211. Applying plugins only on certain subprojects.
settings.gradle
include 'helloA'
include 'helloB'
include 'goodbyeC'
build.gradle
plugins {
id "org.gradle.sample.hello" version "1.0.0" apply false
id "org.gradle.sample.goodbye" version "1.0.0" apply false
}
subprojects { subproject ->
if (subproject.name.startsWith("hello")) {
apply plugin: 'org.gradle.sample.hello'
}
if (subproject.name.startsWith("goodbye")) {
apply plugin: 'org.gradle.sample.goodbye'
}
}
If you then run gradle hello you’ll see that only the helloA and helloB subprojects had the hello plugin
applied.
gradle/subprojects/docs/src/samples/plugins/multiproject $> gradle hello
Parallel execution is an incubating feature.
:helloA:hello
:helloB:hello
Hello!
Hello!
BUILD SUCCEEDED
Plugin Management
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§
Plugin Management
Note: The pluginManagement {} DSL is currently incubating. Please be aware that the DSL and
other configuration may change in later Gradle versions.
§
Custom Plugin Repositories
By default, the plugins {} DSL resolves plugins from the public Gradle Plugin Portal. Many build authors
would also like to resolve plugins from private Maven or Ivy repositories because the plugins contain
proprietary implementation details, or just to have more control over what plugins are available to their
builds.
To specify custom plugin repositories, use the repositories {} block inside pluginManagement {} in
the settings.gradle file:
Example 212. Using plugins from custom plugin repositories.
settings.gradle
pluginManagement {
repositories {
maven {
url 'maven-repo'
}
gradlePluginPortal()
ivy {
url 'ivy-repo'
}
}
}
This tells Gradle to first look in the Maven repository at maven-repo when resolving plugins and then to
check the Gradle Plugin Portal if the plugins are not found in the Maven repository. If you don’t want the
Gradle Plugin Portal to be searched, omit the gradlePluginPortal() line. Finally, the Ivy repository at ivy-repo
will be checked.
§
Plugin Resolution Rules
Plugin resolution rules allow you to modify plugin requests made in plugins {} blocks, e.g. changing the
requested version or explicitly specifying the implementation artifact coordinates.
To add resolution rules, use the resolutionStrategy {} inside the pluginManagement {} block:
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Example 213. Plugin resolution strategy.
settings.gradle
pluginManagement {
resolutionStrategy {
eachPlugin {
if (requested.id.namespace == 'org.gradle.sample') {
useModule('org.gradle.sample:sample-plugins:1.0.0')
}
}
}
repositories {
maven {
url 'maven-repo'
}
gradlePluginPortal()
ivy {
url 'ivy-repo'
}
}
}
This tells Gradle to use the specified plugin implementation artifact instead of using its built-in default
mapping from plugin ID to Maven/Ivy coordinates.
The pluginManagement {} block may only appear in the settings.gradle file, and must be the first
block in the file. Custom Maven and Ivy plugin repositories must contain plugin marker artifacts in addition to
the artifacts which actually implement the plugin. For more information on publishing plugins to custom
repositories read Gradle Plugin Development Plugin.
See PluginManagementSpec for complete documentation for using the pluginManagement {} block.
§
Plugin Marker Artifacts
Since the plugins {} DSL block only allows for declaring plugins by their globally unique plugin id and version
properties, Gradle needs a way to look up the coordinates of the plugin implementation artifact. To do so,
Gradle will look for a Plugin Marker Artifact with the coordinates plugin.id:plugin.id.gradle.plugin:plugin.ve
. This marker needs to have a dependency on the actual plugin implementation. Publishing these markers is
automated by the java-gradle-plugin.
For example, the following complete sample from the sample-plugins project shows how to publish a org.gradle.sa
plugin and a org.gradle.sample.goodbye plugin to both an Ivy and Maven repository using the
combination of the java-gradle-plugin, the maven-publish plugin, and the ivy-publish plugin.
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Example 214. Complete Plugin Publishing Sample
build.gradle
plugins {
id 'java-gradle-plugin'
id 'maven-publish'
id 'ivy-publish'
}
group 'org.gradle.sample'
version '1.0.0'
gradlePlugin {
plugins {
hello {
id = "org.gradle.sample.hello"
implementationClass = "org.gradle.sample.hello.HelloPlugin"
}
goodbye {
id = "org.gradle.sample.goodbye"
implementationClass = "org.gradle.sample.goodbye.GoodbyePlugin"
}
}
}
publishing {
repositories {
maven {
url "../consuming/maven-repo"
}
ivy {
url "../consuming/ivy-repo"
}
}
}
Running gradle publish in the sample directory causes the following repo layouts to exist:
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§
Legacy Plugin Application
With the introduction of the plugins DSL, users should have little reason to use the legacy method of
applying plugins. It is documented here in case a build author cannot use the plugins DSL due to restrictions
in how it currently works.
§
Applying Binary Plugins
Example 215. Applying a binary plugin
build.gradle
apply plugin: 'java'
Plugins can be applied using a plugin id . In the above case, we are using the short name ‘java’ to apply the
JavaPlugin.
Rather than using a plugin id, plugins can also be applied by simply specifying the class of the plugin:
Example 216. Applying a binary plugin by type
build.gradle
apply plugin: JavaPlugin
The JavaPlugin symbol in the above sample refers to the JavaPlugin. This class does not strictly need
to be imported as the org.gradle.api.plugins package is automatically imported in all build scripts
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(see the section called “Default imports”). Furthermore, it is not necessary to append .class to identify a
class literal in Groovy as it is in Java.
§
Applying plugins with the buildscript block
Binary plugins that have been published as external jar files can be added to a project by adding the plugin
to the build script classpath and then applying the plugin. External jars can be added to the build script
classpath using the buildscript {} block as described in the section called “External dependencies for
the build script”.
Example 217. Applying a plugin with the buildscript block
build.gradle
buildscript {
repositories {
jcenter()
}
dependencies {
classpath "com.jfrog.bintray.gradle:gradle-bintray-plugin:0.4.1"
}
}
apply plugin: "com.jfrog.bintray"
§
Finding community plugins
Gradle has a vibrant community of plugin developers who contribute plugins for a wide variety of capabilities.
The Gradle plugin portal provides an interface for searching and exploring community plugins.
§
More on plugins
This chapter aims to serve as an introduction to plugins and Gradle and the role they play. For more
information on the inner workings of plugins, see Writing Custom Plugins.
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Standard Gradle plugins
There are a number of plugins included in the Gradle distribution. These are listed below.
§
Language plugins
These plugins add support for various languages which can be compiled for and executed in the JVM.
Table 13. Language plugins
Plugin
Automatically Works
Id
applies
with
java
java-base
-
Description
Adds Java compilation, testing and bundling capabilities to a project. It serves as the basis for
many of the other Gradle plugins. See also Java Quickstart.
groovy java, groovy-base
Adds support for building Groovy projects. See also Groovy Quickstart.
scala java, scala-base
-
antlr java
-
Adds support for building Scala projects.
Adds support for generating parsers using Antlr.
§
Incubating language plugins
These plugins add support for various languages:
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Table 14. Language plugins
Plugin Id
Automatically applies Works with Description
assembler
-
-
Adds native assembly language capabilities to a project.
-
-
Adds C source compilation capabilities to a project.
cpp
-
-
Adds C++ source compilation capabilities to a project.
objective-c
-
-
Adds Objective-C source compilation capabilities to a project.
objective-cpp
-
-
Adds Objective-C++ source compilation capabilities to a project.
windows-resources -
-
Adds support for including Windows resources in native binaries.
§
Integration plugins
These plugins provide some integration with various runtime technologies.
Table 15. Integration plugins
Plugin Id
Automatically
Works
applies
with
application java, distribution
-
Description
Adds tasks for running and bundling a Java project as a command-line
application.
ear
-
java
Adds support for building J2EE applications.
maven
-
java, warAdds support for publishing artifacts to Maven repositories.
osgi
java-base
java
war
java
-
Adds support for building OSGi bundles.
Adds support for assembling web application WAR files. See also Web
Application Quickstart.
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Incubating integration plugins
§
Incubating integration plugins
These plugins provide some integration with various runtime technologies.
Table 16. Incubating integration plugins
Plugin Id
distribution
Automatically
Works
applies
with
-
-
java-library-distribution java, distribution
-
ivy-publish
maven-publish
-
-
Description
Adds support for building ZIP and TAR distributions.
Adds support for building ZIP and TAR distributions for a Java
library.
java, This plugin provides a new DSL to support publishing artifacts to Ivy
war
repositories, which improves on the existing DSL.
java, This plugin provides a new DSL to support publishing artifacts to
war
Maven repositories, which improves on the existing DSL.
§
Software development plugins
These plugins provide help with your software development process.
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Table 17. Software development plugins
Plugin Id
announce
Automatically
Works
applies
with
-
-
build-announcements announce
-
checkstyle
java-base
-
codenarc
groovy-base
-
eclipse
-
Description
Publish messages to your favourite platforms, such as Twitter or Growl.
Sends local announcements to your desktop about interesting events in
the build lifecycle.
Performs quality checks on your project’s Java source files using
Checkstyle and generates reports from these checks.
Performs quality checks on your project’s Groovy source files using
CodeNarc and generates reports from these checks.
java,groovy
Generates files that are used by Eclipse IDE, thus making it possible to
, scala import the project into Eclipse. See also Java Quickstart.
Does the same as the eclipse plugin plus generates eclipse WTP (Web
eclipse-wtp
-
Tools Platform) configuration files. After importing to eclipse your
ear, war
war/ear projects should be configured to work with WTP. See also Java
Quickstart.
Performs quality checks on your project’s Java source files using
findbugs
java-base
-
idea
-
java
jdepend
java-base
-
pmd
java-base
-
project-report
reporting-base -
Generates reports containing useful information about your Gradle build.
signing
base
Adds the ability to digitally sign built files and artifacts.
-
FindBugs and generates reports from these checks.
Generates files that are used by Intellij IDEA IDE, thus making it
possible to import the project into IDEA.
Performs quality checks on your project’s source files using JDepend
and generates reports from these checks.
Performs quality checks on your project’s Java source files using PMD
and generates reports from these checks.
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Incubating software development plugins
§
Incubating software development plugins
These plugins provide help with your software development process.
Table 18. Software development plugins
Plugin Id
Automatically
applies
Works with
Description
build-dashboard
reporting-base -
Generates build dashboard report.
cunit
-
Adds support for running CUnit tests.
jacoco
reporting-base java
visual-studio
-
-
Provides integration with the JaCoCo code coverage library for Java.
native
language
Adds integration with Visual Studio.
plugins
java-gradle-plugin java
Assists with development of Gradle plugins by providing standard
plugin build configuration and validation.
§
Base plugins
These plugins form the basic building blocks which the other plugins are assembled from. They are available
for you to use in your build files, and are listed here for completeness. However, be aware that they are not
yet considered part of Gradle’s public API. As such, these plugins are not documented in the user guide.
You might refer to their API documentation to learn more about them.
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Table 19. Base plugins
Plugin Id
Description
Adds the standard lifecycle tasks and configures reasonable defaults for the archive tasks:
adds build ConfigurationName tasks. Those tasks assemble the artifacts belonging to the specified
configuration.
adds upload ConfigurationName tasks. Those tasks assemble and upload the artifacts belonging to the
base
specified configuration.
configures reasonable default values for all archive tasks (e.g. tasks that inherit from AbstractArchiveTask).
For example, the archive tasks are tasks of types: Jar, Tar, Zip. Specifically, destinationDir, baseName
and version properties of the archive tasks are preconfigured with defaults. This is extremely useful because it
drives consistency across projects; the consistency regarding naming conventions of archives and their location
after the build completed.
java-base
Adds the source sets concept to the project. Does not add any particular source sets.
groovy-base
Adds the Groovy source sets concept to the project.
scala-base
Adds the Scala source sets concept to the project.
reporting-base Adds some shared convention properties to the project, relating to report generation.
§
Third party plugins
You can find a list of external plugins at the Gradle Plugins site.
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The Project Report Plugin
The Project report plugin adds some tasks to your project which generate reports containing useful
information about your build. These tasks generate the same content that you get by executing the tasks, dependencie
, and properties tasks from the command line (see the section called “Project reporting”). In contrast to
the command line reports, the report plugin generates the reports into a file. There is also an aggregating
task that depends on all report tasks added by the plugin.
We plan to add much more to the existing reports and create additional ones in future releases of Gradle.
§
Usage
To use the Project report plugin, include the following in your build script:
apply plugin: 'project-report'
§
Tasks
The project report plugin defines the following tasks:
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Table 20. Project report plugin - tasks
Task name
Depends on
Type
dependencyReport
-
DependencyReportTask
Description
Generates
the
dependency report.
Generates
an
dependency
htmlDependencyReport -
project
HTML
and
HtmlDependencyReportTask dependency insight report
for the project or a set of
projects.
propertyReport
-
PropertyReportTask
taskReport
-
TaskReportTask
projectReport
dependencyReport, propertyReport
Task
, taskReport, htmlDependencyReport
Generates
the
project
property report.
Generates the project task
report.
Generates
all
project
reports.
§
Project layout
The project report plugin does not require any particular project layout.
§
Dependency management
The project report plugin does not define any dependency configurations.
§
Convention properties
The project report defines the following convention properties:
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Table 21. Project report plugin - convention properties
Property name
Type
Default value
reportsDirName
String
reports
File
reportsDir
Description
The name of the directory to generate reports
into, relative to the build directory.
buildDir / reportsDirName The directory to generate reports into.
(read-only)
A one element set with the
Set<Project> project the plugin was applied The projects to generate the reports for.
projects
to.
projectReportDirName String
File
projectReportDir
These
convention
The name of the directory to generate the project
project
(read-only)
properties
report into, relative to the reports directory.
reportsDir / projectReportDirName
The directory to generate the project report into.
are
provided
by
a
convention
object
of
type
ProjectReportsPluginConvention.
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The Build Dashboard Plugin
Note: The build dashboard plugin is currently incubating. Please be aware that the DSL and other
configuration may change in later Gradle versions.
The Build Dashboard plugin can be used to generate a single HTML dashboard that provides a single point
of access to all of the reports generated by a build.
§
Usage
To use the Build Dashboard plugin, include the following in your build script:
Example 218. Using the Build Dashboard plugin
build.gradle
apply plugin: 'build-dashboard'
Applying the plugin adds the buildDashboard task to your project. The task aggregates the reports for all
tasks that implement the Reporting interface from all projects in the build. It is typically only applied to the
root project.
The buildDashboard task does not depend on any other tasks. It will only aggregate the reporting tasks
that are independently being executed as part of the build run. To generate the build dashboard, simply
include this task in the list of tasks to execute. For example, “ gradle buildDashboard build” will
generate a dashboard for all of the reporting tasks that are dependents of the build task.
§
Tasks
The Build Dashboard plugin adds the following task to the project:
Table 22. Build Dashboard plugin - tasks
Task name
Depends on
Type
Description
buildDashboard
-
GenerateBuildDashboard
Generates build dashboard report.
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Project layout
§
Project layout
The Build Dashboard plugin does not require any particular project layout.
§
Dependency management
The Build Dashboard plugin does not define any dependency configurations.
§
Configuration
You can influence the location of build dashboard plugin generation via ReportingExtension.
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Comparing Builds
Note: Build comparison support is an incubating feature. This means that it is incomplete and not
yet at regular Gradle production quality. This also means that this Gradle User Guide chapter is a
work in progress.
Gradle provides support for comparing the outcomes (e.g. the produced binary archives) of two builds.
There are several reasons why you may want to compare the outcomes of two builds. You may want to
compare:
A build with a newer version of Gradle than it’s currently using (i.e. upgrading the Gradle version).
A Gradle build with a build executed by another tool such as Apache Ant, Apache Maven or something else
(i.e. migrating to Gradle).
The same Gradle build, with the same version, before and after a change to the build (i.e. testing build
changes).
By comparing builds in these scenarios you can make an informed decision about the Gradle upgrade,
migration to Gradle or build change by understanding the differences in the outcomes. The comparison
process produces a HTML report outlining which outcomes were found to be identical and identifying the
differences between non-identical outcomes.
§
Definition of terms
The following are the terms used for build comparison and their definitions.
“Build”
In the context of build comparison, a build is not necessarily a Gradle build. It can be any invokable
“process” that produces observable “outcomes”. At least one of the builds in a comparison will be a
Gradle build.
“Build Outcome”
Something that happens in an observable manner during a build, such as the creation of a zip file or test
execution. These are the things that are compared.
“Source Build”
The build that comparisons are being made against, typically the build in its “current” state. In other
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words, the left hand side of the comparison.
“Target Build”
The build that is being compared to the source build, typically the “proposed” build. In other words, the
right hand side of the comparison.
“Host Build”
The Gradle build that executes the comparison process. It may be the same project as either the “target”
or “source” build or may be a completely separate project. It does not need to be the same Gradle
version as the “source” or “target” builds. The host build must be run with Gradle 1.2 or newer.
“Compared Build Outcome”
Build outcomes that are intended to be logically equivalent in the “source” and “target” builds, and are
therefore meaningfully comparable.
“Uncompared Build Outcome”
A build outcome is uncompared if a logical equivalent from the other build cannot be found (e.g. a build
produces a zip file that the other build does not).
“Unknown Build Outcome”
A build outcome that cannot be understood by the host build. This can occur when the source or target
build is a newer Gradle version than the host build and that Gradle version exposes new outcome types.
Unknown build outcomes can be compared in so far as they can be identified to be logically equivalent to
an unknown build outcome in the other build, but no meaningful comparison of what the build outcome
actually is can be performed. Using the latest Gradle version for the host build will avoid encountering
unknown build outcomes.
§
Current Capabilities
As this is an incubating feature, a limited set of the eventual functionality has been implemented at this time.
§
Supported builds
Only support for comparing Gradle builds is available at this time. Both the source and target build must
execute with Gradle newer or equal to version 1.0. The host build must be at least version 1.2. If the host
build is run with version 3.0 or newer, source and target builds must be at least version 1.2. If the host
build is run with a version older than 2.0, source and target builds must be older than version 3.0. So if you
for example want to compare a build under version 1.1 with a build under version 3.0, you have to execute
the host build with a 2.x version.
Future versions will provide support for executing builds from other build systems such as Apache Ant or
Apache Maven, as well as support for executing arbitrary processes (e.g. shell script based builds)
Supported build outcomes
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§
Supported build outcomes
Only support for comparing build outcomes that are zip archives is supported at this time. This includes jar
, war and ear archives.
Future versions will provide support for comparing outcomes such as test execution (i.e. which tests were
executed, which tests failed, etc.)
§
Comparing Gradle Builds
The compare-gradle-builds plugin can be used to facilitate a comparison between two Gradle builds.
The plugin adds a CompareGradleBuilds task named “compareGradleBuilds” to the project. The
configuration of this task specifies what is to be compared. By default, it is configured to compare the current
build with itself using the current Gradle version by executing the tasks: “ clean assemble”.
apply plugin: 'compare-gradle-builds'
This task can be configured to change what is compared.
compareGradleBuilds {
sourceBuild {
projectDir "/projects/project-a"
gradleVersion "1.1"
}
targetBuild {
projectDir "/projects/project-b"
gradleVersion "1.2"
}
}
The example above specifies a comparison between two different projects using two different Gradle
versions.
§
Trying Gradle upgrades
You can use the build comparison functionality to very quickly try a new Gradle version with your build.
To try your current build with a different Gradle version, simply add the following to the build.gradle of
the root project .
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apply plugin: 'compare-gradle-builds'
compareGradleBuilds {
targetBuild.gradleVersion = "«gradle version»"
}
Then simply execute the compareGradleBuilds task. You will see the console output of the “source” and
“target” builds as they are executing.
§
The comparison “result”
If there are any differences between the compared outcomes , the task will fail. The location of the HTML
report providing insight into the comparison will be given. If all compared outcomes are found to be identical,
and there are no uncompared outcomes, and there are no unknown build outcomes, the task will succeed.
You can configure the task to not fail on compared outcome differences by setting the ignoreFailures
property to true.
compareGradleBuilds {
ignoreFailures = true
}
§
Which archives are compared?
For an archive to be a candidate for comparison, it must be added as an artifact of the archives
configuration. Take a look at Publishing artifacts for more information on how to configure and add artifacts.
The archive must also have been produced by a Zip, Jar, War, Ear task. Future versions of Gradle will
support increased flexibility in this area.
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Publishing artifacts
Note: This chapter describes the original publishing mechanism available in Gradle 1.0: in Gradle
1.3 a new mechanism for publishing was introduced. While this new mechanism is incubating and
not yet complete, it introduces some new concepts and features that do (and will) make Gradle
publishing even more powerful.
You can read about the new publishing plugins in Ivy Publishing (new) and Maven Publishing (new).
Please try them out and give us feedback.
§
Introduction
This chapter is about how you declare the outgoing artifacts of your project, and how to work with them (e.g.
upload them). We define the artifacts of the projects as the files the project provides to the outside world.
This might be a library or a ZIP distribution or any other file. A project can publish as many artifacts as it
wants.
§
Artifacts and configurations
Like dependencies, artifacts are grouped by configurations. In fact, a configuration can contain both artifacts
and dependencies at the same time.
For each configuration in your project, Gradle provides the tasks uploadConfigurationName and buildConfigurat
.[12] Execution of these tasks will build or upload the artifacts belonging to the respective configuration.
the section called “Dependency configurations” shows the configurations added by the Java plugin. Two of
the configurations are relevant for the usage with artifacts. The archives configuration is the standard
configuration to assign your artifacts to. The Java plugin automatically assigns the default jar to this
configuration. We will talk more about the runtime configuration in the section called “More about project
libraries”. As with dependencies, you can declare as many custom configurations as you like and assign
artifacts to them.
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Declaring artifacts
§
Declaring artifacts
§
Archive task artifacts
You can use an archive task to define an artifact:
Example 219. Defining an artifact using an archive task
build.gradle
task myJar(type: Jar)
artifacts {
archives myJar
}
It is important to note that the custom archives you are creating as part of your build are not automatically
assigned to any configuration. You have to explicitly do this assignment.
§
File artifacts
You can also use a file to define an artifact:
Example 220. Defining an artifact using a file
build.gradle
def someFile = file('build/somefile.txt')
artifacts {
archives someFile
}
Gradle will figure out the properties of the artifact based on the name of the file. You can customize these
properties:
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Example 221. Customizing an artifact
build.gradle
task myTask(type: MyTaskType) {
destFile = file('build/somefile.txt')
}
artifacts {
archives(myTask.destFile) {
name 'my-artifact'
type 'text'
builtBy myTask
}
}
There is a map-based syntax for defining an artifact using a file. The map must include a file entry that
defines the file. The map may include other artifact properties:
Example 222. Map syntax for defining an artifact using a file
build.gradle
task generate(type: MyTaskType) {
destFile = file('build/somefile.txt')
}
artifacts {
archives file: generate.destFile, name: 'my-artifact', type: 'text', builtBy: generate
}
§
Publishing artifacts
We have said that there is a specific upload task for each configuration. Before you can do an upload, you
have to configure the upload task and define where to publish the artifacts to. The repositories you have
defined (as described in Declaring Repositories) are not automatically used for uploading. In fact, some of
those repositories only allow downloading artifacts, not uploading. Here is an example of how you can
configure the upload task of a configuration:
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Example 223. Configuration of the upload task
build.gradle
repositories {
flatDir {
name "fileRepo"
dirs "repo"
}
}
uploadArchives {
repositories {
add project.repositories.fileRepo
ivy {
credentials {
username "username"
password "pw"
}
url "http://repo.mycompany.com"
}
}
}
As you can see, you can either use a reference to an existing repository or create a new repository.
If an upload repository is defined with multiple patterns, Gradle must choose a pattern to use for uploading
each file. By default, Gradle will upload to the pattern defined by the url parameter, combined with the
optional layout parameter. If no url parameter is supplied, then Gradle will use the first defined artifactPattern
for uploading, or the first defined ivyPattern for uploading Ivy files, if this is set.
Uploading to a Maven repository is described in the section called “Interacting with Maven repositories”.
§
More about project libraries
If your project is supposed to be used as a library, you need to define what are the artifacts of this library and
what are the dependencies of these artifacts. The Java plugin adds a runtime configuration for this
purpose, with the implicit assumption that the runtime dependencies are the dependencies of the artifact
you want to publish. Of course this is fully customizable. You can add your own custom configuration or let
the existing configurations extend from other configurations. You might have a different group of artifacts
which have a different set of dependencies. This mechanism is very powerful and flexible.
If someone wants to use your project as a library, she simply needs to declare which configuration of the
dependency to depend on. A Gradle dependency offers the configuration property to declare this. If this
is not specified, the default configuration is used (see the section called “Defining the scope of a
dependency with configurations”). Using your project as a library can either happen from within a
multi-project build or by retrieving your project from a repository. In the latter case, an ivy.xml descriptor in
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the repository is supposed to contain all the necessary information. If you work with Maven repositories you
don’t have the flexibility as described above. For how to publish to a Maven repository, see the section the
section called “Interacting with Maven repositories”.
[12] To be exact, the Base plugin provides those tasks. This plugin is automatically applied if you use the
Java plugin.
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The Maven Plugin
Note: This chapter is a work in progress
The Maven plugin adds support for deploying artifacts to Maven repositories.
§
Usage
To use the Maven plugin, include the following in your build script:
Example 224. Using the Maven plugin
build.gradle
apply plugin: 'maven'
§
Tasks
The Maven plugin defines the following tasks:
Table 23. Maven plugin - tasks
Task
name
Depends on Type
All
tasks
that
build
install t h e
associated
archives.
Description
Installs the associated artifacts to the local Maven cache, including Maven metadata
Upload
generation. By default the install task is associated with the archives configuration. This
configuration has by default only the default jar as an element. To learn more about installing to
the local repository, see: the section called “Installing to the local repository”
§
Dependency management
The Maven plugin does not define any dependency configurations.
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Convention properties
§
Convention properties
The Maven plugin defines the following convention properties:
Table 24. Maven plugin - properties
Property name
Type
Default value
Description
mavenPomDir
File
The directory where the generated
${project.buildDir} /poms
POMs are written to.
Instructions
conf2ScopeMappings Conf2ScopeMappingContainer n/a
for
mapping
Gradle
configurations to Maven scopes. See
the
section
called
“Dependency
mapping”.
These properties are provided by a MavenPluginConvention convention object.
§
Convention methods
The maven plugin provides a factory method for creating a POM. This is useful if you need a POM without
the context of uploading to a Maven repo.
Example 225. Creating a standalone pom.
build.gradle
task writeNewPom {
doLast {
pom {
project {
inceptionYear '2008'
licenses {
license {
name 'The Apache Software License, Version 2.0'
url 'http://www.apache.org/licenses/LICENSE-2.0.txt'
distribution 'repo'
}
}
}
}.writeTo("$buildDir/newpom.xml")
}
}
Amongst other things, Gradle supports the same builder syntax as polyglot Maven. To learn more about the
Gradle Maven POM object, see MavenPom. See also: MavenPluginConvention
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§
Interacting with Maven repositories
§
Introduction
With Gradle you can deploy to remote Maven repositories or install to your local Maven repository. This
includes all Maven metadata manipulation and works also for Maven snapshots. In fact, Gradle’s
deployment is 100 percent Maven compatible as we use the native Maven Ant tasks under the hood.
Deploying to a Maven repository is only half the fun if you don’t have a POM. Fortunately Gradle can
generate this POM for you using the dependency information it has.
§
Deploying to a Maven repository
Let’s assume your project produces just the default jar file. Now you want to deploy this jar file to a remote
Maven repository.
Example 226. Upload of file to remote Maven repository
build.gradle
apply plugin: 'maven'
uploadArchives {
repositories {
mavenDeployer {
repository(url: "file://localhost/tmp/myRepo/")
}
}
}
That is all. Calling the uploadArchives task will generate the POM and deploys the artifact and the POM
to the specified repository.
There is more work to do if you need support for protocols other than file. In this case the native Maven
code we delegate to needs additional libraries. Which libraries are needed depends on what protocol you
plan to use. The available protocols and the corresponding libraries are listed in Table 25 (those libraries
have transitive dependencies which have transitive dependencies).[13] For example, to use the ssh protocol
you can do:
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Example 227. Upload of file via SSH
build.gradle
configurations {
deployerJars
}
repositories {
mavenCentral()
}
dependencies {
deployerJars "org.apache.maven.wagon:wagon-ssh:2.2"
}
uploadArchives {
repositories.mavenDeployer {
configuration = configurations.deployerJars
repository(url: "scp://repos.mycompany.com/releases") {
authentication(userName: "me", password: "myPassword")
}
}
}
There are many configuration options for the Maven deployer. The configuration is done via a Groovy
builder. All the elements of this tree are Java beans. To configure the simple attributes you pass a map to
the bean elements. To add bean elements to its parent, you use a closure. In the example above repository
and authentication are such bean elements. Table 26 lists the available bean elements and a link to the
Javadoc of the corresponding class. In the Javadoc you can see the possible attributes you can set for a
particular element.
In Maven you can define repositories and optionally snapshot repositories. If no snapshot repository is
defined, releases and snapshots are both deployed to the repository element. Otherwise snapshots are
deployed to the snapshotRepository element.
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Table 25. Protocol jars for Maven deployment
Protocol
Library
http
org.apache.maven.wagon:wagon-http:2.2
ssh
org.apache.maven.wagon:wagon-ssh:2.2
ssh-external
org.apache.maven.wagon:wagon-ssh-external:2.2
ftp
org.apache.maven.wagon:wagon-ftp:2.2
webdav
org.apache.maven.wagon:wagon-webdav:1.0-beta-2
file
-
Table 26. Configuration elements of the MavenDeployer
Element
Javadoc
root
MavenDeployer
repository
org.apache.maven.artifact.ant.RemoteRepository
authentication
org.apache.maven.artifact.ant.Authentication
releases
org.apache.maven.artifact.ant.RepositoryPolicy
snapshots
org.apache.maven.artifact.ant.RepositoryPolicy
proxy
org.apache.maven.artifact.ant.Proxy
snapshotRepository
org.apache.maven.artifact.ant.RemoteRepository
§
Installing to the local repository
The Maven plugin adds an install task to your project. This task depends on all the archives task of the archives
configuration. It installs those archives to your local Maven repository. If the default location for the local
repository is redefined in a Maven settings.xml, this is considered by this task.
Maven POM generation
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§
Maven POM generation
When deploying an artifact to a Maven repository, Gradle automatically generates a POM for it. The groupId
, artifactId, version and packaging elements used for the POM default to the values shown in the
table below. The dependency elements are created from the project’s dependency declarations.
Table 27. Default Values for Maven POM generation
Maven Element
Default Value
groupId
project.group
artifactId
uploadTask.repositories.mavenDeployer.pom.artifactId (if set) or archiveTask.baseName.
version
project.version
packaging
archiveTask.extension
Here, uploadTask and archiveTask refer to the tasks used for uploading and generating the archive,
respectively (for example uploadArchives and jar). archiveTask.baseName defaults to project.archivesBase
which in turn defaults to project.name.
Note: When you set the “archiveTask.baseName” property to a value other than the default,
you’ll also have to set uploadTask.repositories.mavenDeployer.pom.artifactId to the
same value. Otherwise, the project at hand may be referenced with the wrong artifact ID from
generated POMs for other projects in the same build.
Generated POMs can be found in <buildDir>/poms. They can be further customized via the MavenPom
API. For example, you might want the artifact deployed to the Maven repository to have a different version or
name than the artifact generated by Gradle. To customize these you can do:
Example 228. Customization of pom
build.gradle
uploadArchives {
repositories {
mavenDeployer {
repository(url: "file://localhost/tmp/myRepo/")
pom.version = '1.0Maven'
pom.artifactId = 'myMavenName'
}
}
}
To add additional content to the POM, the pom.project builder can be used. With this builder, any element
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listed in the Maven POM reference can be added.
Example 229. Builder style customization of pom
build.gradle
uploadArchives {
repositories {
mavenDeployer {
repository(url: "file://localhost/tmp/myRepo/")
pom.project {
licenses {
license {
name 'The Apache Software License, Version 2.0'
url 'http://www.apache.org/licenses/LICENSE-2.0.txt'
distribution 'repo'
}
}
}
}
}
}
Note: groupId, artifactId, version, and packaging should always be set directly on the pom object.
Example 230. Modifying auto-generated content
build.gradle
def installer = install.repositories.mavenInstaller
def deployer = uploadArchives.repositories.mavenDeployer
[installer, deployer]*.pom*.whenConfigured {pom ->
pom.dependencies.find {dep -> dep.groupId == 'group3' && dep.artifactId == 'runtime' }
}
If you have more than one artifact to publish, things work a little bit differently. See the section called
“Multiple artifacts per project”.
To customize the settings for the Maven installer (see the section called “Installing to the local repository”),
you can do:
Example 231. Customization of Maven installer
build.gradle
install {
repositories.mavenInstaller {
pom.version = '1.0Maven'
pom.artifactId = 'myName'
}
}
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§
Multiple artifacts per project
Maven can only deal with one artifact per project. This is reflected in the structure of the Maven POM. We
think there are many situations where it makes sense to have more than one artifact per project. In such a
case you need to generate multiple POMs. In such a case you have to explicitly declare each artifact you
want to publish to a Maven repository. The MavenDeployer and the MavenInstaller both provide an API for
this:
Example 232. Generation of multiple poms
build.gradle
uploadArchives {
repositories {
mavenDeployer {
repository(url: "file://localhost/tmp/myRepo/")
addFilter('api') {artifact, file ->
artifact.name == 'api'
}
addFilter('service') {artifact, file ->
artifact.name == 'service'
}
pom('api').version = 'mySpecialMavenVersion'
}
}
}
You need to declare a filter for each artifact you want to publish. This filter defines a boolean expression for
which Gradle artifact it accepts. Each filter has a POM associated with it which you can configure. To learn
more about this have a look at PomFilterContainer and its associated classes.
§
Dependency mapping
The Maven plugin configures the default mapping between the Gradle configurations added by the Java and
War plugin and the Maven scopes. Most of the time you don’t need to touch this and you can safely skip this
section. The mapping works like the following. You can map a configuration to one and only one scope.
Different configurations can be mapped to one or different scopes. You can also assign a priority to a
particular configuration-to-scope mapping. Have a look at Conf2ScopeMappingContainer to learn more.
To access the mapping configuration you can say:
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Example 233. Accessing a mapping configuration
build.gradle
task mappings {
doLast {
println conf2ScopeMappings.mappings
}
}
Gradle exclude rules are converted to Maven excludes if possible. Such a conversion is possible if in the
Gradle exclude rule the group as well as the module name is specified (as Maven needs both in contrast to
Ivy). Per-configuration excludes are also included in the Maven POM, if they are convertible.
[13] It is planned for a future release to provide out-of-the-box support for this
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The Signing Plugin
The signing plugin adds the ability to digitally sign built files and artifacts. These digital signatures can then
be used to prove who built the artifact the signature is attached to as well as other information such as when
the signature was generated.
The signing plugin currently only provides support for generating OpenPGP signatures (which is the
signature format required for publication to the Maven Central Repository).
§
Usage
To use the Signing plugin, include the following in your build script:
Example 234. Using the Signing plugin
build.gradle
apply plugin: 'signing'
§
Signatory credentials
In order to create OpenPGP signatures, you will need a key pair (instructions on creating a key pair using
the GnuPG tools can be found in the GnuPG HOWTOs). You need to provide the signing plugin with your
key information, which means three things:
The public key ID (an 8 character hexadecimal string).
The absolute path to the secret key ring file containing your private key.
The passphrase used to protect your private key.
These items must be supplied as the values of properties signing.keyId, signing.secretKeyRingFile
, and signing.password respectively. Given the personal and private nature of these values, a good
practice is to store them in the user gradle.properties file (described in the section called “System
properties”).
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signing.keyId=24875D73
signing.password=secret
signing.secretKeyRingFile=/Users/me/.gnupg/secring.gpg
If specifying this information (especially signing.password) in the user gradle.properties file is not
feasible for your environment, you can source the information however you need to and set the project
properties manually.
import org.gradle.plugins.signing.Sign
gradle.taskGraph.whenReady { taskGraph ->
if (taskGraph.allTasks.any { it instanceof Sign }) {
// Use Java 6's console to read from the console (no good for
// a CI environment)
Console console = System.console()
console.printf "\n\nWe have to sign some things in this build." +
"\n\nPlease enter your signing details.\n\n"
def id = console.readLine("PGP Key Id: ")
def file = console.readLine("PGP Secret Key Ring File (absolute path): ")
def password = console.readPassword("PGP Private Key Password: ")
allprojects { ext."signing.keyId" = id }
allprojects { ext."signing.secretKeyRingFile" = file }
allprojects { ext."signing.password" = password }
console.printf "\nThanks.\n\n"
}
}
Note that the presence of a null value for any these three properties will cause an exception.
§
Using OpenPGP subkeys
OpenPGP supports subkeys, which are like the normal keys, except they’re bound to a master key pair. One
feature of OpenPGP subkeys is that they can be revoked independently of the master keys which makes key
management easier. A practical case study of how subkeys can be leveraged in software development can
be read on the Debian wiki.
The signing plugin supports OpenPGP subkeys out of the box. Just specify a subkey ID as the value in the signing.key
property.
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Using gpg-agent
§
Using gpg-agent
By default the signing plugin uses a Java-based implementation of PGP for signing. This implementation
cannot use the gpg-agent program for managing private keys, though. If you want to use the gpg-agent, you
can change the signatory implementation used by the signing plugin:
Example 235. Sign with GnuPG
build.gradle
signing {
useGpgCmd()
sign configurations.archives
}
This tells the signing plugin to use the GnupgSignatory instead of the default PgpSignatory. The GnupgSignatory
relies on the gpg2 program to sign the artifacts. Of course, this requires that GnuPG is installed.
Without any further configuration the gpg2 (on Windows: gpg2.exe) executable found on the PATH will be
used. The password is supplied by the gpg-agent and the default key is used for signing.
§
Gnupg signatory configuration
The GnupgSignatory supports a number of configuration options for controlling how gpg is invoked. These
are typically set in gradle.properties:
Example 236. Configure the GnupgSignatory
gradle.properties
signing.gnupg.executable=gpg
signing.gnupg.useLegacyGpg=true
signing.gnupg.homeDir=gnupg-home
signing.gnupg.optionsFile=gnupg-home/gpg.conf
signing.gnupg.keyName=24875D73
signing.gnupg.passphrase=gradle
signing.gnupg.executable
The gpg executable that is invoked for signing. The default value of this property depends on useLegacyGpg
. If that is true then the default value of executable is "gpg" otherwise it is "gpg2".
signing.gnupg.useLegacyGpg
Must be true if GnuPG version 1 is used and false otherwise. The default value of the property is false
.
signing.gnupg.homeDir
Sets the home directory for GnuPG. If not given the default home directory of GnuPG is used.
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signing.gnupg.optionsFile
Sets a custom options file for GnuPG. If not given GnuPG’s default configuration file is used.
signing.gnupg.keyName
The id of the key that should be used for signing. If not given then the default key configured in GnuPG
will be used.
signing.gnupg.passphrase
The passphrase for unlocking the secret key. If not given then the gpg-agent program is used for getting
the passphrase.
All configuration properties are optional.
§
Specifying what to sign
As well as configuring how things are to be signed (i.e. the signatory configuration), you must also specify
what is to be signed. The Signing plugin provides a DSL that allows you to specify the tasks and/or
configurations that should be signed.
§
Signing Configurations
It is common to want to sign the artifacts of a configuration. For example, the Java plugin configures a jar to
build and this jar artifact is added to the archives configuration. Using the Signing DSL, you can specify
that all of the artifacts of this configuration should be signed.
Example 237. Signing a configuration
build.gradle
signing {
sign configurations.archives
}
This will create a task (of type Sign) in your project named “signArchives”, that will build any archives
artifacts (if needed) and then generate signatures for them. The signature files will be placed alongside the
artifacts being signed.
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Example 238. Signing a configuration output
Output of gradle signArchives
> gradle signArchives
:compileJava
:processResources
:classes
:jar
:signArchives
BUILD SUCCESSFUL in 0s
4 actionable tasks: 4 executed
§
Signing Tasks
In some cases the artifact that you need to sign may not be part of a configuration. In this case you can
directly sign the task that produces the artifact to sign.
Example 239. Signing a task
build.gradle
task stuffZip (type: Zip) {
baseName = "stuff"
from "src/stuff"
}
signing {
sign stuffZip
}
This will create a task (of type Sign) in your project named “signStuffZip”, that will build the input task’s
archive (if needed) and then sign it. The signature file will be placed alongside the artifact being signed.
Example 240. Signing a task output
Output of gradle signStuffZip
> gradle signStuffZip
:stuffZip
:signStuffZip
BUILD SUCCESSFUL in 0s
2 actionable tasks: 2 executed
For a task to be “signable”, it must produce an archive of some type. Tasks that do this are the Tar, Zip,
Jar, War and Ear tasks.
Conditional Signing
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§
Conditional Signing
A common usage pattern is to only sign build artifacts under certain conditions. For example, you may not
wish to sign artifacts for non-release versions. To achieve this, you can specify that signing is only required
under certain conditions.
Example 241. Conditional signing
build.gradle
version = '1.0-SNAPSHOT'
ext.isReleaseVersion = !version.endsWith("SNAPSHOT")
signing {
required { isReleaseVersion && gradle.taskGraph.hasTask("uploadArchives") }
sign configurations.archives
}
In this example, we only want to require signing if we are building a release version and we are going to
publish it. Because we are inspecting the task graph to determine if we are going to be publishing, we must
set
the
signing.required
property
to
a
closure
to
defer
the
evaluation.
See
SigningExtension.setRequired(java.lang.Object) for more information.
§
Publishing the signatures
When specifying what is to be signed via the Signing DSL, the resultant signature artifacts are automatically
added to the signatures and archives dependency configurations. This means that if you want to
upload your signatures to your distribution repository along with the artifacts you simply execute the uploadArchives
task as normal.
§
Signing POM files
Note: Signing the generated POM file generated by the Maven Publishing plugin is currently not
supported. Future versions of Gradle might add this functionality.
When deploying signatures for your artifacts to a Maven repository, you will also want to sign the published
POM
file.
The
signing
plugin
adds
a
signing.signPom()
(see:
SigningExtension.signPom(org.gradle.api.artifacts.maven.MavenDeployment,
groovy.lang.Closure)) method that can be used in the beforeDeployment() block in your upload
task configuration.
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Example 242. Signing a POM for deployment
build.gradle
uploadArchives {
repositories {
mavenDeployer {
beforeDeployment { MavenDeployment deployment -> signing.signPom(deployment) }
}
}
}
When signing is not required and the POM cannot be signed due to insufficient configuration (i.e. no
credentials for signing) then the signPom() method will silently do nothing.
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Ivy Publishing (new)
Note: This chapter describes the new incubating Ivy publishing support provided by the “ivy-publish
” plugin. Eventually this new publishing support will replace publishing via the Upload task.
If you are looking for documentation on the original Ivy publishing support using the Upload task
please see Publishing artifacts.
This chapter describes how to publish build artifacts in the Apache Ivy format, usually to a repository for
consumption by other builds or projects. What is published is one or more artifacts created by the build, and
an Ivy module descriptor (normally ivy.xml) that describes the artifacts and the dependencies of the
artifacts, if any.
A published Ivy module can be consumed by Gradle (see Declaring Dependencies) and other tools that
understand the Ivy format.
§
The “ivy-publish” Plugin
The ability to publish in the Ivy format is provided by the “ ivy-publish” plugin.
The “publishing” plugin creates an extension on the project named “ publishing” of type
PublishingExtension. This extension provides a container of named publications and a container of
named repositories. The “ivy-publish” plugin works with IvyPublication publications and
IvyArtifactRepository repositories.
Example 243. Applying the “ivy-publish” plugin
build.gradle
apply plugin: 'ivy-publish'
Applying the “ivy-publish” plugin does the following:
Applies the “publishing” plugin
Establishes a rule to automatically create a GenerateIvyDescriptor task for each IvyPublication
added (see the section called “Publications”).
Establishes a rule to automatically create a PublishToIvyRepository task for the combination of each
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IvyPublication added (see the section called “Publications”), with each IvyArtifactRepository
added (see the section called “Repositories”).
§
Publications
Note: If you are not familiar with project artifacts and configurations, you should read Publishing
artifacts, which introduces these concepts. This chapter also describes “publishing artifacts” using a
different mechanism than what is described in this chapter. The publishing functionality described
here will eventually supersede that functionality.
Publication objects describe the structure/configuration of a publication to be created. Publications are
published to repositories via tasks, and the configuration of the publication object determines exactly what is
published.
All
of
the
publications
of
a
project
are
defined
in
the
PublishingExtension.getPublications() container. Each publication has a unique name within the
project.
For the “ivy-publish” plugin to have any effect, an IvyPublication must be added to the set of
publications. This publication determines which artifacts are actually published as well as the details included
in the associated Ivy module descriptor file. A publication can be configured by adding components,
customizing artifacts, and by modifying the generated module descriptor file directly.
§
Publishing a Software Component
The simplest way to publish a Gradle project to an Ivy repository is to specify a SoftwareComponent to
publish. The components presently available for publication are:
Table 28. Software Components
Name
Provided By
Artifacts
Dependencies
java
Java Plugin
Generated jar file
Dependencies from 'runtime' configuration
web
War Plugin
Generated war file
No dependencies
In the following example, artifacts and runtime dependencies are taken from the java component, which is
added by the Java Plugin.
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Example 244. Publishing a Java module to Ivy
build.gradle
publications {
ivyJava(IvyPublication) {
from components.java
}
}
§
Publishing custom artifacts
It is also possible to explicitly configure artifacts to be included in the publication. Artifacts are commonly
supplied as raw files, or as instances of AbstractArchiveTask (e.g. Jar, Zip).
For each custom artifact, it is possible to specify the name, extension, type, classifier and conf
values to use for publication. Note that each artifacts must have a unique name/classifier/extension
combination.
Configure custom artifacts as follows:
Example 245. Publishing additional artifact to Ivy
build.gradle
task sourceJar(type: Jar) {
from sourceSets.main.java
classifier "source"
}
publishing {
publications {
ivy(IvyPublication) {
from components.java
artifact(sourceJar) {
type "source"
conf "compile"
}
}
}
}
See the IvyPublication class in the API documentation for more detailed information on how artifacts
can be customized.
Identity values for the published project
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§
Identity values for the published project
The generated Ivy module descriptor file contains an <info> element that identifies the module. The default
identity values are derived from the following:
organisation - Project.getGroup()
module - Project.getName()
revision - Project.getVersion()
status - Project.getStatus()
branch - (not set)
Overriding the default identity values is easy: simply specify the organisation, module or revision
attributes when configuring the IvyPublication. The status and branch attributes can be set via the descriptor
property (see IvyModuleDescriptorSpec). The descriptor property can also be used to add
additional custom elements as children of the <info> element.
Example 246. customizing the publication identity
build.gradle
publishing {
publications {
ivy(IvyPublication) {
organisation 'org.gradle.sample'
module 'project1-sample'
revision '1.1'
descriptor.status = 'milestone'
descriptor.branch = 'testing'
descriptor.extraInfo 'http://my.namespace', 'myElement', 'Some value'
from components.java
}
}
}
Tip: Certain repositories are not able to handle all supported characters. For example, the ':'
character cannot be used as an identifier when publishing to a filesystem-backed repository on
Windows.
Gradle will handle any valid Unicode character for organisation, module and revision (as well as artifact
name, extension and classifier). The only values that are explicitly prohibited are ‘\’, ‘/’ and any ISO control
character. The supplied values are validated early during publication.
Modifying the generated module descriptor
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§
Modifying the generated module descriptor
At times, the module descriptor file generated from the project information will need to be tweaked before
publishing. The “ivy-publish” plugin provides a hook to allow such modification.
Example 247. Customizing the module descriptor file
build.gradle
publications {
ivyCustom(IvyPublication) {
descriptor.withXml {
asNode().info[0].appendNode('description',
'A demonstration of ivy descriptor customization')
}
}
}
In this example we are simply adding a 'description' element to the generated Ivy dependency descriptor, but
this hook allows you to modify any aspect of the generated descriptor. For example, you could replace the
version range for a dependency with the actual version used to produce the build.
See IvyModuleDescriptorSpec.withXml(org.gradle.api.Action) in the API documentation for
more information.
It is possible to modify virtually any aspect of the created descriptor should you need to. This means that it is
also possible to modify the descriptor in such a way that it is no longer a valid Ivy module descriptor, so care
must be taken when using this feature.
The identifier (organisation, module, revision) of the published module is an exception; these values cannot
be modified in the descriptor using the withXML hook.
§
Publishing multiple modules
Sometimes it’s useful to publish multiple modules from your Gradle build, without creating a separate Gradle
subproject. An example is publishing a separate API and implementation jar for your library. With Gradle this
is simple:
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Example 248. Publishing multiple modules from a single project
build.gradle
task apiJar(type: Jar) {
baseName "publishing-api"
from sourceSets.main.output
exclude '**/impl/**'
}
publishing {
publications {
impl(IvyPublication) {
organisation 'org.gradle.sample.impl'
module 'project2-impl'
revision '2.3'
from components.java
}
api(IvyPublication) {
organisation 'org.gradle.sample'
module 'project2-api'
revision '2'
}
}
}
If a project defines multiple publications then Gradle will publish each of these to the defined repositories.
Each publication must be given a unique identity as described above.
§
Repositories
Publications are published to repositories. The repositories to publish to are defined by the
PublishingExtension.getRepositories() container.
Example 249. Declaring repositories to publish to
build.gradle
repositories {
ivy {
// change to point to your repo, e.g. http://my.org/repo
url "$buildDir/repo"
}
}
The DSL used to declare repositories for publishing is the same DSL that is used to declare repositories for
dependencies (RepositoryHandler). However, in the context of Ivy publication only the repositories
created by the ivy() methods can be used as publication destinations. You cannot publish an IvyPublication
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to a Maven repository for example.
§
Performing a publish
The “ivy-publish” plugin automatically creates a PublishToIvyRepository task for each
IvyPublication and IvyArtifactRepository combination in the publishing.publications and publishing
containers respectively.
The created task is named “publish« PUBNAME »PublicationTo« REPONAME »Repository”, which is “publishIvyJa
” for this example. This task is of type PublishToIvyRepository.
Example 250. Choosing a particular publication to publish
build.gradle
apply plugin: 'java'
apply plugin: 'ivy-publish'
group = 'org.gradle.sample'
version = '1.0'
publishing {
publications {
ivyJava(IvyPublication) {
from components.java
}
}
repositories {
ivy {
// change to point to your repo, e.g. http://my.org/repo
url "$buildDir/repo"
}
}
}
Output of gradle publishIvyJavaPublicationToIvyRepository
> gradle publishIvyJavaPublicationToIvyRepository
:generateDescriptorFileForIvyJavaPublication
:compileJava NO-SOURCE
:processResources NO-SOURCE
:classes UP-TO-DATE
:jar
:publishIvyJavaPublicationToIvyRepository
BUILD SUCCESSFUL in 0s
3 actionable tasks: 3 executed
The “publish” lifecycle task
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§
The “publish” lifecycle task
The “publish” plugin (that the “ivy-publish” plugin implicitly applies) adds a lifecycle task that can be
used to publish all publications to all applicable repositories named “publish”.
In more concrete terms, executing this task will execute all PublishToIvyRepository tasks in the
project. This is usually the most convenient way to perform a publish.
Example 251. Publishing all publications via the “publish” lifecycle task
Output of gradle publish
> gradle publish
:generateDescriptorFileForIvyJavaPublication
:compileJava NO-SOURCE
:processResources NO-SOURCE
:classes UP-TO-DATE
:jar
:publishIvyJavaPublicationToIvyRepository
:publish
BUILD SUCCESSFUL in 0s
3 actionable tasks: 3 executed
§
Generating the Ivy module descriptor file without publishing
At times it is useful to generate the Ivy module descriptor file (normally ivy.xml) without publishing your
module to an Ivy repository. Since descriptor file generation is performed by a separate task, this is very
easy to do.
The “ivy-publish” plugin creates one GenerateIvyDescriptor task for each registered
IvyPublication, named “generateDescriptorFileFor« PUBNAME »Publication”, which will be “generateDesc
” for the previous example of the “ivyJava” publication.
You can specify where the generated Ivy file will be located by setting the destination property on the
generated task. By default this file is written to “build/publications/« PUBNAME »/ivy.xml”.
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Example 252. Generating the Ivy module descriptor file
build.gradle
model {
tasks.generateDescriptorFileForIvyCustomPublication {
destination = file("$buildDir/generated-ivy.xml")
}
}
Output of gradle generateDescriptorFileForIvyCustomPublication
> gradle generateDescriptorFileForIvyCustomPublication
:generateDescriptorFileForIvyCustomPublication
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
Note: The “ivy-publish” plugin leverages some experimental support for late plugin
configuration, and the GenerateIvyDescriptor task will not be constructed until the publishing
extension is configured. The simplest way to ensure that the publishing plugin is configured when
you attempt to access the GenerateIvyDescriptor task is to place the access inside a model
block, as the example above demonstrates.
The
same
applies
to
any
attempt
to
access
publication-specific
tasks
like
PublishToIvyRepository. These tasks should be referenced from within a model block.
§
Complete example
The following example demonstrates publishing with a multi-project build. Each project publishes a Java
component and a configured additional source artifact. The descriptor file is customized to include the
project description for each project.
Example 253. Publishing a Java module
build.gradle
subprojects {
apply plugin: 'java'
apply plugin: 'ivy-publish'
version = '1.0'
group = 'org.gradle.sample'
repositories {
mavenCentral()
}
task sourceJar(type: Jar) {
from sourceSets.main.java
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classifier "source"
}
}
project(":project1") {
description = "The first project"
dependencies {
compile 'junit:junit:4.12', project(':project2')
}
}
project(":project2") {
description = "The second project"
dependencies {
compile 'commons-collections:commons-collections:3.2.2'
}
}
subprojects {
publishing {
repositories {
ivy {
// change to point to your repo, e.g. http://my.org/repo
url "${rootProject.buildDir}/repo"
}
}
publications {
ivy(IvyPublication) {
from components.java
artifact(sourceJar) {
type "source"
conf "compile"
}
descriptor.withXml {
asNode().info[0].appendNode('description', description)
}
}
}
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}
}
The result is that the following artifacts will be published for each project:
The Ivy module descriptor file: “ivy-1.0.xml”.
The primary “jar” artifact for the Java component: “project1-1.0.jar”.
The source “jar” artifact that has been explicitly configured: “project1-1.0-source.jar”.
When project1 is published, the module descriptor (i.e. the ivy.xml file) that is produced will look like:
Tip: Note that «PUBLICATION-TIME-STAMP» in this example Ivy module descriptor will be the
timestamp of when the descriptor was generated.
Example 254. Example generated ivy.xml
output-ivy.xml
<?xml version="1.0" encoding="UTF-8"?>
<ivy-module version="2.0">
<info organisation="org.gradle.sample" module="project1" revision="1.0" status="integrat
<description>The first project</description>
</info>
<configurations>
<conf name="compile" visibility="public"/>
<conf name="default" visibility="public" extends="compile,runtime"/>
<conf name="runtime" visibility="public"/>
</configurations>
<publications>
<artifact name="project1" type="jar" ext="jar" conf="compile"/>
<artifact name="project1" type="source" ext="jar" conf="compile" m:classifier="source"
</publications>
<dependencies>
<dependency org="junit" name="junit" rev="4.12" conf="compile-&gt;default"/>
<dependency org="org.gradle.sample" name="project2" rev="1.0" conf="compile-&gt;defaul
</dependencies>
</ivy-module>
§
Future features
The “ivy-publish” plugin functionality as described above is incomplete, as the feature is still incubating.
In upcoming Gradle releases, the functionality will be expanded to include (but not limited to):
Convenient customization of module attributes (module, organisation etc.)
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Convenient customization of dependencies reported in module descriptor.
Multiple discrete publications per project
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Maven Publishing (new)
Note: This chapter describes the new incubating Maven publishing support provided by the “maven-publish
” plugin. Eventually this new publishing support will replace publishing via the Upload task.
Note: Signing the generated POM file generated by this plugin is currently not supported. Future
versions of Gradle might add this functionality. Please use the Maven plugin for the purpose of
publishing your artifacts to Maven Central.
If you are looking for documentation on the original Maven publishing support using the Upload
task please see Publishing artifacts.
This chapter describes how to publish build artifacts to an Apache Maven Repository. A module published to
a Maven repository can be consumed by Maven, Gradle (see Declaring Dependencies) and other tools that
understand the Maven repository format.
§
The “maven-publish” Plugin
The ability to publish in the Maven format is provided by the “ maven-publish” plugin.
The “publishing” plugin creates an extension on the project named “ publishing” of type
PublishingExtension. This extension provides a container of named publications and a container of
named repositories. The “maven-publish” plugin works with MavenPublication publications and
MavenArtifactRepository repositories.
Example 255. Applying the 'maven-publish' plugin
build.gradle
apply plugin: 'maven-publish'
Applying the “maven-publish” plugin does the following:
Applies the “publishing” plugin
Establishes a rule to automatically create a GenerateMavenPom task for each MavenPublication added
(see the section called “Publications”).
Establishes a rule to automatically create a PublishToMavenRepository task for the combination of
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each
MavenPublication
added
(see
the
section
called
“Publications” ),
with
each
MavenArtifactRepository added (see the section called “Repositories”).
Establishes a rule to automatically create a PublishToMavenLocal task for each MavenPublication
added (seethe section called “Publications”).
§
Publications
Note: If you are not familiar with project artifacts and configurations, you should read the Publishing
artifacts that introduces these concepts. This chapter also describes “publishing artifacts” using a
different mechanism than what is described in this chapter. The publishing functionality described
here will eventually supersede that functionality.
Publication objects describe the structure/configuration of a publication to be created. Publications are
published to repositories via tasks, and the configuration of the publication object determines exactly what is
published.
All
of
the
publications
of
a
project
are
defined
in
the
PublishingExtension.getPublications() container. Each publication has a unique name within the
project.
For the “maven-publish” plugin to have any effect, a MavenPublication must be added to the set of
publications. This publication determines which artifacts are actually published as well as the details included
in the associated POM file. A publication can be configured by adding components, customizing artifacts,
and by modifying the generated POM file directly.
§
Publishing a Software Component
The simplest way to publish a Gradle project to a Maven repository is to specify a SoftwareComponent to
publish. The components presently available for publication are:
Table 29. Software Components
Name
Provided By
Artifacts
Dependencies
java
The Java Plugin
Generated jar file
Dependencies from 'runtime' configuration
web
The War Plugin
Generated war file
No dependencies
In the following example, artifacts and runtime dependencies are taken from the java component, which is
added by the Java Plugin.
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Example 256. Adding a MavenPublication for a Java component
build.gradle
publishing {
publications {
mavenJava(MavenPublication) {
from components.java
}
}
}
§
Publishing custom artifacts
It is also possible to explicitly configure artifacts to be included in the publication. Artifacts are commonly
supplied as raw files, or as instances of AbstractArchiveTask (e.g. Jar, Zip).
For each custom artifact, it is possible to specify the extension and classifier values to use for
publication. Note that only one of the published artifacts can have an empty classifier, and all other artifacts
must have a unique classifier/extension combination.
Configure custom artifacts as follows:
Example 257. Adding additional artifact to a MavenPublication
build.gradle
task sourceJar(type: Jar) {
from sourceSets.main.allJava
}
publishing {
publications {
mavenJava(MavenPublication) {
from components.java
artifact sourceJar {
classifier "sources"
}
}
}
}
See the MavenPublication class in the API documentation for more information about how artifacts can
be customized.
Identity values in the generated POM
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§
Identity values in the generated POM
The attributes of the generated POM file will contain identity values derived from the following project
properties:
groupId - Project.getGroup()
artifactId - Project.getName()
version - Project.getVersion()
Overriding the default identity values is easy: simply specify the groupId, artifactId or version
attributes when configuring the MavenPublication.
Example 258. customizing the publication identity
build.gradle
publishing {
publications {
maven(MavenPublication) {
groupId 'org.gradle.sample'
artifactId 'project1-sample'
version '1.1'
from components.java
}
}
}
Tip: Certain repositories will not be able to handle all supported characters. For example, the ':'
character cannot be used as an identifier when publishing to a filesystem-backed repository on
Windows.
Maven restricts 'groupId' and 'artifactId' to a limited character set ( [A-Za-z0-9_\\-.]+) and Gradle
enforces this restriction. For 'version' (as well as artifact 'extension' and 'classifier'), Gradle will handle any
valid Unicode character.
The only Unicode values that are explicitly prohibited are ‘ \’, ‘/’ and any ISO control character. Supplied
values are validated early in publication.
§
Modifying the generated POM
The generated POM file may need to be tweaked before publishing. The “ maven-publish” plugin provides
a hook to allow such modification.
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Example 259. Modifying the POM file
build.gradle
publications {
mavenCustom(MavenPublication) {
pom.withXml {
asNode().appendNode('description',
'A demonstration of maven POM customization')
}
}
}
In this example we are adding a 'description' element for the generated POM. With this hook, you can modify
any aspect of the POM. For example, you could replace the version range for a dependency with the actual
version used to produce the build.
See MavenPom.withXml(org.gradle.api.Action) in the API documentation for more information.
It is possible to modify virtually any aspect of the created POM. This means that it is also possible to modify
the POM in such a way that it is no longer a valid Maven POM, so care must be taken when using this
feature.
The identifier (groupId, artifactId, version) of the published module is an exception; these values cannot be
modified in the POM using the withXML hook.
§
Publishing multiple modules
Sometimes it’s useful to publish multiple modules from your Gradle build, without creating a separate Gradle
subproject. An example is publishing a separate API and implementation jar for your library. With Gradle this
is simple:
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Example 260. Publishing multiple modules from a single project
build.gradle
task apiJar(type: Jar) {
baseName "publishing-api"
from sourceSets.main.output
exclude '**/impl/**'
}
publishing {
publications {
impl(MavenPublication) {
groupId 'org.gradle.sample.impl'
artifactId 'project2-impl'
version '2.3'
from components.java
}
api(MavenPublication) {
groupId 'org.gradle.sample'
artifactId 'project2-api'
version '2'
artifact apiJar
}
}
}
If a project defines multiple publications then Gradle will publish each of these to the defined repositories.
Each publication must be given a unique identity as described above.
§
Repositories
Publications are published to repositories. The repositories to publish to are defined by the
PublishingExtension.getRepositories() container.
Example 261. Declaring repositories to publish to
build.gradle
publishing {
repositories {
maven {
// change to point to your repo, e.g. http://my.org/repo
url "$buildDir/repo"
}
}
}
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The DSL used to declare repositories for publication is the same DSL that is used to declare repositories to
consume dependencies from, RepositoryHandler. However, in the context of Maven publication only
MavenArtifactRepository repositories can be used for publication.
§
Performing a publish
The “maven-publish” plugin automatically creates a PublishToMavenRepository task for each
MavenPublication and MavenArtifactRepository combination in the publishing.publications
and publishing.repositories containers respectively.
The created task is named “publish« PUBNAME »PublicationTo« REPONAME »Repository”.
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Example 262. Publishing a project to a Maven repository
build.gradle
apply plugin: 'java'
apply plugin: 'maven-publish'
group = 'org.gradle.sample'
version = '1.0'
publishing {
publications {
mavenJava(MavenPublication) {
from components.java
}
}
}
publishing {
repositories {
maven {
// change to point to your repo, e.g. http://my.org/repo
url "$buildDir/repo"
}
}
}
Output of gradle publish
> gradle publish
:generatePomFileForMavenJavaPublication
:compileJava
:processResources NO-SOURCE
:classes
:jar
:publishMavenJavaPublicationToMavenRepository
:publish
BUILD SUCCESSFUL in 0s
4 actionable tasks: 4 executed
In this example, a task named “publishMavenJavaPublicationToMavenRepository” is created,
which is of type PublishToMavenRepository. This task is wired into the publish lifecycle task.
Executing “gradle publish” builds the POM file and all of the artifacts to be published, and transfers
them to the repository.
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Publishing to Maven Local
§
Publishing to Maven Local
For integration with a local Maven installation, it is sometimes useful to publish the module into the local .m2
repository. In Maven parlance, this is referred to as 'installing' the module. The “ maven-publish” plugin
makes this easy to do by automatically creating a PublishToMavenLocal task for each
MavenPublication in the publishing.publications container. Each of these tasks is wired into the publishToMa
lifecycle task. You do not need to have mavenLocal in your publishing.repositories section.
The created task is named “publish« PUBNAME »PublicationToMavenLocal”.
Example 263. Publish a project to the Maven local repository
Output of gradle publishToMavenLocal
> gradle publishToMavenLocal
:generatePomFileForMavenJavaPublication
:compileJava
:processResources NO-SOURCE
:classes
:jar
:publishMavenJavaPublicationToMavenLocal
:publishToMavenLocal
BUILD SUCCESSFUL in 0s
4 actionable tasks: 4 executed
The resulting task in this example is named “publishMavenJavaPublicationToMavenLocal”. This task
is wired into the publishToMavenLocal lifecycle task. Executing “gradle publishToMavenLocal”
builds the POM file and all of the artifacts to be published, and “installs” them into the local Maven repository.
§
Generating the POM file without publishing
At times it is useful to generate a Maven POM file for a module without actually publishing. Since POM
generation is performed by a separate task, it is very easy to do so.
The task for generating the POM file is of type GenerateMavenPom, and it is given a name based on the
name of the publication: “generatePomFileFor« PUBNAME »Publication”. So in the example below,
where the publication is named “mavenCustom”, the task will be named “generatePomFileForMavenCustomPublica
”.
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Example 264. Generate a POM file without publishing
build.gradle
model {
tasks.generatePomFileForMavenCustomPublication {
destination = file("$buildDir/generated-pom.xml")
}
}
Output of gradle generatePomFileForMavenCustomPublication
> gradle generatePomFileForMavenCustomPublication
:generatePomFileForMavenCustomPublication
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
All details of the publishing model are still considered in POM generation, including components, custom artifacts
, and any modifications made via pom.withXml.
Note: The “maven-publish” plugin leverages some experimental support for late plugin
configuration, and any GenerateMavenPom tasks will not be constructed until the publishing
extension is configured. The simplest way to ensure that the publishing plugin is configured when
you attempt to access the GenerateMavenPom task is to place the access inside a model block,
as the example above demonstrates.
The
same
applies
to
any
attempt
to
access
publication-specific
tasks
like
PublishToMavenRepository. These tasks should be referenced from within a model block.
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The Distribution Plugin
Note: The distribution plugin is currently incubating. Please be aware that the DSL and other
configuration may change in later Gradle versions.
The distribution plugin facilitates building archives that serve as distributions of the project. Distribution
archives typically contain the executable application and other supporting files, such as documentation.
§
Usage
To use the distribution plugin, include the following in your build script:
Example 265. Using the distribution plugin
build.gradle
apply plugin: 'distribution'
The plugin adds an extension named “distributions” of type DistributionContainer to the project.
It also creates a single distribution in the distributions container extension named “ main”. If your build only
produces one distribution you only need to configure this distribution (or use the defaults).
You can run “gradle distZip” to package the main distribution as a ZIP, or “gradle distTar” to create
a TAR file. To build both types of archives just run gradle assembleDist. The files will be created at “ $buildDir /di
”.
You can run “gradle installDist” to assemble the uncompressed distribution into “ $buildDir /install/ main
”.
§
Tasks
The Distribution plugin adds the following tasks to the project:
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Table 30. Distribution plugin - tasks
Task name
Depends on
Type Description
distZip
-
Zip
Creates a ZIP archive of the distribution contents
distTar
-
Tar
Creates a TAR archive of the distribution contents
assembleDist
distTar, distZip
Task Creates ZIP and TAR archives with the distribution contents
installDist
-
Sync Assembles the distribution content and installs it on the current machine
For each extra distribution set you add to the project, the distribution plugin adds the following tasks:
Table 31. Multiple distributions - tasks
Task name
Depends on
Type Description
${distribution.name} DistZip
-
Zip
${distribution.name} DistTar
-
Tar
Creates a ZIP archive of the
distribution contents
Creates a TAR archive of the
distribution contents
${distribution.name}
DistTar, ${distribution.name}
Task Assembles all distribution
DistZip
assemble ${distribution.name.capitalize()}
Dist
archives
Assembles the distribution content
install ${distribution.name.capitalize()}
Dist
Sync and installs it on the current
machine
Example 266. Adding extra distributions
build.gradle
apply plugin: 'distribution'
version = '1.2'
distributions {
custom {}
}
This will add following tasks to the project:
customDistZip
customDistTar
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assembleCustomDist
installCustomDist
Given that the project name is “myproject” and version “1.2”, running “gradle customDistZip” will
produce a ZIP file named “myproject-custom-1.2.zip”.
Running “gradle installCustomDist” will install the distribution contents into “ $buildDir /install/custom
”.
§
Distribution contents
All of the files in the “src/ $distribution.name /dist” directory will automatically be included in the
distribution. You can add additional files by configuring the Distribution object that is part of the
container.
Example 267. Configuring the main distribution
build.gradle
apply plugin: 'distribution'
distributions {
main {
baseName = 'someName'
contents {
from { 'src/readme' }
}
}
}
apply plugin:'maven'
uploadArchives {
repositories {
mavenDeployer {
repository(url: "file://some/repo")
}
}
}
In the example above, the content of the “src/readme” directory will be included in the distribution (along
with the files in the “src/main/dist” directory which are added by default).
The “baseName” property has also been changed. This will cause the distribution archives to be created with
a different name.
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Publishing distributions
§
Publishing distributions
The distribution plugin adds the distribution archives as candidate for default publishing artifacts. With the maven
plugin applied the distribution zip file will be published when running uploadArchives if no other default
artifact is configured
Example 268. publish main distribution
build.gradle
apply plugin:'maven'
uploadArchives {
repositories {
mavenDeployer {
repository(url: "file://some/repo")
}
}
}
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The Announce Plugin
The Gradle announce plugin allows you to send custom announcements during a build. The following
notification systems are supported:
Twitter
notify-send (Ubuntu)
Snarl (Windows)
Growl (macOS)
§
Usage
To use the announce plugin, apply it to your build script:
Example 269. Applying the announce plugin
build.gradle
apply plugin: 'announce'
Next, configure your notification service(s) of choice (see table below for which configuration properties are
available):
Example 270. Configure the announce plugin
build.gradle
announce {
username = 'myId'
password = 'myPassword'
}
Finally, send announcements with the announce method:
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Example 271. Using the announce plugin
build.gradle
task helloWorld {
doLast {
println "Hello, world!"
}
}
helloWorld.doLast {
announce.announce("helloWorld completed!", "twitter")
announce.announce("helloWorld completed!", "local")
}
The announce method takes two String arguments: The message to be sent, and the notification service to
be used. The following table lists supported notification services and their configuration properties.
Table 32. Announce Plugin Notification Services
Notification
Service
Operating System
twitter
Any
snarl
Windows
growl
macOS
notify-send
Ubuntu
local
Configuration
Properties
Further Information
username,
password
Requires the notify-send package to be installed. Use sudo apt-get install libnotify
to install it.
Windows,
Automatically chooses between snarl, growl, and notify-send depending on
macOS, Ubuntu
the current operating system.
§
Configuration
See the AnnouncePluginExtension class in the API documentation.
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The Build Announcements Plugin
Note: The build announcements plugin is currently incubating. Please be aware that the DSL and
other configuration may change in later Gradle versions.
The build announcements plugin uses the announce plugin to send local announcements on important
events in the build.
§
Usage
To use the build announcements plugin, include the following in your build script:
Example 272. Using the build announcements plugin
build.gradle
apply plugin: 'build-announcements'
That’s it. If you want to tweak where the announcements go, you can configure the announce plugin to
change the local announcer.
You can also apply the plugin from an init script:
Example 273. Using the build announcements plugin from an init script
init.gradle
rootProject {
apply plugin: 'build-announcements'
}
Page 320 of 717
Dependency management
Introduction to Dependency Management
Dependency management is a critical feature of every build, and Gradle has placed an emphasis on offering
first-class dependency management that is both easy to understand and compatible with a wide variety of
approaches. If you are familiar with the approach used by either Maven or Ivy you will be delighted to learn
that Gradle is fully compatible with both approaches in addition to being flexible enough to support
fully-customized approaches.
Here are the major highlights of Gradle’s support for dependency management:
Transitive dependency management: Gradle gives you full control of your project’s dependency tree.
Support for non-managed dependencies: If your dependencies are simply files in version control or a shared
drive, Gradle provides powerful functionality to support this.
Support for custom dependency definitions.: Gradle’s Module Dependencies give you the ability to describe
the dependency hierarchy in the build script.
A fully customizable approach to Dependency Resolution: Gradle provides you with the ability to customize
resolution rules making dependency substitution easy.
Full Compatibility with Maven and Ivy: If you have defined dependencies in a Maven POM or an Ivy file,
Gradle provides seamless integration with a range of popular build tools.
Integration with existing dependency management infrastructure: Gradle is compatible with both Maven and
Ivy repositories. If you use Archiva, Nexus, or Artifactory, Gradle is 100% compatible with all repository
formats.
With hundreds of thousands of interdependent open source components each with a range of versions and
incompatibilities, dependency management has a habit of causing problems as builds grow in complexity.
When a build’s dependency tree becomes unwieldy, your build tool shouldn’t force you to adopt a single,
inflexible approach to dependency management. A proper build system has to be designed to be flexible,
and Gradle can handle any situation.
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Flexible dependency management for migrations
§
Flexible dependency management for migrations
Dependency management can be particularly challenging during a migration from one build system to
another. If you are migrating from a tool like Ant or Maven to Gradle, you may be faced with some difficult
situations. For example, one common pattern is an Ant project with version-less jar files stored in the
filesystem. Other build systems require a wholesale replacement of this approach before migrating. With
Gradle, you can adapt your new build to any existing source of dependencies or dependency metadata. This
makes incremental migration to Gradle much easier than the alternative. On most large projects, build
migrations and any change to development process is incremental because most organizations can’t afford
to stop everything and migrate to a build tool’s idea of dependency management.
Even if your project is using a custom dependency management system or something like an Eclipse
.classpath file as master data for dependency management, it is very easy to write a Gradle plugin to use
this data in Gradle. For migration purposes this is a common technique with Gradle. (But, once you’ve
migrated, it might be a good idea to move away from a .classpath file and use Gradle’s dependency
management features directly.)
§
Dependency management and Java
It is ironic that in a language known for its rich library of open source components that Java has no concept
of libraries or versions. In Java, there is no standard way to tell the JVM that you are using version 3.0.5 of
Hibernate, and there is no standard way to say that foo-1.0.jar depends on bar-2.0.jar. This has led
to external solutions often based on build tools. The most popular ones at the moment are Maven and Ivy.
While Maven provides a complete build system, Ivy focuses solely on dependency management.
Both tools rely on descriptor XML files, which contain information about the dependencies of a particular jar.
Both also use repositories where the actual jars are placed together with their descriptor files, and both offer
resolution for conflicting jar versions in one form or the other. Both have emerged as standards for solving
dependency conflicts, and while Gradle originally used Ivy under the hood for its dependency management.
Gradle has replaced this direct dependency on Ivy with a native Gradle dependency resolution engine which
supports a range of approaches to dependency resolution including both POM and Ivy descriptor files.
§
How dependency resolution works
Gradle takes your dependency declarations and repository definitions and attempts to download all of your
dependencies by a process called dependency resolution . Below is a brief outline of how this process
works.
Given a required dependency, Gradle first attempts to resolve the module for that dependency. Each
repository is inspected in order, searching first for a module descriptor file (POM or Ivy file) that indicates the
presence of that module. If no module descriptor is found, Gradle will search for the presence of the primary
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module artifact file indicating that the module exists in the repository.
If the dependency is declared as a dynamic version (like 1.+), Gradle will resolve this to the newest
available static version (like 1.2) in the repository. For Maven repositories, this is done using the maven-metadata.xml
file, while for Ivy repositories this is done by directory listing.
If the module descriptor is a POM file that has a parent POM declared, Gradle will recursively attempt to
resolve each of the parent modules for the POM.
Once each repository has been inspected for the module, Gradle will choose the 'best' one to use. This is
done using the following criteria:
For a dynamic version, a 'higher' static version is preferred over a 'lower' version.
Modules declared by a module descriptor file (Ivy or POM file) are preferred over modules that have an
artifact file only.
Modules from earlier repositories are preferred over modules in later repositories.
When the dependency is declared by a static version and a module descriptor file is found in a repository,
there is no need to continue searching later repositories and the remainder of the process is short-circuited.
All of the artifacts for the module are then requested from the same repository that was chosen in the
process above.
§
The dependency cache
Gradle contains a highly sophisticated dependency caching mechanism, which seeks to minimise the
number of remote requests made in dependency resolution, while striving to guarantee that the results of
dependency resolution are correct and reproducible.
The Gradle dependency cache consists of 2 key types of storage:
A file-based store of downloaded artifacts, including binaries like jars as well as raw downloaded meta-data
like POM files and Ivy files. The storage path for a downloaded artifact includes the SHA1 checksum,
meaning that 2 artifacts with the same name but different content can easily be cached.
A binary store of resolved module meta-data, including the results of resolving dynamic versions, module
descriptors, and artifacts.
Separating the storage of downloaded artifacts from the cache metadata permits us to do some very
powerful things with our cache that would be difficult with a transparent, file-only cache layout.
The Gradle cache does not allow the local cache to hide problems and create other mysterious and difficult
to debug behavior that has been a challenge with many build tools. This new behavior is implemented in a
bandwidth and storage efficient way. In doing so, Gradle enables reliable and reproducible enterprise builds.
Separate metadata cache
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§
Separate metadata cache
Gradle keeps a record of various aspects of dependency resolution in binary format in the metadata cache.
The information stored in the metadata cache includes:
The result of resolving a dynamic version (e.g. 1.+) to a concrete version (e.g. 1.2).
The resolved module metadata for a particular module, including module artifacts and module
dependencies.
The resolved artifact metadata for a particular artifact, including a pointer to the downloaded artifact file.
The absence of a particular module or artifact in a particular repository, eliminating repeated attempts to
access a resource that does not exist.
Every entry in the metadata cache includes a record of the repository that provided the information as well
as a timestamp that can be used for cache expiry.
§
Repository caches are independent
As described above, for each repository there is a separate metadata cache. A repository is identified by its
URL, type and layout. If a module or artifact has not been previously resolved from this repository , Gradle
will attempt to resolve the module against the repository. This will always involve a remote lookup on the
repository, however in many cases no download will be required (see the section called “Artifact reuse”,
below).
Dependency resolution will fail if the required artifacts are not available in any repository specified by the
build, even if the local cache has a copy of this artifact which was retrieved from a different repository.
Repository independence allows builds to be isolated from each other in an advanced way that no build tool
has done before. This is a key feature to create builds that are reliable and reproducible in any environment.
§
Artifact reuse
Before downloading an artifact, Gradle tries to determine the checksum of the required artifact by
downloading the sha file associated with that artifact. If the checksum can be retrieved, an artifact is not
downloaded if an artifact already exists with the same id and checksum. If the checksum cannot be retrieved
from the remote server, the artifact will be downloaded (and ignored if it matches an existing artifact).
As well as considering artifacts downloaded from a different repository, Gradle will also attempt to reuse
artifacts found in the local Maven Repository. If a candidate artifact has been downloaded by Maven, Gradle
will use this artifact if it can be verified to match the checksum declared by the remote server.
Checksum based storage
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§
Checksum based storage
It is possible for different repositories to provide a different binary artifact in response to the same artifact
identifier. This is often the case with Maven SNAPSHOT artifacts, but can also be true for any artifact which
is republished without changing its identifier. By caching artifacts based on their SHA1 checksum, Gradle is
able to maintain multiple versions of the same artifact. This means that when resolving against one
repository Gradle will never overwrite the cached artifact file from a different repository. This is done without
requiring a separate artifact file store per repository.
§
Cache Locking
The Gradle dependency cache uses file-based locking to ensure that it can safely be used by multiple
Gradle processes concurrently. The lock is held whenever the binary meta-data store is being read or
written, but is released for slow operations such as downloading remote artifacts.
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Declaring Dependencies
Gradle builds can declare dependencies on external binaries, raw files and other Gradle projects. You can
find examples for common scenarios in this section. For more information, see the full reference on all types
of dependencies.
§
Declaring a binary dependency
Modern software projects rarely build code in isolation. Projects reference external libraries for the purpose
of reusing existing and proven functionality, so-called binary dependencies . Upon resolution binary
dependencies are downloaded from dedicated repositories and stored in a cache to avoid unnecessary
network traffic.
Figure 6. Resolving binary dependencies from remote repositories
Declaring a concrete version of a binary dependency
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§
Declaring a concrete version of a binary dependency
A typical example for such a library in a Java project is the Spring framework. The following code snippet
declares a compile-time dependency on the Spring web module by its coordinates: org.springframework:spring-we
. Gradle resolves the dependency including its transitive dependencies from the Maven Central repository
and uses it to compile Java source code. The version attribute of the dependency coordinates points to a
concrete version indicating that the underlying artifacts don’t change over time. The use of concrete versions
ensures reproducibility for the aspect of dependency resolution.
Example 274. Declaring a binary dependencies with a concrete version
build.gradle
apply plugin: 'java-library'
repositories {
mavenCentral()
}
dependencies {
implementation 'org.springframework:spring-web:5.0.2.RELEASE'
}
A Gradle project can define other types of repositories hosting binary dependencies. You can learn more
about the syntax and API in the section on declaring repositories. Refer to The Java Plugin for a deep dive
on declaring dependencies for a Java project. The resolution behavior for binary dependencies declarations
is highly customizable.
§
Declaring a dynamic version of a binary dependency
Projects might adopt a more aggressive approach for consuming binary dependencies. For example you
might want to always integrate the latest version of a dependency to consume cutting edge features at any
given time. A dynamic version allows for resolving the latest version or the latest version of a version range
for a given dependency.
Note: Using dynamic versions in a build bears the risk of potentially breaking it. As soon as a new
version of the dependency is released that contains an incompatible API change your source code
might stop compiling.
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Example 275. Declaring a binary dependencies with a dynamic version
build.gradle
apply plugin: 'java-library'
repositories {
mavenCentral()
}
dependencies {
implementation 'org.springframework:spring-web:5.+'
}
A build scan can effectively visualize dynamic dependency versions and their respective, selected versions.
Figure 7. Dynamic dependencies in build scan
By default, Gradle caches dynamic versions of dependencies for 24 hours. The threshold can be configured
as needed for example if you want to resolve new versions earlier.
§
Declaring a changing version of a binary dependency
A team might decide to implement a series of features before releasing a new version of the application or
library. A common strategy to allow consumers to integrate an unfinished version of their artifacts early and
often is to release a so-called changing version . A changing version indicates that the feature set is still
under active development and hasn’t released a stable version for general availability yet.
In Maven repositories, changing versions are commonly referred to as snapshot versions. Snapshot versions
contain the suffix -SNAPSHOT. The following example demonstrates how to declare a snapshot version on
the Spring dependency.
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Example 276. Declaring a binary dependencies with a changing version
build.gradle
apply plugin: 'java-library'
repositories {
mavenCentral()
maven {
url 'https://repo.spring.io/snapshot/'
}
}
dependencies {
implementation 'org.springframework:spring-web:5.0.3.BUILD-SNAPSHOT'
}
By default, Gradle caches changing versions of dependencies for 24 hours. The threshold can be configured
as needed for example if you want to resolve new snapshot versions earlier.
Gradle is flexible enough to treat any version as changing version. All you need to do is to set the property
ExternalModuleDependency.setChanging(boolean) to true.
§
Declaring a file dependency
Projects sometimes do not rely on a binary repository product e.g. JFrog Artifactory or Sonatype Nexus for
hosting and resolving external dependencies. It’s common practice to host those dependencies on a shared
drive or check them into version control alongside the project source code. Those dependencies are referred
to as file dependencies , the reason being that they represent a files without any metadata (like information
about transitive dependencies, the origin or its author) attached to them.
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Figure 8. Resolving file dependencies from the local file system and a shared drive
The following example resolves file dependencies from the directories ant, libs and tools.
Example 277. Declaring multiple file dependencies
build.gradle
configurations {
antContrib
externalLibs
deploymentTools
}
dependencies {
antContrib files('ant/antcontrib.jar')
externalLibs files('libs/commons-lang.jar', 'libs/log4j.jar')
deploymentTools fileTree(dir: 'tools', include: '*.exe')
}
As you can see in the code example, every dependency has to define its exact location in the file system.
The most prominent methods for creating a file reference are Project.files(java.lang.Object[])
and Project.fileTree(java.lang.Object). Alternatively, you can also define the source directory of
one or many file dependencies in the form of a flat directory repository.
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Declaring a project dependency
§
Declaring a project dependency
Software projects often break up software components into modules to improve maintainability and prevent
strong coupling. Modules can define dependencies between each other to reuse code within the same
project.
Gradle can model dependencies between modules. Those dependencies are called project dependencies
because each module is represented by a Gradle project. At runtime, the build automatically ensures that
project dependencies are built in the correct order and added to the classpath for compilation. The chapter
Authoring Multi-Project Builds discusses how to set up and configure multi-project builds in more detail.
Figure 9. Dependencies between projects
The following example declares the dependencies on the utils and api project from the web-service
project. The method Project.project(java.lang.String) creates a reference to a specific
subproject by path.
Example 278. Declaring project dependencies
build.gradle
project(':web-service') {
dependencies {
implementation project(':utils')
implementation project(':api')
}
}
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Defining the scope of a dependency with configurations
§
Defining the scope of a dependency with configurations
§
What is a configuration?
Every dependency declared for a Gradle project applies to a specific scope. For example some
dependencies should be used for compiling source code whereas others only need to be available at
runtime. Gradle represents the scope of a dependency with the help of a Configuration.
Many Gradle plugins add pre-defined configurations to your project. The Java plugin, for example, adds
configurations to represent the various classpaths it needs for source code compilation, executing tests and
the like. See the Java plugin chapter for an example. The sections above demonstrate how to declare
dependencies for different use cases.
Figure 10. Configurations use declared dependencies for specific purposes
§
Defining custom configurations
You can also define configurations yourself, so-called custom configurations . A custom configuration is
useful for separating the scope of dependencies needed for a dedicated purpose.
Let’s say you wanted to declare a dependency on the Jasper Ant task for the purpose of pre-compiling JSP
files that should not end up in the classpath for compiling your source code. It’s fairly simply to achieve that
goal by introducing a custom configuration and using it in a task.
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Example 279. Declaring and using a custom configuration
build.gradle
configurations {
jasper
}
repositories {
mavenCentral()
}
dependencies {
jasper 'org.apache.tomcat.embed:tomcat-embed-jasper:9.0.2'
}
task preCompileJsps {
doLast {
ant.taskdef(classname: 'org.apache.jasper.JspC',
name: 'jasper',
classpath: configurations.jasper.asPath)
ant.jasper(validateXml: false,
uriroot: file('src/main/webapp'),
outputDir: file("$buildDir/compiled-jsps"))
}
}
A project’s configurations are managed by a configurations object. Configurations have a name and can
extend each other. To learn more about this API have a look at ConfigurationContainer.
§
Resolving specific artifacts from a module dependency
Whenever Gradle tries to resolve a dependency from a Maven or Ivy repository, it looks for a metadata file
and the default artifact file, a JAR. The build fails if none of these artifact files can be resolved. Under certain
conditions, you might want to tweak the way Gradle resolves artifacts for a dependency.
The dependency only provides a non-standard artifact without any metadata e.g. a ZIP file.
The dependency metadata declares more than one artifact e.g. as part of an Ivy dependency descriptor.
You only want to download a specific artifact without any of the transitive dependencies declared in the
metadata.
Gradle is a polyglot build tool and not limited to just resolving Java libraries. Let’s assume you wanted to
build a web application using JavaScript as the client technology. Most projects check in external JavaScript
libraries into version control. An external JavaScript library is no different than a reusable Java library so why
not download it from a repository instead?
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Google Hosted Libraries is a distribution platform for popular, open-source JavaScript libraries. With the help
of the artifact-only notation you can download a JavaScript library file e.g. JQuery. The @ character
separates the dependency’s coordinates from the artifact’s file extension.
Example 280. Resolving a JavaScript artifact for a declared dependency
build.gradle
repositories {
ivy {
url 'https://ajax.googleapis.com/ajax/libs'
layout 'pattern', {
artifact '[organization]/[revision]/[module].[ext]'
}
}
}
configurations {
js
}
dependencies {
js 'jquery:jquery:3.2.1@js'
}
Some dependencies ship different "flavors" of the same artifact or they publish multiple artifacts that belong
to a specific version of the dependency but have a different purpose. It’s common for a Java library to
publish the artifact with the compiled class files, another one with just the source code in it and a third one
containing the Javadocs.
In JavaScript, a library may exist as uncompressed or minified artifact. In Gradle, a specific artifact identifier
is called classifier , a term generally used in Maven and Ivy dependency management.
Let’s say we wanted to download the minified artifact of the JQuery library instead of the uncompressed file.
You can provide the classifier min as part of the dependency declaration.
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Example 281. Resolving a JavaScript artifact with classifier for a declared dependency
build.gradle
repositories {
ivy {
url 'https://ajax.googleapis.com/ajax/libs'
layout 'pattern', {
artifact '[organization]/[revision]/[module](.[classifier]).[ext]'
}
}
}
configurations {
js
}
dependencies {
js 'jquery:jquery:3.2.1:min@js'
}
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Declaring Repositories
Gradle can resolve external dependencies from one or many repositories based on Maven, Ivy or flat
directory directory formats. Check out the full reference on all types of repositories for more information.
§
Declaring a publicly-available repository
Organizations building software may want to leverage public binary repositories to download and consume
open source dependencies. Popular public repositories include Maven Central, Bintray JCenter and the
Google Android repository. Gradle provides built-in shortcut methods for the most widely-used repositories.
Figure 11. Declaring a repository with the help of shortcut methods
To declare JCenter as repository, add this code to your build script:
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Example 282. Declaring JCenter repository as source for resolving dependencies
build.gradle
repositories {
jcenter()
}
Under the covers Gradle resolves dependencies from the respective URL of the public repository defined by
the shortcut method. All shortcut methods are available via the RepositoryHandler API. Alternatively,
you can spell out the URL of the repository for more fine-grained control.
§
Declaring a custom repository by URL
Most enterprise projects set up a binary repository available only within an intranet. In-house repositories
enable teams to publish internal binaries, setup user management and security measure and ensure uptime
and availability. Specifying a custom URL is also helpful if you want to declare a less popular, but
publicly-available repository.
Add the following code to declare an in-house repository for your build reachable through a custom URL.
Example 283. Declaring a custom repository by URL
build.gradle
repositories {
maven {
url "http://repo.mycompany.com/maven2"
}
}
Repositories with custom URLs can be specified as Maven or Ivy repositories by calling the corresponding
methods available on the RepositoryHandler API. Gradle supports other protocols than http or https
as part of the custom URL e.g. file, sftp or s3. For a full coverage see the reference manual on
supported transport protocols.
§
Declaring multiple repositories
You can define more than one repository for resolving dependencies. Declaring multiple repositories is
helpful if some dependencies are only available in one repository but not the other. You can mix any type of
repository described in the reference section.
This example demonstrates how to declare various shortcut and custom URL repositories for a project:
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Example 284. Declaring multiple repositories
build.gradle
repositories {
jcenter()
maven {
url "https://maven.springframework.org/release"
}
maven {
url "https://maven.restlet.org"
}
}
Note: The order of declaration determines how Gradle will check for dependencies at runtime. If
Gradle finds a module descriptor in a particular repository, it will attempt to download all of the
artifacts for that module from the same repository . You can learn more about Gradle’s resolution
mechanism in the dedicated section.
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Inspecting Dependencies
Gradle provides sufficient tooling to navigate large dependency graphs and mitigate situations that can lead
to dependency hell. Users can chose to render the full graph of dependencies as well as identify the
selection reason and origin for a dependency. The origin of a dependency can be a declared dependency in
the build script or a transitive dependency in graph plus their corresponding configuration. Gradle offers both
capabilities through visual representation via build scans and as command line tooling.
§
Listing dependencies in a project
A project can declare one or more dependencies. Gradle can visualize the whole dependency tree for every
configuration available in the project.
Rendering the dependency tree is particularly useful if you’d like to identify which dependencies have been
resolved at runtime. It also provides you with information about any dependency conflict resolution that
occurred in the process and clearly indicates the selected version. The dependency report always contains
declared and transitive dependencies.
Let’s say you’d want to create tasks for your project that use the JGit library to execute SCM operations e.g.
to model a release process. You can declare dependencies for any external tooling with the help of a custom
configuration so that it doesn’t doesn’t pollute other contexts like the compilation classpath for your
production source code.
Example 285. Declaring the JGit dependency with a custom configuration
build.gradle
repositories {
jcenter()
}
configurations {
scm
}
dependencies {
scm 'org.eclipse.jgit:org.eclipse.jgit:4.9.2.201712150930-r'
}
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A build scan can visualize dependencies as a navigable, searchable tree. Additional context information can
be rendered by clicking on a specific dependency in the graph.
Figure 12. Dependency tree in a build scan
Every Gradle project provides the task dependencies to render the so-called dependency report from the
command line. By default the dependency report renders dependencies for all configurations. To pair down
on the information provide the optional parameter --configuration.
Example 286. Rendering the dependency report for a custom configuration
Output of gradle -q dependencies --configuration scm
> gradle -q dependencies --configuration scm
-----------------------------------------------------------Root project
-----------------------------------------------------------scm
\--- org.eclipse.jgit:org.eclipse.jgit:4.9.2.201712150930-r
+--- com.jcraft:jsch:0.1.54
+--- com.googlecode.javaewah:JavaEWAH:1.1.6
+--- org.apache.httpcomponents:httpclient:4.3.6
|
+--- org.apache.httpcomponents:httpcore:4.3.3
|
+--- commons-logging:commons-logging:1.1.3
|
\--- commons-codec:commons-codec:1.6
\--- org.slf4j:slf4j-api:1.7.2
The dependencies report provides detailed information about the dependencies available in the graph. Any
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dependency that could not be resolved is marked with FAILED in red color. Dependencies with the same
coordinates that can occur multiple times in the graph are omitted and indicated by an asterisk.
Dependencies that had to undergo conflict resolution render the requested and selected version separated
by a right arrow character.
§
Identifying which dependency version was selected and why
Large software projects inevitably deal with an increased number of dependencies either through direct or
transitive dependencies. The dependencies report provides you with the raw list of dependencies but does
not explain why they have been selected or which dependency is responsible for pulling them into the
graph.
Let’s have a look at a concrete example. A project may request two different versions of the same
dependency either as direct or transitive dependency. Gradle applies version conflict resolution to ensure
that only one version of the dependency exists in the dependency graph. In this example the conflicting
dependency is represented by commons-codec:commons-codec.
Example 287. Declaring the JGit dependency and a conflicting dependency
build.gradle
repositories {
jcenter()
}
configurations {
scm
}
dependencies {
scm 'org.eclipse.jgit:org.eclipse.jgit:4.9.2.201712150930-r'
scm 'commons-codec:commons-codec:1.7'
}
The dependency tree in a build scan renders the selection reason (conflict resolution) as well as the origin of
a dependency if you click on a dependency and select the "Required By" tab.
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Figure 13. Dependency insight capabilities in a build scan
Every Gradle project provides the task dependencyInsight to render the so-called dependency insight
report from the command line. Given a dependency in the dependency graph you can identify the selection
reason and track down the origin of the dependency selection. You can think of the dependency insight
report as the inverse representation of the dependency report for a given dependency. When executing the
task you have to provide the mandatory parameter --dependency to specify the coordinates of the
dependency under inspection. The parameter --configuration is optional but helps with filtering the
output.
Example 288. Using the dependency insight report for a given dependency
Output of gradle -q dependencyInsight --dependency commons-codec --configuration
scm
> gradle -q dependencyInsight --dependency commons-codec --configuration scm
commons-codec:commons-codec:1.7 (conflict resolution)
\--- scm
commons-codec:commons-codec:1.6 -> 1.7
\--- org.apache.httpcomponents:httpclient:4.3.6
\--- org.eclipse.jgit:org.eclipse.jgit:4.9.2.201712150930-r
\--- scm
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Managing Transitive Dependencies
Resolution behavior for transitive dependencies can be customized to a high degree to meet enterprise
requirements.
§
Excluding transitive module dependencies
Declared dependencies in a build script can pull in a lot of transitive dependencies. You might decide that
you do not want a particular transitive dependency as part of the dependency graph for a good reason.
The dependency is undesired due to licensing constraints.
The dependency is not available in any of the declared repositories.
The metadata for the dependency exists but the artifact does not.
The metadata provides incorrect coordinates for a transitive dependency.
Transitive dependencies can be excluded on the level of a declared dependency or a configuration. Let’s
demonstrate both use cases. In the following two examples the build script declares a dependency on
Log4J, a popular logging framework in the Java world. The metadata of the particular version of Log4J also
defines transitive dependencies.
Example 289. Unresolved artifacts for transitive dependencies
build.gradle
apply plugin: 'java'
repositories {
mavenCentral()
}
dependencies {
implementation 'log4j:log4j:1.2.15'
}
If resolved from Maven Central some of the transitive dependencies provide metadata but not the
corresponding binary artifact. As a result any task requiring the binary files will fail e.g. a compilation task.
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> gradle -q compileJava
* What went wrong:
Could not resolve all files for configuration ':compileClasspath'.
> Could not find jms.jar (javax.jms:jms:1.1).
Searched in the following locations:
https://repo.maven.apache.org/maven2/javax/jms/jms/1.1/jms-1.1.jar
> Could not find jmxtools.jar (com.sun.jdmk:jmxtools:1.2.1).
Searched in the following locations:
https://repo.maven.apache.org/maven2/com/sun/jdmk/jmxtools/1.2.1/jmxtools-1.2.1.jar
> Could not find jmxri.jar (com.sun.jmx:jmxri:1.2.1).
Searched in the following locations:
https://repo.maven.apache.org/maven2/com/sun/jmx/jmxri/1.2.1/jmxri-1.2.1.jar
The situation can be fixed by adding a repository containing those dependencies. In the given example
project, the source code does not actually use any of Log4J’s functionality that require the JMS (e.g. JMSAppender
) or JMX libraries. It’s safe to exclude them from the dependency declaration.
Exclusions need to spelled out as a key/value pair via the attributes group and/or module. For more
information, refer to ModuleDependency.exclude(java.util.Map).
Example 290. Excluding transitive dependency for a particular dependency declaration
build.gradle
dependencies {
implementation('log4j:log4j:1.2.15') {
exclude group: 'javax.jms', module: 'jms'
exclude group: 'com.sun.jdmk', module: 'jmxtools'
exclude group: 'com.sun.jmx', module: 'jmxri'
}
}
You may find that other dependencies will want to pull in the same transitive dependency that misses the
artifacts. Alternatively, you can exclude the transitive dependencies for a particular configuration by calling
the method Configuration.exclude(java.util.Map).
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Example 291. Excluding transitive dependency for a particular configuration
build.gradle
configurations {
implementation {
exclude group: 'javax.jms', module: 'jms'
exclude group: 'com.sun.jdmk', module: 'jmxtools'
exclude group: 'com.sun.jmx', module: 'jmxri'
}
}
dependencies {
implementation 'log4j:log4j:1.2.15'
}
Note: As a build script author you often times know that you want to exclude a dependency for all
configurations
available
in
the
project.
You
can
use
the
method
DomainObjectCollection.all(org.gradle.api.Action) to define a global rule.
You might encounter other use cases that don’t quite fit the bill of an exclude rule. For example you want to
automatically select a version for a dependency with a specific requested version or you want to select a
different group for a requested dependency to react to a relocation. Those use cases are better solved by
the ResolutionStrategy API. Some of these use cases are covered in Customizing Dependency
Resolution Behavior.
§
Enforcing a particular dependency version
Gradle resolves any dependency version conflicts by selecting the latest version found in the dependency
graph. Some projects might need to divert from the default behavior and enforce an earlier version of a
dependency e.g. if the source code of the project depends on an older API of a dependency than some of
the external libraries.
Note: Enforcing a version of a dependency requires a conscious decision. Changing the version of
a transitive dependency might lead to runtime errors if external libraries do not properly function
without them. Consider upgrading your source code to use a newer version of the library as an
alternative approach.
Let’s say a project uses the HttpClient library for performing HTTP calls. HttpClient pulls in Commons Codec
as transitive dependency with version 1.10. However, the production source code of the project requires an
API from Commons Codec 1.9 which is not available in 1.10 anymore. A dependency version can be
enforced by declaring it in the build script and setting ExternalDependency.setForce(boolean) to true
.
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Example 292. Enforcing a dependency version
build.gradle
dependencies {
implementation 'org.apache.httpcomponents:httpclient:4.5.4'
implementation('commons-codec:commons-codec:1.9') {
force = true
}
}
If the project requires a specific version of a dependency on a configuration-level then it can be achieved by
calling the method ResolutionStrategy.force(java.lang.Object[]).
Example 293. Enforcing a dependency version on the configuration-level
build.gradle
configurations {
compileClasspath {
resolutionStrategy.force 'commons-codec:commons-codec:1.9'
}
}
dependencies {
implementation 'org.apache.httpcomponents:httpclient:4.5.4'
}
§
Disabling resolution of transitive dependencies
By default Gradle resolves all transitive dependencies specified by the dependency metadata. Sometimes
this behavior may not be desirable e.g. if the metadata is incorrect or defines a large graph of transitive
dependencies. You can tell Gradle to disable transitive dependency management for a dependency by
setting ModuleDependency.setTransitive(boolean) to true. As a result only the main artifact will
be resolved for the declared dependency.
Example 294. Disabling transitive dependency resolution for a declared dependency
build.gradle
dependencies {
implementation('com.google.guava:guava:23.0') {
transitive = false
}
}
Note: Disabling transitive dependency resolution will likely require you to declare the necessary
runtime dependencies in your build script which otherwise would have been resolved automatically.
Not doing so might lead to runtime classpath issues.
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A project can decide to disable transitive dependency resolution completely. You either don’t want to rely on
the metadata published to the consumed repositories or you want to gain full control over the dependencies
in your graph. For more information, see Configuration.setTransitive(boolean).
Example 295. Disabling transitive dependency resolution on the configuration-level
build.gradle
configurations.all {
transitive = false
}
dependencies {
implementation 'com.google.guava:guava:23.0'
}
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Working with Dependencies
For the examples below we have the following dependencies setup:
Example 296. Configuration.copy
build.gradle
configurations {
sealife
alllife
}
dependencies {
sealife "sea.mammals:orca:1.0", "sea.fish:shark:1.0", "sea.fish:tuna:1.0"
alllife configurations.sealife
alllife "air.birds:albatross:1.0"
}
The dependencies have the following transitive dependencies:
shark-1.0 -> seal-2.0, tuna-1.0
orca-1.0 -> seal-1.0
tuna-1.0 -> herring-1.0
You can use the configuration to access the declared dependencies or a subset of those:
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Example 297. Accessing declared dependencies
build.gradle
task dependencies {
doLast {
configurations.alllife.dependencies.each { dep -> println dep.name }
println()
configurations.alllife.allDependencies.each { dep -> println dep.name }
println()
configurations.alllife.allDependencies.findAll { dep -> dep.name != 'orca' }
.each { dep -> println dep.name }
}
}
Output of gradle -q dependencies
> gradle -q dependencies
albatross
albatross
orca
shark
tuna
albatross
shark
tuna
The dependencies task returns only the dependencies belonging explicitly to the configuration. The allDependencies
task includes the dependencies from extended configurations.
To get the library files of the configuration dependencies you can do:
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Example 298. Configuration.files
build.gradle
task allFiles {
doLast {
configurations.sealife.files.each { file ->
println file.name
}
}
}
Output of gradle -q allFiles
> gradle -q allFiles
orca-1.0.jar
shark-1.0.jar
tuna-1.0.jar
seal-2.0.jar
herring-1.0.jar
Sometimes you want the library files of a subset of the configuration dependencies (e.g. of a single
dependency).
Example 299. Configuration.files with spec
build.gradle
task files {
doLast {
configurations.sealife.files { dep -> dep.name == 'orca' }.each { file ->
println file.name
}
}
}
Output of gradle -q files
> gradle -q files
orca-1.0.jar
seal-2.0.jar
The Configuration.files method always retrieves all artifacts of the whole configuration. It then filters
the retrieved files by specified dependencies. As you can see in the example, transitive dependencies are
included.
You can also copy a configuration. You can optionally specify that only a subset of dependencies from the
original configuration should be copied. The copying methods come in two flavors. The copy method copies
only the dependencies belonging explicitly to the configuration. The copyRecursive method copies all the
dependencies, including the dependencies from extended configurations.
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Example 300. Configuration.copy
build.gradle
task copy {
doLast {
configurations.alllife.copyRecursive { dep -> dep.name != 'orca' }
.allDependencies.each { dep -> println dep.name }
println()
configurations.alllife.copy().allDependencies
.each { dep -> println dep.name }
}
}
Output of gradle -q copy
> gradle -q copy
albatross
shark
tuna
albatross
It is important to note that the returned files of the copied configuration are often but not always the same
than the returned files of the dependency subset of the original configuration. In case of version conflicts
between dependencies of the subset and dependencies not belonging to the subset the resolve result might
be different.
Example 301. Configuration.copy vs. Configuration.files
build.gradle
task copyVsFiles {
doLast {
configurations.sealife.copyRecursive { dep -> dep.name == 'orca' }
.each { file -> println file.name }
println()
configurations.sealife.files { dep -> dep.name == 'orca' }
.each { file -> println file.name }
}
}
Output of gradle -q copyVsFiles
> gradle -q copyVsFiles
orca-1.0.jar
seal-1.0.jar
orca-1.0.jar
seal-2.0.jar
In the example above, orca has a dependency on seal-1.0 whereas shark has a dependency on seal-2.0
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. The original configuration has therefore a version conflict which is resolved to the newer seal-2.0
version. The files method therefore returns seal-2.0 as a transitive dependency of orca. The copied
configuration only has orca as a dependency and therefore there is no version conflict and seal-1.0 is
returned as a transitive dependency.
Once a configuration is resolved it is immutable. Changing its state or the state of one of its dependencies
will cause an exception. You can always copy a resolved configuration. The copied configuration is in the
unresolved state and can be freshly resolved.
To learn more about the API of the configuration class see the API documentation: Configuration.
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Customizing Dependency Resolution
Behavior
In most cases, Gradle’s default dependency management will resolve the dependencies that you want in
your build. In some cases, however, it can be necessary to tweak dependency resolution to ensure that your
build receives exactly the right dependencies.
There are a number of ways that you can influence how Gradle resolves dependencies.
§
Using dependency resolve rules
A dependency resolve rule is executed for each resolved dependency, and offers a powerful api for
manipulating a requested dependency prior to that dependency being resolved. This feature is incubating,
but currently offers the ability to change the group, name and/or version of a requested dependency,
allowing a dependency to be substituted with a completely different module during resolution.
Dependency resolve rules provide a very powerful way to control the dependency resolution process, and
can be used to implement all sorts of advanced patterns in dependency management. Some of these
patterns are outlined below. For more information and code samples see the ResolutionStrategy class
in the API documentation.
§
Modelling releasable units
Often an organisation publishes a set of libraries with a single version; where the libraries are built, tested
and published together. These libraries form a 'releasable unit', designed and intended to be used as a
whole. It does not make sense to use libraries from different releasable units together.
But it is easy for transitive dependency resolution to violate this contract. For example:
module-a depends on releasable-unit:part-one:1.0
module-b depends on releasable-unit:part-two:1.1
A build depending on both module-a and module-b will obtain different versions of libraries within the
releasable unit.
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Dependency resolve rules give you the power to enforce releasable units in your build. Imagine a releasable
unit defined by all libraries that have 'org.gradle' group. We can force all of these libraries to use a consistent
version:
Example 302. Forcing consistent version for a group of libraries
build.gradle
configurations.all {
resolutionStrategy.eachDependency { DependencyResolveDetails details ->
if (details.requested.group == 'org.gradle') {
details.useVersion '1.4'
}
}
}
§
Implementing a custom versioning scheme
In some corporate environments, the list of module versions that can be declared in Gradle builds is
maintained and audited externally. Dependency resolve rules provide a neat implementation of this pattern:
In the build script, the developer declares dependencies with the module group and name, but uses a
placeholder version, for example: 'default'.
The 'default' version is resolved to a specific version via a dependency resolve rule, which looks up the
version in a corporate catalog of approved modules.
This rule implementation can be neatly encapsulated in a corporate plugin, and shared across all builds
within the organisation.
Example 303. Using a custom versioning scheme
build.gradle
configurations.all {
resolutionStrategy.eachDependency { DependencyResolveDetails details ->
if (details.requested.version == 'default') {
def version = findDefaultVersionInCatalog(details.requested.group, details.req
details.useVersion version
}
}
}
def findDefaultVersionInCatalog(String group, String name) {
//some custom logic that resolves the default version into a specific version
"1.0"
}
Blacklisting a particular version with a replacement
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§
Blacklisting a particular version with a replacement
Dependency resolve rules provide a mechanism for blacklisting a particular version of a dependency and
providing a replacement version. This can be useful if a certain dependency version is broken and should
not be used, where a dependency resolve rule causes this version to be replaced with a known good
version. One example of a broken module is one that declares a dependency on a library that cannot be
found in any of the public repositories, but there are many other reasons why a particular module version is
unwanted and a different version is preferred.
In example below, imagine that version 1.2.1 contains important fixes and should always be used in
preference to 1.2. The rule provided will enforce just this: any time version 1.2 is encountered it will be
replaced with 1.2.1. Note that this is different from a forced version as described above, in that any other
versions of this module would not be affected. This means that the 'newest' conflict resolution strategy would
still select version 1.3 if this version was also pulled transitively.
Example 304. Blacklisting a version with a replacement
build.gradle
configurations.all {
resolutionStrategy.eachDependency { DependencyResolveDetails details ->
if (details.requested.group == 'org.software' && details.requested.name == 'some-l
//prefer different version which contains some necessary fixes
details.useVersion '1.2.1'
}
}
}
§
Substituting a dependency module with a compatible replacement
At times a completely different module can serve as a replacement for a requested module dependency.
Examples include using 'groovy' in place of 'groovy-all', or using 'log4j-over-slf4j' instead of 'log4j'
. Starting with Gradle 1.5 you can make these substitutions using dependency resolve rules:
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Example 305. Changing dependency group and/or name at the resolution
build.gradle
configurations.all {
resolutionStrategy.eachDependency { DependencyResolveDetails details ->
if (details.requested.name == 'groovy-all') {
//prefer 'groovy' over 'groovy-all':
details.useTarget group: details.requested.group, name: 'groovy', version: det
}
if (details.requested.name == 'log4j') {
//prefer 'log4j-over-slf4j' over 'log4j', with fixed version:
details.useTarget "org.slf4j:log4j-over-slf4j:1.7.10"
}
}
}
§
Dependency Substitution Rules
Dependency substitution rules work similarly to dependency resolve rules. In fact, many capabilities of
dependency resolve rules can be implemented with dependency substitution rules. They allow project and
module dependencies to be transparently substituted with specified replacements. Unlike dependency
resolve rules, dependency substitution rules allow project and module dependencies to be substituted
interchangeably.
Adding a dependency substitution rule to a configuration changes the timing of when that configuration is
resolved. Instead of being resolved on first use, the configuration is instead resolved when the task graph is
being constructed. This can have unexpected consequences if the configuration is being further modified
during task execution, or if the configuration relies on modules that are published during execution of another
task.
To explain:
A Configuration can be declared as an input to any Task, and that configuration can include project
dependencies when it is resolved.
If a project dependency is an input to a Task (via a configuration), then tasks to build the project artifacts
must be added to the task dependencies.
In order to determine the project dependencies that are inputs to a task, Gradle needs to resolve the Configuration
inputs.
Because the Gradle task graph is fixed once task execution has commenced, Gradle needs to perform this
resolution prior to executing any tasks.
In the absence of dependency substitution rules, Gradle knows that an external module dependency will
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never transitively reference a project dependency. This makes it easy to determine the full set of project
dependencies for a configuration through simple graph traversal. With this functionality, Gradle can no
longer make this assumption, and must perform a full resolve in order to determine the project
dependencies.
§
Substituting an external module dependency with a project dependency
One use case for dependency substitution is to use a locally developed version of a module in place of one
that is downloaded from an external repository. This could be useful for testing a local, patched version of a
dependency.
The module to be replaced can be declared with or without a version specified.
Example 306. Substituting a module with a project
build.gradle
configurations.all {
resolutionStrategy.dependencySubstitution {
substitute module("org.utils:api") with project(":api")
substitute module("org.utils:util:2.5") with project(":util")
}
}
Note that a project that is substituted must be included in the multi-project build (via settings.gradle).
Dependency substitution rules take care of replacing the module dependency with the project dependency
and wiring up any task dependencies, but do not implicitly include the project in the build.
§
Substituting a project dependency with a module replacement
Another way to use substitution rules is to replace a project dependency with a module in a multi-project
build. This can be useful to speed up development with a large multi-project build, by allowing a subset of
the project dependencies to be downloaded from a repository rather than being built.
The module to be used as a replacement must be declared with a version specified.
Example 307. Substituting a project with a module
build.gradle
configurations.all {
resolutionStrategy.dependencySubstitution {
substitute project(":api") with module("org.utils:api:1.3")
}
}
When a project dependency has been replaced with a module dependency, that project is still included in the
overall multi-project build. However, tasks to build the replaced dependency will not be executed in order to
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build the resolve the depending Configuration.
§
Conditionally substituting a dependency
A common use case for dependency substitution is to allow more flexible assembly of sub-projects within a
multi-project build. This can be useful for developing a local, patched version of an external dependency or
for building a subset of the modules within a large multi-project build.
The following example uses a dependency substitution rule to replace any module dependency with the
group "org.example", but only if a local project matching the dependency name can be located.
Example 308. Conditionally substituting a dependency
build.gradle
configurations.all {
resolutionStrategy.dependencySubstitution.all { DependencySubstitution dependency ->
if (dependency.requested instanceof ModuleComponentSelector && dependency.requeste
def targetProject = findProject(":${dependency.requested.module}")
if (targetProject != null) {
dependency.useTarget targetProject
}
}
}
}
Note that a project that is substituted must be included in the multi-project build (via settings.gradle).
Dependency substitution rules take care of replacing the module dependency with the project dependency,
but do not implicitly include the project in the build.
§
Specifying default dependencies for a configuration
A configuration can be configured with default dependencies to be used if no dependencies are explicitly set
for the configuration. A primary use case of this functionality is for developing plugins that make use of
versioned tools that the user might override. By specifying default dependencies, the plugin can use a
default version of the tool only if the user has not specified a particular version to use.
Example 309. Specifying default dependencies on a configuration
build.gradle
configurations {
pluginTool {
defaultDependencies { dependencies ->
dependencies.add(this.project.dependencies.create("org.gradle:my-util:1.0"))
}
}
}
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§
Enabling Ivy dynamic resolve mode
Gradle’s Ivy repository implementations support the equivalent to Ivy’s dynamic resolve mode. Normally,
Gradle will use the rev attribute for each dependency definition included in an ivy.xml file. In dynamic
resolve mode, Gradle will instead prefer the revConstraint attribute over the rev attribute for a given
dependency definition. If the revConstraint attribute is not present, the rev attribute is used instead.
To enable dynamic resolve mode, you need to set the appropriate option on the repository definition. A
couple of examples are shown below. Note that dynamic resolve mode is only available for Gradle’s Ivy
repositories. It is not available for Maven repositories, or custom Ivy DependencyResolver
implementations.
Example 310. Enabling dynamic resolve mode
build.gradle
// Can enable dynamic resolve mode when you define the repository
repositories {
ivy {
url "http://repo.mycompany.com/repo"
resolve.dynamicMode = true
}
}
// Can use a rule instead to enable (or disable) dynamic resolve mode for all repositories
repositories.withType(IvyArtifactRepository) {
resolve.dynamicMode = true
}
§
Component metadata rules
Each module (also called component ) has metadata associated with it, such as its group, name, version,
dependencies, and so on. This metadata typically originates in the module’s descriptor. Metadata rules allow
certain parts of a module’s metadata to be manipulated from within the build script. They take effect after a
module’s descriptor has been downloaded, but before it has been selected among all candidate versions.
This makes metadata rules another instrument for customizing dependency resolution.
One piece of module metadata that Gradle understands is a module’s status scheme . This concept, also
known from Ivy, models the different levels of maturity that a module transitions through over time. The
default status scheme, ordered from least to most mature status, is integration, milestone, release.
Apart from a status scheme, a module also has a (current) status , which must be one of the values in its
status scheme. If not specified in the (Ivy) descriptor, the status defaults to integration for Ivy modules
and Maven snapshot modules, and release for Maven modules that aren’t snapshots.
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A module’s status and status scheme are taken into consideration when a latest version selector is
resolved. Specifically, latest.someStatus will resolve to the highest module version that has status someStatus
or a more mature status. For example, with the default status scheme in place, latest.integration will
select the highest module version regardless of its status (because integration is the least mature
status), whereas latest.release will select the highest module version with status release. Here is
what this looks like in code:
Example 311. 'Latest' version selector
build.gradle
dependencies {
config1 "org.sample:client:latest.integration"
config2 "org.sample:client:latest.release"
}
task listConfigs {
doLast {
configurations.config1.each { println it.name }
println()
configurations.config2.each { println it.name }
}
}
Output of gradle -q listConfigs
> gradle -q listConfigs
client-1.5.jar
client-1.4.jar
The next example demonstrates latest selectors based on a custom status scheme declared in a
component metadata rule that applies to all modules:
Example 312. Custom status scheme
build.gradle
dependencies {
config3 "org.sample:api:latest.silver"
components {
all { ComponentMetadataDetails details ->
if (details.id.group == "org.sample" && details.id.name == "api") {
details.statusScheme = ["bronze", "silver", "gold", "platinum"]
}
}
}
}
Component metadata rules can be applied to a specified module. Modules must be specified in the form of
"group:module".
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Example 313. Custom status scheme by module
build.gradle
dependencies {
config4 "org.sample:lib:latest.prod"
components {
withModule('org.sample:lib') { ComponentMetadataDetails details ->
details.statusScheme = ["int", "rc", "prod"]
}
}
}
Gradle can also create component metadata rules utilizing Ivy-specific metadata for modules resolved from
an Ivy repository. Values from the Ivy descriptor are made available via the IvyModuleDescriptor
interface.
Example 314. Ivy component metadata rule
build.gradle
dependencies {
config6 "org.sample:lib:latest.rc"
components {
withModule("org.sample:lib") { ComponentMetadataDetails details, IvyModuleDescript
if (ivyModule.branch == 'testing') {
details.status = "rc"
}
}
}
}
Note that any rule that declares specific arguments must always include a ComponentMetadataDetails
argument as the first argument. The second Ivy metadata argument is optional.
Component metadata rules can also be defined using a rule source object. A rule source object is any object
that contains exactly one method that defines the rule action and is annotated with @Mutate.
This method:
must return void.
must have ComponentMetadataDetails as the first argument.
may have an additional parameter of type IvyModuleDescriptor.
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Example 315. Rule source component metadata rule
build.gradle
dependencies {
config5 "org.sample:api:latest.gold"
components {
withModule('org.sample:api', new CustomStatusRule())
}
}
class CustomStatusRule {
@Mutate
void setStatusScheme(ComponentMetadataDetails details) {
details.statusScheme = ["bronze", "silver", "gold", "platinum"]
}
}
§
Component Selection Rules
Component selection rules may influence which component instance should be selected when multiple
versions are available that match a version selector. Rules are applied against every available version and
allow the version to be explicitly rejected by rule. This allows Gradle to ignore any component instance that
does not satisfy conditions set by the rule. Examples include:
For a dynamic version like '1.+' certain versions may be explicitly rejected from selection
For a static version like '1.4' an instance may be rejected based on extra component metadata such as the
Ivy branch attribute, allowing an instance from a subsequent repository to be used.
Rules are configured via the ComponentSelectionRules object. Each rule configured will be called with a
ComponentSelection object as an argument which contains information about the candidate version
being considered. Calling ComponentSelection.reject(java.lang.String) causes the given
candidate version to be explicitly rejected, in which case the candidate will not be considered for the
selector.
The following example shows a rule that disallows a particular version of a module but allows the dynamic
version to choose the next best candidate.
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Example 316. Component selection rule
build.gradle
configurations {
rejectConfig {
resolutionStrategy {
componentSelection {
// Accept the highest version matching the requested version that isn't '1
all { ComponentSelection selection ->
if (selection.candidate.group == 'org.sample' && selection.candidate.m
selection.reject("version 1.5 is broken for 'org.sample:api'")
}
}
}
}
}
}
dependencies {
rejectConfig "org.sample:api:1.+"
}
Note that version selection is applied starting with the highest version first. The version selected will be the
first version found that all component selection rules accept. A version is considered accepted no rule
explicitly rejects it.
Similarly, rules can be targeted at specific modules. Modules must be specified in the form of
"group:module".
Example 317. Component selection rule with module target
build.gradle
configurations {
targetConfig {
resolutionStrategy {
componentSelection {
withModule("org.sample:api") { ComponentSelection selection ->
if (selection.candidate.version == "1.5") {
selection.reject("version 1.5 is broken for 'org.sample:api'")
}
}
}
}
}
}
Component selection rules can also consider component metadata when selecting a version. Possible
metadata arguments that can be considered are ComponentMetadata and IvyModuleDescriptor.
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Example 318. Component selection rule with metadata
build.gradle
configurations {
metadataRulesConfig {
resolutionStrategy {
componentSelection {
// Reject any versions with a status of 'experimental'
all { ComponentSelection selection, ComponentMetadata metadata ->
if (selection.candidate.group == 'org.sample' && metadata.status == 'e
selection.reject("don't use experimental candidates from 'org.samp
}
}
// Accept the highest version with either a "release" branch or a status o
withModule('org.sample:api') { ComponentSelection selection, IvyModuleDesc
if (descriptor.branch != "release" && metadata.status != 'milestone')
selection.reject("'org.sample:api' must have testing branch or mil
}
}
}
}
}
}
Note that a ComponentSelection argument is always required as the first parameter when declaring a
component selection rule with additional Ivy metadata parameters, but the metadata parameters can be
declared in any order.
Lastly, component selection rules can also be defined using a rule source object. A rule source object is any
object that contains exactly one method that defines the rule action and is annotated with @Mutate.
This method:
must return void.
must have ComponentSelection as the first argument.
may have additional parameters of type ComponentMetadata and/or IvyModuleDescriptor.
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Example 319. Component selection rule using a rule source object
build.gradle
class RejectTestBranch {
@Mutate
void evaluateRule(ComponentSelection selection, IvyModuleDescriptor ivy) {
if (ivy.branch == "test") {
selection.reject("reject test branch")
}
}
}
configurations {
ruleSourceConfig {
resolutionStrategy {
componentSelection {
all new RejectTestBranch()
}
}
}
}
§
Module replacement rules
Module replacement rules allow a build to declare that a legacy library has been replaced by a new one. A
good example when a new library replaced a legacy one is the "google-collections" -> "guava" migration.
The
team
that
created
google-collections
decided
to
change
the
module
name
from
"com.google.collections:google-collections" into "com.google.guava:guava". This is a legal scenario in the
industry: teams need to be able to change the names of products they maintain, including the module
coordinates. Renaming of the module coordinates has impact on conflict resolution.
To explain the impact on conflict resolution, let’s consider the "google-collections" -> "guava" scenario. It
may happen that both libraries are pulled into the same dependency graph. For example, "our" project
depends on guava but some of our dependencies pull in a legacy version of google-collections. This can
cause runtime errors, for example during test or application execution. Gradle does not automatically resolve
the google-collections VS guava conflict because it is not considered as a "version conflict". It’s because the
module coordinates for both libraries are completely different and conflict resolution is activated when
"group" and "name" coordinates are the same but there are different versions available in the dependency
graph (for more info, refer to the section on conflict resolution). Traditional remedies to this problem are:
Declare exclusion rule to avoid pulling in "google-collections" to graph. It is probably the most popular
approach.
Avoid dependencies that pull in legacy libraries.
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Upgrade the dependency version if the new version no longer pulls in a legacy library.
Downgrade to "google-collections". It’s not recommended, just mentioned for completeness.
Traditional approaches work but they are not general enough. For example, an organisation wants to resolve
the google-collections VS guava conflict resolution problem in all projects. Starting from Gradle 2.2 it is
possible to declare that certain module was replaced by other. This enables organisations to include the
information about module replacement in the corporate plugin suite and resolve the problem holistically for
all Gradle-powered projects in the enterprise.
Example 320. Declaring module replacement
build.gradle
dependencies {
modules {
module("com.google.collections:google-collections") {
replacedBy("com.google.guava:guava")
}
}
}
For more examples and detailed API, refer to the DSL reference for ComponentMetadataHandler.
What happens when we declare that "google-collections" are replaced by "guava"? Gradle can use this
information for conflict resolution. Gradle will consider every version of "guava" newer/better than any
version of "google-collections". Also, Gradle will ensure that only guava jar is present in the classpath /
resolved file list. Note that if only "google-collections" appears in the dependency graph (e.g. no "guava")
Gradle will not eagerly replace it with "guava". Module replacement is an information that Gradle uses for
resolving conflicts. If there is no conflict (e.g. only "google-collections" or only "guava" in the graph) the
replacement information is not used.
Currently it is not possible to declare that certain modules is replaced by a set of modules. However, it is
possible to declare that multiple modules are replaced by a single module.
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Troubleshooting Dependency Resolution
Managing large dependency graphs can be challenging. This section describes techniques for
troubleshooting issues you might encounter in your project.
§
Putting the version in the filename (version the jar)
The version of a library must be part of the filename. While the version of a jar is usually in the Manifest file,
it isn’t readily apparent when you are inspecting a project. If someone asks you to look at a collection of 20
jar files, which would you prefer? A collection of files with names like commons-beanutils-1.3.jar or a
collection of files with names like spring.jar? If dependencies have file names with version numbers you
can quickly identify the versions of your dependencies.
If versions are unclear you can introduce subtle bugs which are very hard to find. For example there might
be a project which uses Hibernate 2.5. Think about a developer who decides to install version 3.0.5 of
Hibernate on her machine to fix a critical security bug but forgets to notify others in the team of this change.
She may address the security bug successfully, but she also may have introduced subtle bugs into a
codebase that was using a now-deprecated feature from Hibernate. Weeks later there is an exception on the
integration machine which can’t be reproduced on anyone’s machine. Multiple developers then spend days
on this issue only finally realising that the error would have been easy to uncover if they knew that Hibernate
had been upgraded from 2.5 to 3.0.5.
Versions in jar names increase the expressiveness of your project and make them easier to maintain. This
practice also reduces the potential for error.
§
Resolving version conflicts
Conflicting versions of the same jar should be detected and either resolved or cause an exception. If you
don’t use transitive dependency management, version conflicts are undetected and the often accidental
order of the classpath will determine what version of a dependency will win. On a large project with many
developers changing dependencies, successful builds will be few and far between as the order of
dependencies may directly affect whether a build succeeds or fails (or whether a bug appears or disappears
in production).
If you haven’t had to deal with the curse of conflicting versions of jars on a classpath, here is a small
anecdote of the fun that awaits you. In a large project with 30 submodules, adding a dependency to a
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subproject changed the order of a classpath, swapping Spring 2.5 for an older 2.4 version. While the build
continued to work, developers were starting to notice all sorts of surprising (and surprisingly awful) bugs in
production. Worse yet, this unintentional downgrade of Spring introduced several security vulnerabilities into
the system, which now required a full security audit throughout the organization.
In short, version conflicts are bad, and you should manage your transitive dependencies to avoid them. You
might also want to learn where conflicting versions are used and consolidate on a particular version of a
dependency across your organization. With a good conflict reporting tool like Gradle, that information can be
used to communicate with the entire organization and standardize on a single version. If you think version
conflicts don’t happen to you, think again. It is very common for different first-level dependencies to rely on a
range of different overlapping versions for other dependencies, and the JVM doesn’t yet offer an easy way to
have different versions of the same jar in the classpath (see the section called “Dependency management
and Java”).
Gradle offers the following conflict resolution strategies:
Newest: The newest version of the dependency is used. This is Gradle’s default strategy, and is often an
appropriate choice as long as versions are backwards-compatible.
Fail: A version conflict results in a build failure. This strategy requires all version conflicts to be resolved
explicitly in the build script. See ResolutionStrategy for details on how to explicitly choose a particular
version.
While the strategies introduced above are usually enough to solve most conflicts, Gradle provides more
fine-grained mechanisms to resolve version conflicts:
Configuring a first level dependency as forced . This approach is useful if the dependency in conflict is
already a first level dependency. See examples in DependencyHandler.
Configuring any dependency (transitive or not) as forced . This approach is useful if the dependency in
conflict is a transitive dependency. It also can be used to force versions of first level dependencies. See
examples in ResolutionStrategy.
Configuring dependency resolution to prefer modules that are part of your build (transitive or not). This
approach is useful if your build contains custom forks of modules (as part of Authoring Multi-Project Builds or
as include in Composite builds). See examples in ResolutionStrategy.
Dependency resolve rules are an incubating feature give you fine-grained control over the version selected
for a particular dependency.
To deal with problems due to version conflicts, reports with dependency graphs are also very helpful. Such
reports are another feature of dependency management.
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Using dynamic versions and changing modules
§
Using dynamic versions and changing modules
There are many situations when you want to use the latest version of a particular dependency, or the latest
in a range of versions. This can be a requirement during development, or you may be developing a library
that is designed to work with a range of dependency versions. You can easily depend on these constantly
changing dependencies by using a dynamic version . A dynamic version can be either a version range (e.g. 2.+
) or it can be a placeholder for the latest version available (e.g. latest.integration).
Alternatively, sometimes the module you request can change over time, even for the same version. An
example of this type of changing module is a Maven SNAPSHOT module, which always points at the latest
artifact published. In other words, a standard Maven snapshot is a module that never stands still so to speak,
it is a “changing module”.
The main difference between a dynamic version and a changing module is that when you resolve a
dynamic version , you’ll get the real, static version as the module name. When you resolve a changing
module , the artifacts are named using the version you requested, but the underlying artifacts may change
over time.
By default, Gradle caches dynamic versions and changing modules for 24 hours. You can override the
default cache modes using command line options. You can also change the cache expiry times in your build
programmatically using the resolution strategy.
§
Controlling dependency caching programmatically
You can fine-tune certain aspects of caching using the ResolutionStrategy for a configuration.
By default, Gradle caches dynamic versions for 24 hours. To change how long Gradle will cache the
resolved version for a dynamic version, use:
Example 321. Dynamic version cache control
build.gradle
configurations.all {
resolutionStrategy.cacheDynamicVersionsFor 10, 'minutes'
}
By default, Gradle caches changing modules for 24 hours. To change how long Gradle will cache the
meta-data and artifacts for a changing module, use:
Example 322. Changing module cache control
build.gradle
configurations.all {
resolutionStrategy.cacheChangingModulesFor 4, 'hours'
}
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For more details, take a look at the API documentation for ResolutionStrategy.
§
Controlling dependency caching from the command line
§
Avoiding network access with offline mode
The --offline command line switch tells Gradle to always use dependency modules from the cache,
regardless if they are due to be checked again. When running with offline, Gradle will never attempt to
access the network to perform dependency resolution. If required modules are not present in the
dependency cache, build execution will fail.
§
Forcing all dependencies to be re-resolved
At times, the Gradle Dependency Cache can be out of sync with the actual state of the configured
repositories. Perhaps a repository was initially misconfigured, or perhaps a “non-changing” module was
published incorrectly. To refresh all dependencies in the dependency cache, use the --refresh-dependencies
option on the command line.
The --refresh-dependencies option tells Gradle to ignore all cached entries for resolved modules and
artifacts. A fresh resolve will be performed against all configured repositories, with dynamic versions
recalculated, modules refreshed, and artifacts downloaded. However, where possible Gradle will check if the
previously downloaded artifacts are valid before downloading again. This is done by comparing published
SHA1 values in the repository with the SHA1 values for existing downloaded artifacts.
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Extending the build
Writing Custom Task Classes
Gradle supports two types of task. One such type is the simple task, where you define the task with an
action closure. We have seen these in Build Script Basics. For this type of task, the action closure
determines the behaviour of the task. This type of task is good for implementing one-off tasks in your build
script.
The other type of task is the enhanced task, where the behaviour is built into the task, and the task provides
some properties which you can use to configure the behaviour. We have seen these in Authoring Tasks.
Most Gradle plugins use enhanced tasks. With enhanced tasks, you don’t need to implement the task
behaviour as you do with simple tasks. You simply declare the task and configure the task using its
properties. In this way, enhanced tasks let you reuse a piece of behaviour in many different places, possibly
across different builds.
The behaviour and properties of an enhanced task is defined by the task’s class. When you declare an
enhanced task, you specify the type, or class of the task.
Implementing your own custom task class in Gradle is easy. You can implement a custom task class in
pretty much any language you like, provided it ends up compiled to bytecode. In our examples, we are going
to use Groovy as the implementation language. Groovy, Java or Kotlin are all good choices as the language
to use to implement a task class, as the Gradle API has been designed to work well with these languages. In
general, a task implemented using Java or Kotlin, which are statically typed, will perform better than the
same task implemented using Groovy.
§
Packaging a task class
There are several places where you can put the source for the task class.
Build script
You can include the task class directly in the build script. This has the benefit that the task class is
automatically compiled and included in the classpath of the build script without you having to do anything.
However, the task class is not visible outside the build script, and so you cannot reuse the task class
outside the build script it is defined in.
buildSrc project
You can put the source for the task class in the rootProjectDir /buildSrc/src/main/groovy
directory. Gradle will take care of compiling and testing the task class and making it available on the
classpath of the build script. The task class is visible to every build script used by the build. However, it is
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not visible outside the build, and so you cannot reuse the task class outside the build it is defined in.
Using the buildSrc project approach separates the task declaration - that is, what the task should do from the task implementation - that is, how the task does it.
See Organizing Build Logic for more details about the buildSrc project.
Standalone project
You can create a separate project for your task class. This project produces and publishes a JAR which
you can then use in multiple builds and share with others. Generally, this JAR might include some
custom plugins, or bundle several related task classes into a single library. Or some combination of the
two.
In our examples, we will start with the task class in the build script, to keep things simple. Then we will look
at creating a standalone project.
§
Writing a simple task class
To implement a custom task class, you extend DefaultTask.
Example 323. Defining a custom task
build.gradle
class GreetingTask extends DefaultTask {
}
This task doesn’t do anything useful, so let’s add some behaviour. To do so, we add a method to the task
and mark it with the TaskAction annotation. Gradle will call the method when the task executes. You don’t
have to use a method to define the behaviour for the task. You could, for instance, call doFirst() or doLast()
with a closure in the task constructor to add behaviour.
Example 324. A hello world task
build.gradle
class GreetingTask extends DefaultTask {
@TaskAction
def greet() {
println 'hello from GreetingTask'
}
}
// Create a task using the task type
task hello(type: GreetingTask)
Output of gradle -q hello
> gradle -q hello
hello from GreetingTask
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Let’s add a property to the task, so we can customize it. Tasks are simply POGOs, and when you declare a
task, you can set the properties or call methods on the task object. Here we add a greeting property, and
set the value when we declare the greeting task.
Example 325. A customizable hello world task
build.gradle
class GreetingTask extends DefaultTask {
String greeting = 'hello from GreetingTask'
@TaskAction
def greet() {
println greeting
}
}
// Use the default greeting
task hello(type: GreetingTask)
// Customize the greeting
task greeting(type: GreetingTask) {
greeting = 'greetings from GreetingTask'
}
Output of gradle -q hello greeting
> gradle -q hello greeting
hello from GreetingTask
greetings from GreetingTask
§
A standalone project
Now we will move our task to a standalone project, so we can publish it and share it with others. This project
is simply a Groovy project that produces a JAR containing the task class. Here is a simple build script for the
project. It applies the Groovy plugin, and adds the Gradle API as a compile-time dependency.
Example 326. A build for a custom task
build.gradle
apply plugin: 'groovy'
dependencies {
compile gradleApi()
compile localGroovy()
}
Note: The code for this example can be found at samples/customPlugin/plugin in the ‘-all’
distribution of Gradle.
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We just follow the convention for where the source for the task class should go.
Example 327. A custom task
src/main/groovy/org/gradle/GreetingTask.groovy
package org.gradle
import org.gradle.api.DefaultTask
import org.gradle.api.tasks.TaskAction
class GreetingTask extends DefaultTask {
String greeting = 'hello from GreetingTask'
@TaskAction
def greet() {
println greeting
}
}
§
Using your task class in another project
To use a task class in a build script, you need to add the class to the build script’s classpath. To do this, you
use a buildscript { } block, as described in the section called “External dependencies for the build
script”. The following example shows how you might do this when the JAR containing the task class has
been published to a local repository:
Example 328. Using a custom task in another project
build.gradle
buildscript {
repositories {
maven {
url uri('../repo')
}
}
dependencies {
classpath group: 'org.gradle', name: 'customPlugin',
version: '1.0-SNAPSHOT'
}
}
task greeting(type: org.gradle.GreetingTask) {
greeting = 'howdy!'
}
Writing tests for your task class
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§
Writing tests for your task class
You can use the ProjectBuilder class to create Project instances to use when you test your task
class.
Example 329. Testing a custom task
src/test/groovy/org/gradle/GreetingTaskTest.groovy
class GreetingTaskTest {
@Test
public void canAddTaskToProject() {
Project project = ProjectBuilder.builder().build()
def task = project.task('greeting', type: GreetingTask)
assertTrue(task instanceof GreetingTask)
}
}
§
Incremental tasks
Note: Incremental tasks are an incubating feature.
Since the introduction of the implementation described above (early in the Gradle 1.6 release cycle),
discussions within the Gradle community have produced superior ideas for exposing the information
about changes to task implementors to what is described below. As such, the API for this feature will
almost certainly change in upcoming releases. However, please do experiment with the current
implementation and share your experiences with the Gradle community.
The feature incubation process, which is part of the Gradle feature lifecycle (see Appendix C), exists
for this purpose of ensuring high quality final implementations through incorporation of early user
feedback.
With Gradle, it’s very simple to implement a task that is skipped when all of its inputs and outputs are up to
date (see the section called “Up-to-date checks (AKA Incremental Build)” ). However, there are times when
only a few input files have changed since the last execution, and you’d like to avoid reprocessing all of the
unchanged inputs. This can be particularly useful for a transformer task, that converts input files to output
files on a 1:1 basis.
If you’d like to optimise your build so that only out-of-date inputs are processed, you can do so with an
incremental task .
Implementing an incremental task
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§
Implementing an incremental task
For a task to process inputs incrementally, that task must contain an incremental task action . This is a task
action method that contains a single IncrementalTaskInputs parameter, which indicates to Gradle that
the action will process the changed inputs only.
The
incremental
task
action
may
supply
an
IncrementalTaskInputs.outOfDate(org.gradle.api.Action) action for processing any input file
that is out-of-date, and a IncrementalTaskInputs.removed(org.gradle.api.Action) action that
executes for any input file that has been removed since the previous execution.
Example 330. Defining an incremental task action
build.gradle
class IncrementalReverseTask extends DefaultTask {
@InputDirectory
def File inputDir
@OutputDirectory
def File outputDir
@Input
def inputProperty
@TaskAction
void execute(IncrementalTaskInputs inputs) {
println inputs.incremental ? 'CHANGED inputs considered out of date'
: 'ALL inputs considered out of date'
if (!inputs.incremental)
project.delete(outputDir.listFiles())
inputs.outOfDate { change ->
println "out of date: ${change.file.name}"
def targetFile = new File(outputDir, change.file.name)
targetFile.text = change.file.text.reverse()
}
inputs.removed { change ->
println "removed: ${change.file.name}"
def targetFile = new File(outputDir, change.file.name)
targetFile.delete()
}
}
}
Note: The code for this example can be found at samples/userguide/tasks/incrementalTask
in the ‘-all’ distribution of Gradle.
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If for some reason the task is not run incremental, e.g. by running with --rerun-tasks, only the outOfDate
action is executed, even if there were deleted input files. You should consider handling this case at the
beginning, as is done in the example above.
For a simple transformer task like this, the task action simply needs to generate output files for any
out-of-date inputs, and delete output files for any removed inputs.
A task may only contain a single incremental task action.
§
Which inputs are considered out of date?
When Gradle has history of a previous task execution, and the only changes to the task execution context
since that execution are to input files, then Gradle is able to determine which input files need to be
reprocessed
by
the
task.
In
this
case,
the
IncrementalTaskInputs.outOfDate(org.gradle.api.Action) action will be executed for any
input
file
that
was
added
or
modified ,
and
the
IncrementalTaskInputs.removed(org.gradle.api.Action) action will be executed for any
removed input file.
However, there are many cases where Gradle is unable to determine which input files need to be
reprocessed. Examples include:
There is no history available from a previous execution.
You are building with a different version of Gradle. Currently, Gradle does not use task history from a
different version.
An upToDateWhen criteria added to the task returns false.
An input property has changed since the previous execution.
One or more output files have changed since the previous execution.
In any of these cases, Gradle will consider all of the input files to be outOfDate . The
IncrementalTaskInputs.outOfDate(org.gradle.api.Action) action will be executed for every
input file, and the IncrementalTaskInputs.removed(org.gradle.api.Action) action will not be
executed at all.
You can check if Gradle was able to determine the incremental changes to input files with
IncrementalTaskInputs.isIncremental().
§
An incremental task in action
Given the incremental task implementation above, we can explore the various change scenarios by
example. Note that the various mutation tasks ('updateInputs', 'removeInput', etc) are only present for
demonstration purposes: these would not normally be part of your build script.
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First, consider the IncrementalReverseTask executed against a set of inputs for the first time. In this
case, all inputs will be considered “out of date”:
Example 331. Running the incremental task for the first time
build.gradle
task incrementalReverse(type: IncrementalReverseTask) {
inputDir = file('inputs')
outputDir = file("$buildDir/outputs")
inputProperty = project.properties['taskInputProperty'] ?: 'original'
}
Build layout
incrementalTask/
build.gradle
inputs/
1.txt
2.txt
3.txt
Output of gradle -q incrementalReverse
> gradle -q incrementalReverse
ALL inputs considered out of date
out of date: 1.txt
out of date: 2.txt
out of date: 3.txt
Naturally when the task is executed again with no changes, then the entire task is up to date and no files are
reported to the task action:
Example 332. Running the incremental task with unchanged inputs
Output of gradle -q incrementalReverse
> gradle -q incrementalReverse
When an input file is modified in some way or a new input file is added, then re-executing the task results in
those files being reported to IncrementalTaskInputs.outOfDate(org.gradle.api.Action):
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Example 333. Running the incremental task with updated input files
build.gradle
task updateInputs() {
doLast {
file('inputs/1.txt').text = 'Changed content for existing file 1.'
file('inputs/4.txt').text = 'Content for new file 4.'
}
}
Output of gradle -q updateInputs incrementalReverse
> gradle -q updateInputs incrementalReverse
CHANGED inputs considered out of date
out of date: 1.txt
out of date: 4.txt
When an existing input file is removed, then re-executing the task results in that file being reported to
IncrementalTaskInputs.removed(org.gradle.api.Action):
Example 334. Running the incremental task with an input file removed
build.gradle
task removeInput() {
doLast {
file('inputs/3.txt').delete()
}
}
Output of gradle -q removeInput incrementalReverse
> gradle -q removeInput incrementalReverse
CHANGED inputs considered out of date
removed: 3.txt
When an output file is deleted (or modified), then Gradle is unable to determine which input files are out of
date.
In
this
case,
all
input
files
are
reported
to
the
IncrementalTaskInputs.outOfDate(org.gradle.api.Action) action, and no input files are
reported to the IncrementalTaskInputs.removed(org.gradle.api.Action) action:
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Example 335. Running the incremental task with an output file removed
build.gradle
task removeOutput() {
doLast {
file("$buildDir/outputs/1.txt").delete()
}
}
Output of gradle -q removeOutput incrementalReverse
> gradle -q removeOutput incrementalReverse
ALL inputs considered out of date
out of date: 1.txt
out of date: 2.txt
out of date: 3.txt
When a task input property is modified, Gradle is unable to determine how this property impacted the task
outputs, so all input files are assumed to be out of date. So similar to the changed output file example, all
input files are reported to the IncrementalTaskInputs.outOfDate(org.gradle.api.Action)
action,
and
no
input
files
are
reported
to
the
IncrementalTaskInputs.removed(org.gradle.api.Action) action:
Example 336. Running the incremental task with an input property changed
Output of gradle -q -PtaskInputProperty=changed incrementalReverse
> gradle -q -PtaskInputProperty=changed incrementalReverse
ALL inputs considered out of date
out of date: 1.txt
out of date: 2.txt
out of date: 3.txt
§
Storing incremental state for cached tasks
Using Gradle’s IncrementalTaskInputs is not the only way to create tasks that only works on changes
since the last execution. Tools like the Kotlin compiler provide incrementality as a built-in feature. The way
this is typically implemented is that the tool stores some analysis data about the state of the previous
execution in some file. If such state files are relocatable, then they can be declared as outputs of the task.
This way when the task’s results are loaded from cache, the next execution can already use the analysis
data loaded from cache, too.
However, if the state files are non-relocatable, then they can’t be shared via the build cache. Indeed, when
the task is loaded from cache, any such state files must be cleaned up to prevent stale state to confuse the
tool during the next execution. Gradle can ensure such stale files are removed if they are declared via task.localState
or a property is marked with the @LocalState annotation.
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The Worker API
§
The Worker API
Note: The Worker API is an incubating feature.
As can be seen from the discussion of incremental tasks, the work that a task performs can be viewed as
discrete units (i.e. a subset of inputs that are transformed to a certain subset of outputs). Many times, these
units of work are highly independent of each other, meaning they can be performed in any order and simply
aggregated together to form the overall action of the task. In a single threaded execution, these units of work
would execute in sequence, however if we have multiple processors, it would be desirable to perform
independent units of work concurrently. By doing so, we can fully utilize the available resources at build time
and complete the activity of the task faster.
The Worker API provides a mechanism for doing exactly this. It allows for safe, concurrent execution of
multiple items of work during a task action. But the benefits of the Worker API are not confined to
parallelizing the work of a task. You can also configure a desired level of isolation such that work can be
executed in an isolated classloader or even in an isolated process. Furthermore, the benefits extend beyond
even the execution of a single task. Using the Worker API, Gradle can begin to execute tasks in parallel by
default. In other words, once a task has submitted its work to be executed asynchronously, and has exited
the task action, Gradle can then begin the execution of other independent tasks in parallel, even if those
tasks are in the same project.
§
Using the Worker API
In order to submit work to the Worker API, two things must be provided: an implementation of the unit of
work, and a configuration for the unit of work. The implementation is simply a class that extends java.lang.Runnable
. This class should have a constructor that is annotated with javax.inject.Inject and accepts
parameters that configure the class for a single unit of work. When a unit of work is submitted to the
WorkerExecutor, an instance of this class will be created and the parameters configured for the unit of
work will be passed to the constructor.
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Example 337. Creating a unit of work implementation
build.gradle
import org.gradle.workers.WorkerExecutor
import javax.inject.Inject
// The implementation of a single unit of work
class ReverseFile implements Runnable {
File fileToReverse
File destinationFile
@Inject
public ReverseFile(File fileToReverse, File destinationFile) {
this.fileToReverse = fileToReverse
this.destinationFile = destinationFile
}
@Override
public void run() {
destinationFile.text = fileToReverse.text.reverse()
}
}
The configuration of the worker is represented by a WorkerConfiguration and is set by configuring an
instance of this object at the time of submission. However, in order to submit the unit of work, it is necessary
to first acquire the WorkerExecutor. To do this, a constructor should be provided that is annotated with javax.inject
and accepts a WorkerExecutor parameter. Gradle will inject the instance of WorkerExecutor at runtime
when the task is created.
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Example 338. Submitting a unit of work for execution
build.gradle
class ReverseFiles extends SourceTask {
final WorkerExecutor workerExecutor
@OutputDirectory
File outputDir
// The WorkerExecutor will be injected by Gradle at runtime
@Inject
public ReverseFiles(WorkerExecutor workerExecutor) {
this.workerExecutor = workerExecutor
}
@TaskAction
void reverseFiles() {
// Create and submit a unit of work for each file
source.files.each { file ->
workerExecutor.submit(ReverseFile.class) { WorkerConfiguration config ->
// Use the minimum level of isolation
config.isolationMode = IsolationMode.NONE
// Constructor parameters for the unit of work implementation
config.params file, project.file("${outputDir}/${file.name}")
}
}
}
}
Note that one element of the WorkerConfiguration is the params property. These are the parameters
passed to the constructor of the unit of work implementation for each item of work submitted. Any
parameters provided to the unit of work must be java.io.Serializable.
Once all of the work for a task action has been submitted, it is safe to exit the task action. The work will be
executed asynchronously and in parallel (up to the setting of max-workers). Of course, any tasks that are
dependent on this task (and any subsequent task actions of this task) will not begin executing until all of the
asynchronous work completes. However, other independent tasks that have no relationship to this task can
begin executing immediately.
If any failures occur while executing the asynchronous work, the task will fail and a
WorkerExecutionException will be thrown detailing the failure for each failed work item. This will be
treated like any failure during task execution and will prevent any dependent tasks from executing.
In some cases, however, it might be desirable to wait for work to complete before exiting the task action.
This is possible using the WorkerExecutor.await() method. As in the case of allowing the work to
complete asynchronously, any failures that occur while executing an item of work will be surfaced as a
WorkerExecutionException thrown from the WorkerExecutor.await() method.
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Note: Note that Gradle will only begin running other independent tasks in parallel when a task has
exited
a
task
action
and
returned
control
of
execution
to
Gradle.
When
WorkerExecutor.await() is used, execution does not leave the task action. This means that
Gradle will not allow other tasks to begin executing and will wait for the task action to complete
before doing so.
Example 339. Waiting for asynchronous work to complete
build.gradle
// Create and submit a unit of work for each file
source.files.each { file ->
workerExecutor.submit(ReverseFile.class) { config ->
config.isolationMode = IsolationMode.NONE
// Constructor parameters for the unit of work implementation
config.params file, project.file("${outputDir}/${file.name}")
}
}
// Wait for all asynchronous work to complete before continuing
workerExecutor.await()
logger.lifecycle("Created ${outputDir.listFiles().size()} reversed files in ${project.rela
§
Isolation Modes
Gradle provides three isolation modes that can be configured on a unit of work and are specified using the
IsolationMode enum:
IsolationMode.NONE
This states that the work should be run in a thread with a minimum of isolation. For instance, it will share
the same classloader that the task is loaded from. This is the fastest level of isolation.
IsolationMode.CLASSLOADER
This states that the work should be run in a thread with an isolated classloader. The classloader will have
the classpath from the classloader that the unit of work implementation class was loaded from as well as
any
additional
classpath
entries
added
through
WorkerConfiguration.classpath(java.lang.Iterable).
IsolationMode.PROCESS
This states that the work should be run with a maximum level of isolation by executing the work in a
separate process. The classloader of the process will use the classpath from the classloader that the unit
of work was loaded from as well as any additional classpath entries added through
WorkerConfiguration.classpath(java.lang.Iterable). Furthermore, the process will be a
Worker Daemon which will stay alive and can be reused for future work items that may have the same
requirements. This process can be configured with different settings than the Gradle JVM using
WorkerConfiguration.forkOptions(org.gradle.api.Action).
Worker Daemons
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§
Worker Daemons
When using IsolationMode.PROCESS, gradle will start a long-lived Worker Daemon process that can be
reused for future work items.
Example 340. Submitting an item of work to run in a worker daemon
build.gradle
workerExecutor.submit(ReverseFile.class) { WorkerConfiguration config ->
// Run this work in an isolated process
config.isolationMode = IsolationMode.PROCESS
// Configure the options for the forked process
config.forkOptions { JavaForkOptions options ->
options.maxHeapSize = "512m"
options.systemProperty "org.gradle.sample.showFileSize", "true"
}
// Constructor parameters for the unit of work implementation
config.params file, project.file("${outputDir}/${file.name}")
}
When a unit of work for a Worker Daemon is submitted, Gradle will first look to see if a compatible, idle
daemon already exists. If so, it will send the unit of work to the idle daemon, marking it as busy. If not, it will
start a new daemon. When evaluating compatibility, Gradle looks at a number of criteria, all of which can be
controlled through WorkerConfiguration.forkOptions(org.gradle.api.Action).
executable
A daemon is considered compatible only if it uses the same java executable.
classpath
A daemon is considered compatible if its classpath contains all of the classpath entries requested. Note
that a daemon is considered compatible if it has more classpath entries in addition to those requested.
heap settings
A daemon is considered compatible if it has at least the same heap size settings as requested. In other
words, a daemon that has higher heap settings than requested would be considered compatible.
jvm arguments
A daemon is considered compatible if it has set all of the jvm arguments requested. Note that a daemon
is considered compatible if it has additional jvm arguments beyond those requested (except for
arguments treated specially such as heap settings, assertions, debug, etc).
system properties
A daemon is considered compatible if it has set all of the system properties requested with the same
values. Note that a daemon is considered compatible if it has additional system properties beyond those
requested.
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environment variables
A daemon is considered compatible if it has set all of the environment variables requested with the same
values. Note that a daemon is considered compatible if it has more environment variables in addition to
those requested.
bootstrap classpath
A daemon is considered compatible if it contains all of the bootstrap classpath entries requested. Note
that a daemon is considered compatible if it has more bootstrap classpath entries in addition to those
requested.
debug
A daemon is considered compatible only if debug is set to the same value as requested (true or false).
enable assertions
A daemon is considered compatible only if enable assertions is set to the same value as requested (true
or false).
default character encoding
A daemon is considered compatible only if the default character encoding is set to the same value as
requested.
Worker daemons will remain running until either the build daemon that started them is stopped, or system
memory becomes scarce. When available system memory is low, Gradle will begin stopping worker
daemons in an attempt to minimize memory consumption.
§
Re-using logic between task classes
There are different ways to re-use logic between task classes. The easiest case is when you can extract the
logic you want to share in a separate method or class and then use the extracted piece of code in your
tasks. For example, the Copy task re-uses the logic of the Project.copy(org.gradle.api.Action)
method. Another option is to add a task dependency on the task which outputs you want to re-use. Other
options include using task rules or the worker API.
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Writing Custom Plugins
A Gradle plugin packages up reusable pieces of build logic, which can be used across many different
projects and builds. Gradle allows you to implement your own plugins, so you can reuse your build logic, and
share it with others.
You can implement a Gradle plugin in any language you like, provided the implementation ends up compiled
as bytecode. In our examples, we are going to use Groovy as the implementation language. Groovy, Java or
Kotlin are all good choices as the language to use to implement a plugin, as the Gradle API has been
designed to work well with these languages. In general, a plugin implemented using Java or Kotlin, which
are statically typed, will perform better than the same plugin implemented using Groovy.
§
Packaging a plugin
There are several places where you can put the source for the plugin.
Build script
You can include the source for the plugin directly in the build script. This has the benefit that the plugin is
automatically compiled and included in the classpath of the build script without you having to do anything.
However, the plugin is not visible outside the build script, and so you cannot reuse the plugin outside the
build script it is defined in.
buildSrc project
You can put the source for the plugin in the rootProjectDir /buildSrc/src/main/groovy
directory. Gradle will take care of compiling and testing the plugin and making it available on the
classpath of the build script. The plugin is visible to every build script used by the build. However, it is not
visible outside the build, and so you cannot reuse the plugin outside the build it is defined in.
See Organizing Build Logic for more details about the buildSrc project.
Standalone project
You can create a separate project for your plugin. This project produces and publishes a JAR which you
can then use in multiple builds and share with others. Generally, this JAR might include some plugins, or
bundle several related task classes into a single library. Or some combination of the two.
In our examples, we will start with the plugin in the build script, to keep things simple. Then we will look at
creating a standalone project.
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Writing a simple plugin
§
Writing a simple plugin
To create a Gradle plugin, you need to write a class that implements the Plugin interface. When the plugin
is applied to a project, Gradle creates an instance of the plugin class and calls the instance’s
Plugin.apply(T) method. The project object is passed as a parameter, which the plugin can use to
configure the project however it needs to. The following sample contains a greeting plugin, which adds a hello
task to the project.
Example 341. A custom plugin
build.gradle
class GreetingPlugin implements Plugin<Project> {
void apply(Project project) {
project.task('hello') {
doLast {
println 'Hello from the GreetingPlugin'
}
}
}
}
// Apply the plugin
apply plugin: GreetingPlugin
Output of gradle -q hello
> gradle -q hello
Hello from the GreetingPlugin
One thing to note is that a new instance of a plugin is created for each project it is applied to. Also note that
the Plugin class is a generic type. This example has it receiving the Project type as a type parameter. A
plugin can instead receive a parameter of type Settings, in which case the plugin can be applied in a
settings script, or a parameter of type Gradle, in which case the plugin can be applied in an initialization
script.
§
Making the plugin configurable
Most plugins need to obtain some configuration from the build script. One method for doing this is to use
extension objects . The Gradle Project has an associated ExtensionContainer object that contains all
the settings and properties for the plugins that have been applied to the project. You can provide
configuration for your plugin by adding an extension object to this container. An extension object is simply a
Java Bean compliant class. Groovy is a good language choice to implement an extension object because
plain old Groovy objects contain all the getter and setter methods that a Java Bean requires. Java and Kotlin
are other good choices.
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Let’s add a simple extension object to the project. Here we add a greeting extension object to the project,
which allows you to configure the greeting.
Example 342. A custom plugin extension
build.gradle
class GreetingPluginExtension {
String message = 'Hello from GreetingPlugin'
}
class GreetingPlugin implements Plugin<Project> {
void apply(Project project) {
// Add the 'greeting' extension object
def extension = project.extensions.create('greeting', GreetingPluginExtension)
// Add a task that uses configuration from the extension object
project.task('hello') {
doLast {
println extension.message
}
}
}
}
apply plugin: GreetingPlugin
// Configure the extension
greeting.message = 'Hi from Gradle'
Output of gradle -q hello
> gradle -q hello
Hi from Gradle
In this example, GreetingPluginExtension is a plain old Groovy object with a property called message.
The extension object is added to the plugin list with the name greeting. This object then becomes
available as a project property with the same name as the extension object.
Oftentimes, you have several related properties you need to specify on a single plugin. Gradle adds a
configuration closure block for each extension object, so you can group settings together. The following
example shows you how this works.
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Example 343. A custom plugin with configuration closure
build.gradle
class GreetingPluginExtension {
String message
String greeter
}
class GreetingPlugin implements Plugin<Project> {
void apply(Project project) {
def extension = project.extensions.create('greeting', GreetingPluginExtension)
project.task('hello') {
doLast {
println "${extension.message} from ${extension.greeter}"
}
}
}
}
apply plugin: GreetingPlugin
// Configure the extension using a DSL block
greeting {
message = 'Hi'
greeter = 'Gradle'
}
Output of gradle -q hello
> gradle -q hello
Hi from Gradle
In this example, several settings can be grouped together within the greeting closure. The name of the
closure block in the build script (greeting) needs to match the extension object name. Then, when the
closure is executed, the fields on the extension object will be mapped to the variables within the closure
based on the standard Groovy closure delegate feature.
§
Working with files in custom tasks and plugins
When developing custom tasks and plugins, it’s a good idea to be very flexible when accepting input
configuration for file locations. To do this, you can leverage the Project.file(java.lang.Object)
method to resolve values to files as late as possible.
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Example 344. Evaluating file properties lazily
build.gradle
class GreetingToFileTask extends DefaultTask {
def destination
File getDestination() {
project.file(destination)
}
@TaskAction
def greet() {
def file = getDestination()
file.parentFile.mkdirs()
file.write 'Hello!'
}
}
task greet(type: GreetingToFileTask) {
destination = { project.greetingFile }
}
task sayGreeting(dependsOn: greet) {
doLast {
println file(greetingFile).text
}
}
ext.greetingFile = "$buildDir/hello.txt"
Output of gradle -q sayGreeting
> gradle -q sayGreeting
Hello!
In this example, we configure the greet task destination property as a closure, which is evaluated with
the Project.file(java.lang.Object) method to turn the return value of the closure into a File
object at the last minute. You will notice that in the example above we specify the greetingFile property
value after we have configured to use it for the task. This kind of lazy evaluation is a key benefit of accepting
any value when setting a file property, then resolving that value when reading the property.
§
Mapping extension properties to task properties
Capturing user input from the build script through an extension and mapping it to input/output properties of a
custom task is considered a best practice. The end user only interacts with the exposed DSL defined by the
extension. The imperative logic is hidden in the plugin implementation.
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The extension declaration in the build script as well as the mapping between extension properties and
custom task properties occurs during Gradle’s configuration phase of the build lifecycle. To avoid evaluation
order issues, the actual value of a mapped property has to be resolved during the execution phase. For
more information please see the section called “Build phases”. Gradle’s API offers types for representing a
property that should be lazily evaluated e.g. during execution time. Refer to Lazy Configuration for more
information.
The following demonstrates the usage of the type for mapping an extension property to a task property:
Example 345. Mapping extension properties to task properties
build.gradle
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class GreetingPlugin implements Plugin<Project> {
void apply(Project project) {
def extension = project.extensions.create('greeting', GreetingPluginExtension, pro
project.tasks.create('hello', Greeting) {
message = extension.message
outputFiles = extension.outputFiles
}
}
}
class GreetingPluginExtension {
final Property<String> message
final ConfigurableFileCollection outputFiles
GreetingPluginExtension(Project project) {
message = project.objects.property(String)
message.set('Hello from GreetingPlugin')
outputFiles = project.files()
}
void setOutputFiles(FileCollection outputFiles) {
this.outputFiles.setFrom(outputFiles)
}
}
class Greeting extends DefaultTask {
final Property<String> message = project.objects.property(String)
final ConfigurableFileCollection outputFiles = project.files()
void setOutputFiles(FileCollection outputFiles) {
this.outputFiles.setFrom(outputFiles)
}
@TaskAction
void printMessage() {
outputFiles.each {
logger.quiet "Writing message 'Hi from Gradle' to file"
it.text = message.get()
}
}
}
apply plugin: GreetingPlugin
greeting {
message = 'Hi from Gradle'
outputFiles = files('a.txt', 'b.txt')
}
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Note: The code for this example can be found at samples/userguide/tasks/mapExtensionPropertiesToT
in the ‘-all’ distribution of Gradle.
Output of gradle -q hello
> gradle -q hello
Writing message 'Hi from Gradle' to file
Writing message 'Hi from Gradle' to file
§
A standalone project
Now we will move our plugin to a standalone project, so we can publish it and share it with others. This
project is simply a Groovy project that produces a JAR containing the plugin classes. Here is a simple build
script for the project. It applies the Groovy plugin, and adds the Gradle API as a compile-time dependency.
Example 346. A build for a custom plugin
build.gradle
apply plugin: 'groovy'
dependencies {
compile gradleApi()
compile localGroovy()
}
Note: The code for this example can be found at samples/customPlugin/plugin in the ‘-all’
distribution of Gradle.
So how does Gradle find the Plugin implementation? The answer is you need to provide a properties file in
the jar’s META-INF/gradle-plugins directory that matches the id of your plugin.
Example 347. Wiring for a custom plugin
src/main/resources/META-INF/gradle-plugins/org.samples.greeting.properties
implementation-class=org.gradle.GreetingPlugin
Notice that the properties filename matches the plugin id and is placed in the resources folder, and that the implementat
property identifies the Plugin implementation class.
§
Creating a plugin id
Plugin ids are fully qualified in a manner similar to Java packages (i.e. a reverse domain name). This helps
to avoid collisions and provides a way to group plugins with similar ownership.
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Your plugin id should be a combination of components that reflect namespace (a reasonable pointer to you
or your organization) and the name of the plugin it provides. For example if you had a Github account named
"foo" and your plugin was named "bar", a suitable plugin id might be com.github.foo.bar. Similarly, if
the plugin was developed at the baz organization, the plugin id might be org.baz.bar.
Plugin ids should conform to the following:
May contain any alphanumeric character, '.', and '-'.
Must contain at least one '.' character separating the namespace from the name of the plugin.
Conventionally use a lowercase reverse domain name convention for the namespace.
Conventionally use only lowercase characters in the name.
org.gradle and com.gradleware namespaces may not be used.
Cannot start or end with a '.' character.
Cannot contain consecutive '.' characters (i.e. '..').
Although there are conventional similarities between plugin ids and package names, package names are
generally more detailed than is necessary for a plugin id. For instance, it might seem reasonable to add
"gradle" as a component of your plugin id, but since plugin ids are only used for Gradle plugins, this would
be superfluous. Generally, a namespace that identifies ownership and a name are all that are needed for a
good plugin id.
§
Publishing your plugin
If you are publishing your plugin internally for use within your organization, you can publish it like any other
code artifact. See the ivy and maven chapters on publishing artifacts.
If you are interested in publishing your plugin to be used by the wider Gradle community, you can publish it
to the Gradle plugin portal. This site provides the ability to search for and gather information about plugins
contributed by the Gradle community. See the instructions here on how to make your plugin available on this
site.
§
Using your plugin in another project
To use a plugin in a build script, you need to add the plugin classes to the build script’s classpath. To do this,
you use a “buildscript { }” block, as described in the section called “Applying plugins with the buildscript
block”. The following example shows how you might do this when the JAR containing the plugin has been
published to a local repository:
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Example 348. Using a custom plugin in another project
build.gradle
buildscript {
repositories {
maven {
url uri('../repo')
}
}
dependencies {
classpath group: 'org.gradle', name: 'customPlugin',
version: '1.0-SNAPSHOT'
}
}
apply plugin: 'org.samples.greeting'
Alternatively, if your plugin is published to the plugin portal, you can use the incubating plugins DSL (see the
section called “Applying plugins with the plugins DSL”) to apply the plugin:
Example 349. Applying a community plugin with the plugins DSL
build.gradle
plugins {
id 'com.jfrog.bintray' version '0.4.1'
}
§
Writing tests for your plugin
You can use the ProjectBuilder class to create Project instances to use when you test your plugin
implementation.
Example 350. Testing a custom plugin
src/test/groovy/org/gradle/GreetingPluginTest.groovy
class GreetingPluginTest {
@Test
public void greeterPluginAddsGreetingTaskToProject() {
Project project = ProjectBuilder.builder().build()
project.pluginManager.apply 'org.samples.greeting'
assertTrue(project.tasks.hello instanceof GreetingTask)
}
}
Using the Java Gradle Plugin development plugin
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§
Using the Java Gradle Plugin development plugin
You can use the incubating Java Gradle Plugin development plugin to eliminate some of the boilerplate
declarations in your build script and provide some basic validations of plugin metadata. This plugin will
automatically apply the Java plugin, add the gradleApi() dependency to the compile configuration, and
perform plugin metadata validations as part of the jar task execution.
Example 351. Using the Java Gradle Plugin Development plugin
build.gradle
plugins {
id 'java-gradle-plugin'
}
When publishing plugins to custom plugin repositories using the ivy or maven publish plugins, the Java
Gradle Plugin development plugin will also generate plugin marker artifacts named based on the plugin id
which depend on the plugin’s implementation artifact.
§
Providing a configuration DSL for the plugin
As we saw above, you can use an extension object to provide configuration for your plugin. Using an
extension object also extends the Gradle DSL to add a project property and DSL block for the plugin. An
extension object is simply a regular object, and so you can provide DSL elements nested inside this block by
adding properties and methods to the extension object.
Gradle provides several conveniences to help create a well-behaved DSL for your plugin.
§
Nested DSL elements
When Gradle creates a task or extension object, Gradle decorates the implementation class to mix in DSL
support. To create a nested DSL element you can use the ObjectFactory type to create objects that are
similarly decorated. These decorated objects can then be made visible to the DSL through properties and
methods of the plugin’s extension:
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Example 352. Nested DSL elements
build.gradle
class Person {
String name
}
class GreetingPluginExtension {
String message
final Person greeter
@javax.inject.Inject
GreetingPluginExtension(ObjectFactory objectFactory) {
// Create a Person instance
greeter = objectFactory.newInstance(Person)
}
void greeter(Action<? super Person> action) {
action.execute(greeter)
}
}
class GreetingPlugin implements Plugin<Project> {
void apply(Project project) {
// Create the extension, passing in an ObjectFactory for it to use
def extension = project.extensions.create('greeting', GreetingPluginExtension, pro
project.task('hello') {
doLast {
println "${extension.message} from ${extension.greeter.name}"
}
}
}
}
apply plugin: GreetingPlugin
greeting {
message = 'Hi'
greeter {
name = 'Gradle'
}
}
Output of gradle -q hello
> gradle -q hello
Hi from Gradle
In this example, the plugin passes the project’s ObjectFactory to the extension object through its
constructor. The constructor uses this to create a nested object and makes this object available to the DSL
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through the greeter property.
§
Configuring a collection of objects
Gradle provides some utility classes for maintaining collections of objects, intended to work well with the
Gradle DSL.
Example 353. Managing a collection of objects
build.gradle
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class Book {
final String name
File sourceFile
Book(String name) {
this.name = name
}
}
class DocumentationPlugin implements Plugin<Project> {
void apply(Project project) {
// Create a container of Book instances
def books = project.container(Book)
books.all {
sourceFile = project.file("src/docs/$name")
}
// Add the container as an extension object
project.extensions.books = books
}
}
apply plugin: DocumentationPlugin
// Configure the container
books {
quickStart {
sourceFile = file('src/docs/quick-start')
}
userGuide {
}
developerGuide {
}
}
task books {
doLast {
books.each { book ->
println "$book.name -> $book.sourceFile"
}
}
}
Output of gradle -q books
> gradle -q books
developerGuide -> /home/user/gradle/samples/userguide/organizeBuildLogic/customPluginWithD
quickStart -> /home/user/gradle/samples/userguide/organizeBuildLogic/customPluginWithDomai
userGuide -> /home/user/gradle/samples/userguide/organizeBuildLogic/customPluginWithDomain
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The
Project.container(java.lang.Class)
methods
create
instances
of
NamedDomainObjectContainer, that have many useful methods for managing and configuring the
objects. In order to use a type with any of the project.container methods, it MUST expose a property
named “name” as the unique, and constant, name for the object. The project.container(Class)
variant of the container method creates new instances by attempting to invoke the constructor of the class
that takes a single string argument, which is the desired name of the object. See the above link for project.container
method variants that allow custom instantiation strategies.
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Gradle Plugin Development Plugin
Note: The Java Gradle plugin development plugin is currently incubating. Please be aware that the
DSL and other configuration may change in later Gradle versions.
The Java Gradle Plugin development plugin can be used to assist in the development of Gradle plugins. It
automatically applies the Java plugin, adds the gradleApi() dependency to the compile configuration and
performs validation of plugin metadata during jar task execution.
The plugin also integrates with TestKit, a library that aids in writing and executing functional tests for plugin
code. It automatically adds the gradleTestKit() dependency to the test compile configuration and
generates a plugin classpath manifest file consumed by a GradleRunner instance if found. Please refer to
the section called “Automatic injection with the Java Gradle Plugin Development plugin” for more on its
usage, configuration options and samples.
§
Usage
To use the Java Gradle Plugin Development plugin, include the following in your build script:
Example 354. Using the Java Gradle Plugin Development plugin
build.gradle
plugins {
id 'java-gradle-plugin'
}
Applying the plugin automatically applies the Java plugin and adds the gradleApi() dependency to the
compile configuration. It also adds some validations to the build.
The following validations are performed:
There is a plugin descriptor defined for the plugin.
The plugin descriptor contains an implementation-class property.
The implementation-class property references a valid class file in the jar.
Each property getter or the corresponding field must be annotated with a property annotation like @InputFile
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and @OutputDirectory. Properties that don’t participate in up-to-date checks should be annotated with @Internal
.
Any failed validations will result in a warning message.
For each plugin you are developing, add an entry to the gradlePlugin {} script block:
Example 355. Using the gradlePlugin {} block.
build.gradle
gradlePlugin {
plugins {
simplePlugin {
id = 'org.gradle.sample.simple-plugin'
implementationClass = 'org.gradle.sample.SimplePlugin'
}
}
}
The gradlePlugin {} block defines the plugins being built by the project including the id and implementationClass
of the plugin. From this data about the plugins being developed, Gradle can automatically:
Generate the plugin descriptor in the jar file’s META-INF directory.
Configure the Maven or Ivy publishing plugins to publish a Plugin Marker Artifact for each plugin.
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Organizing Build Logic
Gradle offers a variety of ways to organize your build logic. First of all you can put your build logic directly in
the action closure of a task. If a couple of tasks share the same logic you can extract this logic into a
method. If multiple projects of a multi-project build share some logic you can define this method in the parent
project. If the build logic gets too complex for being properly modeled by methods then you likely should
implement your logic with classes to encapsulate your logic.[14] Gradle makes this very easy. Just drop your
classes in a certain directory and Gradle automatically compiles them and puts them in the classpath of your
build script.
Here is a summary of the ways you can organise your build logic:
POGOs. You can declare and use plain old Groovy objects (POGOs) directly in your build script. The build
script is written in Groovy, after all, and Groovy provides you with lots of excellent ways to organize code.
Inherited properties and methods. In a multi-project build, sub-projects inherit the properties and methods of
their parent project.
Configuration injection. In a multi-project build, a project (usually the root project) can inject properties and
methods into another project.
buildSrc project. Drop the source for your build classes into a certain directory and Gradle automatically
compiles them and includes them in the classpath of your build script.
Shared scripts. Define common configuration in an external build, and apply the script to multiple projects,
possibly across different builds.
Custom tasks. Put your build logic into a custom task, and reuse that task in multiple places.
Custom plugins. Put your build logic into a custom plugin, and apply that plugin to multiple projects. The
plugin must be in the classpath of your build script. You can achieve this either by using build sources or
by adding an external library that contains the plugin.
Execute an external build. Execute another Gradle build from the current build.
External libraries. Use external libraries directly in your build file.
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Inherited properties and methods
§
Inherited properties and methods
Any method or property defined in a project build script is also visible to all the sub-projects. You can use
this to define common configurations, and to extract build logic into methods which can be reused by the
sub-projects.
Example 356. Using inherited properties and methods
build.gradle
// Define an extra property
ext.srcDirName = 'src/java'
// Define a method
def getSrcDir(project) {
return project.file(srcDirName)
}
child/build.gradle
task show {
doLast {
// Use inherited property
println 'srcDirName: ' + srcDirName
// Use inherited method
File srcDir = getSrcDir(project)
println 'srcDir: ' + rootProject.relativePath(srcDir)
}
}
Output of gradle -q show
> gradle -q show
srcDirName: src/java
srcDir: child/src/java
§
Injected configuration
You can use the configuration injection technique discussed in the section called “Cross project
configuration” and the section called “Subproject configuration” to inject properties and methods into various
projects. This is generally a better option than inheritance, for a number of reasons: The injection is explicit
in the build script, You can inject different logic into different projects, And you can inject any kind of
configuration such as repositories, plug-ins, tasks, and so on. The following sample shows how this works.
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Example 357. Using injected properties and methods
build.gradle
subprojects {
// Define a new property
ext.srcDirName = 'src/java'
// Define a method using a closure as the method body
ext.srcDir = { file(srcDirName) }
// Define a task
task show {
doLast {
println 'project: ' + project.path
println 'srcDirName: ' + srcDirName
File srcDir = srcDir()
println 'srcDir: ' + rootProject.relativePath(srcDir)
}
}
}
// Inject special case configuration into a particular project
project(':child2') {
ext.srcDirName = "$srcDirName/legacy"
}
child1/build.gradle
// Use injected property and method. Here, we override the injected value
srcDirName = 'java'
def dir = srcDir()
Output of gradle -q show
> gradle -q show
project: :child1
srcDirName: java
srcDir: child1/java
project: :child2
srcDirName: src/java/legacy
srcDir: child2/src/java/legacy
§
Configuring the project using an external build script
You can configure the current project using an external build script. All of the Gradle build language is
available in the external script. You can even apply other scripts from the external script.
Build scripts can be local files or remotely accessible files downloaded via a URL.
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Remote files will be cached and made available when Gradle runs offline. On each build, Gradle will check if
the remote file has changed and will only download the build script file again if it has changed. URLs that
contain query strings will not be cached.
Example 358. Configuring the project using an external build script
build.gradle
apply from: 'other.gradle'
other.gradle
println "configuring $project"
task hello {
doLast {
println 'hello from other script'
}
}
Output of gradle -q hello
> gradle -q hello
configuring root project 'configureProjectUsingScript'
hello from other script
§
Build sources in the buildSrc project
When you run Gradle, it checks for the existence of a directory called buildSrc. Gradle then automatically
compiles and tests this code and puts it in the classpath of your build script. You don’t need to provide any
further instruction. This can be a good place to add your custom tasks and plugins.
For multi-project builds there can be only one buildSrc directory, which has to be in the root project
directory.
Listed below is the default build script that Gradle applies to the buildSrc project:
Default buildSrc build script.
apply plugin: 'groovy'
dependencies {
compile gradleApi()
compile localGroovy()
}
This means that you can just put your build source code in this directory and stick to the layout convention
for a Java/Groovy project (see Table 36).
If you need more flexibility, you can provide your own build.gradle. Gradle applies the default build script
regardless of whether there is one specified. This means you only need to declare the extra things you need.
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Below is an example. Notice that this example does not need to declare a dependency on the Gradle API, as
this is done by the default build script:
Example 359. Custom buildSrc build script
buildSrc/build.gradle
repositories {
mavenCentral()
}
dependencies {
testCompile 'junit:junit:4.12'
}
The buildSrc project can be a multi-project build, just like any other regular multi-project build. However,
all of the projects that should be on the classpath of the actual build must be runtime dependencies of the
root project in buildSrc. You can do this by adding this to the configuration of each project you wish to
export:
Example 360. Adding subprojects to the root buildSrc project
buildSrc/build.gradle
rootProject.dependencies {
runtime project(path)
}
Note: The code for this example can be found at samples/multiProjectBuildSrc in the ‘-all’
distribution of Gradle.
§
Running another Gradle build from a build
You can use the GradleBuild task. You can use either of the dir or buildFile properties to specify
which build to execute, and the tasks property to specify which tasks to execute.
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Example 361. Running another build from a build
build.gradle
task build(type: GradleBuild) {
buildFile = 'other.gradle'
tasks = ['hello']
}
other.gradle
task hello {
doLast {
println "hello from the other build."
}
}
Output of gradle -q build
> gradle -q build
hello from the other build.
§
External dependencies for the build script
If your build script needs to use external libraries, you can add them to the script’s classpath in the build
script itself. You do this using the buildscript() method, passing in a closure which declares the build
script classpath.
Example 362. Declaring external dependencies for the build script
build.gradle
buildscript {
repositories {
mavenCentral()
}
dependencies {
classpath group: 'commons-codec', name: 'commons-codec', version: '1.2'
}
}
The closure passed to the buildscript() method configures a ScriptHandler instance. You declare
the build script classpath by adding dependencies to the classpath configuration. This is the same way
you declare, for example, the Java compilation classpath. You can use any of the dependency types
described in the section called “Dependency types”, except project dependencies.
Having declared the build script classpath, you can use the classes in your build script as you would any
other classes on the classpath. The following example adds to the previous example, and uses classes from
the build script classpath.
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Example 363. A build script with external dependencies
build.gradle
import org.apache.commons.codec.binary.Base64
buildscript {
repositories {
mavenCentral()
}
dependencies {
classpath group: 'commons-codec', name: 'commons-codec', version: '1.2'
}
}
task encode {
doLast {
def byte[] encodedString = new Base64().encode('hello world\n'.getBytes())
println new String(encodedString)
}
}
Output of gradle -q encode
> gradle -q encode
aGVsbG8gd29ybGQK
For multi-project builds, the dependencies declared with a project’s buildscript() method are available
to the build scripts of all its sub-projects.
Build script dependencies may be Gradle plugins. Please consult Using Gradle Plugins for more information
on Gradle plugins.
Every project automatically has a buildEnvironment task of type BuildEnvironmentReportTask that
can be invoked to report on the resolution of the build script dependencies.
§
Ant optional dependencies
For reasons we don’t fully understand yet, external dependencies are not picked up by Ant’s optional tasks.
But you can easily do it in another way.[15]
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Example 364. Ant optional dependencies
build.gradle
configurations {
ftpAntTask
}
dependencies {
ftpAntTask("org.apache.ant:ant-commons-net:1.9.9") {
module("commons-net:commons-net:1.4.1") {
dependencies "oro:oro:2.0.8:jar"
}
}
}
task ftp {
doLast {
ant {
taskdef(name: 'ftp',
classname: 'org.apache.tools.ant.taskdefs.optional.net.FTP',
classpath: configurations.ftpAntTask.asPath)
ftp(server: "ftp.apache.org", userid: "anonymous", password: "me@myorg.com") {
fileset(dir: "htdocs/manual")
}
}
}
}
This is also a good example for the usage of client modules. The POM file in Maven Central for the
ant-commons-net task does not provide the right information for this use case.
§
Summary
Gradle offers you a variety of ways of organizing your build logic. You can choose what is right for your
domain and find the right balance between unnecessary indirections, and avoiding redundancy and a hard to
maintain code base. It is our experience that even very complex custom build logic is rarely shared between
different builds. Other build tools enforce a separation of this build logic into a separate project. Gradle
spares you this unnecessary overhead and indirection.
[14] Which might range from a single class to something very complex.
[15] In fact, we think this is a better solution. Only if your buildscript and Ant’s optional task need the same
library would you have to define it twice. In such a case it would be nice if Ant’s optional task would
automatically pick up the classpath defined in the “gradle.settings” file.
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Lazy Configuration
As a build grows in complexity, knowing when and where a particular value is configured can become
difficult to reason about. Gradle provides several ways to manage this complexity using lazy configuration .
§
Lazy properties
Note: The Provider API is currently incubating. Please be aware that the DSL and other
configuration may change in later Gradle versions.
Gradle provides lazy properties, which delay the calculation of a property’s value until it’s absolutely
required. Lazy types are faster, more understandable and better instrumented than the internal convention
mapping mechanisms. This provides two main benefits to build script and plugin authors:
1. Build authors can wire together Gradle models without worrying when a particular property’s value will be
known. For example, when you want to map properties in an extension to task properties but the values
aren’t known until the build script configures them.
2. Build authors can avoid resource intensive work during the configuration phase, which can have a direct
impact on maximum build performance. For example, when a property value comes from parsing a file.
Gradle represents lazy properties with two interfaces:
Provider are properties that can only be queried and cannot be changed.
Properties with these types are read-only.
The method Provider.get() returns the current value of the property.
A
Provider
can
be
created
by
the
factory
method
ProviderFactory.provider(java.util.concurrent.Callable).
Property are properties that can be queried and overwritten.
Properties with these types are configurable.
Property implements the Provider interface.
The method Property.set(T) specifies a value for the property, overwriting whatever value may have
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been present.
The method Property.set(org.gradle.api.provider.Provider) specifies a Provider for the
value for the property, overwriting whatever value may have been present. This allows you to wire together Provider
and Property instances before the values are configured.
A Property can be created by the factory method ObjectFactory.property(java.lang.Class).
Neither of these types nor their subtypes are intended to be implemented by a build script or plugin author.
Gradle provides several factory methods to create instances of these types. See the Quick Reference for all
of the types and factories available.
Lazy properties are intended to be passed around and only evaluated when required (usually, during the
execution phase). For more information about the Gradle build phases, please see the section called “Build
phases”.
The following demonstrates a task with a read-only property and a configurable property:
Example 365. Using a read-only and configurable property
build.gradle
class Greeting extends DefaultTask {
// Configurable by the user
@Input
final Property<String> message = project.objects.property(String)
// Read-only property calculated from the message
@Internal
final Provider<String> fullMessage = message.map { it + " from Gradle" }
@TaskAction
void printMessage() {
logger.quiet(fullMessage.get())
}
}
task greeting(type: Greeting) {
// Note that this is effectively calling Property.set()
message = 'Hi'
}
Output of gradle greeting
> gradle greeting
:greeting
Hi from Gradle
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
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The Greeting task has a Property<String> for the mutable part of the message and a Provider<String>
for the calculated, read-only, message.
Note: Note that Groovy Gradle DSL will generate setter methods for each Property-typed property
in a task implementation. These setter methods allow you to configure the property using the
assignment (=) operator as a convenience.
§
Creating a Property or Provider
If provider types are not intended to be implemented directly by build script or plugin authors, how do you
create a new one? Gradle provides various factory APIs to create new instances of both Provider and
Property:
ProviderFactory.provider(java.util.concurrent.Callable) instantiates a new Provider.
An instance of the ProviderFactory can be referenced from Project.getProviders() or by injecting
ProviderFactory through a constructor or method.
ObjectFactory.property(java.lang.Class) instantiates a new Property. An instance of the
ObjectFactory can be referenced from Project.getObjects() or by injecting ObjectFactory
through a constructor or method.
Note: Project does not provide a specific method signature for creating a provider from a groovy.lang.Closur
. When writing a plugin with Groovy, you can use the method signature accepting a java.util.concurrent.Cal
parameter. Groovy’s Closure to type coercion will take care of the rest.
§
Working with files and Providers
In Working With Files, we introduced four collection types for File-like objects:
Table 33. Collection of files recap
Read-only Type
Configurable Type
FileCollection
ConfigurableFileCollection
FileTree
ConfigurableFileTree
All of these types are also considered Provider types.
In this section, we are going to introduce more strongly typed models for a FileSystemLocation:
Directory and RegularFile. These types shouldn’t be confused with the standard Java java.io.File type
as they tell Gradle to expect more specific values (a directory or a non-directory, regular file).
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Gradle provides two specialized Property subtypes for dealing with these types: RegularFileProperty
and
DirectoryProperty .
ProjectLayout
has
methods
to
create
these:
ProjectLayout.fileProperty() and ProjectLayout.directoryProperty().
A DirectoryProperty can also be used to create a lazily evaluated Provider for a Directory and RegularFile
via
DirectoryProperty.dir(java.lang.String)
and
DirectoryProperty.file(java.lang.String) respectively. These methods create paths that are
relative to the location set for the original DirectoryProperty.
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Example 366. Using file and directory property
build.gradle
class FooExtension {
final DirectoryProperty someDirectory
final RegularFileProperty someFile
final ConfigurableFileCollection someFiles
FooExtension(Project project) {
someDirectory = project.layout.directoryProperty()
someFile = project.layout.fileProperty()
someFiles = project.files()
}
}
project.extensions.create('foo', FooExtension, project)
foo {
someDirectory = project.layout.projectDirectory.dir('some-directory')
someFile = project.layout.buildDirectory.file('some-file')
someFiles.from project.files(someDirectory, someFile)
}
task print {
doLast {
def someDirectory = project.foo.someDirectory.get().asFile
logger.quiet("foo.someDirectory = " + someDirectory)
logger.quiet("foo.someFiles contains someDirectory? " + project.foo.someFiles.cont
def someFile = project.foo.someFile.get().asFile
logger.quiet("foo.someFile = " + someFile)
logger.quiet("foo.someFiles contains someFile? " + project.foo.someFiles.contains(
}
}
Output of gradle print
> gradle print
:print
foo.someDirectory = /home/user/gradle/samples/providers/fileAndDirectoryProperty/some-dire
foo.someFiles contains someDirectory? true
foo.someFile = /home/user/gradle/samples/providers/fileAndDirectoryProperty/build/some-fil
foo.someFiles contains someFile? true
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
This example shows how Provider types can be used inside an extension. Lazy values for
Project.getBuildDir()
Project.getLayout()
and
with
Project.getProjectDir()
can
be
accessed
ProjectLayout.getBuildDirectory()
through
and
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ProjectLayout.getProjectDirectory().
§
Working with task dependencies and Providers
Many builds have several tasks that depend on each other. This usually means that one task processes the
outputs of another task as an input. For these outputs and inputs, we need to know their locations on the file
system and appropriately configure each task to know where to look. This can be cumbersome if any of
these values are configurable by a user or configured by multiple plugins.
To make this easier, Gradle offers convenient APIs for defining files or directories as task inputs and outputs
in a descriptive way. As an example consider the following plugin with a producer and consumer task, which
are wired together via inputs and outputs:
Example 367. Implicit task dependency
build.gradle
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class Producer extends DefaultTask {
@OutputFile
final RegularFileProperty outputFile = newOutputFile()
@TaskAction
void produce() {
String message = 'Hello, World!'
def output = outputFile.get().asFile
output.text = message
logger.quiet("Wrote '${message}' to ${output}")
}
}
class Consumer extends DefaultTask {
@InputFile
final RegularFileProperty inputFile = newInputFile()
@TaskAction
void consume() {
def input = inputFile.get().asFile
def message = input.text
logger.quiet("Read '${message}' from ${input}")
}
}
task producer(type: Producer)
task consumer(type: Consumer)
// Wire property from producer to consumer task
consumer.inputFile = producer.outputFile
// Set values for the producer lazily
// Note that the consumer does not need to be changed again.
producer.outputFile = layout.buildDirectory.file('file.txt')
// Change the base output directory.
// Note that this automatically changes producer.outputFile and consumer.inputFile
buildDir = 'output'
Output of gradle consumer
> gradle consumer
:producer
Wrote 'Hello, World!' to /home/user/gradle/samples/providers/implicitTaskDependency/output
:consumer
Read 'Hello, World!' from /home/user/gradle/samples/providers/implicitTaskDependency/outpu
BUILD SUCCESSFUL in 0s
2 actionable tasks: 2 executed
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In the example above, the task outputs and inputs are connected before any location is defined. This is
possible because the input and output properties use the Provider API. The output property is created with
DefaultTask.newOutputFile()
and
the
input
property
is
created
with
DefaultTask.newInputFile(). Values are only resolved when they are needed during execution. The
setters can be called at any time before the task is executed and the change will automatically affect all
related input and output properties.
Another thing to note is the absence of any explicit task dependency. Properties created via newOutputFile()
and newOutputDirectory() bring knowledge about which task is generating them, so using them as task
input will implicitly link tasks together.
§
Working with collection Providers
In this section, we are going to explore lazy collections. They work exactly like any other Provider and, just
like FileSystemLocation providers, they have additional modeling around them. There are two provider
interfaces available, one for List values and another for Set values:
For List values the interface is called ListProperty. You can create a new ListProperty using
ObjectFactory.listProperty(java.lang.Class) and specifying the element’s type.
For Set values the interface is called SetProperty. You can create a new SetProperty using
ObjectFactory.setProperty(java.lang.Class) and specifying the element’s type.
This
type
of
property
allows
you
to
overwrite
the
entire
collection
HasMultipleValues.set(java.lang.Iterable)
value
with
and
HasMultipleValues.set(org.gradle.api.provider.Provider) or add new elements through the
various add methods:
HasMultipleValues.add(T): Add a single concrete element to the collection
HasMultipleValues.add(org.gradle.api.provider.Provider): Add a lazily evaluated element
to the collection
HasMultipleValues.addAll(org.gradle.api.provider.Provider): Add a lazily evaluated
collection of elements to the list
Just like every Provider, the collection is calculated when Provider.get() is called. The following
example show the ListProperty in action:
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Example 368. List property
build.gradle
task print {
doLast {
ListProperty<String> list = project.objects.listProperty(String)
// Resolve the list
logger.quiet('The list contains: ' + list.get())
// Add elements to the empty list
list.add(project.provider { 'element-1' })
list.add('element-2')
// Add a provider element
// Add a concrete element
// Resolve the list
logger.quiet('The list contains: ' + list.get())
// Overwrite the entire list with a new list
list.set(['element-3', 'element-4'])
// Resolve the list
logger.quiet('The list contains: ' + list.get())
// Add more elements through a list provider
list.addAll(project.provider { ['element-5', 'element-6'] })
// Resolve the list
logger.quiet('The list contains: ' + list.get())
}
}
Output of gradle print
> gradle
:print
The list
The list
The list
The list
print
contains:
contains:
contains:
contains:
[]
[element-1, element-2]
[element-3, element-4]
[element-3, element-4, element-5, element-6]
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
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Guidelines
§
Guidelines
This section will introduce guidelines to be successful with the Provider API. To see those guidelines in
action, have a look at gradle-site-plugin, a Gradle plugin demonstrating established techniques and practices
for plugin development.
The Property and Provider types have all of the overloads you need to query or configure a value. For
this reason, you should follow the following guidelines:
For configurable properties, expose the Property directly through a single getter.
For non-configurable properties, expose an Provider directly through a single getter.
Avoid simplifying calls like obj.getProperty().get() and obj.getProperty().set(T) in your code
by introducing additional getters and setters.
When migrating your plugin to use providers, follow these guidelines:
If it’s a new property, expose it as a Property or Provider using a single getter.
If it’s incubating, change it to use a Property or Provider using a single getter.
If it’s a stable property, add a new Property or Provider and deprecate the old one. You should wire the
old getter/setters into the new property as appropriate.
§
Future development
Going forward, new properties will use the Provider API. The Groovy Gradle DSL adds convenience
methods to make the use of Providers mostly transparent in build scripts. Existing tasks will have their
existing "raw" properties replaced by Providers as needed and in a backwards compatible way. New tasks
will be designed with the Provider API.
The Provider API is incubating. Please create new issues at gradle/gradle to report bugs or to submit use
cases for new features.
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Provider API Quick Reference
§
Provider API Quick Reference
Table 34. Lazy properties summary
Description Read-only
Configurable
Factory
ProjectLayout.fileProperty()
A
file
on Provider<
disk
RegularFile>
RegularFileProperty
Directory.file(java.lang.String)
DirectoryProperty.file(java.lang.String)
A file used
as a task
input/output
DefaultTask.newInputFile()
Provider<
RegularFile>
RegularFileProperty
DefaultTask.newOutputFile()
ProjectLayout.directoryProperty()
A
directory Provider<
on disk
Directory>
DirectoryProperty
Directory.dir(java.lang.String)
DirectoryProperty.dir(java.lang.String)
A
directory
used as a Provider<
task
Directory>
DefaultTask.newInputDirectory()
DirectoryProperty
DefaultTask.newOutputDirectory()
input/output
Collection of
files
Hierarchy of
files
FileCollection ConfigurableFileCollection Project.files(java.lang.Object[])
FileTree
List of any P r o v i d e r
type
<List<T>>
Set of any P r o v i d e r
type
Any
type
<Set<T>>
other
Provider<T>
ConfigurableFileTree
Project.fileTree(java.lang.Object)
ListProperty
ObjectFactory.listProperty(java.lang.Class)
SetProperty
ObjectFactory.setProperty(java.lang.Class)
Property<T>
ObjectFactory.property(java.lang.Class)
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Initialization Scripts
Gradle provides a powerful mechanism to allow customizing the build based on the current environment.
This mechanism also supports tools that wish to integrate with Gradle.
Note that this is completely different from the “init” task provided by the “build-init” incubating plugin
(see Build Init Plugin).
§
Basic usage
Initialization scripts (a.k.a. init scripts ) are similar to other scripts in Gradle. These scripts, however, are run
before the build starts. Here are several possible uses:
Set up enterprise-wide configuration, such as where to find custom plugins.
Set up properties based on the current environment, such as a developer’s machine vs. a continuous
integration server.
Supply personal information about the user that is required by the build, such as repository or database
authentication credentials.
Define machine specific details, such as where JDKs are installed.
Register build listeners. External tools that wish to listen to Gradle events might find this useful.
Register build loggers. You might wish to customize how Gradle logs the events that it generates.
One main limitation of init scripts is that they cannot access classes in the buildSrc project (see the
section called “Build sources in the buildSrc project” for details of this feature).
§
Using an init script
There are several ways to use an init script:
Specify a file on the command line. The command line option is -I or --init-script followed by the path
to the script. The command line option can appear more than once, each time adding another init script.
Put a file called init.gradle in the USER_HOME /.gradle/ directory.
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Put a file that ends with .gradle in the USER_HOME /.gradle/init.d/ directory.
Put a file that ends with .gradle in the GRADLE_HOME /init.d/ directory, in the Gradle distribution. This
allows you to package up a custom Gradle distribution containing some custom build logic and plugins. You
can combine this with the Gradle wrapper as a way to make custom logic available to all builds in your
enterprise.
If more than one init script is found they will all be executed, in the order specified above. Scripts in a given
directory are executed in alphabetical order. This allows, for example, a tool to specify an init script on the
command line and the user to put one in their home directory for defining the environment and both scripts
will run when Gradle is executed.
§
Writing an init script
Similar to a Gradle build script, an init script is a Groovy script. Each init script has a Gradle instance
associated with it. Any property reference and method call in the init script will delegate to this Gradle
instance.
Each init script also implements the Script interface.
§
Configuring projects from an init script
You can use an init script to configure the projects in the build. This works in a similar way to configuring
projects in a multi-project build. The following sample shows how to perform extra configuration from an init
script before the projects are evaluated. This sample uses this feature to configure an extra repository to be
used only for certain environments.
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Example 369. Using init script to perform extra configuration before projects are evaluated
build.gradle
repositories {
mavenCentral()
}
task showRepos {
doLast {
println "All repos:"
println repositories.collect { it.name }
}
}
init.gradle
allprojects {
repositories {
mavenLocal()
}
}
Output of gradle --init-script init.gradle -q showRepos
> gradle --init-script init.gradle -q showRepos
All repos:
[MavenLocal, MavenRepo]
§
External dependencies for the init script
In the section called “External dependencies for the build script” it was explained how to add external
dependencies to a build script. Init scripts can also declare dependencies. You do this with the initscript()
method, passing in a closure which declares the init script classpath.
Example 370. Declaring external dependencies for an init script
init.gradle
initscript {
repositories {
mavenCentral()
}
dependencies {
classpath group: 'org.apache.commons', name: 'commons-math', version: '2.0'
}
}
The closure passed to the initscript() method configures a ScriptHandler instance. You declare the
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init script classpath by adding dependencies to the classpath configuration. This is the same way you
declare, for example, the Java compilation classpath. You can use any of the dependency types described in
the section called “Declaring dependencies”, except project dependencies.
Having declared the init script classpath, you can use the classes in your init script as you would any other
classes on the classpath. The following example adds to the previous example, and uses classes from the
init script classpath.
Example 371. An init script with external dependencies
init.gradle
import org.apache.commons.math.fraction.Fraction
initscript {
repositories {
mavenCentral()
}
dependencies {
classpath group: 'org.apache.commons', name: 'commons-math', version: '2.0'
}
}
println Fraction.ONE_FIFTH.multiply(2)
Output of gradle --init-script init.gradle -q doNothing
> gradle --init-script init.gradle -q doNothing
2 / 5
§
Init script plugins
Similar to a Gradle build script or a Gradle settings file, plugins can be applied on init scripts.
Example 372. Using plugins in init scripts
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init.gradle
apply plugin:EnterpriseRepositoryPlugin
class EnterpriseRepositoryPlugin implements Plugin<Gradle> {
private static String ENTERPRISE_REPOSITORY_URL = "https://repo.gradle.org/gradle/repo
void apply(Gradle gradle) {
// ONLY USE ENTERPRISE REPO FOR DEPENDENCIES
gradle.allprojects{ project ->
project.repositories {
// Remove all repositories not pointing to the enterprise repository url
all { ArtifactRepository repo ->
if (!(repo instanceof MavenArtifactRepository) ||
repo.url.toString() != ENTERPRISE_REPOSITORY_URL) {
project.logger.lifecycle "Repository ${repo.url} removed. Only $EN
remove repo
}
}
// add the enterprise repository
maven {
name "STANDARD_ENTERPRISE_REPO"
url ENTERPRISE_REPOSITORY_URL
}
}
}
}
}
build.gradle
repositories{
mavenCentral()
}
task showRepositories {
doLast {
repositories.each {
println "repository: ${it.name} ('${it.url}')"
}
}
}
Output of gradle -q -I init.gradle showRepositories
> gradle -q -I init.gradle showRepositories
repository: STANDARD_ENTERPRISE_REPO ('https://repo.gradle.org/gradle/repo')
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The plugin in the init script ensures that only a specified repository is used when running the build.
When applying plugins within the init script, Gradle instantiates the plugin and calls the plugin instance’s
Plugin.apply(T) method. The gradle object is passed as a parameter, which can be used to configure
all aspects of a build. Of course, the applied plugin can be resolved as an external dependency as described
in the section called “External dependencies for the init script”
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Testing Build Logic with TestKit
Note: The Gradle TestKit is currently incubating. Please be aware that its API and other
characteristics may change in later Gradle versions.
The Gradle TestKit (a.k.a. just TestKit) is a library that aids in testing Gradle plugins and build logic
generally. At this time, it is focused on functional testing. That is, testing build logic by exercising it as part of
a programmatically executed build. Over time, the TestKit will likely expand to facilitate other kinds of tests.
§
Usage
To use the TestKit, include the following in your plugin’s build:
Example 373. Declaring the TestKit dependency
build.gradle
dependencies {
testCompile gradleTestKit()
}
The gradleTestKit() encompasses the classes of the TestKit, as well as the Gradle Tooling API client. It
does not include a version of JUnit, TestNG, or any other test execution framework. Such a dependency
must be explicitly declared.
Example 374. Declaring the JUnit dependency
build.gradle
dependencies {
testCompile 'junit:junit:4.12'
}
§
Functional testing with the Gradle runner
The GradleRunner facilitates programmatically executing Gradle builds, and inspecting the result.
A contrived build can be created (e.g. programmatically, or from a template) that exercises the “logic under
test”. The build can then be executed, potentially in a variety of ways (e.g. different combinations of tasks
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and arguments). The correctness of the logic can then be verified by asserting the following, potentially in
combination:
The build’s output;
The build’s logging (i.e. console output);
The set of tasks executed by the build and their results (e.g. FAILED, UP-TO-DATE etc.).
After creating and configuring a runner instance, the build can be executed via the
GradleRunner.build() or GradleRunner.buildAndFail() methods depending on the anticipated
outcome.
The following demonstrates the usage of Gradle runner in a Java JUnit test:
Example 375. Using GradleRunner with JUnit
BuildLogicFunctionalTest.java
import org.gradle.testkit.runner.BuildResult;
import org.gradle.testkit.runner.GradleRunner;
import org.junit.Before;
import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.TemporaryFolder;
import
import
import
import
import
java.io.BufferedWriter;
java.io.File;
java.io.FileWriter;
java.io.IOException;
java.util.Collections;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertTrue;
import static org.gradle.testkit.runner.TaskOutcome.*;
public class BuildLogicFunctionalTest {
@Rule public final TemporaryFolder testProjectDir = new TemporaryFolder();
private File buildFile;
@Before
public void setup() throws IOException {
buildFile = testProjectDir.newFile("build.gradle");
}
@Test
public void testHelloWorldTask() throws IOException {
String buildFileContent = "task helloWorld {" +
"
doLast {" +
"
println 'Hello world!'" +
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"
}" +
"}";
writeFile(buildFile, buildFileContent);
BuildResult result = GradleRunner.create()
.withProjectDir(testProjectDir.getRoot())
.withArguments("helloWorld")
.build();
assertTrue(result.getOutput().contains("Hello world!"));
assertEquals(SUCCESS, result.task(":helloWorld").getOutcome());
}
private void writeFile(File destination, String content) throws IOException {
BufferedWriter output = null;
try {
output = new BufferedWriter(new FileWriter(destination));
output.write(content);
} finally {
if (output != null) {
output.close();
}
}
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}
}
Any test execution framework can be used.
As Gradle build scripts are written in the Groovy programming language, and as many plugins are
implemented in Groovy, it is often a productive choice to write Gradle functional tests in Groovy.
Furthermore, it is recommended to use the (Groovy based) Spock test execution framework as it offers
many compelling features over the use of JUnit.
The following demonstrates the usage of Gradle runner in a Groovy Spock test:
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Example 376. Using GradleRunner with Spock
BuildLogicFunctionalTest.groovy
import org.gradle.testkit.runner.GradleRunner
import static org.gradle.testkit.runner.TaskOutcome.*
import org.junit.Rule
import org.junit.rules.TemporaryFolder
import spock.lang.Specification
class BuildLogicFunctionalTest extends Specification {
@Rule final TemporaryFolder testProjectDir = new TemporaryFolder()
File buildFile
def setup() {
buildFile = testProjectDir.newFile('build.gradle')
}
def "hello world task prints hello world"() {
given:
buildFile << """
task helloWorld {
doLast {
println 'Hello world!'
}
}
"""
when:
def result = GradleRunner.create()
.withProjectDir(testProjectDir.root)
.withArguments('helloWorld')
.build()
then:
result.output.contains('Hello world!')
result.task(":helloWorld").outcome == SUCCESS
}
}
It is a common practice to implement any custom build logic (like plugins and task types) that is more
complex in nature as external classes in a standalone project. The main driver behind this approach is
bundle the compiled code into a JAR file, publish it to a binary repository and reuse it across various
projects.
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Getting the plugin-under-test into the test build
§
Getting the plugin-under-test into the test build
The GradleRunner uses the Tooling API to execute builds. An implication of this is that the builds are
executed in a separate process (i.e. not the same process executing the tests). Therefore, the test build
does not share the same classpath or classloaders as the test process and the code under test is not
implicitly available to the test build.
Starting with version 2.13, Gradle provides a conventional mechanism to inject the code under test into the
test build.
For earlier versions of Gradle (before 2.13), it is possible to manually make the code under test available via
some extra configuration. The following example demonstrates having the build generate a file containing
the implementation classpath of the code under test, and making it available at test runtime.
Example 377. Making the code under test classpath available to the tests
build.gradle
// Write the plugin's classpath to a file to share with the tests
task createClasspathManifest {
def outputDir = file("$buildDir/$name")
inputs.files sourceSets.main.runtimeClasspath
outputs.dir outputDir
doLast {
outputDir.mkdirs()
file("$outputDir/plugin-classpath.txt").text = sourceSets.main.runtimeClasspath.jo
}
}
// Add the classpath file to the test runtime classpath
dependencies {
testRuntime files(createClasspathManifest)
}
Note: The code for this example can be found at samples/testKit/gradleRunner/manualClasspathInjec
in the ‘-all’ distribution of Gradle.
The tests can then read this value, and inject the classpath into the test build by using the method
GradleRunner.withPluginClasspath(java.lang.Iterable). This classpath is then available to
use to locate plugins in a test build via the plugins DSL (see Using Gradle Plugins). Applying plugins with the
plugins DSL requires the definition of a plugin identifier. The following is an example (in Groovy) of doing this
from within a Spock Framework setup() method, which is analogous to a JUnit @Before method.
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Example 378. Injecting the code under test classes into test builds
src/test/groovy/org/gradle/sample/BuildLogicFunctionalTest.groovy
List<File> pluginClasspath
def setup() {
buildFile = testProjectDir.newFile('build.gradle')
def pluginClasspathResource = getClass().classLoader.findResource("plugin-classpath.tx
if (pluginClasspathResource == null) {
throw new IllegalStateException("Did not find plugin classpath resource, run `test
}
pluginClasspath = pluginClasspathResource.readLines().collect { new File(it) }
}
def "hello world task prints hello world"() {
given:
buildFile << """
plugins {
id 'org.gradle.sample.helloworld'
}
"""
when:
def result = GradleRunner.create()
.withProjectDir(testProjectDir.root)
.withArguments('helloWorld')
.withPluginClasspath(pluginClasspath)
.build()
then:
result.output.contains('Hello world!')
result.task(":helloWorld").outcome == SUCCESS
}
Note: The code for this example can be found at samples/testKit/gradleRunner/manualClasspathInjec
in the ‘-all’ distribution of Gradle.
This approach works well when executing the functional tests as part of the Gradle build. When executing
the functional tests from an IDE, there are extra considerations. Namely, the classpath manifest file points to
the class files etc. generated by Gradle and not the IDE. This means that after making a change to the
source of the code under test, the source must be recompiled by Gradle. Similarly, if the effective classpath
of the code under test changes, the manifest must be regenerated. In either case, executing the testClasses
task of the build will ensure that things are up to date.
Some IDEs provide a convenience option to delegate the "test classpath generation and execution" to the
build. In IntelliJ you can find this option under Preferences… > Build, Execution, Deployment > Build Tools >
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Gradle > Runner > Delegate IDE build/run actions to gradle. Please consult the documentation of your IDE
for more information.
§
Working with Gradle versions prior to 2.8
The GradleRunner.withPluginClasspath(java.lang.Iterable) method will not work when
executing the build with a Gradle version earlier than 2.8 (see:the section called “The Gradle version used to
test”), as this feature is not supported on such Gradle versions.
Instead, the code must be injected via the build script itself. The following sample demonstrates how this can
be done.
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Example 379. Injecting the code under test classes into test builds for Gradle versions prior to 2.8
src/test/groovy/org/gradle/sample/BuildLogicFunctionalTest.groovy
List<File> pluginClasspath
def setup() {
buildFile = testProjectDir.newFile('build.gradle')
def pluginClasspathResource = getClass().classLoader.findResource("plugin-classpath.tx
if (pluginClasspathResource == null) {
throw new IllegalStateException("Did not find plugin classpath resource, run `test
}
pluginClasspath = pluginClasspathResource.readLines().collect { new File(it) }
}
def "hello world task prints hello world with pre Gradle 2.8"() {
given:
def classpathString = pluginClasspath
.collect { it.absolutePath.replace('\\', '\\\\') } // escape backslashes in Window
.collect { "'$it'" }
.join(", ")
buildFile << """
buildscript {
dependencies {
classpath files($classpathString)
}
}
apply plugin: "org.gradle.sample.helloworld"
"""
when:
def result = GradleRunner.create()
.withProjectDir(testProjectDir.root)
.withArguments('helloWorld')
.withGradleVersion("2.7")
.build()
then:
result.output.contains('Hello world!')
result.task(":helloWorld").outcome == SUCCESS
}
Note: The code for this example can be found at samples/testKit/gradleRunner/manualClasspathInjec
in the ‘-all’ distribution of Gradle.
Automatic injection with the Java Gradle Plugin Development plugin
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§
Automatic injection with the Java Gradle Plugin Development plugin
The Java Gradle Plugin development plugin can be used to assist in the development of Gradle plugins.
Starting with Gradle version 2.13, the plugin provides a direct integration with TestKit. When applied to a
project, the plugin automatically adds the gradleTestKit() dependency to the test compile configuration.
Furthermore, it automatically generates the classpath for the code under test and injects it via
GradleRunner.withPluginClasspath() for any GradleRunner instance created by the user. It’s
important to note that the mechanism currently only works if the plugin under test is applied using the
plugins DSL. If the target Gradle version is prior to 2.8, automatic plugin classpath injection is not performed.
The plugin uses the following conventions for applying the TestKit dependency and injecting the classpath:
Source set containing code under test: sourceSets.main
Source set used for injecting the plugin classpath: sourceSets.test
Any
of
these
conventions
can
be
reconfigured
with
the
help
of
the
class
GradlePluginDevelopmentExtension.
The following Groovy-based sample demonstrates how to automatically inject the plugin classpath by using
the standard conventions applied by the Java Gradle Plugin Development plugin.
Example 380. Using the Java Gradle Development plugin for generating the plugin metadata
build.gradle
apply plugin: 'groovy'
apply plugin: 'java-gradle-plugin'
dependencies {
testCompile('org.spockframework:spock-core:1.0-groovy-2.4') {
exclude module: 'groovy-all'
}
}
Note: The code for this example can be found at samples/testKit/gradleRunner/automaticClasspathIn
in the ‘-all’ distribution of Gradle.
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Example 381. Automatically injecting the code under test classes into test builds
src/test/groovy/org/gradle/sample/BuildLogicFunctionalTest.groovy
def "hello world task prints hello world"() {
given:
buildFile << """
plugins {
id 'org.gradle.sample.helloworld'
}
"""
when:
def result = GradleRunner.create()
.withProjectDir(testProjectDir.root)
.withArguments('helloWorld')
.withPluginClasspath()
.build()
then:
result.output.contains('Hello world!')
result.task(":helloWorld").outcome == SUCCESS
}
Note: The code for this example can be found at samples/testKit/gradleRunner/automaticClasspathIn
in the ‘-all’ distribution of Gradle.
The following build script demonstrates how to reconfigure the conventions provided by the Java Gradle
Plugin Development plugin for a project that uses a custom Test source set.
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Example 382. Reconfiguring the classpath generation conventions of the Java Gradle Development plugin
build.gradle
apply plugin: 'groovy'
apply plugin: 'java-gradle-plugin'
sourceSets {
functionalTest {
groovy {
srcDir file('src/functionalTest/groovy')
}
resources {
srcDir file('src/functionalTest/resources')
}
compileClasspath += sourceSets.main.output + configurations.testRuntime
runtimeClasspath += output + compileClasspath
}
}
task functionalTest(type: Test) {
testClassesDirs = sourceSets.functionalTest.output.classesDirs
classpath = sourceSets.functionalTest.runtimeClasspath
}
check.dependsOn functionalTest
gradlePlugin {
testSourceSets sourceSets.functionalTest
}
dependencies {
functionalTestCompile('org.spockframework:spock-core:1.0-groovy-2.4') {
exclude module: 'groovy-all'
}
}
Note: The code for this example can be found at samples/testKit/gradleRunner/automaticClasspathIn
in the ‘-all’ distribution of Gradle.
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Controlling the build environment
§
Controlling the build environment
The runner executes the test builds in an isolated environment by specifying a dedicated "working directory"
in a directory inside the JVM’s temp directory (i.e. the location specified by the java.io.tmpdir system
property, typically /tmp). Any configuration in the default Gradle user home directory (e.g. ~/.gradle/gradle.proper
) is not used for test execution. The TestKit does not expose a mechanism for fine grained control of
environment variables etc. Future versions of the TestKit will provide improved configuration options.
The TestKit uses dedicated daemon processes that are automatically shut down after test execution.
§
The Gradle version used to test
The Gradle runner requires a Gradle distribution in order to execute the build. The TestKit does not depend
on all of Gradle’s implementation.
By default, the runner will attempt to find a Gradle distribution based on where the GradleRunner class
was loaded from. That is, it is expected that the class was loaded from a Gradle distribution, as is the case
when using the gradleTestKit() dependency declaration.
When using the runner as part of tests being executed by Gradle (e.g. executing the test task of a plugin
project), the same distribution used to execute the tests will be used by the runner. When using the runner
as part of tests being executed by an IDE , the same distribution of Gradle that was used when importing the
project will be used. This means that the plugin will effectively be tested with the same version of Gradle that
it is being built with.
Alternatively, a different and specific version of Gradle to use can be specified by the any of the following GradleRunner
methods:
GradleRunner.withGradleVersion(java.lang.String)
GradleRunner.withGradleInstallation(java.io.File)
GradleRunner.withGradleDistribution(java.net.URI)
This can potentially be used to test build logic across Gradle versions. The following demonstrates a
cross-version compatibility test written as Groovy Spock test:
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Example 383. Specifying a Gradle version for test execution
BuildLogicFunctionalTest.groovy
import org.gradle.testkit.runner.GradleRunner
import static org.gradle.testkit.runner.TaskOutcome.*
import org.junit.Rule
import org.junit.rules.TemporaryFolder
import spock.lang.Specification
import spock.lang.Unroll
class BuildLogicFunctionalTest extends Specification {
@Rule final TemporaryFolder testProjectDir = new TemporaryFolder()
File buildFile
def setup() {
buildFile = testProjectDir.newFile('build.gradle')
}
@Unroll
def "can execute hello world task with Gradle version #gradleVersion"() {
given:
buildFile << """
task helloWorld {
doLast {
logger.quiet 'Hello world!'
}
}
"""
when:
def result = GradleRunner.create()
.withGradleVersion(gradleVersion)
.withProjectDir(testProjectDir.root)
.withArguments('helloWorld')
.build()
then:
result.output.contains('Hello world!')
result.task(":helloWorld").outcome == SUCCESS
where:
gradleVersion << ['2.6', '2.7']
}
}
Feature support when testing with different Gradle versions
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§
Feature support when testing with different Gradle versions
It is possible to use the GradleRunner to execute builds with Gradle 1.0 and later. However, some runner
features are not supported on earlier versions. In such cases, the runner will throw an exception when
attempting to use the feature.
The following table lists the features that are sensitive to the Gradle version being used.
Table 35. Gradle version compatibility
Minimum
Feature
Version
<link>Inspecting
executed tasks</link>
Plugin
classpath
injection
Inspecting build output
in debug mode
Automatic
plugin
classpath injection
2.5
2.8
2.9
Description
Inspecting the executed tasks, using BuildResult.getTasks() and similar methods.
Injecting
Inspecting
code
under
test
via
the
build’s
text
output
when
run
in
debug
mode,
using
BuildResult.getOutput().
Injecting
2.13
the
GradleRunner.withPluginClasspath(java.lang.Iterable).
the
code
under
test
automatically
via
GradleRunner.withPluginClasspath() by applying the Java Gradle Plugin
Development plugin.
§
Debugging build logic
The runner uses the Tooling API to execute builds. An implication of this is that the builds are executed in a
separate process (i.e. not the same process executing the tests). Therefore, executing your tests in debug
mode does not allow you to debug your build logic as you may expect. Any breakpoints set in your IDE will
be not be tripped by the code being exercised by the test build.
The TestKit provides two different ways to enable the debug mode:
Setting “org.gradle.testkit.debug” system property to true for the JVM using the GradleRunner
(i.e. not the build being executed with the runner);
Calling the GradleRunner.withDebug(boolean) method.
The system property approach can be used when it is desirable to enable debugging support without making
an adhoc change to the runner configuration. Most IDEs offer the capability to set JVM system properties for
test execution, and such a feature can be used to set this system property.
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Testing with the Build Cache
§
Testing with the Build Cache
To enable the Build Cache in your tests, you can pass the --build-cache argument to GradleRunner or
use one of the other methods described in the section called “Enable the Build Cache”. You can then check
for the task outcome TaskOutcome.FROM_CACHE when your plugin’s custom task is cached. This outcome
is only valid for Gradle 3.5 and newer.
Example 384. Testing cacheable tasks
BuildLogicFunctionalTest.groovy
def "cacheableTask is loaded from cache"() {
given:
buildFile << """
plugins {
id 'org.gradle.sample.helloworld'
}
"""
when:
def result = runner()
.withArguments( '--build-cache', 'cacheableTask')
.build()
then:
result.task(":cacheableTask").outcome == SUCCESS
when:
new File(testProjectDir.root, 'build').deleteDir()
result = runner()
.withArguments( '--build-cache', 'cacheableTask')
.build()
then:
result.task(":cacheableTask").outcome == FROM_CACHE
}
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Building JVM projects
Java Quickstart
§
The Java plugin
As we have seen, Gradle is a general-purpose build tool. It can build pretty much anything you care to
implement in your build script. Out-of-the-box, however, it doesn’t build anything unless you add code to your
build script to do so.
Most Java projects are pretty similar as far as the basics go: you need to compile your Java source files, run
some unit tests, and create a JAR file containing your classes. It would be nice if you didn’t have to code all
this up for every project. Luckily, you don’t have to. Gradle solves this problem through the use of plugins . A
plugin is an extension to Gradle which configures your project in some way, typically by adding some
pre-configured tasks which together do something useful. Gradle ships with a number of plugins, and you
can easily write your own and share them with others. One such plugin is the Java plugin . This plugin adds
some tasks to your project which will compile and unit test your Java source code, and bundle it into a JAR
file.
The Java plugin is convention based. This means that the plugin defines default values for many aspects of
the project, such as where the Java source files are located. If you follow the convention in your project, you
generally don’t need to do much in your build script to get a useful build. Gradle allows you to customize
your project if you don’t want to or cannot follow the convention in some way. In fact, because support for
Java projects is implemented as a plugin, you don’t have to use the plugin at all to build a Java project, if you
don’t want to.
We have in-depth coverage with many examples about the Java plugin, dependency management and
multi-project builds in later chapters. In this chapter we want to give you an initial idea of how to use the Java
plugin to build a Java project.
§
A basic Java project
Let’s look at a simple example. To use the Java plugin, add the following to your build file:
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Example 385. Using the Java plugin
build.gradle
apply plugin: 'java'
Note: The code for this example can be found at samples/java/quickstart in the ‘-all’
distribution of Gradle.
This is all you need to define a Java project. This will apply the Java plugin to your project, which adds a
number of tasks to your project.
What tasks are available?
You can use gradle tasks to list the tasks of a project. This will let you see the tasks that the
Java plugin has added to your project.
Gradle expects to find your production source code under src/main/java and your test source code
under src/test/java. In addition, any files under src/main/resources will be included in the JAR file
as resources, and any files under src/test/resources will be included in the classpath used to run the
tests. All output files are created under the build directory, with the JAR file ending up in the build/libs
directory.
§
Building the project
The Java plugin adds quite a few tasks to your project. However, there are only a handful of tasks that you
will need to use to build the project. The most commonly used task is the build task, which does a full build
of the project. When you run gradle build, Gradle will compile and test your code, and create a JAR file
containing your main classes and resources:
Example 386. Building a Java project
Output of gradle build
> gradle build
:compileJava
:processResources
:classes
:jar
:assemble
:compileTestJava
:processTestResources
:testClasses
:test
:check
:build
BUILD SUCCESSFUL in 0s
6 actionable tasks: 6 executed
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Some other useful tasks are:
clean
Deletes the build directory, removing all built files.
assemble
Compiles and jars your code, but does not run the unit tests. Other plugins add more artifacts to this task.
For example, if you use the War plugin, this task will also build the WAR file for your project.
check
Compiles and tests your code. Other plugins add more checks to this task. For example, if you use the checkstyle
plugin, this task will also run Checkstyle against your source code.
§
External dependencies
Usually, a Java project will have some dependencies on external JAR files. To reference these JAR files in
the project, you need to tell Gradle where to find them. In Gradle, artifacts such as JAR files, are located in a
repository . A repository can be used for fetching the dependencies of a project, or for publishing the artifacts
of a project, or both. For this example, we will use the public Maven repository:
Example 387. Adding Maven repository
build.gradle
repositories {
mavenCentral()
}
Let’s add some dependencies. Here, we will declare that our production classes have a compile-time
dependency on commons collections, and that our test classes have a compile-time dependency on junit:
Example 388. Adding dependencies
build.gradle
dependencies {
compile group: 'commons-collections', name: 'commons-collections', version: '3.2.2'
testCompile group: 'junit', name: 'junit', version: '4.+'
}
You can find out more in Dependency Management for Java Projects.
Customizing the project
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§
Customizing the project
The Java plugin adds a number of properties to your project. These properties have default values which are
usually sufficient to get started. It’s easy to change these values if they don’t suit. Let’s look at this for our
sample. Here we will specify the version number for our Java project, along with the Java version our source
is written in. We also add some attributes to the JAR manifest.
Example 389. Customization of MANIFEST.MF
build.gradle
sourceCompatibility = 1.7
version = '1.0'
jar {
manifest {
attributes 'Implementation-Title': 'Gradle Quickstart',
'Implementation-Version': version
}
}
What properties are available?
You can use gradle properties to list the properties of a project. This will allow you to see the
properties added by the Java plugin, and their default values.
The tasks which the Java plugin adds are regular tasks, exactly the same as if they were declared in the
build file. This means you can use any of the mechanisms shown in earlier chapters to customize these
tasks. For example, you can set the properties of a task, add behaviour to a task, change the dependencies
of a task, or replace a task entirely. In our sample, we will configure the test task, which is of type Test, to
add a system property when the tests are executed:
Example 390. Adding a test system property
build.gradle
test {
systemProperties 'property': 'value'
}
§
Publishing the JAR file
Usually the JAR file needs to be published somewhere. To do this, you need to tell Gradle where to publish
the JAR file. In Gradle, artifacts such as JAR files are published to repositories. In our sample, we will
publish to a local directory. You can also publish to a remote location, or multiple locations.
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Example 391. Publishing the JAR file
build.gradle
uploadArchives {
repositories {
flatDir {
dirs 'repos'
}
}
}
To publish the JAR file, run gradle uploadArchives.
§
Creating an Eclipse project
To create the Eclipse-specific descriptor files, like .project, you need to add another plugin to your build
file:
Example 392. Eclipse plugin
build.gradle
apply plugin: 'eclipse'
Now execute gradle eclipse command to generate Eclipse project files. More information about the eclipse
task can be found in The Eclipse Plugins.
§
Summary
Here’s the complete build file for our sample:
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Example 393. Java example - complete build file
build.gradle
apply plugin: 'java'
apply plugin: 'eclipse'
sourceCompatibility = 1.7
version = '1.0'
jar {
manifest {
attributes 'Implementation-Title': 'Gradle Quickstart',
'Implementation-Version': version
}
}
repositories {
mavenCentral()
}
dependencies {
compile group: 'commons-collections', name: 'commons-collections', version: '3.2.2'
testCompile group: 'junit', name: 'junit', version: '4.+'
}
test {
systemProperties 'property': 'value'
}
uploadArchives {
repositories {
flatDir {
dirs 'repos'
}
}
}
§
Multi-project Java build
Now let’s look at a typical multi-project build. Below is the layout for the project:
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Example 394. Multi-project build - hierarchical layout
Build layout
multiproject/
api/
services/webservice/
shared/
services/shared/
Note: The code for this example can be found at samples/java/multiproject in the ‘-all’
distribution of Gradle.
Here we have four projects. Project api produces a JAR file which is shipped to the client to provide them a
Java client for your XML webservice. Project webservice is a webapp which returns XML. Project shared
contains code used both by api and webservice. Project services/shared has code that depends on
the shared project.
§
Defining a multi-project build
To define a multi-project build, you need to create a settings file . The settings file lives in the root directory of
the source tree, and specifies which projects to include in the build. It must be called settings.gradle.
For this example, we are using a simple hierarchical layout. Here is the corresponding settings file:
Example 395. Multi-project build - settings.gradle file
settings.gradle
include "shared", "api", "services:webservice", "services:shared"
You can find out more about the settings file in Authoring Multi-Project Builds.
§
Common configuration
For most multi-project builds, there is some configuration which is common to all projects. In our sample, we
will define this common configuration in the root project, using a technique called configuration injection .
Here, the root project is like a container and the subprojects method iterates over the elements of this
container - the projects in this instance - and injects the specified configuration. This way we can easily
define the manifest content for all archives, and some common dependencies:
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Example 396. Multi-project build - common configuration
build.gradle
subprojects {
apply plugin: 'java'
apply plugin: 'eclipse-wtp'
repositories {
mavenCentral()
}
dependencies {
testCompile 'junit:junit:4.12'
}
version = '1.0'
jar {
manifest.attributes provider: 'gradle'
}
}
Notice that our sample applies the Java plugin to each subproject. This means the tasks and configuration
properties we have seen in the previous section are available in each subproject. So, you can compile, test,
and JAR all the projects by running gradle build from the root project directory.
Also note that these plugins are only applied within the subprojects section, not at the root level, so the
root build will not expect to find Java source files in the root project, only in the subprojects.
§
Dependencies between projects
You can add dependencies between projects in the same build, so that, for example, the JAR file of one
project is used to compile another project. In the api build file we will add a dependency on the shared
project. Due to this dependency, Gradle will ensure that project shared always gets built before project api.
Example 397. Multi-project build - dependencies between projects
api/build.gradle
dependencies {
compile project(':shared')
}
See the section called “Disabling the build of dependency projects” for how to disable this functionality.
Creating a distribution
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§
Creating a distribution
We also add a distribution, that gets shipped to the client:
Example 398. Multi-project build - distribution file
api/build.gradle
task dist(type: Zip) {
dependsOn spiJar
from 'src/dist'
into('libs') {
from spiJar.archivePath
from configurations.runtime
}
}
artifacts {
archives dist
}
§
Where to next?
In this chapter, you have seen how to do some of the things you commonly need to build a Java based
project. This chapter is not exhaustive, and there are many other things you can do with Java projects in
Gradle. You can find out more about the Java plugin in The Java Plugin, and you can find more sample Java
projects in the samples/java directory in the Gradle distribution.
Otherwise, continue on to Dependency Management for Java Projects.
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The Java Plugin
The Java plugin adds Java compilation along with testing and bundling capabilities to a project. It serves as
the basis for many of the other Gradle plugins.
§
Usage
To use the Java plugin, include the following in your build script:
Example 399. Using the Java plugin
build.gradle
apply plugin: 'java'
§
Source sets
The Java plugin introduces the concept of a source set . A source set is simply a group of source files which
are compiled and executed together. These source files may include Java source files and resource files.
Other plugins add the ability to include Groovy and Scala source files in a source set. A source set has an
associated compile classpath, and runtime classpath.
One use for source sets is to group source files into logical groups which describe their purpose. For
example, you might use a source set to define an integration test suite, or you might use separate source
sets to define the API and implementation classes of your project.
The Java plugin defines two standard source sets, called main and test. The main source set contains
your production source code, which is compiled and assembled into a JAR file. The test source set
contains your test source code, which is compiled and executed using JUnit or TestNG. These can be unit
tests, integration tests, acceptance tests, or any combination that is useful to you.
§
Tasks
The Java plugin adds a number of tasks to your project, as shown below.
compileJava(type: JavaCompile)
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Compiles production Java source files using javac. Depends on all tasks which produce the compile
classpath. This includes the jar task for project dependencies included in the compile configuration.
processResources(type: Copy)
Copies production resources into the production resources directory.
classes(type: Task)
Assembles the production classes and resources directories.
compileTestJava(type: JavaCompile)
Compiles test Java source files using javac. Depends on compile, plus all tasks which produce the test
compile classpath.
processTestResources(type: Copy)
Copies test resources into the test resources directory.
testClasses(type: Task)
Assembles the test classes and resources directories. Depends on compileTestJava task and processTestReso
task. Some plugins add additional test compilation tasks.
jar(type: Jar)
Assembles the JAR file. Depends on compile.
javadoc(type: Javadoc)
Generates API documentation for the production Java source, using Javadoc. Depends on compile.
test(type: Test)
Runs the unit tests using JUnit or TestNG. Depends on compile, compileTest, plus all tasks which
produce the test runtime classpath.
uploadArchives(type: Upload)
Uploads artifacts in the archives configuration, including the JAR file. Depends on the tasks which
produce the artifacts in the archives configuration, including jar.
clean(type: Delete)
Deletes the project build directory.
cleanTaskName(type: Delete)
Deletes files created by specified task. cleanJar will delete the JAR file created by the jar task, and cleanTest
will delete the test results created by the test task.
For each source set you add to the project, the Java plugin adds the following compilation tasks:
SourceSet Tasks
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§
SourceSet Tasks
compileSourceSetJava(type: JavaCompile)
Compiles the given source set’s Java source files using javac. Depends on all tasks which produce the
source set’s compile classpath.
processSourceSetResources(type: Copy)
Copies the given source set’s resources into the resources directory.
sourceSetClasses(type: Task)
Assembles the given source set’s classes and resources directories. Depends on the compile SourceSet Java
task and the process SourceSet Resources task. Some plugins add additional compilation tasks for
the source set.
§
Lifecycle Tasks
The Java plugin also adds a number of tasks which form a lifecycle for the project:
assemble(type: Task)
Assembles all the archives in the project. Depends on all archive tasks in the project, including jar.
Some plugins add additional archive tasks to the project.
check(type: Task)
Performs all verification tasks in the project. Depends on all verification tasks in the project, including test
. Some plugins add additional verification tasks to the project.
build(type: Task)
Performs a full build of the project. Depends on check and assemble.
buildNeeded(type: Task)
Performs a full build of the project and all projects it depends on. Depends on build and buildNeeded
tasks in all project lib dependencies of the testRuntime configuration.
buildDependents(type: Task)
Performs a full build of the project and all projects which depend on it. Depends on build and buildDependents
tasks in all projects with a project lib dependency on this project in a testRuntime configuration.
buildConfigName(type: Task)
Assembles the artifacts in the specified configuration. The task is added by the Base plugin which is
implicitly applied by the Java plugin. Depends on the tasks which produce the artifacts in configuration
ConfigName .
uploadConfigName(type: Upload)
Assembles and uploads the artifacts in the specified configuration. The task is added by the Base plugin
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which is implicitly applied by the Java plugin. Depends on the tasks which uploads the artifacts in
configuration ConfigName .
The following diagram shows the relationships between these tasks.
Figure 14. Java plugin - tasks
§
Project layout
The Java plugin assumes the project layout shown below. None of these directories need to exist or have
anything in them. The Java plugin will compile whatever it finds, and handles anything which is missing.
Table 36. Java plugin - default project layout
Directory
Meaning
src/main/java
Production Java source
src/main/resources
Production resources
src/test/java
Test Java source
src/test/resources
Test resources
src/ sourceSet /java
Java source for the given source set
src/ sourceSet /resources
Resources for the given source set
§
Changing the project layout
You configure the project layout by configuring the appropriate source set. This is discussed in more detail in
the following sections. Here is a brief example which changes the main Java and resource source
directories.
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Example 400. Custom Java source layout
build.gradle
sourceSets {
main {
java {
srcDirs = ['src/java']
}
resources {
srcDirs = ['src/resources']
}
}
}
§
Dependency management
The Java plugin adds a number of dependency configurations to your project, as shown below. It assigns
those configurations to tasks such as compileJava and test.
Dependency configurations
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§
Dependency configurations
compile
Compile time dependencies.
compileOnly
Compile time only dependencies, not used at runtime.
compileClasspath extends compile, compileOnly
Compile classpath, used when compiling source. Used by task compileJava.
runtime extends compile
Runtime dependencies.
testCompile extends compile
Additional dependencies for compiling tests.
testCompileOnly
Additional dependencies only for compiling tests, not used at runtime.
testCompileClasspath extends testCompile, testCompileOnly
Test compile classpath, used when compiling test sources. Used by task compileTestJava.
testRuntime extends runtime, testCompile
Additional dependencies for running tests only. Used by task test.
archives
Artifacts (e.g. jars) produced by this project. Used by tasks uploadArchives.
default extends runtime
The default configuration used by a project dependency on this project. Contains the artifacts and
dependencies required by this project at runtime.
Figure 15. Java plugin - dependency configurations
For each source set you add to the project, the Java plugins adds the following dependency configurations:
SourceSet dependency configurations
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§
SourceSet dependency configurations
sourceSetCompile
Compile time dependencies for the given source set.
sourceSetCompileOnly
Compile time only dependencies for the given source set, not used at runtime.
sourceSetCompileClasspath extends compileSourceSetJava
Compile classpath, used when compiling source. Used by sourceSet Compile, sourceSet CompileOnly
.
sourceSetRuntime
Runtime dependencies for the given source set. Used by sourceSet Compile.
§
Convention properties
The Java plugin adds a number of convention properties to the project, shown below. You can use these
properties in your build script as though they were properties of the project object.
Directory properties
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§
Directory properties
String reportsDirName
The name of the directory to generate reports into, relative to the build directory. Default value: reports
(read-only) File reportsDir
The directory to generate reports into. Default value: buildDir / reportsDirName
String testResultsDirName
The name of the directory to generate test result .xml files into, relative to the build directory. Default
value: test-results
(read-only) File testResultsDir
The directory to generate test result .xml files into. Default value: buildDir / testResultsDirName
String testReportDirName
The name of the directory to generate the test report into, relative to the reports directory. Default value: tests
(read-only) File testReportDir
The directory to generate the test report into. Default value: reportsDir /testReportDirName
String libsDirName
The name of the directory to generate libraries into, relative to the build directory. Default value: libs
(read-only) File libsDir
The directory to generate libraries into. Default value: buildDir / libsDirName
String distsDirName
The name of the directory to generate distributions into, relative to the build directory. Default value: distributions
(read-only) File distsDir
The directory to generate distributions into. Default value: buildDir / distsDirName
String docsDirName: :_The name of the directory to generate documentation into, relative to the build
directory._ Default value: docs
(read-only) File docsDir
The directory to generate documentation into. Default value: buildDir / docsDirName
String dependencyCacheDirName
The name of the directory to use to cache source dependency information, relative to the build directory.
Default value: dependency-cache
Other convention properties
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§
Other convention properties
(read-only) SourceSetContainer sourceSets
Contains the project’s source sets. Default value: Not null SourceSetContainer
JavaVersion sourceCompatibility
Java version compatibility to use when compiling Java source. Default value: version of the current JVM
in use JavaVersion. Can also set using a String or a Number, e.g. '1.5' or 1.5.
JavaVersion targetCompatibility
Java version to generate classes for. Default value: sourceCompatibility . Can also set using a
String or Number, e.g. '1.5' or 1.5.
String archivesBaseName
The basename to use for archives, such as JAR or ZIP files. Default value: projectName
Manifest manifest
The manifest to include in all JAR files. Default value: an empty manifest.
These properties are provided by convention objects of type JavaPluginConvention, and
BasePluginConvention.
§
Working with source sets
You can access the source sets of a project using the sourceSets property. This is a container for the
project’s source sets, of type SourceSetContainer. There is also a sourceSets { } script block, which
you can pass a closure to configure the source set container. The source set container works pretty much
the same way as other containers, such as tasks.
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Example 401. Accessing a source set
build.gradle
// Various ways to access the main source set
println sourceSets.main.output.classesDirs
println sourceSets['main'].output.classesDirs
sourceSets {
println main.output.classesDirs
}
sourceSets {
main {
println output.classesDirs
}
}
// Iterate over the source sets
sourceSets.all {
println name
}
To configure an existing source set, you simply use one of the above access methods to set the properties
of the source set. The properties are described below. Here is an example which configures the main Java
and resources directories:
Example 402. Configuring the source directories of a source set
build.gradle
sourceSets {
main {
java {
srcDirs = ['src/java']
}
resources {
srcDirs = ['src/resources']
}
}
}
§
Source set properties
The following table lists some of the important properties of a source set. You can find more details in the
API documentation for SourceSet.
(read-only) String name
The name of the source set, used to identify it. Default value: Not null
(read-only) SourceSetOutput output
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The output files of the source set, containing its compiled classes and resources. Default value: Not null
FileCollection output.classesDirs
The directories to generate the classes of this source set into. Default value: Not null
File output.resourcesDir
The directory to generate the resources of this source set into. Default value: buildDir /resources/ name
FileCollection compileClasspath
The classpath to use when compiling the source files of this source set. Default value: compileSourceSet
configuration.
FileCollection runtimeClasspath
The classpath to use when executing the classes of this source set. Default value: output + runtimeSourceSet
configuration.
(read-only) SourceDirectorySet java
The Java source files of this source set. Contains only .java files found in the Java source directories,
and excludes all other files. Default value: Not null
Set<File> java.srcDirs
The source directories containing the Java source files of this source set. Default value: [ projectDir /src/ name /j
. Can set using anything described in the section called “Specifying a set of input files”.
File java.outputDir
The directory to generate compiled Java sources into. Default value: buildDir /classes/java/ sourceSetName
. Can set using anything described in the section called “Locating files”.
(read-only) SourceDirectorySet resources
The resources of this source set. Contains only resources, and excludes any .java files found in the
resource source directories. Other plugins, such as the Groovy plugin, exclude additional types of files
from this collection. Default value: Not null
Set<File> resources.srcDirs
The source directories containing the resources of this source set. Default value: [ projectDir /src/ name /resour
. Can set using anything described in the section called “Specifying a set of input files”.
(read-only) SourceDirectorySet allJava
All .java files of this source set. Some plugins, such as the Groovy plugin, add additional Java source
files to this collection. Default value: java
(read-only) SourceDirectorySet allSource
All source files of this source set. This include all resource files and all Java source files. Some plugins,
such as the Groovy plugin, add additional source files to this collection. Default value: resources + java
Defining new source sets
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§
Defining new source sets
To define a new source set, you simply reference it in the sourceSets { } block. Here’s an example:
Example 403. Defining a source set
build.gradle
sourceSets {
intTest
}
When you define a new source set, the Java plugin adds some dependency configurations for the source
set, as shown in the section called “SourceSet dependency configurations” . You can use these
configurations to define the compile and runtime dependencies of the source set.
Example 404. Defining source set dependencies
build.gradle
sourceSets {
intTest
}
dependencies {
intTestCompile 'junit:junit:4.12'
intTestRuntime 'org.ow2.asm:asm-all:4.0'
}
The Java plugin also adds a number of tasks which assemble the classes for the source set, as shown in the
section called “SourceSet Tasks”. For example, for a source set called intTest, compiling the classes for
this source set is done by running gradle intTestClasses.
Example 405. Compiling a source set
Output of gradle intTestClasses
> gradle intTestClasses
:compileIntTestJava
:processIntTestResources
:intTestClasses
BUILD SUCCESSFUL in 0s
2 actionable tasks: 2 executed
§
Some source set examples
Adding a JAR containing the classes of a source set:
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Example 406. Assembling a JAR for a source set
build.gradle
task intTestJar(type: Jar) {
from sourceSets.intTest.output
}
Generating Javadoc for a source set:
Example 407. Generating the Javadoc for a source set
build.gradle
task intTestJavadoc(type: Javadoc) {
source sourceSets.intTest.allJava
}
Adding a test suite to run the tests in a source set:
Example 408. Running tests in a source set
build.gradle
task intTest(type: Test) {
testClassesDirs = sourceSets.intTest.output.classesDirs
classpath = sourceSets.intTest.runtimeClasspath
}
§
Javadoc
The javadoc task is an instance of Javadoc. It supports the core Javadoc options and the options of the
standard doclet described in the reference documentation of the Javadoc executable. For a complete list of
supported Javadoc options consult the API documentation of the following classes: CoreJavadocOptions
and StandardJavadocDocletOptions.
Javadoc properties
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§
Javadoc properties
FileCollection classpath
Default value: sourceSets.main.output + sourceSets.main.compileClasspath
FileTree source
Default value: sourceSets.main.allJava. Can set using anything described in the section called
“Specifying a set of input files”.
File destinationDir
Default value: docsDir /javadoc
String title
Default value: The name and version of the project
§
Clean
The clean task is an instance of Delete. It simply removes the directory denoted by its dir property.
§
Clean properties
File dir
Default value: buildDir
§
Resources
The Java plugin uses the Copy task for resource handling. It adds an instance for each source set in the
project. You can find out more about the copy task in the section called “Copying files”.
§
ProcessResources properties
Object srcDirs
Default value: sourceSet .resources. Can set using anything described in the section called
“Specifying a set of input files”.
File destinationDir
Default value: sourceSet .output.resourcesDir. Can set using anything described in the section
called “Locating files”.
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CompileJava
§
CompileJava
The Java plugin adds a JavaCompile instance for each source set in the project. Some of the most
common configuration options are shown below.
§
Compile properties
FileCollection classpath
Default value: sourceSet .compileClasspath
FileTree source
Default value: sourceSet .java. Can set using anything described in the section called “Specifying a
set of input files”.
File destinationDir
Default value: sourceSet .java.outputDir
By default, the Java compiler runs in the Gradle process. Setting options.fork to true causes
compilation to occur in a separate process. In the case of the Ant javac task, this means that a new process
will be forked for each compile task, which can slow down compilation. Conversely, Gradle’s direct compiler
integration (see above) will reuse the same compiler process as much as possible. In both cases, all fork
options specified with options.forkOptions will be honored.
§
Incremental Java compilation
Starting with Gradle 2.1, it is possible to compile Java incrementally. See the JavaCompile task for
information on how to enable it.
Main goals for incremental compilations are:
Avoid wasting time compiling source classes that don’t have to be compiled. This means faster builds,
especially when a change to a source class or a jar does not incur recompilation of many source classes that
depend on the changed input.
Change as few output classes as possible. Classes that don’t need to be recompiled remain unchanged in
the output directory. An example scenario when this is really useful is using JRebel - the fewer output
classes are changed the quicker the JVM can use refreshed classes.
The incremental compilation at a high level:
The detection of the correct set of stale classes is reliable at some expense of speed. The algorithm uses
bytecode analysis and deals gracefully with compiler optimizations (inlining of non-private constants),
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transitive class dependencies, etc. Example: When a class with a public constant changes, we eagerly
compile classes that use the same constants to avoid problems with constants inlined by the compiler.
To make incremental compilation fast, we cache class analysis results and jar snapshots. The initial
incremental compilation can be slower due to the cold caches.
§
Known issues
If a compile task fails due to a compile error, it will do a full compilation again the next time it is invoked.
Because of type erasure, the incremental compiler is not able to recognize when a type is only used in a
type parameter, and never actually used in the code. For example, imagine that you have the following code:
List<? extends A> list = Lists.newArrayList(); but that no member of A is in practice used in
the code, then changes to A will not trigger recompilation of the class. In practice, this should very rarely be
an issue.
§
Compile avoidance
If a dependent project has changed in an ABI-compatible way (only its private API has changed), then Java
compilation tasks will be up-to-date. This means that if project A depends on project B and a class in B is
changed in an ABI-compatible way (typically, changing only the body of a method), then Gradle won’t
recompile A.
Some of the types of changes that do not affect the public API and are ignored:
Changing a method body
Changing a comment
Adding, removing or changing private methods, fields, or inner classes
Adding, removing or changing a resource
Changing the name of jars or directories in the classpath
Renaming a parameter
Compile-avoidance is deactivated if annotation processors are found on the compile classpath, because for
annotation processors the implementation details matter. To better separate these concerns, it’s
recommended to declare annotation processors separately: the CompileOptions for the JavaCompile
task type define a annotationProcessorPath property that can be used to declare annotation
processors. It’s recommended to use a distinct configuration for annotation processors:
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Example 409. Declaring annotation processors
build.gradle
configurations {
apt
}
dependencies {
// The dagger compiler and its transitive dependencies will only be found on annotatio
apt 'com.google.dagger:dagger-compiler:2.8'
// And we still need the Dagger annotations on the compile classpath itself
implementation 'com.google.dagger:dagger:2.8'
}
compileJava {
options.annotationProcessorPath = configurations.apt
}
§
Test
The test task is an instance of Test. It automatically detects and executes all unit tests in the test source
set. It also generates a report once test execution is complete. JUnit and TestNG are both supported. Have
a look at Test for the complete API.
§
Test execution
Tests are executed in a separate JVM, isolated from the main build process. The Test task’s API allows you
some control over how this happens.
There are a number of properties which control how the test process is launched. This includes things such
as system properties, JVM arguments, and the Java executable to use.
You can specify whether or not to execute your tests in parallel. Gradle provides parallel test execution by
running multiple test processes concurrently. Each test process executes only a single test at a time, so you
generally don’t need to do anything special to your tests to take advantage of this. The maxParallelForks
property specifies the maximum number of test processes to run at any given time. The default is 1, that is,
do not execute the tests in parallel.
The test process sets the org.gradle.test.worker system property to a unique identifier for that test
process, which you can use, for example, in files names or other resource identifiers.
You can specify that test processes should be restarted after it has executed a certain number of test
classes. This can be a useful alternative to giving your test process a very large heap. The forkEvery
property specifies the maximum number of test classes to execute in a test process. The default is to
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execute an unlimited number of tests in each test process.
The task has an ignoreFailures property to control the behavior when tests fail. The Test task always
executes every test that it detects. It stops the build afterwards if ignoreFailures is false and there are
failing tests. The default value of ignoreFailures is false.
The testLogging property allows you to configure which test events are going to be logged and at which
detail level. By default, a concise message will be logged for every failed test. See
TestLoggingContainer for how to tune test logging to your preferences.
§
Debugging
The test task provides a Test.getDebug() property that can be set to launch to make the JVM wait for a
debugger to attach to port 5005 before proceeding with test execution.
This can also be enabled at invocation time via the --debug-jvm task option (since Gradle 1.12).
§
Test filtering
Starting with Gradle 1.10, it is possible to include only specific tests, based on the test name pattern.
Filtering is a different mechanism than test class inclusion / exclusion that will be described in the next few
paragraphs (-Dtest.single, test.include and friends). The latter is based on files, e.g. the physical
location of the test implementation class. File-level test selection does not support many interesting
scenarios that are possible with test-level filtering. Some of them Gradle handles now and some will be
satisfied in future releases:
Filtering at the level of specific test methods; executing a single test method
Filtering based on custom annotations (future)
Filtering based on test hierarchy; executing all tests that extend a certain base class (future)
Filtering based on some custom runtime rule, e.g. particular value of a system property or some static state
(future)
Test filtering feature has following characteristic:
Fully qualified class name or fully qualified method name is supported, e.g. “org.gradle.SomeTest”,
“org.gradle.SomeTest.someMethod”
Wildcard '*' is supported for matching any characters
Command line option “--tests” is provided to conveniently extend the test filter for an individual Gradle
execution. This is especially useful for the classic 'single test method execution' use case. When the
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command line option is used, the inclusions declared in the build script are still honored. That is, the
command line filters are always applied on top of the filter definition in the build script. It is possible to supply
multiple “--tests” options and tests matching any of those patterns will be included.
Gradle tries to filter the tests given the limitations of the test framework API. Some advanced, synthetic tests
may not be fully compatible with filtering. However, the vast majority of tests and use cases should be
handled neatly.
Test filtering supersedes the file-based test selection. The latter may be completely replaced in future. We
will grow the test filtering API and add more kinds of filters.
Example 410. Filtering tests in the build script
build.gradle
test {
filter {
//include specific method in any of the tests
includeTestsMatching "*UiCheck"
//include all tests from package
includeTestsMatching "org.gradle.internal.*"
//include all integration tests
includeTestsMatching "*IntegTest"
}
}
For more details and examples please see the TestFilter reference.
Some examples of using the command line option:
gradle test --tests org.gradle.SomeTest.someSpecificFeature
gradle test --tests \*SomeTest.someSpecificFeature
gradle test --tests \*SomeSpecificTest
gradle test --tests \*SomeSpecificTestSuite
gradle test --tests all.in.specific.package\*
gradle test --tests \*IntegTest
gradle test --tests \*IntegTest\*ui\*
gradle test --tests "com.example.MyTestSuite"
gradle test --tests "com.example.ParameterizedTest"
gradle test --tests "*ParameterizedTest.foo*"
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gradle test --tests "*ParameterizedTest.*[2]"
gradle someTestTask --tests \*UiTest someOtherTestTask --tests \*WebTest\*ui
This is something you can combine with continuous build using --continuous (or -t, for short) to
re-execute a subset of tests immediately after every change.
gradle test --continuous --tests "com.mypackage.foo.*"
§
Single test execution via System Properties
Note: This mechanism has been superseded by 'Test Filtering', described above.
Setting a system property of taskName.single = testNamePattern will only execute tests that match the
specified testNamePattern . The taskName can be a full multi-project path like “:sub1:sub2:test” or just the
task name. The testNamePattern will be used to form an include pattern of “**/testNamePattern*.class”. If no
tests with this pattern can be found, an exception is thrown. This is to shield you from false security. If tests
of more than one subproject are executed, the pattern is applied to each subproject. An exception is thrown
if no tests can be found for a particular subproject. In such a case you can use the path notation of the
pattern, so that the pattern is applied only to the test task of a specific subproject. Alternatively you can
specify the fully qualified task name to be executed. You can also specify multiple patterns. Examples:
gradle -Dtest.single=ThisUniquelyNamedTest test
gradle -Dtest.single=a/b/ test
gradle -DintegTest.single=\*IntegrationTest integTest
gradle -D:proj1:test.single=Customer build
gradle -D:proj1:integTest.single=c/d/
§
Test detection
The Test task detects which classes are test classes by inspecting the compiled test classes. By default it
scans all .class files. You can set custom includes / excludes, only those classes will be scanned.
Depending on the test framework used (JUnit / TestNG) the test class detection uses different criteria.
When using JUnit, we scan for both JUnit 3 and 4 test classes. If any of the following criteria match, the
class is considered to be a JUnit test class:
Class or a super class extends TestCase or GroovyTestCase
Class or a super class is annotated with @RunWith
Class or a super class contain a method annotated with @Test
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When using TestNG, we scan for methods annotated with @Test.
Note that abstract classes are not executed. Gradle also scans up the inheritance tree into jar files on the
test classpath.
If you don’t want to use test class detection, you can disable it by setting scanForTestClasses to false.
This will make the test task only use includes / excludes to find test classes. If scanForTestClasses is
false and no include / exclude patterns are specified, the defaults are “ **/*Tests.class”, “**/*Test.class
” and “**/Abstract*.class” for include and exclude, respectively.
§
Test grouping
JUnit and TestNG allows sophisticated groupings of test methods.
For grouping JUnit test classes and methods JUnit 4.8 introduces the concept of categories. [16] The test
task allows the specification of the JUnit categories you want to include and exclude.
Example 411. JUnit Categories
build.gradle
test {
useJUnit {
includeCategories 'org.gradle.junit.CategoryA'
excludeCategories 'org.gradle.junit.CategoryB'
}
}
The TestNG framework has a quite similar concept. In TestNG you can specify different test groups. [17] The
test groups that should be included or excluded from the test execution can be configured in the test task.
Example 412. Grouping TestNG tests
build.gradle
test {
useTestNG {
excludeGroups 'integrationTests'
includeGroups 'unitTests'
}
}
§
Test execution order in TestNG
TestNG allows explicit control of the execution order of tests.
The preserveOrder property controls whether tests are executed in deterministic order. Preserving the
order guarantees that the complete test (including @BeforeXXX and @AfterXXX) is run in a test thread
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before the next test is run. While preserving the order of tests is the default behavior when directly working
with testng.xml files, the TestNG API, that is used for running tests programmatically, as well as Gradle’s
TestNG integration execute tests in unpredictable order by default.[18] Preserving the order of tests was
introduced with TestNG version 5.14.5. Setting the preserveOrder property to true for an older TestNG
version will cause the build to fail.
Example 413. Preserving order of TestNG tests
build.gradle
test {
useTestNG {
preserveOrder true
}
}
The groupByInstance property controls whether tests should be grouped by instances. Grouping by
instances will result in resolving test method dependencies for each instance instead of running the
dependees of all instances before running the dependants. The default behavior is not to group tests by
instances.[19] Grouping tests by instances was introduced with TestNG version 6.1. Setting the groupByInstances
property to true for an older TestNG version will cause the build to fail.
Example 414. Grouping TestNG tests by instances
build.gradle
test {
useTestNG {
groupByInstances true
}
}
§
Test reporting
The Test task generates the following results by default.
An HTML test report.
The results in an XML format that is compatible with the Ant JUnit report task. This format is supported by
many other tools, such as CI servers.
Results in an efficient binary format. The task generates the other results from these binary results.
There is also a stand-alone TestReport task type which can generate the HTML test report from the binary
results generated by one or more Test task instances. To use this task type, you need to define a destinationDir
and the test results to include in the report. Here is a sample which generates a combined report for the unit
tests from subprojects:
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Example 415. Creating a unit test report for subprojects
build.gradle
subprojects {
apply plugin: 'java'
// Disable the test report for the individual test task
test {
reports.html.enabled = false
}
}
task testReport(type: TestReport) {
destinationDir = file("$buildDir/reports/allTests")
// Include the results from the `test` task in all subprojects
reportOn subprojects*.test
}
You should note that the TestReport type combines the results from multiple test tasks and needs to
aggregate the results of individual test classes. This means that if a given test class is executed by multiple
test tasks, then the test report will include executions of that class, but it can be hard to distinguish individual
executions of that class and their output.
§
TestNG parameterized methods and reporting
TestNG supports parameterizing test methods, allowing a particular test method to be executed multiple
times with different inputs. Gradle includes the parameter values in its reporting of the test method
execution.
Given a parameterized test method named aTestMethod that takes two parameters, it will be reported with
the name: aTestMethod(toStringValueOfParam1,
toStringValueOfParam2). This makes
identifying the parameter values for a particular iteration easy.
§
Test convention values
File testClassesDirs
Default value: sourceSets.test.output.classesDirs
FileCollection classpath
Default value: sourceSets.test.runtimeClasspath
File testResultsDir
Default value: testResultsDir
File testReportDir
Default value: testReportDir
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§
Jar
The jar task creates a JAR file containing the class files and resources of the project. The JAR file is
declared as an artifact in the archives dependency configuration. This means that the JAR is available in
the classpath of a dependent project. If you upload your project into a repository, this JAR is declared as part
of the dependency descriptor. You can learn more about how to work with archives in the section called
“Creating archives” and artifact configurations in Publishing artifacts.
§
Manifest
Each jar or war object has a manifest property with a separate instance of Manifest. When the archive is
generated, a corresponding MANIFEST.MF file is written into the archive.
Example 416. Customization of MANIFEST.MF
build.gradle
jar {
manifest {
attributes("Implementation-Title": "Gradle",
"Implementation-Version": version)
}
}
You can create stand-alone instances of a Manifest. You can use that for example, to share manifest
information between jars.
Example 417. Creating a manifest object.
build.gradle
ext.sharedManifest = manifest {
attributes("Implementation-Title": "Gradle",
"Implementation-Version": version)
}
task fooJar(type: Jar) {
manifest = project.manifest {
from sharedManifest
}
}
You can merge other manifests into any Manifest object. The other manifests might be either described by
a file path or, like in the example above, by a reference to another Manifest object.
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Example 418. Separate MANIFEST.MF for a particular archive
build.gradle
task barJar(type: Jar) {
manifest {
attributes key1: 'value1'
from sharedManifest, 'src/config/basemanifest.txt'
from('src/config/javabasemanifest.txt',
'src/config/libbasemanifest.txt') {
eachEntry { details ->
if (details.baseValue != details.mergeValue) {
details.value = baseValue
}
if (details.key == 'foo') {
details.exclude()
}
}
}
}
}
Manifests are merged in the order they are declared by the from statement. If the base manifest and the
merged manifest both define values for the same key, the merged manifest wins by default. You can fully
customize the merge behavior by adding eachEntry actions in which you have access to a
ManifestMergeDetails instance for each entry of the resulting manifest. The merge is not immediately
triggered by the from statement. It is done lazily, either when generating the jar, or by calling writeTo or effectiveMan
You can easily write a manifest to disk.
Example 419. Saving a MANIFEST.MF to disk
build.gradle
jar.manifest.writeTo("$buildDir/mymanifest.mf")
§
Uploading
How to upload your archives is described in Publishing artifacts.
§
Compiling and testing Java 6/7
Gradle can only run on Java version 7 or higher. However, support for running Gradle on Java 7 has been
deprecated and is scheduled to be removed in Gradle 5.0. There are two reasons for deprecating support for
Java 7:
Java 7 reached end of life. Therefore, Oracle ceased public availability of security fixes and upgrades for
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Java 7 as of April 2015.
Once support for Java 7 has ceased (likely with Gradle 5.0), Gradle’s implementation can start to use Java 8
APIs optimized for performance and usability.
Gradle still supports compiling, testing, generating Javadoc and executing applications for Java 6 and Java
7. Java 5 is not supported.
To use Java 6 or Java 7, the following tasks need to be configured:
JavaCompile task to fork and use the correct Java home
Javadoc task to use the correct javadoc executable
Test and the JavaExec task to use the correct java executable.
The following sample shows how the build.gradle needs to be adjusted. In order to be able to make the
build machine-independent, the location of the old Java home and target version should be configured in GRADLE_USER_H
[20]
in the user’s home directory on each developer machine, as shown in the example.
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Example 420. Configure Java 6 build
gradle.properties
# in $HOME/.gradle/gradle.properties
javaHome=/Library/Java/JavaVirtualMachines/1.7.0.jdk/Contents/Home
targetJavaVersion=1.7
build.gradle
assert hasProperty('javaHome'): "Set the property 'javaHome' in your your gradle.propertie
assert hasProperty('targetJavaVersion'): "Set the property 'targetJavaVersion' in your you
sourceCompatibility = targetJavaVersion
def javaExecutablesPath = new File(javaHome, 'bin')
def javaExecutables = [:].withDefault { execName ->
def executable = new File(javaExecutablesPath, execName)
assert executable.exists(): "There is no ${execName} executable in ${javaExecutablesPa
executable
}
tasks.withType(AbstractCompile) {
options.with {
fork = true
forkOptions.javaHome = file(javaHome)
}
}
tasks.withType(Javadoc) {
executable = javaExecutables.javadoc
}
tasks.withType(Test) {
executable = javaExecutables.java
}
tasks.withType(JavaExec) {
executable = javaExecutables.java
}
[16] The JUnit wiki contains a detailed description on how to work with JUnit categories:
https://github.com/junit-team/junit/wiki/Categories.
[ 17 ]
The
TestNG
documentation
contains
more
details
about
test
groups:
http://testng.org/doc/documentation-main.html#test-groups.
[18] The TestNG documentation contains more details about test ordering when working with testng.xml
files: http://testng.org/doc/documentation-main.html#testng-xml.
[19] The TestNG documentation contains more details about grouping tests by instances:
http://testng.org/doc/documentation-main.html#dependencies-with-annotations.
Page 483 of 717
[20] For more details on gradle.properties see the section called “Gradle properties”
Page 484 of 717
The Java Library Plugin
The Java Library plugin expands the capabilities of the Java plugin by providing specific knowledge about
Java libraries. In particular, a Java library exposes an API to consumers (i.e., other projects using the Java
or the Java Library plugin). All the source sets, tasks and configurations exposed by the Java plugin are
implicitly available when using this plugin.
§
Usage
To use the Java Library plugin, include the following in your build script:
Example 421. Using the Java Library plugin
build.gradle
apply plugin: 'java-library'
§
API and implementation separation
The key difference between the standard Java plugin and the Java Library plugin is that the latter introduces
the concept of an API exposed to consumers. A library is a Java component meant to be consumed by other
components. It’s a very common use case in multi-project builds, but also as soon as you have external
dependencies.
The plugin exposes two configurations that can be used to declare dependencies: api and implementation
. The api configuration should be used to declare dependencies which are exported by the library API,
whereas the implementation configuration should be used to declare dependencies which are internal to
the component.
Example 422. Declaring API and implementation dependencies
build.gradle
dependencies {
api 'commons-httpclient:commons-httpclient:3.1'
implementation 'org.apache.commons:commons-lang3:3.5'
}
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Dependencies appearing in the api configurations will be transitively exposed to consumers of the library,
and as such will appear on the compile classpath of consumers. Dependencies found in the implementation
configuration will, on the other hand, not be exposed to consumers, and therefore not leak into the
consumers' compile classpath. This comes with several benefits:
dependencies do not leak into the compile classpath of consumers anymore, so you will never accidentally
depend on a transitive dependency
faster compilation thanks to reduced classpath size
less recompilations when implementation dependencies change: consumers would not need to be
recompiled
cleaner publishing: when used in conjunction with the new maven-publish plugin, Java libraries produce
POM files that distinguish exactly between what is required to compile against the library and what is
required to use the library at runtime (in other words, don’t mix what is needed to compile the library itself
and what is needed to compile against the library).
Note: The compile configuration still exists but should not be used as it will not offer the
guarantees that the api and implementation configurations provide.
§
Recognizing API and implementation dependencies
This section will help you spot API and Implementation dependencies in your code using simple rules of
thumb. Basically, an API dependency is a type that is exposed in the library binary interface, often referred to
ABI (Application Binary Interface). This includes, but is not limited to:
types used in super classes or interfaces
types used in public method parameters, including generic parameter types (where public is something that
is visible to compilers. I.e. , public , protected and package private members in the Java world)
types used in public fields
public annotation types
In opposition, any type that is used in the following list is irrelevant to the ABI, and therefore should be
declared as implementation dependency:
types exclusively used in method bodies
types exclusively used in private members
types exclusively found in internal classes (future versions of Gradle will let you declare which packages
belong to the public API)
In the following sample, we can make the difference between an API dependency and an implementation
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dependency:
Example 423. Making the difference between API and implementation
src/main/java/org/gradle/HttpClientWrapper.java
// The following types can appear anywhere in the code
// but say nothing about API or implementation usage
import org.apache.commons.httpclient.*;
import org.apache.commons.httpclient.methods.*;
import org.apache.commons.lang3.exception.ExceptionUtils;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
public class HttpClientWrapper {
private final HttpClient client; // private member: implementation details
// HttpClient is used as a parameter of a public method
// so "leaks" into the public API of this component
public HttpClientWrapper(HttpClient client) {
this.client = client;
}
// public methods belongs to your API
public byte[] doRawGet(String url) {
GetMethod method = new GetMethod(url);
try {
int statusCode = doGet(method);
return method.getResponseBody();
} catch (Exception e) {
ExceptionUtils.rethrow(e); // this dependency is internal only
} finally {
method.releaseConnection();
}
return null;
}
// GetMethod is used in a private method, so doesn't belong to the API
private int doGet(GetMethod method) throws Exception {
int statusCode = client.executeMethod(method);
if (statusCode != HttpStatus.SC_OK) {
System.err.println("Method failed: " + method.getStatusLine());
}
return statusCode;
}
}
We can see that our class imports third party classes, but imports alone won’t tell us if a dependency is an
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API or implementation dependency. For this, we need to look at the methods. The public constructor of HttpClientWrap
uses HttpClient as a parameter, so it exposed to consumers and therefore belongs to the API.
On the other hand, the ExceptionUtils type, coming from the commons-lang library, is only used in a
method body, so it’s an implementation dependency.
Therefore, we can deduce that commons-httpclient is an API dependency, whereas commons-lang is
an implementation dependency, which directly translates into the build file:
Example 424. Declaring API and implementation dependencies
build.gradle
dependencies {
api 'commons-httpclient:commons-httpclient:3.1'
implementation 'org.apache.commons:commons-lang3:3.5'
}
As a guideline, you should prefer the implementation configuration first: leakage of implementation types
to consumers would then directly lead to a compile error of consumers, which would be solved either by
removing the type from the public API, or promoting the dependency as an API dependency instead.
§
The Java Library plugin configurations
The following graph describes the main configurations setup when the Java Library plugin is in use.
The configurations in green are the ones a user should use to declare dependencies
The configurations in pink are the ones used when a component compiles, or runs against the library
The configurations in blue are internal to the component, for its own use
The configurations in white are configurations inherited from the Java plugin
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And the next graph describes the test configurations setup:
Note: The compile , testCompile , runtime and testRuntime configurations inherited from the Java
plugin are still available but are deprecated. You should avoid using them, as they are only kept for
backwards compatibility.
The role of each configuration is described in the following tables:
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Table 37. Java Library plugin - configurations used to declare dependencies
Configuration
Can be
Role
name
Declaring API
api
Can be
consumed resolved
no
no
implementation no
no
dependencies
Declaring
implementation
dependencies
compile
only yes
yes
dependencies
runtime
no
no
no
no
dependencies
testImplementation
Test
dependencies
compile
only yes
yes
dependencies
internal and not meant to be exposed to consumers.
runtime
required at compile time, but should not leak into the runtime. This
typically includes dependencies which are shaded when found at
This is where you should declare dependencies which are only
required at runtime, and not at compile time.
This is where you should declare dependencies which are used to
compile tests.
required at test compile time, but should not leak into the runtime. This
typically includes dependencies which are shaded when found at
runtime.
Declaring test
testRuntimeOnly
This is where you should declare dependencies which are purely
This is where you should declare dependencies which are only
Declaring test
testCompileOnly
exported to consumers, for compile.
runtime.
Declaring
runtimeOnly
This is where you should declare dependencies which are transitively
This is where you should declare dependencies which are only
Declaring
compileOnly
Description
no
no
dependencies
This is where you should declare dependencies which are only
required at test runtime, and not at test compile time.
Table 38. Java Library plugin - configurations used by consumers
Configuration
name
Role
Can be
Can be
consumed resolved
For
apiElements
compiling
against this
This configuration is meant to be used by consumers, to retrieve all the
yes
no
For
this library
elements necessary to compile against this library. Unlike the default
configuration, this doesn’t leak implementation or runtime dependencies.
library
runtimeElements executing
Description
yes
no
This configuration is meant to be used by consumers, to retrieve all the
elements necessary to run against this library.
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Table 39. Java Library plugin - configurations used by the library itself
Configuration name
compileClasspath
runtimeClasspath
testCompileClasspath
testRuntimeClasspath
Can be
Role
For compiling this
library
Description
This configuration contains the compile classpath of this library,
no
yes
and is therefore used when invoking the java compiler to compile
it.
For executing this
library
For compiling the
tests of this library
For
Can be
consumed resolved
executing
tests of this library
no
yes
no
yes
no
yes
This configuration contains the runtime classpath of this library
This configuration contains the test compile classpath of this
library.
This configuration contains the test runtime classpath of this
library
§
Known issues
§
Compatibility with other plugins
At the moment the Java Library plugin is only wired to behave correctly with the java plugin. Other plugins,
such as the Groovy plugin, may not behave correctly. In particular, if the Groovy plugin is used in addition to
the java-library plugin, then consumers may not get the Groovy classes when they consume the library.
To workaround this, you need to explicitly wire the Groovy compile dependency, like this:
Example 425. Configuring the Groovy plugin to work with Java Library
a/build.gradle
configurations {
apiElements {
outgoing.variants.getByName('classes').artifact(
file: compileGroovy.destinationDir,
type: ArtifactTypeDefinition.JVM_CLASS_DIRECTORY,
builtBy: compileGroovy)
}
}
Increased memory usage for consumers
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§
Increased memory usage for consumers
When a project uses the Java Library plugin, consumers will use the output classes directory of this project
directly on their compile classpath, instead of the jar file if the project uses the Java plugin. An indirect
consequence is that up-to-date checking will require more memory, because Gradle will snapshot individual
class files instead of a single jar. This may lead to increased memory consumption for large projects.
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Web Application Quickstart
Note: This chapter is a work in progress.
This chapter introduces the Gradle support for web applications. Gradle recommends two plugins for web
application development: the War plugin and the Gretty plugin. The War plugin extends the Java plugin to
build a WAR file for your project. The Gretty plugin allows you to deploy your web application to an
embedded Jetty web container.
§
Building a WAR file
To build a WAR file, you apply the War plugin to your project:
Example 426. War plugin
build.gradle
apply plugin: 'war'
Note: The code for this example can be found at samples/webApplication/quickstart in
the ‘-all’ distribution of Gradle.
This also applies the Java plugin to your project. Running gradle build will compile, test and WAR your
project. Gradle will look for the source files to include in the WAR file in src/main/webapp. Your compiled
classes and their runtime dependencies are also included in the WAR file, in the WEB-INF/classes and WEB-INF/lib
directories, respectively.
Groovy web applications
You can combine multiple plugins in a single project, so you can use the War and Groovy plugins
together to build a Groovy based web application. The appropriate Groovy libraries will be added to
the WAR file for you.
§
Running your web application
To run your web application, you apply the Gretty plugin to your project:
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Example 427. Running web application with Gretty plugin
build.gradle
buildscript {
repositories {
jcenter()
}
dependencies {
classpath 'org.akhikhl.gretty:gretty:2.0.0'
}
}
apply plugin: 'org.akhikhl.gretty'
This also applies the War plugin to your project. Running gradle appRun will run your web application in
an embedded servlet container. Running gradle appRunWar will build the WAR file, and then run it in an
embedded web container.
§
Summary
You can find out more about the War plugin in The War Plugin. You can find more sample Java projects in
the samples/webApplication directory in the Gradle distribution.
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The War Plugin
The War plugin extends the Java plugin to add support for assembling web application WAR files. It disables
the default JAR archive generation of the Java plugin and adds a default WAR archive task.
§
Usage
To use the War plugin, include the following in your build script:
Example 428. Using the War plugin
build.gradle
apply plugin: 'war'
§
Tasks
The War plugin adds the following tasks to the project.
Table 40. War plugin - tasks
Task name
Depends on
Type
Description
war
compile
War
Assembles the application WAR file.
The War plugin adds the following dependencies to tasks added by the Java plugin.
Table 41. War plugin - additional task dependencies
Task name
Depends on
assemble
war
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Figure 16. War plugin - tasks
§
Project layout
Table 42. War plugin - project layout
Directory
Meaning
src/main/webapp
Web application sources
§
Dependency management
The War plugin adds two dependency configurations named providedCompile and providedRuntime.
Those two configurations have the same scope as the respective compile and runtime configurations,
except that they are not added to the WAR archive. It is important to note that those provided
configurations work transitively. Let’s say you add commons-httpclient:commons-httpclient:3.0 to
any of the provided configurations. This dependency has a dependency on commons-codec. Because this
is a “provided” configuration, this means that neither of these dependencies will be added to your WAR,
even if the commons-codec library is an explicit dependency of your compile configuration. If you don’t
want this transitive behavior, simply declare your provided dependencies like commons-httpclient:commons-httpc
.
§
Convention properties
Table 43. War plugin - directory properties
Property name
Type
webAppDirName String
File
webAppDir
(read-only)
Default value
src/main/webapp
Description
The name of the web application source directory, relative to the
project directory.
projectDir / webAppDirName
The web application source directory.
These properties are provided by a WarPluginConvention convention object.
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§
War
The default behavior of the War task is to copy the content of src/main/webapp to the root of the archive.
Your webapp directory may of course contain a WEB-INF sub-directory, which may contain a web.xml file.
Your compiled classes are compiled to WEB-INF/classes. All the dependencies of the runtime
[21]
configuration are copied to WEB-INF/lib.
The War class in the API documentation has additional useful information.
§
Customizing
Here is an example with the most important customization options:
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Example 429. Customization of war plugin
build.gradle
configurations {
moreLibs
}
repositories {
flatDir { dirs "lib" }
jcenter()
}
dependencies {
compile module(":compile:1.0") {
dependency ":compile-transitive-1.0@jar"
dependency ":providedCompile-transitive:1.0@jar"
}
providedCompile "javax.servlet:servlet-api:2.5"
providedCompile module(":providedCompile:1.0") {
dependency ":providedCompile-transitive:1.0@jar"
}
runtime ":runtime:1.0"
providedRuntime ":providedRuntime:1.0@jar"
testCompile "junit:junit:4.12"
moreLibs ":otherLib:1.0"
}
war {
from 'src/rootContent' // adds a file-set to the root of the archive
webInf { from 'src/additionalWebInf' } // adds a file-set to the WEB-INF dir.
classpath fileTree('additionalLibs') // adds a file-set to the WEB-INF/lib dir.
classpath configurations.moreLibs // adds a configuration to the WEB-INF/lib dir.
webXml = file('src/someWeb.xml') // copies a file to WEB-INF/web.xml
}
Of course one can configure the different file-sets with a closure to define excludes and includes.
[21] The runtime configuration extends the compile configuration.
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The Ear Plugin
The Ear plugin adds support for assembling web application EAR files. It adds a default EAR archive task. It
doesn’t require the Java plugin, but for projects that also use the Java plugin it disables the default JAR
archive generation.
§
Usage
To use the Ear plugin, include the following in your build script:
Example 430. Using the Ear plugin
build.gradle
apply plugin: 'ear'
§
Tasks
The Ear plugin adds the following tasks to the project.
Table 44. Ear plugin - tasks
Task name
Depends on
Type Description
ear
compile (only if the Java plugin is also applied)
Ear
Assembles the application EAR file.
The Ear plugin adds the following dependencies to tasks added by the base plugin.
Table 45. Ear plugin - additional task dependencies
Task name
Depends on
assemble
ear
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Project layout
§
Project layout
Table 46. Ear plugin - project layout
Directory
Meaning
src/main/application
Ear resources, such as a META-INF directory
§
Dependency management
The Ear plugin adds two dependency configurations: deploy and earlib. All dependencies in the deploy
configuration are placed in the root of the EAR archive, and are not transitive. All dependencies in the earlib
configuration are placed in the 'lib' directory in the EAR archive and are transitive.
§
Convention properties
Table 47. Ear plugin - directory properties
Property name
Type
Default value
appDirName
String
src/main/application
libDirName
String
lib
Description
The name of the application source
directory, relative to the project directory.
The name of the lib directory inside the
generated EAR.
Metadata
A deployment descriptor
to
generate
a
deployment
descriptor file, e.g. application.xml. If
this file already exists in the appDirName/META-INF
with sensible DeploymentDescriptor
defaults
deploymentDescriptor org.gradle.plugins.ear.descriptor.
then the existing file contents will be used
named application.xml
and the explicit configuration in the ear.deploymentDescri
will be ignored.
These properties are provided by a EarPluginConvention convention object.
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Ear
§
Ear
The default behavior of the Ear task is to copy the content of src/main/application to the root of the
archive. If your application directory doesn’t contain a META-INF/application.xml deployment
descriptor then one will be generated for you.
The Ear class in the API documentation has additional useful information.
§
Customizing
Here is an example with the most important customization options:
Page 501 of 717
Example 431. Customization of ear plugin
build.gradle
apply plugin: 'ear'
apply plugin: 'java'
repositories { mavenCentral() }
dependencies {
// The following dependencies will be the ear modules and
// will be placed in the ear root
deploy project(path: ':war', configuration: 'archives')
// The following dependencies will become ear libs and will
// be placed in a dir configured via the libDirName property
earlib group: 'log4j', name: 'log4j', version: '1.2.15', ext: 'jar'
}
ear {
appDirName 'src/main/app' // use application metadata found in this folder
// put dependent libraries into APP-INF/lib inside the generated EAR
libDirName 'APP-INF/lib'
deploymentDescriptor { // custom entries for application.xml:
//
fileName = "application.xml" // same as the default value
//
version = "6" // same as the default value
applicationName = "customear"
initializeInOrder = true
displayName = "Custom Ear" // defaults to project.name
// defaults to project.description if not set
description = "My customized EAR for the Gradle documentation"
//
libraryDirectory = "APP-INF/lib" // not needed, above libDirName setting does thi
//
module("my.jar", "java") // won't deploy as my.jar isn't deploy dependency
//
webModule("my.war", "/") // won't deploy as my.war isn't deploy dependency
securityRole "admin"
securityRole "superadmin"
withXml { provider -> // add a custom node to the XML
provider.asNode().appendNode("data-source", "my/data/source")
}
}
}
You can also use customization options that the Ear task provides, such as from and metaInf.
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Using custom descriptor file
§
Using custom descriptor file
You may already have appropriate settings in a application.xml file and want to use that instead of
configuring the ear.deploymentDescriptor section of the build script. To accommodate that goal, place
the META-INF/application.xml in the right place inside your source folders (see the appDirName
property). The file contents will be used and the explicit configuration in the ear.deploymentDescriptor
will be ignored.
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The Jetty Plugin
Note: This plugin has been removed as of Gradle 4.0. We recommend using the Gretty plugin
instead.
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The Application Plugin
The Application plugin facilitates creating an executable JVM application. It makes it easy to start the
application locally during development, and to package the application as a TAR and/or ZIP including
operating system specific start scripts.
Applying the Application plugin also implicitly applies the Java plugin. The main source set is effectively the
“application”.
Applying the Application plugin also implicitly applies the Distribution plugin. A main distribution is created
that packages up the application, including code dependencies and generated start scripts.
§
Usage
To use the application plugin, include the following in your build script:
Example 432. Using the application plugin
build.gradle
apply plugin: 'application'
The only mandatory configuration for the plugin is the specification of the main class (i.e. entry point) of the
application.
Example 433. Configure the application main class
build.gradle
mainClassName = "org.gradle.sample.Main"
You can run the application by executing the run task (type: JavaExec). This will compile the main source
set, and launch a new JVM with its classes (along with all runtime dependencies) as the classpath and using
the specified main class. You can launch the application in debug mode with gradle run --debug-jvm
(see JavaExec.setDebug(boolean)).
If your application requires a specific set of JVM settings or system properties, you can configure the applicationDefau
property. These JVM arguments are applied to the run task and also considered in the generated start
scripts of your distribution.
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Example 434. Configure default JVM settings
build.gradle
applicationDefaultJvmArgs = ["-Dgreeting.language=en"]
If your application’s start scripts should be in a different directory than bin, you can configure the executableDir
property.
Example 435. Configure custom directory for start scripts
build.gradle
executableDir = "custom_bin_dir"
§
The distribution
A distribution of the application can be created, by way of the Distribution plugin (which is automatically
applied). A main distribution is created with the following content:
Table 48. Distribution content
Location
Content
(root dir)
src/dist
lib
All runtime dependencies and main source set class files.
bin
Start scripts (generated by createStartScripts task).
Static files to be added to the distribution can be simply added to src/dist. More advanced customization
can be done by configuring the CopySpec exposed by the main distribution.
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Example 436. Include output from other tasks in the application distribution
build.gradle
task createDocs {
def docs = file("$buildDir/docs")
outputs.dir docs
doLast {
docs.mkdirs()
new File(docs, "readme.txt").write("Read me!")
}
}
distributions {
main {
contents {
from(createDocs) {
into "docs"
}
}
}
}
By specifying that the distribution should include the task’s output files (see the section called “Task inputs
and outputs”), Gradle knows that the task that produces the files must be invoked before the distribution can
be assembled and will take care of this for you.
Example 437. Automatically creating files for distribution
Output of gradle distZip
> gradle distZip
:createDocs
:compileJava
:processResources NO-SOURCE
:classes
:jar
:startScripts
:distZip
BUILD SUCCESSFUL in 0s
5 actionable tasks: 5 executed
You can run gradle installDist to create an image of the application in build/install/projectName
. You can run gradle distZip to create a ZIP containing the distribution, gradle distTar to create an
application TAR or gradle assemble to build both.
Customizing start script generation
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§
Customizing start script generation
The application plugin can generate Unix (suitable for Linux, macOS etc.) and Windows start scripts out of
the box. The start scripts launch a JVM with the specified settings defined as part of the original build and
runtime environment (e.g. JAVA_OPTS env var). The default script templates are based on the same scripts
used to launch Gradle itself, that ship as part of a Gradle distribution.
The start scripts are completely customizable. Please refer to the documentation of CreateStartScripts
for more details and customization examples.
§
Tasks
The Application plugin adds the following tasks to the project.
Table 49. Application plugin - tasks
Task name
Depends on
Type
Description
run
classes
JavaExec
Starts the application.
startScripts jar
CreateStartScripts Creates OS specific scripts to run the project as a JVM application.
Sync
installDist jar, startScripts
distZip
jar, startScripts
Zip
distTar
jar, startScripts
Tar
Installs the application into a specified directory.
Creates a full distribution ZIP archive including runtime libraries
and OS specific scripts.
Creates a full distribution TAR archive including runtime libraries
and OS specific scripts.
§
Convention properties
The application plugin adds some properties to the project, which you can use to configure its behaviour.
See the Project class in the API documentation.
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The Java Library Distribution Plugin
Note: The Java library distribution plugin is currently incubating. Please be aware that the DSL and
other configuration may change in later Gradle versions.
The Java library distribution plugin adds support for building a distribution ZIP for a Java library. The
distribution contains the JAR file for the library and its dependencies.
§
Usage
To use the Java library distribution plugin, include the following in your build script:
Example 438. Using the Java library distribution plugin
build.gradle
apply plugin: 'java-library-distribution'
To define the name for the distribution you have to set the baseName property as shown below:
Example 439. Configure the distribution name
build.gradle
distributions {
main{
baseName = 'my-name'
}
}
The plugin builds a distribution for your library. The distribution will package up the runtime dependencies of
the library. All files stored in src/main/dist will be added to the root of the archive distribution. You can
run “gradle distZip” to create a ZIP file containing the distribution.
§
Tasks
The Java library distribution plugin adds the following tasks to the project.
Page 509 of 717
Table 50. Java library distribution plugin - tasks
Task name
Depends on
Type
Description
distZip
jar
Zip
Creates a full distribution ZIP archive including runtime libraries.
§
Including other resources in the distribution
All of the files from the src/dist directory are copied. To include any static files in the distribution, simply
arrange them in the src/dist directory, or add them to the content of the distribution.
Example 440. Include files in the distribution
build.gradle
distributions {
main {
baseName = 'my-name'
contents {
from { 'src/dist' }
}
}
}
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Groovy Quickstart
To build a Groovy project, you use the Groovy plugin . This plugin extends the Java plugin to add Groovy
compilation capabilities to your project. Your project can contain Groovy source code, Java source code, or
a mix of the two. In every other respect, a Groovy project is identical to a Java project, which we have
already seen in Java Quickstart.
§
A basic Groovy project
Let’s look at an example. To use the Groovy plugin, add the following to your build file:
Example 441. Groovy plugin
build.gradle
apply plugin: 'groovy'
Note: The code for this example can be found at samples/groovy/quickstart in the ‘-all’
distribution of Gradle.
This will also apply the Java plugin to the project, if it has not already been applied. The Groovy plugin
extends the compile task to look for source files in directory src/main/groovy, and the compileTest
task to look for test source files in directory src/test/groovy. The compile tasks use joint compilation for
these directories, which means they can contain a mixture of Java and Groovy source files.
To use the Groovy compilation tasks, you must also declare the Groovy version to use and where to find the
Groovy libraries. You do this by adding a dependency to the groovy configuration. The compile
configuration inherits this dependency, so the Groovy libraries will be included in classpath when compiling
Groovy and Java source. For our sample, we will use Groovy 2.2.0 from the public Maven repository:
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Example 442. Dependency on Groovy
build.gradle
repositories {
mavenCentral()
}
dependencies {
compile 'org.codehaus.groovy:groovy-all:2.4.10'
}
Here is our complete build file:
Example 443. Groovy example - complete build file
build.gradle
apply plugin: 'eclipse'
apply plugin: 'groovy'
repositories {
mavenCentral()
}
dependencies {
compile 'org.codehaus.groovy:groovy-all:2.4.10'
testCompile 'junit:junit:4.12'
}
Running gradle build will compile, test and JAR your project.
§
Summary
This chapter describes a very simple Groovy project. Usually, a real project will require more than this.
Because a Groovy project is a Java project, whatever you can do with a Java project, you can also do with a
Groovy project.
You can find out more about the Groovy plugin in The Groovy Plugin, and you can find more sample Groovy
projects in the samples/groovy directory in the Gradle distribution.
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The Groovy Plugin
The Groovy plugin extends the Java plugin to add support for Groovy projects. It can deal with Groovy code,
mixed Groovy and Java code, and even pure Java code (although we don’t necessarily recommend to use it
for the latter). The plugin supports joint compilation , which allows you to freely mix and match Groovy and
Java code, with dependencies in both directions. For example, a Groovy class can extend a Java class that
in turn extends a Groovy class. This makes it possible to use the best language for the job, and to rewrite
any class in the other language if needed.
§
Usage
To use the Groovy plugin, include the following in your build script:
Example 444. Using the Groovy plugin
build.gradle
apply plugin: 'groovy'
§
Tasks
The Groovy plugin adds the following tasks to the project.
Table 51. Groovy plugin - tasks
Task name
Depends on
Type
Description
compileGroovy
compileJava
GroovyCompile Compiles production Groovy source files.
compileTestGroovy
compileTestJava
GroovyCompile Compiles test Groovy source files.
GroovyCompile Compiles the given source set’s Groovy source files.
compile SourceSet Groovy
compile SourceSet Java
groovydoc
-
Groovydoc
Generates API documentation for the production Groovy
source files.
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The Groovy plugin adds the following dependencies to tasks added by the Java plugin.
Table 52. Groovy plugin - additional task dependencies
Task name
Depends on
classes
compileGroovy
testClasses
compileTestGroovy
sourceSet Classes
compile SourceSet Groovy
Figure 17. Groovy plugin - tasks
§
Project layout
The Groovy plugin assumes the project layout shown in Table 53. All the Groovy source directories can
contain Groovy and Java code. The Java source directories may only contain Java source code. [22] None of
these directories need to exist or have anything in them; the Groovy plugin will simply compile whatever it
finds.
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Table 53. Groovy plugin - project layout
Directory
Meaning
src/main/java
Production Java source
src/main/resources
Production resources
src/main/groovy
Production Groovy sources. May also contain Java sources for joint compilation.
src/test/java
Test Java source
src/test/resources
Test resources
src/test/groovy
Test Groovy sources. May also contain Java sources for joint compilation.
src/ sourceSet /java
Java source for the given source set
src/ sourceSet /resources Resources for the given source set
src/ sourceSet /groovy
Groovy sources for the given source set. May also contain Java sources for joint compilation.
§
Changing the project layout
Just like the Java plugin, the Groovy plugin allows you to configure custom locations for Groovy production
and test sources.
Example 445. Custom Groovy source layout
build.gradle
sourceSets {
main {
groovy {
srcDirs = ['src/groovy']
}
}
test {
groovy {
srcDirs = ['test/groovy']
}
}
}
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Dependency management
§
Dependency management
Because Gradle’s build language is based on Groovy, and parts of Gradle are implemented in Groovy,
Gradle already ships with a Groovy library. Nevertheless, Groovy projects need to explicitly declare a Groovy
dependency. This dependency will then be used on compile and runtime class paths. It will also be used to
get hold of the Groovy compiler and Groovydoc tool, respectively.
If Groovy is used for production code, the Groovy dependency should be added to the compile
configuration:
Example 446. Configuration of Groovy dependency
build.gradle
repositories {
mavenCentral()
}
dependencies {
compile 'org.codehaus.groovy:groovy-all:2.4.10'
}
If Groovy is only used for test code, the Groovy dependency should be added to the testCompile
configuration:
Example 447. Configuration of Groovy test dependency
build.gradle
dependencies {
testCompile 'org.codehaus.groovy:groovy-all:2.4.10'
}
To use the Groovy library that ships with Gradle, declare a localGroovy() dependency. Note that different
Gradle versions ship with different Groovy versions; as such, using localGroovy() is less safe then
declaring a regular Groovy dependency.
Example 448. Configuration of bundled Groovy dependency
build.gradle
dependencies {
compile localGroovy()
}
The Groovy library doesn’t necessarily have to come from a remote repository. It could also come from a
local lib directory, perhaps checked in to source control:
Page 516 of 717
Example 449. Configuration of Groovy file dependency
build.gradle
repositories {
flatDir { dirs 'lib' }
}
dependencies {
compile module('org.codehaus.groovy:groovy:2.4.10') {
dependency('org.ow2.asm:asm-all:5.0.3')
dependency('antlr:antlr:2.7.7')
dependency('commons-cli:commons-cli:1.2')
module('org.apache.ant:ant:1.9.4') {
dependencies('org.apache.ant:ant-junit:1.9.4@jar',
'org.apache.ant:ant-launcher:1.9.4')
}
}
}
§
Automatic configuration of groovyClasspath
The GroovyCompile and Groovydoc tasks consume Groovy code in two ways: on their classpath, and
on their groovyClasspath. The former is used to locate classes referenced by the source code, and will
typically contain the Groovy library along with other libraries. The latter is used to load and execute the
Groovy compiler and Groovydoc tool, respectively, and should only contain the Groovy library and its
dependencies.
Unless a task’s groovyClasspath is configured explicitly, the Groovy (base) plugin will try to infer it from
the task’s classpath. This is done as follows:
If a groovy-all(-indy) Jar is found on classpath, that jar will be added to groovyClasspath.
If a groovy(-indy) jar is found on classpath, and the project has at least one repository declared, a
corresponding groovy(-indy) repository dependency will be added to groovyClasspath.
Otherwise, execution of the task will fail with a message saying that groovyClasspath could not be
inferred.
Note that the “-indy” variation of each jar refers to the version with invokedynamic support.
§
Convention properties
The Groovy plugin does not add any convention properties to the project.
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Source set properties
§
Source set properties
The Groovy plugin adds the following convention properties to each source set in the project. You can use
these properties in your build script as though they were properties of the source set object.
Table 54. Groovy plugin - source set properties
Property name
Type
Default value Description
The Groovy source files of this source set. Contains all .groovy
SourceDirectorySet
groovy
Set<File>.
groovy.srcDirs
Not null
(read-only)
and .java files found in the Groovy source directories,
and excludes all other types of files.
Can
set
using
anything described in the section
called “Specifying a set of input
The source directories containing the Groovy source
[ projectDirfiles
/src/
of name
this source
/groovy]
set. May also contain Java source
files for joint compilation.
files”.
All Groovy source files of this source set. Contains only
allGroovy
FileTree (read-only)
Not null
the .groovy files found in the Groovy source
directories.
These properties are provided by a convention object of type GroovySourceSet.
The Groovy plugin also modifies some source set properties:
Table 55. Groovy plugin - source set properties
Property name
Change
allJava
Adds all .java files found in the Groovy source directories.
allSource
Adds all source files found in the Groovy source directories.
§
GroovyCompile
The Groovy plugin adds a GroovyCompile task for each source set in the project. The task type extends
the JavaCompile task (see the section called “CompileJava”). The GroovyCompile task supports most
configuration options of the official Groovy compiler.
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Table 56. Groovy plugin - GroovyCompile properties
Task Property
Type
Default Value
classpath
FileCollection
sourceSet .compileClasspath
source
FileTree. Can set using anything described in the
section called “Specifying a set of input files”.
destinationDir File.
groovyClasspath FileCollection
sourceSet .groovy
sourceSet .groovy.outputDir
groovy configuration if non-empty; Groovy
library found on classpath otherwise
§
Compiling and testing for Java 6 or Java 7
The Groovy compiler will always be executed with the same version of Java that was used to start Gradle.
You should set sourceCompatibility and targetCompatibility to 1.6 or 1.7. If you also have
Java sources, you can follow the same steps as for the Java plugin to ensure the correct Java compiler is
used.
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Example 450. Configure Java 6 build for Groovy
gradle.properties
# in $HOME/.gradle/gradle.properties
java6Home=/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home
build.gradle
sourceCompatibility = 1.6
targetCompatibility = 1.6
assert hasProperty('java6Home') : "Set the property 'java6Home' in your your gradle.proper
def javaExecutablesPath = new File(java6Home, 'bin')
def javaExecutables = [:].withDefault { execName ->
def executable = new File(javaExecutablesPath, execName)
assert executable.exists() : "There is no ${execName} executable in ${javaExecutablesP
executable
}
tasks.withType(AbstractCompile) {
options.with {
fork = true
forkOptions.javaHome = file(java6Home)
}
}
tasks.withType(Javadoc) {
executable = javaExecutables.javadoc
}
tasks.withType(Test) {
executable = javaExecutables.java
}
tasks.withType(JavaExec) {
executable = javaExecutables.java
}
[22] We are using the same conventions as introduced by Russel Winder’s Gant tool ( https://gant.github.io/).
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The Scala Plugin
The Scala plugin extends the Java plugin to add support for Scala projects. It can deal with Scala code,
mixed Scala and Java code, and even pure Java code (although we don’t necessarily recommend to use it
for the latter). The plugin supports joint compilation , which allows you to freely mix and match Scala and
Java code, with dependencies in both directions. For example, a Scala class can extend a Java class that in
turn extends a Scala class. This makes it possible to use the best language for the job, and to rewrite any
class in the other language if needed.
§
Usage
To use the Scala plugin, include the following in your build script:
Example 451. Using the Scala plugin
build.gradle
apply plugin: 'scala'
§
Tasks
The Scala plugin adds the following tasks to the project.
Table 57. Scala plugin - tasks
Task name
Depends on
Type
Description
compileScala
compileJava
ScalaCompile Compiles production Scala source files.
compileTestScala
compileTestJava
ScalaCompile Compiles test Scala source files.
ScalaCompile Compiles the given source set’s Scala source files.
compile SourceSet Scala
compile SourceSet Java
scaladoc
-
ScalaDoc
Generates API documentation for the production Scala
source files.
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The Scala plugin adds the following dependencies to tasks added by the Java plugin.
Table 58. Scala plugin - additional task dependencies
Task name
Depends on
classes
compileScala
testClasses
compileTestScala
sourceSet Classes
compile SourceSet Scala
Figure 18. Scala plugin - tasks
§
Project layout
The Scala plugin assumes the project layout shown below. All the Scala source directories can contain
Scala and Java code. The Java source directories may only contain Java source code. None of these
directories need to exist or have anything in them; the Scala plugin will simply compile whatever it finds.
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Table 59. Scala plugin - project layout
Directory
Meaning
src/main/java
Production Java source
src/main/resources
Production resources
src/main/scala
Production Scala sources. May also contain Java sources for joint compilation.
src/test/java
Test Java source
src/test/resources
Test resources
src/test/scala
Test Scala sources. May also contain Java sources for joint compilation.
src/ sourceSet /java
Java source for the given source set
src/ sourceSet /resources Resources for the given source set
src/ sourceSet /scala
Scala sources for the given source set. May also contain Java sources for joint compilation.
§
Changing the project layout
Just like the Java plugin, the Scala plugin allows you to configure custom locations for Scala production and
test sources.
Example 452. Custom Scala source layout
build.gradle
sourceSets {
main {
scala {
srcDirs = ['src/scala']
}
}
test {
scala {
srcDirs = ['test/scala']
}
}
}
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Dependency management
§
Dependency management
Scala projects need to declare a scala-library dependency. This dependency will then be used on
compile and runtime class paths. It will also be used to get hold of the Scala compiler and Scaladoc tool,
respectively.[23]
If Scala is used for production code, the scala-library dependency should be added to the compile
configuration:
Example 453. Declaring a Scala dependency for production code
build.gradle
repositories {
mavenCentral()
}
dependencies {
compile 'org.scala-lang:scala-library:2.11.8'
testCompile 'org.scalatest:scalatest_2.11:3.0.0'
testCompile 'junit:junit:4.12'
}
If Scala is only used for test code, the scala-library dependency should be added to the testCompile
configuration:
Example 454. Declaring a Scala dependency for test code
build.gradle
dependencies {
testCompile "org.scala-lang:scala-library:2.11.1"
}
§
Automatic configuration of scalaClasspath
The ScalaCompile and ScalaDoc tasks consume Scala code in two ways: on their classpath, and on
their scalaClasspath. The former is used to locate classes referenced by the source code, and will
typically contain scala-library along with other libraries. The latter is used to load and execute the Scala
compiler and Scaladoc tool, respectively, and should only contain the scala-compiler library and its
dependencies.
Unless a task’s scalaClasspath is configured explicitly, the Scala (base) plugin will try to infer it from the
task’s classpath. This is done as follows:
If a scala-library jar is found on classpath, and the project has at least one repository declared, a
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corresponding scala-compiler repository dependency will be added to scalaClasspath.
Otherwise, execution of the task will fail with a message saying that scalaClasspath could not be
inferred.
§
Configuring the Zinc compiler
The Scala plugin uses a configuration named zinc to resolve the Zinc compiler and its dependencies.
Gradle will provide a default version of Zinc, but if you need to use a particular Zinc version, you can add an
explicit dependency like “com.typesafe.zinc:zinc:0.3.6” to the zinc configuration. Gradle supports
version 0.3.0 of Zinc and above; however, due to a regression in the Zinc compiler, versions 0.3.2 through
0.3.5.2 cannot be used.
Example 455. Declaring a version of the Zinc compiler to use
build.gradle
dependencies {
zinc 'com.typesafe.zinc:zinc:0.3.9'
}
Note: It is important to take care when declaring your scala-library dependency. The Zinc
compiler itself needs a compatible version of scala-library that may be different from the
version required by your application. Gradle takes care of adding a compatible version of scala-library
for you, but over-broad dependency resolution rules could force an incompatible version to be used
instead.
For example, using configurations.all to force a particular version of scala-library would
also override the version used by the Zinc compiler:
Example 456. Forcing a scala-library dependency for all configurations
Note: build.gradle
configurations.all {
resolutionStrategy.force "org.scala-lang:scala-library:2.11.7"
}
The best way to avoid this problem is to be more selective when configuring the scala-library
dependency (such as not using a configuration.all rule or using a conditional to prevent the
rule from being applied to the zinc configuration). Sometimes this rule may come from a plugin or
other code that you do not have control over. In such a case, you can force a correct version of the
library on the zinc configuration only:
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Example 457. Forcing a scala-library dependency for the zinc configuration
Note: build.gradle
configurations.zinc {
resolutionStrategy.force "org.scala-lang:scala-library:2.10.5"
}
You can diagnose problems with the version of the Zinc compiler selected by running
dependencyInsight for the zinc configuration.
§
Convention properties
The Scala plugin does not add any convention properties to the project.
§
Source set properties
The Scala plugin adds the following convention properties to each source set in the project. You can use
these properties in your build script as though they were properties of the source set object.
Table 60. Scala plugin - source set properties
Property name
Type
Default value Description
The Scala source files of this source set. Contains all .scala
scala
SourceDirectorySet (read-only) Not null
and .java files found in the Scala source directories,
and excludes all other types of files.
Set<File>. Can set using anything
The source directories containing the Scala source files
scala.srcDirs described in the section called [ projectDirof/src/
this source
name /scala]
set. May also contain Java source files for
joint compilation.
“Specifying a set of input files”.
allScala
FileTree (read-only)
Not null
All Scala source files of this source set. Contains only
the .scala files found in the Scala source directories.
These convention properties are provided by a convention object of type ScalaSourceSet.
The Scala plugin also modifies some source set properties:
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Table 61. Scala plugin - source set properties
Property name
Change
allJava
Adds all .java files found in the Scala source directories.
allSource
Adds all source files found in the Scala source directories.
§
Compiling in external process
Scala compilation takes place in an external process.
Memory settings for the external process default to the defaults of the JVM. To adjust memory settings,
configure the scalaCompileOptions.forkOptions property as needed:
Example 458. Adjusting memory settings
build.gradle
tasks.withType(ScalaCompile) {
configure(scalaCompileOptions.forkOptions) {
memoryMaximumSize = '1g'
jvmArgs = ['-XX:MaxPermSize=512m']
}
}
§
Incremental compilation
By compiling only classes whose source code has changed since the previous compilation, and classes
affected by these changes, incremental compilation can significantly reduce Scala compilation time. It is
particularly effective when frequently compiling small code increments, as is often done at development time.
The Scala plugin defaults to incremental compilation by integrating with Zinc, a standalone version of sbt's
incremental Scala compiler. If you want to disable the incremental compilation, set force = true in your
build file:
Example 459. Forcing all code to be compiled
build.gradle
tasks.withType(ScalaCompile) {
scalaCompileOptions.with {
force = true
}
}
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Note: This will only cause all classes to be recompiled if at least one input source file has changed. If there
are no changes to the source files, the compileScala task will still be considered UP-TO-DATE as usual.
The Zinc-based Scala Compiler supports joint compilation of Java and Scala code. By default, all Java and
Scala code under src/main/scala will participate in joint compilation. Even Java code will be compiled
incrementally.
Incremental compilation requires dependency analysis of the source code. The results of this analysis are
stored in the file designated by scalaCompileOptions.incrementalOptions.analysisFile (which
has a sensible default). In a multi-project build, analysis files are passed on to downstream ScalaCompile
tasks to enable incremental compilation across project boundaries. For ScalaCompile tasks added by the
Scala plugin, no configuration is necessary to make this work. For other ScalaCompile tasks that you
might add, the property scalaCompileOptions.incrementalOptions.publishedCode needs to be
configured to point to the classes folder or Jar archive by which the code is passed on to compile class paths
of downstream ScalaCompile tasks. Note that if publishedCode is not set correctly, downstream tasks
may not recompile code affected by upstream changes, leading to incorrect compilation results.
Note that Zinc’s Nailgun based daemon mode is not supported. Instead, we plan to enhance Gradle’s own
compiler daemon to stay alive across Gradle invocations, reusing the same Scala compiler. This is expected
to yield another significant speedup for Scala compilation.
§
Compiling and testing for Java 6 or Java 7
The Scala compiler ignores Gradle’s targetCompatibility and sourceCompatibility settings. In
Scala 2.11, the Scala compiler always compiles to Java 6 compatible bytecode. In Scala 2.12, the Scala
compiler always compiles to Java 8 compatible bytecode. If you also have Java sources, you can follow the
same steps as for the Java plugin to ensure the correct Java compiler is used.
Page 528 of 717
Example 460. Configure Java 6 build for Scala
gradle.properties
# in $HOME/.gradle/gradle.properties
java6Home=/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home
build.gradle
sourceCompatibility = 1.6
assert hasProperty('java6Home') : "Set the property 'java6Home' in your your gradle.proper
def javaExecutablesPath = new File(java6Home, 'bin')
def javaExecutables = [:].withDefault { execName ->
def executable = new File(javaExecutablesPath, execName)
assert executable.exists() : "There is no ${execName} executable in ${javaExecutablesP
executable
}
tasks.withType(AbstractCompile) {
options.with {
fork = true
forkOptions.javaHome = file(java6Home)
}
}
tasks.withType(Test) {
executable = javaExecutables.java
}
tasks.withType(JavaExec) {
executable = javaExecutables.java
}
tasks.withType(Javadoc) {
executable = javaExecutables.javadoc
}
§
Eclipse Integration
When the Eclipse plugin encounters a Scala project, it adds additional configuration to make the project work
with Scala IDE out of the box. Specifically, the plugin adds a Scala nature and dependency container.
Page 529 of 717
IntelliJ IDEA Integration
§
IntelliJ IDEA Integration
When the IDEA plugin encounters a Scala project, it adds additional configuration to make the project work
with IDEA out of the box. Specifically, the plugin adds a Scala SDK (IntelliJ IDEA 14+) and a Scala compiler
library that matches the Scala version on the project’s class path. The Scala plugin is backwards compatible
with earlier versions of IntelliJ IDEA and it is possible to add a Scala facet instead of the default Scala SDK
by configuring targetVersion on IdeaModel.
Example 461. Explicitly specify a target IntelliJ IDEA version
build.gradle
idea {
targetVersion = "13"
}
[23] See the section called “Automatic configuration of scalaClasspath”.
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The ANTLR Plugin
The ANTLR plugin extends the Java plugin to add support for generating parsers using ANTLR.
Note: The ANTLR plugin supports ANTLR version 2, 3 and 4.
§
Usage
To use the ANTLR plugin, include the following in your build script:
Example 462. Using the ANTLR plugin
build.gradle
apply plugin: 'antlr'
§
Tasks
The ANTLR plugin adds a number of tasks to your project, as shown below.
Table 62. ANTLR plugin - tasks
Task name
Depends
on
Type
Description
generateGrammarSource
-
AntlrTask Generates the source files for all production ANTLR grammars.
generateTestGrammarSource
-
AntlrTask Generates the source files for all test ANTLR grammars.
generate SourceSet GrammarSource
-
AntlrTask
Generates the source files for all ANTLR grammars for the given
source set.
The ANTLR plugin adds the following dependencies to tasks added by the Java plugin.
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Table 63. ANTLR plugin - additional task dependencies
Task name
Depends on
compileJava
generateGrammarSource
compileTestJava
generateTestGrammarSource
compile SourceSet Java
generate SourceSet GrammarSource
§
Project layout
Table 64. ANTLR plugin - project layout
Directory
Meaning
Production ANTLR grammar files. If the ANTLR grammar is organized in packages, the structure in the antlr
src/main/antlr folder should reflect the package structure. This ensures that the generated sources end up in the correct
target subfolder.
src/test/antlr Test ANTLR grammar files.
src/ sourceSet /antlr
ANTLR grammar files for the given source set.
§
Dependency management
The ANTLR plugin adds an antlr dependency configuration which provides the ANTLR implementation to
use. The following example shows how to use ANTLR version 3.
Example 463. Declare ANTLR version
build.gradle
repositories {
mavenCentral()
}
dependencies {
antlr "org.antlr:antlr:3.5.2" // use ANTLR version 3
// antlr "org.antlr:antlr4:4.5" // use ANTLR version 4
}
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If no dependency is declared, antlr:antlr:2.7.7 will be used as the default. To use a different ANTLR
version add the appropriate dependency to the antlr dependency configuration as above.
§
Convention properties
The ANTLR plugin does not add any convention properties.
§
Source set properties
The ANTLR plugin adds the following properties to each source set in the project.
Table 65. ANTLR plugin - source set properties
Property name
Type
Default value Description
The ANTLR grammar files of this source set. Contains
antlr
SourceDirectorySet (read-only) Not null
all .g or .g4 files found in the ANTLR source
directories, and excludes all other types of files.
Set<File>. Can set using anything
The source directories containing the ANTLR grammar
antlr.srcDirs described in the section called [ projectDir /src/ name /antlr]
files of this source set.
“Specifying a set of input files”.
§
Controlling the ANTLR generator process
The ANTLR tool is executed in a forked process. This allows fine grained control over memory settings for
the ANTLR process. To set the heap size of an ANTLR process, the maxHeapSize property of AntlrTask
can be used. To pass additional command-line arguments, append to the arguments property of
AntlrTask.
Example 464. setting custom max heap size and extra arguments for ANTLR
build.gradle
generateGrammarSource {
maxHeapSize = "64m"
arguments += ["-visitor", "-long-messages"]
}
Page 533 of 717
The Checkstyle Plugin
The Checkstyle plugin performs quality checks on your project’s Java source files using Checkstyle and
generates reports from these checks.
§
Usage
To use the Checkstyle plugin, include the following in your build script:
Example 465. Using the Checkstyle plugin
build.gradle
apply plugin: 'checkstyle'
The plugin adds a number of tasks to the project that perform the quality checks. You can execute the
checks by running gradle check.
Note that Checkstyle will run with the same Java version used to run Gradle.
§
Tasks
The Checkstyle plugin adds the following tasks to the project:
Table 66. Checkstyle plugin - tasks
Task name
Depends on
Type
checkstyleMain
classes
Checkstyle Runs Checkstyle against the production Java source files.
checkstyleTest
testClasses
Checkstyle Runs Checkstyle against the test Java source files.
checkstyleSourceSet sourceSet Classes Checkstyle
Description
Runs Checkstyle against the given source set’s Java source
files.
The Checkstyle plugin adds the following dependencies to tasks defined by the Java plugin.
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Table 67. Checkstyle plugin - additional task dependencies
Task name
Depends on
check
All Checkstyle tasks, including checkstyleMain and checkstyleTest.
§
Project layout
By default, the Checkstyle plugin expects the following project layout, but this can be changed:
Table 68. Checkstyle plugin - project layout
File
Meaning
config/checkstyle
Other Checkstyle configuration files (e.g., suppressions.xml)
config/checkstyle/checkstyle.xml
Checkstyle configuration file
§
Dependency management
The Checkstyle plugin adds the following dependency configurations:
Table 69. Checkstyle plugin - dependency configurations
Name
Meaning
checkstyle
The Checkstyle libraries to use
§
Configuration
See the CheckstyleExtension class in the API documentation.
§
Built-in variables
The Checkstyle plugin defines a config_loc property that can be used in Checkstyle configuration files to
define paths to other configuration files like suppressions.xml.
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Example 466. Using the config_loc property
config/checkstyle/checkstyle.xml
<module name="SuppressionFilter">
<property name="file" value="${config_loc}/suppressions.xml"/>
</module>
§
Customizing the HTML report
The HTML report generated by the Checkstyle task can be customized using a XSLT stylesheet, for
example to highlight specific errors or change its appearance:
Example 467. Customizing the HTML report
build.gradle
tasks.withType(Checkstyle) {
reports {
xml.enabled false
html.enabled true
html.stylesheet resources.text.fromFile('config/xsl/checkstyle-custom.xsl')
}
}
View a sample Checkstyle stylesheet.
Page 536 of 717
The CodeNarc Plugin
The CodeNarc plugin performs quality checks on your project’s Groovy source files using CodeNarc and
generates reports from these checks.
§
Usage
To use the CodeNarc plugin, include the following in your build script:
Example 468. Using the CodeNarc plugin
build.gradle
apply plugin: 'codenarc'
The plugin adds a number of tasks to the project that perform the quality checks when used with the Groovy
Plugin. You can execute the checks by running gradle check.
§
Tasks
The CodeNarc plugin adds the following tasks to the project:
Table 70. CodeNarc plugin - tasks
Task name
Depends on Type
Description
codenarcMain
-
CodeNarc Runs CodeNarc against the production Groovy source files.
codenarcTest
-
CodeNarc Runs CodeNarc against the test Groovy source files.
codenarcSourceSet
-
CodeNarc Runs CodeNarc against the given source set’s Groovy source files.
The CodeNarc plugin adds the following dependencies to tasks defined by the Groovy plugin.
Page 537 of 717
Table 71. CodeNarc plugin - additional task dependencies
Task name
Depends on
check
All CodeNarc tasks, including codenarcMain and codenarcTest.
§
Project layout
The CodeNarc plugin expects the following project layout:
Table 72. CodeNarc plugin - project layout
File
Meaning
config/codenarc/codenarc.xml
CodeNarc configuration file
§
Dependency management
The CodeNarc plugin adds the following dependency configurations:
Table 73. CodeNarc plugin - dependency configurations
Name
Meaning
codenarc
The CodeNarc libraries to use
§
Configuration
See the CodeNarcExtension class in the API documentation.
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The FindBugs Plugin
The FindBugs plugin performs quality checks on your project’s Java source files using FindBugs and
generates reports from these checks.
§
Usage
To use the FindBugs plugin, include the following in your build script:
Example 469. Using the FindBugs plugin
build.gradle
apply plugin: 'findbugs'
The plugin adds a number of tasks to the project that perform the quality checks. You can execute the
checks by running gradle check.
Note that Findbugs will run with the same Java version used to run Gradle.
§
Tasks
The FindBugs plugin adds the following tasks to the project:
Table 74. FindBugs plugin - tasks
Task name
Depends on
Type
Description
findbugsMain
classes
FindBugs Runs FindBugs against the production Java source files.
findbugsTest
testClasses
FindBugs Runs FindBugs against the test Java source files.
findbugsSourceSet sourceSet Classes FindBugs Runs FindBugs against the given source set’s Java source files.
The FindBugs plugin adds the following dependencies to tasks defined by the Java plugin.
Page 539 of 717
Table 75. FindBugs plugin - additional task dependencies
Task name
Depends on
check
All FindBugs tasks, including findbugsMain and findbugsTest.
§
Dependency management
The FindBugs plugin adds the following dependency configurations:
Table 76. FindBugs plugin - dependency configurations
Name
Meaning
findbugs
The FindBugs libraries to use
§
Configuration
See the FindBugsExtension class in the API documentation.
§
Customizing the HTML report
The HTML report generated by the FindBugs task can be customized using a XSLT stylesheet, for example
to highlight specific errors or change its appearance:
Example 470. Customizing the HTML report
build.gradle
tasks.withType(FindBugs) {
reports {
xml.enabled false
html.enabled true
html.stylesheet resources.text.fromFile('config/xsl/findbugs-custom.xsl')
}
}
View a sample FindBugs stylesheet.
Page 540 of 717
The JDepend Plugin
The JDepend plugin performs quality checks on your project’s source files using JDepend and generates
reports from these checks.
§
Usage
To use the JDepend plugin, include the following in your build script:
Example 471. Using the JDepend plugin
build.gradle
apply plugin: 'jdepend'
The plugin adds a number of tasks to the project that perform the quality checks. You can execute the
checks by running gradle check.
Note that JDepend will run with the same Java version used to run Gradle.
§
Tasks
The JDepend plugin adds the following tasks to the project:
Table 77. JDepend plugin - tasks
Task name
Depends on
Type
Description
jdependMain
classes
JDepend Runs JDepend against the production Java source files.
jdependTest
testClasses
JDepend Runs JDepend against the test Java source files.
jdependSourceSet
sourceSet Classes JDepend Runs JDepend against the given source set’s Java source files.
The JDepend plugin adds the following dependencies to tasks defined by the Java plugin.
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Table 78. JDepend plugin - additional task dependencies
Task name
Depends on
check
All JDepend tasks, including jdependMain and jdependTest.
§
Dependency management
The JDepend plugin adds the following dependency configurations:
Table 79. JDepend plugin - dependency configurations
Name
Meaning
jdepend
The JDepend libraries to use
§
Configuration
See the JDependExtension class in the API documentation.
Page 542 of 717
The PMD Plugin
The PMD plugin performs quality checks on your project’s Java source files using PMD and generates
reports from these checks.
§
Usage
To use the PMD plugin, include the following in your build script:
Example 472. Using the PMD plugin
build.gradle
apply plugin: 'pmd'
The plugin adds a number of tasks to the project that perform the quality checks. You can execute the
checks by running gradle check.
Note that PMD will run with the same Java version used to run Gradle.
§
Tasks
The PMD plugin adds the following tasks to the project:
Table 80. PMD plugin - tasks
Task name
Depends on
Type
Description
pmdMain
-
Pmd
Runs PMD against the production Java source files.
pmdTest
-
Pmd
Runs PMD against the test Java source files.
pmdSourceSet
-
Pmd
Runs PMD against the given source set’s Java source files.
The PMD plugin adds the following dependencies to tasks defined by the Java plugin.
Page 543 of 717
Table 81. PMD plugin - additional task dependencies
Task name
Depends on
check
All PMD tasks, including pmdMain and pmdTest.
§
Dependency management
The PMD plugin adds the following dependency configurations:
Table 82. PMD plugin - dependency configurations
Name
Meaning
pmd
The PMD libraries to use
§
Configuration
See the PmdExtension class in the API documentation.
Page 544 of 717
The JaCoCo Plugin
Note: The JaCoCo plugin is currently incubating. Please be aware that the DSL and other
configuration may change in later Gradle versions.
The JaCoCo plugin provides code coverage metrics for Java code via integration with JaCoCo.
§
Getting Started
To get started, apply the JaCoCo plugin to the project you want to calculate code coverage for.
Example 473. Applying the JaCoCo plugin
build.gradle
apply plugin: "jacoco"
If the Java plugin is also applied to your project, a new task named jacocoTestReport is created that
depends on the test task. The report is available at $buildDir /reports/jacoco/test. By default, a
HTML report is generated.
§
Configuring the JaCoCo Plugin
The JaCoCo plugin adds a project extension named jacoco of type JacocoPluginExtension, which
allows configuring defaults for JaCoCo usage in your build.
Example 474. Configuring JaCoCo plugin settings
build.gradle
jacoco {
toolVersion = "0.7.9"
reportsDir = file("$buildDir/customJacocoReportDir")
}
Page 545 of 717
Table 83. Gradle defaults for JaCoCo properties
Property
Gradle default
reportsDir
$buildDir /reports/jacoco
§
JaCoCo Report configuration
The JacocoReport task can be used to generate code coverage reports in different formats. It implements
the standard Gradle type Reporting and exposes a report container of type JacocoReportsContainer.
Example 475. Configuring test task
build.gradle
jacocoTestReport {
reports {
xml.enabled false
csv.enabled false
html.destination file("${buildDir}/jacocoHtml")
}
}
§
Enforcing code coverage metrics
Note: This feature requires the use of JaCoCo version 0.6.3 or higher.
The JacocoCoverageVerification task can be used to verify if code coverage metrics are met based
on
configured
rules.
Its
API
exposes
the
method
JacocoCoverageVerification.violationRules(org.gradle.api.Action) which is used as
Page 546 of 717
main entry point for configuring rules. Invoking any of those methods returns an instance of
JacocoViolationRulesContainer providing extensive configuration options. The build fails if any of the
configured rules are not met. JaCoCo only reports the first violated rule.
Code coverage requirements can be specified for a project as a whole, for individual files, and for particular
JaCoCo-specific types of coverage, e.g., lines covered or branches covered. The following example
describes the syntax.
Example 476. Configuring violation rules
build.gradle
jacocoTestCoverageVerification {
violationRules {
rule {
limit {
minimum = 0.5
}
}
rule {
enabled = false
element = 'CLASS'
includes = ['org.gradle.*']
limit {
counter = 'LINE'
value = 'TOTALCOUNT'
maximum = 0.3
}
}
}
}
Note: The code for this example can be found at samples/testing/jacoco/quickstart in
the ‘-all’ distribution of Gradle.
The JacocoCoverageVerification task is not a task dependency of the check task provided by the
Java plugin. There is a good reason for it. The task is currently not incremental as it doesn’t declare any
outputs. Any violation of the declared rules would automatically result in a failed build when executing the check
task. This behavior might not be desirable for all users. Future versions of Gradle might change the
behavior.
§
JaCoCo specific task configuration
The JaCoCo plugin adds a JacocoTaskExtension extension to all tasks of type Test. This extension
allows the configuration of the JaCoCo specific properties of the test task.
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Example 477. Configuring test task
build.gradle
test {
jacoco {
append = false
destinationFile = file("$buildDir/jacoco/jacocoTest.exec")
classDumpDir = file("$buildDir/jacoco/classpathdumps")
}
}
Table 84. Default values of the JaCoCo Task extension
Property
Gradle default
enabled
true
destPath
$buildDir /jacoco
append
true
includes
[]
excludes
[]
excludeClassLoaders
[]
includeNoLocationClasses
false
sessionId
auto-generated
dumpOnExit
true
output
Output.FILE
address
-
port
-
classDumpPath
-
jmx
false
Page 548 of 717
While all tasks of type Test are automatically enhanced to provide coverage information when the java
plugin has been applied, any task that implements JavaForkOptions can be enhanced by the JaCoCo
plugin. That is, any task that forks Java processes can be used to generate coverage information.
For example you can configure your build to generate code coverage using the application plugin.
Example 478. Using application plugin to generate code coverage data
build.gradle
apply plugin: "application"
apply plugin: "jacoco"
mainClassName = "org.gradle.MyMain"
jacoco {
applyTo run
}
task applicationCodeCoverageReport(type:JacocoReport){
executionData run
sourceSets sourceSets.main
}
Note: The code for this example can be found at samples/testing/jacoco/application in
the ‘-all’ distribution of Gradle.
Example 479. Coverage reports generated by applicationCodeCoverageReport
Build layout
application/
build/
jacoco/
run.exec
reports/jacoco/applicationCodeCoverageReport/html/
index.html
§
Tasks
For projects that also apply the Java Plugin, The JaCoCo plugin automatically adds the following tasks:
Page 549 of 717
Table 85. JaCoCo plugin - tasks
Depends
Task name
on
jacocoTestReport
-
jacocoTestCoverageVerification -
Type
JacocoReport
JacocoCoverageVerification
Description
Generates code coverage report for the
test task.
Verifies code coverage metrics based
on specified rules for the test task.
§
Dependency management
The JaCoCo plugin adds the following dependency configurations:
Table 86. JaCoCo plugin - dependency configurations
Name
jacocoAnt
Meaning
The JaCoCo Ant library used for running the JacocoReport, JacocoMerge and JacocoCoverageVerification
tasks.
jacocoAgent The JaCoCo agent library used for instrumenting the code under test.
Page 550 of 717
The OSGi Plugin
The OSGi plugin provides a factory method to create an OsgiManifest object. OsgiManifest extends
Manifest. To learn more about generic manifest handling, see the section called “Manifest”. If the Java
plugins is applied, the OSGi plugin replaces the manifest object of the default jar with an OsgiManifest
object. The replaced manifest is merged into the new one.
Note: The OSGi plugin makes heavy use of the BND tool. A separate plugin implementation is
maintained by the BND authors that has more advanced features.
§
Usage
To use the OSGi plugin, include the following in your build script:
Example 480. Using the OSGi plugin
build.gradle
apply plugin: 'osgi'
§
Implicitly applied plugins
Applies the Java base plugin.
§
Tasks
The OSGi plugin adds the following tasks to the project:
Table 87. OSGi plugin - tasks
Task name
Depends on Type Description
osgiClasses classes
Sync Copies all classes from the main source set to a single directory that is processed by BND.
Page 551 of 717
Convention object
§
Convention object
The OSGi plugin adds the following convention object: OsgiPluginConvention
§
Convention properties
The OSGi plugin does not add any convention properties to the project.
§
Convention methods
The OSGi plugin adds the following methods. For more details, see the API documentation of the convention
object.
Table 88. OSGi methods
Method
Return Type
Description
osgiManifest()
OsgiManifest
Returns an OsgiManifest object.
osgiManifest(Closure cl)
OsgiManifest
Returns an OsgiManifest object configured by the closure.
The classes in the classes dir are analyzed regarding their package dependencies and the packages they
expose. Based on this the Import-Package and the Export-Package values of the OSGi Manifest are
calculated. If the classpath contains jars with an OSGi bundle, the bundle information is used to specify
version information for the Import-Package value. Beside the explicit properties of the OsgiManifest
object you can add instructions.
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Example 481. Configuration of OSGi MANIFEST.MF file
build.gradle
jar {
manifest { // the manifest of the default jar is of type OsgiManifest
name = 'overwrittenSpecialOsgiName'
instruction 'Private-Package',
'org.mycomp.package1',
'org.mycomp.package2'
instruction 'Bundle-Vendor', 'MyCompany'
instruction 'Bundle-Description', 'Platform2: Metrics 2 Measures Framework'
instruction 'Bundle-DocURL', 'http://www.mycompany.com'
}
}
task fooJar(type: Jar) {
manifest = osgiManifest {
instruction 'Bundle-Vendor', 'MyCompany'
}
}
The first argument of the instruction call is the key of the property. The other arguments form the value. To
learn more about the available instructions have a look at the BND tool.
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The Eclipse Plugins
The Eclipse plugins generate files that are used by the Eclipse IDE, thus making it possible to import the
project into Eclipse (File - Import… - Existing Projects into Workspace).
The eclipse-wtp is automatically applied whenever the eclipse plugin is applied to a War or Ear project.
For utility projects (i.e. Java projects used by other web projects), you need to apply the eclipse-wtp
plugin explicitly.
What exactly the eclipse plugin generates depends on which other plugins are used:
Table 89. Eclipse plugin behavior
Plugin
Description
None
Generates minimal .project file.
Java
Adds Java configuration to .project. Generates .classpath and JDT settings file.
Groovy
Adds Groovy configuration to .project file.
Scala
Adds Scala support to .project and .classpath files.
War
Adds web application support to .project file.
Ear
Adds ear application support to .project file.
The eclipse-wtp plugin generates all WTP settings files and enhances the .project file. If a Java or
War is applied, .classpath will be extended to get a proper packaging structure for this utility library or
web application project.
Both Eclipse plugins are open to customization and provide a standardized set of hooks for adding and
removing content from the generated files.
Page 554 of 717
Usage
§
Usage
To use either the Eclipse or the Eclipse WTP plugin, include one of the lines in your build script:
Example 482. Using the Eclipse plugin
build.gradle
apply plugin: 'eclipse'
Example 483. Using the Eclipse WTP plugin
build.gradle
apply plugin: 'eclipse-wtp'
Note: Internally, the eclipse-wtp plugin also applies the eclipse plugin so you don’t need to apply both.
Both Eclipse plugins add a number of tasks to your projects. The main tasks that you will use are the eclipse
and cleanEclipse tasks.
§
Tasks
The Eclipse plugins add the tasks shown below to a project.
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Table 90. Eclipse plugin - tasks
Task name
Depends on
Type
Description
Task
Generates all Eclipse configuration files
Delete
Removes all Eclipse configuration files
-
Delete
Removes the .project file.
cleanEclipseClasspath -
Delete
Removes the .classpath file.
cleanEclipseJdt
-
Delete
eclipseProject
-
GenerateEclipseProject
eclipseClasspath
-
GenerateEclipseClasspath Generates the .classpath file.
eclipseJdt
-
GenerateEclipseJdt
all
eclipse
Eclipse
configuration
file generation
tasks
all
cleanEclipse
Eclipse
configuration
file clean tasks
cleanEclipseProject
Removes the .settings/org.eclipse.jdt.core.prefs
file.
Generates the .project file.
Generates the .settings/org.eclipse.jdt.core.prefs
file.
Table 91. Eclipse WTP plugin - additional tasks
Task name
Depends
on
Type
cleanEclipseWtpComponent -
Delete
cleanEclipseWtpFacet
-
Delete
eclipseWtpComponent
-
GenerateEclipseWtpComponent
eclipseWtpFacet
-
GenerateEclipseWtpFacet
Description
Removes the .settings/org.eclipse.wst.common.co
file.
Removes the .settings/org.eclipse.wst.common.proje
file.
Generates the .settings/org.eclipse.wst.common.co
file.
Generates the .settings/org.eclipse.wst.common.proj
file.
Page 556 of 717
Configuration
§
Configuration
Table 92. Configuration of the Eclipse plugins
Model
Reference name
EclipseModel
eclipse
EclipseProject
eclipse.project
Allows configuring project information
EclipseClasspath
eclipse.classpath
Allows configuring classpath information.
EclipseJdt
eclipse.jdt
Allows configuring jdt information (source/target Java compatibility).
EclipseWtpComponent eclipse.wtp.component
EclipseWtpFacet
eclipse.wtp.facet
Description
Top level element that enables configuration of the Eclipse plugin in a
DSL-friendly fashion.
Allows configuring wtp component information only if eclipse-wtp
plugin was applied.
Allows configuring wtp facet information only if eclipse-wtp plugin
was applied.
§
Customizing the generated files
The Eclipse plugins allow you to customize the generated metadata files. The plugins provide a DSL for
configuring model objects that model the Eclipse view of the project. These model objects are then merged
with the existing Eclipse XML metadata to ultimately generate new metadata. The model objects provide
lower level hooks for working with domain objects representing the file content before and after merging with
the model configuration. They also provide a very low level hook for working directly with the raw XML for
adjustment before it is persisted, for fine tuning and configuration that the Eclipse and Eclipse WTP plugins
do not model.
§
Merging
Sections of existing Eclipse files that are also the target of generated content will be amended or overwritten,
depending on the particular section. The remaining sections will be left as-is.
Disabling merging with a complete rewrite
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§
Disabling merging with a complete rewrite
To completely rewrite existing Eclipse files, execute a clean task together with its corresponding generation
task, like “gradle cleanEclipse eclipse” (in that order). If you want to make this the default behavior,
add “tasks.eclipse.dependsOn(cleanEclipse)” to your build script. This makes it unnecessary to
execute the clean task explicitly.
This strategy can also be used for individual files that the plugins would generate. For instance, this can be
done for the “.classpath” file with “gradle cleanEclipseClasspath eclipseClasspath”.
§
Hooking into the generation lifecycle
The Eclipse plugins provide objects modeling the sections of the Eclipse files that are generated by Gradle.
The generation lifecycle is as follows:
1. The file is read; or a default version provided by Gradle is used if it does not exist
2. The beforeMerged hook is executed with a domain object representing the existing file
3. The existing content is merged with the configuration inferred from the Gradle build or defined explicitly in
the eclipse DSL
4. The whenMerged hook is executed with a domain object representing contents of the file to be persisted
5. The withXml hook is executed with a raw representation of the XML that will be persisted
6. The final XML is persisted
The following table lists the domain object used for each of the Eclipse model types:
Table 93. Advanced configuration hooks
Model
beforeMerged { arg -> } whenMerged { arg -> } withXml { arg -> } withProperties { arg ->
argument type
argument type
argument type
argument type
EclipseProject
Project
Project
XmlProvider
-
EclipseClasspath
Classpath
Classpath
XmlProvider
-
EclipseJdt
Jdt
Jdt
-
java.util.Properties
EclipseWtpComponent WtpComponent
WtpComponent
XmlProvider
-
EclipseWtpFacet
WtpFacet
XmlProvider
-
WtpFacet
Partial overwrite of existing content
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§
Partial overwrite of existing content
A complete overwrite causes all existing content to be discarded, thereby losing any changes made directly
in the IDE. Alternatively, the beforeMerged hook makes it possible to overwrite just certain parts of the
existing content. The following example removes all existing dependencies from the Classpath domain
object:
Example 484. Partial Overwrite for Classpath
build.gradle
eclipse.classpath.file {
beforeMerged { classpath ->
classpath.entries.removeAll { entry -> entry.kind == 'lib' || entry.kind == 'var'
}
}
The resulting .classpath file will only contain Gradle-generated dependency entries, but not any other
dependency entries that may have been present in the original file. (In the case of dependency entries, this
is also the default behavior.) Other sections of the .classpath file will be either left as-is or merged. The
same could be done for the natures in the .project file:
Example 485. Partial Overwrite for Project
build.gradle
eclipse.project.file.beforeMerged { project ->
project.natures.clear()
}
§
Modifying the fully populated domain objects
The whenMerged hook allows to manipulate the fully populated domain objects. Often this is the preferred
way to customize Eclipse files. Here is how you would export all the dependencies of an Eclipse project:
Example 486. Export Classpath Entries
build.gradle
eclipse.classpath.file {
whenMerged { classpath ->
classpath.entries.findAll { entry -> entry.kind == 'lib' }*.exported = false
}
}
Modifying the XML representation
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§
Modifying the XML representation
The withXml hook allows to manipulate the in-memory XML representation just before the file gets written
to disk. Although Groovy’s XML support makes up for a lot, this approach is less convenient than
manipulating the domain objects. In return, you get total control over the generated file, including sections
not modeled by the domain objects.
Example 487. Customizing the XML
build.gradle
apply plugin: 'eclipse-wtp'
eclipse.wtp.facet.file.withXml { provider ->
provider.asNode().fixed.find { it.@facet == 'jst.java' }.@facet = 'jst2.java'
}
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The IDEA Plugin
The IDEA plugin generates files that are used by IntelliJ IDEA, thus making it possible to open the project
from IDEA (File - Open Project). Both external dependencies (including associated source and Javadoc
files) and project dependencies are considered.
What exactly the IDEA plugin generates depends on which other plugins are used:
Table 94. IDEA plugin behavior
Plugin Description
None Generates an IDEA module file. Also generates an IDEA project and workspace file if the project is the root project.
Java
Adds Java configuration to the module and project files.
One focus of the IDEA plugin is to be open to customization. The plugin provides a standardized set of
hooks for adding and removing content from the generated files.
§
Usage
To use the IDEA plugin, include this in your build script:
Example 488. Using the IDEA plugin
build.gradle
apply plugin: 'idea'
The IDEA plugin adds a number of tasks to your project. The main tasks that you will use are the idea and cleanIdea
tasks.
§
Tasks
The IDEA plugin adds the tasks shown below to a project. Notice that the clean task does not depend on
the cleanIdeaWorkspace task. This is because the workspace typically contains a lot of user specific
temporary data and it is not desirable to manipulate it outside IDEA.
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Table 95. IDEA plugin - Tasks
Task name
Depends on
Type
idea
ideaProject, ideaModule, ideaWorkspace
-
Generates all IDEA configuration files
cleanIdea
cleanIdeaProject, cleanIdeaModule
Delete
Removes all IDEA configuration files
cleanIdeaProject
-
Delete
Removes the IDEA project file
cleanIdeaModule
-
Delete
Removes the IDEA module file
cleanIdeaWorkspace -
Delete
Removes the IDEA workspace file
ideaProject
-
GenerateIdeaProject
ideaModule
-
GenerateIdeaModule
ideaWorkspace
-
GenerateIdeaWorkspace
Description
Generates the .ipr file. This task is
only added to the root project.
Generates the .iml file
Generates the .iws file. This task is
only added to the root project.
§
Configuration
Table 96. Configuration of the idea plugin
Model
Reference name
Description
IdeaModel
idea
Top level element that enables configuration of the idea plugin in a DSL-friendly fashion
IdeaProject
idea.project
Allows configuring project information
IdeaModule
idea.module
Allows configuring module information
IdeaWorkspace idea.workspace Allows configuring the workspace XML
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Customizing the generated files
§
Customizing the generated files
The IDEA plugin provides hooks and behavior for customizing the generated content. The workspace file
can effectively only be manipulated via the withXml hook because its corresponding domain object is
essentially empty.
The tasks recognize existing IDEA files, and merge them with the generated content.
§
Merging
Sections of existing IDEA files that are also the target of generated content will be amended or overwritten,
depending on the particular section. The remaining sections will be left as-is.
§
Disabling merging with a complete overwrite
To completely rewrite existing IDEA files, execute a clean task together with its corresponding generation
task, like “gradle cleanIdea idea” (in that order). If you want to make this the default behavior, add “ tasks.idea.d
” to your build script. This makes it unnecessary to execute the clean task explicitly.
This strategy can also be used for individual files that the plugin would generate. For instance, this can be
done for the “.iml” file with “gradle cleanIdeaModule ideaModule”.
§
Hooking into the generation lifecycle
The plugin provides objects modeling the sections of the metadata files that are generated by Gradle. The
generation lifecycle is as follows:
1. The file is read; or a default version provided by Gradle is used if it does not exist
2. The beforeMerged hook is executed with a domain object representing the existing file
3. The existing content is merged with the configuration inferred from the Gradle build or defined explicitly in
the eclipse DSL
4. The whenMerged hook is executed with a domain object representing contents of the file to be persisted
5. The withXml hook is executed with a raw representation of the XML that will be persisted
6. The final XML is persisted The following table lists the domain object used for each of the model types:
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Table 97. Idea plugin hooks
Model
beforeMerged { arg
} argument whenMerged { arg
} argument withXml { arg
type
type
type
IdeaProject
Project
Project
XmlProvider
IdeaModule
Module
Module
XmlProvider
Workspace
XmlProvider
IdeaWorkspace Workspace
} argument
§
Partial rewrite of existing content
A complete rewrite causes all existing content to be discarded, thereby losing any changes made directly in
the IDE. The beforeMerged hook makes it possible to overwrite just certain parts of the existing content.
The following example removes all existing dependencies from the Module domain object:
Example 489. Partial Rewrite for Module
build.gradle
idea.module.iml {
beforeMerged { module ->
module.dependencies.clear()
}
}
The resulting module file will only contain Gradle-generated dependency entries, but not any other
dependency entries that may have been present in the original file. (In the case of dependency entries, this
is also the default behavior.) Other sections of the module file will be either left as-is or merged. The same
could be done for the module paths in the project file:
Example 490. Partial Rewrite for Project
build.gradle
idea.project.ipr {
beforeMerged { project ->
project.modulePaths.clear()
}
}
§
Modifying the fully populated domain objects
The whenMerged hook allows you to manipulate the fully populated domain objects. Often this is the
preferred way to customize IDEA files. Here is how you would export all the dependencies of an IDEA
module:
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Example 491. Export Dependencies
build.gradle
idea.module.iml {
whenMerged { module ->
module.dependencies*.exported = true
}
}
§
Modifying the XML representation
The withXml hook allows you to manipulate the in-memory XML representation just before the file gets
written to disk. Although Groovy’s XML support makes up for a lot, this approach is less convenient than
manipulating the domain objects. In return, you get total control over the generated file, including sections
not modeled by the domain objects.
Example 492. Customizing the XML
build.gradle
idea.project.ipr {
withXml { provider ->
provider.node.component
.find { it.@name == 'VcsDirectoryMappings' }
.mapping.@vcs = 'Git'
}
}
§
Further things to consider
The paths of dependencies in the generated IDEA files are absolute. If you manually define a path variable
pointing to the Gradle dependency cache, IDEA will automatically replace the absolute dependency paths
with this path variable. you can configure this path variable via the “ idea.pathVariables” property, so
that it can do a proper merge without creating duplicates.
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The Software model
Rule based model configuration
Note: Support for rule based configuration is currently incubating. Please be aware that the DSL,
APIs and other configuration may change in later Gradle versions.
Rule based model configuration enables configuration logic to itself have dependencies on other elements
of configuration, and to make use of the resolved states of those other elements of configuration while
performing its own configuration.
§
Background
Rule based model configuration facilitates easier domain modelling: communicating intent (i.e. the what)
over mechanics (i.e. the how). Domain modelling is a core tenet of Gradle and provides Gradle with several
advantages over prior generation build tools such as Apache Ant that focus on the execution model. It allows
humans to understand builds at a level that is meaningful to them.
As well as helping humans, a strong domain model also helps the dutiful machines. Plugins can more
effectively collaborate around a strong domain model (e.g. plugins can say something about Java
applications, such as providing conventions). Very importantly, by having a model of the what instead of the
how Gradle can make intelligent choices on just how to do the how.
Gradle’s support for building native software and Play Framework applications already uses this
configuration model. Gradle also includes some initial support for building Java libraries using this
configuration model.
§
Motivations for change
Domain modelling in Gradle isn’t new. The Java plugin’s SourceSet concept is an example of domain
modelling, as is the modelling of NativeBinary in the native plugin suite.
A distinguishing characteristic of Gradle compared to other build tools that also embrace modelling is that
Gradle’s model is open and collaborative. Gradle is fundamentally a tool for modelling software construction
and then realizing the model, via tasks such as compilation etc. Different domain plugins (e.g. Java, C++,
Android) provide models that other plugins can collaborate with and build upon.
While Gradle has long employed sophisticated techniques when it comes to realizing the model (i.e. what we
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know as building code), the next generation of Gradle builds will employ some of the same techniques to
creation of the model itself. By defining build tasks as effectively a graph of dependent functions with explicit
inputs and outputs, Gradle is able to order, cache, parallelize and apply other optimizations to the work.
Using a “graph of tasks” for the production of software is a long established idea, and necessary given the
complexity of software production. The task graph effectively defines the rules of execution that Gradle must
follow. The term “Rule based model configuration” refers to applying the same concepts to building the
model that builds the task graph.
Another key motivation is performance and scale. Aspects of the current approach that Gradle takes to
modelling the build reduce parallelism opportunities and limit scalability. The software model is being
designed with the requirements of modern software delivery in mind, where immediate responsiveness is
critical for projects large and small.
§
Basic Concepts
§
The “model space”
The term “model space” is used to refer to the formal model, which can be read and modified by rules.
A counterpart to the model space is the “project space”, which should be familiar to readers. The “project
space” is a graph of objects (e.g project.repositories, project.tasks etc.) having a Project as
its root. A build script is effectively adding and configuring objects of this graph. For the most part, the
“project space” is opaque to Gradle. It is an arbitrary graph of objects that Gradle only partially understands.
Each project also has its own model space, which is distinct from the project space. A key characteristic of
the “model space” is that Gradle knows much more about it (which is knowledge that can be put to good
use). The objects in the model space are “managed”, to a greater extent than objects in the project space.
The origin, structure, state, collaborators and relationships of objects in the model space are first class
constructs. This is effectively the characteristic that functionally distinguishes the model space from the
project space: the objects of the model space are defined in ways that Gradle can understand them
intimately, as opposed to an object that is the result of running relatively opaque code. A “rule” is effectively
a building block of this definition.
The model space will eventually replace the project space, becoming the only “space”.
§
Rules
The model space is defined by “rules”. A rule is just a function (in the abstract sense) that either produces a
model element, or acts upon a model element. Every rule has a single subject and zero or more inputs. Only
the subject can be changed by a rule, while the inputs are effectively immutable.
Gradle guarantees that all inputs are fully “realized“ before the rule executes. The process of “realizing” a
model element is effectively executing all the rules for which it is the subject, transitioning it to its final state.
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There is a strong analogy here to Gradle’s task graph and task execution model. Just as tasks depend on
each other and Gradle ensures that dependencies are satisfied before executing a task, rules effectively
depend on each other (i.e. a rule depends on all rules whose subject is one of the inputs) and Gradle
ensures that all dependencies are satisfied before executing the rule.
Model elements are very often defined in terms of other model elements. For example, a compile task’s
configuration can be defined in terms of the configuration of the source set that it is compiling. In this
scenario, the compile task would be the subject of a rule and the source set an input. Such a rule could
configure the task subject based on the source set input without concern for how it was configured, who it
was configured by or when the configuration was specified.
There are several ways to declare rules, and in several forms.
§
Rule sources
One way to define rules is via a RuleSource subclass. If an object extends RuleSource and contains any
methods annotated by '@Mutate', then each such method defines a rule. For each such method, the first
argument is the subject, and zero or more subsequent arguments may follow and are inputs of the rule.
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Example 493. applying a rule source plugin
build.gradle
@Managed
interface Person {
void setFirstName(String name)
String getFirstName()
void setLastName(String name)
String getLastName()
}
class PersonRules extends RuleSource {
@Model void person(Person p) {}
//Create a rule that modifies a Person and takes no other inputs
@Mutate void setFirstName(Person p) {
p.firstName = "John"
}
//Create a rule that modifies a ModelMap<Task> and takes as input a Person
@Mutate void createHelloTask(ModelMap<Task> tasks, Person p) {
tasks.create("hello") {
doLast {
println "Hello $p.firstName $p.lastName!"
}
}
}
}
apply plugin: PersonRules
Output of gradle hello
> gradle hello
:hello
Hello John Smith!
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
Each of the different methods of the rule source are discrete, independent rules. Their order, or the fact that
they belong to the same class, do not affect their behavior.
Example 494. a model creation rule
build.gradle
@Model void person(Person p) {}
This rule declares that there is a model element at path "person" (defined by the method name), of type Person
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. This is the form of the Model type rule for Managed types. Here, the person object is the rule subject. The
method could potentially have a body, that mutated the person instance. It could also potentially have more
parameters, which would be the rule inputs.
Example 495. a model mutation rule
build.gradle
//Create a rule that modifies a Person and takes no other inputs
@Mutate void setFirstName(Person p) {
p.firstName = "John"
}
This Mutate rule mutates the person object. The first parameter to the method is the subject. Here, a
by-type reference is used as no Path annotation is present on the parameter. It could also potentially have
more parameters, that would be the rule inputs.
Example 496. creating a task
build.gradle
//Create a rule that modifies a ModelMap<Task> and takes as input a Person
@Mutate void createHelloTask(ModelMap<Task> tasks, Person p) {
tasks.create("hello") {
doLast {
println "Hello $p.firstName $p.lastName!"
}
}
}
This Mutate rule effectively adds a task, by mutating the tasks collection. The subject here is the "tasks"
node, which is available as a ModelMap of Task. The only input is our person element. As the person is
being used as an input here, it will have been realised before executing this rule. That is, the task container
effectively depends on the person element. If there are other configuration rules for the person element,
potentially specified in a build script or other plugin, they will also be guaranteed to have been executed.
As Person is a Managed type in this example, any attempt to modify the person parameter in this method
would result in an exception being thrown. Managed objects enforce immutability at the appropriate point in
their lifecycle.
Rule source plugins can be packaged and distributed in the same manner as other types of plugins (see
Writing Custom Plugins). They also may be applied in the same manner (to project objects) as Plugin
implementations (i.e. via Project.apply(java.util.Map)).
Please see the documentation for RuleSource for more information on constraints on how rule sources
must be implemented and for more types of rules.
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Advanced Concepts
§
Advanced Concepts
§
Model paths
A model path identifies the location of an element relative to the root of its model space. A common
representation is a period-delimited set of names. For example, the model path "tasks" is the path to the
element that is the task container. Assuming a task whose name is hello, the path "tasks.hello" is the
path to this task.
§
Managed model elements
Currently, any kind of Java object can be part of the model space. However, there is a difference between
“managed” and “unmanaged” objects.
A “managed” object is transparent and enforces immutability once realized. Being transparent means that its
structure is understood by the rule infrastructure and as such each of its properties are also individual
elements in the model space.
An “unmanaged” object is opaque to the model space and does not enforce immutability. Over time, more
mechanisms will be available for defining managed model elements culminating in all model elements being
managed in some way.
Managed models can be defined by attaching the @Managed annotation to an interface:
Example 497. a managed type
build.gradle
@Managed
interface Person {
void setFirstName(String name)
String getFirstName()
void setLastName(String name)
String getLastName()
}
By defining a getter/setter pair, you are effectively declaring a managed property. A managed property is a
property for which Gradle will enforce semantics such as immutability when a node of the model is not the
subject of a rule. Therefore, this example declares properties named firstName and lastName on the
managed type Person . These properties will only be writable when the view is mutable, that is to say when
the Person is the subject of a Rule (see below the explanation for rules).
Managed properties can be of any scalar type. In addition, properties can also be of any type which is itself
managed:
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Property type
Nullable
String
Yes
Example
Example 498. a String property
build.gradle
void setFirstName(String name)
String getFirstName()
Example 499. a File property
File
Yes
build.gradle
void setHomeDirectory(File homeDir)
File getHomeDirectory()
Example 500. a Long property
Integer, Boolean, Byte, Short, Float
Yes
, Long, Double
build.gradle
void setId(Long id)
Long getId()
Example 501. a boolean property
int, boolean, byte, short, floatNo
, long, double
build.gradle
void setEmployed(boolean isEmployed)
boolean isEmployed()
Example 502. an int property
build.gradle
void setAge(int age)
int getAge()
Example 503. a managed property
Another managed type.
Only if read/write
build.gradle
void setMother(Person mother)
Person getMother()
Example 504. an enumeration type property
An enumeration type.
Yes
build.gradle
void setMaritalStatus(MaritalStatus status)
MaritalStatus getMaritalStatus()
Example 505. a managed set
A ManagedSet. A managed set Only if read/write
supports the creation of new named
model elements, but not their
build.gradle
ModelSet<Person> getChildren()
removal.
A Set or List of scalar types. All Only if read/write
classic operations on collections are
supported: add, remove, clear…
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Example 506. a scalar collection
build.gradle
void setUserGroups(List<String> groups)
List<String> getUserGroups()
If the type of a property is itself a managed type, it is possible to declare only a getter, in which case you are
declaring a read-only property. A read-only property will be instantiated by Gradle, and cannot be replaced
with another object of the same type (for example calling a setter). However, the properties of that property
can potentially be changed, if, and only if, the property is the subject of a rule. If it’s not the case, the
property is immutable, like any classic read/write managed property, and properties of the property cannot
be changed at all.
Managed types can be defined out of interfaces or abstract classes and are usually defined in plugins, which
are written either in Java or Groovy. Please see the Managed annotation for more information on creating
managed model objects.
§
Model element types
There are particular types (language types) supported by the model space and can be generalised as
follows:
Table 98. Type definitions
Type
Definition
A scalar type is one of the following:
a primitive type (e.g. int) or its boxed type (e.g Integer)
a BigInteger or BigDecimal
Scalar
a String
a File
an enumeration type
Scalar Collection
A java.util.List or java.util.Set containing one of the scalar types
Managed type
Any class which is a valid managed model (i.e.annotated with @ Managed)
Managed collection
A ModelMap or ModelSet
There are various contexts in which these types can be used:
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Table 99. Model type support
Context
Supported types
Any managed type
Creating
elements
top
level
model
FunctionalSourceSet (when the LanguageBasePlugin plugin has been applied)
Subtypes of LanguageSourceSet which have been registered via ComponentType
The properties (attributes) of a managed model elements may be one or more of the following:
A managed type
A type which is annotated with @Unmanaged
Properties of managed model A Scalar Collection
elements
A Managed collection containing managed types
A
Managed
collection
containing
FunctionalSourceSet 's
(when
the
LanguageBasePlugin plugin has been applied)
Subtypes of LanguageSourceSet which have been registered via ComponentType
§
Language source sets
FunctionalSourceSets and subtypes of LanguageSourceSet (which have been registered via
ComponentType) can be added to the model space via rules or via the model DSL.
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Example 507. strongly modelling sources sets
build.gradle
apply plugin: 'java-lang'
//Creating LanguageSourceSets via rules
class LanguageSourceSetRules extends RuleSource {
@Model
void mySourceSet(JavaSourceSet javaSource) {
javaSource.source.srcDir("src/main/my")
}
}
apply plugin: LanguageSourceSetRules
//Creating LanguageSourceSets via the model DSL
model {
another(JavaSourceSet) {
source {
srcDir "src/main/another"
}
}
}
//Using FunctionalSourceSets
@Managed
interface SourceBundle {
FunctionalSourceSet getFreeSources()
FunctionalSourceSet getPaidSources()
}
model {
sourceBundle(SourceBundle) {
freeSources.create("main", JavaSourceSet)
freeSources.create("resources", JvmResourceSet)
paidSources.create("main", JavaSourceSet)
paidSources.create("resources", JvmResourceSet)
}
}
Note: The code for this example can be found at samples/modelRules/language-support in
the ‘-all’ distribution of Gradle.
Output of gradle help
> gradle help
:help
References, binding and scopes
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§
References, binding and scopes
As previously mentioned, a rule has a subject and zero or more inputs. The rule’s subject and inputs are
declared as “references” and are “bound” to model elements before execution by Gradle. Each rule must
effectively forward declare the subject and inputs as references. Precisely how this is done depends on the
form of the rule. For example, the rules provided by a RuleSource declare references as method
parameters.
A reference is either “by-path” or “by-type”.
A “by-type” reference identifies a particular model element by its type. For example, a reference to the
TaskContainer effectively identifies the "tasks" element in the project model space. The model space is
not exhaustively searched for candidates for by-type binding; rather, a rule is given a scope (discussed later)
that determines the search space for a by-type binding.
A “by-path” reference identifies a particular model element by its path in model space. By-path references
are always relative to the rule scope; there is currently no way to path “out” of the scope. All by-path
references also have an associated type, but this does not influence what the reference binds to. The
element identified by the path must however by type compatible with the reference, or a fatal “binding failure”
will occur.
§
Binding scope
Rules are bound within a “scope”, which determines how references bind. Most rules are bound at the
project scope (i.e. the root of the model graph for the project). However, rules can be scoped to a node
within the graph. The ModelMap.named(java.lang.String, java.lang.Class) method is an
example of a mechanism for applying scoped rules. Rules declared in the build script using the model {}
block, or via a RuleSource applied as a plugin use the root of the model space as the scope. This can be
considered the default scope.
By-path references are always relative to the rule scope. When the scope is the root, this effectively allows
binding to any element in the graph. When it is not, then only the children of the scope can be referenced
using "by-path" notation.
When binding by-type references, the following elements are considered:
The scope element itself.
The immediate children of the scope element.
The immediate children of the model space (i.e. project space) root.
For the common case, where the rule is effectively scoped to the root, only the immediate children of the root
need to be considered.
Binding to all elements in a scope matching type
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§
Binding to all elements in a scope matching type
Mutating or validating all elements of a given type in some scope is a common use-case. To accommodate
this, rules can be applied via the @Each annotation.
In the example below, a @Defaults rule is applied to each FileItem in the model setting a default file size
of "1024". Another rule applies a RuleSource to every DirectoryItem that makes sure all file sizes are
positive and divisible by "16".
Example 508. a DSL example applying a rule to every element in a scope
build.gradle
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@Managed interface Item extends Named {}
@Managed interface FileItem extends Item {
void setSize(int size)
int getSize()
}
@Managed interface DirectoryItem extends Item {
ModelMap<Item> getChildren()
}
class PluginRules extends RuleSource {
@Defaults void setDefaultFileSize(@Each FileItem file) {
file.size = 1024
}
@Rules void applyValidateRules(ValidateRules rules, @Each DirectoryItem directory)
}
apply plugin: PluginRules
abstract class ValidateRules extends RuleSource {
@Validate
void validateSizeIsPositive(ModelMap<FileItem> files) {
files.each { file ->
assert file.size > 0
}
}
@Validate
void validateSizeDivisibleBySixteen(ModelMap<FileItem> files) {
files.each { file ->
assert file.size % 16 == 0
}
}
}
model {
root(DirectoryItem) {
children {
dir(DirectoryItem) {
children {
file1(FileItem)
file2(FileItem) { size = 2048 }
}
}
file3(FileItem)
}
}
}
Page 579 of 717
{}
Note: The code for this example can be found at samples/modelRules/ruleSourcePluginEach
in the ‘-all’ distribution of Gradle.
§
The model DSL
In addition to using a RuleSource, it is also possible to declare a model and rules directly in a build script
using the “model DSL”.
Tip: The model DSL makes heavy use of various Groovy DSL features. Please have a read of the
section called “Some Groovy basics” for an introduction to these Groovy features.
The general form of the model DSL is:
model {
«rule-definitions»
}
All rules are nested inside a model block. There may be any number of rule definitions inside each model
block, and there may be any number of model blocks in a build script. You can also use a model block in
build scripts that are applied using apply from: $uri.
There are currently 2 kinds of rule that you can define using the model DSL: configuration rules, and creation
rules.
§
Configuration rules
You can define a rule that configures a particular model element. A configuration rule has the following form:
model {
«model-path-to-subject» {
«configuration code»
}
}
Continuing with the example so far of the model element "person" of type Person being present, the
following DSL snippet adds a configuration rule for the person that sets its lastName property.
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Example 509. DSL configuration rule
build.gradle
model {
person {
lastName = "Smith"
}
}
A configuration rule specifies a path to the subject that should be configured and a closure containing the
code to run when the subject is configured. The closure is executed with the subject passed as the closure
delegate. Exactly what code you can provide in the closure depends on the type of the subject. This is
discussed below.
You should note that the configuration code is not executed immediately but is instead executed only when
the subject is required. This is an important behaviour of model rules and allows Gradle to configure only
those elements that are required for the build, which helps reduce build time. For example, let’s run a task
that uses the "person" object:
Example 510. Configuration run when required
build.gradle
model {
person {
println "configuring person"
lastName = "Smith"
}
}
Output of gradle showPerson
> gradle showPerson
configuring person
:showPerson
Hello John Smith!
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
You can see that before the task is run, the "person" element is configured by running the rule closure. Now
let’s run a task that does not require the "person" element:
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Example 511. Configuration not run when not required
Output of gradle somethingElse
> gradle somethingElse
:somethingElse
Not using person
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
In this instance, you can see that the "person" element is not configured at all.
§
Creation rules
It is also possible to create model elements at the root level. The general form of a creation rule is:
model {
«element-name»(«element-type») {
«initialization code»
}
}
The following model rule creates the "person" element:
Example 512. DSL creation rule
build.gradle
model {
person(Person) {
firstName = "John"
}
}
A creation rule definition specifies the path of the element to create, plus its public type, represented as a
Java interface or class. Only certain types of model elements can be created.
A creation rule may also provide a closure containing the initialization code to run when the element is
created. The closure is executed with the element passed as the closure delegate. Exactly what code you
can provide in the closure depends on the type of the subject. This is discussed below.
The initialization closure is optional and can be omitted, for example:
Example 513. DSL creation rule without initialization
build.gradle
model {
barry(Person)
}
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You should note that the initialization code is not executed immediately but is instead executed only when
the element is required. The initialization code is executed before any configuration rules are run. For
example:
Example 514. Initialization before configuration
build.gradle
model {
person {
println "configuring person"
println "last name is $lastName, should be Smythe"
lastName = "Smythe"
}
person(Person) {
println "creating person"
firstName = "John"
lastName = "Smith"
}
}
Output of gradle showPerson
> gradle showPerson
creating person
configuring person
last name is Smith, should be Smythe
:showPerson
Hello John Smythe!
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
Notice that the creation rule appears in the build script after the configuration rule, but its code runs before
the code of the configuration rule. Gradle collects up all the rules for a particular subject before running any
of them, then runs the rules in the appropriate order.
§
Model rule closures
Most DSL rules take a closure containing some code to run to configure the subject. The code you can use
in this closure depends on the type of the subject of the rule.
Tip: You can use the model report to determine the type of a particular model element.
In general, a rule closure may contain arbitrary code, mixed with some type specific DSL syntax.
ModelMap<T> subject
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§
ModelMap<T> subject
A ModelMap is basically a map of model elements, indexed by some name. When a ModelMap is used as
the subject of a DSL rule, the rule closure can use any of the methods defined on the ModelMap interface.
A rule closure with ModelMap as a subject can also include nested creation or configuration rules. These
behave in a similar way to the creation and configuration rules that appear directly under the model block.
Here is an example of a nested creation rule:
Example 515. Nested DSL creation rule
build.gradle
model {
people {
john(Person) {
firstName = "John"
}
}
}
As before, a nested creation rule defines a name and public type for the element, and optionally, a closure
containing code to use to initialize the element. The code is run only when the element is required in the
build.
Here is an example of a nested configuration rule:
Example 516. Nested DSL configuration rule
build.gradle
model {
people {
john {
lastName = "Smith"
}
}
}
As before, a nested configuration rule defines the name of the element to configure and a closure containing
code to use to configure the element. The code is run only when the element is required in the build.
ModelMap introduces several other kinds of rules. For example, you can define a rule that targets each of
the elements in the map. The code in the rule closure is executed once for each element in the map, when
that element is required. Let’s run a task that requires all of the children of the "people" element:
Page 584 of 717
Example 517. DSL configuration rule for each element in a map
build.gradle
model {
people {
john(Person) {
println "creating $it"
firstName = "John"
lastName = "Smith"
}
all {
println "configuring $it"
}
barry(Person) {
println "creating $it"
firstName = "Barry"
lastName = "Barry"
}
}
}
Output of gradle listPeople
> gradle listPeople
creating Person 'people.barry'
configuring Person 'people.barry'
creating Person 'people.john'
configuring Person 'people.john'
:listPeople
Hello Barry Barry!
Hello John Smith!
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
Any method on ModelMap that accepts an Action as its last parameter can also be used to define a
nested rule.
§
@Managed type subject
When a managed type is used as the subject of a DSL rule, the rule closure can use any of the methods
defined on the managed type interface.
A rule closure can also configure the properties of the element using nested closures. For example:
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Example 518. Nested DSL property configuration
build.gradle
model {
person {
address {
city = "Melbourne"
}
}
}
Note: Currently, the nested closures do not define rules and are executed immediately. Please be
aware that this behaviour will change in a future Gradle release.
§
All other subjects
For all other types, the rule closure can use any of the methods defined by the type. There is no special DSL
defined for these elements.
§
Automatic type coercion
Scalar properties in managed types can be assigned CharSequence values (e.g. String, GString, etc.)
and they will be converted to the actual property type for you. This works for all scalar types including `File`s,
which will be resolved relative to the current project.
Example 519. a DSL example showing type conversions
build.gradle
enum Temperature {
TOO_HOT,
TOO_COLD,
JUST_RIGHT
}
@Managed
interface Item {
void setName(String n); String getName()
void setQuantity(int q); int getQuantity()
void setPrice(float p); float getPrice()
void setTemperature(Temperature t)
Temperature getTemperature()
void setDataFile(File f); File getDataFile()
}
Page 586 of 717
class ItemRules extends RuleSource {
@Model
void item(Item item) {
def data = item.dataFile.text.trim()
def (name, quantity, price, temp) = data.split(',')
item.name = name
item.quantity = quantity
item.price = price
item.temperature = temp
}
@Defaults
void setDefaults(Item item) {
item.dataFile = 'data.csv'
}
@Mutate
void createDataTask(ModelMap<Task> tasks, Item item) {
tasks.create('showData') {
doLast {
println """
Item '$item.name'
quantity:
$item.quantity
price:
$item.price
temperature: $item.temperature"""
}
}
}
}
apply plugin: ItemRules
model {
item {
price = "${price * (quantity < 10 ? 2 : 0.5)}"
Page 587 of 717
}
}
Note: The code for this example can be found at samples/modelRules/modelDslCoercion in
the ‘-all’ distribution of Gradle.
In the above example, an Item is created and is initialized in setDefaults() by providing the path to the
data file. In the item() method the resolved File is parsed to extract and set the data. In the DSL block at
the end, the price is adjusted based on the quantity; if there are fewer than 10 remaining the price is
doubled, otherwise it is reduced by 50%. The GString expression is a valid value since it resolves to a float
value in string form.
Finally, in createDataTask() we add the showData task to display all of the configured values.
§
Declaring input dependencies
Rules declared in the DSL may depend on other model elements through the use of a special syntax, which
is of the form:
$.«path-to-model-element»
Paths are a period separated list of identifiers. To directly depend on the firstName of the person, the
following could be used:
$.person.firstName
Example 520. a DSL rule using inputs
build.gradle
model {
tasks {
hello(Task) {
def p = $.person
doLast {
println "Hello $p.firstName $p.lastName!"
}
}
}
}
Note: The code for this example can be found at samples/modelRules/modelDsl in the ‘-all’
distribution of Gradle.
In the above snippet, the $.person construct is an input reference. The construct returns the value of the
model element at the specified path, as its default type (i.e. the type advertised by the Model Report). It may
appear anywhere in the rule that an expression may normally appear. It is not limited to the right hand side
Page 588 of 717
of variable assignments.
The input element is guaranteed to be fully configured before the rule executes. That is, all of the rules that
mutate the element are guaranteed to have been previously executed, leaving the target element in its final,
immutable, state.
Most model elements enforce immutability when being used as inputs. Any attempt to mutate such an
element will result in a runtime error. However, some legacy type objects do not currently implement such
checks. Regardless, it is always invalid to attempt to mutate an input to a rule.
§
Using ModelMap<T> as an input
When you use a ModelMap as input, each item in the map is made available as a property.
§
The model report
The built-in ModelReport task displays a hierarchical view of the elements in the model space. Each item
prefixed with a + on the model report is a model element and the visual nesting of these elements correlates
to the model path (e.g. tasks.help). The model report displays the following details about each model
element:
Table 100. Model report - model element details
Detail
Description
Type
This is the underlying type of the model element and is typically a fully qualified class name.
Value
Is conditionally displayed on the report when a model element can be represented as a string.
Creator
Rules
Every model element has a creator. A creator signifies the origin of the model element (i.e. what created the model
element).
Is a listing of the rules, excluding the creator rule, which are executed for a given model element. The order in which
the rules are displayed reflects the order in which they are executed.
Example 521. model task output
Output of gradle model
> gradle model
:model
-----------------------------------------------------------Root project
------------------------------------------------------------
Page 589 of 717
+ person
| Type:
Person
| Creator:
PersonRules#person(Person)
| Rules:
person { ... } @ build.gradle line 59, column 3
PersonRules#setFirstName(Person)
+ age
| Type:
int
| Value:
0
| Creator:
PersonRules#person(Person)
+ children
| Type:
org.gradle.model.ModelSet<Person>
| Creator:
PersonRules#person(Person)
+ employed
| Type:
boolean
| Value:
false
| Creator:
PersonRules#person(Person)
+ father
| Type:
Person
| Value:
null
| Creator:
PersonRules#person(Person)
+ firstName
| Type:
java.lang.String
| Value:
John
| Creator:
PersonRules#person(Person)
+ homeDirectory
| Type:
java.io.File
| Value:
null
| Creator:
PersonRules#person(Person)
+ id
| Type:
java.lang.Long
| Value:
null
| Creator:
PersonRules#person(Person)
+ lastName
| Type:
java.lang.String
| Value:
Smith
| Creator:
PersonRules#person(Person)
+ maritalStatus
| Type:
MaritalStatus
| Creator:
PersonRules#person(Person)
+ mother
| Type:
Person
| Value:
null
| Creator:
PersonRules#person(Person)
+ userGroups
| Type:
java.util.List<java.lang.String>
| Value:
null
| Creator:
PersonRules#person(Person)
+ tasks
Page 590 of 717
+
+
+
+
+
+
+
+
| Type:
org.gradle.model.ModelMap<org.gradle.api.Task>
| Creator:
Project.<init>.tasks()
| Rules:
PersonRules#createHelloTask(ModelMap<Task>, Person)
buildEnvironment
| Type:
org.gradle.api.tasks.diagnostics.BuildEnvironmentReportTask
| Value:
task ':buildEnvironment'
| Creator:
tasks.addPlaceholderAction(buildEnvironment)
| Rules:
copyToTaskContainer
components
| Type:
org.gradle.api.reporting.components.ComponentReport
| Value:
task ':components'
| Creator:
tasks.addPlaceholderAction(components)
| Rules:
copyToTaskContainer
dependencies
| Type:
org.gradle.api.tasks.diagnostics.DependencyReportTask
| Value:
task ':dependencies'
| Creator:
tasks.addPlaceholderAction(dependencies)
| Rules:
copyToTaskContainer
dependencyInsight
| Type:
org.gradle.api.tasks.diagnostics.DependencyInsightReportTask
| Value:
task ':dependencyInsight'
| Creator:
tasks.addPlaceholderAction(dependencyInsight)
| Rules:
HelpTasksPlugin.Rules#addDefaultDependenciesReportConfiguration(DependencyIn
copyToTaskContainer
dependentComponents
| Type:
org.gradle.api.reporting.dependents.DependentComponentsReport
| Value:
task ':dependentComponents'
| Creator:
tasks.addPlaceholderAction(dependentComponents)
| Rules:
copyToTaskContainer
hello
| Type:
org.gradle.api.Task
| Value:
task ':hello'
| Creator:
PersonRules#createHelloTask(ModelMap<Task>, Person) > create(hell
| Rules:
copyToTaskContainer
help
| Type:
org.gradle.configuration.Help
| Value:
task ':help'
| Creator:
tasks.addPlaceholderAction(help)
| Rules:
copyToTaskContainer
init
| Type:
org.gradle.buildinit.tasks.InitBuild
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+
+
+
+
+
| Value:
task ':init'
| Creator:
tasks.addPlaceholderAction(init)
| Rules:
copyToTaskContainer
model
| Type:
org.gradle.api.reporting.model.ModelReport
| Value:
task ':model'
| Creator:
tasks.addPlaceholderAction(model)
| Rules:
copyToTaskContainer
projects
| Type:
org.gradle.api.tasks.diagnostics.ProjectReportTask
| Value:
task ':projects'
| Creator:
tasks.addPlaceholderAction(projects)
| Rules:
copyToTaskContainer
properties
| Type:
org.gradle.api.tasks.diagnostics.PropertyReportTask
| Value:
task ':properties'
| Creator:
tasks.addPlaceholderAction(properties)
| Rules:
copyToTaskContainer
tasks
| Type:
org.gradle.api.tasks.diagnostics.TaskReportTask
| Value:
task ':tasks'
| Creator:
tasks.addPlaceholderAction(tasks)
| Rules:
copyToTaskContainer
wrapper
| Type:
org.gradle.api.tasks.wrapper.Wrapper
| Value:
task ':wrapper'
| Creator:
tasks.addPlaceholderAction(wrapper)
Page 592 of 717
| Rules:
copyToTaskContainer
§
Limitations and future direction
Rule based model configuration is the future of Gradle. This area is fledgling, but under very active
development. Early experiments have demonstrated that this approach is more efficient, able to provide
richer diagnostics and authoring assistance and is more extensible. However, there are currently many
limitations.
The majority of the development to date has been focused on proving the efficacy of the approach, and
building the internal rule execution engine and model graph mechanics. The user facing aspects (e.g the
DSL, rule source classes) are yet to be optimized for conciseness and general usability. Likewise, many
necessary configuration patterns and constructs are not yet able to be expressed via the API.
In conjunction with the addition of better syntax, a richer toolkit of configuration constructs and generally
more expressive power, more tooling will be added that will enable build engineers and users alike to
comprehend, modify and extend builds in new ways.
Due to the inherent nature of the rule based approach, it is more efficient at constructing the build model
than today’s Gradle. However, in the future Gradle will also leverage the parallelism that this approach
enables both at configuration and execution time. Moreover, due to increased transparency of the model
Gradle will be able to further reduce build times by caching and pre-computing the build model. Beyond
improved general build performance, this will greatly improve the experience when using Gradle from tools
such as IDEs.
As this area of Gradle is under active development, it will be changing rapidly. Please be sure to consult the
documentation of Gradle corresponding to the version you are using and to watch for changes announced in
the release notes for future versions.
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Software model concepts
Note: Support for the software model is currently incubating. Please be aware that the DSL, APIs
and other configuration may change in later Gradle versions.
The software model describes how a piece of software is built and how the components of the software
relate to each other. The software model is organized around some key concepts:
A component is a general concept that represents some logical piece of software. Examples of components
are a command-line application, a web application or a library. A component is often composed of other
components. Most Gradle builds will produce at least one component.
A library is a reusable component that is linked into or combined into some other component. In the Java
ecosystem, a library is often built as a Jar file, and then later bundled into an application of some kind. In the
native ecosystem, a library may be built as a shared library or static library, or both.
A source set represents a logical group of source files. Most components are built from source sets of
various languages. Some source sets contain source that is written by hand, and some source sets may
contain source that is generated from something else.
A binary represents some output that is built for a component. A component may produce multiple different
output binaries. For example, for a C++ library, both a shared library and a static library binary may be
produced. Each binary is initially configured to be built from the component sources, but additional source
sets can be added to specific binary variants.
A variant represents some mutually exclusive binary of a component. A library, for example, might target
Java 7 and Java 8, effectively producing two distinct binaries: a Java 7 Jar and a Java 8 Jar. These are
different variants of the library.
The API of a library represents the artifacts and dependencies that are required to compile against that
library. The API typically consists of a binary together with a set of dependencies.
Page 594 of 717
Implementing model rules in a plugin
A plugin can define rules by extending RuleSource and adding methods that define the rules. The plugin
class can either extend RuleSource directly or can implement Plugin and include a nested RuleSource
subclass.
Refer to the API docs for RuleSource for more details.
§
Applying additional rules
A rule method annotated with Rules can apply a RuleSource to a target model element.
Page 595 of 717
Building Java Libraries
Note: Support for building Java libraries using the software model is currently incubating. Please be
aware that the DSL, APIs and other configuration may change in later Gradle versions.
The Java software plugins are intended to replace the Java plugin, and leverage the Gradle software model
to achieve the best performance, improved expressiveness and support for variant-aware dependency
management.
§
Features
The Java software plugins provide:
Support for building Java libraries and other components that run on the JVM.
Support for several source languages.
Support for building different variants of the same software, for different Java versions, or for any purpose.
Build time definition and enforcement of Java library API.
Compile avoidance.
Dependency management between Java software components.
§
Java Software Model
The Java software plugins provide a software model that describes Java based software and how it should
be built. This Java software model extends the base Gradle software model, to add support for building JVM
libraries. A JVM library is a kind of library that is built for and runs on the JVM. It may be built from Java
source, or from various other languages. All JVM libraries provide an API of some kind.
§
Usage
To use the Java software plugins, include the following in your build script:
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Example 522. Using the Java software plugins
build.gradle
plugins {
id 'jvm-component'
id 'java-lang'
}
§
Creating a library
A library is created by declaring a JvmLibrarySpec under the components element of the model:
Example 523. Creating a java library
build.gradle
model {
components {
main(JvmLibrarySpec)
}
}
Output of gradle build
> gradle build
:compileMainJarMainJava
:processMainJarMainResources
:createMainJar
:mainApiJar
:mainJar
:assemble
:check UP-TO-DATE
:build
BUILD SUCCESSFUL in 0s
4 actionable tasks: 4 executed
This example creates a library named main, which will implicitly create a JavaSourceSet named java.
The conventions of the legacy Java plugin are observed, where Java sources are expected to be found in src/main/jav
, while resources are expected to be found in src/main/resources.
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Source Sets
§
Source Sets
Source sets represent logical groupings of source files in a library. A library can define multiple source sets
and all sources will be compiled and included in the resulting binaries. When a library is added to a build, the
following source sets are added by default.
Table 101. Java plugin - default source sets
Source Set
Type
Directory
java
JavaSourceSet
src/${library.name}/java
resources
JvmResourceSet
src/${library.name}/resources
It is possible to configure an existing source set through the sources container:
Example 524. Configuring a source set
build.gradle
components {
main {
sources {
java {
// configure the "java" source set
}
}
}
}
It is also possible to create an additional source set, using the JavaSourceSet type:
Example 525. Creating a new source set
build.gradle
components {
main {
sources {
mySourceSet(JavaSourceSet) {
// configure the "mySourceSet" source set
}
}
}
}
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Tasks
§
Tasks
By default, when the plugins above are applied, no new tasks are added to the build. However, when
libraries are defined, conventional tasks are added which build and package each binary of the library.
For each binary of a library, a single lifecycle task is created which executes all tasks associated with
building the binary. To build all binaries, the standard build lifecycle task can be used.
Table 102. Java plugin - lifecycle tasks
Component Type
Binary Type
Lifecycle Task
JvmLibrarySpec
JvmBinarySpec
${library.name}${binary.name}
For each source set added to a library, tasks are added to compile or process the source files for each
binary.
Table 103. Java plugin - source set tasks
Source Set Type
Task name
Type
Description
Compiles
the
JavaSourceSet compile${library.name}${binary.name}${library.name}${sourceset.name} PlatformJavaCompile sources of
a
given
source set.
Copies the
resources
in
the
given
JvmResourceSet process${library.name}${binary.name}${library.name}${sourceset.name} ProcessResources
source set
to
the
classes
output
directory.
For each binary in a library, a packaging task is added to create the jar for that binary.
Table 104. Java plugin - packaging tasks
Binary Type
Task name
Depends on
Type Description
all PlatformJavaCompile and
JvmBinarySpec create${library.name}${binary.name} ProcessResources
associated with the binary
Packages
tasks Jar classes
the
and
compiled
processed
resources of the binary.
Page 599 of 717
§
Finding out more about your project
Gradle provides a report that you can run from the command-line that shows details about the components
and binaries that your project produces. To use this report, just run gradle components. Below is an
example of running this report for one of the sample projects:
Example 526. The components report
Output of gradle components
> gradle components
:components
-----------------------------------------------------------Root project
-----------------------------------------------------------JVM library 'main'
-----------------Source sets
Java source 'main:java'
srcDir: src/main/java
Java source 'main:mySourceSet'
srcDir: src/main/mySourceSet
JVM resources 'main:resources'
srcDir: src/main/resources
Binaries
Jar 'main:jar'
build using task: :mainJar
target platform: java7
tool chain: JDK 7 (1.7)
classes dir: build/classes/main/jar
resources dir: build/resources/main/jar
API Jar file: build/jars/main/jar/api/main.jar
Jar file: build/jars/main/jar/main.jar
Note: currently not all plugins register their components, so some components may not be v
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
Page 600 of 717
Dependencies
§
Dependencies
A component in the Java software model can declare dependencies on other Java libraries. If component main
depends on library util, this means that the API of util is required when compiling the sources of main,
and the runtime of util is required when running or testing main. The terms 'API' and 'runtime' are
examples of usages of a Java library.
§
Library usage
The 'API' usage of a Java library consists of:
Artifact(s): the Jar file(s) containing the public classes of that library
Dependencies: the set of other libraries that are required to compile against that library
When library main is compiled with a dependency on util, the 'API' dependencies of 'util' are resolved
transitively, resulting in the complete set of libraries required to compile. For each of these libraries (including
'util'), the 'API' artifacts will be included in the compile classpath.
Similarly, the 'runtime' usage of a Java library consists of artifacts and dependencies. When a Java
component is tested or bundled into an application, the runtime usage of any runtime dependencies will be
resolved transitively into the set of libraries required at runtime. The runtime artifacts of these libraries will
then be included in the testing or runtime classpath.
§
Dependency types
Two types of Java library dependencies can be declared:
Dependencies on a library defined in a local Gradle project
Dependencies on a library published to a Maven repository
Dependencies onto libraries published to an Ivy repository are not yet supported.
§
Declaring dependencies
Dependencies may be declared for a specific JavaSourceSet, for an entire JvmLibrarySpec or as part
of the JvmApiSpec of a component:
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Example 527. Declaring a dependency onto a library
build.gradle
model {
components {
server(JvmLibrarySpec) {
sources {
java {
dependencies {
library 'core'
}
}
}
}
core(JvmLibrarySpec) {
dependencies {
library 'commons'
}
}
commons(JvmLibrarySpec) {
api {
dependencies {
library 'collections'
}
}
}
collections(JvmLibrarySpec)
}
}
Output of gradle serverJar
> gradle serverJar
:compileCollectionsJarCollectionsJava
:collectionsApiJar
:compileCommonsJarCommonsJava
:commonsApiJar
:compileCoreJarCoreJava
:processCoreJarCoreResources
:coreApiJar
:compileServerJarServerJava
:createServerJar
:serverApiJar
:serverJar
BUILD SUCCESSFUL in 0s
10 actionable tasks: 10 executed
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Dependencies declared for a source set will only be used for compiling that particular source set.
Dependencies declared for a component will be used when compiling all source sets for the component.
Dependencies declared for the component api are used for compiling all source sets for the component,
and are also exported as part of the component’s API. See Enforcing API boundaries at compile time for
more details.
The previous example declares a dependency for the java source set of the server library onto the core
library of the same project. However, it is possible to create a dependency on a library in a different project
as well:
Example 528. Declaring a dependency onto a project with an explicit library
build.gradle
client(JvmLibrarySpec) {
sources {
java {
dependencies {
project ':util' library 'main'
}
}
}
}
Output of gradle clientJar
> gradle clientJar
:util:compileMainJarMainJava
:util:mainApiJar
:compileClientJarClientJava
:clientApiJar
:createClientJar
:clientJar
BUILD SUCCESSFUL in 0s
5 actionable tasks: 5 executed
When the target project defines a single library, the library selector can be omitted altogether:
Example 529. Declaring a dependency onto a project with an implicit library
build.gradle
dependencies {
project ':util'
}
Dependencies onto libraries published to Maven repositories can be declared via module identifiers
consisting of a group name, a module name plus an optional version selector:
Page 603 of 717
Example 530. Declaring a dependency onto a library published to a Maven repository
build.gradle
verifier(JvmLibrarySpec) {
dependencies {
module 'asm'
group 'org.ow2.asm' version '5.0.4'
module 'asm-analysis' group 'org.ow2.asm'
}
}
Output of gradle verifierJar
> gradle verifierJar
:compileVerifierJarVerifierJava
:createVerifierJar
:verifierApiJar
:verifierJar
BUILD SUCCESSFUL in 0s
3 actionable tasks: 3 executed
A shorthand notation for module identifiers can also be used:
Example 531. Declaring a module dependency using shorthand notation
build.gradle
dependencies {
module 'org.ow2.asm:asm:5.0.4'
module 'org.ow2.asm:asm-analysis'
}
Module dependencies will be resolved against the configured repositories as usual:
Example 532. Configuring repositories for dependency resolution
build.gradle
repositories {
mavenCentral()
}
The DependencySpecContainer class provides a complete reference of the dependencies DSL.
§
Defining a Library API
Every library has an API, which consists of artifacts and dependencies that are required to compile against
the library. The library may be explicitly declared for a component, or may be implied based on other
component metadata.
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By default, all public types of a library are considered to be part of its API. In many cases this is not ideal;
a library will contain many public types that intended for internal use within that library. By explicitly declaring
an API for a Java library, Gradle can provide compile-time encapsulation of these internal-but-public types.
The types to include in a library API are declared at the package level. Packages containing API types are
considered to be exported .
By default, dependencies of a library are not considered to be part of its API. By explicitly declaring a
dependency as part of the library API, this dependency will then be made available to consumers when
compiling. Dependencies declared this way are considered to be exported , and are known as 'API
dependencies'.
Note: JDK 9 will introduce Jigsaw , the reference implementation of the Java Module System .
Jigsaw will provide both compile-time and run-time enforcement of API encapsulation.
Gradle anticipates the arrival of JDK 9 and the Java Module System with an approach to specifying
and enforcing API encapsulation at compile-time. This allows Gradle users to leverage the many
benefits of strong encapsulation, and prepare their software projects for migration to JDK 9.
§
Some terminology
An API is a set of classes, interfaces, methods that are exposed to a consumer.
An API specification is the specification of classes, interfaces or methods that belong to an API, together
with the set of dependencies that are part of the API. It can be found in various forms, like module-info.java
in Jigsaw, or the api { … } block that Gradle defines as part of those stories. Usually, we can simplify this
to a list of packages, called exported packages .
A runtime jar consists of API classes and non-API classes used at execution time. There can be multiple
runtime jars depending on combinations of the variant dimensions: target platform, hardware infrastructure,
target application server, …
API classes are classes of a variant which match the API specification
Non-API classes are classes of a variant which do not match the API specification .
A stubbed API class is an API class for which its implementation and non public members have been
removed. It is meant to be used when a consumer is going to be compiled against an API .
An API jar is a collection of API classes . There can be multiple API jars depending on the combinations of
variant dimensions.
A stubbed API jar is a collection of stubbed API classes . There can be multiple stubbed API jars depending
on the combinations of variant dimensions.
An ABI (application binary interface) corresponds to the public signature of an API, that is to say the set of
stubbed API classes that it exposes (and their API visible members).
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We avoid the use of the term implementation because it is too vague: both API classes and Non-API
classes can have an implementation. For example, an API class can be an interface, but also a concrete
class. Implementation is an overloaded term in the Java ecosystem, and often refers to a class implementing
an interface. This is not the case here: a concrete class can be member of an API, but to compile against an
API, you don’t need the implementation of the class: all you need is the signatures.
§
Specifying API classes
Example 533. Specifying api packages
build.gradle
model {
components {
main(JvmLibrarySpec) {
api {
exports 'org.gradle'
exports 'org.gradle.utils'
}
}
}
}
§
Specifying API dependencies
Example 534. Specifying api dependencies
build.gradle
commons(JvmLibrarySpec) {
api {
dependencies {
library 'collections'
}
}
}
§
Compile avoidance
When you define an API for your library, Gradle enforces the usage of that API at compile-time. This comes
with 3 direct consequences:
Trying to use a non-API class in a dependency will now result in a compilation error.
Changing the implementation of an API class will not result in recompilation of consumers if the ABI doesn’t
change (that is to say, all public methods have the same signature but not necessarily the same body).
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Changing the implementation of a non-API class will not result in recompilation of consumers. This means
that changes to non-API classes will not trigger recompilation of downstream dependencies, because the
ABI of the component doesn’t change.
Given a main component that exports org.gradle, org.gradle.utils and defines those classes:
Example 535. Main sources
src/main/java/org/gradle/Person.java
package org.gradle;
public class Person {
private final String name;
public Person(String name) {
this.name = name;
}
public String getName() {
return name;
}
}
src/main/java/org/gradle/internal/PersonInternal.java
package org.gradle.internal;
import org.gradle.Person;
public class PersonInternal extends Person {
public PersonInternal(String name) {
super(name);
}
}
src/main/java/org/gradle/utils/StringUtils.java
package org.gradle.utils;
public abstract class StringUtils {
}
Compiling a component client that declares a dependency onto main will succeed:
Page 607 of 717
Example 536. Client component
build.gradle
model {
components {
client(JvmLibrarySpec) {
sources {
java {
dependencies {
library 'main'
}
}
}
}
}
}
src/client/java/org/gradle/Client.java
package org.gradle;
public class Client {
private Person person;
public void setPerson(Person p) { this.person = p; }
public Person getPerson() { return person; }
}
Output of gradle :clientJar
> gradle :clientJar
:compileMainJarMainJava
:processMainJarMainResources
:mainApiJar
:compileClientJarClientJava
:clientApiJar
:createClientJar
:clientJar
BUILD SUCCESSFUL in 0s
6 actionable tasks: 6 executed
But trying to compile a component brokenclient that declares a dependency onto main but uses an non-API
class of main will result in a compile-time error:
Page 608 of 717
Example 537. Broken client component
src/brokenclient/java/org/gradle/Client.java
package org.gradle;
import org.gradle.internal.PersonInternal;
public class Client {
private PersonInternal person;
public void setPerson(PersonInternal p) { this.person = p; }
public PersonInternal getPerson() { return person; }
}
Output of gradle :brokenclientJar
> gradle :brokenclientJar
:compileMainJarMainJava
:processMainJarMainResources
:mainApiJar
:compileBrokenclientJarBrokenclientJava FAILED
4 actionable tasks: 4 executed
On the other hand, if Person.java in client is updated and its API hasn’t changed, client will not be
recompiled.
Example 538. Making non-API implementation-only change
src/main/java/org/gradle/Person.java
package org.gradle;
public class Person {
private final String name;
public Person(String name) {
// we updated the body if this method
// but the signature doesn't change
// so we will not recompile components
// that depend on this class
this.name = name.toUpperCase();
}
public String getName() {
return name;
}
}
This is in particular important for incremental builds of large projects, where we can avoid the compilation of
dependencies in chain, and then dramatically reduce build duration:
Page 609 of 717
Example 539. Recompiling the client
Output of gradle :clientJar
> gradle :clientJar
:compileMainJarMainJava
:processMainJarMainResources UP-TO-DATE
:mainApiJar
:compileClientJarClientJava UP-TO-DATE
:clientApiJar UP-TO-DATE
:createClientJar UP-TO-DATE
:clientJar UP-TO-DATE
BUILD SUCCESSFUL in 0s
6 actionable tasks: 2 executed, 4 up-to-date
Page 610 of 717
Platform aware dependency management
§
Platform aware dependency management
§
Specifying the target platform
The software model extracts the target platform as a core concept. In the Java world, this means that a
library can be built, or resolved, against a specific version of Java. For example, if you compile a library for
Java 5, we know that such a library can be consumed by a library built for Java 6, but the opposite is not
true. Gradle lets you define which platforms a library targets, and will take care of:
generating a binary for each target platform (eg, a Java 5 jar as well as a Java 6 jar)
resolving dependencies against a matching platform
The targetPlatform DSL defines which platforms a library should be built against:
Example 540. Declaring target platforms
core/build.gradle
model {
components {
main(JvmLibrarySpec) {
targetPlatform 'java5'
targetPlatform 'java6'
}
}
}
Output of gradle :core:build
> gradle :core:build
:core:compileMainJava5JarMainJava
:core:processMainJava5JarMainResources
:core:createMainJava5Jar
:core:mainJava5ApiJar
:core:mainJava5Jar
:core:compileMainJava6JarMainJava
:core:compileMainJava6JarMainJava6JarJava
:core:processMainJava6JarMainResources
:core:createMainJava6Jar
:core:mainJava6ApiJar
:core:mainJava6Jar
:core:assemble
:core:check UP-TO-DATE
:core:build
BUILD SUCCESSFUL in 0s
9 actionable tasks: 9 executed
Page 611 of 717
When building the application, Gradle generates two binaries: java5MainJar and java6MainJar
corresponding to the target versions of Java. These artifacts will participate in dependency resolution as
described here.
§
Binary specific source sets
For each JvmLibrarySpec it is possible to define additional source sets for each binary. A common use
case for this is having specific dependencies for each variant and source sets that conform to those
dependencies. The example below configures a java6 source set on the main.java6Jar binary:
Example 541. Declaring binary specific sources
core/build.gradle
main {
binaries.java6Jar {
sources {
java(JavaSourceSet) {
source.srcDir 'src/main/java6'
}
}
}
}
Output of gradle clean :core:mainJava6Jar
> gradle clean :core:mainJava6Jar
:core:clean UP-TO-DATE
:server:clean UP-TO-DATE
:core:compileMainJava6JarMainJava
:core:compileMainJava6JarMainJava6JarJava
:core:processMainJava6JarMainResources
:core:createMainJava6Jar
:core:mainJava6ApiJar
:core:mainJava6Jar
BUILD SUCCESSFUL in 0s
7 actionable tasks: 5 executed, 2 up-to-date
§
Dependency resolution
When a library targets multiple versions of Java and depends on another library, Gradle will make its best
effort to resolve the dependency to the most appropriate version of the dependency library. In practice, this
means that Gradle chooses the highest compatible version:
for a binary B built for Java n
for a dependency binary D built for Java m
Page 612 of 717
D is compatible with B if m<=n
for multiple compatible binaries D(java 5), D(java 6), …D(java m), choose the compatible D binary
with the highest Java version
Example 542. Declaring target platforms
server/build.gradle
model {
components {
main(JvmLibrarySpec) {
targetPlatform 'java5'
targetPlatform 'java6'
sources {
java {
dependencies {
project ':core' library 'main'
}
}
}
}
}
}
Output of gradle clean :server:build
> gradle clean :server:build
:core:clean UP-TO-DATE
:server:clean UP-TO-DATE
:core:compileMainJava5JarMainJava
:core:processMainJava5JarMainResources
:core:mainJava5ApiJar
:server:compileMainJava5JarMainJava
:server:createMainJava5Jar
:server:mainJava5ApiJar
:server:mainJava5Jar
:core:compileMainJava6JarMainJava
:core:compileMainJava6JarMainJava6JarJava
:core:processMainJava6JarMainResources
:core:mainJava6ApiJar
:server:compileMainJava6JarMainJava
:server:createMainJava6Jar
:server:mainJava6ApiJar
:server:mainJava6Jar
:server:assemble
:server:check UP-TO-DATE
:server:build
BUILD SUCCESSFUL in 0s
15 actionable tasks: 13 executed, 2 up-to-date
Page 613 of 717
In the example above, Gradle automatically chooses the Java 6 variant of the dependency for the Java 6
variant of the server component, and chooses the Java 5 version of the dependency for the Java 5 variant
of the server component.
§
Custom variant resolution
The Java plugin, in addition to the target platform resolution, supports resolution of custom variants. Custom
variants can be defined on custom binary types, as long as they extend JarBinarySpec. Users interested
in testing this incubating feature can check out the documentation of the Variant annotation.
Page 614 of 717
Testing Java libraries
§
Testing Java libraries
§
Standalone JUnit test suites
The Java software model supports defining standalone JUnit test suites as components of the model.
Standalone test suite are components that are self contained, in the sense that there is no component under
test: everything being tested must belong to the test suite sources.
A test suite is declared by creating a component of type JUnitTestSuiteSpec, which is available when
you apply the junit-test-suite plugin:
Example 543. Using the JUnit plugin
build.gradle
plugins {
id 'jvm-component'
id 'java-lang'
id 'junit-test-suite'
}
model {
testSuites {
test(JUnitTestSuiteSpec) {
jUnitVersion '4.12'
}
}
}
In the example above, test is the name of our test suite. By convention, Gradle will create two source sets
for the test suite, based on the name of the component: one for Java sources, and the other for resources: src/test/ja
and src/test/resources. If the component was named integTest, then sources and resources would
have been found respectively in src/integTest/java and src/integTest/resources.
Once the component is created, the test suite can be executed running the <<test suite name>>BinaryTest
task:
Page 615 of 717
Example 544. Executing the test suite
src/test/java/org/gradle/MyTest.java
package org.gradle;
import org.junit.Test;
import static org.junit.Assert.*;
public class MyTest {
@Test
public void myTestMethod() {
assertEquals(4, "test".length());
}
}
Output of gradle testBinaryTest
> gradle testBinaryTest
:compileTestBinaryTestJava
:processTestBinaryTestResources
:testBinaryTest
BUILD SUCCESSFUL in 0s
3 actionable tasks: 3 executed
It is possible to configure source sets in a similar way as libraries.
A test suite being a component can also declare dependencies onto other components.
A test suite can also contain resources, in which case it is possible to configure the resource processing
task:
Example 545. Executing the test suite
build.gradle
model {
tasks.processTestBinaryTestResources {
// uncomment lines
filter { String line ->
line.replaceAll('<!-- (.+?) -->', '$1')
}
}
}
§
Testing JVM libraries with JUnit
It is likely that you will want to test another JVM component. The Java software model supports it exactly like
standalone test suites, by just declaring an additional component under test:
Page 616 of 717
Example 546. Declaring a component under test
build.gradle
model {
components {
main(JvmLibrarySpec)
}
testSuites {
test(JUnitTestSuiteSpec) {
jUnitVersion '4.12'
testing $.components.main
}
}
}
Output of gradle testMainJarBinaryTest
> gradle testMainJarBinaryTest
:compileMainJarMainJava
:processMainJarMainResources
:compileTestMainJarBinaryTestJava
:testMainJarBinaryTest
BUILD SUCCESSFUL in 0s
4 actionable tasks: 4 executed
Note that the syntax to choose the component under test is a reference ( $.). You can select any JvmComponentSpec
as the component under test. It’s also worth noting that when you declare a component under test, a test
suite is created for each binary of the component under test (for example, if the component under test has a
Java 7 and Java 8 version, 2 different test suite binaries would be automatically created).
§
Declaring Java toolchains
You can declare the list of local JVM installations using the javaInstallations model block. Gradle will
use this information to locate your JVMs and probe their versions. Please note that this information is not yet
used by Gradle to select the appropriate JDK or JRE when compiling your Java sources, or when executing
Java applications. A local Java installation can be declared using the LocalJava type, independently of the
fact they are a JDK or a JRE:
Page 617 of 717
Example 547. Declaring local Java installations
build.gradle
model {
javaInstallations {
openJdk6(LocalJava) {
path '/usr/lib/jvm/jdk1.6.0-amd64'
}
oracleJre7(LocalJava) {
path '/usr/lib/jvm/jre1.7.0'
}
ibmJdk8(LocalJava) {
path '/usr/lib/jvm/jdk1.8.0'
}
}
}
Page 618 of 717
Building Play applications
Note: Support for building Play applications is currently incubating. Please be aware that the DSL,
APIs and other configuration may change in later Gradle versions.
Play is a modern web application framework. The Play plugin adds support for building, testing and running
Play applications with Gradle.
The Play plugin makes use of the Gradle software model.
§
Usage
To use the Play plugin, include the following in your build script to apply the play plugin and add the
Lightbend repositories:
Example 548. Using the Play plugin
build.gradle
plugins {
id 'play'
}
repositories {
jcenter()
maven {
name "lightbend-maven-release"
url "https://repo.lightbend.com/lightbend/maven-releases"
}
ivy {
name "lightbend-ivy-release"
url "https://repo.lightbend.com/lightbend/ivy-releases"
layout "ivy"
}
}
Note that defining the Lightbend repositories is necessary. In future versions of Gradle, this will be replaced
with a more convenient syntax.
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Limitations
§
Limitations
The Play plugin currently has a few limitations.
Gradle does not yet support aggregate reverse routes introduced in Play 2.4.x.
A given project may only define a single Play application. This means that a single project cannot build more
than one Play application. However, a multi-project build can have many projects that each define their own
Play application.
Play applications can only target a single “platform” (combination of Play, Scala and Java version) at a time.
This means that it is currently not possible to define multiple variants of a Play application that, for example,
produce jars for both Scala 2.10 and 2.11. This limitation may be lifted in future Gradle versions.
Support for generating IDE configurations for Play applications is limited to IDEA.
§
Software Model
The Play plugin uses a software model to describe a Play application and how to build it. The Play software
model extends the base Gradle software model to add support for building Play applications. A Play
application is represented by a PlayApplicationSpec component type. The plugin automatically creates
a single PlayApplicationBinarySpec instance when it is applied. Additional Play components cannot
be added to a project.
Figure 19. Play plugin - software model
The Play application component
Page 620 of 717
§
The Play application component
A Play application component describes the application to be built and consists of several configuration
elements. One type of element that describes the application are the source sets that define where the
application controller, route, template and model class source files should be found. These source sets are
logical groupings of files of a particular type and a default source set for each type is created when the play
plugin is applied.
Table 105. Default Play source sets
Source Set
Type
Directory
Filters
java
JavaSourceSet
app
**/*.java
scala
ScalaLanguageSourceSet
app
**/*.scala
routes
RoutesSourceSet
conf
routes, *.routes
twirlTemplates
TwirlSourceSet
app
**/*.scala.*
javaScript
JavaScriptSourceSet
app/assets
**/*.js
These source sets can be configured or additional source sets can be added to the Play component. See
Configuring Play for further information.
Another element of configuring a Play application is the platform . To build a Play application, Gradle needs
to understand which versions of Play, Scala and Java to use. The Play component specifies this requirement
as a PlayPlatform. If these values are not configured, a default version of Play, Scala and Java will be
used. See Targeting a certain version of Play for information on configuring the Play platform.
Note that only a single platform can be specified for a given Play component. This means that only a single
version of Play, Scala and Java can be used to build a Play component. In other words, a Play component
can only produce one set of outputs, and those outputs will be built using the versions specified by the
platform configured on the component.
§
The Play application binary
A Play application component is compiled and packaged to produce a set of outputs which are represented
by a PlayApplicationBinarySpec. The Play binary specifies the jar files produced by building the
component as well as providing elements by which additional content can be added to those jar files. It also
exposes the tasks involved in building the component and creating the binary.
See Configuring Play for examples of configuring the Play binary.
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Project Layout
§
Project Layout
The Play plugin follows the typical Play application layout. You can configure source sets to include
additional directories or change the defaults.
app
assets
javascripts
controllers
models
views
build.gradle
conf
public
images
javascripts
stylesheets
test
Application source code.
Assets that require compilation.
JavaScript source code to be minified.
Application controller source code.
Application business source code.
Application UI templates.
Your project's build script.
Main application configuration file and routes files.
Public assets.
Application image files.
Typically JavaScript source code.
Typically CSS source code.
Test source code.
§
Tasks
The Play plugin hooks into the normal Gradle lifecycle tasks such as assemble, check and build, but it
also adds several additional tasks which form the lifecycle of a Play project:
Table 106. Play plugin - lifecycle tasks
Task name
Depends on
Type Description
playBinary All compile tasks for source sets added to the Play application. Task
Performs
a
build
of
just
the
Play
application.
dist
createPlayBinaryZipDist, createPlayBinaryTarDistTask Assembles the Play distribution.
stage
stagePlayBinaryDist
Task Stages the Play distribution.
The plugin also provides tasks for running, testing and packaging your Play application:
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Table 107. Play plugin - running and testing tasks
Task name
Depends on
Type
runPlayBinary playBinary to build Play application.
testPlayBinary
PlayRun
Description
Runs the Play application for local development.
See how this works with continuous build.
playBinary to build Play application and compilePlayBinaryTests
Test
Runs JUnit/TestNG tests for the Play application.
.
For the different types of sources in a Play application, the plugin adds the following compilation tasks:
Table 108. Play plugin - source set tasks
Task name
compilePlayBinaryScala
Source
Type
Scala and
Java
Type
PlatformScalaCompile
Description
Compiles all Scala and Java sources
defined by the Play application.
Compiles Twirl templates with the Twirl
compiler. Gradle supports all of the
compilePlayBinaryPlayTwirlTemplates
Twirl
templates
TwirlCompile
built-in Twirl template formats (HTML,
XML,
TXT
and
JavaScript).
Twirl
templates need to match the pattern *.scala.*
.
Play
compilePlayBinaryPlayRoutes
Route
RoutesCompile
files
minifyPlayBinaryJavaScript
JavaScript
files
JavaScriptMinify
Compiles
routes
files
into
Scala
sources.
Minifies JavaScript files with the Google
Closure compiler.
§
Finding out more about your project
Gradle provides a report that you can run from the command-line that shows some details about the
components and binaries that your project produces. To use this report, just run gradle components.
Below is an example of running this report for one of the sample projects:
Page 623 of 717
Example 549. The components report
Output of gradle components
> gradle components
:components
-----------------------------------------------------------Root project
-----------------------------------------------------------Play Application 'play'
----------------------Source sets
Java source 'play:java'
srcDir: app
includes: **/*.java
JavaScript source 'play:javaScript'
srcDir: app/assets
includes: **/*.js
JVM resources 'play:resources'
srcDir: conf
Routes source 'play:routes'
srcDir: conf
includes: routes, *.routes
Scala source 'play:scala'
srcDir: app
includes: **/*.scala
Twirl template source 'play:twirlTemplates'
srcDir: app
includes: **/*.scala.*
Binaries
Play Application Jar 'play:binary'
build using task: :playBinary
target platform: Play Platform (Play 2.3.10, Scala: 2.11, Java: Java SE 8)
toolchain: Default Play Toolchain
classes dir: build/playBinary/classes
resources dir: build/playBinary/resources
JAR file: build/playBinary/lib/basic.jar
Note: currently not all plugins register their components, so some components may not be v
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
Page 624 of 717
Running a Play application
§
Running a Play application
The runPlayBinary task starts the Play application under development. During development it is
beneficial to execute this task as a continuous build. Continuous build is a generic feature that supports
automatically re-running a build when inputs change. The runPlayBinary task is “continuous build
aware” in that it behaves differently when run as part of a continuous build.
When not run as part of a continuous build, the runPlayBinary task will block the build. That is, the task
will not complete as long as the application is running. When running as part of a continuous build, the task
will start the application if not running and otherwise propagate any changes to the code of the application to
the running instance. This is useful for quickly iterating on your Play application with an
edit->rebuild->refresh cycle. Changes to your application will not take affect until the end of the overall build.
To enable continuous build, run Gradle with -t runPlayBinary or --continuous runPlayBinary.
Users of Play used to such a workflow with Play’s default build system should note that compile errors are
handled differently. If a build failure occurs during a continuous build, the Play application will not be
reloaded. Instead, you will be presented with an exception message. The exception message will only
contain the overall cause of the build failure. More detailed information will only be available from the
console.
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Configuring a Play application
§
Configuring a Play application
§
Targeting a certain version of Play
By default, Gradle uses Play 2.3.10, Scala 2.11 and the version of Java used to start the build. A Play
application
can
select
a
different
version
by
specifying
a
target
PlayApplicationSpec.platform(java.lang.Object) on the Play application component.
Example 550. Selecting a version of the Play Framework
build.gradle
model {
components {
play {
platform play: '2.5.18', scala: '2.11', java: '1.8'
injectedRoutesGenerator = true
}
}
}
The following versions of Play and Scala are supported:
Table 109. Play supported versions
Play
Scala
Java
2.6.x
2.11 and 2.12
1.8
2.5.x
2.11
1.8
2.4.x
2.10 and 2.11
1.8
2.3.x
2.10 and 2.11
1.6, 1.7 and 1.8
§
Adding dependencies
You can add compile, test and runtime dependencies to a Play application through Configuration
created by the Play plugin.
If you are coming from SBT, the Play SBT plugin provides short names for common dependencies. For
instance, if your project has a dependency on ws, you will need to add a dependency to com.typesafe.play:play-ws
where 2.11 is your Scala version and 2.3.9 is your Play framework version.
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Other dependencies that have short names, such as jacksons may actually be multiple dependencies. For
those dependencies, you will need to work out the dependency coordinates from a dependency report.
play is used for compile time dependencies.
playTest is used for test compile time dependencies.
playRun is used for run time dependencies.
Example 551. Adding dependencies to a Play application
build.gradle
dependencies {
play "commons-lang:commons-lang:2.6"
}
Note: Play 2.6 has a more modular architecture and, because of that, you may need to add some
dependencies manually. For example, Guice support was moved to a separated module .
Considering the following definition for a Play 2.6 project:
Example 552. A Play 2.6 project
Note: build.gradle
model {
components {
play {
platform play: '2.6.7', scala: '2.12', java: '1.8'
injectedRoutesGenerator = true
}
}
}
You can add Guice dependency like:
Example 553. Adding Guice dependency in Play 2.6 project
Note: build.gradle
dependencies {
play "com.typesafe.play:play-guice_2.12:2.6.7"
}
Of course, pay attention to keep Play version and Scala version for the dependency consistent with
the platform versions.
§
Configuring the default source sets
You can further configure the default source sets to do things like add new directories, add filters, etc.
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Example 554. Configuring extra source sets to a Play application
build.gradle
model {
components {
play {
sources {
java {
source.srcDir "additional/java"
}
javaScript {
source {
srcDir "additional/javascript"
exclude "**/old_*.js"
}
}
}
}
}
}
§
Adding extra source sets
If your Play application has additional sources that exist in non-standard directories, you can add extra
source sets that Gradle will automatically add to the appropriate compile tasks.
Example 555. Adding extra source sets to a Play application
build.gradle
model {
components {
play {
sources {
extraJava(JavaSourceSet) {
source.srcDir "extra/java"
}
extraTwirl(TwirlSourceSet) {
source.srcDir "extra/twirl"
}
extraRoutes(RoutesSourceSet) {
source.srcDir "extra/routes"
}
}
}
}
}
Configuring compiler options
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§
Configuring compiler options
If your Play application requires additional Scala compiler flags, you can add these arguments directly to the
Scala compiler task.
Example 556. Configuring Scala compiler options
build.gradle
model {
components {
play {
binaries.all {
tasks.withType(PlatformScalaCompile) {
scalaCompileOptions.additionalParameters = ["-feature", "-language:imp
}
}
}
}
}
§
Configuring routes style
Note: The injected router is only supported in Play Framework 2.4 or better.
If your Play application’s router uses dependency injection to access your controllers, you’ll need to
configure your application to not use the default static router. Under the covers, the Play plugin is using the InjectedRou
instead of the default StaticRoutesGenerator to generate the router classes.
Example 557. Configuring routes style
build.gradle
model {
components {
play {
injectedRoutesGenerator = true
}
}
}
§
Configuring Twirl templates
A custom Twirl template format can be configured independently for each Twirl source set. See the
TwirlSourceSet for an example.
Injecting a custom asset pipeline
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§
Injecting a custom asset pipeline
Gradle Play support comes with a simplistic asset processing pipeline that minifies JavaScript assets.
However, many organizations have their own custom pipeline for processing assets. You can easily hook the
results of your pipeline into the Play binary by utilizing the PublicAssets property on the binary.
Example 558. Configuring a custom asset pipeline
build.gradle
model {
components {
play {
binaries.all { binary ->
tasks.create("addCopyrightToPlay${binary.name.capitalize()}Assets", AddCop
source "raw-assets"
copyrightFile = project.file('copyright.txt')
destinationDir = project.file("${buildDir}/play${binary.name.capitaliz
// Hook this task into the binary
binary.assets.addAssetDir destinationDir
binary.assets.builtBy copyrightTask
}
}
}
}
}
class AddCopyrights extends SourceTask {
@InputFile
File copyrightFile
@OutputDirectory
File destinationDir
@TaskAction
void generateAssets() {
String copyright = copyrightFile.text
getSource().files.each { File file ->
File outputFile = new File(destinationDir, file.name)
outputFile.text = "${copyright}\n${file.text}"
}
}
}
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Multi-project Play applications
§
Multi-project Play applications
Play applications can be built in multi-project builds as well. Simply apply the play plugin in the appropriate
subprojects and create any project dependencies on the play configuration.
Example 559. Configuring dependencies on Play subprojects
build.gradle
dependencies {
play project(":admin")
play project(":user")
play project(":util")
}
See the play/multiproject sample provided in the Gradle distribution for a working example.
§
Packaging a Play application for distribution
Gradle provides the capability to package your Play application so that it can easily be distributed and run in
a target environment. The distribution package (zip file) contains the Play binary jars, all dependencies, and
generated scripts that set up the classpath and run the application in a Play-specific Netty container.
The distribution can be created by running the dist lifecycle task and places the distribution in the $buildDir/distrib
directory. Alternatively, one can validate the contents by running the stage lifecycle task which copies the
files to the $buildDir/stage directory using the layout of the distribution package.
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Table 110. Play distribution tasks
Task name
Depends on
Type
Description
Generates scripts to run
createPlayBinaryStartScripts -
CreateStartScripts the
Play
application
distribution.
Copies
stagePlayBinaryDist
playBinary, createPlayBinaryStartScripts
Copy
all
jar
dependencies
files,
and
scripts into a staging
directory.
Bundles
Zip
createPlayBinaryZipDist
the
application
standalone
Play
as
a
distribution
packaged as a zip.
Bundles
Tar
createPlayBinaryTarDist
the
application
standalone
Play
as
a
distribution
packaged as a tar.
Task
Lifecycle task for staging
stage
stagePlayBinaryDist
dist
createPlayBinaryZipDist, createPlayBinaryTarDist
Task
creating
a Play distribution.
Lifecycle
task
a
for
Play
distribution.
§
Adding additional files to your Play application distribution
You can add additional files to the distribution package using the Distribution API.
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Example 560. Add extra files to a Play application distribution
build.gradle
model {
distributions {
playBinary {
contents {
from("README.md")
from("scripts") {
into "bin"
}
}
}
}
}
§
Building a Play application with an IDE
If you want to generate IDE metadata configuration for your Play project, you need to apply the appropriate
IDE plugin. Gradle supports generating IDE metadata for IDEA only for Play projects at this time.
To generate IDEA’s metadata, apply the idea plugin along with the play plugin.
Example 561. Applying both the Play and IDEA plugins
build.gradle
plugins {
id 'play'
id 'idea'
}
Source code generated by routes and Twirl templates cannot be generated by IDEA directly, so changes
made to those files will not affect compilation until the next Gradle build. You can run the Play application
with Gradle in continuous build to automatically rebuild and reload the application whenever something
changes.
§
Resources
For additional information about developing Play applications:
Play types in the Gradle DSL Guide:
PlayApplicationBinarySpec
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PlayApplicationSpec
PlayPlatform
JvmClasses
PublicAssets
PlayDistributionContainer
JavaScriptMinify
PlayRun
RoutesCompile
TwirlCompile
Play Framework Documentation.
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Building native software
Note: Support for building native software is currently incubating. Please be aware that the DSL,
APIs and other configuration may change in later Gradle versions.
The native software plugins add support for building native software components, such as executables or
shared libraries, from code written in C++, C and other languages. While many excellent build tools exist for
this space of software development, Gradle offers developers its trademark power and flexibility together
with dependency management practices more traditionally found in the JVM development space.
The native software plugins make use of the Gradle software model.
§
Features
The native software plugins provide:
Support for building native libraries and applications on Windows, Linux, macOS and other platforms.
Support for several source languages.
Support for building different variants of the same software, for different architectures, operating systems, or
for any purpose.
Incremental parallel compilation, precompiled headers.
Dependency management between native software components.
Unit test execution.
Generate Visual studio solution and project files.
Deep integration with various tool chain, including discovery of installed tool chains.
§
Supported languages
The following source languages are currently supported:
C
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C++
Objective-C
Objective-C++
Assembly
Windows resources
§
Tool chain support
Gradle offers the ability to execute the same build using different tool chains. When you build a native binary,
Gradle will attempt to locate a tool chain installed on your machine that can build the binary. You can fine
tune exactly how this works, see the section called “Tool chains” for details.
The following tool chains are supported:
Operating System
Tool Chain
Linux
GCC
Linux
Clang
macOS
XCode
Notes
Uses the Clang tool chain bundled with
XCode.
Windows
Visual C++
Windows XP and later, Visual C++
2010/2012/2013/2015/2017.
Windows
GCC with Cygwin 32
Windows XP and later.
Windows
GCC with MinGW
Windows XP and later. Mingw-w64 is
currently not supported.
The following tool chains are unofficially supported. They generally work fine, but are not tested
continuously:
Operating System
Tool Chain
macOS
GCC from Macports
macOS
Clang from Macports
Windows
GCC with Cygwin 64
Notes
Windows XP and later.
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UNIX-like
GCC
UNIX-like
Clang
§
Tool chain installation
Note: Note that if you are using GCC then you currently need to install support for C++, even if you
are not building from C++ source. This restriction will be removed in a future Gradle version.
To build native software, you will need to have a compatible tool chain installed:
§
Windows
To build on Windows, install a compatible version of Visual Studio. The native plugins will discover the Visual
Studio installations and select the latest version. There is no need to mess around with environment
variables or batch scripts. This works fine from a Cygwin shell or the Windows command-line.
Alternatively, you can install Cygwin with GCC or MinGW. Clang is currently not supported.
§
macOS
To build on macOS, you should install XCode. The native plugins will discover the XCode installation using
the system PATH.
The native plugins also work with GCC and Clang bundled with Macports. To use one of the Macports tool
chains, you will need to make the tool chain the default using the port select command and add
Macports to the system PATH.
§
Linux
To build on Linux, install a compatible version of GCC or Clang. The native plugins will discover GCC or
Clang using the system PATH.
§
Native software model
The native software model builds on the base Gradle software model.
To build native software using Gradle, your project should define one or more native components . Each
component represents either an executable or a library that Gradle should build. A project can define any
number of components. Gradle does not define any components by default.
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For each component, Gradle defines a source set for each language that the component can be built from.
A source set is essentially just a set of source directories containing source files. For example, when you
apply the c plugin and define a library called helloworld, Gradle will define, by default, a source set
containing the C source files in the src/helloworld/c directory. It will use these source files to build the helloworld
library. This is described in more detail below.
For each component, Gradle defines one or more binaries as output. To build a binary, Gradle will take the
source files defined for the component, compile them as appropriate for the source language, and link the
result into a binary file. For an executable component, Gradle can produce executable binary files. For a
library component, Gradle can produce both static and shared library binary files. For example, when you
define a library called helloworld and build on Linux, Gradle will, by default, produce libhelloworld.so
and libhelloworld.a binaries.
In many cases, more than one binary can be produced for a component. These binaries may vary based on
the tool chain used to build, the compiler/linker flags supplied, the dependencies provided, or additional
source files provided. Each native binary produced for a component is referred to as a variant . Binary
variants are discussed in detail below.
§
Parallel Compilation
Gradle uses the single build worker pool to concurrently compile and link native components, by default. No
special configuration is required to enable concurrent building.
By default, the worker pool size is determined by the number of available processors on the build machine
(as reported to the build JVM). To explicitly set the number of workers use the --max-workers
command-line option or org.gradle.workers.max system property. There is generally no need to
change this setting from its default.
The build worker pool is shared across all build tasks. This means that when using parallel project execution,
the maximum number of concurrent individual compilation operations does not increase. For example, if the
build machine has 4 processing cores and 10 projects are compiling in parallel, Gradle will only use 4 total
workers, not 40.
§
Building a library
To build either a static or shared native library, you define a library component in the components
container. The following sample defines a library called hello:
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Example 562. Defining a library component
build.gradle
model {
components {
hello(NativeLibrarySpec)
}
}
A library component is represented using NativeLibrarySpec. Each library component can produce at
least one shared library binary (SharedLibraryBinarySpec) and at least one static library binary (
StaticLibraryBinarySpec).
§
Building an executable
To build a native executable, you define an executable component in the components container. The
following sample defines an executable called main:
Example 563. Defining executable components
build.gradle
model {
components {
main(NativeExecutableSpec) {
sources {
c.lib library: "hello"
}
}
}
}
An executable component is represented using NativeExecutableSpec. Each executable component
can produce at least one executable binary (NativeExecutableBinarySpec).
For each component defined, Gradle adds a FunctionalSourceSet with the same name. Each of these
functional source sets will contain a language-specific source set for each of the languages supported by the
project.
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Assembling or building dependents
§
Assembling or building dependents
Sometimes, you may need to assemble (compile and link) or build (compile, link and test) a component or
binary and its dependents (things that depend upon the component or binary). The native software model
provides tasks that enable this capability. First, the dependent components report gives insight about the
relationships between each component. Second, the build and assemble dependents tasks allow you to
assemble or build a component and its dependents in one step.
In the following example, the build file defines OpenSSL as a dependency of libUtil and libUtil as a
dependency of LinuxApp and WindowsApp. Test suites are treated similarly. Dependents can be thought
of as reverse dependencies.
Figure 20. Dependent Components Example
Note: By following the dependencies backwards, you can see LinuxApp and WindowsApp are
dependents of libUtil. When libUtil is changed, Gradle will need to recompile or relink LinuxApp
and WindowsApp.
When you assemble dependents of a component, the component and all of its dependents are compiled
and linked, including any test suite binaries. Gradle’s up-to-date checks are used to only compile or link if
something has changed. For instance, if you have changed source files in a way that do not affect the
headers of your project, Gradle will be able to skip compilation for dependent components and only need to
re-link with the new library. Tests are not run when assembling a component.
When you build dependents of a component, the component and all of its dependent binaries are compiled,
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linked and checked . Checking components means running any check task including executing any test
suites, so tests are run when building a component.
In the following sections, we will demonstrate the usage of the assembleDependents*, buildDependents*
and dependentComponents tasks with a sample build that contains a CUnit test suite. The build script for
the sample is the following:
Example 564. Sample build
build.gradle
apply plugin: "c"
apply plugin: 'cunit-test-suite'
model {
flavors {
passing
failing
}
platforms {
x86 {
architecture "x86"
}
}
components {
operators(NativeLibrarySpec) {
targetPlatform "x86"
}
}
testSuites {
operatorsTest(CUnitTestSuiteSpec) {
testing $.components.operators
}
}
}
Note: The code for this example can be found at samples/native-binaries/cunit in the ‘-all’
distribution of Gradle.
§
Dependent components report
Gradle provides a report that you can run from the command-line that shows a graph of components in your
project and components that depend upon them. The following is an example of running gradle dependentComponent
on the sample project:
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Example 565. Dependent components report
Output of gradle dependentComponents
> gradle dependentComponents
:dependentComponents
-----------------------------------------------------------Root project
-----------------------------------------------------------operators - Components that depend on native library 'operators'
+--- operators:failingSharedLibrary
+--- operators:failingStaticLibrary
+--- operators:passingSharedLibrary
\--- operators:passingStaticLibrary
Some test suites were not shown, use --test-suites or --all to show them.
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
Note: See DependentComponentsReport API documentation for more details.
By default, non-buildable binaries and test suites are hidden from the report. The dependentComponents
task provides options that allow you to see all dependents by using the --all option:
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Example 566. Dependent components report
Output of gradle dependentComponents --all
> gradle dependentComponents --all
:dependentComponents
-----------------------------------------------------------Root project
-----------------------------------------------------------operators - Components that depend on native library 'operators'
+--- operators:failingSharedLibrary
+--- operators:failingStaticLibrary
|
\--- operatorsTest:failingCUnitExe (t)
+--- operators:passingSharedLibrary
\--- operators:passingStaticLibrary
\--- operatorsTest:passingCUnitExe (t)
operatorsTest - Components that depend on Cunit test suite 'operatorsTest'
+--- operatorsTest:failingCUnitExe (t)
\--- operatorsTest:passingCUnitExe (t)
(t) - Test suite binary
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
Here is the corresponding report for the operators component, showing dependents of all its binaries:
Example 567. Report of components that depends on the operators component
Output of gradle dependentComponents --component operators
> gradle dependentComponents --component operators
:dependentComponents
-----------------------------------------------------------Root project
-----------------------------------------------------------operators - Components that depend on native library 'operators'
+--- operators:failingSharedLibrary
+--- operators:failingStaticLibrary
+--- operators:passingSharedLibrary
\--- operators:passingStaticLibrary
Some test suites were not shown, use --test-suites or --all to show them.
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
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Here is the corresponding report for the operators component, showing dependents of all its binaries,
including test suites:
Example 568. Report of components that depends on the operators component, including test suites
Output of gradle dependentComponents --test-suites --component operators
> gradle dependentComponents --test-suites --component operators
:dependentComponents
-----------------------------------------------------------Root project
-----------------------------------------------------------operators - Components that depend on native library 'operators'
+--- operators:failingSharedLibrary
+--- operators:failingStaticLibrary
|
\--- operatorsTest:failingCUnitExe (t)
+--- operators:passingSharedLibrary
\--- operators:passingStaticLibrary
\--- operatorsTest:passingCUnitExe (t)
(t) - Test suite binary
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
§
Assembling dependents
For each NativeBinarySpec, Gradle will create a task named assembleDependents${component.name}${binar
that assembles (compile and link) the binary and all of its dependent binaries.
For each NativeComponentSpec, Gradle will create a task named assembleDependents${component.name}
that assembles all the binaries of the component and all of their dependent binaries.
For example, to assemble the dependents of the "passing" flavor of the "static" library binary of the
"operators" component, you would run the assembleDependentsOperatorsPassingStaticLibrary
task:
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Example 569. Assemble components that depends on the passing/static binary of the operators component
Output of gradle assembleDependentsOperatorsPassingStaticLibrary --max-workers=1
> gradle assembleDependentsOperatorsPassingStaticLibrary --max-workers=1
:compileOperatorsTestPassingCUnitExeOperatorsC
:operatorsTestCUnitLauncher
:compileOperatorsTestPassingCUnitExeOperatorsTestC
:compileOperatorsTestPassingCUnitExeOperatorsTestCunitLauncher
:linkOperatorsTestPassingCUnitExe
:operatorsTestPassingCUnitExe
:assembleDependentsOperatorsTestPassingCUnitExe
:compileOperatorsPassingStaticLibraryOperatorsC
:createOperatorsPassingStaticLibrary
:operatorsPassingStaticLibrary
:assembleDependentsOperatorsPassingStaticLibrary
BUILD SUCCESSFUL in 0s
7 actionable tasks: 7 executed
In the output above, the targeted binary gets assembled as well as the test suite binary that depends on it.
You can also assemble all of the dependents of a component (i.e. of all its binaries/variants) using the
corresponding component task, e.g. assembleDependentsOperators. This is useful if you have many
combinations of build types, flavors and platforms and want to assemble all of them.
§
Building dependents
For each NativeBinarySpec, Gradle will create a task named buildDependents${component.name}${binary.v
that builds (compile, link and check) the binary and all of its dependent binaries.
For each NativeComponentSpec, Gradle will create a task named buildDependents${component.name}
that builds all the binaries of the component and all of their dependent binaries.
For example, to build the dependents of the "passing" flavor of the "static" library binary of the "operators"
component, you would run the buildDependentsOperatorsPassingStaticLibrary task:
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Example 570. Build components that depends on the passing/static binary of the operators component
Output of gradle buildDependentsOperatorsPassingStaticLibrary --max-workers=1
> gradle buildDependentsOperatorsPassingStaticLibrary --max-workers=1
:compileOperatorsTestPassingCUnitExeOperatorsC
:operatorsTestCUnitLauncher
:compileOperatorsTestPassingCUnitExeOperatorsTestC
:compileOperatorsTestPassingCUnitExeOperatorsTestCunitLauncher
:linkOperatorsTestPassingCUnitExe
:operatorsTestPassingCUnitExe
:installOperatorsTestPassingCUnitExe
:runOperatorsTestPassingCUnitExe
:checkOperatorsTestPassingCUnitExe
:buildDependentsOperatorsTestPassingCUnitExe
:compileOperatorsPassingStaticLibraryOperatorsC
:createOperatorsPassingStaticLibrary
:operatorsPassingStaticLibrary
:buildDependentsOperatorsPassingStaticLibrary
BUILD SUCCESSFUL in 0s
9 actionable tasks: 9 executed
In the output above, the targeted binary as well as the test suite binary that depends on it are built and the
test suite has run.
You can also build all of the dependents of a component (i.e. of all its binaries/variants) using the
corresponding component task, e.g. buildDependentsOperators.
§
Tasks
For each NativeBinarySpec that can be produced by a build, a single lifecycle task is constructed that
can be used to create that binary, together with a set of other tasks that do the actual work of compiling,
linking or assembling the binary.
Component Type
Native Binary Type
NativeExecutableSpec
NativeExecutableBinarySpec ${component.name} Executable
${project.buildDir} /exe/ ${componen
NativeLibrarySpec
SharedLibraryBinarySpec
${component.name} SharedLibrary
${project.buildDir} /libs/ ${compone
NativeLibrarySpec
StaticLibraryBinarySpec
${component.name} StaticLibrary
${project.buildDir} /libs/ ${compone
Check tasks
Lifecycle task
Location of created binary
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§
Check tasks
For each NativeBinarySpec that can be produced by a build, a single check task is constructed that can
be used to assemble and check that binary.
Component Type
Native Binary Type
Check task
NativeExecutableSpec
NativeExecutableBinarySpec
check ${component.name} Executable
NativeLibrarySpec
SharedLibraryBinarySpec
check ${component.name} SharedLibrary
NativeLibrarySpec
StaticLibraryBinarySpec
check ${component.name} StaticLibrary
The built-in check task depends on all the check tasks for binaries in the project. Without either CUnit or
GoogleTest plugins, the binary check task only depends on the lifecycle task that assembles the binary, see
the section called “Tasks”.
When the CUnit or GoogleTest plugins are applied, the task that executes the test suites for a component
are automatically wired to the appropriate check task .
You can also add custom check tasks as follows:
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Example 571. Adding a custom check task
build.gradle
apply plugin: "cpp"
// You don't need to apply the plugin below if you're already using CUnit or GoogleTest su
apply plugin: TestingModelBasePlugin
task myCustomCheck {
doLast {
println 'Executing my custom check'
}
}
model {
components {
hello(NativeLibrarySpec) {
binaries.all {
// Register our custom check task to all binaries of this component
checkedBy $.tasks.myCustomCheck
}
}
}
}
Note: The code for this example can be found at samples/native-binaries/custom-check
in the ‘-all’ distribution of Gradle.
Now, running check or any of the check tasks for the hello binaries will run the custom check task:
Example 572. Running checks for a given binary
Output of gradle checkHelloSharedLibrary
> gradle checkHelloSharedLibrary
:myCustomCheck
Executing my custom check
:checkHelloSharedLibrary
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
§
Working with shared libraries
For each executable binary produced, the cpp plugin provides an install${binary.name} task, which
creates a development install of the executable, along with the shared libraries it requires. This allows you to
run the executable without needing to install the shared libraries in their final locations.
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Finding out more about your project
§
Finding out more about your project
Gradle provides a report that you can run from the command-line that shows some details about the
components and binaries that your project produces. To use this report, just run gradle components.
Below is an example of running this report for one of the sample projects:
Example 573. The components report
Output of gradle components
> gradle components
:components
-----------------------------------------------------------Root project
-----------------------------------------------------------Native library 'hello'
---------------------Source sets
C++ source 'hello:cpp'
srcDir: src/hello/cpp
Binaries
Shared library 'hello:sharedLibrary'
build using task: :helloSharedLibrary
build type: build type 'debug'
flavor: flavor 'default'
target platform: platform 'current'
tool chain: Tool chain 'clang' (Clang)
shared library file: build/libs/hello/shared/libhello.dylib
Static library 'hello:staticLibrary'
build using task: :helloStaticLibrary
build type: build type 'debug'
flavor: flavor 'default'
target platform: platform 'current'
tool chain: Tool chain 'clang' (Clang)
static library file: build/libs/hello/static/libhello.a
Native executable 'main'
-----------------------Source sets
C++ source 'main:cpp'
srcDir: src/main/cpp
Binaries
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Executable 'main:executable'
build using task: :mainExecutable
install using task: :installMainExecutable
build type: build type 'debug'
flavor: flavor 'default'
target platform: platform 'current'
tool chain: Tool chain 'clang' (Clang)
executable file: build/exe/main/main
Note: currently not all plugins register their components, so some components may not be v
Page 650 of 717
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
§
Language support
Presently, Gradle supports building native software from any combination of source languages listed below.
A native binary project will contain one or more named FunctionalSourceSet instances (eg 'main', 'test',
etc), each of which can contain LanguageSourceSets containing source files, one for each language.
C
C++
Objective-C
Objective-C++
Assembly
Windows resources
§
C++ sources
C++ language support is provided by means of the 'cpp' plugin.
Example 574. The 'cpp' plugin
build.gradle
apply plugin: 'cpp'
C++ sources to be included in a native binary are provided via a CppSourceSet, which defines a set of C++
source files and optionally a set of exported header files (for a library). By default, for any named component
the CppSourceSet contains .cpp source files in src/${name}/cpp, and header files in src/${name}/headers
.
While the cpp plugin defines these default locations for each CppSourceSet, it is possible to extend or
override these defaults to allow for a different project layout.
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Example 575. C++ source set
build.gradle
sources {
cpp {
source {
srcDir "src/source"
include "**/*.cpp"
}
}
}
For a library named 'main', header files in src/main/headers are considered the "public" or "exported"
headers. Header files that should not be exported should be placed inside the src/main/cpp directory
(though be aware that such header files should always be referenced in a manner relative to the file
including them).
§
C sources
C language support is provided by means of the 'c' plugin.
Example 576. The 'c' plugin
build.gradle
apply plugin: 'c'
C sources to be included in a native binary are provided via a CSourceSet, which defines a set of C source
files and optionally a set of exported header files (for a library). By default, for any named component the
CSourceSet contains .c source files in src/${name}/c, and header files in src/${name}/headers.
While the c plugin defines these default locations for each CSourceSet, it is possible to extend or override
these defaults to allow for a different project layout.
Example 577. C source set
build.gradle
sources {
c {
source {
srcDir "src/source"
include "**/*.c"
}
exportedHeaders {
srcDir "src/include"
}
}
}
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For a library named 'main', header files in src/main/headers are considered the "public" or "exported"
headers. Header files that should not be exported should be placed inside the src/main/c directory
(though be aware that such header files should always be referenced in a manner relative to the file
including them).
§
Assembler sources
Assembly language support is provided by means of the 'assembler' plugin.
Example 578. The 'assembler' plugin
build.gradle
apply plugin: 'assembler'
Assembler sources to be included in a native binary are provided via a AssemblerSourceSet, which
defines a set of Assembler source files. By default, for any named component the AssemblerSourceSet
contains .s source files under src/${name}/asm.
§
Objective-C sources
Objective-C language support is provided by means of the 'objective-c' plugin.
Example 579. The 'objective-c' plugin
build.gradle
apply plugin: 'objective-c'
Objective-C sources to be included in a native binary are provided via a ObjectiveCSourceSet, which
defines a set of Objective-C source files. By default, for any named component the
ObjectiveCSourceSet contains .m source files under src/${name}/objectiveC.
§
Objective-C++ sources
Objective-C++ language support is provided by means of the 'objective-cpp' plugin.
Example 580. The 'objective-cpp' plugin
build.gradle
apply plugin: 'objective-cpp'
Objective-C++ sources to be included in a native binary are provided via a ObjectiveCppSourceSet,
which defines a set of Objective-C++ source files. By default, for any named component the
ObjectiveCppSourceSet contains .mm source files under src/${name}/objectiveCpp.
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Configuring the compiler, assembler and linker
§
Configuring the compiler, assembler and linker
Each binary to be produced is associated with a set of compiler and linker settings, which include
command-line arguments as well as macro definitions. These settings can be applied to all binaries, an
individual binary, or selectively to a group of binaries based on some criteria.
Example 581. Settings that apply to all binaries
build.gradle
model {
binaries {
all {
// Define a preprocessor macro for every binary
cppCompiler.define "NDEBUG"
// Define toolchain-specific compiler and linker options
if (toolChain in Gcc) {
cppCompiler.args "-O2", "-fno-access-control"
linker.args "-Xlinker", "-S"
}
if (toolChain in VisualCpp) {
cppCompiler.args "/Zi"
linker.args "/DEBUG"
}
}
}
}
Each binary is associated with a particular NativeToolChain, allowing settings to be targeted based on
this value.
It is easy to apply settings to all binaries of a particular type:
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Example 582. Settings that apply to all shared libraries
build.gradle
// For any shared library binaries built with Visual C++,
// define the DLL_EXPORT macro
model {
binaries {
withType(SharedLibraryBinarySpec) {
if (toolChain in VisualCpp) {
cCompiler.args "/Zi"
cCompiler.define "DLL_EXPORT"
}
}
}
}
Furthermore, it is possible to specify settings that apply to all binaries produced for a particular executable
or library component:
Example 583. Settings that apply to all binaries produced for the 'main' executable component
build.gradle
model {
components {
main(NativeExecutableSpec) {
targetPlatform "x86"
binaries.all {
if (toolChain in VisualCpp) {
sources {
platformAsm(AssemblerSourceSet) {
source.srcDir "src/main/asm_i386_masm"
}
}
assembler.args "/Zi"
} else {
sources {
platformAsm(AssemblerSourceSet) {
source.srcDir "src/main/asm_i386_gcc"
}
}
assembler.args "-g"
}
}
}
}
}
The example above will apply the supplied configuration to all executable binaries built.
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Similarly, settings can be specified to target binaries for a component that are of a particular type: eg all
shared libraries for the main library component.
Example 584. Settings that apply only to shared libraries produced for the 'main' library component
build.gradle
model {
components {
main(NativeLibrarySpec) {
binaries.withType(SharedLibraryBinarySpec) {
// Define a preprocessor macro that only applies to shared libraries
cppCompiler.define "DLL_EXPORT"
}
}
}
}
§
Windows Resources
When using the VisualCpp tool chain, Gradle is able to compile Window Resource (rc) files and link them
into a native binary. This functionality is provided by the 'windows-resources' plugin.
Example 585. The 'windows-resources' plugin
build.gradle
apply plugin: 'windows-resources'
Windows resources to be included in a native binary are provided via a WindowsResourceSet, which
defines a set of Windows Resource source files. By default, for any named component the
WindowsResourceSet contains .rc source files under src/${name}/rc.
As with other source types, you can configure the location of the windows resources that should be included
in the binary.
Example 586. Configuring the location of Windows resource sources
build-resource-only-dll.gradle
sources {
rc {
source {
srcDirs "src/hello/rc"
}
exportedHeaders {
srcDirs "src/hello/headers"
}
}
}
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You are able to construct a resource-only library by providing Windows Resource sources with no other
language sources, and configure the linker as appropriate:
Example 587. Building a resource-only dll
build-resource-only-dll.gradle
model {
components {
helloRes(NativeLibrarySpec) {
binaries.all {
rcCompiler.args "/v"
linker.args "/noentry", "/machine:x86"
}
sources {
rc {
source {
srcDirs "src/hello/rc"
}
exportedHeaders {
srcDirs "src/hello/headers"
}
}
}
}
}
}
The example above also demonstrates the mechanism of passing extra command-line arguments to the
resource compiler. The rcCompiler extension is of type PreprocessingTool.
§
Library Dependencies
Dependencies for native components are binary libraries that export header files. The header files are used
during compilation, with the compiled binary dependency being used during linking and execution. Header
files should be organized into subdirectories to prevent clashes of commonly named headers. For instance,
if your mylib project has a logging.h header, it will make it less likely the wrong header is used if you
include it as "mylib/logging.h" instead of "logging.h".
§
Dependencies within the same project
A set of sources may depend on header files provided by another binary component within the same project.
A common example is a native executable component that uses functions provided by a separate native
library component.
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Such a library dependency can be added to a source set associated with the executable component:
Example 588. Providing a library dependency to the source set
build.gradle
sources {
cpp {
lib library: "hello"
}
}
Alternatively, a library dependency can be provided directly to the NativeExecutableBinarySpec for the
executable.
Example 589. Providing a library dependency to the binary
build.gradle
model {
components {
hello(NativeLibrarySpec) {
sources {
c {
source {
srcDir "src/source"
include "**/*.c"
}
exportedHeaders {
srcDir "src/include"
}
}
}
}
main(NativeExecutableSpec) {
sources {
cpp {
source {
srcDir "src/source"
include "**/*.cpp"
}
}
}
binaries.all {
// Each executable binary produced uses the 'hello' static library binary
lib library: 'hello', linkage: 'static'
}
}
}
}
Project Dependencies
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§
Project Dependencies
For a component produced in a different Gradle project, the notation is similar.
Example 590. Declaring project dependencies
build.gradle
project(":lib") {
apply plugin: "cpp"
model {
components {
main(NativeLibrarySpec)
}
// For any shared library binaries built with Visual C++,
// define the DLL_EXPORT macro
binaries {
withType(SharedLibraryBinarySpec) {
if (toolChain in VisualCpp) {
cppCompiler.define "DLL_EXPORT"
}
}
}
}
}
project(":exe") {
apply plugin: "cpp"
model {
components {
main(NativeExecutableSpec) {
sources {
cpp {
lib project: ':lib', library: 'main'
}
}
}
}
}
}
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Precompiled Headers
§
Precompiled Headers
Precompiled headers are a performance optimization that reduces the cost of compiling widely used headers
multiple times. This feature precompiles a header such that the compiled object file can be reused when
compiling each source file rather than recompiling the header each time. This support is available for C,
C++, Objective-C, and Objective-C++ builds.
To configure a precompiled header, first a header file needs to be defined that includes all of the headers
that should be precompiled. It must be specified as the first included header in every source file where the
precompiled header should be used. It is assumed that this header file, and any headers it contains, make
use of header guards so that they can be included in an idempotent manner. If header guards are not used
in a header file, it is possible the header could be compiled more than once and could potentially lead to a
broken build.
Example 591. Creating a precompiled header file
src/hello/headers/pch.h
#ifndef PCH_H
#define PCH_H
#include <iostream>
#include "hello.h"
#endif
Example 592. Including a precompiled header file in a source file
src/hello/cpp/hello.cpp
#include "pch.h"
void LIB_FUNC Greeter::hello () {
std::cout << "Hello world!" << std::endl;
}
Precompiled headers are specified on a source set. Only one precompiled header file can be specified on a
given source set and will be applied to all source files that declare it as the first include. If a source files does
not include this header file as the first header, the file will be compiled in the normal manner (without making
use of the precompiled header object file). The string provided should be the same as that which is used in
the "#include" directive in the source files.
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Example 593. Configuring a precompiled header
build.gradle
model {
components {
hello(NativeLibrarySpec) {
sources {
cpp {
preCompiledHeader "pch.h"
}
}
}
}
}
A precompiled header must be included in the same way for all files that use it. Usually, this means the
header file should exist in the source set "headers" directory or in a directory included on the compiler
include path.
§
Native Binary Variants
For each executable or library defined, Gradle is able to build a number of different native binary variants.
Examples of different variants include debug vs release binaries, 32-bit vs 64-bit binaries, and binaries
produced with different custom preprocessor flags.
Binaries produced by Gradle can be differentiated on build type, platform, and flavor. For each of these
'variant dimensions', it is possible to specify a set of available values as well as target each component at
one, some or all of these. For example, a plugin may define a range of support platforms, but you may
choose to only target Windows-x86 for a particular component.
§
Build types
A build type determines various non-functional aspects of a binary, such as whether debug information is
included, or what optimisation level the binary is compiled with. Typical build types are 'debug' and 'release',
but a project is free to define any set of build types.
Example 594. Defining build types
build.gradle
model {
buildTypes {
debug
release
}
}
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If no build types are defined in a project, then a single, default build type called 'debug' is added.
For a build type, a Gradle project will typically define a set of compiler/linker flags per tool chain.
Example 595. Configuring debug binaries
build.gradle
model {
binaries {
all {
if (toolChain in Gcc && buildType == buildTypes.debug) {
cppCompiler.args "-g"
}
if (toolChain in VisualCpp && buildType == buildTypes.debug) {
cppCompiler.args '/Zi'
cppCompiler.define 'DEBUG'
linker.args '/DEBUG'
}
}
}
}
Note: At this stage, it is completely up to the build script to configure the relevant compiler/linker
flags for each build type. Future versions of Gradle will automatically include the appropriate debug
flags for any 'debug' build type, and may be aware of various levels of optimisation as well.
§
Platform
An executable or library can be built to run on different operating systems and cpu architectures, with a
variant being produced for each platform. Gradle defines each OS/architecture combination as a
NativePlatform, and a project may define any number of platforms. If no platforms are defined in a
project, then a single, default platform 'current' is added.
Note: Presently, a Platform consists of a defined operating system and architecture. As we
continue to develop the native binary support in Gradle, the concept of Platform will be extended to
include things like C-runtime version, Windows SDK, ABI, etc. Sophisticated builds may use the
extensibility of Gradle to apply additional attributes to each platform, which can then be queried to
specify particular includes, preprocessor macros or compiler arguments for a native binary.
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Example 596. Defining platforms
build.gradle
model {
platforms {
x86 {
architecture "x86"
}
x64 {
architecture "x86_64"
}
itanium {
architecture "ia-64"
}
}
}
For a given variant, Gradle will attempt to find a NativeToolChain that is able to build for the target
platform. Available tool chains are searched in the order defined. See the tool chains section below for more
details.
§
Flavor
Each component can have a set of named flavors, and a separate binary variant can be produced for
each flavor. While the build type and target platform variant dimensions have a defined meaning in
Gradle, each project is free to define any number of flavors and apply meaning to them in any way.
An example of component flavors might differentiate between 'demo', 'paid' and 'enterprise' editions of the
component, where the same set of sources is used to produce binaries with different functions.
Example 597. Defining flavors
build.gradle
model {
flavors {
english
french
}
components {
hello(NativeLibrarySpec) {
binaries.all {
if (flavor == flavors.french) {
cppCompiler.define "FRENCH"
}
}
}
}
}
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In the example above, a library is defined with a 'english' and 'french' flavor. When compiling the 'french'
variant, a separate macro is defined which leads to a different binary being produced.
If no flavor is defined for a component, then a single default flavor named 'default' is used.
§
Selecting the build types, platforms and flavors for a component
For a default component, Gradle will attempt to create a native binary variant for each and every
combination of buildType and flavor defined for the project. It is possible to override this on a
per-component basis, by specifying the set of targetBuildTypes and/or targetFlavors. By default,
Gradle will build for the default platform, see above, unless specified explicitly on a per-component basis by
specifying a set of targetPlatforms.
Example 598. Targeting a component at particular platforms
build.gradle
model {
components {
hello(NativeLibrarySpec) {
targetPlatform "x86"
targetPlatform "x64"
}
main(NativeExecutableSpec) {
targetPlatform "x86"
targetPlatform "x64"
sources {
cpp.lib library: 'hello', linkage: 'static'
}
}
}
}
Here you can see that the TargetedNativeComponent.targetPlatform(java.lang.String)
method is used to specify a platform that the NativeExecutableSpec named main should be built for.
A
similar
mechanism
exists
for
TargetedNativeComponent.targetBuildTypes(java.lang.String[])
selecting
and
TargetedNativeComponent.targetFlavors(java.lang.String[]).
§
Building all possible variants
When a set of build types, target platforms, and flavors is defined for a component, a NativeBinarySpec
model element is created for every possible combination of these. However, in many cases it is not possible
to build a particular variant, perhaps because no tool chain is available to build for a particular platform.
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If a binary variant cannot be built for any reason, then the NativeBinarySpec associated with that variant
will not be buildable. It is possible to use this property to create a task to generate all possible variants on
a particular machine.
Example 599. Building all possible variants
build.gradle
model {
tasks {
buildAllExecutables(Task) {
dependsOn $.binaries.findAll { it.buildable }
}
}
}
§
Tool chains
A single build may utilize different tool chains to build variants for different platforms. To this end, the core
'native-binary' plugins will attempt to locate and make available supported tool chains. However, the set of
tool chains for a project may also be explicitly defined, allowing additional cross-compilers to be configured
as well as allowing the install directories to be specified.
§
Defining tool chains
The supported tool chain types are:
Gcc
Clang
VisualCpp
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Example 600. Defining tool chains
build.gradle
model {
toolChains {
visualCpp(VisualCpp) {
// Specify the installDir if Visual Studio cannot be located
// installDir "C:/Apps/Microsoft Visual Studio 10.0"
}
gcc(Gcc) {
// Uncomment to use a GCC install that is not in the PATH
// path "/usr/bin/gcc"
}
clang(Clang)
}
}
Each tool chain implementation allows for a certain degree of configuration (see the API documentation for
more details).
§
Using tool chains
It is not necessary or possible to specify the tool chain that should be used to build. For a given variant,
Gradle will attempt to locate a NativeToolChain that is able to build for the target platform. Available tool
chains are searched in the order defined.
Note: When a platform does not define an architecture or operating system, the default target of the
tool chain is assumed. So if a platform does not define a value for operatingSystem, Gradle will
find the first available tool chain that can build for the specified architecture.
The core Gradle tool chains are able to target the following architectures out of the box. In each case, the
tool chain will target the current operating system. See the next section for information on cross-compiling for
other operating systems.
Tool Chain
Architectures
GCC
x86, x86_64
Clang
x86, x86_64
Visual C++
x86, x86_64, ia-64
So for GCC running on linux, the supported target platforms are 'linux/x86' and 'linux/x86_64'. For GCC
running on Windows via Cygwin, platforms 'windows/x86' and 'windows/x86_64' are supported. (The Cygwin
POSIX runtime is not yet modelled as part of the platform, but will be in the future.)
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If no target platforms are defined for a project, then all binaries are built to target a default platform named
'current'. This default platform does not specify any architecture or operatingSystem value, hence
using the default values of the first available tool chain.
Gradle provides a hook that allows the build author to control the exact set of arguments passed to a tool
chain executable. This enables the build author to work around any limitations in Gradle, or assumptions that
Gradle makes. The arguments hook should be seen as a 'last-resort' mechanism, with preference given to
truly modelling the underlying domain.
Example 601. Reconfigure tool arguments
build.gradle
model {
toolChains {
visualCpp(VisualCpp) {
eachPlatform {
cppCompiler.withArguments { args ->
args << "-DFRENCH"
}
}
}
clang(Clang) {
eachPlatform {
cCompiler.withArguments { args ->
Collections.replaceAll(args, "CUSTOM", "-DFRENCH")
}
linker.withArguments { args ->
args.remove "CUSTOM"
}
staticLibArchiver.withArguments { args ->
args.remove "CUSTOM"
}
}
}
}
}
§
Cross-compiling with GCC
Cross-compiling is possible with the Gcc and Clang tool chains, by adding support for additional target
platforms. This is done by specifying a target platform for a toolchain. For each target platform a custom
configuration can be specified.
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Example 602. Defining target platforms
build.gradle
model {
toolChains {
gcc(Gcc) {
target("arm"){
cppCompiler.withArguments { args ->
args << "-m32"
}
linker.withArguments { args ->
args << "-m32"
}
}
target("sparc")
}
}
platforms {
arm {
architecture "arm"
}
sparc {
architecture "sparc"
}
}
components {
main(NativeExecutableSpec) {
targetPlatform "arm"
targetPlatform "sparc"
}
}
}
§
Visual Studio IDE integration
Gradle has the ability to generate Visual Studio project and solution files for the native components defined
in your build. This ability is added by the visual-studio plugin. For a multi-project build, all projects with
native components should have this plugin applied.
When the visual-studio plugin is applied, a task name ${component.name}VisualStudio is created
for each defined component. This task will generate a Visual Studio Solution file for the named component.
This solution will include a Visual Studio Project for that component, as well as linking to project files for each
depended-on binary.
The content of the generated visual studio files can be modified via API hooks, provided by the visualStudio
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extension. Take a look at the 'visual-studio' sample, or see VisualStudioExtension.getProjects()
and VisualStudioExtension.getSolutions() in the API documentation for more details.
§
CUnit support
The Gradle cunit plugin provides support for compiling and executing CUnit tests in your native-binary
project. For each NativeExecutableSpec and NativeLibrarySpec defined in your project, Gradle will
create a matching CUnitTestSuiteSpec component, named ${component.name}Test.
§
CUnit sources
Gradle will create a CSourceSet named 'cunit' for each CUnitTestSuiteSpec component in the project.
This source set should contain the cunit test files for the component under test. Source files can be located
in the conventional location (src/${component.name}Test/cunit) or can be configured like any other
source set.
Gradle initialises the CUnit test registry and executes the tests, utilising some generated CUnit launcher
sources. Gradle will expect and call a function with the signature void gradle_cunit_register() that
you can use to configure the actual CUnit suites and tests to execute.
Example 603. Registering CUnit tests
suite_operators.c
#include <CUnit/Basic.h>
#include "gradle_cunit_register.h"
#include "test_operators.h"
int suite_init(void) {
return 0;
}
int suite_clean(void) {
return 0;
}
void gradle_cunit_register() {
CU_pSuite pSuiteMath = CU_add_suite("operator tests", suite_init, suite_clean);
CU_add_test(pSuiteMath, "test_plus", test_plus);
CU_add_test(pSuiteMath, "test_minus", test_minus);
}
Note: Due to this mechanism, your CUnit sources may not contain a main method since this will
clash with the method provided by Gradle.
Building CUnit executables
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§
Building CUnit executables
A
CUnitTestSuiteSpec
component
has
an
associated
NativeExecutableSpec
or
NativeLibrarySpec component. For each NativeBinarySpec configured for the main component, a
matching CUnitTestSuiteBinarySpec will be configured on the test suite component. These test suite
binaries can be configured in a similar way to any other binary instance:
Example 604. Configuring CUnit tests
build.gradle
model {
binaries {
withType(CUnitTestSuiteBinarySpec) {
lib library: "cunit", linkage: "static"
if (flavor == flavors.failing) {
cCompiler.define "PLUS_BROKEN"
}
}
}
}
Note: Both the CUnit sources provided by your project and the generated launcher require the core
CUnit headers and libraries. Presently, this library dependency must be provided by your project for
each CUnitTestSuiteBinarySpec.
§
Running CUnit tests
For each CUnitTestSuiteBinarySpec, Gradle will create a task to execute this binary, which will run all
of the registered CUnit tests. Test results will be found in the ${build.dir} /test-results directory.
Example 605. Running CUnit tests
build.gradle
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apply plugin: "c"
apply plugin: 'cunit-test-suite'
model {
flavors {
passing
failing
}
platforms {
x86 {
architecture "x86"
}
}
repositories {
libs(PrebuiltLibraries) {
cunit {
headers.srcDir "libs/cunit/2.1-2/include"
binaries.withType(StaticLibraryBinary) {
staticLibraryFile =
file("libs/cunit/2.1-2/lib/" +
findCUnitLibForPlatform(targetPlatform))
}
}
}
}
components {
operators(NativeLibrarySpec) {
targetPlatform "x86"
}
}
testSuites {
operatorsTest(CUnitTestSuiteSpec) {
testing $.components.operators
}
}
}
model {
binaries {
withType(CUnitTestSuiteBinarySpec) {
lib library: "cunit", linkage: "static"
if (flavor == flavors.failing) {
cCompiler.define "PLUS_BROKEN"
}
}
}
}
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Note: The code for this example can be found at samples/native-binaries/cunit in the ‘-all’
distribution of Gradle.
Output of gradle -q runOperatorsTestFailingCUnitExe
> gradle -q runOperatorsTestFailingCUnitExe
There were test failures:
1. /home/user/gradle/samples/native-binaries/cunit/src/operatorsTest/c/test_plus.c:6
2. /home/user/gradle/samples/native-binaries/cunit/src/operatorsTest/c/test_plus.c:7
Note: The current support for CUnit is quite rudimentary. Plans for future integration include:
Note: Allow tests to be declared with Javadoc-style annotations.
Note: Improved HTML reporting, similar to that available for JUnit.
Note: Real-time feedback for test execution.
Note: Support for additional test frameworks.
§
GoogleTest support
The Gradle google-test plugin provides support for compiling and executing GoogleTest tests in your
native-binary project. For each NativeExecutableSpec and NativeLibrarySpec defined in your
project, Gradle will create a matching GoogleTestTestSuiteSpec component, named ${component.name}Test
.
§
GoogleTest sources
Gradle will create a CppSourceSet named 'cpp' for each GoogleTestTestSuiteSpec component in the
project. This source set should contain the GoogleTest test files for the component under test. Source files
can be located in the conventional location (src/${component.name}Test/cpp) or can be configured
like any other source set.
§
Building GoogleTest executables
A GoogleTestTestSuiteSpec component has an associated NativeExecutableSpec or
NativeLibrarySpec component. For each NativeBinarySpec configured for the main component, a
matching GoogleTestTestSuiteBinarySpec will be configured on the test suite component. These test
suite binaries can be configured in a similar way to any other binary instance:
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-
Example 606. Registering GoogleTest tests
build.gradle
model {
binaries {
withType(GoogleTestTestSuiteBinarySpec) {
lib library: "googleTest", linkage: "static"
if (flavor == flavors.failing) {
cppCompiler.define "PLUS_BROKEN"
}
if (targetPlatform.operatingSystem.linux) {
cppCompiler.args '-pthread'
linker.args '-pthread'
}
}
}
}
Note: The code for this example can be found at samples/native-binaries/google-test in
the ‘-all’ distribution of Gradle.
Note: The GoogleTest sources provided by your project require the core GoogleTest headers and
libraries. Presently, this library dependency must be provided by your project for each
GoogleTestTestSuiteBinarySpec.
§
Running GoogleTest tests
For each GoogleTestTestSuiteBinarySpec, Gradle will create a task to execute this binary, which will
run all of the registered GoogleTest tests. Test results will be found in the ${build.dir} /test-results
directory.
Note: The current support for GoogleTest is quite rudimentary. Plans for future integration include:
Note: Improved HTML reporting, similar to that available for JUnit.
Note: Real-time feedback for test execution.
Note: Support for additional test frameworks.
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Extending the software model
Note: Support for the software model is currently incubating. Please be aware that the DSL, APIs
and other configuration may change in later Gradle versions.
One of the strengths of Gradle has always been its extensibility, and its adaptability to new domains. The
software model takes this extensibility to a new level, enabling the deep modeling of specific domains via
richly typed DSLs. The following chapter describes how the model and the corresponding DSLs can be
extended to support domains like Java, Play Framework or native software development. Before reading this
you should be familiar with the Gradle software model rule based configuration and concepts.
The following build script is an example of using a custom software model for building Markdown based
documentation:
Example 607. an example of using a custom software model
build.gradle
import sample.documentation.DocumentationComponent
import sample.documentation.TextSourceSet
import sample.markdown.MarkdownSourceSet
apply plugin:sample.documentation.DocumentationPlugin
apply plugin:sample.markdown.MarkdownPlugin
model {
components {
docs(DocumentationComponent) {
sources {
reference(TextSourceSet)
userguide(MarkdownSourceSet) {
generateIndex = true
smartQuotes = true
}
}
}
}
}
Note: The code for this example can be found at samples/customModel/languageType/ in
the ‘-all’ distribution of Gradle.
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The rest of this chapter is dedicated to explaining what is going on behind this build script.
§
Concepts
A custom software model type has a public type, a base interface and internal views. Multiple such types
then collaborate to define a custom software model.
§
Public type and base interfaces
Extended types declare a public type that extends a base interface :
Components extend the ComponentSpec base interface
Binaries extend the BinarySpec base interface
Source sets extend the LanguageSourceSet base interface
The public type is exposed to build logic.
§
Internal views
Adding internal views to your model type, you can make some data visible to build logic via a public type,
while hiding the rest of the data behind the internal view types. This is covered in a dedicated section below.
§
Components all the way down
Components are composed of other components. A source set is just a special kind of component
representing sources. It might be that the sources are provided, or generated. Similarly, some components
are composed of different binaries, which are built by tasks. All buildable components are built by tasks. In
the software model, you will write rules to generate both binaries from components and tasks from binaries.
§
Components
To declare a custom component type one must extend ComponentSpec, or one of the following, depending
on the use case:
SourceComponentSpec represents a component which has sources
VariantComponentSpec represents a component which generates different binaries based on context
(target platforms, build flavors, …). Such a component generally produces multiple binaries.
GeneralComponentSpec is a convenient base interface for components that are built from sources and
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variant-aware. This is the typical case for a lot of software components, and therefore it should be in most of
the cases the base type to be extended.
The core software model includes more types that can be used as base for extension. For example:
LibrarySpec and ApplicationSpec can also be extended in this manner. Theses are no-op extensions
of GeneralComponentSpec used to describe a software model better by distinguishing libraries and
applications components. TestSuiteSpec should be used for all components that describe a test suite.
Example 608. Declare a custom component
DocumentationComponent.groovy
@Managed
interface DocumentationComponent extends GeneralComponentSpec {}
Types extending ComponentSpec are registered via a rule annotated with ComponentType:
Example 609. Register a custom component
DocumentationPlugin.groovy
class DocumentationPlugin extends RuleSource {
@ComponentType
void registerComponent(TypeBuilder<DocumentationComponent> builder) {}
}
§
Binaries
To declare a custom binary type one must extend BinarySpec.
Example 610. Declare a custom binary
DocumentationBinary.groovy
@Managed
interface DocumentationBinary extends BinarySpec {
File getOutputDir()
void setOutputDir(File outputDir)
}
Types extending BinarySpec are registered via a rule annotated with ComponentType:
Example 611. Register a custom binary
DocumentationPlugin.groovy
class DocumentationPlugin extends RuleSource {
@ComponentType
void registerBinary(TypeBuilder<DocumentationBinary> builder) {}
}
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Source sets
§
Source sets
To declare a custom source set type one must extend LanguageSourceSet.
Example 612. Declare a custom source set
MarkdownSourceSet.groovy
@Managed
interface MarkdownSourceSet extends LanguageSourceSet {
boolean isGenerateIndex()
void setGenerateIndex(boolean generateIndex)
boolean isSmartQuotes()
void setSmartQuotes(boolean smartQuotes)
}
Types extending LanguageSourceSet are registered via a rule annotated with ComponentType:
Example 613. Register a custom source set
MarkdownPlugin.groovy
class MarkdownPlugin extends RuleSource {
@ComponentType
void registerMarkdownLanguage(TypeBuilder<MarkdownSourceSet> builder) {}
}
Setting the language name is mandatory.
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Putting it all together
§
Putting it all together
§
Generating binaries from components
Binaries generation from components is done via rules annotated with ComponentBinaries. This rule
generates a DocumentationBinary named exploded for each DocumentationComponent and sets its
outputDir property:
Example 614. Generates documentation binaries
DocumentationPlugin.groovy
class DocumentationPlugin extends RuleSource {
@ComponentBinaries
void generateDocBinaries(ModelMap<DocumentationBinary> binaries, VariantComponentSpec
binaries.create("exploded") { binary ->
outputDir = new File(buildDir, "${component.name}/${binary.name}")
}
}
}
§
Generating tasks from binaries
Tasks generation from binaries is done via rules annotated with BinaryTasks. This rule generates a Copy
task for each TextSourceSet of each DocumentationBinary:
Example 615. Generates tasks for text source sets
DocumentationPlugin.groovy
class DocumentationPlugin extends RuleSource {
@BinaryTasks
void generateTextTasks(ModelMap<Task> tasks, final DocumentationBinary binary) {
binary.inputs.withType(TextSourceSet) { textSourceSet ->
def taskName = binary.tasks.taskName("compile", textSourceSet.name)
def outputDir = new File(binary.outputDir, textSourceSet.name)
tasks.create(taskName, Copy) {
from textSourceSet.source
destinationDir = outputDir
}
}
}
}
This rule generates a MarkdownCompileTask task for each MarkdownSourceSet of each DocumentationBinary
:
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Example 616. Register a custom source set
MarkdownPlugin.groovy
class MarkdownPlugin extends RuleSource {
@BinaryTasks
void processMarkdownDocumentation(ModelMap<Task> tasks, final DocumentationBinary bina
binary.inputs.withType(MarkdownSourceSet) { markdownSourceSet ->
def taskName = binary.tasks.taskName("compile", markdownSourceSet.name)
def outputDir = new File(binary.outputDir, markdownSourceSet.name)
tasks.create(taskName, MarkdownHtmlCompile) { compileTask ->
compileTask.source = markdownSourceSet.source
compileTask.destinationDir = outputDir
compileTask.smartQuotes = markdownSourceSet.smartQuotes
compileTask.generateIndex = markdownSourceSet.generateIndex
}
}
}
}
See the sample source for more on the MarkdownCompileTask task.
§
Using your custom model
This build script demonstrate usage of the custom model defined in the sections above:
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Example 617. an example of using a custom software model
build.gradle
import sample.documentation.DocumentationComponent
import sample.documentation.TextSourceSet
import sample.markdown.MarkdownSourceSet
apply plugin:sample.documentation.DocumentationPlugin
apply plugin:sample.markdown.MarkdownPlugin
model {
components {
docs(DocumentationComponent) {
sources {
reference(TextSourceSet)
userguide(MarkdownSourceSet) {
generateIndex = true
smartQuotes = true
}
}
}
}
}
Note: The code for this example can be found at samples/customModel/languageType/ in
the ‘-all’ distribution of Gradle.
And in the components reports for such a build script we can see our model types properly registered:
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Example 618. components report
Output of gradle -q components
> gradle -q components
-----------------------------------------------------------Root project
-----------------------------------------------------------DocumentationComponent 'docs'
----------------------------Source sets
Markdown source 'docs:userguide'
srcDir: src/docs/userguide
Text source 'docs:reference'
srcDir: src/docs/reference
Binaries
DocumentationBinary 'docs:exploded'
build using task: :docsExploded
Note: currently not all plugins register their components, so some components may not be v
§
About internal views
Internal views can be added to an already registered type or to a new custom type. In other words, using
internal views, you can attach extra properties to already registered components, binaries and source sets
types like JvmLibrarySpec, JarBinarySpec or JavaSourceSet and to the custom types you write.
Let’s start with a simple component public type and its internal view declarations:
Example 619. public type and internal view declaration
build.gradle
@Managed interface MyComponent extends ComponentSpec {
String getPublicData()
void setPublicData(String data)
}
@Managed interface MyComponentInternal extends MyComponent {
String getInternalData()
void setInternalData(String internal)
}
The type registration is as follows:
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Example 620. type registration
build.gradle
class MyPlugin extends RuleSource {
@ComponentType
void registerMyComponent(TypeBuilder<MyComponent> builder) {
builder.internalView(MyComponentInternal)
}
}
The internalView(type) method of the type builder can be called several times. This is how you would
add several internal views to a type.
Now, let’s mutate both public and internal data using some rule:
Example 621. public and internal data mutation
build.gradle
class MyPlugin extends RuleSource {
@Mutate
void mutateMyComponents(ModelMap<MyComponentInternal> components) {
components.all { component ->
component.publicData = "Some PUBLIC data"
component.internalData = "Some INTERNAL data"
}
}
}
Our internalData property should not be exposed to build logic. Let’s check this using the model task on
the following build file:
Example 622. example build script and model report output
build.gradle
apply plugin: MyPlugin
model {
components {
my(MyComponent)
}
}
Output of gradle -q model
> gradle -q model
-----------------------------------------------------------Root project
-----------------------------------------------------------+ components
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| Type:
org.gradle.platform.base.ComponentSpecContainer
| Creator:
ComponentBasePlugin.PluginRules#components(ComponentSpecContainer)
| Rules:
components { ... } @ build.gradle line 42, column 5
MyPlugin#mutateMyComponents(ModelMap<MyComponentInternal>)
+ my
| Type:
MyComponent
| Creator:
components { ... } @ build.gradle line 42, column 5 > create(my)
| Rules:
MyPlugin#mutateMyComponents(ModelMap<MyComponentInternal>) > all()
+ publicData
| Type:
java.lang.String
| Value:
Some PUBLIC data
| Creator:
components { ... } @ build.gradle line 42, column 5 > create(
+ tasks
| Type:
org.gradle.model.ModelMap<org.gradle.api.Task>
| Creator:
Project.<init>.tasks()
+ assemble
| Type:
org.gradle.api.DefaultTask
| Value:
task ':assemble'
| Creator:
tasks.addPlaceholderAction(assemble)
| Rules:
copyToTaskContainer
+ build
| Type:
org.gradle.api.DefaultTask
| Value:
task ':build'
| Creator:
tasks.addPlaceholderAction(build)
| Rules:
copyToTaskContainer
+ buildEnvironment
| Type:
org.gradle.api.tasks.diagnostics.BuildEnvironmentReportTask
| Value:
task ':buildEnvironment'
| Creator:
tasks.addPlaceholderAction(buildEnvironment)
| Rules:
copyToTaskContainer
+ check
| Type:
org.gradle.api.DefaultTask
| Value:
task ':check'
| Creator:
tasks.addPlaceholderAction(check)
| Rules:
copyToTaskContainer
+ clean
| Type:
org.gradle.api.tasks.Delete
| Value:
task ':clean'
| Creator:
tasks.addPlaceholderAction(clean)
| Rules:
copyToTaskContainer
+ components
| Type:
org.gradle.api.reporting.components.ComponentReport
Page 683 of 717
+
+
+
+
+
+
+
+
| Value:
task ':components'
| Creator:
tasks.addPlaceholderAction(components)
| Rules:
copyToTaskContainer
dependencies
| Type:
org.gradle.api.tasks.diagnostics.DependencyReportTask
| Value:
task ':dependencies'
| Creator:
tasks.addPlaceholderAction(dependencies)
| Rules:
copyToTaskContainer
dependencyInsight
| Type:
org.gradle.api.tasks.diagnostics.DependencyInsightReportTask
| Value:
task ':dependencyInsight'
| Creator:
tasks.addPlaceholderAction(dependencyInsight)
| Rules:
HelpTasksPlugin.Rules#addDefaultDependenciesReportConfiguration(DependencyIn
copyToTaskContainer
dependentComponents
| Type:
org.gradle.api.reporting.dependents.DependentComponentsReport
| Value:
task ':dependentComponents'
| Creator:
tasks.addPlaceholderAction(dependentComponents)
| Rules:
copyToTaskContainer
help
| Type:
org.gradle.configuration.Help
| Value:
task ':help'
| Creator:
tasks.addPlaceholderAction(help)
| Rules:
copyToTaskContainer
init
| Type:
org.gradle.buildinit.tasks.InitBuild
| Value:
task ':init'
| Creator:
tasks.addPlaceholderAction(init)
| Rules:
copyToTaskContainer
model
| Type:
org.gradle.api.reporting.model.ModelReport
| Value:
task ':model'
| Creator:
tasks.addPlaceholderAction(model)
| Rules:
copyToTaskContainer
projects
| Type:
org.gradle.api.tasks.diagnostics.ProjectReportTask
| Value:
task ':projects'
| Creator:
tasks.addPlaceholderAction(projects)
| Rules:
copyToTaskContainer
properties
| Type:
org.gradle.api.tasks.diagnostics.PropertyReportTask
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| Value:
task ':properties'
| Creator:
tasks.addPlaceholderAction(properties)
| Rules:
copyToTaskContainer
+ tasks
| Type:
org.gradle.api.tasks.diagnostics.TaskReportTask
| Value:
task ':tasks'
| Creator:
tasks.addPlaceholderAction(tasks)
| Rules:
copyToTaskContainer
+ wrapper
| Type:
org.gradle.api.tasks.wrapper.Wrapper
| Value:
task ':wrapper'
| Creator:
tasks.addPlaceholderAction(wrapper)
Page 685 of 717
| Rules:
copyToTaskContainer
We can see in this report that publicData is present and that internalData is not.
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Glossary
Page 687 of 717
Dependency Types
§
External module dependencies
External module dependencies are the most common dependencies. They refer to a module in an external
repository.
Example 623. Module dependencies
build.gradle
dependencies {
runtime group: 'org.springframework', name: 'spring-core', version: '2.5'
runtime 'org.springframework:spring-core:2.5',
'org.springframework:spring-aop:2.5'
runtime(
[group: 'org.springframework', name: 'spring-core', version: '2.5'],
[group: 'org.springframework', name: 'spring-aop', version: '2.5']
)
runtime('org.hibernate:hibernate:3.0.5') {
transitive = true
}
runtime group: 'org.hibernate', name: 'hibernate', version: '3.0.5', transitive: true
runtime(group: 'org.hibernate', name: 'hibernate', version: '3.0.5') {
transitive = true
}
}
See the DependencyHandler class in the API documentation for more examples and a complete
reference.
Gradle provides different notations for module dependencies. There is a string notation and a map notation.
A module dependency has an API which allows further configuration. Have a look at
ExternalModuleDependency to learn all about the API. This API provides properties and configuration
methods. Via the string notation you can define a subset of the properties. With the map notation you can
define all properties. To have access to the complete API, either with the map or with the string notation, you
can assign a single dependency to a configuration together with a closure.
Note: If you declare a module dependency, Gradle looks for a module descriptor file ( pom.xml or ivy.xml
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) in the repositories. If such a module descriptor file exists, it is parsed and the artifacts of this
module (e.g. hibernate-3.0.5.jar) as well as its dependencies (e.g. cglib) are downloaded. If
no such module descriptor file exists, Gradle looks for a file called hibernate-3.0.5.jar to
retrieve. In Maven, a module can have one and only one artifact. In Gradle and Ivy, a module can
have multiple artifacts. Each artifact can have a different set of dependencies.
§
File dependencies
File dependencies allow you to directly add a set of files to a configuration, without first adding them to a
repository. This can be useful if you cannot, or do not want to, place certain files in a repository. Or if you do
not want to use any repositories at all for storing your dependencies.
To add some files as a dependency for a configuration, you simply pass a file collection as a dependency:
Example 624. File dependencies
build.gradle
dependencies {
runtime files('libs/a.jar', 'libs/b.jar')
runtime fileTree(dir: 'libs', include: '*.jar')
}
File dependencies are not included in the published dependency descriptor for your project. However, file
dependencies are included in transitive project dependencies within the same build. This means they cannot
be used outside the current build, but they can be used with the same build.
You can declare which tasks produce the files for a file dependency. You might do this when, for example,
the files are generated by the build.
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Example 625. Generated file dependencies
build.gradle
dependencies {
compile files("$buildDir/classes") {
builtBy 'compile'
}
}
task compile {
doLast {
println 'compiling classes'
}
}
task list(dependsOn: configurations.compile) {
doLast {
println "classpath = ${configurations.compile.collect { File file -> file.name }}"
}
}
Output of gradle -q list
> gradle -q list
compiling classes
classpath = [classes]
§
Project dependencies
Gradle distinguishes between external dependencies and dependencies on projects which are part of the
same multi-project build. For the latter you can declare Project Dependencies .
Example 626. Project dependencies
build.gradle
dependencies {
compile project(':shared')
}
For more information see the API documentation for ProjectDependency.
Multi-project builds are discussed in Authoring Multi-Project Builds.
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Gradle distribution-specific dependencies
§
Gradle distribution-specific dependencies
§
Gradle API dependency
You can declare a dependency on the API of the current version of Gradle by using the
DependencyHandler.gradleApi() method. This is useful when you are developing custom Gradle
tasks or plugins.
Example 627. Gradle API dependencies
build.gradle
dependencies {
compile gradleApi()
}
§
Gradle TestKit dependency
You can declare a dependency on the TestKit API of the current version of Gradle by using the
DependencyHandler.gradleTestKit() method. This is useful for writing and executing functional tests
for Gradle plugins and build scripts.
Example 628. Gradle TestKit dependencies
build.gradle
dependencies {
testCompile gradleTestKit()
}
Testing Build Logic with TestKit explains the use of TestKit by example.
§
Local Groovy dependency
You can declare a dependency on the Groovy that is distributed with Gradle by using the
DependencyHandler.localGroovy() method. This is useful when you are developing custom Gradle
tasks or plugins in Groovy.
Example 629. Gradle's Groovy dependencies
build.gradle
dependencies {
compile localGroovy()
}
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Repository Types
§
Flat directory repository
Some projects might prefer to store dependencies on a shared drive or as part of the project source code
instead of a binary repository product. If you want to use a (flat) filesystem directory as a repository, simply
type:
Example 630. Flat repository resolver
build.gradle
repositories {
flatDir {
dirs 'lib'
}
flatDir {
dirs 'lib1', 'lib2'
}
}
This adds repositories which look into one or more directories for finding dependencies. Note that this type of
repository does not support any meta-data formats like Ivy XML or Maven POM files. Instead, Gradle will
dynamically generate a module descriptor (without any dependency information) based on the presence of
artifacts. However, as Gradle prefers to use modules whose descriptor has been created from real
meta-data rather than being generated, flat directory repositories cannot be used to override artifacts with
real meta-data from other repositories. For example, if Gradle finds only jmxri-1.2.1.jar in a flat
directory repository, but jmxri-1.2.1.pom in another repository that supports meta-data, it will use the
second repository to provide the module.
For the use case of overriding remote artifacts with local ones consider using an Ivy or Maven repository
instead whose URL points to a local directory. If you only work with flat directory repositories you don’t need
to set all attributes of a dependency.
§
Maven Central repository
Maven Central is a popular repository hosting open source libraries for consumption by Java projects.
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To declare the central Maven repository for your build add this to your script:
Example 631. Adding central Maven repository
build.gradle
repositories {
mavenCentral()
}
§
JCenter Maven repository
Bintray's JCenter is an up-to-date collection of all popular Maven OSS artifacts, including artifacts published
directly to Bintray.
To declare the JCenter Maven repository add this to your build script:
Example 632. Adding Bintray's JCenter Maven repository
build.gradle
repositories {
jcenter()
}
§
Google Maven repository
The Google repository hosts Android-specific artifacts including the Android SDK. For usage examples, see
the relevant documentation.
To declare the Google Maven repository add this to your build script:
Example 633. Adding Google Maven repository
build.gradle
repositories {
google()
}
§
Local Maven repository
Gradle can consume dependencies available in the local Maven repository. Declaring this repository is
beneficial for teams that publish to the local Maven repository with one project and consume the artifacts by
Gradle in another project.
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Note: Gradle stores resolved dependencies in its own cache. A build does not need to declare the
local Maven repository even if you resolve dependencies from a Maven-based, remote repository.
To declare the local Maven cache as a repository add this to your build script:
Example 634. Adding the local Maven cache as a repository
build.gradle
repositories {
mavenLocal()
}
Gradle uses the same logic as Maven to identify the location of your local Maven cache. If a local repository
location is defined in a settings.xml, this location will be used. The settings.xml in USER_HOME /.m2
takes precedence over the settings.xml in M2_HOME /conf. If no settings.xml is available, Gradle
uses the default location USER_HOME /.m2/repository.
§
Custom Maven repositories
Many organizations host dependencies in an in-house Maven repository only accessible within the
company’s network. Gradle can declare Maven repositories by URL.
For adding a custom Maven repository you can do:
Example 635. Adding custom Maven repository
build.gradle
repositories {
maven {
url "http://repo.mycompany.com/maven2"
}
}
Sometimes a repository will have the POMs published to one location, and the JARs and other artifacts
published at another location. To define such a repository, you can do:
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Example 636. Adding additional Maven repositories for JAR files
build.gradle
repositories {
maven {
// Look for POMs and artifacts, such as JARs, here
url "http://repo2.mycompany.com/maven2"
// Look for artifacts here if not found at the above location
artifactUrls "http://repo.mycompany.com/jars"
artifactUrls "http://repo.mycompany.com/jars2"
}
}
Gradle will look at the first URL for the POM and the JAR. If the JAR can’t be found there, the artifact URLs
are used to look for JARs.
§
Accessing password-protected Maven repositories
You can specify credentials for Maven repositories secured by basic authentication.
Example 637. Accessing password-protected Maven repository
build.gradle
repositories {
maven {
url "http://repo.mycompany.com/maven2"
credentials {
username "user"
password "password"
}
}
}
§
Custom Ivy repositories
Organizations might decide to host dependencies in an in-house Ivy repository. Gradle can declare Ivy
repositories by URL.
§
Defining an Ivy repository with a standard layout
To declare an Ivy repository using the standard layout no additional customization is needed. You just
declare the URL.
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Example 638. Ivy repository
build.gradle
repositories {
ivy {
url "http://repo.mycompany.com/repo"
}
}
§
Defining a named layout for an Ivy repository
You can specify that your repository conforms to the Ivy or Maven default layout by using a named layout.
Example 639. Ivy repository with named layout
build.gradle
repositories {
ivy {
url "http://repo.mycompany.com/repo"
layout "maven"
}
}
Valid named layout values are 'gradle' (the default), 'maven', 'ivy' and 'pattern'. See
IvyArtifactRepository.layout(java.lang.String,
groovy.lang.Closure) in the API
documentation for details of these named layouts.
§
Defining custom pattern layout for an Ivy repository
To define an Ivy repository with a non-standard layout, you can define a 'pattern' layout for the
repository:
Example 640. Ivy repository with pattern layout
build.gradle
repositories {
ivy {
url "http://repo.mycompany.com/repo"
layout "pattern", {
artifact "[module]/[revision]/[type]/[artifact].[ext]"
}
}
}
To define an Ivy repository which fetches Ivy files and artifacts from different locations, you can define
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separate patterns to use to locate the Ivy files and artifacts:
Each artifact or ivy specified for a repository adds an additional pattern to use. The patterns are used
in the order that they are defined.
Example 641. Ivy repository with multiple custom patterns
build.gradle
repositories {
ivy {
url "http://repo.mycompany.com/repo"
layout "pattern", {
artifact "3rd-party-artifacts/[organisation]/[module]/[revision]/[artifact]-[r
artifact "company-artifacts/[organisation]/[module]/[revision]/[artifact]-[rev
ivy "ivy-files/[organisation]/[module]/[revision]/ivy.xml"
}
}
}
Optionally, a repository with pattern layout can have its 'organisation' part laid out in Maven style, with
forward slashes replacing dots as separators. For example, the organisation my.company would then be
represented as my/company.
Example 642. Ivy repository with Maven compatible layout
build.gradle
repositories {
ivy {
url "http://repo.mycompany.com/repo"
layout "pattern", {
artifact "[organisation]/[module]/[revision]/[artifact]-[revision].[ext]"
m2compatible = true
}
}
}
§
Accessing password-protected Ivy repositories
You can specify credentials for Ivy repositories secured by basic authentication.
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Example 643. Ivy repository with authentication
build.gradle
repositories {
ivy {
url "http://repo.mycompany.com"
credentials {
username "user"
password "password"
}
}
}
§
Supported repository transport protocols
Maven and Ivy repositories support the use of various transport protocols. At the moment the following
protocols are supported:
Table 111. Repository transport protocols
Type
Credential types
file
none
http
username/password
https
username/password
sftp
username/password
s3
access key/secret key/session token or Environment variables
gcs
default application credentials sourced from well known files, Environment variables etc.
Note: Username and password should never be checked in plain text into version control as part of
your build file. You can store the credentials in a local gradle.properties file and use one of the
open source Gradle plugins for encrypting and consuming credentials e.g. the credentials plugin.
The transport protocol is part of the URL definition for a repository. The following build script demonstrates
how to create a HTTP-based Maven and Ivy repository:
Page 698 of 717
Example 644. Declaring a Maven and Ivy repository
build.gradle
repositories {
maven {
url "http://repo.mycompany.com/maven2"
}
ivy {
url "http://repo.mycompany.com/repo"
}
}
The following example shows how to declare SFTP repositories:
Example 645. Using the SFTP protocol for a repository
build.gradle
repositories {
maven {
url "sftp://repo.mycompany.com:22/maven2"
credentials {
username "user"
password "password"
}
}
ivy {
url "sftp://repo.mycompany.com:22/repo"
credentials {
username "user"
password "password"
}
}
}
When using an AWS S3 backed repository you need to authenticate using AwsCredentials, providing
access-key and a private-key. The following example shows how to declare a S3 backed repository and
providing AWS credentials:
Page 699 of 717
Example 646. Declaring a S3 backed Maven and Ivy repository
build.gradle
repositories {
maven {
url "s3://myCompanyBucket/maven2"
credentials(AwsCredentials) {
accessKey "someKey"
secretKey "someSecret"
// optional
sessionToken "someSTSToken"
}
}
ivy {
url "s3://myCompanyBucket/ivyrepo"
credentials(AwsCredentials) {
accessKey "someKey"
secretKey "someSecret"
// optional
sessionToken "someSTSToken"
}
}
}
You can also delegate all credentials to the AWS sdk by using the AwsImAuthentication. The following
example shows how:
Example 647. Declaring a S3 backed Maven and Ivy repository using IAM
build.gradle
repositories {
maven {
url "s3://myCompanyBucket/maven2"
authentication {
awsIm(AwsImAuthentication) // load from EC2 role or env var
}
}
ivy {
url "s3://myCompanyBucket/ivyrepo"
authentication {
awsIm(AwsImAuthentication)
}
}
}
When using a Google Cloud Storage backed repository default application credentials will be used with no
further configuration required:
Page 700 of 717
Example 648. Declaring a Google Cloud Storage backed Maven and Ivy repository using default application crede
build.gradle
repositories {
maven {
url "gcs://myCompanyBucket/maven2"
}
ivy {
url "gcs://myCompanyBucket/ivyrepo"
}
}
§
S3 configuration properties
The following system properties can be used to configure the interactions with s3 repositories:
Table 112. S3 configuration properties
Property
org.gradle.s3.endpoint
org.gradle.s3.maxErrorRetry
Description
Used to override the AWS S3 endpoint when using a non AWS, S3 API compatible, storage
service.
Specifies the maximum number of times to retry a request in the event that the S3 server
responds with a HTTP 5xx status code. When not specified a default value of 3 is used.
§
S3 URL formats
S3 URL’s are 'virtual-hosted-style' and must be in the following format s3://<bucketName>[.<regionSpecificEndp
e.g. s3://myBucket.s3.eu-central-1.amazonaws.com/maven/release
myBucket is the AWS S3 bucket name.
s3.eu-central-1.amazonaws.com is the optional region specific endpoint.
/maven/release is the AWS S3 key (unique identifier for an object within a bucket)
§
S3 proxy settings
A proxy for S3 can be configured using the following system properties:
https.proxyHost
Page 701 of 717
https.proxyPort
https.proxyUser
https.proxyPassword
http.nonProxyHosts
If the 'org.gradle.s3.endpoint' property has been specified with a http (not https) URI the following system
proxy settings can be used:
http.proxyHost
http.proxyPort
http.proxyUser
http.proxyPassword
http.nonProxyHosts
§
AWS S3 V4 Signatures (AWS4-HMAC-SHA256)
Some of the AWS S3 regions (eu-central-1 - Frankfurt) require that all HTTP requests are signed in
accordance with AWS’s signature version 4. It is recommended to specify S3 URL’s containing the region
specific endpoint when using buckets that require V4 signatures. e.g. s3://somebucket.s3.eu-central-1.amazona
Note: When a region-specific endpoint is not specified for buckets requiring V4 Signatures, Gradle
will use the default AWS region (us-east-1) and the following warning will appear on the console:
Attempting to re-send the request to …. with AWS V4 authentication. To avoid this warning in the
future, use region-specific endpoint to access buckets located in regions that require V4 signing.
Failing to specify the region-specific endpoint for buckets requiring V4 signatures means:
Note: 3 round-trips to AWS, as opposed to one, for every file upload and download.
Note: Depending on location - increased network latencies and slower builds.
Note: Increased likelihood of transmission failures.
§
Google Cloud Storage configuration properties
The following system properties can be used to configure the interactions with Google Cloud Storage
repositories:
Page 702 of 717
Table 113. Google Cloud Storage configuration properties
Property
org.gradle.gcs.endpoint
org.gradle.gcs.servicePath
Description
Used to override the Google Cloud Storage endpoint when using a non-Google Cloud Platform,
Google Cloud Storage API compatible, storage service.
Used to override the Google Cloud Storage root service path which the Google Cloud Storage client
builds requests from, defaults to /.
§
Google Cloud Storage URL formats
Google Cloud Storage URL’s are 'virtual-hosted-style' and must be in the following format gcs://<bucketName>/<obje
e.g. gcs://myBucket/maven/release
myBucket is the Google Cloud Storage bucket name.
/maven/release is the Google Cloud Storage key (unique identifier for an object within a bucket)
§
Configuring HTTP authentication schemes
When configuring a repository using HTTP or HTTPS transport protocols, multiple authentication schemes
are available. By default, Gradle will attempt to use all schemes that are supported by the Apache HttpClient
library, documented here. In some cases, it may be preferable to explicitly specify which authentication
schemes should be used when exchanging credentials with a remote server. When explicitly declared, only
those schemes are used when authenticating to a remote repository. The following example show how to
configure a repository to use only digest authentication:
Example 649. Configure repository to use only digest authentication
build.gradle
repositories {
maven {
url 'https://repo.mycompany.com/maven2'
credentials {
username "user"
password "password"
}
authentication {
digest(DigestAuthentication)
}
}
}
Page 703 of 717
Currently supported authentication schemes are:
Table 114. Authentication schemes
Type
BasicAuthentication
Description
Basic access authentication over HTTP. When using this scheme, credentials are sent
preemptively.
DigestAuthentication Digest access authentication over HTTP.
§
Using preemptive authentication
Gradle’s default behavior is to only submit credentials when a server responds with an authentication
challenge in the form of a HTTP 401 response. In some cases, the server will respond with a different code
(ex. for repositories hosted on GitHub a 404 is returned) causing dependency resolution to fail. To get
around this behavior, credentials may be sent to the server preemptively. To enable preemptive
authentication simply configure your repository to explicitly use the BasicAuthentication scheme:
Example 650. Configure repository to use preemptive authentication
build.gradle
repositories {
maven {
url 'https://repo.mycompany.com/maven2'
credentials {
username "user"
password "password"
}
authentication {
basic(BasicAuthentication)
}
}
}
Page 704 of 717
Appendix
A
Gradle Samples
Listed below are some of the stand-alone samples which are included in the Gradle distribution. You can find
these samples in the GRADLE_HOME /samples directory of the distribution.
Table A.1. Samples included in the distribution
Sample
Description
announce
A project which uses the announce plugin
application
A project which uses the application plugin
buildCache/build-src
Configure the build cache consistently for buildSrc and the main build
buildCache/configure-built-in-caches Configuration options for the build cache
Recommended cache configuration: Developer push to a local build cache
buildCache/developer-ci-setup
and pull from local and remote build cache, continuous integration server
pushes to and pulls from the remote cache.
buildCache/http-build-cache
Use a remote HTTP build cache
buildDashboard
A project which uses the build-dashboard plugin
codeQuality
A project which uses the various code quality plugins.
customBuildLanguage
customDistribution
customPlugin
This sample demonstrates how to add some custom elements to the build
DSL. It also demonstrates the use of custom plug-ins to organize build logic.
This sample demonstrates how to create a custom Gradle distribution and
use it with the Gradle wrapper.
A set of projects that show how to implement, test, publish and use a custom
plugin and task.
Page 706 of 717
ear/earCustomized/ear
Web application ear project with customized contents
ear/earWithWar
Web application ear project
groovy/crossCompilation
A project doing cross compilation for a Groovy Project to Java 6
groovy/customizedLayout
Groovy project with a custom source layout
groovy/mixedJavaAndGroovy
Project containing a mix of Java and Groovy source
groovy/multiproject
Build made up of multiple Groovy projects. Also demonstrates how to exclude
certain source files, and the use of a custom Groovy AST transformation.
groovy/quickstart
Groovy quickstart sample
java-library/multiproject
Java Library multiproject
java-library/quickstart
Java Library quickstart project
java/base
Java base project
java/crossCompilation
A project doing cross compilation to Java 6
java/customizedLayout
Java project with a custom source layout
java/multiproject
java/quickstart
java/withIntegrationTests
This sample demonstrates how an application can be composed using
multiple Java projects.
Java quickstart project
This sample demonstrates how to use a source set to add an integration test
suite to a Java project.
This example demonstrates the use of the java gradle plugin development
javaGradlePlugin
plugin. By applying the plugin, the java plugin is automatically applied as well
as the gradleApi() dependency. Furthermore, validations are performed
against the plugin metadata during jar execution.
Demonstrates how to deploy and install to a Maven repository. Also
maven/pomGeneration
demonstrates how to deploy a javadoc JAR along with the main JAR, how to
customize the contents of the generated POM, and how to deploy snapshots
and releases to different repositories.
Page 707 of 717
maven/quickstart
Demonstrates how to deploy and install artifacts to a Maven repository.
osgi
A project which builds an OSGi bundle
plugins
providers/fileAndDirectoryProperty
providers/implicitTaskDependency
A set of projects that show how to implement, test, publish and use a custom
plugins with the latest technology.
A set of examples using the Provider API for File-like properties
An example project using the Provider API to model the relationship between
a producer and consumer task.
providers/listProperty
A set of examples using the Provider API for collection properties
providers/propertyAndProvider
An example of using the Provider API with the Groovy Gradle DSL
scala/crossCompilation
A project doing cross compilation for a Scala project to Java 6
scala/customizedLayout
Scala project with a custom source layout
scala/force
Scala quickstart project
scala/mixedJavaAndScala
A project containing a mix of Java and Scala source.
scala/quickstart
Scala quickstart project
scala/zinc
Scala project using the Zinc based Scala compiler.
testing/testReport
toolingApi/customModel
toolingApi/eclipse
toolingApi/idea
toolingApi/model
Generates an HTML test report that includes the test results from all
subprojects.
A sample of how a plugin can expose its own custom tooling model to tooling
API clients.
An application that uses the tooling API to build the Eclipse model for a
project.
An application that uses the tooling API to extract information needed by
IntelliJ IDEA.
An application that uses the tooling API to build the model for a Gradle build.
Page 708 of 717
toolingApi/runBuild
An application that uses the tooling API to run a Gradle task.
userguide/distribution
A project which uses the distribution plugin
userguide/javaLibraryDistribution
A project which uses the Java library distribution plugin
webApplication/customized
Web application with customized WAR contents.
webApplication/quickstart
Web application quickstart project
§
Sample customBuildLanguage
This sample demonstrates how to add some custom elements to the build DSL. It also demonstrates the use
of custom plug-ins to organize build logic.
The build is composed of 2 types of projects. The first type of project represents a product, and the second
represents a product module. Each product includes one or more product modules, and each product
module may be included in multiple products. That is, there is a many-to-many relationship between these
products and product modules. For each product, the build produces a ZIP containing the runtime classpath
for each product module included in the product. The ZIP also contains some product-specific files.
The custom elements can be seen in the build script for the product projects (for example, basicEdition/build.grad
). Notice that the build script uses the product { } element. This is a custom element.
The build scripts of each project contain only declarative elements. The bulk of the work is done by 2 custom
plug-ins found in buildSrc/src/main/groovy.
§
Sample customDistribution
This sample demonstrates how to create a custom Gradle distribution and use it with the Gradle wrapper.
This sample contains the following projects:
The plugin directory contains the project that implements a custom plugin, and bundles the plugin into a
custom Gradle distribution.
The consumer directory contains the project that uses the custom distribution.
Page 709 of 717
Sample customPlugin
§
Sample customPlugin
A set of projects that show how to implement, test, publish and use a custom plugin and task.
This sample contains the following projects:
The plugin directory contains the project that implements and publishes the plugin.
The consumer directory contains the project that uses the plugin.
§
Sample java/multiproject
This sample demonstrates how an application can be composed using multiple Java projects.
This build creates a client-server application which is distributed as 2 archives. First, there is a client ZIP
which includes an API JAR, which a 3rd party application would compile against, and a client runtime. Then,
there is a server WAR which provides a web service.
§
Sample plugins
A set of projects that show how to implement, test, publish and use a custom plugins with the latest
technology.
This sample contains the following projects:
The buildscript directory contains a project that uses the old buildscript syntax for using plugins.
The dsl directory contains the a project that uses the new plugins syntax for using plugins.
The publishing directory contains a complete example of the modern publishing plugins working with the
java-gradle-plugin to produce two plugins shipped in the same jar and being published to both an ivy and
maven repository.
The consuming directory contains an example of resolving plugins from custom repositories instead the
Gradle Plugin Portal.
Page 710 of 717
B
Potential Traps
§
Groovy script variables
For Gradle users it is important to understand how Groovy deals with script variables. Groovy has two types
of script variables. One with a local scope and one with a script-wide scope.
Page 711 of 717
Example B.1. Variables scope: local and script wide
scope.groovy
String localScope1 = 'localScope1'
def localScope2 = 'localScope2'
scriptScope = 'scriptScope'
println localScope1
println localScope2
println scriptScope
closure = {
println localScope1
println localScope2
println scriptScope
}
def method() {
try {
localScope1
} catch (MissingPropertyException e) {
println 'localScope1NotAvailable'
}
try {
localScope2
} catch(MissingPropertyException e) {
println 'localScope2NotAvailable'
}
println scriptScope
}
closure.call()
method()
Output of groovy scope.groovy
> groovy scope.groovy
localScope1
localScope2
scriptScope
localScope1
localScope2
scriptScope
localScope1NotAvailable
localScope2NotAvailable
scriptScope
Variables which are declared with a type modifier are visible within closures but not visible within methods.
Page 712 of 717
Configuration and execution phase
§
Configuration and execution phase
It is important to keep in mind that Gradle has a distinct configuration and execution phase (see Build
Lifecycle).
Example B.2. Distinct configuration and execution phase
build.gradle
def classesDir = file('build/classes')
classesDir.mkdirs()
task clean(type: Delete) {
delete 'build'
}
task compile(dependsOn: 'clean') {
doLast {
if (!classesDir.isDirectory()) {
println 'The class directory does not exist. I can not operate'
// do something
}
// do something
}
}
Output of gradle -q compile
> gradle -q compile
The class directory does not exist. I can not operate
As the creation of the directory happens during the configuration phase, the clean task removes the
directory during the execution phase.
Page 713 of 717
C
The Feature Lifecycle
Gradle is under constant development and improvement. New versions are delivered on a regular and
frequent basis (approximately every 6 weeks). Continuous improvement combined with frequent delivery
allows new features to be made available to users early and for invaluable real world feedback to be
incorporated into the development process. Getting new functionality into the hands of users regularly is a
core value of the Gradle platform. At the same time, API and feature stability is taken very seriously and is
also considered a core value of the Gradle platform. This is something that is engineered into the
development process by design choices and automated testing, and is formalised by the section called
“Backwards Compatibility Policy”.
The Gradle feature lifecycle has been designed to meet these goals. It also serves to clearly communicate
to users of Gradle what the state of a feature is. The term feature typically means an API or DSL method or
property in this context, but it is not restricted to this definition. Command line arguments and modes of
execution (e.g. the Build Daemon) are two examples of other kinds of features.
§
States
Features can be in one of 4 states:
Internal
Incubating
Public
Deprecated
§
Internal
Internal features are not designed for public use and are only intended to be used by Gradle itself. They can
change in any way at any point in time without any notice. Therefore, we recommend avoiding the use of
such features. Internal features are not documented. If it appears in this User Guide, the DSL Reference or
the API Reference documentation then the feature is not internal.
Internal features may evolve into public features.
Incubating
Page 714 of 717
§
Incubating
Features are introduced in the incubating state to allow real world feedback to be incorporated into the
feature before it is made public and locked down to provide backwards compatibility. It also gives users who
are willing to accept potential future changes early access to the feature so they can put it into use
immediately.
A feature in an incubating state may change in future Gradle versions until it is no longer incubating.
Changes to incubating features for a Gradle release will be highlighted in the release notes for that release.
The incubation period for new features varies depending on the scope, complexity and nature of the feature.
Features in incubation are clearly indicated to be so. In the source code, all methods/properties/classes that
are incubating are annotated with Incubating, which is also used to specially mark them in the DSL and
API references. If an incubating feature is discussed in this User Guide, it will be explicitly said to be in the
incubating state.
§
Public
The default state for a non-internal feature is public . Anything that is documented in the User Guide, DSL
Reference or API references that is not explicitly said to be incubating or deprecated is considered public.
Features are said to be promoted from an incubating state to public. The release notes for each release
indicate which previously incubating features are being promoted by the release.
A public feature will never be removed or intentionally changed without undergoing deprecation. All public
features are subject to the backwards compatibility policy.
§
Deprecated
Some features will become superseded or irrelevant due to the natural evolution of Gradle. Such features
will eventually be removed from Gradle after being deprecated . A deprecated feature will never be changed,
until it is finally removed according to the backwards compatibility policy.
Deprecated features are clearly indicated to be so. In the source code, all methods/properties/classes that
are deprecated are annotated with “@java.lang.Deprecated” which is reflected in the DSL and API
references. In most cases, there is a replacement for the deprecated element, and this will be described in
the documentation. Using a deprecated feature will also result in a runtime warning in Gradle’s output.
Use of deprecated features should be avoided. The release notes for each release indicate any features that
are being deprecated by the release.
Page 715 of 717
Backwards Compatibility Policy
§
Backwards Compatibility Policy
Gradle provides backwards compatibility across major versions (e.g. 1.x, 2.x, etc.). Once a public feature
is introduced or promoted in a Gradle release it will remain indefinitely or until it is deprecated. Once
deprecated, it may be removed in the next major release. Deprecated features may be supported across
major releases, but this is not guaranteed.
Page 716 of 717
D
Documentation licenses
§
Gradle Documentation
Copyright © 2007-2016 Gradle, Inc.
Copies of this document may be made for your own use and for distribution to others, provided that you do
not charge any fee for such copies and further provided that each copy contains this Copyright Notice,
whether distributed in print or electronically.
§
Header link icon
Copyright © 2011–2013 VisualEditor team.
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated
documentation files (the "Software"), to deal in the Software without restriction, including without limitation
the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and
to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions
of the Software.
The Software is provided "as is", without warranty of any kind, express or implied, including but not limited to
the warranties of merchantability, fitness for a particular purpose and noninfringement. In no event shall the
authors or copyright holders be liable for any claim, damages or other liability, whether in an action of
contract, tort or otherwise, arising from, out of or in connection with the Software or the use or other dealings
in the Software.
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