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Reference Documentation
Version 1.2.0
Last Updated Novermber 10, 2008 (Latest documentation)
Copyright © 2004-2008 Mark Pollack, Rick Evans, Aleksandar Seovic, Bruno Baia, Federico
Spinazzi, Rob Harrop, Griffin Caprio, Ruben Bartelink, Choy Rim, The Spring Java Team
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.
1. Preface ................................................................................................................................................ 1
2. Introduction ......................................................................................................................................... 2
2.1. Overview .................................................................................................................................... 2
2.2. Background ................................................................................................................................. 2
2.3. Modules ...................................................................................................................................... 3
2.4. Usage Scenarios .......................................................................................................................... 4
2.5. Quickstart applications ................................................................................................................. 4
2.6. License Information ..................................................................................................................... 5
2.7. Support ....................................................................................................................................... 5
3. Background information ....................................................................................................................... 6
3.1. Inversion of Control .................................................................................................................... 6
4. Migrating from 1.1 M2 ........................................................................................................................ 7
4.1. Introduction ................................................................................................................................. 7
4.2. Important Changes ...................................................................................................................... 7
4.2.1. Namespaces .................................................................................................................. 7
4.2.2. Core ............................................................................................................................. 8
4.2.3. Web ............................................................................................................................. 8
4.2.4. Data ............................................................................................................................. 8
I. Core Technologies ................................................................................................................................ 9
5. The IoC container ........................................................................................................................ 10
5.1. Introduction ................................................................................................................... 10
5.2. Basics - containers and objects ....................................................................................... 10
5.2.1. The container ............................................................................................ 10
5.2.2. Instantiating a container ............................................................................ 12
5.2.3. The Objects .............................................................................................. 15
5.2.4. Object creation ......................................................................................... 17
5.2.5. Object creation of generic types ................................................................. 19
5.2.6. Using the container ................................................................................... 21
5.3. Dependencies ................................................................................................................ 21
5.3.1. Injecting dependencies .............................................................................. 21
5.3.2. Dependencies and configuration in detail .................................................... 29
5.3.3. Declarative Event Listener Registration ...................................................... 37
5.3.4. Using depends-on ..................................................................................... 39
5.3.5. Lazily-instantiated objects ......................................................................... 39
5.3.6. Autowiring collaborators ........................................................................... 40
5.3.7. Checking for dependencies ........................................................................ 41
5.3.8. Method Injection ....................................................................................... 42
5.3.9. Setting a reference using the members of other objects and classes. ............... 45
5.3.10. Provided IFactoryObject implementations ................................................. 49
5.4. Object Scopes ............................................................................................................... 50
5.4.1. The singleton scope .................................................................................. 50
5.4.2. The prototype scope .................................................................................. 51
5.4.3. Singleton objecgts with prototype-object dependencies ................................ 51
5.4.4. The other scopes ....................................................................................... 52
5.5. Type conversion ............................................................................................................ 52
5.5.1. Type Conversion for Enumerations ............................................................ 52
5.5.2. Built-in TypeConverters ............................................................................ 52
5.5.3. Custom Type Conversion .......................................................................... 53
5.6. Customizing the nature of an object ................................................................................ 55
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5.6.1. Lifecycle interfaces ................................................................................... 55
5.6.2. Knowing who you are ............................................................................... 57
5.7. Object definition inheritance .......................................................................................... 57
5.8. Interacting with the container ......................................................................................... 58
5.8.1. Obtaining an IFactoryObject, not its product ............................................... 60
5.9. Container extension points ............................................................................................. 60
5.9.1. Customizing objects with IObjectPostProcessors ......................................... 60
5.9.2. Customizing configuration metadata with ObjectFactoryPostProcessors ........ 64
5.9.3. Customizing instantiation logic using IFactoryObjects ................................. 70
5.10. The IApplicationContext .............................................................................................. 71
5.10.1. IObjectFactory or IApplicationContext? .................................................... 71
5.11. Configuration of IApplicationContext ........................................................................... 72
5.11.1. Registering custom parsers ...................................................................... 73
5.11.2. Registering custom resource handlers ....................................................... 74
5.11.3. Registering Type Aliases ......................................................................... 74
5.11.4. Registering Type Converters .................................................................... 75
5.12. Added functionality of the IApplicationContext ............................................................. 76
5.12.1. Context Hierarchies ................................................................................. 76
5.12.2. Using IMessageSource ............................................................................ 77
5.12.3. Using resources within Spring.NET .......................................................... 79
5.12.4. Loosely coupled events ........................................................................... 79
5.12.5. Event notification from IApplicationContext ............................................. 80
5.13. Customized behavior in the ApplicationContext ............................................................. 82
5.13.1. The IApplicationContextAware marker interface ....................................... 82
5.13.2. The IObjectPostProcessor ........................................................................ 82
5.13.3. The IObjectFactoryPostProcessor ............................................................. 82
5.13.4. The PropertyPlaceholderConfigurer .......................................................... 82
5.14. Configuration of ApplicationContext without using XML ............................................... 82
5.15. Service Locator access ................................................................................................. 83
5.16. Stereotype attributes ..................................................................................................... 84
6. The IObjectWrapper and Type conversion ..................................................................................... 85
6.1. Introduction ................................................................................................................... 85
6.2. Manipulating objects using the IObjectWrapper ............................................................... 85
6.2.1. Setting and getting basic and nested properties ............................................ 85
6.2.2. Other features worth mentioning ................................................................ 87
6.3. Type conversion ............................................................................................................ 87
6.3.1. Type Conversion for Enumerations ............................................................ 88
6.4. Built-in TypeConverters ................................................................................................. 88
6.4.1. Custom type converters ............................................................................. 89
7. Resources .................................................................................................................................... 90
7.1. Introduction ................................................................................................................... 90
7.2. The IResource interface ................................................................................................. 90
7.3. Built-in IResource implementations ................................................................................ 91
7.3.1. Registering custom IResource implementations ........................................... 91
7.4. The IResourceLoader ..................................................................................................... 92
7.5. The IResourceLoaderAware interface ............................................................................. 92
7.6. Application contexts and IResource paths ....................................................................... 93
8. Threading and Concurrency Support ............................................................................................. 94
8.1. Introduction ................................................................................................................... 94
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8.2. Thread Local Storage ..................................................................................................... 94
8.3. Synchronization Primitives ............................................................................................. 95
8.3.1. ISync ........................................................................................................ 95
8.3.2. SyncHolder ............................................................................................... 95
8.3.3. Latch ........................................................................................................ 96
8.3.4. Semaphore ................................................................................................ 96
9. Object Pooling ............................................................................................................................. 98
9.1. Introduction ................................................................................................................... 98
9.2. Interfaces and Implementations ...................................................................................... 98
10. Spring.NET miscellanea .............................................................................................................. 99
10.1. Introduction ................................................................................................................. 99
10.2. PathMatcher ................................................................................................................ 99
10.2.1. General rules .......................................................................................... 99
10.2.2. Matching filenames ................................................................................. 99
10.2.3. Matching subdirectories ......................................................................... 100
10.2.4. Case does matter, slashes don't ............................................................... 101
11. Expression Evaluation ............................................................................................................... 102
11.1. Introduction ............................................................................................................... 102
11.2. Evaluating Expressions ............................................................................................... 102
11.3. Language Reference ................................................................................................... 103
11.3.1. Literal expressions ................................................................................. 103
11.3.2. Properties, Arrays, Lists, Dictionaries, Indexers ....................................... 104
11.3.3. Methods ................................................................................................ 105
11.3.4. Operators .............................................................................................. 105
11.3.5. Assignment ........................................................................................... 108
11.3.6. Expression lists ..................................................................................... 108
11.3.7. Types .................................................................................................... 108
11.3.8. Type Registration .................................................................................. 109
11.3.9. Constructors .......................................................................................... 109
11.3.10. Variables ............................................................................................. 109
11.3.11. Ternary Operator (If-Then-Else) ........................................................... 110
11.3.12. List Projection and Selection ................................................................ 110
11.3.13. Collection Processors and Aggregators .................................................. 111
11.3.14. Spring Object References ..................................................................... 114
11.3.15. Lambda Expressions ............................................................................ 115
11.3.16. Delegate Expressions ........................................................................... 116
11.3.17. Null Context ....................................................................................... 116
11.4. Classes used in the examples ...................................................................................... 116
12. Validation Framework .............................................................................................................. 119
12.1. Introduction ............................................................................................................... 119
12.2. Example Usage .......................................................................................................... 119
12.3. Validator Groups ....................................................................................................... 120
12.4. Validators .................................................................................................................. 121
12.4.1. Condition Validator ............................................................................... 121
12.4.2. Required Validator ................................................................................ 122
12.4.3. Regular Expression Validator ................................................................. 122
12.4.4. Generic Validator .................................................................................. 123
12.4.5. Conditional Validator Execution ............................................................. 123
12.5. Validator Actions ....................................................................................................... 124
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12.5.1. Error Message Action ............................................................................
12.5.2. Generic Actions ....................................................................................
12.6. Validator References ..................................................................................................
12.7. Progammatic usage ....................................................................................................
12.8. Usage tips within ASP.NET .......................................................................................
12.8.1. Rendering Validation Errors ...................................................................
13. Aspect Oriented Programming with Spring.NET ........................................................................
13.1. Introduction ...............................................................................................................
13.1.1. AOP concepts .......................................................................................
13.1.2. Spring.NET AOP capabilities .................................................................
13.1.3. AOP Proxies in Spring.NET ..................................................................
13.2. Pointcut API in Spring.NET .......................................................................................
13.2.1. Concepts ...............................................................................................
13.2.2. Operations on pointcuts .........................................................................
13.2.3. Convenience pointcut implementations ...................................................
13.2.4. Custom pointcuts ...................................................................................
13.3. Advice API in Spring.NET .........................................................................................
13.3.1. Advice Lifecycle ...................................................................................
13.3.2. Advice types .........................................................................................
13.4. Advisor API in Spring.NET .......................................................................................
13.5. Using the ProxyFactoryObject to create AOP proxies ...................................................
13.5.1. Basics ...................................................................................................
13.5.2. ProxyFactoryObject Properties ...............................................................
13.5.3. Proxying Interfaces ................................................................................
13.5.4. Proxying Classes ...................................................................................
13.5.5. Concise proxy definitions ......................................................................
13.6. Proxying mechanisms .................................................................................................
13.6.1. InheritanceBasedAopConfigurer .............................................................
13.7. Creating AOP Proxies Programatically with the ProxyFactory ......................................
13.8. Manipulating Advised Objects ....................................................................................
13.9. Using the "autoproxy" facility ....................................................................................
13.9.1. Autoproxy object definitions ..................................................................
13.9.2. Using attribute-driven auto-proxying ......................................................
13.10. Using AOP Namespace ............................................................................................
13.11. Using TargetSources ................................................................................................
13.11.1. Hot swappable target sources ...............................................................
13.11.2. Pooling target sources ..........................................................................
13.11.3. Prototype target sources .......................................................................
13.11.4. ThreadLocal target sources ...................................................................
13.12. Defining new Advice types .......................................................................................
13.13. Further reading and resources ...................................................................................
14. Aspect Library ..........................................................................................................................
14.1. Introduction ...............................................................................................................
14.2. Caching .....................................................................................................................
14.3. Exception Handling ....................................................................................................
14.3.1. Language Reference ..............................................................................
14.4. Logging .....................................................................................................................
14.5. Retry .........................................................................................................................
14.5.1. Language Reference ..............................................................................
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14.6. Transactions ...............................................................................................................
14.7. Parameter Validation ..................................................................................................
15. Common Logging .....................................................................................................................
15.1. Introduction ...............................................................................................................
16. Testing .....................................................................................................................................
16.1. Introduction ...............................................................................................................
16.2. Unit testing ................................................................................................................
16.3. Integration testing ......................................................................................................
16.3.1. Context management and caching ...........................................................
16.3.2. Dependency Injection of test fixtures ......................................................
16.3.3. Transaction management ........................................................................
16.3.4. Convenience variables ...........................................................................
16.3.5. ............................................................................................................
16.4. Further Resources ......................................................................................................
II. Middle Tier Data Access ..................................................................................................................
17. Transaction management ...........................................................................................................
17.1. Introduction ...............................................................................................................
17.2. Motivations ................................................................................................................
17.3. Key Abstractions .......................................................................................................
17.4. Resource synchronization with transactions .................................................................
17.4.1. High-level approach ..............................................................................
17.4.2. Low-level approach ...............................................................................
17.5. Declarative transaction management ............................................................................
17.5.1. Understanding Spring's declarative transaction implementation .................
17.5.2. A First Example ....................................................................................
17.5.3. Declarative transactions using the transaction namespace .........................
17.5.4. Transaction attribute settings ..................................................................
17.5.5. Declarative Transactions using AutoProxy ..............................................
17.5.6. Declarative Transactions using TransactionProxyFactoryObject ................
17.5.7. Concise proxy definitions ......................................................................
17.5.8. Declarative Transactions using ProxyFactoryObject .................................
17.6. Programmatic transaction management ........................................................................
17.6.1. Using the TransactionTemplate ..............................................................
17.6.2. Using the PlatformTransactionManager ..................................................
17.7. Choosing between programmatic and declarative transaction management .....................
17.8. Transaction lifecycle and status information ................................................................
18. DAO support ............................................................................................................................
18.1. Introduction ...............................................................................................................
18.2. Consistent exception hierarchy ....................................................................................
18.3. Consistent abstract classes for DAO support ................................................................
19. DbProvider ...............................................................................................................................
19.1. Introduction ...............................................................................................................
19.2. IDbProvider and DbProviderFactory ...........................................................................
19.3. XML based configuration ...........................................................................................
19.4. Connection String management ...................................................................................
19.5. Additional IDbProvider implementations .....................................................................
19.5.1. UserCredentialsDbProvider ....................................................................
19.5.2. MultiDelegatingDbProvider ...................................................................
20. Data access using ADO.NET ....................................................................................................
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20.1. Introduction ...............................................................................................................
Motivations ........................................................................................................................
20.3. Provider Abstraction ..................................................................................................
20.3.1. Creating an instance of IDbProvider .......................................................
20.4. Namespaces ...............................................................................................................
20.5. Approaches to Data Access ........................................................................................
20.6. Introduction to AdoTemplate ......................................................................................
20.6.1. Execute Callback ...................................................................................
20.6.2. Execute Callback in .NET 2.0 ................................................................
20.6.3. Execute Callback in .NET 1.1 ................................................................
20.6.4. Quick Guide to AdoTemplate Methods ...................................................
20.6.5. Quick Guide to AdoTemplate Properties .................................................
20.7. Transaction Management ............................................................................................
20.8. Exception Translation .................................................................................................
20.9. Parameter Management ..............................................................................................
20.9.1. IDbParametersBuilder ............................................................................
20.9.2. IDbParameters .......................................................................................
20.10. Custom IDataReader implementations .......................................................................
20.11. Basic data access operations .....................................................................................
20.11.1. ExecuteNonQuery ................................................................................
20.11.2. ExecuteScalar ......................................................................................
20.12. Queries and Lightweight Object Mapping ..................................................................
20.12.1. ResultSetExtractor ...............................................................................
20.12.2. RowCallback .......................................................................................
20.12.3. RowMapper ........................................................................................
20.12.4. Query for a single object ......................................................................
20.12.5. Query using a CommandCreator ...........................................................
20.13. DataTable and DataSet .............................................................................................
20.13.1. DataTables ..........................................................................................
20.13.2. DataSets ..............................................................................................
20.14. TableAdapters and participation in transactional context .............................................
20.15. Database operations as Objects .................................................................................
20.15.1. AdoQuery ...........................................................................................
20.15.2. MappingAdoQuery ..............................................................................
20.15.3. AdoNonQuery .....................................................................................
20.15.4. Stored Procedure .................................................................................
21. Object Relational Mapping (ORM) data access ..........................................................................
21.1. Introduction ...............................................................................................................
21.2. NHibernate ................................................................................................................
21.2.1. Resource management ...........................................................................
21.2.2. Transaction Management .......................................................................
21.2.3. SessionFactory set up in a Spring container .............................................
21.2.4. The HibernateTemplate ..........................................................................
21.2.5. Implementing Spring-based DAOs without callbacks ...............................
21.2.6. Implementing DAOs based on plain Hibernate 1.2/2.0 API .......................
21.2.7. Programmatic transaction demarcation ....................................................
21.2.8. Declarative transaction demarcation ........................................................
21.2.9. Transaction management strategies .........................................................
21.2.10. Web Session Management ...................................................................
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21.2.11. Session Scope ..................................................................................... 255
III. The Web ........................................................................................................................................ 256
22. Spring.NET Web Framework .................................................................................................... 257
22.1. Introduction ............................................................................................................... 257
22.2. Background ............................................................................................................... 258
22.3. Automatic context loading and hierarchical contexts .................................................... 259
22.3.1. Configuration ........................................................................................ 259
22.3.2. Context Hierarchy ................................................................................. 261
22.4. Dependency Injection for ASP.NET Pages .................................................................. 262
22.4.1. Injecting Dependencies into Controls ...................................................... 264
22.4.2. Injecting dependencies into custom HTTP modules ................................. 264
22.4.3. Injecting dependencies into HTTP handlers and handler factories .............. 264
22.4.4. Injecting dependencies into custom providers .......................................... 266
22.4.5. Customizing control dependency injection .............................................. 266
22.5. Web object scopes ..................................................................................................... 267
22.6. Master Pages in ASP.NET 1.1 .................................................................................... 268
22.6.1. Linking child pages to their master ......................................................... 269
22.7. Bidirectional Data Binding and Model Management ..................................................... 269
22.7.1. Data Binding Under the Hood ................................................................ 274
22.7.2. Using DataBindingPanel ........................................................................ 278
22.7.3. Customizing Model Persistence .............................................................. 279
22.8. Localization and Message Sources .............................................................................. 280
22.8.1. Automatic Localization Using Localizers ("Push" Localization) ................ 280
22.8.2. Global Message Sources ........................................................................ 282
22.8.3. Working with Localizers ........................................................................ 283
22.8.4. Applying Resources Manually ("Pull" Localization) ................................ 284
22.8.5. Localizing Images within a Web Application .......................................... 284
22.8.6. User Culture Management ..................................................................... 285
22.8.7. Changing Cultures ................................................................................. 286
22.9. Result Mapping ......................................................................................................... 287
22.9.1. Registering user defined transfer modes .................................................. 289
22.10. Client-Side Scripting ................................................................................................ 290
22.10.1. Registering Scripts within the head HTML section ................................. 290
22.10.2. Adding CSS Definitions to the head Section .......................................... 291
22.10.3. Well-Known Directories ...................................................................... 291
22.11. Spring User Controls ................................................................................................ 291
22.11.1. Validation Controls .............................................................................. 291
22.11.2. Databinding Controls ........................................................................... 291
22.11.3. Calendar Control ................................................................................. 292
22.11.4. Panel Control ...................................................................................... 292
23. ASP.NET AJAX ....................................................................................................................... 293
23.1. Introduction ............................................................................................................... 293
23.2. Web Services ............................................................................................................. 293
23.2.1. Exposing Web Services ......................................................................... 293
23.2.2. Calling Web Services by using JavaScript ............................................... 294
IV. Services ......................................................................................................................................... 295
24. Introduction to Spring Services ................................................................................................. 296
24.1. Introduction ............................................................................................................... 296
25. .NET Remoting ......................................................................................................................... 298
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25.1. Introduction ............................................................................................................... 298
25.2. Publishing SAOs on the Server ................................................................................... 298
25.2.1. SAO Singleton ...................................................................................... 298
25.2.2. SAO SingleCall ..................................................................................... 299
25.2.3. IIS Application Configuration ................................................................ 300
25.3. Accessing a SAO on the Client .................................................................................. 301
25.4. CAO best practices .................................................................................................... 302
25.5. Registering a CAO object on the Server ...................................................................... 302
25.5.1. Applying AOP advice to exported CAO objects ...................................... 303
25.6. Accessing a CAO on the Client .................................................................................. 303
25.6.1. Applying AOP advice to client side CAO objects. ................................... 304
25.7. XML Schema for configuration .................................................................................. 304
25.8. Additional Resources ................................................................................................. 304
26. .NET Enterprise Services .......................................................................................................... 305
26.1. Introduction ............................................................................................................... 305
26.2. Serviced Components ................................................................................................. 305
26.3. Server Side ................................................................................................................ 305
26.4. Client Side ................................................................................................................ 307
27. Web Services ........................................................................................................................... 308
27.1. Introduction ............................................................................................................... 308
27.2. Server-side ................................................................................................................. 308
27.2.1. Removing the need for .asmx files .......................................................... 308
27.2.2. Injecting dependencies into web services ................................................ 309
27.2.3. Exposing PONOs as Web Services ......................................................... 311
27.2.4. Exporting an AOP Proxy as a Web Service ............................................. 312
27.3. Client-side ................................................................................................................. 313
27.3.1. Using VS.NET generated proxy ............................................................. 313
27.3.2. Generating proxies dynamically ............................................................. 314
27.3.3. Configuring the proxy instance .............................................................. 314
28. Windows Communication Foundation (WCF) ............................................................................ 316
28.1. Introduction ............................................................................................................... 316
28.2. Configuring WCF services via Dependency Injection ................................................... 316
28.2.1. Dependency Injection ............................................................................ 316
28.3. Apply AOP advice to WCF services ........................................................................... 318
28.4. Creating client side proxies declaratively ..................................................................... 318
28.5. Exporting PONOs as WCF Services ........................................................................... 319
V. Integration ....................................................................................................................................... 320
29. Message Oriented Middleware - Apache ActiveMQ ................................................................... 321
29.1. Introduction ............................................................................................................... 321
29.1.1. Separation of Concerns .......................................................................... 322
29.1.2. Interoperability and provider portability .................................................. 322
29.1.3. The role of Messaging API in a 'WCF world' .......................................... 323
29.2. Using Spring Messaging ............................................................................................. 323
29.2.1. Messaging Template overview ............................................................... 323
29.2.2. Connections .......................................................................................... 324
29.2.3. Caching Messaging Resources ............................................................... 324
29.2.4. Destination Management ........................................................................ 324
29.2.5. Message Listener Containers .................................................................. 325
29.2.6. Transaction Management ....................................................................... 325
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29.3. Sending a Message ....................................................................................................
29.3.1. Using MessageConverters ......................................................................
29.4. Session and Producer Callback ...................................................................................
29.5. Receiving a message ..................................................................................................
29.5.1. Synchronous Reception ..........................................................................
29.5.2. Asynchronous Reception ........................................................................
29.5.3. The ISessionAwareMessageListener interface .........................................
29.5.4. MessageListenerAdapater .......................................................................
29.5.5. Processing messages within a messaging transaction ................................
29.5.6. Messaging Namespace support ...............................................................
30. Message Oriented Middleware - MSMQ ....................................................................................
30.1. Introduction ...............................................................................................................
30.2. A quick tour for the impatient ....................................................................................
30.3. Using Spring MSMQ .................................................................................................
30.3.1. MessageQueueTemplate .........................................................................
30.3.2. MessageQueueFactoryObject .................................................................
30.3.3. MessageQueue and IMessageConverter resource management ..................
30.3.4. Message Listener Containers ..................................................................
30.4. MessageConverters ....................................................................................................
30.4.1. Using MessageConverters ......................................................................
30.5. Interface based message processing .............................................................................
30.5.1. ............................................................................................................
30.6. Comparison with using WCF ......................................................................................
31. Scheduling and Thread Pooling .................................................................................................
31.1. Introduction ...............................................................................................................
31.2. Using the Quartz.NET Scheduler ................................................................................
31.2.1. Using the JobDetailObject .....................................................................
31.2.2. Using the MethodInvokingJobDetailFactoryObject ..................................
31.2.3. Wiring up jobs using triggers and the SchedulerFactoryObject ..................
VI. VS.NET Integration ........................................................................................................................
32. Visual Studio.NET Integration ..................................................................................................
32.1. XML Editing and Validation ......................................................................................
32.2. Versions of XML Schema ..........................................................................................
32.3. Integrated API help ....................................................................................................
VII. Quickstart applications ..................................................................................................................
33. IoC Quickstarts .........................................................................................................................
33.1. Introduction ...............................................................................................................
33.2. Movie Finder .............................................................................................................
33.2.1. Getting Started - Movie Finder ...............................................................
33.2.2. First Object Definition ...........................................................................
33.2.3. Setter Injection ......................................................................................
33.2.4. Constructor Injection .............................................................................
33.2.5. Summary ..............................................................................................
33.2.6. Logging ................................................................................................
33.3. ApplicationContext and IMessageSource .....................................................................
33.3.1. Introduction ..........................................................................................
33.4. ApplicationContext and IEventRegistry .......................................................................
33.4.1. Introduction ..........................................................................................
33.5. Pooling example ........................................................................................................
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34.
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40.
33.5.1. Implementing Spring.Pool.IPoolableObjectFactory ..................................
33.5.2. Being smart using pooled objects ...........................................................
33.5.3. Using the executor to do a parallel grep ..................................................
33.6. AOP ..........................................................................................................................
AOP Guide ..............................................................................................................................
34.1. Introduction ...............................................................................................................
34.2. The basics .................................................................................................................
34.2.1. Applying advice ....................................................................................
34.2.2. Using Pointcuts - the basics ...................................................................
34.3. Going deeper .............................................................................................................
34.3.1. Other types of Advice ...........................................................................
34.3.2. Using Attributes to define Pointcuts .......................................................
34.4. The Spring.NET AOP Cookbook ................................................................................
34.4.1. Caching ................................................................................................
34.4.2. Performance Monitoring ........................................................................
34.4.3. Retry Rules ...........................................................................................
34.5. Spring.NET AOP Best Practices .................................................................................
Portable Service Abstraction Quick Start ...................................................................................
35.1. Introduction ...............................................................................................................
35.2. .NET Remoting Example ............................................................................................
35.3. Implementation ..........................................................................................................
35.4. Running the application ..............................................................................................
35.5. Remoting Schema ......................................................................................................
35.6. .NET Enterprise Services Example ..............................................................................
35.7. Web Services Example ...............................................................................................
35.8. Additional Resources .................................................................................................
Web Quickstarts .......................................................................................................................
36.1. Introduction ...............................................................................................................
SpringAir - Reference Application .............................................................................................
37.1. Introduction ...............................................................................................................
37.2. Getting Started ...........................................................................................................
37.3. Container configuration ..............................................................................................
37.4. Bi-directional data binding .........................................................................................
37.5. Declarative Validation ................................................................................................
37.6. Internationalization .....................................................................................................
37.7. Web Services .............................................................................................................
Data Access QuickStart ............................................................................................................
38.1. Introduction ...............................................................................................................
38.1.1. Database configuration ..........................................................................
38.1.2. CommandCallback ................................................................................
Transactions QuickStart ............................................................................................................
39.1. Introduction ...............................................................................................................
39.2. Application Overview ................................................................................................
39.2.1. Interfaces ..............................................................................................
39.3. Implementation ..........................................................................................................
39.4. Configuration .............................................................................................................
39.4.1. Rollback Rules ......................................................................................
39.5. Adding additional Aspects ..........................................................................................
NHibernate QuickStart ..............................................................................................................
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40.1. Introduction ............................................................................................................... 417
41. Quartz QuickStart ..................................................................................................................... 418
41.1. Introduction ............................................................................................................... 418
41.2. Application Overview ................................................................................................ 418
41.3. Standard job scheduling ............................................................................................. 418
41.4. Scheduling arbitrary methods as jobs .......................................................................... 419
42. NMS QuickStart ....................................................................................................................... 421
42.1. Introduction ............................................................................................................... 421
42.2. Message Destinations ................................................................................................. 421
42.3. Gateways ................................................................................................................... 422
42.4. Message Data ............................................................................................................ 422
42.5. Message Handlers ...................................................................................................... 424
42.6. Message Converters ................................................................................................... 425
42.7. Messaging Infrastructure ............................................................................................ 425
42.8. Running the application .............................................................................................. 427
43. MSMQ QuickStart .................................................................................................................... 428
43.1. Introduction ............................................................................................................... 428
43.2. Message Destinations ................................................................................................. 428
43.3. Gateways ................................................................................................................... 428
43.4. Message Data ............................................................................................................ 428
43.5. Message Handlers ...................................................................................................... 428
43.6. MessageConverters .................................................................................................... 428
43.7. Messaging Infrastructure ............................................................................................ 429
43.8. Running the application .............................................................................................. 431
44. WCF QuickStart ....................................................................................................................... 432
44.1. Introduction ............................................................................................................... 432
44.2. The server side .......................................................................................................... 432
44.2.1. WCF Dependency Injection and AOP in self-hosted application ................ 433
44.2.2. WCF Dependency Injection and AOP in IIS web application .................... 433
44.3. Client access .............................................................................................................. 433
VIII. Spring.NET for Java developers ................................................................................................... 435
45. Spring.NET for Java Developers ............................................................................................... 436
45.1. Introduction ............................................................................................................... 436
45.2. Beans to Objects ........................................................................................................ 436
45.3. PropertyEditors to TypeConverters .............................................................................. 437
45.4. ResourceBundle-ResourceManager ............................................................................. 437
45.5. Exceptions ................................................................................................................. 437
45.6. Application Configuration .......................................................................................... 437
45.7. AOP Framework ........................................................................................................ 438
45.7.1. Cannot specify target name at the end of interceptorNames for
ProxyFactoryObject .......................................................................................... 438
A. XML Schema-based configuration .................................................................................................... 440
A.1. Introduction ............................................................................................................................ 440
A.2. XML Schema-based configuration ........................................................................................... 440
A.2.1. Referencing the schemas .......................................................................................... 440
A.2.2. The tx (transaction) schema ...................................................................................... 441
A.2.3. The aop schema ....................................................................................................... 442
A.2.4. The db schema ......................................................................................................... 443
A.2.5. The remoting schema ............................................................................................... 443
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The Spring.NET Framework
A.2.6. The nms messaging schema ......................................................................................
A.2.7. The validation schema ..............................................................................................
A.2.8. The objects schema ..................................................................................................
A.3. Setting up your IDE ................................................................................................................
B. Extensible XML authoring ...............................................................................................................
B.1. Introduction ............................................................................................................................
B.2. Authoring the schema ..............................................................................................................
B.3. Coding a INamespaceParser .....................................................................................................
B.4. Coding an IObjectDefinitionParser ...........................................................................................
B.5. Registering the handler and the schema ....................................................................................
B.5.1. NamespaceParsersSectionHandler ..............................................................................
B.6. Using a custom extension in your Spring XML configuration ....................................................
B.7. Further Resources ...................................................................................................................
C. Spring.NET's spring-objects.xsd .......................................................................................................
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Chapter 1. Preface
Developing software applications is hard enough even with good tools and technologies. Spring provides a lightweight solution for building enterprise-ready applications. Spring provides a consistent and transparent means
to configure your application and integrate AOP into your software. Highlights of Spring's functionality are
providing declarative transaction management for your middle tier as well as a full-featured ASP.NET framework.
Spring could potentially be a one-stop-shop for many areas of enterprise application development; however,
Spring is modular, allowing you to use just those parts of it that you need, without having to bring in the rest. You
can use just the IoC container to configure your application and use traditional ADO.NET based data access code,
but you could also choose to use just the Hibernate integration code or the ADO.NET abstraction layer. Spring
has been (and continues to be) designed to be non-intrusive, meaning dependencies on the framework itself are
generally none (or absolutely minimal, depending on the area of use).
This document provides a reference guide to Spring's features. Since this document is still to be considered very
much work-in-progress, if you have any requests or comments, please post them on the user mailing list or on
the support forums at forum.springframework.net.
Before we go on, a few words of gratitude are due to Christian Bauer (of the Hibernate team), who prepared and
adapted the DocBook-XSL software in order to be able to create Hibernate's reference guide, thus also allowing us
to create this one. Also thanks to Russell Healy for doing an extensive and valuable review of some of the material.
Spring Framework (Version 1.2.0)
1
Chapter 2. Introduction
2.1. Overview
Spring.NET is an application framework that provides comprehensive infrastructural support for developing
enterprise .NET applications. It allows you to remove incidental complexity when using the base class libraries
makes best practices, such as test driven development, easy practices. Spring.NET is created, supported and
sustained by SpringSource.
The design of Spring.NET is based on the Java version of the Spring Framework, which has shown real-world
benefits and is used in thousands of enterprise applications world wide. Spring .NET is not a quick port from the
Java version, but rather a 'spiritual port' based on following proven architectural and design patterns in that are
not tied to a particular platform. The breadth of functionality in Spring .NET spans application tiers which allows
you to treat it as a ‘one stop shop’ but that is not required. Spring .NET is not an all-or-nothing solution. You can
use the functionality in its modules independently. These modules are described below.
Enterprise applications typically are composed of a number of a variety of physical tiers and within each tier
functionality is often split into functional layers. The business service layer for example typically uses a objects
in the data access layer to fulfill a use-case. No matter how your application is architected, at the end of the day
there are a variety of objects that collaborate with one another to form the application proper. The objects in an
application can thus be said to have dependencies between themselves.
The .NET platform provides a wealth of functionality for architecting and building applications, ranging all the
way from the very basic building blocks of primitive types and classes (and the means to define new classes), to
rich full-featured application servers and web frameworks. One area that is decidedly conspicuous by its absence
is any means of taking the basic building blocks and composing them into a coherent whole; this area has typically
been left to the purvey of the architects and developers tasked with building an application (or applications). Now
to be fair, there are a number of design patterns devoted to the business of composing the various classes and
object instances that makeup an all-singing, all-dancing application. Design patterns such as Factory, Abstract
Factory, Builder, Decorator, and Service Locator (to name but a few) have widespread recognition and acceptance
within the software development industry (presumably that is why these patterns have been formalized as patterns
in the first place). This is all very well, but these patterns are just that: best practices given a name, typically
together with a description of what the pattern does, where the pattern is typically best applied, the problems
that the application of the pattern addresses, and so forth. Notice that the last paragraph used the phrase “... a
description of what the pattern does...”; pattern books and wikis are typically listings of such formalized best
practice that you can certainly take away, mull over, and then implement yourself in your application.
The Spring Framework takes best practices that have been proven over the years in numerous applications and
formalized as design patterns, and actually codifies these patterns as first class objects that you as an architect
and developer can take away and integrate into your own application(s). This is a Very Good Thing Indeed as
attested to by the numerous organizations and institutions that have used the Spring Framework to engineer robust,
maintainable applications. For example, the IoC component of the Spring Framework addresses the enterprise
concern of taking the classes, objects, and services that are to compose an application, by providing a formalized
means of composing these various disparate components into a fully working application ready for use
2.2. Background
In early 2004, Martin Fowler asked the readers of his site: when talking about Inversion of Control: “the question
is, what aspect of control are [they] inverting?”. Fowler then suggested renaming the principle (or at least giving
Spring Framework (Version 1.2.0)
2
Introduction
it a more self-explanatory name), and started to use the term Dependency Injection. His article then continued
to explain the ideas underpinning the Inversion of Control (IoC) and Dependency Injection (DI) principle. If
you need a decent insight into IoC and DI, please do refer to the article : http://martinfowler.com/articles/
injection.html.
2.3. Modules
The Spring Framework contains a lot of features, which are well-organized into modules shown in the diagram
below. The diagram below shows the various core modules of Spring.NET.
Click on the module name for more information.
Spring.Core is the most fundamental part of the framework allowing you to configure your application using
Dependency Injection. Other supporting functionality, listed below, is located in Spring.Core
Spring.Aop - Use this module to perform Aspect-Oriented Programming (AOP). AOP centralizes common
functionality that can then be declaratively applied across your application in a targeted manner. Spring's aspect
library provides predefined easy to use aspects for transactions, logging, performance monitoring, caching,
method retry, and exception handling.
Spring.Data - Use this module to achieve greater efficiency and consistency in writing data access functionality
in ADO.NET and to perform declarative transaction management.
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3
Introduction
Spring.Data.NHibernate - Use this module to integrate NHibernate with Spring’s declarative transaction
management functionality allowing easy mixing of ADO.NET and NHibernate operations within the same
transaction. NHibernate 1.0 users will benefit from ease of use APIs to perform data access operations.
Spring.Web - Use this module to raise the level of abstraction when writing ASP.NET web applications allowing
you to effectively address common pain-points in ASP.NET such as data binding, validation, and ASP.NET page/
control/module/provider configuration.
Spring.Web.Extensions - Use this module to raise the level of abstraction when writing ASP.NET web
applications allowing you to effectively address common pain-points in ASP.NET such as data binding,
validation, and ASP.NET page/control/module/provider configuration.
Spring.Services - Use this module to adapt plain .NET objects so they can be used with a specific distributed
communication technology, such as .NET Remoting, Enterprise Services, and ASMX Web Services. These
services can be configured via dependency injection and ‘decorated’ by applying AOP.
Spring.Testing.NUnit - Use this module to perform integration testing with NUnit.
The Spring.Core module also includes the following additional features
• Expression Language - provides efficient querying and manipulation of an object graphs at runtime.
• Validation Framework - a robust UI agnostic framework for creating complex validation rules for business
objects either programatically or declaratively.
• Data binding Framework - a UI agnostic framework for performing data binding.
• Dynamic Reflection - provides a high performance reflection API
• Threading - provides additional concurrency abstractions such as Latch, Semaphore and Thread Local Storage.
• Resource abstraction - provides a common interface to treat the InputStream from a file and from a URL in a
polymorphic and protocol-independent manner.
2.4. Usage Scenarios
With the building blocks described above you can use Spring in all sorts of scenarios, from simple stand alone
console applications to fully-fledged enterprise applications using Spring's transaction management functionality
and web framework integration.
It is important to note that the Spring Framework does not force you to use everything within it; it is not an allor-nothing solution. Existing front-ends built using standard ASP.NET can be integrated perfectly well with a
Spring-based middle-tier, allowing you to use the transaction and/or data access features that Spring offers. The
only things you need to do is wire up your business logic using Spring's IoC container and integrate it into your
web layer using WebApplicationContext to locate middle tier services and/or configure your standard ASP.NET
pages with depdenency injection.
While the Spring framework does not force any particular application architecure it encourages the use of a well
layered application architecture with distinct tiers for the presentation, service, data access, and database.
2.5. Quickstart applications
There are several sample applications that showcase individual features. If you are already familiar with the
concepts of dependency injection, AOP, or have experience using the Java version of the Spring framework you
Spring Framework (Version 1.2.0)
4
Introduction
may find jumping into the examples a better way to bootstrap the learning processing process. The following
quickstart applications are available and can be found in the examples directory in the distribution. Click on the
links for additional information.
• Movie Finder - A simple demonstration of Dependency Injection (DI) techniques using Spring's Inversion of
Control (IoC) container.
• Application Context - Demonstrates IoC container features such as localization, accessing of ResourceSet
objects, and applying resources to object properties.
• Aspect Oriented Programming - Demonstrates use of the AOP framework to add additional behavior to your
existing objects. Examples of programmatic and declarative AOP configuration are shown.
• Distributed Computing - A calculator demonstrating remote service abstractions that let you 'export' a
plain .NET object (PONO) via .NET Remoting, Web Services, or an EnterpriseService ServiceComponent.
Corresponding client side proxies are also demonstrated.
• WCF - Shows a WCF based calculator example that configures your WCF service via dependency injection
and apply AOP advice.
• Web Application - SpringAir -A ticket booking application that demonstrates the ASP.NET framework
showing features such as DI for ASP.NET pages, data binding, validation, and localization.
• Web Development - Introductory examples showing use of dependency injection and Spring's bi-directional
data binding in ASP.NET.
• Data Access - Demonstrates the ADO.NET framework showing how to simplify developing ADO.NET based
data access layers.
• Transaction Management : Demonstrates the use of declarative transaction management for both local and
distributed transaction in both .NET 1.1 and 2.0.
• AJAX : Demonstrates how to access a plain .NET object as a webservice in client side JavaScript
• NHibernate Northwind: Demonstrates use of Spring's NHibernate integration to simplify the use of NHibernate.
Web tier is also included showing how to use the Open-Session In View approach to session management in
the web tier.
• Quartz Quickstart - Application that shows the use of Quartz.NET integration for scheduling.
• NMS - Applicatoin demonstrating NMS helper classes.
2.6. License Information
Spring.NET is licensed according to the terms of the Apache License, Version 2.0. The full text of this license are
available online at http://www.apache.org/licenses/LICENSE-2.0 . You can also view the full text of the license
in the license.txt file located in the root installation directory.
2.7. Support
Training and support are available through SpringSource in addition to the mailing lists and forums you can find
on the main Spring.NET website.
Spring Framework (Version 1.2.0)
5
Chapter 3. Background information
3.1. Inversion of Control
In early 2004, Martin Fowler asked the readers of his site: when talking about Inversion of Control: "the question,
is what aspect of control are they inverting?". After talking about the term Inversion of Control Martin suggests
renaming the pattern, or at least giving it a more self-explanatory name, and starts to use the term Dependency
Injection. His article continues to explain some of the ideas behind this important software engineering principle.
Other references you may find useful are
• Wikipedia Article - Dependency Injection
• CodeProject article - Dependency Injection for Loose Coupling
Spring Framework (Version 1.2.0)
6
Chapter 4. Migrating from 1.1 M2
4.1. Introduction
Several API changes were made after 1.1 M2 (before 1.1 RC1)due primarily by the need to refactor the code base
to remove circular dependency cycles, which are now all removed. Class and schema name changes were also
made to provide a more consistent naming convention across the codebase. As a result of these changes, you can
not simply drop in the new .dlls as you may have done in previous release. This document serves as a high level
guide to the most likely areas where you will need to make changes to either your configuration or your code.
The file, BreakingChanges-1.1.txt, in the root directory of the distribution contains the full listing of breaking
changes made for RC1 and higher
4.2. Important Changes
This section covers the common areas were you will need to make changes in code/configuration when migration
from M2 to RC1or higher.
4.2.1. Namespaces
Note: If you previously installed Spring .xsd files to your VS.NET installation directory, remove them manually,
and copy over the new ones, which have the -1.1.xsd suffix.
The names of the section handlers to register custom schemas has changed, from ConfigParsersSectionHandler
to NamespaceParsersSectionHandler.
The target namespaces have changed, the 'directory' named /schema/ has been removed. For example, the target
schema changed from http://www.springframework.net/schema/tx to http://www.springframework.net/tx.
A typical declaration to use custom schemas within your configuration file looks like this
<objects xmlns='http://www.springframework.net'
xmlns:db="http://www.springframework.net/database"
xmlns:tx="http://www.springframework.net/tx"
xmlns:aop="http://www.springframework.net/aop">
The class XmlParserRegistry was renamed to NamespaceParserRegistry.
Renamed
Spring.Validation.ValidationConfigParser
to
Spring.Validation.Config.ValidationNamespaceParser
Renamed from DatabaseConfigParser to DatabaseNamespaceParser
Renamed/Moved Remoting.RemotingConfigParser to Remoting.Config.RemotingNamespaceParser
A typical registration of custom parsers within your configuration file looks like this
<configuration>
<configSections>
<sectionGroup name="spring">
<section name="parsers" type="Spring.Context.Support.NamespaceParsersSectionHandler, Spring.Core"/>
</sectionGroup>
</configSections>
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Migrating from 1.1 M2
<spring>
<parsers>
<parser type="Spring.Aop.Config.AopNamespaceParser, Spring.Aop" />
<parser type="Spring.Data.Config.DatabaseNamespaceParser, Spring.Data" />
<parser type="Spring.Transaction.Config.TxNamespaceParser, Spring.Data" />
</parsers>
</spring>
A manual registration would look like this
NamespaceParserRegistry.RegisterParser(typeof(AopNamespaceParser));
NamespaceParserRegistry.RegisterParser(typeof(DatabaseNamespaceParser));
NamespaceParserRegistry.RegisterParser(typeof(TxNamespaceParser));
4.2.2. Core
Moved Spring.Util.DynamicReflection to Spring.Reflection.Dynamic
Moved TypeRegistry and related classes from Spring.Context.Support to Spring.Core.TypeResolution
Moved Spring.Objects.TypeConverters to Spring.Core.TypeConvesion
4.2.3. Web
Moved Spring.Web.Validation to Spring.Web.UI.Validation
4.2.4. Data
Changed schema to use 'provider' instead of 'dbProvider' element, usage is now <db:provider ... /> and not
<db:dbProvider .../>
Moved TransactionTemplate,
Spring.Data.Support
TransactionDelegate
and
ITransactionCallback
from
Spring.Data
to
Moved AdoTemplate, AdoAccessor, AdoDaoSupport, RowMapperResultSetExtractor from Spring.Data to
Spring.Data.Core
Moved
AdoPlatformTransactionManager,
ServiceDomainPlatformTransactionManager,
TxScopeTransactionManager from Spring.Data to Spring.Data.Core
Spring Framework (Version 1.2.0)
and
8
Part I. Core Technologies
This initial part of the reference documentation covers all of those technologies that are absolutely integral to
the Spring Framework.
Foremost amongst these is the Spring Framework's Inversion of Control (IoC) container. A thorough treatment
of the Spring Framework's IoC container is closely followed by comprehensive coverage of Spring's AspectOriented Programming (AOP) technologies. The Spring Framework has its own AOP framework, which is
conceptually easy to understand, and which successfully addresses the 80% sweet spot of AOP requirements in
enterprise programming.
The core functionality also includes an expression language for lightweight scripting and a ui-agnostic validation
framework.
Finally, the adoption of the test-driven-development (TDD) approach to software development is certainly
advocated by the Spring team, and so coverage of Spring's support for integration testing is covered (alongside
best practices for unit testing). The Spring team have found that the correct use of IoC certainly does make both
unit and integration testing easier (in that the presence of properties and appropriate constructors on classes makes
them easier to wire together on a test without having to set up service locator registries and suchlike)... the chapter
dedicated solely to testing will hopefully convince you of this as well.
• Chapter 5, The IoC container
• Chapter 6, The IObjectWrapper and Type conversion
• Chapter 7, Resources
• Chapter 8, Threading and Concurrency Support
• Chapter 9, Object Pooling
• Chapter 11, Expression Evaluation
• Chapter 10, Spring.NET miscellanea
• Chapter 12, Validation Framework
• Chapter 13, Aspect Oriented Programming with Spring.NET
• Chapter 14, Aspect Library
• Chapter 15, Common Logging
• Chapter 16, Testing
Spring Framework (Version 1.2.0)
9
Chapter 5. The IoC container
5.1. Introduction
This chapter covers the Spring Framework's implementation of the Inversion of Control (IoC) 1 principle
The
Spring.Core
Control
container.
assembly
provides
the
basis
for
the
Spring.NET
Inversion
of
The
IObjectFactory
[http://www.springframework.net/doc/api/html/
Spring.Objects.Factory.IObjectFactory.html] interface provides an advanced configuration mechanism
capable of managing objects of any nature. The IApplicationContext [http://www.springframework.net/
doc/api/html/Spring.Context.IApplicationContext.html] interface builds on top of the IObjectFactory
(it is a sub-interface) and adds other functionality such as easier integration with Spring.NET's Aspect Oriented
Programming (AOP) features, message resource handling (for use in internationalization), event propagation and
application layer-specific context such as WebApplicationContext for use in web applications.
In short, the IObjectFactory provides the configuration framework and basic functionality, while the
IApplicationContext adds more enterprise-centric functionality to it. The IApplicationContext is a complete
superset of the IObjectFactory, and any description of IObjectFactory capabilities and behavior should be
considered to apply to IApplicationContexts as well.
This chapter is divided into two parts, with the first part covering the basic principles that apply to both the
IObjectFactory and IApplicationContext, with the second part covering those features that apply only to the
IApplicationContext interface.
If you are new to Spring.NET or IoC containers in general, you may want to consider starting with Chapter 33,
IoC Quickstarts, which contains a number of introductory level examples that actually demonstrate a lot of what
is described in detail below. Don't worry if you don't absorb everything at once... those examples serve only to
paint a picture of how Spring.NET hangs together in really broad brushstrokes. Once you have finished with those
examples, you can come back to this section which will fill in all the fine detail.
5.2. Basics - containers and objects
5.2.1. The container
The IObjectFactory is the actual representation of the Spring IoC container that is responsible for instantiating,
configuring, and managing a number of objects.
The IObjectFactory interface is the central IoC container interface in Spring. Its responsibilities include
instantiating or sourcing application objects, configuring such objects, and assembling the dependencies between
these objects.
There are a number of implementations of the IObjectFactory interface that come supplied straight out-ofthe-box with Spring. The most commonly used IObjectFactory implementation is the XmlObjectFactory
class. This implementation allows you to express the objects that compose your application, and the doubtless
rich interdependencies between such objects, in terms of XML. The XmlObjectFactory takes this XML
configuration metadata and uses it to create a fully configured system or application. Interaction with the
IObjectFactory interface is discussed in Section 5.2.6, “Using the container”. Additional features offered by
1
See the section entitled Section 3.1, “Inversion of Control”
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The IoC container
another implementation of IObjectFactory, the IApplicationContext, are discussed in section Section 5.10,
“The IApplicationContext”.
5.2.1.1. Configuration metadata
As can be seen in the above image, the Spring IoC container consumes some form of configuration metadata; this
configuration metadata is nothing more than how you (as an application developer) inform the Spring container
as to how to “instantiate, configure, and assemble [the objects in your application]”. This configuration metadata
is typically supplied in a simple and intuitive XML format. When using XML-based configuration metadata,
you write object definitions for those object that you want the Spring IoC container to manage, and then let the
container do it's stuff.
Note
XML-based metadata is by far the most commonly used form of configuration metadata. It is not
however the only form of configuration metadata that is allowed. The Spring IoC container itself is
totally decoupled from the format in which this configuration metadata is actually written. Attribute
based metadata will be part of an upcoming release and it is already part of the Spring Java framework.
Spring configuration consists of at least one object definition that the container must manage, but typically
there will be more than one object definition. When using XML-based configuration metadata, these object are
configured as <object/> elements inside a top-level <objects/> element.
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The IoC container
These object definitions correspond to the actual objects that make up your application. Typically you will have
object definitions for your service layer objects, your data access objects (DAOs), presentation objects such as
ASP.NET page instances, infrastructure objects such as NHibernate SessionFactories, and so forth. Typically one
does not configure fine-grained domain objects in the container, because it is usually the responsibility of DAOs
and business logic to create/load domain objects.
Find below an example of the basic structure of XML-based configuration metadata.
<objects xmlns="http://www.springframework.net">
<object id="..." type="...">
<!-- collaborators and configuration for this object go here -->
</object>
<object id="...." type="...">
<!-- collaborators and configuration for this object go here -->
</object>
<!-- more object definitions go here -->
</objects>
5.2.2. Instantiating a container
Instantiating a Spring IoC container is straightforward.
IApplicationContext context = new XmlApplicationContext(
"file://services.xml",
"assembly://MyAssembly/MyDataAccess/data-access.xml");
// an IApplicationContext is also an IObjectFactory (via inheritance)
IObjectFactory factory = context;
You can also create an container by using a custom configuration section in the standard .NET application (or
web) configuration file. Once the container has been created you may never need to explicitly interact with it
again in your code, for example when configuring ASP.NET pages.
You may be wondering what the assembly URL is all about. The above example uses Spring.NET's IResource
[http://www.springframework.net/doc/api/html/Spring.Core.IO.IResource.html] abstraction. The IResource
interface provides a simple and uniform interface to a wide array of IO resources that can represent themselves
as System.IO.Stream. An example for a file based resource, not using the URL syntax but an implementation
of the IResource interface for file is shown below.
[C#]
IResource input = new FileSystemResource ("objects.xml");
IObjectFactory factory = new XmlObjectFactory(input);
These resources are most frequently files or URLs but can also be resources that have been embedded inside
a .NET assembly. A simple URI syntax is used to describe the location of the resource, which follows the standard
conventions for files, i.e. file://object.xml and other well known protocols such as http.
The following snippet shows the use of the URI syntax for referring to a resource that has been embedded inside
a .NET assembly, assembly://<AssemblyName>/<NameSpace>/<ResourceName>. The IResource abstraction is
explained further in Section 7.1, “Introduction”.
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Note
To create an embedded resource using Visual Studio you must set the Build Action of the .xml
configuration file to Embedded Resource in the file property editor. Also, you will need to explicitly
rebuild the project containing the configuration file if it is the only change you make between
successive builds. If using NAnt to build, add a <resources> section to the csc task. For example
usage, look at the Spring.Core.Tests.build file included the distribution.
The preferred way to create an IApplicationContext or IObjectFactory is to use a custom configuration section
in the standard .NET application configuration file (one of App.config or Web.config). A custom configuration
section that creates the same IApplicationContext as the previous example is
<spring>
<context type="Spring.Context.Support.XmlApplicationContext, Spring.Core">
<resource uri="file://services.xml"/>
<resource uri="assembly://MyAssembly/MyDataAccess/data-access.xml"/>
</context>
</spring>
The context type (specified as the value of the type attribute of the context element) is wholly optional,
and defaults to the Spring.Context.Support.XmlApplicationContext class, so the following XML snippet is
functionally equivalent to the first.
<spring>
<context>
<resource uri="file://services.xml"/>
<resource uri="assembly://MyAssembly/MyDataAccess/data-access.xml"/>
</context>
</spring>
To acquire a reference to an IApplicationContext using a custom configuration section, one simply uses the
following code;
IApplicationContext ctx = ContextRegistry.GetContext();
The ContextRegistry is used to both instantiate the application context and to perform service locator style
access to other objects. (See Section 5.15, “Service Locator access” for more information). The glue that makes
this possible is an implementation of the Base Class Library (BCL) provided IConfigurationSectionHandler
interface, namely the Spring.Context.Support.ContextHandler class. The handler class needs to be registered
in the configSections section of the .NET configuration file as shown below.
<configSections>
<sectionGroup name="spring">
<section name="context" type="Spring.Context.Support.ContextHandler, Spring.Core"/>
</sectionGroup>
</configSections>
This declaration now enables the use of a custom context section starting at the spring root element.
In some usage scenarios, user code will not have to explicitly instantiate an appropriate implementation of the
IObjectFactory interface, since Spring.NET code will do it. For example, the ASP.NET web layer provides
support code to load a Spring.NET IApplicationContext automatically as part of the normal startup process of
an ASP.NET web application. Similar support for WinForms applications is being investigated.
While programmatic manipulation of IObjectFactory instances will be described later, the following sections
will concentrate on describing the configuration of objects managed by IObjectFactory instances.
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Spring.NET comes with an XSD schema to make the validation of the XML object definitions a whole lot easier.
The XSD document is thoroughly documented so feel free to take a peek inside (see Appendix C, Spring.NET's
spring-objects.xsd). The XSD is currently used in the implementation code to validate the XML document. The
XSD schema serves a dual purpose in that it also facilitates the editing of XML object definitions inside an XSD
aware editor (typically Visual Studio) by providing validation (and Intellisense support in the case of Visual
Studio). You may wish to refer to Chapter 32, Visual Studio.NET Integration for more information regarding
such integration.
Your XML object definitions can also be defined within the standard .NET application configuration file by
registering the Spring.Context.Support.DefaultSectionHandler class as the configuration section handler for
inline object definitions. This allows you to completely configure one or more IApplicationContext instances
within a single standard .NET application configuration file as shown in the following example.
<configuration>
<configSections>
<sectionGroup name="spring">
<section name="context" type="Spring.Context.Support.ContextHandler, Spring.Core"/>
<section name="objects" type="Spring.Context.Support.DefaultSectionHandler, Spring.Core" />
</sectionGroup>
</configSections>
<spring>
<context>
<resource uri="config://spring/objects"/>
</context>
<objects xmlns="http://www.springframework.net">
...
</objects>
</spring>
</configuration>
Other options available to structure the configuration files are described in Section 5.12.1, “Context Hierarchies”
and Section 5.2.2.1, “Composing XML-based configuration metadata”.
The IApplicationContext can be configured to register other resource handlers, custom parsers to integrate
user-contributed XML schema into the object definitions section, type converters, and define type aliases. These
features are discussed in section Section 5.11, “Configuration of IApplicationContext”
5.2.2.1. Composing XML-based configuration metadata
It is often useful to split up container definitions into multiple XML files. One way to then load an application
context which is configured from all these XML fragments is to use the application context constructor which
takes multiple resource locations. With an object factory, an object definition reader can be used multiple times
to read definitions from each file in turn.
Generally, the Spring.NET team prefers the above approach, assembling individual files because it keeps
container configuration files unaware of the fact that they are being combined with others. However, an alternate
approach is to compose one XML object definition file using one or more occurrences of the import element to
load definitions from other files. Any import elements must be placed before object elements in the file doing
the importing. Let's look at a sample:
<objects xmlns="http://www.springframework.net">
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<import resource="services.xml"/>
<import resource="resources/messageSource.xml"/>
<import resource="/resources/themeSource.xml"/>
<object id="object1" type="..."/>
<object id="object2" type="..."/>
</objects>
In this example, external object definitions are being loaded from 3 files, services.xml, messageSource.xml,
and themeSource.xml. All location paths are considered relative to the definition file doing the importing, so
services.xml in this case must be in the same directory as the file doing the importing, while messageSource.xml
and themeSource.xml must be in a resources location below the location of the importing file. As you can see,
a leading slash is actually ignored, but given that these are considered relative paths, it is probably better form
not to use the slash at all. The contents of the files being imported must be fully valid XML object definition files
according to the XSD, including the top level objects element.
5.2.3. The Objects
A Spring IoC container manages one or more objects. these objects are created using the configuration metadata
that has been supplied to the container (typically in the form of XML <object/> definitions).
Within the container itself, these object definitions are represented as IObjectDefinition objects, which contain
(among other information) the following metadata:
• A type name: typically this is the actual implementation class of the object being defined..
• Object behavioral configuration elements, which state how the object should behave in the Spring.NET IoC
container (i.e. prototype or singleton, lifecycle callbacks, and so forth)
• references to other objects which are needed for the object to do its work: these references are also called
collaborators or dependencies.
• other configuration settings to set in the newly created object. An example would be the number of threads to
use in an object that manages a worker thread pool, or the size limit of the pool.
The concepts listed above directly translate to a set of elements the object definition consists of. These elements
are listed below, along with a link to further documentation about each of them.
Table 5.1. Object definition explanation
Feature
More info
type
Section 5.2.4, “Object creation”
id and name
Section 5.2.3.1, “Naming objects”
singleton or prototype
Section 5.4, “Object Scopes”
object properties
Section 5.3.1, “Injecting dependencies”
constructor arguments
Section 5.3.1, “Injecting dependencies”
autowiring mode
Section 5.3.6, “Autowiring collaborators”
dependency checking mode
Section 5.3.7, “Checking for dependencies”
initialization method
Section 5.6.1, “Lifecycle interfaces”
destruction method
Section 5.6.1, “Lifecycle interfaces”
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Besides object definitions which contain information on how to create a specific object, certain IObjectFactory
implementations also permit the registration of existing objects that have been created outside the factory (by user
code). The DefaultListableObjectFactory class supports this through the RegisterSingleton(..) method.
(Typical applications solely work with objects defined through metadata object definitions though.)
5.2.3.1. Naming objects
Every object has one or more ids (also called identifiers, or names; these terms refer to the same thing). These
ids must be unique within the container the object is hosted in. An object will almost always have only one id,
but if an object has more than one id, the extra ones can essentially be considered aliases.
When using XML-based configuration metadata, you use the 'id' or 'name'attributes to specify the object
identifier(s). The 'id' attribute allows you to specify exactly one id, and as it is a real XML element ID attribute,
the XML parser is able to do some extra validation when other elements reference the id; as such, it is the preferred
way to specify an object id. However, the XML specification does limit the characters which are legal in XML
IDs. This is usually not a constraint, but if you have a need to use one of these special XML characters, or want
to introduce other aliases to the object, you may also or instead specify one or more object ids, separated by a
comma (,), semicolon (;), or whitespace in the 'name' attribute.
Please note that you are not required to supply a name for a object. If no name is supplied explicitly, the container
will generate a unique name for that object. The motivations for not supplying a name for a object will be discussed
later (one use case is inner objects).
5.2.3.1.1. Aliasing objects
In an object definition itself, you may supply more than one name for the object, by using a combination of the
id and name attributes as discussed in Section 5.2.3.1, “Naming objects”. This approach to aliasing objects has
some limitations when you would like to assemble the main application configuration file from multiple files.
This usage pattern is common when each configuration file represents a logical layer or component within the
application. In this case you may want to refer to a common object dependency using a name that is specific to
each file. If the common object dependency is defined in the main application configuration file itself, then one
can use the name element as an alias mechanism. However, if the main application configuration file should not
be responsible for defining the common object dependency, since it logically 'belongs' to one of the other layers
or components, you can not use the name attribute to achieve this goal.
In this case, you can define an alias using an explicit alias element contained in the main application configuration
file.
<alias name="fromName" alias="toName"/>
This allows an object named fromName to be referred to as toName across all application configuration files.
As a concrete example, consider the case where the configuration file 'a.xml' (representing component A) defines
a connection object called componentA-connection. In another file, 'b.xml' (representing component B) would
like to refer to the connection as componentB-connection. And the main application, MyApp, defines its own
XML fragment to assembles the final application configuration from all three fragments and would like to refer
to the connection as myApp-connection. This scenario can be easily handled by adding to the MyApp XML
fragment the following standalone aliases:
<alias name="componentA-connection" alias="componentB-connection"/>
<alias name="componentA-connection" alias="myApp-connection"/>
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Now each component and the main app can refer to the connection via a name that is unique and guaranteed not
to clash with any other definition (effectively there is a namespace), yet they refer to the same object.
5.2.4. Object creation
An object definition essentially is a recipe for creating one or more objects. The container looks at the recipe for
a named object when asked, and uses the configuration metadata encapsulated by that object definition to create
(or acquire) an actual object.
If you are using XML-based configuration metadata, you can specify the type of object that is to be instantiated
using the 'type' attribute of the <object/> element. This 'type' attribute (which internally eventually boils
down to being a Type property on a IObjectDefinition instance) is normally mandatory (see XXX “Instantiation
using an instance factory method” and XXX “Object definition inheritance” for the two exceptions) and is used
for one of two purposes. The type property specifies the type of of the object to be constructed in the common case
where the container itself directly creates the object by calling its constructor reflectively (somewhat equivalent
to C# code using the 'new' operator). In the less common case where the container invokes a static, factory
method on a class to create the object, the type property specifies the actual class containing the static factory
method that is to be invoked to create the object (the type of the object returned from the invocation of the static
factory method may be the same type or another type entirely, it doesn't matter).
5.2.4.1. Object creation via constructor invocation
When creating an object using the constructor approach, all normal classes are usable by and compatible with
Spring. That is, the type being created does not need to implement any specific interfaces or be coded in a specific
fashion. Just specifying the object type should be enough. However, depending on what type of IoC you are
going to use for that specific object, you may need to create a default constructor (i.e. a constructor that has no
parameters) in the source code definition of your class.
The XmlObjectFactory implementation of the IObjectFactory interface can consume object definitions that
have been defined in XML, for example...
<object id="exampleObject" type="Examples.ExampleObject, ExamplesLibrary"/>
The mechanism for supplying arguments to the constructor (if required), or setting properties of the object instance
after it has been constructed, is described shortly.
This XML fragment describes an object definition that will be identified by the exampleObject name, instances of
which will be of the Examples.ExampleObject type that has been compiled into the ExamplesLibrary assembly.
Take special note of the structure of the type attribute's value... the namespace-qualified name of the class is
specified, followed by a comma, followed by (at a bare minimum) the name of the assembly that contains the
class. In the preceding example, the ExampleObject class is defined in the Examples namespace, and it has been
compiled into the ExamplesLibrary assembly.
The name of the assembly that contains the type must be specified in the type attribute. Furthermore, it is
recommended that you specify the fully qualified assembly name 2 in order to guarantee that the type that
Spring.NET uses to instantiate your object (s) is indeed the one that you expect. Usually this is only an issue if
you are using classes from (strongly named) assemblies that have been installed into the Global Assembly Cache
(GAC).
2
More information about assembly names can be found in the Assembly Names section of the .NET Framework Developer's Guide (installed
as part of the .NET SDK), or online at Microsoft's MSDN website, by searching for Assembly Names.
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If you have defined nested classes use the addition symbol, +, to reference the nested class. For example, if the
class Examples.ExampleObject had a nested class Person the XML declaration would be
<object id="exampleObject" type="Examples.ExampleObject+Person, ExamplesLibrary"/>
If you are defining classes that have been compiled into assemblies that are available to your application (such as
the bin directory in the case of ASP.NET applications) via the standard assembly probing mechanisms, then you
can specify simply the name of the assembly (e.g. ExamplesLibrary.Data)... this way, when (or if) the assemblies
used by your application are updated, you won't have to change the value of every <object/> definition's type
attribute to reflect the new version number (if the version number has changed)... Spring.NET will automatically
locate and use the newer versions of your assemblies (and their attendant classes) from that point forward.
5.2.4.2. Object creation via a static factory method
When defining an object which is to be created using a static factory method, along with the type attribute which
specifies the type containing the static factory method, another attribute named factory-method is needed to
specify the name of the factory method itself. Spring.NET expects to be able to call this method (with an optional
list of arguments as described later) and get back a live object, which from that point on is treated as if it had been
created normally via a constructor. One use for such an object definition is to call static factories in legacy code.
Following is an example of an object definition which specifies that the object is to be created by calling a factorymethod. Note that the definition does not specify the type (class) of the returned object, only the type containing
the factory method. In this example, CreateInstance must be a static method.
<object id="exampleObject"
type="Examples.ExampleObjectFactory, ExamplesLibrary"
factory-method="CreateInstance"/>
The mechanism for supplying (optional) arguments to the factory method, or setting properties of the object
instance after it has been returned from the factory, will be described shortly.
5.2.4.3. Object creation via an instance factory method
In a fashion similar to instantiation using a static factory method, instantiation using an instance factory method is
where a non-static method of an existing object from the container is invoked to create the new object. To use this
mechanism, the 'type' attribute must be left empty, and the 'factory-object' attribute must specify the name
of an object in the current (or parent/ancestor) container that contains the instance method that is to be invoked
to create the object. The name of the factory method itself should still be set via the 'factory-method' attribute.
<!-- the factory object, which contains an instance method called 'CreateInstance' -->
<object id="exampleFactory" type="...">
<!-- inject any dependencies required by this object -->
</object>
<!-- the object that is to be created by the factory object -->
<object id="exampleObject"
factory-method="CreateInstance"
factory-object="exampleFactory"/>
Although the mechanisms for setting object properties are still to be discussed, one implication of this approach
is that the factory object itself can be managed and configured via Dependency Injection, by the container.
Note
When the Spring documentation makes mention of a 'factory object', this will be a reference to an
object that is configured in the Spring container that will create objects via an instance or static factory
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method. When the documentation mentions a IFactoryObject (notice the capitalization) this is a
reference to a Spring-specific IFactoryObject .
5.2.5. Object creation of generic types
Generic types can also be created in much the same manner an non-generic types.
5.2.5.1. Object creation of generic types via constructor invocation
The following examples shows the definition of simple generic types and how they can be created in Spring's
XML based configuration file.
namespace GenericsPlay
{
public class FilterableList<T>
{
private List<T> list;
private String name;
public List<T> Contents
{
get { return list; }
set { list = value; }
}
public String Name
{
get { return name; }
set { name = value; }
}
public List<T> ApplyFilter(string filterExpression)
{
/// should really apply filter to list ;)
return new List<T>();
}
}
}
The XML configuration to create and configure this object is shown below
<object id="myFilteredIntList" type="GenericsPlay.FilterableList&lt;int>, GenericsPlay">
<property name="Name" value="My Integer List"/>
</object>
There are a few items to note in terms how to specify a generic type. First, the left bracket that specifies the
generic type, i.e. <, is replaced with the string &lt; due to XML escape syntax for the less than symbol. Yes, we
all realize this is less than ideal from the readability point of view. Second, the generic type arguments can not be
fully assembly qualified as the comma is used to separate generic type arguments. Alternative characters used to
overcome the two quirks can be implemented in the future but so far, all proposals don't seem to help clarify the
text. The suggested solution to improve readability is to use type aliases as shown below
<typeAliases>
<alias name="GenericDictionary" type=" System.Collections.Generic.Dictionary&lt;,>" />
<alias name="myDictionary" type="System.Collections.Generic.Dictionary&lt;int,string>" />
</typeAliases>
So that instead of something like this
<object id="myGenericObject"
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type="GenericsPlay.ExampleGenericObject&lt;System.Collections.Generic.Dictionary&lt;int , string>>, Gene
It can be shortened to
<object id="myOtherGenericObject"
type="GenericsPlay.ExampleGenericObject&lt;GenericDictionary&lt;int , string>>, GenericsPlay" />
or even shorter
<object id="myOtherOtherGenericObject"
type="GenericsPlay.ExampleGenericObject&lt;MyIntStringDictionary>, GenericsPlay" />
Refer to Section 5.11, “Configuration of IApplicationContext” for additional information on using type aliases.
5.2.5.2. Object creation of generic types via static factory method
The following classes are used to demonstrate the ability to create instances of generic types that themselves are
created via a static generic factory method.
public class TestGenericObject<T, U>
{
public TestGenericObject()
{
}
private IList<T> someGenericList = new List<T>();
private IDictionary<string, U> someStringKeyedDictionary =
new Dictionary<string, U>();
public IList<T> SomeGenericList
{
get { return someGenericList; }
set { someGenericList = value; }
}
public IDictionary<string, U> SomeStringKeyedDictionary
{
get { return someStringKeyedDictionary; }
set { someStringKeyedDictionary = value; }
}
}
The accompanying factory class is
public class TestGenericObjectFactory
{
public static TestGenericObject<V, W> StaticCreateInstance<V, W>()
{
return new TestGenericObject<V, W>();
}
public TestGenericObject<V, W> CreateInstance<V, W>()
{
return new TestGenericObject<V, W>();
}
}
The XML snippet to create an instance of TestGenericObject where V is a List of integers and W is an integer
is shown below
<object id="myTestGenericObject"
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type="GenericsPlay.TestGenericObjectFactory, GenericsPlay"
factory-method="StaticCreateInstance&lt;System.Collections.Generic.List&lt;int>,int>"
/>
The StaticCreateInstance method is responsible for instantiating the object that will be associated with the id
'myTestGenericObject'.
5.2.5.3. Object creation of generic types via instance factory method
Using the class from the previous example the XML snippet to create an instance of a generic type via an instance
factory method is shown below
<object id="exampleFactory" type="GenericsPlay.TestGenericObject&lt;int,string>, GenericsPlay"/>
<object id="anotherTestGenericObject"
factory-object="exampleFactory"
factory-method="CreateInstance&lt;System.Collections.Generic.List&lt;int>,int>"/>
This creates an instance of TestGenericObject<List<int>,int>
5.2.6. Using the container
An IApplicationContext is essentially nothing more than the interface for an advanced factory capable of
maintaining a registry of different objects and their dependencies. The IApplicationContext enables you to
read object definitions and access them. You create one and read in some object definition in the XML format
as follows:
IApplicationContext context = new XmlApplicationContext("file://objects.xml");
Basically that is all there is to it. Using GetObject(string) or the indexer [string], you can retrieve instances
of your object; the client-side view of the IApplicationContext is simple. The IApplicationContext interface
has just a few other methods related to finding objects in the contianer, but ideally your application code should
never use them... indeed, your application code should have no calls to the GetObject(string) method at all,
and thus no dependency on Spring APIs at all.
5.3. Dependencies
Your typical enterprise application is not made up of a single object. Even the simplest of applications will
no doubt have at least a handful of objects that work together to present what the end-user sees as a coherent
application. This next section explains how you go from defining a number of object definitions that stand-alone,
each to themselves, to a fully realized application where objects work (or collaborate) together to achieve some
goal (usually an application that does what the end-user wants).
5.3.1. Injecting dependencies
The basic principle behind Dependency Injection (DI) is that objects define their dependencies (that is to say the
other objects they work with) only through constructor arguments, arguments to a factory method, or properties
which are set on the object instance after it has been constructed or returned from a factory method. Then, it is
the job of the container to actually inject those dependencies when it creates the object. This is fundamentally the
inverse, hence the name Inversion of Control (IoC), of the object itself being in control of instantiating or locating
its dependencies on its own using direct construction of classes, or something like the Service Locator pattern.
It becomes evident upon usage that code gets much cleaner when the DI principle is applied, and reaching a higher
grade of decoupling is much easier when objects do not look up their dependencies, but are provided with them
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(and additionally do not even know where the dependencies are located and of what concrete class they are). DI
exists in two major variants, namely Constructor Injection and Setter Injection.
5.3.1.1. Constructor Injection
Constructor-based DI is effected by invoking a constructor with a number of arguments, each representing a
dependency. Additionally, calling a static factory method with specific arguments to construct the object, can be
considered almost equivalent, and the rest of this text will consider arguments to a constructor and arguments to
a static factory method similarly. Find below an example of a class that could only be dependency injected using
constructor injection. Notice that there is nothing special about this class.
public class SimpleMovieLister
{
// the SimpleMovieLister has a dependency on a MovieFinder
private IMovieFinder movieFinder;
// a constructor so that the Spring container can 'inject' a MovieFinder
public MovieLister(IMovieFinder movieFinder)
{
this.movieFinder = movieFinder;
}
// business logic that actually 'uses' the injected IMovieFinder is omitted...
}
5.3.1.1.1. Constructor Argument Resolution
Constructor argument resolution matching occurs using the argument's type. If there is no potential for ambiguity
in the constructor arguments of a object definition, then the order in which the constructor arguments are defined
in a object definition is the order in which those arguments will be supplied to the appropriate constructor when
it is being instantiated. Consider the following class:
namespace X.Y
{
public class Foo
{
public Foo(Bar bar, Baz baz)
{
// ...
}
}
}
There is no potential for ambiguity here (assuming of course that Bar and Baz classes are not related in an
inheritance hierarchy). Thus the following configuration will work just fine, and you do not need to specify the
constructor argument indexes and / or types explicitly.
<object name="Foo" type="X.Y.Foo, Example">
<constructor-arg>
<object type="X.Y.Bar, Example"/>
</constructor-arg>
<constructor-arg>
<object type="X.Y.Baz, Example"/>
</constructor-arg>
</object>
When another object is referenced, the type is known, and matching can occur (as was the case with the preceding
example). When a simple type is used, such as <value>true<value>, Spring cannot determine the type of the
value, and so cannot match by type without help. Consider the following class:
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using System;
namespace SimpleApp
{
public class ExampleObject
{
private int years;
//No. of years to the calculate the Ultimate Answer
private string ultimateAnswer;
//The Answer to Life, the Universe, and Everything
public ExampleObject(int years, string ultimateAnswer)
{
this.years = years;
this.ultimateAnswer = ultimateAnswer;
}
}
5.3.1.1.1.1. Constructor Argument Type Matching
The above scenario can use type matching with simple types by explicitly specifying the type of the constructor
argument using the type attribute. For example:
<object name="exampleObject" type="SimpleApp.ExampleObject, SimpleApp">
<constructor-arg type="int" value="7500000"/>
<constructor-arg type="string" value="42"/>
</object>
The type attribute specifies the System.Type of the constructor argument, such as System.Int32. Alias' are
available to for common simple types (and their array equivalents). These alias' are...
Table 5.2. Type aliases
Type
Alias'
Array Alias'
System.Char
char, Char
char[], Char()
System.Int16
short, Short
short[], Short()
System.Int32
int, Integer
int[], Integer()
System.Int64
long, Long
long[], Long()
System.UInt16
ushort
ushort[]
System.UInt32
uint
uint[]
System.UInt64
ulong
ulong[]
System.Float
float, Single
float[], Single()
System.Double
double, Double
double[], Double()
System.Date
date, Date
date[], Date()
System.Decimal
decimal, Decimal
decimal[], Decimal()
System.Bool
bool, Boolean
bool[], Boolean()
System.String
string, String
string[], String()
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5.3.1.1.1.2. Constructor Argument Index
Constructor arguments can have their index specified explicitly by use of the index attribute. For example:
<object name="exampleObject" type="SimpleApp.ExampleObject, SimpleApp">
<constructor-arg index="0" value="7500000"/>
<constructor-arg index="1" value="42"/>
</object>
As well as solving the ambiguity problem of multiple simple values, specifying an index also solves the problem
of ambiguity where a constructor may have two arguments of the same type. Note that the index is 0 based.
5.3.1.1.1.3. Constructor Arguments by Name
Constructor arguments can also be specified by name by using the name attribute of the <constructor-arg>
element.
<object name="exampleObject" type="SimpleApp.ExampleObject, SimpleApp">
<constructor-arg name="years" value="7500000"/>
<constructor-arg name="ultimateAnswer" value="42"/>
</object>
5.3.1.2. Setter Injection
Setter-based DI is realized by calling setter methods on your objects after invoking a no-argument constructor or
no-argument static factory method to instantiate your object.
Find below an example of a class that can only be dependency injected using pure setter injection.
public class MovieLister
{
private IMovieFinder movieFinder;
public IMovieFinder MovieFinder
{
set
{
movieFinder = value;
}
}
// business logic that actually 'uses' the injected IMovieFinder is omitted...
}
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Constructor- or Setter-based DI?
The Spring team generally advocates the usage of setter injection, since a large number of constructor
arguments can get unwieldy, especially when some properties are optional. The presence of setter methods
also makes objects of that class amenable to being re-configured (or re-injected) at some later time (for
management purposes).
Constructor-injection is favored by some purists though and with good reason. Supplying all of an object's
dependencies means that that object is never returned to client (calling) code in a less than totally initialized
state. The flip side is that the object becomes less amenable to re-configuration (or re-injection).
There is no hard and fast rule here. Use whatever type of DI makes the most sense for a particular class;
sometimes, when dealing with third party classes to which you do not have the source, the choice will
already have been made for you - a legacy class may not expose any setter methods, and so constructor
injection will be the only type of DI available to you.
Since you can mix both, Constructor- and Setter-based DI, it is a good rule of thumb to use constructor
arguments for mandatory dependencies and setters for optional dependencies.
The IObjectFactory supports both of these variants for injecting dependencies into objects it manages. (It in
fact also supports injecting setter-based dependencies after some dependencies have already been supplied via
the constructor approach.) The configuration for the dependencies comes in the form of the IObjectDefinition
class, which is used together with TypeConverters to know how to convert properties from one format to another.
However, most users of Spring.NET will not be dealing with these classes directly (that is programatically), but
rather with an XML definition file which will be converted internally into instances of these classes, and used to
load an entire Spring IoC container instance.
Object dependency resolution generally happens as follows:
1. The IObjectFactory is created and initialized with a configuration which describes all the objects. Most
Spring.NET users use an IObjectFactory or IApplicationContext variant that supports XML format
configuration files.
2. Each object has dependencies expressed in the form of properties, constructor arguments, or arguments to the
static-factory method when that is used instead of a normal constructor. These dependencies will be provided
to the object, when the object is actually created.
3. Each property or constructor argument is either an actual definition of the value to set, or a reference to another
object in the container.
4. Each property or constructor argument which is a value must be able to be converted from whatever format it
was specified in, to the actual System.Type of that property or constructor argument. By default Spring.NET
can convert a value supplied in string format to all built-in types, such as int, long, string, bool, etc.
Spring.NET uses TypeConverter definitions to be able to convert string values to other, arbitrary types. Refer
to Section 6.3, “Type conversion” for more information regarding type conversion, and how you can design
your classes to be convertible by Spring.NET.
The Spring container validates the configuration of each object as the container is created, including the validation
that properties which are object references are actually referring to valid object. However, the object properties
themselves are not set until the object is actually created. For those object that defined as singletons and set to
be pre-instantiated (such as singleton object in an IApplicationContext), creation happens at the time that the
container is created, but otherwise this is only when the object is requested. When an object actually has to be
created, this will potentially cause a graph of other objects to be created, as its dependencies and its dependencies'
dependencies (and so on) are created and assigned.
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Circular Dependencies
If you are using predominantly constructor injection it is possible to write and configure your classes and
objects such that an unresolvable circular dependency scenario is created.
Consider the scenario where you have class A, which requires an instance of class B to be provided via
constructor injection, and class B, which requires an instance of class A to be provided via constructor
injection. If you configure object for classes A and B to be injected into each other, the Spring IoC container
will detect this circular reference at runtime, and throw a ObjectCurrentlyInCreationException.
One possible solution to this issue is to edit the source code of some of your classes to be configured via
setters instead of via constructors. Another solution is not to use constructor injection and stick to setter
injection only. In other words, while it should generally be avoided in all but the rarest of circumstances, it
is possible to configure circular dependencies with setter injection.
Unlike the typical case (with no circular dependencies), a circular dependency between object A and object
B will force one of the objects to be injected into the other prior to being fully initialized itself (a classic
chicken/egg scenario).
You can generally trust Spring.NET to do the right thing. It will detect configuration issues, such as references
to non-existent object definitions and circular dependencies, at container load-time. It will actually set properties
and resolve dependencies as late as possible, which is when the object is actually created. This means that a
Spring container which has loaded correctly can later generate an exception when you request an object if there
is a problem creating that object or one of its dependencies. This could happen if the object throws an exception
as a result of a missing or invalid property, for example. This potentially delayed visibility of some configuration
issues is why IApplicationContext by default pre-instantiates singleton objects. At the cost of some upfront
time and memory to create these objects before they are actually needed, you find out about configuration issues
when the IApplicationContext is created, not later. If you wish, you can still override this default behavior and
set any of these singleton objects to lazy-load (not be preinstantiated)
If no circular dependencies are involved (see sidebar for a discussion of circular dependencies), when one or more
collaborating objects are being injected into a dependent object, each collaborating object is totally configured
prior to being passed (via one of the DI flavors) to the dependent object. This means that if object A has a
dependency on object B, the Spring IoC container will totally configure object B prior to invoking the setter
method on object A; you can read 'totally configure' to mean that the object will be instantiated (if not a preinstantiated singleton), all of its dependencies will be set, and the relevant lifecycle methods (such as a configured
init method or the IIntializingObject callback method) will all be invoked.
5.3.1.3. Some examples
First, an example of using XML-based configuration metadata for setter-based DI. Find below a smallpart of a
Spring XML configuration file specifying some object definitions.
<object id="exampleObject" type="Examples.ExampleObject, ExamplesLibrary">
<!-- setter injection using the ref attribute -->
<property name="objectOne" ref="anotherExampleObject"/>
<property name="objectTwo" ref="yetAnotherObject"/>
<property name="IntegerProperty" value="1"/>
</object>
<object id="anotherExampleObject" type="Examples.AnotherObject, ExamplesLibrary"/>
<object id="yetAnotherObject" type="Examples.YetAnotherObject, ExamplesLibrary"/>
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[C#]
public class ExampleObject
{
private AnotherObject objectOne;
private YetAnotherObject objectTwo;
private int i;
public AnotherObject ObjectOne
{
set { this.objectOne = value; }
}
public YetAnotherObject ObjectTwo
{
set { this.objectTwo = value; }
}
public int IntegerProperty
{
set { this.i = value; }
}
}
As you can see, setters have been declared to match against the properties specified in the XML file. Find below
an example of using constructor-based DI.
<object id="exampleObject" type="Examples.ExampleObject, ExamplesLibrary">
<constructor-arg name="objectOne" ref="anotherExampleObject"/>
<constructor-arg name="objectTwo" ref="yetAnotherObject"/>
<constructor-arg name="IntegerProperty" value="1"/>
</object>
<object id="anotherExampleObject" type="Examples.AnotherObject, ExamplesLibrary"/>
<object id="yetAnotherObject" type="Examples.YetAnotherObject, ExamplesLibrary"/>
[Visual Basic.NET]
Public Class ExampleObject
Private myObjectOne As AnotherObject
Private myObjectTwo As YetAnotherObject
Private i As Integer
Public Sub New (
anotherObject as AnotherObject,
yetAnotherObject as YetAnotherObject,
i as Integer)
myObjectOne = anotherObject
myObjectTwo = yetAnotherObject
Me.i = i
End Sub
End Class
As you can see, the constructor arguments specified in the object definition will be used to pass in as arguments
to the constructor of the ExampleObject.
Now consider a variant of this where instead of using a constructor, Spring is told to call a static factory method
to return an instance of the object
<object id="exampleObject" type="Examples.ExampleFactoryMethodObject, ExamplesLibrary"
factory-method="CreateInstance">
<constructor-arg name="objectOne" ref="anotherExampleObject"/>
<constructor-arg name="objectTwo" ref="yetAnotherObject"/>
<constructor-arg name="intProp" value="1"/>
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</object>
<object id="anotherExampleObject" type="Examples.AnotherObject, ExamplesLibrary"/>
<object id="yetAnotherObject" type="Examples.YetAnotherObject, ExamplesLibrary"/>
[C#]
public class ExampleFactoryMethodObject
{
private AnotherObject objectOne;
private YetAnotherObject objectTwo;
private int i;
// a private constructor
private ExampleFactoryMethodObject()
{
}
public static ExampleFactoryMethodObject CreateInstance(AnotherObject objectOne,
YetAnotherObject objectTwo,
int intProp)
{
ExampleFactoryMethodObject fmo = new ExampleFactoryMethodObject();
fmo.AnotherObject = objectOne;
fmo.YetAnotherObject = objectTwo;
fmo.IntegerProperty = intProp;
return fmo;
}
// Property definitions
}
Note that arguments to the static factory method are supplied via constructor-arg elements, exactly the same as if
a constructor had actually been used. These arguments are optional. Also, it is important to realize that the type
of the class being returned by the factory method does not have to be of the same type as the class which contains
the static factory method, although in this example it is. An instance (non-static) factory method, mentioned
previously, would be used in an essentially identical fashion (aside from the use of the factory-object attribute
instead of the type attribute), so will not be detailed here.
Note that Setter Injection and Constructor Injectionare not mutually exclusive. It is perfectly reasonable to use
both for a single object definition, as can be seen in the following example:
<object id="exampleObject" type="Examples.MixedIocObject, ExamplesLibrary">
<constructor-arg name="objectOne" ref="anotherExampleObject"/>
<property name="objectTwo" ref="yetAnotherObject"/>
<property name="IntegerProperty" value="1"/>
</object>
<object id="anotherExampleObject" type="Examples.AnotherObject, ExamplesLibrary"/>
<object id="yetAnotherObject" type="Examples.YetAnotherObject, ExamplesLibrary"/>
[C#]
public class MixedIocObject
{
private AnotherObject objectOne;
private YetAnotherObject objectTwo;
private int i;
public MixedIocObject (AnotherObject obj)
{
this.objectOne = obj;
}
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public YetAnotherObject ObjectTwo
{
set { this.objectTwo = value; }
}
public int IntegerProperty
{
set { this.i = value; }
}
}
5.3.2. Dependencies and configuration in detail
As mentioned in the previous section, object properties and constructor arguments can be defined as either
references to other managed objects (collaborators), or values defined inline. Spring's XML-based configuration
metadata supports a number of sub-element types within its <property/> and <constructor-arg/> elements
for this purpose.a
5.3.2.1. Straight values (primitives, strings, etc.)
The <value/> element specifies a property or constructor argument as a human-readable string representation.
As mentioned previously, TypeConverter instances are used to convert these string values from a
System.String to the actual property or argument type. Custom TypeConverter implementations in the
Spring.Objects.TypeConverters namespace are used to augment the functionality offered by the .NET BCL's
default TypeConverter implementations.
In the following example, we use a SqlConnection from the System.Data.SqlClient namespace of the BCL.
This class (like many other existing classes) can easily be used in a Spring.NET object factory, as it offers a
convenient public property for configuration of its ConnectionString property.
<objects xmlns="http://www.springframework.net">
<object id="myConnection" type="System.Data.SqlClient.SqlConnection">
<!-- results in a call to the setter of the ConnectionString property -->
<property
name="ConnectionString"
value="Integrated Security=SSPI;database=northwind;server=mySQLServer"/>
</object>
</objects>
5.3.2.1.1. The idref element
An idref element is simply a shorthand and error-proof way to set a property to the String id or name of another
object in the container.
<object id="theTargetObject" type="...">
. . .
</object>
<object id="theClientObject" type="...">
<property name="targetName">
<idref object="theTargetObject"/>
</property>
</object>
This is exactly equivalent at runtime to the following fragment:
<object id="theTargetObject" type="...">
. . .
</object>
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<object id="theClientObject" type="...">
<property name="targetName" value="theTargetObject"/>
</object>
The main reason the first form is preferable to the second is that using the idref tag will allow Spring.NET to
validate at deployment time that the other object actually exists. In the second variation, the class that is having
its targetName property injected is forced to do its own validation, and that will only happen when that class is
actually instantiated by the container, possibly long after the container is actually up and running.
Additionally, if the object being referred to is in the same actual XML file, and the object name is the object
id, the local attribute may be used, which will allow the XML parser itself to validate the object name even
earlier, at parse time.
<property name="targetName">
<idref local="theTargetObject"/>
</property>
5.3.2.1.2. Whitespace Handling
Usually all leading and trailing whitespaces are trimmed from a <value /> element's text. In some cases it is
necessary to maintain whitespaces exactly as they are written into the xml element. The parser does understand
the xml:space attribute in this case:
<property name="myProp">
<value xml:space="preserve"> &#x000a;&#x000d;&#x0009;</value>
</property>
The above configuration will result in the string " \n\r\t". Note, that you don't have to explicitely specifiy the 'xml'
namespace on top of your configuration.
5.3.2.2. Referring to collaborating objects
The ref element is the final element allowed inside a property definition element. It is used to set the value of
the specified property to be a reference to another object managed by the container, a collaborator, so to speak. As
you saw in the previous example to set collection properties, we used the SqlConnection instance from the initial
example as a collaborator and specified it using a <ref object/> element. As mentioned in a previous section, the
referred-to object is considered to be a dependency of the object who's property is being set, and will be initialized
on demand as needed (if it is a singleton object it may have already been initialized by the container) before the
property is set. All references are ultimately just a reference to another object, but there are 3 variations on how
the id/name of the other object may be specified, which determines how scoping and validation is handled.
Specifying the target object by using the object attribute of the ref tag is the most general form, and will allow
creating a reference to any object in the same IObjectFactory / IApplicationContext (whether or not in the
same XML file), or parent IObjectFactory / IApplicationContext. The value of the object attribute may be
the same as either the id attribute of the target object, or one of the values in the name attribute of the target object.
<ref object="someObject"/>
Specifying the target object by using the local attribute leverages the ability of the XML parser to validate XML
id references within the same file. The value of the local attribute must be the same as the id attribute of the
target object. The XML parser will issue an error if no matching element is found in the same file. As such, using
the local variant is the best choice (in order to know about errors are early as possible) if the target object is in
the same XML file.
<ref local="someObject"/>
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Specifying the target object by using the parent attribute allows a reference to be created to an object that is in
a parent IObjectFactory (orIApplicationContext) of the current IObjectFactory (or IApplicationContext).
The value of the parent attribute may be the same as either the id attribute of the target object, or one of the
values in the name attribute of the target object, and the target object must be in a parent IObjectFactory or
IApplicationContext of the current one. The main use of this object reference variant is when there is a need
to wrap an existing object in a parent context with some sort of proxy (which may have the same name as the
parent), and needs the original object so it may wrap it.
<ref parent="someObject"/>
5.3.2.3. Inline objects
An object element inside the property element is used to define an object value inline, instead of referring to
an object defined elsewhere in the container. The inline object definition does not need to have any id or name
defined (indeed, if any are defined, they will be ignored).
<object id="outer" type="...">
<!-- Instead of using a reference to target, just use an inner object -->
<property name="target">
<object type="ExampleApp.Person, ExampleApp">
<property name="name" value="Tony"/>
<property name="age" value="51"/>
</object>
</property>
</object>
5.3.2.4. Setting collection values
The list, set, name-values and dictionary elements allow properties and arguments of the type IList, ISet,
NameValueCollection and IDictionary, respectively, to be defined and set.
<objects xmlns="http://www.springframework.net">
<object id="moreComplexObject" type="Example.ComplexObject">
<!-results in a call to the setter of the SomeList (System.Collections.IList) property
-->
<property name="SomeList">
<list>
<value>a list element followed by a reference</value>
<ref object="myConnection"/>
</list>
</property>
<!-results in a call to the setter of the SomeDictionary (System.Collections.IDictionary) property
-->
<property name="SomeDictionary">
<dictionary>
<entry key="a string => string entry" value="just some string"/>
<entry key-ref="myKeyObject" value-ref="myConnection"/>
</dictionary>
</property>
<!-results in a call to the setter of the SomeNameValue (System.Collections.NameValueCollection) property
-->
<property name="SomeNameValue">
<name-values>
<add key="HarryPotter" value="The magic property"/>
<add key="JerrySeinfeld" value="The funny (to Americans) property"/>
</name-values>
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</property>
<!-results in a call to the setter of the SomeSet (Spring.Collections.ISet) property
-->
<property name="someSet">
<set>
<value>just some string</value>
<ref object="myConnection"/>
</set>
</property>
</object>
</objects>
Many classes in the BCL expose only read-only properties for collection classes. When Spring.NET encounters
a read-only collection, it will configure the collection by using the getter property to obtain a reference to the
collection class and then proceed to add the additional elements to the existing collection. This results in an
additive behavior for collection properties that are exposed in this manner.
Note that the value of a Dictionary entry, or a set value, can also again be any of the elements:
(object | ref | idref | expression | list | set | dictionary |
name-values | value | null)
The shortcut forms for value and references are useful to reduce XML verbosity when setting collection properties.
See Section 5.3.2.8, “Value and ref shortcut forms” for more information.
5.3.2.5. Setting generic collection values
Spring supports setting values for classes that expose properties based on the generic collection interfaces
IList<T> and IDictionary<TKey, TValue>. The type parameter for these collections is specified by
using the XML attribute element-type for IList<T> and the XML attributes key-type and valuetype for IDictionary<TKey, TValue>. The values of the collection are automaticaly converted from a
string to the appropriate type. If you are using your own user-defined type as a generic type parameter
you will likely need to register a custom type converter. Refer to Section 5.5, “Type conversion” for
more information. The implementations of IList<T> and IDictionary<TKey, TValue> that is created are
System.Collections.Generic.List and System.Collections.Generic.Dictionary.
The following class represents a lottery ticket and demonstrates how to set the values of a generic IList.
public class LotteryTicket {
List<int> list;
DateTime date;
public List<int> Numbers {
set { list = value; }
get { return list; }
}
public DateTime Date {
get { return date; }
set { date = value; }
}
}
The XML fragment that can be used to configure this class is shown below
<object id="MyLotteryTicket" type="GenericsPlay.Lottery.LotteryTicket, GenericsPlay">
<property name="Numbers">
<list element-type="int">
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<value>11</value>
<value>21</value>
<value>23</value>
<value>34</value>
<value>36</value>
<value>38</value>
</list>
</property>
<property name="Date" value="4/16/2006"/>
</object>
The following shows the definition of a more complex class that demonstrates the use of generics using
the Spring.Expressions.IExpression interface as the generic type parameter for the IList element-type
and the value-type for IDictionary. Spring.Expressions.IExpression has an associated type converter,
Spring.Objects.TypeConverters.ExpressionConverter that is already pre-registered with Spring.
public class GenericExpressionHolder
{
private System.Collections.Generic.IList<IExpression> expressionsList;
private System.Collections.Generic.IDictionary<string,IExpression> expressionsDictionary;
public System.Collections.Generic.IList<IExpression> ExpressionsList
{
set { this.expressionsList = value; }
}
public System.Collections.Generic.IDictionary<string, IExpression> ExpressionsDictionary
{
set { this.expressionsDictionary = value; }
}
public IExpression this[int index]
{
get
{
return this.expressionsList[index];
}
}
public IExpression this[string key]
{
get { return this.expressionsDictionary[key]; }
}
}
An example XML configuration of this class is shown below
<object id="genericExpressionHolder"
type="Spring.Objects.Factory.Xml.GenericExpressionHolder,
Spring.Core.Tests">
<property name="ExpressionsList">
<list element-type="Spring.Expressions.IExpression, Spring.Core">
<value>1 + 1</value>
<value>date('1856-7-9').Month</value>
<value>'Nikola Tesla'.ToUpper()</value>
<value>DateTime.Today > date('1856-7-9')</value>
</list>
</property>
<property name="ExpressionsDictionary">
<dictionary key-type="string" value-type="Spring.Expressions.IExpression, Spring.Core">
<entry key="zero">
<value>1 + 1</value>
</entry>
<entry key="one">
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<value>date('1856-7-9').Month</value>
</entry>
<entry key="two">
<value>'Nikola Tesla'.ToUpper()</value>
</entry>
<entry key="three">
<value>DateTime.Today > date('1856-7-9')</value>
</entry>
</dictionary>
</property>
</object>
5.3.2.6. Setting null values
The <null> element is used to handle null values. Spring.NET treats empty arguments for properties and
constructor arguments as empty string instances. The following configuration demonstrates this behaviour...
<object type="Examples.ExampleObject, ExamplesLibrary">
<property name="email"><value></value></property>
<!-- equivalent, using value attribute as opposed to nested <value/> element...
<property name="email" value=""/>
</object>
This results in the email property being set to the empty string value (""), in much the same way as can be seen
in the following snippet of C# code...
exampleObject.Email = "";
The special <null/> element may be used to indicate a null value; to wit...
<object type="Examples.ExampleObject, ExamplesLibrary">
<property name="email"><null/></property>
</object>
This results in the email property being set to null, again in much the same way as can be seen in the following
snippet of C# code...
exampleObject.Email = null;
5.3.2.7. Setting indexer properties
An indexer lets you set and get values from a collection using a familiar bracket [] notation. Spring's XML
configuration supports the setting of indexer properties. Overloaded indexers as well as multiparameter indexers
are also supported. The property expression parser described in Chapter 11, Expression Evaluation is used to
perform the type conversion of the indexer name argument from a string in the XML file to a matching target
type. As an example consider the following class
public class Person
{
private IList favoriteNames = new ArrayList();
private IDictionary properties = new Hashtable();
public Person()
{
favoriteNames.Add("p1");
favoriteNames.Add("p2");
}
public string this[int index]
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{
get { return (string) favoriteNames[index]; }
set { favoriteNames[index] = value; }
}
public string this[string keyName]
{
get { return (string) properties[keyName]; }
set { properties.Add(keyName, value); }
}
}
The XML configuration snippet to populate this object with data is shown below
<object id="person" type="Test.Objects.Person, Test.Objects">
<property name="[0]" value="Master Shake"/>
<property name="['one']" value="uno"/>
</object>
Note
The use of the property expression parser in Release 1.0.2 changed how you configure indexer
properties. The following section describes this usage.
The older style configuration uses the following syntax
<object id="objectWithIndexer" type="Spring.Objects.TestObject, Spring.Core.Tests">
<property name="Item[0]" value="my string value"/>
</object>
You can also change the name used to identify the indexer by adorning your indexer method
declaration with the attribute [IndexerName("MyItemName")]. You would then use the string
MyItemName[0] to configure the first element of that indexer.
There are some limitations to be aware in the older indexer configuration. The indexer can only
be of a single parameter that is convertible from a string to the indexer parameter type. Also,
multiple indexers are not supported. You can get around that last limitation currently if you use the
IndexerName attribute.
5.3.2.8. Value and ref shortcut forms
There are also some shortcut forms that are less verbose than using the full value and ref elements. The property,
constructor-arg, and entry elements all support a value attribute which may be used instead of embedding a
full value element. Therefore, the following:
<property name="myProperty">
<value>hello</value>
</property>
<constructor-arg>
<value>hello</value>
</constructor-arg>
<entry key="myKey">
<value>hello</value>
</entry>
are equivalent to:
<property name="myProperty" value="hello"/>
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<constructor-arg value="hello"/>
<entry key="myKey" value="hello"/>
In general, when typing definitions by hand, you will probably prefer to use the less verbose shortcut form.
The property and constructor-arg elements support a similar shortcut ref attribute which may be used instead
of a full nested ref element. Therefore, the following...
<property name="myProperty">
<ref object="anotherObject"/>
</property>
<constructor-arg index="0">
<ref object="anotherObject"/>
</constructor-arg>
is equivalent to...
<property name="myProperty" ref="anotherObject"/>
<constructor-arg index="0" ref="anotherObject"/>
Note
The shortcut form is equivalent to a <ref object="xxx"> element; there is no shortcut for either
the <ref local="xxx"> or <ref parent="xxx"> elements. For a local or parent ref, you must still
use the long form.
Finally, the entry element allows a shortcut form the specify the key and/or value of a dictionary, in the form of
key/key-ref and value/value-ref attributes. Therefore, the following
<entry>
<key>
<ref object="MyKeyObject"/>
</key>
<ref object="MyValueObject"/>
</entry>
Is equivalent to:
<entry key-ref="MyKeyObject" value-ref="MyValueObject"/>
As mentioned previously, the equivalence is to <ref object="xxx"> and not the local or parent forms of object
references.
5.3.2.9. Compound property names and Spring expression references
Note that compound or nested property names are perfectly legal when setting object properties. Property names
are interpreted using the Spring Expression Language (SpEL) and therefore can leverage its many features to set
property names. For example, in this object definition a simple nested property name is configured
<object id="foo" type="Spring.Foo, Spring.Foo">
<property name="bar.baz.name" value="Bingo"/>
</object>
As an example of some alternative ways to declare the property name, you can use SpEL's support for indexers
to configure a Dictionary key value pair as an alternative to the nested <dictionary> element. More importantly,
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you can use the 'expression' element to refer to a Spring expression as the value of the property. Simple examples
of this are shown below
<property name=“minValue” expression=“int.MinValue” />
<property name=“weekFromToday” expression="DateTime.Today + 7"/>
Using SpEL's support for method evaluation, you can easily call static method on various helper classes in your
XML configuraiton.
5.3.3. Declarative Event Listener Registration
In C# events are built right into the language thanks to the event keyword. Under the scenes, events are essentially
a shorthand notation for delegates with some additional guidelines as to what the parameters to an event handler
method should be (i.e. a sender System.Object and an System.EventArgs object).
public class EventSource
public event EventHandler Click;
In use, .NET events are combined with one or more event handler methods. Each handler method is
programmatically added, or removed, from the event and corresponds to an object's method that should be invoked
when a particular event occurs. When more than one handler method is added to an event, then each of the
registered methods will be invoked in turn when an event occurs.
TestObject source = new TestObject();
TestEventHandler eventListener1 = new TestEventHandler();
TestEventHandler eventListener2 = new TestEventHandler();
source.Click += eventListener1.HandleEvent; // Adding the first event handler method to the event
source.Click += eventListener2.HandleEvent; // Adding a second event handler method to the event
source.OnClick(); // First eventListener1.HandleEvent is invoked, then eventListener2.HandleEvent
When OnClick() is invoked, the event is fired.
public void OnClick()
{
if (Click != null)
{
Click(this, EventArgs.Empty); // Fire the event off to the registered handler methods
}
}
One of the not so nice things about using events is that, without employing late binding, you declare the objects
that are registered with a particular event programmatically. Spring .NET offers a way to declaratively register
your handler methods with particular events using the <listener> element inside your <object> elements.
5.3.3.1. Declarative event handlers
Rather than having to specifically declare in your code that you are adding a method to be invoked on an event,
using the <listener> element you can register a plain object's methods with the corresponding event declaratively
in your application configuration.
Using the listener element you can:
• Configure a method to be invoked when an event is fired.
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• Register a collection of handler methods based on a regular expression.
• Register a handler method against an event name that contains a regular expression.
5.3.3.2. Configuring a method to be invoked when an event is fired
The same event registration in the example above can be achieved using configuration using the <listener>
element.
<object id="eventListener1" type="SpringdotNETEventsExample.TestEventHandler, SpringdotNETEventsExample">
<!-- wired up to an event exposed on an instance -->
<listener event="Click" method="HandleEvent">
<ref object="source"/>
</listener>
</object>
<object id="eventListener2" type="SpringdotNETEventsExample.TestEventHandler, SpringdotNETEventsExample">
<!-- wired up to an event exposed on an instance -->
<listener event="Click" method="HandleEvent">
<ref object="source"/>
</listener>
</object>
In this case the two different objects will have their HandleEvent method invoked, as indicated explicitly using
the method attribute, when a Click event, as specified by the event attribute, is triggered on the object referred
to by the ref element.
5.3.3.3. Registering a collection of handler methods based on a regular expression
Regular expressions can be employed to wire up more than one handler method to an object that contains one
or more events.
<object id="eventListener" type="SpringdotNETEventsExample.TestEventHandler, SpringdotNETEventsExample">
<listener method="Handle.+">
<ref object="source"/>
</listener>
</object>
Here all the eventListener's handler methods that begin with 'Handle', and that have the corresponding two
parameters of a System.Object and a System.EventArgs, will be registered against all events exposed by the
source object.
You can also use the name of the event in regular expression to filter your handler methods based on the type
of event triggered.
<object id="eventListener" type="SpringdotNETEventsExample.TestEventHandler, SpringdotNETEventsExample">
<!-- For the Click event, the HandleClick handler method will be invoked. -->
<listener method="Handle${event}">
<ref object="source"/>
</listener>
</object>
5.3.3.4. Registering a handler method against an event name that contains a regular
expression
Finally, you can register an object's handler methods against a selection of events, filtering based on their name
using a regular expression.
<object id="eventListener" type="SpringdotNETEventsExample.TestEventHandler, SpringdotNETEventsExample">
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<listener method="HandleEvent" event="Cl.+">
<ref object="source"/>
</listener>
</object>
In this example the eventListener's HandleEvent handler method will be invoked for any event that begins with
'Cl'.
5.3.4. Using depends-on
For most situations, the fact that an object is a dependency of another is expressed by the fact that one object is set
as a property of another. This is typically accomploished with the <ref/> element in XML-based configuration
metadata. For the relatively infrequent situations where dependencies between objects are less direct (for example,
when a static initializer in a class needs to be triggered) the 'depends-on' attribute may be used to explicitly force
one or more objects to be initialized before the object using this element is initialized. Find below an example of
using the 'depends-on' attribute to express a dependency on a single object..
<object id="objectOne" type="Examples.ExampleObject, ExamplesLibrary" depends-on="manager">
<property name="manager" ref="manager"/>
</object>
<object id="manager" type="Examples.ManagerObject, ExamplesLibrary"/>
If you need to express a dependency on multiple objects, you can supply a list of object names as the value of the
'depends-on' attribute, with commas, whitespace and semicolons all valid delimiters, like so:
<object id="objectOne" type="Examples.ExampleObject, ExamplesLibrary" depends-on="manager,accountDao">
<property name="manager" ref="manager" />
</object>
<object id="manager" type="Examples.ManagerObject, ExamplesLibrary" />
<object id="accountDao" type="Examples.AdoAccountDao, ExamplesLibrary" />
Note
The 'depends-on' attribute and property is used not only to specify an initialization time dependency,
but also to specify the corresponding destroy time dependency (in the case of singleton objects only).
Dependent objects that are defined in the 'depends-on' attribute will be destroyed after the relevant
object itself is destroyed. This thus allows you to control shutdown order too
5.3.5. Lazily-instantiated objects
The default behavior for IApplicationContext implementations is to eagerly pre-instantiate all singleton objects
at startup. Pre-instantiation means that an IApplicationContext will eagerly create and configure all of its
singleton objects as part of its initialization process. Generally this is a good thing, because it means that any errors
in the configuration or in the surrounding environment will be discovered immediately (as opposed to possibly
hours or even days down the line).
However, there are times when this behavior is not what is wanted. If you do not want a singleton object to
be pre-instantiated when using an IApplicationContext, you can selectively control this by marking an object
definition as lazy-initialized. A lazily-initialized object indicates to the IoC container whether or not an object
instance should be created at startup or when it is first requested.
When configuring objects via XML, this lazy loading is controlled by the 'lazy-init'attribute on the <object/
> element; for example:
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<object id="lazy" type="MyCompany.ExpensiveToCreateObject, MyApp" lazy-init="true"/>
<object name="not.lazy" type="MyCompany.AnotherObject, MyApp"/>
When the above configuration is consumed by an IApplicationContext, the object named 'lazy' will not
be eagerly pre-instantiated when the IApplicationContext is starting up, whereas the 'not.lazy' object will be
eagerly pre-instantiated.
One thing to understand about lazy-initialization is that even though an object definition may be marked up
as being lazy-initialized, if the lazy-initialized object is the dependency of a singleton object that is not lazyinitialized, when the IApplicationContext is eagerly pre-instantiating the singleton, it will have to satisfy all
of the singletons dependencies, one of which will be the lazy-initialized object! So don't be confused if the IoC
container creates one of the objects that you have explicitly configured as lazy-initialized at startup; all that means
is that the lazy-initialized object is being injected into a non-lazy-initialized singleton object elsewhere.
It is also possible to control lazy-initialization at the container level by using the 'default-lazy-init'attribute
on the <objects/> element; for example:
<objects default-lazy-init="true">
<!-- no objects will be pre-instantiated... -->
</objects>
5.3.6. Autowiring collaborators
The Spring container is able to autowire relationships between collaborating objects. This means that it is possible
to automatically let Spring resolve collaborators (other objects) for your object by inspecting the contents of the
IoC container.. The autowiring functionality has five modes. Autowiring is specified per object and can thus be
enabled for some object, while other objects will not be autowired. Using autowiring, it is possible to reduce or
eliminate the need to specify properties or constructor arguments, thus saving a significant amount of typing.
When using XML-based configuration metadata, the autowire mode for an object definition is specified by using
the autowire attribute of the <object/> element. The following values are allowed:
Table 5.3. Autowiring modes
Mode
Explanation
no
No autowiring at all. This is the default value and you are encouraged not to change this
for large applications, since specifying your collaborators explicitly gives you a feeling for
what you're actually doing (always a bonus) and is a great way of somewhat documenting
the structure of your system.
byName
This option will inspect the objects within the container, and look for an object named exactly
the same as the property which needs to be autowired. For example, if you have an object
definition that is set to autowire by name, and it contains a Master property, Spring.NET will
look for an object definition named Master, and use it as the value of the Master property
on your object definition.
byType
This option gives you the ability to resolve collaborators by type instead of by name.
Supposing you have an IObjectDefinition with a collaborator typed SqlConnection,
Spring.NET will search the entire object factory for an object definition of type
SqlConnection and use it as the collaborator. If 0 (zero) or more than 1 (one) object
definitions of the desired type exist in the container, a failure will be reported and you won't
be able to use autowiring for that specific object.
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Mode
Explanation
constructor
This is analogous to byType, but applies to constructor arguments. If there isn't exactly one
object of the constructor argument type in the object factory, a fatal error is raised.
autodetect
Chooses constructor or byType through introspection of the object class. If a default
constructor is found, byType gets applied.
Note that explicit dependencies in property and constructor-arg settings always override autowiring. Please also
note that it is not currently possible to autowire so-called simple properties such as primitives, Strings, and Types
(and arrays of such simple properties). (This is by-design and should be considered a feature.) When using either
the byType or constructor autowiring mode, it is possible to wire arrays and typed-collections. In such cases all
autowire candidates within the container that match the expected type will be provided to satisfy the dependency.
Strongly-typed IDictionaries can even be autowired if the expected key type is string. An autowired IDictionary
values will consist of all object instances that match the expected type, and the IDictionary's keys will contain
the corresponding object names.
Autowire behavior can be combined with dependency checking, which will be performed after all autowiring
has been completed. It is important to understand the various advantages and disadvantages of autowiring. Some
advantages of autowiring include:
• Autowiring can significantly reduce the volume of configuration required. However, mechanisms such as the
use of a object template (discussed elsewhere in this chapter) are also valuable in this regard.
• Autowiring can cause configuration to keep itself up to date as your objects evolve. For example, if you need
to add an additional dependency to a class, that dependency can be satisfied automatically without the need to
modify configuration. Thus there may be a strong case for autowiring during development, without ruling out
the option of switching to explicit wiring when the code base becomes more stable.
Some disadvantages of autowiring:
• Autowiring is more magical than explicit wiring. Although, as noted in the above table, Spring is careful to
avoid guessing in case of ambiguity which might have unexpected results, the relationships between your
Spring-managed objects are no longer documented explicitly.
• Wiring information may not be available to tools that may generate documentation from a Spring container.
Another issue to consider when autowiring by type is that multiple object definitions within the container may
match the type specified by the setter method or constructor argument to be autowired. For arrays, collections, or
IDictionary, this is not necessarily a problem. However for dependencies that expect a single value, this ambiguity
will not be arbitrarily resolved. Instead, if no unique object definition is available, an Exception will be thrown.
When deciding whether to use autowiring, there is no wrong or right answer in all cases. A degree of consistency
across a project is best though; for example, if autowiring is not used in general, it might be confusing to developers
to use it just to wire one or two object definitions.
5.3.7. Checking for dependencies
Spring.NET has the ability to try to check for the existence of unresolved dependencies of an object deployed
into the container. These are properties of the object, which do not have actual values set for them in the object
definition, or alternately provided automatically by the autowiring feature.
This feature is sometimes useful when you want to ensure that all properties (or all properties of a certain type) are
set on an object. Of course, in many cases an object class will have default values for many properties, or some
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properties do not apply to all usage scenarios, so this feature is of limited use. Dependency checking can also
be enabled and disabled per object, just as with the autowiring functionality. The default dependency checking
mode is to not check dependencies. Dependency checking can be handled in several different modes. In XMLbased configuration, this is specified via the dependency-check attribute in an object definition, which may have
the following values.
Table 5.4. Dependency checking modes
Mode
Explanation
none
No dependency checking. Properties of the object which have no value specified for them
are simply not set.
simple
Dependency checking is done for primitive types and collections (this means everything
except collaborators).
object
Dependency checking is done for collaborators only.
all
Dependency checking is done for collaborators, primitive types and collections.
5.3.8. Method Injection
For most users, the majority of the objects in the container will be singletons. When a singleton object needs to
collaborate with (use) another singleton object, or a non-singleton object needs to collaborate with another nonsingleton object, the typical and common approach of handling this dependency (by defining one object to be
a property of the other) is quite adequate. There is however a problem when the object lifecycles are different.
Consider a singleton object A which needs to use a non-singleton (prototype) object B, perhaps on each method
invocation on A. The container will only create the singleton object A once, and thus only get the opportunity
to set its properties once. There is no opportunity for the container to provide object A with a new instance of
object B every time one is needed.
One solution to this problem is to forego some inversion of control. Object A can be made aware of the container
by implementing the IObjectFactoryAware interface, and use programmatic means to ask the container via a
GetObject("B") call for (a typically new) object B every time it needs it. Find below an admittedly somewhat
contrived example of this approach
using System.Collections;
using Spring.Objects.Factory;
namespace Fiona.Apple
{
public class CommandManager : IObjectFactoryAware
{
private IObjectFactory objectFactory;
public object Process(IDictionary commandState)
{
// grab a new instance of the appropriate Command
Command command = CreateCommand();
// set the state on the (hopefully brand new) Command instance
command.State = commandState;
return command.Execute();
}
// the Command returned here could be an implementation that executes asynchronously, or whatever
protected Command CreateCommand()
{
return (Command) objectFactory.GetObject("command"); // notice the Spring API dependency
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}
public IObjectFactory ObjectFactory
{
set { objectFactory = value; }
}
}
}
The above example is generally not a desirable solution since the business code is then aware of and coupled to
the Spring Framework. Method Injection, a somewhat advanced feature of the Spring IoC container, allows this
use case to be handled in a clean fashion.
5.3.8.1. Lookup Method Injection
Lookup method injection refers to the ability of the container to override abstract or concrete methods on
container managed objects, to return the result of looking up another named object in the container. The lookup
will typically be of a prototype object as in the scenario described above. The Spring framework implements
this method injection by a dynamically generating a subclass overriding the method using the classes in the
System.Reflection.Emit namespace. You can read more about the motivation for Method Injection in this blog
entry [http://blog.springframework.com/rod/?p=1].
So if you look at the code from the previous code snipped (the CommandManager class), the Spring container is
going to dynamically override the implementation of the CreateCommand() method. Your CommandManager class
is not going to have any Spring dependencies, as can be seen in this reworked example below:
using System.Collections;
namespace Fiona.Apple
{
public abstract class CommandManager
{
public object Process(IDictionary commandState)
{
Command command = CreateCommand();
command.State = commandState;
return command.Execute();
}
// okay... but where is the implementation of this method?
protected abstract Command CreateCommand();
}
}
In the client class containing the method to be injected (the CommandManager in this case) the method definition
must observe the following form:
<public|protected> [abstract] <return-type> TheMethodName(no-arguments);
If the method is abstract, the dynamically-generated subclass will implement the method. Otherwise, the
dynamically-generated subclass will override the concrete method defined in the original class. Let's look at an
example:
<!-- a stateful object deployed as a prototype (non-singleton) -->
<object id="command" class="Fiona.Apple.AsyncCommand, Fiona" singleton="false">
<!-- inject dependencies here as required -->
</object>
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<!-- commandProcessor uses a statefulCommandHelpder -->
<object id="commandManager" type="Fiona.Apple.CommandManager, Fiona">
<lookup-method name="CreateCommand" object="command"/>
</object>
The object identified as commandManager will call its own method CreateCommand whenever it needs a new
instance of the command object. It is important to note that the person deploying the objects must be careful to
deploy the command object as prototype (if that is actually what is needed). If it is deployed as a singleton the same
instance of singleShotHelper will be returned each time!
Note that lookup method injection can be combined with Constructor Injection (supplying optional constructor
arguments to the object being constructed), and also with Setter Injection (settings properties on the object being
constructed).
5.3.8.2. Arbitrary method replacement
A less commonly useful form of method injection than Lookup Method Injection is the ability to replace arbitrary
methods in a managed object with another method implementation. Users may safely skip the rest of this section
(which describes this somewhat advanced feature), until this functionality is actually needed.
In an XmlObjectFactory, the replaced-method element may be used to replace an existing method
implementation with another. Consider the following class, with a method ComputeValue, which we want to
override:
public class MyValueCalculator {
public virtual string ComputeValue(string input) {
// ... some real code
}
// ... some other methods
}
A class implementing the Spring.Objects.Factory.Support.IMethodReplacer interface is needed to provide
the new (injected) method definition.
/// <summary>
/// Meant to be used to override the existing ComputeValue(string)
/// implementation in MyValueCalculator.
/// </summary>
public class ReplacementComputeValue : IMethodReplacer
{
public object Implement(object target, MethodInfo method, object[] arguments)
{
// get the input value, work with it, and return a computed result...
string value = (string) arguments[0];
// compute...
return result;
}
}
The object definition to deploy the original class and specify the method override would look like this:
<object id="myValueCalculator" type="Examples.MyValueCalculator, ExampleAssembly">
<!-- arbitrary method replacement -->
<replaced-method name="ComputeValue" replacer="replacementComputeValue">
<arg-type match="String"/>
</replaced-method>
</object>
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<object id="replacementComputeValue" type="Examples.ReplacementComputeValue, ExampleAssembly"/>
One or more contained arg-type elements within the replaced-method element may be used to indicate the
method signature of the method being overridden. Note that the signature for the arguments is actually only
needed in the case that the method is actually overloaded and there are multiple variants within the class. For
convenience, the type string for an argument may be a substring of the fully qualified type name. For example,
all the following would match System.String.
System.String
String
Str
Since the number of arguments is often enough to distinguish between each possible choice, this shortcut can
save a lot of typing, by just using the shortest string which will match an argument.
5.3.9. Setting a reference using the members of other objects and classes.
This section details those configuration scenarios that involve the setting of properties and constructor arguments
using the members of other objects and classes. This kind of scenario is quite common, especially when dealing
with legacy classes that you cannot (or won't) change to accommodate some of Spring.NET's conventions...
consider the case of a class that has a constructor argument that can only be calculated by going to say, a database.
The MethodInvokingFactoryObject handles exactly this scenario ... it will allow you to inject the result of an
arbitrary method invocation into a constructor (as an argument) or as the value of a property setter. Similarly,
PropertyRetrievingFactoryObject and FieldRetrievingFactoryObject allow you to retrieve values from
another object's property or field value. These classes implement the IFactoryObject interface which indicates
to Spring.NET that this object is itself a factory and the factories product, not the factory itself, is what will be
associated with the object id. Factory objects are discussed further in Section 5.9.3, “Customizing instantiation
logic using IFactoryObjects”
5.3.9.1. Setting a reference to the value of property.
The PropertyRetrievingFactoryObject is an IFactoryObject that addresses the scenario of setting one of the
properties and / or constructor arguments of an object to the value of a property exposed on another object or
class. One can use it to get the value of any public property exposed on either an instance or a class (in the case
of a property exposed on a class, the property must obviously be static).
In the case of a property exposed on an instance, the target object that a PropertyRetrievingFactoryObject
will evaluate can be either an object instance specified directly inline or a reference to another arbitrary object.
In the case of a static property exposed on a class, the target object will be the class (the .NET System.Type)
exposing the property.
The result of evaluating the property lookup may then be used in another object definition as a property
value or constructor argument. Note that nested properties are supported for both instance and class property
lookups. The IFactoryObject is discussed more generally in Section 5.9.3, “Customizing instantiation logic
using IFactoryObjects”.
Here's an example where a property path is used against another object instance. In this case, an inner object
definition is used and the property path is nested, i.e. spouse.age.
<object name="person" type="Spring.Objects.TestObject, Spring.Core.Tests">
<property name="age" value="20"/>
<property name="spouse">
<object type="Spring.Objects.TestObject, Spring.Core.Tests">
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<property name="age" value="21"/>
</object>
</property>
</object>
// will result in 21, which is the value of property 'spouse.age' of object 'person'
<object name="theAge" type="Spring.Objects.Factory.Config.PropertyRetrievingFactoryObject, Spring.Core">
<property name="TargetObject" ref="person"/>
<property name="TargetProperty" value="spouse.age"/>
</object>
An example of using a PropertyRetrievingFactoryObject to evaluate a static property is shown below.
<object id="cultureAware"
type="Spring.Objects.Factory.Xml.XmlObjectFactoryTests+MyTestObject, Spring.Core.Tests">
<property name="culture" ref="cultureFactory"/>
</object>
<object id="cultureFactory"
type="Spring.Objects.Factory.Config.PropertyRetrievingFactoryObject, Spring.Core">
<property name="StaticProperty">
<value>System.Globalization.CultureInfo.CurrentUICulture, Mscorlib</value>
</property>
</object>
Similarly, an example showing the use of an instance property is shown below.
<object id="instancePropertyCultureAware"
type="Spring.Objects.Factory.Xml.XmlObjectFactoryTests+MyTestObject, Spring.Core.Tests">
<property name="Culture" ref="instancePropertyCultureFactory"/>
</object>
<object id="instancePropertyCultureFactory"
type="Spring.Objects.Factory.Config.PropertyRetrievingFactoryObject, Spring.Core">
<property name="TargetObject" ref="instancePropertyCultureAwareSource"/>
<property name="TargetProperty" value="MyDefaultCulture"/>
</object>
<object id="instancePropertyCultureAwareSource"
type="Spring.Objects.Factory.Xml.XmlObjectFactoryTests+MyTestObject, Spring.Core.Tests"/>
5.3.9.2. Setting a reference to the value of field.
The FieldRetrievingFactoryObject class addresses much the same area of concern as the
PropertyRetrievingFactoryObject described in the previous section. However, as its name might suggest, the
FieldRetrievingFactoryObject class is concerned with looking up the value of a public field exposed on either
an instance or a class (and similarly, in the case of a field exposed on a class, the field must obviously be static).
The following example demonstrates using a FieldRetrievingFactoryObject to look up the value of a (public,
static) field exposed on a class
<object id="withTypesField"
type="Spring.Objects.Factory.Xml.XmlObjectFactoryTests+MyTestObject, Spring.Core.Tests">
<property name="Types" ref="emptyTypesFactory"/>
</object>
<object id="emptyTypesFactory"
type="Spring.Objects.Factory.Config.FieldRetrievingFactoryObject, Spring.Core">
<property name="TargetType" value="System.Type, Mscorlib"/>
<property name="TargetField" value="EmPTytypeS"/>
</object>
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The example in the next section demonstrates the look up of a (public) field exposed on an object instance.
<object id="instanceCultureAware"
type="Spring.Objects.Factory.Xml.XmlObjectFactoryTests+MyTestObject, Spring.Core.Tests">
<property name="Culture" ref="instanceCultureFactory"/>
</object>
<object id="instanceCultureFactory"
type="Spring.Objects.Factory.Config.FieldRetrievingFactoryObject, Spring.Core">
<property name="TargetObject" ref="instanceCultureAwareSource"/>
<property name="TargetField" value="Default"/>
</object>
<object id="instanceCultureAwareSource"
type="Spring.Objects.Factory.Xml.XmlObjectFactoryTests+MyTestObject, Spring.Core.Tests"/>
5.3.9.3. Setting a property or constructor argument to the return value of a method invocation.
The MethodInvokingFactoryObject rounds out the trio of classes that permit the setting of
properties and constructor arguments using the members of other objects and classes. Whereas the
PropertyRetrievingFactoryObject and FieldRetrievingFactoryObject classes dealt with simply looking up
and returning the value of property or field on an object or class, the MethodInvokingFactoryObject allows one
to set a constructor or property to the return value of an arbitrary method invocation,
The MethodInvokingFactoryObject class handles both the case of invoking an (instance) method on another
object in the container, and the case of a static method call on an arbitrary class. Additionally, it is
sometimes necessary to invoke a method just to perform some sort of initialization.... while the mechanisms
for handling object initialization have yet to be introduced (see Section 5.6.1.1, “IInitializingObject / initmethod”), these mechanisms do not permit any arguments to be passed to any initialization method, and are
confined to invoking an initialization method on the object that has just been instantiated by the container. The
MethodInvokingFactoryObject allows one to invoke pretty much any method on any object (or class in the case
of a static method).
The following example (in an XML based IObjectFactory definition) uses the MethodInvokingFactoryObject
class to force a call to a static factory method prior to the instantiation of the object...
<object id="force-init"
type="Spring.Objects.Factory.Config.MethodInvokingFactoryObject, Spring.Core">
<property name="StaticMethod">
<value>ExampleNamespace.ExampleInitializerClass.Initialize</value>
</property>
</object>
<object id="myService" depends-on="force-init"/>
Note that the definition for the myService object has used the depends-on attribute to refer to the force-init
object, which will force the initialization of the force-init object first (and thus the calling of its configured
StaticMethod static initializer method, when myService is first initialized. Please note that in order to effect this
initialization, the MethodInvokingFactoryObject object must be operating in singleton mode (the default.. see
the next paragraph).
Note that since this class is expected to be used primarily for accessing factory methods, this factory defaults
to operating in singleton mode. As such, as soon as all of the properties for a MethodInvokingFactoryObject
object have been set, and if the MethodInvokingFactoryObject object is still in singleton mode, the method
will be invoked immediately and the return value cached for later access. The first request by the container for
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the factory to produce an object will cause the factory to return the cached return value for the current request
(and all subsequent requests). The IsSingleton property may be set to false, to cause this factory to invoke the
target method each time it is asked for an object (in this case there is obviously no caching of the return value).
A static target method may be specified by setting the targetMethod property to a string representing the static
method name, with TargetType specifying the Type that the static method is defined on. Alternatively, a target
instance method may be specified, by setting the TargetObject property to the name of another Spring.NET
managed object definition (the target object), and the TargetMethod property to the name of the method to call
on that target object.
Arguments for the method invocation may be specified in two ways (or even a mixture of both)... the first involves
setting the Arguments property to the list of arguments for the method that is to be invoked. Note that the ordering
of these arguments is significant... the order of the values passed to the Arguments property must be the same
as the order of the arguments defined on the method signature, including the argument Type. This is shown in
the example below
<object id="myObject" type="Spring.Objects.Factory.Config.MethodInvokingFactoryObject, Spring.Core">
<property name="TargetType" value="Whatever.MyClassFactory, MyAssembly"/>
<property name="TargetMethod" value="GetInstance"/>
<!-- the ordering of arguments is significant -->
<property name="Arguments">
<list>
<value>1st</value>
<value>2nd</value>
<value>and 3rd arguments</value>
<!-- automatic Type-conversion will be performed prior to invoking the method -->
</list>
</property>
</object>
The second way involves passing an arguments dictionary to the NamedArguments property... this dictionary maps
argument names (Strings) to argument values (any object). The argument names are not case-sensitive, and order
is (obviously) not significant (since dictionaries by definition do not have an order). This is shown in the example
below
<object id="myObject" type="Spring.Objects.Factory.Config.MethodInvokingFactoryObject, Spring.Core">
<property name="TargetObject">
<object type="Whatever.MyClassFactory, MyAssembly"/>
</property>
<property name="TargetMethod" value="Execute"/>
<!-- the ordering of named arguments is not significant -->
<property name="NamedArguments">
<dictionary>
<entry key="argumentName"><value>1st</value></entry>
<entry key="finalArgumentName"><value>and 3rd arguments</value></entry>
<entry key="anotherArgumentName"><value>2nd</value></entry>
</dictionary>
</property>
</object>
The following example shows how use MethodInvokingFactoryObject to call an instance method.
<object id="myMethodObject" type="Whatever.MyClassFactory, MyAssembly" />
<object id="myObject" type="Spring.Objects.Factory.Config.MethodInvokingFactoryObject, Spring.Core">
<property name="TargetObject" ref="myMethodObject"/>
<property name="TargetMethod" value="Execute"/>
</object>
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The above example could also have been written using an anonymous inner object definition... if the object on
which the method is to be invoked is not going to be used outside of the factory object definition, then this is the
preferred idiom because it limits the scope of the object on which the method is to be invoked to the surrounding
factory object.
Finally, if you want to use MethodInvokingFactoryObject in conjunction with a method that has a variable
length argument list, then please note that the variable arguments need to be passed (and configured) as a list.
Let us consider the following method definition that uses the params keyword (in C#), and its attendant (XML)
configuration...
[C#]
public class MyClassFactory
{
public object CreateObject(Type objectType, params string[] arguments)
{
return ... // implementation elided for clarity...
}
}
<object id="myMethodObject" type="Whatever.MyClassFactory, MyAssembly" />
<object id="paramsMethodObject" type="Spring.Objects.Factory.Config.MethodInvokingFactoryObject, Spring.Core">
<property name="TargetObject" ref="myMethodObject"/>
<property name="TargetMethod" value="CreateObject"/>
<property name="Arguments">
<list>
<value>System.String</value>
<!-- here is the 'params string[] arguments' -->
<list>
<value>1st</value>
<value>2nd</value>
</list>
</list>
</object>
5.3.10. Provided IFactoryObject implementations
In
addition
to
PropertyRetrievingFactoryObject,
MethodInvokingFactoryObject,
and
Spring.NET comes with other useful implementations of the IFactoryObject
interface. These are discussed below.
FieldRetrievingFactoryObject
5.3.10.1. Common logging
The LogFactoryObject is useful when you would like to share a Common.Logging log object across a
number of classes instead of creating a logging instance per class or class hierarchy. Information on the
Common.Logging project can be found here [http://netcommon.sourceforge.net/]. In the example shown below
the same logging instance, with a logging category name of "DAOLogger", is used in both the SimpleAccountDao
and SimpleProductDao data access objects.
<objects xmlns="http://www.springframework.net"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.net
http://www.springframework.net/xsd/spring-objects.xsd" >
<object name="daoLogger" type="Spring.Objects.Factory.Config.LogFactoryObject, Spring.Core">
<property name="logName" value="DAOLogger"/>
</object>
<object name="productDao" type="PropPlayApp.SimpleProductDao, PropPlayApp ">
<property name="maxResults" value="100"/>
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<property name="dbConnection" ref="myConnection"/>
<property name="log" ref="daoLogger"/>
</object>
<object name="accountDao" type="PropPlayApp.SimpleAccountDao, PropPlayApp ">
<property name="maxResults" value="100"/>
<property name="dbConnection" ref="myConnection"/>
<property name="log" ref="daoLogger"/>
</object>
<object name="myConnection" type="System.Data.Odbc.OdbcConnection, System.Data">
<property name="connectionstring" value="dsn=MyDSN;uid=sa;pwd=myPassword;"/>
</object>
</objects>
5.4. Object Scopes
When you create a object definition what you are actually creating is a recipe for creating actual instances of the
class defined by that object definition. The idea that a object definition is a recipe is important, because it means
that, just like a class, you can potentially have many object instances created from a single recipe.
You can control not only the various dependencies and configuration values that are to be plugged into an object
that is created from a particular object definition, but also the scope of the objects created from a particular object
definition. This approach is very powerful and gives you the flexibility to choose the scope of the objects you
create through configuration instead of having to 'bake in' the scope of an object at the .NET class level. Objects
can be defined to be deployed in one of a number of scopes: out of the box, the Spring Framework supports
exactly five scopes (of which three are available only if you are using a web-aware ApplicationContext).
The scopes supported out of the box are listed below:
Table 5.5. Object Scopes
Scope
Description
singleton
Scopes a single object definition to a single object instance per Spring IoC
container.
prototype
Scopes a single object definition to any number of object instances.
request
Scopes a single object definition to the lifecycle of a single HTTP request;
that is each and every HTTP request will have its own instance of an object
created off the back of a single object definition. Only valid in the context
of a web-aware Spring ApplicationContext.
session
Scopes a single object definition to the lifecycle of a HTTP Session. Only
valid in the context of a web-aware Spring ApplicationContext.
application
Scopes a single object definition to the lifecycle of a web application. Only
valid in the context of a web-aware Spring ApplicationContext.
5.4.1. The singleton scope
When an object is a singleton, only one shared instance of the object will be managed, and all requests for objects
with an id or ids matching that object definition will result in that one specific object instance being returned by
the Spring container.
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To put it another way, when you define an object definition and it is scoped as a singleton, then the Spring IoC
container will create exactly one instance of the object defined by that object definition. This single instance will
be stored in a cache of such singleton object, and all subsequent requests and references for that named object
will result in the cached object being returned.
Please be aware that Spring's concept of a singleton object is quite different from the Singleton pattern as defined
in the seminal Gang of Four (GoF) patterns book. The GoF Singleton hard codes the scope of an object such
that one and only one instance of a particular class will ever be created per ApplicationDomain. The scope of the
Spring singleton is best described as per container and per object. This means that if you define one object for a
particular class in a single Spring container, then the Spring container will create one and only one instance of
the class defined by that object definition. The singleton scope is the default scope in Spring. To define an object
as a singleton in XML, you would write configuration like so:
<object id="accountService" type="MyApp.DefaultAccountService, MyApp"/>
<!-- the following is equivalent, though redundant (singleton scope is the default) -->
<object id="accountService" type="MyApp.DefaultAccountService, MyApp" singleton="true"/>
5.4.2. The prototype scope
The non-singleton, prototype scope of object deployment results in the creation of a new object instance every
time a request for that specific object is made (that is, it is injected into another object or it is requested via a
programmatic GetObject() method call on the container). As a rule of thumb, you should use the prototype scope
for all objects that are stateful, while the singleton scope should be used for stateless objects.
To define an object as a prototype in XML, you would write configuration like so:
<object id="exampleObject" type="Examples.ExampleObject, ExamplesLibrary" singleton="false"/>
There is one quite important thing to be aware of when deploying an object in the prototype scope, in that the
lifecycle of the object changes slightly. Spring does not manage the complete lifecycle of a prototype object: the
container instantiates, configures, decorates and otherwise assembles a prototype object, hands it to the client and
then has no further knowledge of that prototype instance. This means that while initialization lifecycle callback
methods will be called on all objects regardless of scope, in the case of prototypes, any configured destruction
lifecycle callbacks will not be called. It is the responsibility of the client code to clean up prototype scoped objects
and release any expensive resources that the prototype object(s) are holding onto. (One possible way to get the
Spring container to release resources used by singleton-scoped objects is through the use of a custom object post
processor which would hold a reference to the objects that need to be cleaned up.)
In some respects, you can think of the Spring containers role when talking about a prototype-scoped object as
somewhat of a replacement for the C# 'new' operator. All lifecycle aspects past that point have to be handled by
the client. (The lifecycle of a object in the Spring container is further described in the section entitled “Lifecycle
callbacks”.)
5.4.3. Singleton objecgts with prototype-object dependencies
When using singleton-scoped objects that have dependencies on objects that are scoped as prototypes, please
be aware that dependencies are resolved at instantiation time. This means that if you dependency inject a
prototype-scoped object into a singleton-scoped object, a brand new prototype object will be instantiated and then
dependency injected into the singleton object... but that is all. That exact same prototype instance will be the sole
instance that is ever supplied to the singleton-scoped object, which is fine if that is what you want.
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However, sometimes what you actually want is for the singleton-scoped object to be able to acquire a brand
new instance of the prototype-scoped object again and again and again at runtime. In that case it is no use just
dependency injecting a prototype-scoped object into your singleton object, because as explained above, that
only happens once when the Spring container is instantiating the singleton object and resolving and injecting its
dependencies. If you are in the scenario where you need to get a brand new instance of a (prototype) object again
and again and again at runtime, you are referred to the section entitled “Method Injection”.
5.4.4. The other scopes
The other scopes, namely request, session, and application are for use only in web-based applications. Please refer
to the web documentation on object scopes for more information.
5.5. Type conversion
Type converters are responsible for converting objects from one type to another. When using the XML based file
to configure the IoC container, string based property values are converted to the target property type. Spring will
rely on the standard .NET support for type conversion unless an alternative TypeConverter is registered for a
given type. How to register custom TypeConverters will be described shortly. As a reminder, the standard .NET
type converter support works by associating a TypeConverter attribute with the class definition by passing the
type of the converter as an attribute argument. 3 For example, an abbreviated class definition for the BCL type
Font is shown below.
[Serializable, TypeConverter(typeof(FontConverter)), ...]
public sealed class Font : MarshalByRefObject, ICloneable, ISerializable, IDisposable
{
// Methods
... etc ..
}
5.5.1. Type Conversion for Enumerations
The default type converter for enumerations is the System.ComponentModel.EnumConverter class. To specify
the value for an enumerated property, simply use the name of the property. For example the TestObject class
has a property of the enumerated type FileMode. One of the values for this enumeration is named Create. The
following XML fragment shows how to configure this property
<object id="rod" type="Spring.Objects.TestObject, Spring.Core.Tests">
<property name="name" value="Rod"/>
<property name="FileMode" value="Create"/>
</object>
5.5.2. Built-in TypeConverters
Spring.NET pre-registers a number of custom TypeConverter instances (for example, to convert a type expressed
as a string into a real System.Type object). Each of those is listed below and they are all located in the
Spring.Objects.TypeConverters namespace of the Spring.Core library.
3
More information about creating custom TypeConverter implementations can be found online at Microsoft's MSDN website, by searching
for Implementing a Type Converter.
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Table 5.6. Built-in TypeConverters
Type
Explanation
RuntimeTypeConverter
Parses strings representing System.Types to actual System.Types
and the other way around.
FileInfoConverter
Capable of resolving strings to a System.IO.FileInfo object.
StringArrayConverter
Capable of resolving a comma-delimited list of strings to a stringarray and vice versa.
UriConverter
Capable of resolving a string representation of a Uri to an actual Uriobject.
CredentialConverter
Capable of resolving a string representation of a credential for Web
client authentication into an instance of System.Net.ICredentials
StreamConverter
Capable of resolving Spring IResource Uri (string) to its
corresponding InputStream-object.
ResourceConverter
Capable of resolving Spring IResource Uri (string) to an IResource
object.
ResourceManagerConverter
Capable of resolving a two part string (resource name, assembly
name) to a System.Resources.ResourceManager object.
RgbColorConverter
Capable of resolving a comma separated list of Red, Green, Blue
integer values to a System.Drawing.Color structure.
ExpressionConverter
Capable of resolving a string into an instance of an object that
implements the IExpression interface.
NameValueConverter
Capable
of
resolving
an
XML
formatted
string
to
a
Specialized.NameValueCollection
RegexConverter
Capable of resolving a string into an instance of Regex
RegistryKeyConverter
Capable of resolving a string into a Microsoft.Win32.RegistryKey
object.
Spring.NET uses the standard .NET mechanisms for the resolution of System.Types, including, but not limited to
checking any configuration files associated with your application, checking the Global Assembly Cache (GAC),
and assembly probing.
5.5.3. Custom Type Conversion
There are a few ways to register custom type converters. The fundamental storage area in Spring for
custom type converters is the TypeConverterRegistry class. The most convenient way if using an XML
based implementation of IObjectFactory or IApplicationContext is to use the custom configuration section
handler TypeConverterSectionHandler This is demonstrated in section Section 5.11, “Configuration of
IApplicationContext”
An alternate approach, present for legacy reasons in the port of Spring.NET from the Java code base, is to
use the object factory post-processor Spring.Objects.Factory.Config.CustomConverterConfigurer. This is
described in the next section.
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If
you
are
constructing
your
RegisterCustomConverter(Type
ConfigurableObjectFactory
IoC
container
requiredType,
Programatically
TypeConverter
then
you
should use
converter) method of
the
the
interface.
5.5.3.1. Using CustomConverterConfigurer
This section shows in detail how to define a custom type converter that does not use the .NET TypeConverter
attribute. The type converter class is standalone and inherits from the TypeConverter class. It uses the legacy
factory post-processor approach.
Consider a user class ExoticType, and another class DependsOnExoticType which needs ExoticType set as a
property:
public class ExoticType
{
private string name;
public ExoticType(string name)
{
this.name = name;
}
public string Name
{
get { return this.name; }
}
}
and
public class DependsOnExoticType
{
public DependsOnExoticType() {}
private ExoticType exoticType;
public ExoticType ExoticType
{
get { return this.exoticType; }
set { this.exoticType = value; }
}
public override string ToString()
{
return exoticType.Name;
}
}
When things are properly set up, we want to be able to assign the type property as a string, which a TypeConverter
will convert into a real ExoticType object behind the scenes:
<object name="sample" type="SimpleApp.DependsOnExoticType, SimpleApp">
<property name="exoticType" value="aNameForExoticType"/>
</object>
The TypeConverter looks like this:
public class ExoticTypeConverter : TypeConverter
{
public ExoticTypeConverter()
{
}
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public override bool CanConvertFrom (
ITypeDescriptorContext context,
Type sourceType)
{
if (sourceType == typeof (string))
{
return true;
}
return base.CanConvertFrom (context, sourceType);
}
public override object ConvertFrom (
ITypeDescriptorContext context,
CultureInfo culture, object value)
{
string s = value as string;
if (s != null)
{
return new ExoticType(s.ToUpper());
}
return base.ConvertFrom (context, culture, value);
}
}
Finally, we use the CustomConverterConfigurer to register the new TypeConverter with the
IApplicationContext, which will then be able to use it as needed:
<object id="customConverterConfigurer"
type="Spring.Objects.Factory.Config.CustomConverterConfigurer, Spring.Core">
<property name="CustomConverters">
<dictionary>
<entry key="SimpleApp.ExoticType">
<object type="SimpleApp.ExoticTypeConverter"/>
</entry>
</dictionary>
</property>
</object>
5.6. Customizing the nature of an object
5.6.1. Lifecycle interfaces
Spring.NET uses several marker interfaces to change the behaviour of your object in the container,
namely the Spring.NET specific IInitializingObject interface and the standard System.IDisposable
interfaces. Implementing either of the aforementioned interfaces will result in the container calling the
AfterPropertiesSet() method for the former and the Dispose() method for the latter, thus allowing you to do
things upon the initialization and destruction of your objects.
Internally, Spring.NET uses implementations of the IObjectPostProcessor interface to process any marker
interfaces it can find and call the appropriate methods. If you need custom features or other lifecycle
behavior Spring.NET doesn't offer out-of-the-box, you can implement an IObjectPostProcessor yourself. More
information about this can be found in Section 5.9.1, “Customizing objects with IObjectPostProcessors”.
All the different lifecycle marker interfaces are described below.
5.6.1.1. IInitializingObject / init-method
The Spring.Objects.Factory.IInitializingObject interface gives you the ability to perform initialization
work after all the necessary properties on an object are set by the container. The IInitializingObject interface
specifies exactly one method:
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• void AfterPropertiesSet(): called after all properties have been set by the container. This method enables
you to do checking to see if all necessary properties have been set correctly, or to perform further initialization
work. You can throw any Exception to indicate misconfiguration, initialization failures, etc.
Note
Generally, the use of the IInitializingObject can be avoided. The Spring.Core library provides
support for a generic init-method, given to the object definition in the object configuration store (be
it XML, or a database, etc).
<object id="exampleInitObject" type="Examples.ExampleObject" init-method="init"/>
[C#]
public class ExampleObject
{
public void Init()
{
// do some initialization work
}
}
Is exactly the same as...
<object id="exampleInitObject" type="Examples.AnotherExampleObject"/>
[C#]
public class AnotherExampleObject : IInitializingObject
{
public void AfterPropertiesSet()
{
// do some initialization work
}
}
but does not couple the code to Spring.NET.
Note
When deploying an object in prototype mode, the lifecycle of the object changes slightly. By
definition, Spring.NET cannot manage the complete lifecycle of a non-singleton / prototype object,
since after it is created, it is given to the client and the container no longer keeps a reference to the
object. You can think of Spring.NET's role when talking about a non-singleton ( prototype ) object
as a replacement for the new operator. Any lifecycle aspects past that point have to be handled by
the client.
5.6.1.2. IDisposable / destroy-method
The System.IDisposable interface provides you with the ability to get a callback when an IObjectFactory is
destroyed. The IDisposable interface specifies exactly one method:
• void Dispose(): and is called on destruction of the container. This allows you to release any resources you
are keeping in this object (such as database connections). You can throw any Exception here... however, any
such Exception will not stop the destruction of the container - it will only get logged.
Note
Note: If you choose you can avoid having your class implement IDisposable since the Spring.Core
library provides support for a generic destroy-method, given to the object definition in the object
configuration store (be it XML, or a database, etc).
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<object id="exampleInitObject" type="Examples.ExampleObject" destroy-method="cleanup"/>
[C#]
public class ExampleObject
{
public void cleanup()
{
// do some destruction work (such as closing any open connection (s))
}
}
is exactly the same as:
<object id="exampleInitObject" type="Examples.AnotherExampleObject"/>
[C#]
public class AnotherExampleObject : IDisposable
{
public void Dispose()
{
// do some destruction work
}
}
5.6.2. Knowing who you are
5.6.2.1. IObjectFactoryAware
A class which implements the Spring.Objects.Factory.IObjectFactoryAware interface is provided with a
reference to the IObjectFactory that created it. The interface specifies one (write-only) property:
• IObjectFactory
ObjectFactory: the property that will be set after the initialization methods
(AfterPropertiesSet and the init-method).
This allows objects to manipulate the IObjectFactory that created them Programatically, through the
IObjectFactory interface, or by casting the reference to a known subclass of this which exposes additional
functionality. Primarily this would consist of programmatic retrieval of other objects. While there are cases when
this capability is useful, it should generally be avoided, since it couples the code to Spring.NET, and does not
follow the Inversion of Control style, where collaborators are provided to objects as properties.
5.6.2.2. IObjectNameAware
The Spring.Objects.Factory.IObjectNameAware interface gives you the ability to let the container set the name
of the object definition on the object instance itself. In those cases where your object needs to know what its name
is, implement this interface.
• string ObjectName: the property that will be set to let the object know what its name is.
5.7. Object definition inheritance
An object definition potentially contains a large amount of configuration information, including container specific
information (i.e. initialization method, static factory method name, etc.) and constructor arguments and property
values. A child object definition is an object definition that inherits configuration data from a parent definition.
It is then able to override some values, or add others, as needed. Using parent and child object definitions can
potentially save a lot of typing. Effectively, this is a form of templating.
When working with an IObjectFactory Programatically, child object definitions are represented by the
ChildObjectDefinition class. Most users will never work with them on this level, instead configuring object
definitions declaratively in something like the XmlObjectFactory. In an XmlObjectFactory object definition, a
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child object definition is indicated simply by using the parent attribute, specifying the parent object definition
as the value of this attribute.
<object id="inheritedTestObject" type="Spring.Objects.TestObject, Spring.Core.Tests">
<property name="name" value="parent"/>
<property name="age" value="1"/>
</object>
<object id="inheritsWithDifferentClass" type="Spring.Objects.DerivedTestObject, Spring.Core.Tests"
parent="inheritedTestObject" init-method="Initialize">
<property name="name" value="override"/>
<!-- age will inherit value of 1 from parent -->
</object>
A child object definition will use the object class from the parent definition if none is specified, but can also
override it. In the latter case, the child object class must be compatible with the parent, i.e. it must accept the
parent's property values.
A child object definition will inherit constructor argument values, property values and method overrides from
the parent, with the option to add new values. If init method, destroy method and/or static factory method are
specified, they will override the corresponding parent settings.
The remaining settings will always be taken from the child definition: depends on, autowire mode, dependency
check, singleton, lazy init.
In the case where the parent definition does not specify a class...
<object id="inheritedTestObjectWithoutClass" abstract="true">
<property name="name" value="parent"/>
<property name="age" value="1"/>
</object>
<object id="inheritsWithClass" type="Spring.Objects.DerivedTestObject, Spring.Core.Tests"
parent="inheritedTestObjectWithoutClass" init-method="Initialize">
<property name="name" value="override"/>
<!-- age will inherit value of 1 from parent -->
</object>
... the parent object cannot be instantiated on its own since it incomplete, and it is also explicitly marked as
abstract. When a definition is defined to be abstract like this, it is usable only as a pure template object definition
that will serve as a parent definition for child definitions. Trying to use such an abstract parent object on its own
(by referring to it as a ref property of another object, or doing an explicit GetObject() with the parent object
id), will result in an error. The container's internal PreInstantiateSingletons method will completely ignore
object definitions that are considered abstract.
Note
Application contexts (but not simple object factories) will by default pre-instantiate all singletons.
Therefore it is important (at least for singleton objects) that if you have a (parent) object definition
which you intend to use only as a template, and this definition specifies a class, you must make sure
to set the abstract attribute to true , otherwise the application context will actually (attempt to) preinstantiate the abstract object.
5.8. Interacting with the container
The Spring container is essentially nothing more than an advanced factory capable of maintaining a registry of
different objects and their dependencies. The IObjectFactory enables you to read object definitions and access
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them using the object factory. When using just the IObjectFactory you would create an instance of one and then
read in some object definitions in the XML format as follows:
[C#]
IResource input = new FileSystemResource ("objects.xml");
XmlObjectFactory factory = new XmlObjectFactory(input);
That is pretty much it. Using GetObject(string) (or the more concise indexer method factory ["string"])
you can retrieve instances of your objects...
[C#]
object foo = factory.GetObject ("foo"); // gets the object defined as 'foo'
object bar = factory ["bar"];
// same thing, just using the indexer
You'll get a reference to the same object if you defined it as a singleton (the default) or you'll get a new instance
each time if you set the singleton property of your object definition to false.
<object id="exampleObject" type="Examples.ExampleObject, ExamplesLibrary"/>
<object id="anotherObject" type="Examples.ExampleObject, ExamplesLibrary" singleton="false"/>
[C#]
object one = factory ["exampleObject"];
object two = factory ["exampleObject"];
Console.WriteLine (one == two)
object three = factory ["anotherObject"];
object four = factory ["anotherObject"];
Console.WriteLine (three == four);
// gets the object defined as 'exampleObject'
// prints 'true'
// gets the object defined as 'anotherObject'
// prints 'false'
The client-side view of the IObjectFactory is surprisingly simple. The IObjectFactory interface has only seven
methods (and the aforementioned indexer) for clients to call:
• bool ContainsObject(string): returns true if the IObjectFactory contains an object definition that matches
the given name.
• object GetObject(string): returns an instance of the object registered under the given name. Depending
on how the object was configured by the IObjectFactory configuration, either a singleton (and thus shared)
instance or a newly created object will be returned. An ObjectsException will be thrown when either the object
could not be found (in which case it'll be a NoSuchObjectDefinitionException), or an exception occurred
while instantiated and preparing the object.
• Object this [string]: this is the indexer for the IObjectFactory interface. It functions in all other respects
in exactly the same way as the GetObject(string) method. The rest of this documentation will always refer
to the GetObject(string) method, but be aware that you can use the indexer anywhere that you can use the
GetObject(string) method.
• Object GetObject(string, Type): returns an object, registered under the given name. The object returned
will be cast to the given Type. If the object could not be cast, corresponding exceptions will be thrown
(ObjectNotOfRequiredTypeException). Furthermore, all rules of the GetObject(string) method apply (see
above).
• bool IsSingleton(string): determines whether or not the object definition registered under the given name
is a singleton or a prototype. If the object definition corresponding to the given name could not be found, an
exception will be thrown (NoSuchObjectDefinitionException)
• string[] GetAliases(string): returns the aliases for the given object name, if any were defined in the
IObjectDefinition.
• void ConfigureObject(object target): Injects dependencies into the supplied target instance. The name
of the abstract object definition is the System.Type.FullName of the target instance. This method is typically
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used when objects are instantiated outside the control of a developer, for example when ASP.NET instantiates
web controls and when a WinForms application creates UserControls.
• void ConfigureObject(object target, string name): Offers the same functionality as the previously
listed Configure method but uses a named object definition instead of using the type's full name.
A sub-interface of IObjectFactory, IConfigurableObjectFactory adds some convenient methods such as
• void RegisterSingleton(string name, object objectInstance) : Register the given existing object as
singleton in the object factory under the given object name.
• void RegisterAlias(string name, string theAlias); Given an object name, create an alias.
Check the SDK docs for additional details on IConfigurableObjectFactory methods and properties and the full
IObjectFactory class hierarchy.
5.8.1. Obtaining an IFactoryObject, not its product
Sometimes there is a need to ask an IObjectFactory for an actual IFactoryObject instance itself, not the object
it produces. This may be done by prepending the object id with & when calling the GetObject method of the
IObjectFactory and IApplicationContext interfaces. So for a given IFactoryObject with an id myObject,
invoking GetObject("myObject") on the IObjectFactory will return the product of the IFactoryObject, but
invoking GetObject("&myObject") will return the IFactoryObject instance itself.
5.9. Container extension points
The IoC component of the Spring Framework has been designed for extension. There is typically no need for an
application developer to subclass any of the various IObjectFactory or IApplicationContext implementation
classes. The Spring IoC container can be infinitely extended by plugging in implementations of special integration
interfaces. The next few sections are devoted to detailing all of these various integration interfaces.
5.9.1. Customizing objects with IObjectPostProcessors
The first extension point that we will look at is the Spring.Objects.Factory.Config.IObjectPostProcessor
interface. This interface defines a number of callback methods that you as an application developer can implement
in order to provide your own (or override the containers default) instantiation logic, dependency-resolution logic,
and so forth. If you want to do some custom logic after the Spring container has finished instantiating, configuring
and otherwise initializing an object, you can plug in one or more IObjectPostProcessor implementations.
You can configure multiple IObjectPostProcessors if you wish. You can control the order in which
these IObjectPostProcessor execute by setting the 'Order' property (you can only set this property if the
IObjectPostProcessor implements the IOrdered interface; if you write your own IObjectPostProcessor you
should consider implementing the IOrdered interface too); consult the SDK docs for the IObjectPostProcessor
and IOrdered interfaces for more details.
Note
IObjectPostProcessor operate on object instances; that is to say, the Spring IoC container will have
instantiated a object instance for you, and then IObjectPostProcessors get a chance to do their
stuff. If you want to change the actual object definition (that is the recipe that defines the object),
then you rather need to use a IObjectFactoryPostProcessor (described below in the section entitled
Customizing configuration metadata with IObjectFactoryPostProcessors.
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Also, IObjectPostProcessors are scoped per-container. This is only relevant if you are using
container hierarchies. If you define a IObjectPostProcessor in one container, it will only do its
stuff on the objects in that container. Objects that are defined in another container will not be postprocessed by IObjectPostProcessors in another container, even if both containers are part of the
same hierarchy.
The Spring.Objects.Factory.Config.IObjectPostProcessor interface, which consists of two callback
methods shown below.
object PostProcessBeforeInitialization(object instance, string name);
object PostProcessAfterInitialization(object instance, string name);
When such a class is registered as a post-processor with the container, for each object instance that is created
by the container,(see below for how this registration is effected), for each object instance that is created by the
container, the post-processor will get a callback from the container both before any initialization methods (such
as the AfterPropertiesSet method of the IInitializingObject interface and any declared init method) are
called, and also afterwards. The post-processor is free to do what it wishes with the object, including ignoring the
callback completely. An object post-processor will typically check for marker interfaces, or do something such
as wrap an object with a proxy. Some Spring.NET AOP infrastructure classes are implemented as object postprocessors as they do this proxy-wrapping logic.
Other extensions to the IObjectPostProcessors interface are IInstantiationAwareObjectPostProcessor and
IDestructionAwareObjectPostProcessor defined below
public interface IInstantiationAwareObjectPostProcessor : IObjectPostProcessor
{
object PostProcessBeforeInstantiation(Type objectType, string objectName);
bool PostProcessAfterInstantiation(object objectInstance, string objectName);
IPropertyValues PostProcessPropertyValues(IPropertyValues pvs, PropertyInfo[] pis, object objectInstance, s
}
public interface IDestructionAwareObjectPostProcessor : IObjectPostProcessor
{
void PostProcessBeforeDestruction (object instance, string name);
}
The PostProcessBeforeInstantiation callback method is called right before the container creates the object.
If the object returned by this method is not null then the default instantiation behavior of the container is short
circuited. The returned object is the one registered with the container and no other IObjectPostProcessor
callbacks will be invoked on it. This mechanism is useful if you would like to expose a proxy to the object instead
of the actual target object. The PostProcessAfterInstantiation callback method is called after the object has
been instantiated but before Spring performs property population based on explicit properties or autowiring. A
return value of false would short circuit the standard Spring based property population. The callback method
PostProcessPropertyValues is called after Spring collects all the property values to apply to the object, but
before they are applied. This gives you the opportunity to perform additional processing such as making sure
that a property is set to a value if it contains a [Required] attribute or to perform attribute based wiring, i.e.
adding the attribute [Inject("objectName")] on a property. Both of these features are scheduled to be included
in Spring .12.
The
callback
contains
a
single
PostProcessBeforeDestruction, which is called before a singleton's destroy method is invoked.
IDestructionAwareObjectPostProcessor
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It is important to know that the IObjectFactory treats object post-processors slightly differently than the
IApplicationContext. An IApplicationContext will automatically detect any objects which are deployed into
it that implement the IObjectPostProcessor interface, and register them as post-processors, to be then called
appropriately by the factory on object creation. Nothing else needs to be done other than deploying the postprocessor in a similar fashion to any other object. On the other hand, when using plain IObjectFactories, object
post-processors have to manually be explicitly registered, with a code sequence such as...
ConfigurableObjectFactory factory = new .....; // create an IObjectFactory
... // now register some objects
// now register any needed IObjectPostProcessors
MyObjectPostProcessor pp = new MyObjectPostProcessor();
factory.AddObjectPostProcessor(pp);
// now start using the factory
...
This explicit registration step is not convenient, and this is one of the reasons why the various
IApplicationContext implementations are preferred above plain IObjectFactory implementations in the vast
majority of Spring-backed applications, especially when using IObjectPostProcessors.
Note
IObjectPostProcessors and AOP auto-proxying
Classes that implement the IObjectPostProcessor interface are special, and so they are treated
differently by the container. All IObjectPostProcessors and their directly referenced object will
be instantiated on startup, as part of the special startup phase of the IApplicationContext, then
all those IObjectPostProcessors will be registered in a sorted fashion - and applied to all
further objects. Since AOP auto-proxying is implemented as a IObjectPostProcessor itself, no
IObjectPostProcessors or directly referenced objects are eligible for auto-proxying (and thus will
not have aspects 'woven' into them). For any such object, you should see an info log message: “Object
'foo' is not eligible for getting processed by all IObjectPostProcessors (for example: not eligible
for auto-proxying)”.
5.9.1.1. Example: Hello World, IObjectPostProcessor-style
This first example is hardly compelling, but serves to illustrate basic usage. All we are going to do is code a
custom IObjectPostProcessor implementation that simply invokes the ToString() method of each object as it is
created by the container and prints the resulting string to the system console. Yes, it is not hugely useful, but
serves to get the basic concepts across before we move into the second example which is actually useful. The
basis of the example is the MovieFinder quickstart that is included with the Spring.NET distribution.
Find below the custom IObjectPostProcessor implementation class definition
using System;
using Spring.Objects.Factory.Config;
namespace Spring.IocQuickStart.MovieFinder
{
public class TracingObjectPostProcessor : IObjectPostProcessor
{
public object PostProcessBeforeInitialization(object instance, string name)
{
return instance;
}
public object PostProcessAfterInitialization(object instance, string name)
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{
Console.WriteLine("Object '" + name + "' created : " + instance.ToString());
return instance;
}
}
}
And the following configuration
<?xml version="1.0" encoding="utf-8" ?>
<objects xmlns="http://www.springframework.net" >
<description>An example that demonstrates simple IoC features.</description>
<object id="MyMovieLister"
type="Spring.IocQuickStart.MovieFinder.MovieLister, Spring.IocQuickStart.MovieFinder">
<property name="movieFinder" ref="MyMovieFinder"/>
</object>
<object id="MyMovieFinder"
type="Spring.IocQuickStart.MovieFinder.SimpleMovieFinder, Spring.IocQuickStart.MovieFinder"/>
<!-- when the above objects are instantiated, this custom IObjectPostProcessor implementation
will output the fact to the system console -->
<object type="Spring.IocQuickStart.MovieFinder.TracingObjectPostProcessor, Spring.IocQuickStart.MovieFinder"/>
</objects>
Notice how the TracingObjectPostProcessor is simply defined; it doesn't even have a name, and because it is a
object it can be dependency injected just like any other object.
Find below a small driver script to exercise the above code and configuration;
IApplicationContext ctx =
new XmlApplicationContext(
"assembly://Spring.IocQuickStart.MovieFinder/Spring.IocQuickStart.MovieFinder/AppContext.xml");
MovieLister lister = (MovieLister) ctx.GetObject("MyMovieLister");
Movie[] movies = lister.MoviesDirectedBy("Roberto Benigni");
LOG.Debug("Searching for movie...");
foreach (Movie movie in movies)
{
LOG.Debug(string.Format("Movie Title = '{0}', Director = '{1}'.", movie.Title, movie.Director));
}
LOG.Debug("MovieApp Done.");
The output of executing the above program will be:
INFO
- Object 'Spring.IocQuickStart.MovieFinder.TracingObjectPostProcessor' is not eligible for being processed
(for example: not eligible for auto-proxying).
Object 'MyMovieFinder' created : Spring.IocQuickStart.MovieFinder.SimpleMovieFinder
Object 'MyMovieLister' created : Spring.IocQuickStart.MovieFinder.MovieLister
DEBUG - Searching for movie...
DEBUG - Movie Title = 'La vita e bella', Director = 'Roberto Benigni'.
DEBUG - MovieApp Done.
5.9.1.2. Example: the RequiredAttributeObjectPostProcessor
Using callback interfaces or annotations in conjunction with a custom IObjectPostProcessor implementation
is a common means of extending the Spring IoC container. The [Required] attribute in the
Spring.Objects.Factory.Attributes namespace can be used to mark a property as being 'required-to-be-set'
(i.e. an setter property with this attribute applied must be configured to be dependency injected with a value), else
an ObjectInitializationException will be thrown by the container at runtime.
The best way to illustrate the usage of this attribute is with an example.
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public class MovieLister
{
// the MovieLister has a dependency on the MovieFinder
private IMovieFinder _movieFinder;
// a setter property so that the Spring container can 'inject' a MovieFinder
[Required]
public IMovieFinder MovieFinder
{
set { _movieFinder = value; }
}
// business logic that actually 'uses' the injected MovieFinder is omitted...
}
Hopefully the above class definition reads easy on the eye. Any and all IObjectDefinitions for the MovieLister
class must be provided with a value.
Let's look at an example of some XML configuraiton that will not pass validation.
<object id="MyMovieLister"
type="Spring.IocQuickStart.MovieFinder.MovieLister, Spring.IocQuickStart.MovieFinder">
<!-- whoops, no MovieFinder is set (and this property is [Required]) -->
</object>
At runtime the following message will be generated by the Spring container
Error creating context 'spring.root': Property 'MovieFinder' required for object 'MyMovieLister'
There is one last little piece of Spring configuration that is required to actually 'switch on' this behavior. Simply
annotating the 'setter' properties of your classes is not enough to get this behavior. You need to enable a component
that is aware of the [Required] attribute and that can process it appropriately.
This component is the RequiredAttributeObjectPostProcessor class. This is a special IObjectPostProcessor
implementation that is [Required]-aware and actually provides the 'blow up if this required property has not
been set' logic. It is very easy to configure; simply drop the following object definition into your Spring XML
configuration.
<object type="Spring.Objects.Factory.Attributes.RequiredAttributeObjectPostProcessor, Spring.Core"/>
Finally, one can configure an instance of the RequiredAttributeObjectPostProcessor class to look for another
Attribute type. This is great if you already have your own [Required]-style attribute. Simply plug it into
the definition of a RequiredAttributeObjectPostProcessor and you are good to go. By way of an example,
let's suppose you (or your organization / team) have defined an attribute called [Mandatory]. You can make a
RequiredAttributeObjectPostProcessor instance [Mandatory]-aware like so:
<object type="Spring.Objects.Factory.Attributes.RequiredAttributeObjectPostProcessor, Spring.Core">
<property name="RequiredAttributeType" value="MyApp.Attributes.MandatoryAttribute, MyApp"/>
</object>
5.9.2. Customizing configuration metadata with
ObjectFactoryPostProcessors
The
next
extension
point
that
we
will
look
at
is
the
Spring.Objects.Factory.Config.IObjectFactoryPostProcessor. The semantics of this interface are similar
to the IObjectPostProcessor, with one major difference. IObjectFactoryPostProcessors operate on; that is
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to say, the Spring IoC container will allow IObjectFactoryPostProcessors to read the configuration metadata
and potentially change it before the container has actually instantiated any other objects. By implementing this
interface, you will receive a callback after the all the object definitions have been loaded into the IoC container
but before they have been instantiated. The signature of the interface is shown below
public interface IObjectFactoryPostProcessor
{
void PostProcessObjectFactory (IConfigurableListableObjectFactory factory);
}
You can configure multiple IObjectFactoryPostProcessors if you wish. You can control the order in
which these IObjectFactoryPostProcessors execute by setting the 'Order' property (you can only set this
property if the IObjectFactoryPostProcessors implements the IOrdered interface; if you write your own
IObjectFactoryPostProcessors you should consider implementing the IOrdered interface too); consult the
SDK docs for the IObjectFactoryPostProcessors and IOrdered interfaces for more details.
Note
If you want to change the actual object instances (the objects that are created from the configuration
metadata), then you rather need to use a IObjectObjectPostProcessor (described above in the
section entitled Customizing objects with IObjectPostProcessors.
Also, IObjectFactoryPostProcessors are scoped per-container. This is only relevant if you are
using container hierarchies. If you define a IObjectFactoryPostProcessors in one container, it will
only do its stuff on the object definitions in that container. Object definitions in another container
will not be post-processed by IObjectFactoryPostProcessors in another container, even if both
containers are part of the same hierarchy.
An object factory post-processor is executed manually (in the case of a IObjectFactory) or automatically
(in the case of an IApplicationContext) to apply changes of some sort to the configuration metadata
that defines a container. Spring.NET includes a number of pre-existing object factory post-processors,
such as PropertyResourceConfigurer and PropertyPlaceHolderConfigurer, both described below and
ObjectNameAutoProxyCreator, which is very useful for wrapping other objects transactionally or with any other
kind of proxy, as described later in this manual.
In an IObjectFactory, the process of applying an IObjectFactoryPostProcessor is manual, and will be similar
to this:
XmlObjectFactory factory = new XmlObjectFactory(new FileSystemResource("objects.xml"));
// create placeholderconfigurer to bring in some property
// values from a Properties file
PropertyPlaceholderConfigurer cfg = new PropertyPlaceholderConfigurer();
cfg.setLocation(new FileSystemResource("ado.properties"));
// now actually do the replacement
cfg.PostProcessObjectFactory(factory);
This explicit registration step is not convenient, and this is one of the reasons why the various
IApplicationContext implementations are preferred above plain IObjectFactory implementations in the vast
majority of Spring-backed applications, especially when using IObjectFactoryPostProcessors.
An IApplicationContext will detect any objects which are deployed into it that implement the
ObjectFactoryPostProcessor interface, and automatically use them as object factory post-processors, at the
appropriate time. Nothing else needs to be done other than deploying these post-processor in a similar fashion
to any other object.
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Note
Just as in the case of IObjectPostProcessors, you typically don't want to have
IObjectFactoryPostProcessors marked as being lazily-initialized. If they are marked as such, then
the Spring container will never instantiate them, and thus they won't get a chance to apply their custom
logic. If you are using the 'default-lazy-init' attribute on the declaration of your <objects/> element, be
sure to mark your various IObjectFactoryPostProcessor object definitions with 'lazy-init="false"'.
5.9.2.1. Example: The PropertyPlaceholderConfigurer
The PropertyPlaceholderConfigurer is an excellent solution when you want to externalize a few properties
from a file containing object definitions. This is useful to allow the person deploying an application to customize
environment specific properties (for example database configuration strings, usernames, and passwords), without
the complexity or risk of modifying the main XML definition file or files for the container.
Variable substitution is performed on simple property values, lists, dictionaries, sets, constructor values, object
type name, and object names in runtime object references. Furthermore, placeholder values can also crossreference other placeholders.
Note that IApplicationContexts are able to automatically recognize and apply objects deployed in them
that implement the IObjectFactoryPostProcessor interface. This means that as described here, applying
a PropertyPlaceholderConfigurer is much more convenient when using an IApplicationContext. For
this reason, it is recommended that users wishing to use this or other object factory postprocessors use an
IApplicationContext instead of an IObjectFactory.
In the example below a data access object needs to be configured with a database connection and also a value for
the maximum number of results to return in a query. Instead of hard coding the values into the main Spring.NET
configuration file we use place holders, in the NAnt style of ${variableName}, and obtain their values from
NameValueSections in the standard .NET application configuration file. The Spring.NET configuration file looks
like:
<configuration>
<configSections>
<sectionGroup name="spring">
<section name="context" type="Spring.Context.Support.ContextHandler, Spring.Core"/>
</sectionGroup>
<section name="DaoConfiguration" type="System.Configuration.NameValueSectionHandler"/>
<section name="DatabaseConfiguration" type="System.Configuration.NameValueSectionHandler"/>
</configSections>
<DaoConfiguration>
<add key="maxResults" value="1000"/>
</DaoConfiguration>
<DatabaseConfiguration>
<add key="connection.string" value="dsn=MyDSN;uid=sa;pwd=myPassword;"/>
</DatabaseConfiguration>
<spring>
<context>
<resource uri="assembly://DaoApp/DaoApp/objects.xml"/>
</context>
</spring>
</configuration>
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Notice the presence of two NameValueSections in the configuration file. These name value pairs will be referred
to in the Spring.NET configuration file. In this example we are using an embedded assembly resource for the
location of the Spring.NET configuration file so as to reduce the chance of accidental tampering in deployment.
This Spring.NET configuration file is shown below.
<objects xmlns="http://www.springframework.net"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.net
http://www.springframework.net/xsd/spring-objects.xsd" >
<object name="productDao" type="DaoApp.SimpleProductDao, DaoApp ">
<property name="maxResults" value="${maxResults}"/>
<property name="dbConnection" ref="myConnection"/>
</object>
<object name="myConnection" type="System.Data.Odbc.OdbcConnection, System.Data">
<property name="connectionstring" value="${connection.string}"/>
</object>
<object name="appConfigPropertyHolder"
type="Spring.Objects.Factory.Config.PropertyPlaceholderConfigurer, Spring.Core">
<property name="configSections">
<value>DaoConfiguration,DatabaseConfiguration</value>
</property>
</object>
</objects>
The values of ${maxResults} and ${connection.string} match the key names used
in the two NameValueSectionHandlers DaoConfiguration and DatabaseConfiguration. The
PropertyPlaceholderConfigurer refers to these two sections via a comma delimited list of section names
in the configSections property. If you are using section groups, prefix the section group name, for example
myConfigSection/DaoConfiguraiton.
The PropertyPlaceholderConfigurer class also supports retrieving name value pairs from other
IResource locations. These can be specified using the Location and Locations properties of the
PropertyPlaceHolderConfigurer class.
If there are properties with the same name in different resource locations the default behavior is that the last
property processed overrides the previous values. This is behavior is controlled by the LastLocationOverrides
property. True enables overriding while false will append the values as one would normally expect using
NameValueCollection.Add.
Note
In an ASP.NET environment you must specify the full, four-part name of the assembly when using
a NameValueFileSectionHandler
<section name="hibernateConfiguration"
type="System.Configuration.NameValueFileSectionHandler, System,
Version=1.0.3300.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"/>
5.9.2.1.1. Type, Ref, and Expression substitution
The PropertyPlaceholderConfigurer can be used to substitute type names, which is sometimes useful when you
have to pick a particular implementation class at runtime. For example:
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<object id="MyMovieFinder" type="${custom.moviefinder.type}"/>
If the class is unable to be resolved at runtime to a valid type, resolution of the object will fail once it is about to be
created (which is during the PreInstantiateSingletons() phase of an ApplicationContext for a non-lazy-init object.)
Similarly you can replace 'ref' and 'expression' metadata, as shown below
<object id="TestObject" type="Simple.TestObject, MyAssembly">
<property name="age" expression="${ageExpression}"/>
<property name="spouse" ref="${spouse-ref}"/>
</object>
5.9.2.1.2. Replacement with Environment Variables
You may also use the value environment variables to replace property placeholders. The use of environment
variables is controlled via the property EnvironmentVariableMode. This property is an enumeration of the
type EnvironmentVariablesMode and has three values, Never, Fallback, and Override. Fallback is the
default value and will resolve a property placeholder if it was not already done so via a value from a
resource location. Override will apply environment variables before applying values defined from a resource
location. Never will, quite appropriately, disable environment variable substitution. An example of how the
PropertyPlaceholderConfigurer XML is modified to enable override usage is shown below
<object name="appConfigPropertyHolder"
type="Spring.Objects.Factory.Config.PropertyPlaceholderConfigurer, Spring.Core">
<property name="configSections" value="DaoConfiguration,DatabaseConfiguration"/>
<property name="EnvironmentVariableMode" value="Override"/>
</object>
</objects>
5.9.2.2. Example: The PropertyOverrideConfigurer
The
PropertyOverrideConfigurer,
another object factory post-processor, is similar to the
PropertyPlaceholderConfigurer, but in contrast to the latter, the original definitions can have default values
or no values at all for object properties. If an overriding configuration file does not have an entry for a certain
object property, the default context definition is used.
Note that the object factory definition is not aware of being overridden, so it is not immediately obvious when
looking at the XML definition file that the override configurer is being used. In case that there are multiple
PropertyOverrideConfigurer instances that define different values for the same object property, the last one
will win (due to the overriding mechanism).
The example usage is similar to when using PropertyPlaceHolderConfigurer except that the key name refers
to the name given to the object in the Spring.NET configuration file and is suffixed via 'dot' notation with the
name of the property For example, if the application configuration file is
<configuration>
<configSections>
<sectionGroup name="spring">
<section name="context" type="Spring.Context.Support.ContextHandler, Spring.Core"/>
</sectionGroup>
<section name="DaoConfigurationOverride" type="System.Configuration.NameValueSectionHandler"/>
</configSections>
<DaoConfigurationOverride>
<add key="productDao.maxResults" value="1000"/>
</DaoConfigurationOverride>
<spring>
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<context>
<resource uri="assembly://DaoApp/DaoApp/objects.xml"/>
</context>
</spring>
</configuration>
Then the value of 1000 will be used to overlay the value of 2000 set in the Spring.NET configuration file shown
below
<objects xmlns="http://www.springframework.net"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.net http://www.springframework.net/xsd/spring-objects.xsd
<object name="productDao" type="PropPlayApp.SimpleProductDao, PropPlayApp " >
<property name="maxResults" value="2000"/>
<property name="dbConnection" ref="myConnection"/>
<property name="log" ref="daoLog"/>
</object>
<object name="daoLog" type="Spring.Objects.Factory.Config.LogFactoryObject, Spring.Core">
<property name="logName" value="DAOLogger"/>
</object>
<object name="myConnection" type="System.Data.Odbc.OdbcConnection, System.Data">
<property name="connectionstring">
<value>dsn=MyDSN;uid=sa;pwd=myPassword;</value>
</property>
</object>
<object name="appConfigPropertyOverride" type="Spring.Objects.Factory.Config.PropertyOverrideConfigurer, Spr
<property name="configSections">
<value>DaoConfigurationOverride</value>
</property>
</object>
</objects>
5.9.2.3. IVariableSource
The IVariableSource is the base interface for providing the ability to get the value of property placeholders (namevalue) pairs from a variety of sources. Out of the box, Spring.NET supports a number of variable sources that
allow users to obtain variable values from .NET config files, java-style property files, environment variables,
command line arguments and the registry and the new connection strings configuration section in .NET 2.0. The
list of implementing classes is listed below. Please refer to the SDK documentation for more information.
• ConfigSectionVariableSource
• PropertyFileVariableSource
• EnvironmentVariableSource
• CommandLineArgsVariableSource
• RegistryVariableSource
• SpecialFolderVariableSource
• ConnectionStringsVariableSource
You use this by defining an instance of Spring.Objects.Factory.Config.VariablePlaceholderConfigurer in
your configuration and set the property VariableSource to a single IVariableSource instance or the list property
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to a list of IVariableSource instances. In the case of the same property defined in multiple
IVariableSource implementations, the first one in the list that contains the property value will be used.
VariableSources
<object type="Spring.Objects.Factory.Config.VariablePlaceholderConfigurer, Spring.Core">
<property name="VariableSources">
<list>
<object type="Spring.Objects.Factory.Config.ConfigSectionVariableSource, Spring.Core">
<property name="SectionNames" value="CryptedConfiguration" />
</object>
</list>
</property>
</object>
The IVariableSource interface is shown below
public interface IVariableSource
{
string ResolveVariable(string name);
}
This is a simple contract to implement if you should decide to create your own custom implemention. Look at
the source code of the current implementations for some inspiration if you go that route. To register your own
custom implemenation, simply configure VariablePlaceholderConfigurer to refer to your class.
5.9.3. Customizing instantiation logic using IFactoryObjects
The Spring.Objects.Factory.IFactoryObject interface is to be implemented by objects that are themselves
factories.
The IFactoryObject interface is a point of pluggability into the Spring IoC containers instantiation logic. If you
have some complex initialization code that is better expressed in C# as opposed to a (potentially) verbose amount
of XML, you can create your own IFactoryObject, write the complex initialization inside that class, and then
plug your custom IFactoryObject into the container.
The IFactoryObject interface provides one method and two (read-only) properties:
• object GetObject(): has to return an instance of the object this factory creates. The instance can possibly be
shared (depending on whether this factory provides singletons or prototypes).
• bool IsSingleton: has to return true if this IFactoryObject returns singletons, false otherwise.
• Type ObjectType: has to return either the object type returned by the GetObject() method or null if the type
isn't known in advance.
IFactoryObject
The IFactoryObject concept and interface is used in a number of places within the Spring Framework. Some
examples of its use is described in Section 5.3.9, “Setting a reference using the members of other objects and
classes.” for the PropertyRetrievingFactoryObject and FieldRetrievingFactoryObject. An additional use
of creating an custom IFactoryObject implementation is to retrieve an object from an embedded resource file and
use it to set another objects dependency. An example of this is provided here [http://jira.springframework.org/
browse/SPRNET-133#action_19743].
Finally, there is sometimes a need to ask a container for an actual IFactoryObject instance itself, not the object
it produces. This may be achieved by prepending the object id with '&' (sans quotes) when calling the GetObject
method of the IObjectFactory (including IApplicationContext). So for a given IFactoryObject with an id of
'myObject', invoking GetObject("myObject") on the container will return the product of the IFactoryObject,
but invoking GetObject("&myObject") will return the IFactoryObject instance itself.
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5.9.3.1. IConfigurableFactoryObject
The Spring.Objects.Factory.IConfigurableFactoryObject interface inherits from IFactoryObject interface
and adds the following property.
• IObjectDefinition ProductTemplate : Gets the template object definition that should be used to configure
the instance of the object managed by this factory.
IConfigurableFactoryObject
implementions you already have examples of in Section 27.3, “Client-side” are
WebServiceProxyFactory.
5.10. The IApplicationContext
While the Spring.Objects namespace provides basic functionality for managing and manipulating objects,
often in a programmatic way, the Spring.Context namespace introduces the IApplicationContext interface,
which enhances the functionality provided by the IObjectFactory interface in a more framework-oriented
style. Many users will use ApplicationContext in a completely declarative fashion, not even having to create
it manually, but instead relying on support classes such as the .NET configuration section handlers such as
ContextHandler and WebContextHandler together to declaratively define the ApplicationContext and retrieve it
though a ContextRegistry. (Of course it is still possible to create an IApplicationContext Programatically).
The basis for the context module is the IApplicationContext interface, located in the Spring.Context
namespace. Deriving from the IObjectFactory interface, it provides all the functionality of the IObjectFactory.
To be able to work in a more framework-oriented fashion, using layering and hierarchical contexts, the
Spring.Context namespace also provides the following functionality
• Loading of multiple (hierarchical) contexts, allowing some of them to be focused and used on one particular
layer, for example the web layer of an application.
• Access to localized resources at the application level by implementing IMessageSource.
• Uniform access to resources that can be read in as an InputStream, such as URLs and files by implementing
IResourceLoader
• Loosely Coupled Event Propagation. Publishers and subscribers of events do not have to be directly aware of
each other as they register their interest indirectly through the application context.
5.10.1. IObjectFactory or IApplicationContext?
Short version: use an IApplicationContext unless you have a really good reason for not doing so. For those of
you that are looking for slightly more depth as to the 'but why' of the above recommendation, keep reading.
As the IApplicationContext includes all the functionality the object factory via its inheritance of the
IObjectFactory interface, it is generally recommended to be used over the IObjectFactory except for a few
limited situations where memory consumption might be critical. This may become more important if the .NET
Compact Framework is supported. The history of IObjectFactory comes from the Spring Java framework, where
the use of Spring in Applets was a concern to reduce memory consumption. However, for most 'typical' enterprise
applications and systems, the IApplicationContext is what you will want to use. Spring generally makes heavy
use of the IObjectPostProcessor extension point (to effect proxying and suchlike), and if you are using just a
plain IObjectFactory then a fair amount of support such as transactions and AOP will not take effect (at least
not without some extra steps on your part), which could be confusing because nothing will actually be wrong
with the configuration.
Find below a feature matrix that lists what features are provided by the IObjectFactory and
IApplicationContext interfaces (and attendant implementations). The following sections describe functionality
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that IApplicationContext adds to the basic IObjectFactory capabilities in a lot more depth than the said feature
matrix.)
Table 5.7. Feature Matrix
Feature
IObjectFactory
IApplicationContext
Object instantiation/wiring
Yes
Yes
Automatic IObjectPostProcessor
registration
No
Yes
Automatic
No
Yes
No
Yes
No
Yes
Singleton service locator style
access
No
Yes
Declarative registration of custom
resource protocol handler, XML
Parsers for object definitions, and
type aliases
No
Yes
IObjectFactoryPostProcessor
registration
Convenient IMessageSource
access
ApplicationEvent
publication
5.11. Configuration of IApplicationContext
Well known locations in the .NET application configuration file are used to register resource handlers, custom
parsers, type alias, and custom type converts in addition to the context and objects sections mentioned previously.
A sample .NET application configuration file showing all these features is shown below. Each section requires
the use of a custom configuration section handler. Note that the types shown for resource handlers and parsers
are fictional.
<configuration>
<configSections>
<sectionGroup name="spring">
<section name="context" type="Spring.Context.Support.ContextHandler, Spring.Core"/>
<section name="objects" type="Spring.Context.Support.DefaultSectionHandler, Spring.Core" />
<section
<section
<section
<section
name="parsers" type="Spring.Context.Support.NamespaceParsersSectionHandler, Spring.Core"/>
name="resources" type="Spring.Context.Support.ResourceHandlersSectionHandler, Spring.Core"/>
name="typeAliases" type="Spring.Context.Support.TypeAliasesSectionHandler, Spring.Core"/>
name="typeConverters" type="Spring.Context.Support.TypeConvertersSectionHandler, Spring.Core"/>
</sectionGroup>
</configSections>
<spring>
<parsers>
<parser type="Spring.Aop.Config.AopNamespaceParser, Spring.Aop" />
<parser type="Spring.Data.Config.DatabaseNamespaceParser, Spring.Data" />
</parsers>
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<resources>
<handler protocol="db" type="MyCompany.MyApp.Resources.MyDbResource"/>
</resources>
<context caseSensitive="false">
<resource uri="config://spring/objects"/>
<resource uri="db://user:[email protected]/MyDefinitionsTable"/>
</context>
<typeAliases>
<alias name="WebServiceExporter" type="Spring.Web.Services.WebServiceExporter, Spring.Web"/>
<alias name="DefaultPointcutAdvisor" type="Spring.Aop.Support.DefaultPointcutAdvisor, Spring.Aop"/>
<alias name="AttributePointcut" type="Spring.Aop.Support.AttributeMatchMethodPointcut, Spring.Aop"/>
<alias name="CacheAttribute" type="Spring.Attributes.CacheAttribute, Spring.Core"/>
<alias name="MyType" type="MyCompany.MyProject.MyNamespace.MyType, MyAssembly"/>
</typeAliases>
<typeConverters>
<converter for="Spring.Expressions.IExpression, Spring.Core" type="Spring.Objects.TypeConverters.Expressio
<converter for="MyTypeAlias" type="MyCompany.MyProject.Converters.MyTypeConverter, MyAssembly"/>
</typeConverters>
<objects xmlns="http://www.springframework.net">
...
</objects>
</spring>
</configuration>
The new sections are described below. The attribute caseSensitive allows the for both IObjectFactory and
IApplicationContext implementations to not pay attention to the case of the object names. This is important in
web applications so that ASP.NET pages can be resolved in a case independent manner. The default value is true.
5.11.1. Registering custom parsers
Instead of using the default XML schema that is generic in nature to define an object's properties and dependencies,
you can create your own XML schema specific to an application domain. This has the benefit of being easier to
type and getting XML intellisense for the schema being used. The downside is that you need to write code that will
transform this XML into Spring object definitions. One would typically implement a custom parser by deriving
from the class ObjectsNamespaceParser and overriding the methods int ParseRootElement(XmlElement
root, XmlResourceReader reader) and int ParseElement(XmlElement element, XmlResourceReader
reader). Registering custom parsers outside of App.config will be addressed in a future release.
To
register
a
custom
parser
register
a
section
handler
of
the
type
Spring.Context.Support.NamespaceParsersSectionHandler in the configSecitons section of App.config. The
parser configuration section contains one or more <parser> elements each with a type attribute. Below is an
example that registers all the namespaces provided in Spring.
Note
As of Spring.NET 1.2.0 it is no longer necessary to explicitly configure the namespace parsers
that come with Spring via a custom section in App.config. You will still need to register custom
namespace parsers if you are writing your own.
<configuration>
<configSections>
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<sectionGroup name="spring">
<!-- other configuration section handler defined here -->
<section name="parsers" type="Spring.Context.Support.NamespaceParsersSectionHandler, Spring.Core"/>
</sectionGroup>
</configSections>
<spring>
<parsers>
<parser type="Spring.Aop.Config.AopNamespaceParser, Spring.Aop" />
<parser type="Spring.Data.Config.DatabaseNamespaceParser, Spring.Data" />
<parser type="Spring.Transaction.Config.TxNamespaceParser, Spring.Data" />
<parser type="Spring.Validation.Config.ValidationNamespaceParser, Spring.Core" />
<parser type="Spring.Remoting.Config.RemotingNamespaceParser, Spring.Services" />
</parsers>
</spring>
</configuration>
You can also register custom parser programmatically using the NamespaceParserRegistry. Here is an example
taken from the code used in the Transactions Quickstart application.
NamespaceParserRegistry.RegisterParser(typeof(DatabaseNamespaceParser));
NamespaceParserRegistry.RegisterParser(typeof(TxNamespaceParser));
NamespaceParserRegistry.RegisterParser(typeof(AopNamespaceParser));
IApplicationContext context =
new XmlApplicationContext("assembly://Spring.TxQuickStart.Tests/Spring.TxQuickStart/system-test-local-conf
5.11.2. Registering custom resource handlers
Creating a custom resource handler means implementing the IResource interface. The base class
AbstractResource is a useful starting point. Look at the Spring source for classes such as FileSystemResource
or AssemblyResource for implementation tips. You can register your custom resource handler either within
App.config, as shown in the program listing at the start of this section using a .ResourceHandlersSectionHandler
or define an object of the type Spring.Objects.Factory.Config.ResourceHandlerConfigurer as you would
any other Spring managed object. An example of the latter is shown below:
<object id="myResourceHandlers" type="Spring.Objects.Factory.Config.ResourceHandlersSectionHandler, Spring.Core">
<property name="ResourceHandlers">
<dictionary>
<entry key="db" value="MyCompany.MyApp.Resources.MyDbResource, MyAssembly"/>
</dictionary>
</property>
</object>
5.11.3. Registering Type Aliases
Type aliases allow you to simplify Spring configuration file by replacing fully qualified type name with an alias
for frequently used types. Aliases can be registered both within a config file and programatically and can be used
anywhere in the context config file where a fully qualified type name is expected. Type aliases can also be defined
for generic types.
One way to configure a type alias is to define them in a custom config section in the Web/App.config file for your
application, as well as the custom configuration section handler. See the previous XML configuration listing for
an example that makes an alias for the WebServiceExporter type. Once you have aliases defined, you can simply
use them anywhere where you would normally specify a fully qualified type name:
<object id="MyWebService" type="WebServiceExporter">
...
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</object>
<object id="cacheAspect" type="DefaultPointcutAdvisor">
<property name="Pointcut">
<object type="AttributePointcut">
<property name="Attribute" value="CacheAttribute"/>
</object>
</property>
<property name="Advice" ref="aspNetCacheAdvice"/>
</object>
To
register
a
type
alias
register
a
section
handler
of
the
type
Spring.Context.Support.TypeAliasesSectionHandler in the configSecitons section of App.config. The type
alias configuration section contains one or more <alias> elements each with a name and a type attribute. Below
is an example that registers the alias for WebServiceExporter
<configuration>
<configSections>
<sectionGroup name="spring">
<!-- other configuration section handler defined here -->
<section name="parsers" type="Spring.Context.Support.TypeAliasesSectionHandler, Spring.Core"/>
</sectionGroup>
</configSections>
<spring>
<typeAliases>
<alias name="WebServiceExporter" type="Spring.Web.Services.WebServiceExporter, Spring.Web"/>
</typeAliases>
</spring>
</configuration>
For an example showing type aliases for generic types see Section 5.2.5, “Object creation of generic types”.
Another way is to define an object of the type Spring.Objects.Factory.Config.TypeAliasConfigurer within
the regular <objects> section of any standard Spring configuration file. This approach allows for more modularity
in defining type aliases, for example if you can't access App.config/Web.config. An example of registration using
a TypeAliasConfigurer is shown below
<object id="myTypeAlias" type="Spring.Objects.Factory.Config.TypeAliasConfigurer, Spring.Core">
<property name="TypeAliases">
<dictionary>
<entry key="WebServiceExporter" value="Spring.Web.Services.WebServiceExporter, Spring.Web"/>
<entry key="DefaultPointcutAdvisor" value="Spring.Aop.Support.DefaultPointcutAdvisor, Spring.Aop"/
<entry key="MyType" value="MyCompany.MyProject.MyNamespace.MyType, MyAssembly"/>
</dictionary>
</property>
</object>
5.11.4. Registering Type Converters
The standard .NET mechanism for specifying a type converter is to add a TypeConverter attribute to a type
definition to specify the type of the Converter. This is the preferred way of defining type converters if you control
the source code for the type that you want to define a converter for. However, this configuration section allows
you to specify converters for the types that you don't control, and it also allows you to override some of the
standard type converters, such as the ones that are defined for some of the types in the .NET Base Class Library.
You
can
specify
the
type
converters
in
App.config
by
using
Spring.Context.Support.TypeConvertersSectionHandler as shown before or define an object of the
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type Spring.Objects.Factory.Config.CustomConverterConfigurer. An example of registration using a
CustomConverterConfigurer is shown below
<object id="myTypeConverters" type="Spring.Objects.Factory.Config.CustomConverterConfigurer, Spring.Core">
<property name="CustomConverters">
<dictionary>
<entry key="System.Date" value="MyCompany.MyProject.MyNamespace.MyCustomDateConverter, MyAssembly"
</dictionary>
</property>
</object>
5.12. Added functionality of the IApplicationContext
As already stated in the previous section, the IApplicationContext has a couple of features that distinguish it
from the IObjectFactory. Let us review them one-by-one.
5.12.1. Context Hierarchies
You can structure the configuration information of application context into hierarchies that naturally reflect the
internal layering of your application. As an example, abstract object definitions may appear in a parent application
context configuration file, possibly as an embedded assembly resource so as not to invite accidental changes.
<spring>
<context>
<resource uri="assembly://MyAssembly/MyProject/root-objects.xml"/>
<context name="mySubContext">
<resource uri="file://objects.xml"/>
</context>
</context>
</spring>
The nesting of context elements reflects the parent-child hierarchy you are creating. The nesting can be to any
level though it is unlikely one would need a deep application hierarchy. The xml file must contain the <objects>
as the root name. Another example of a hierarchy, but using sections in the application configuration file is shown
below.
<configSections>
<sectionGroup name="spring">
<section name="context" type="Spring.Context.Support.ContextHandler, Spring.Core"/>
<section name="objects" type="Spring.Context.Support.DefaultSectionHandler, Spring.Core" />
<sectionGroup name="child">
<section name="objects" type="Spring.Context.Support.DefaultSectionHandler, Spring.Core" />
</sectionGroup>
</sectionGroup>
</configSections>
<spring>
<context name="ParentContext">
<resource uri="config://spring/objects"/>
<context name="ChildContext">
<resource uri="config://spring/child/objects"/>
</context>
</context>
<objects xmlns="http://www.springframework.net">
...
</objects>
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<child>
<objects xmlns="http://www.springframework.net">
...
</objects>
</child>
</spring>
As
a
reminder,
the
the context tag is optional and defaults to
Spring.Context.Support.XmlApplicationContext. The name of the context can be used in conjunction with
the service locator class, ContextRegistry, discussed in Section 5.15, “Service Locator access”
type
attribute
of
5.12.2. Using IMessageSource
The IApplicationContext interface extends an interface called IMessageSource and provides localization (i18n
or internationalization) services for text messages and other resource data types such as images. This functionality
makes it easier to use .NET's localization features at an application level and also offers some performance
enhancements due to caching of retrieved resources. Together with the NestingMessageSource, capable of
hierarchical message resolving, these are the basic interfaces Spring.NET provides for localization. Let's quickly
review the methods defined there:
• string
GetMessage(string
CurrentUICulture.
• string
GetMessage(string
IMessageSource
name):
name,
retrieves a message from the IMessageSource and using
CultureInfo
cultureInfo):
retrieves a message from the
using a specified culture.
• string GetMessage(string name, params object[] args): retrieves a message from the IMessageSource
using a variable list of arguments as replacement values in the message. The CurrentUICulture is used to resolve
the message.
• string GetMessage(string name, CultureInfo cultureInfo, params object[] args): retrieves a
message from the IMessageSource using a variable list of arguments as replacement values in the message.
The specified culture is used to resolve the message.
• string GetMessage(string name, string defaultMessage, CultureInfo culture, params object[]
arguments): retrieves a message from the IMessageSource using a variable list of arguments as replacement
values in the message. The specified culture is used to resolve the message. If no message can be resolved,
the default message is used.
• string GetMessage(IMessageSourceResolvable resolvable, CultureInfo culture) : all properties used
in the methods above are also wrapped in a class - the MessageSourceResolvable, which you can use in this
method.
• object GetResourceObject(string name):Get a localized resource object, i.e. Icon, Image, etc. given the
resource name. The CurrentUICulture is used to resolve the resource object.
• object GetResourceObject(string name, CultureInfo cultureInfo):Get a localized resource object, i.e.
Icon, Image, etc. given the resource name. The specified culture is used to resolve the resource object.
• void ApplyResources(object value, string objectName, CultureInfo cultureInfo): Uses a
ComponentResourceManager to apply resources to all object properties that have a matching key name.
Resource key names are of the form objectName.propertyName
When an IApplicationContext gets loaded, it automatically searches for an IMessageSource object defined in
the context. The object has to have the name messageSource. If such an object is found, all calls to the methods
described above will be delegated to the message source that was found. If no message source was found, the
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checks to see if it has a parent containing a similar object, with a similar name. If so, it
uses that object as the IMessageSource. If it can't find any source for messages, an empty StaticMessageSource
will be instantiated in order to be able to accept calls to the methods defined above.
IApplicationContext
Fallback behavior
The fallback rules for localized resources seem to have a bug that is fixed by applying Service Pack 1
for .NET 1.1. This affects the use of IMessageSource.GetMessage methods that specify CultureInfo.
The core of the issue in the .NET BCL is the method ResourceManager.GetObject that accepts
CultureInfo.
Spring.NET provides two IMessageSource implementations. These are ResourceSetMessageSource and
StaticMessageSource. Both implement IHierarchicalMessageSource to resolve messages hierarchically. The
StaticMessageSource is hardly ever used but provides programmatic ways to add messages to the source. The
ResourceSetMessageSource is more interesting and an example is provided for in the distribution and discussed
more extensively in the Chapter 33, IoC Quickstarts section. The ResourceSetMessageSource is configured by
providing a list of ResourceManagers. When a message code is to be resolved, the list of ResourceManagers
is searched to resolve the code. For each ResourceManager a ResourceSet is retrieved and asked to resolve
the code. Note that this search does not replace the standard hub-and-spoke search for localized resources. The
ResourceManagers list specifies the multiple 'hubs' where the standard search starts.
<object name="messageSource" type="Spring.Context.Support.ResourceSetMessageSource, Spring.Core">
<property name="resourceManagers">
<list>
<value>Spring.Examples.AppContext.MyResource, Spring.Examples.AppContext</value>
</list>
</property>
</object>
You can specify the arguments to construct a ResourceManager as a two part string value containing the
base name of the resource and the assembly name. This will be converted to a ResourceManager via the
ResourceManagerConverter TypeConverter. This converter can be similarly used to set a property on any object
that is of the type ResourceManager. You may also specify an instance of the ResourceManager to use via
an object reference. The convenience class Spring.Objects.Factory.Config.ResourceManagerFactoryObject
can be used to conveniently create an instance of a ResourceManager.
<object name="myResourceManager" type="Spring.Objects.Factory.Config.ResourceManagerFactoryObject, Spring.Core">
<property name="baseName">
<value>Spring.Examples.AppContext.MyResource</value>
</property>
<property name="assemblyName">
<value>Spring.Examples.AppContext</value>
</property>
</object>
In application code, a call to GetMessage will retrieve a properly localized message string based on a
code value. Any arguments present in the retrieved string are replaced using String.Format semantics. The
ResourceManagers, ResourceSets and retrieved strings are cached to provide quicker lookup performance. The
key 'HelloMessage' is contained in the resource file with a value of Hello {0} {1}. The following call on the
application context will return the string Hello Mr. Anderson. Note that the caching of ResourceSets is via the
concatenation of the ResourceManager base name and the CultureInfo string. This combination must be unique.
string msg = ctx.GetMessage("HelloMessage",
new object[] {"Mr.", "Anderson"},
CultureInfo.CurrentCulture );
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It is possible to chain the resolution of messages by passing arguments that are themselves messages to be resolved
giving you greater flexibility in how you can structure your message resolution. This is achieved by passing
as an argument a class that implements IMessageResolvable instead of a string literal. The convenience class
DefaultMessageResolvable is available for this purpose. As an example if the resource file contains a key name
error.required that has the value '{0} is required {1}' and another key name field.firstname with the
value 'First name'. The following code will create the string 'First name is required dude!'
string[] codes = {"field.firstname"};
DefaultMessageResolvable dmr = new DefaultMessageResolvable(codes, null);
ctx.GetMessage("error.required",
new object[] { dmr, "dude!" },
CultureInfo.CurrentCulture ));
The examples directory in the distribution contains an example program, Spring.Examples.AppContext, that
demonstrates usage of these features.
The IMessageSourceAware interface can also be used to acquire a reference to any IMessageSource that has
been defined. Any object that is defined in an IApplicationContext that implements the IMessageSourceAware
interface will be injected with the application context's IMessageSource when it (the object) is being created and
configured.
5.12.3. Using resources within Spring.NET
A lot of applications need to access resources. Resources here, might mean files, but also news feeds from the
Internet or normal web pages. Spring.NET provides a clean and transparent way of accessing resources in a
protocol independent way. The IApplicationContext has a method (GetResource(string)) to take care of this.
Refer to Section 7.1, “Introduction” for more information on the string format to use and the IResource abstraction
in general.
5.12.4. Loosely coupled events
The Eventing Registry allows developers to utilize a loosely coupled event wiring mechanism. By decoupling the
event publication and the event subscription, most of the mundane event wiring is handled by the IoC container.
Event publishers can publish their event to a central registry, either all of their events or a subset based on criteria
such as delegate type, name, return value, etc... Event subscribers can choose to subscribe to any number of
published events. Subscribers can subscriber to events based on the type of object exposing them, allowing one
subscriber to handle all events of a certain type without regards to how many different instances of that type are
created.
The Spring.Objects.Events.IEventRegistry interface represents the central registry and defines publish and
subscribe methods.
• void PublishEvents( object sourceObject ): publishes all events of the source object to subscribers that
implement the correct handler methods.
• void Subscribe(object subscriber ): The subscriber receives all events from the source object for which
it has matching handler methods.
• void Subscribe(object subscriber, Type targetSourceType ): The subscriber receives all events from
a source object of a particular type for which it has matching handler methods.
• void Unsubscribe(object subscriber ): Unsubscribe all events from the source object for which it has
matching handler methods.
• void Unsubscribe(object subscriber, Type targetSourceType ): Unsubscribe all events from a source
object of a particular type for which it has matching handler methods.
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implements this interface and delegates the implementation to an instance of
Spring.Objects.Events.Support.EventRegistry. You are free to create and use as many EventRegistries as
you like but since it is common to use only one in an application, IApplicationContext provides convenient
access to a single instance.
IApplicationContext
Within the example/Spring/Spring.Examples.EventRegistry directory you will find an example on how to use
this functionality. When you open up the project, the most interesting file is the EventRegistryApp.cs file. This
application loads a set of object definitions from the application configuration file into an IApplicationContext
instance. From there, three objects are loaded up: one publisher and two subscribers. The publisher publishes its
events to the IApplicationContext instance:
// Create the Application context using configuration file
IApplicationContext ctx = ContextRegistry.GetContext();
// Gets the publisher from the application context
MyEventPublisher publisher = (MyEventPublisher)ctx.GetObject("MyEventPublisher");
// Publishes events to the context.
ctx.PublishEvents( publisher );
One of the two subscribers subscribes to all events published to the IApplicationContext instance, using the
publisher type as the filter criteria.
// Gets first instance of subscriber
MyEventSubscriber subscriber = (MyEventSubscriber)ctx.GetObject("MyEventSubscriber");
// Gets second instance of subscriber
MyEventSubscriber subscriber2 = (MyEventSubscriber)ctx.GetObject("MyEventSubscriber");
// Subscribes the first instance to the any events published by the type MyEventPublisher
ctx.Subscribe( subscriber, typeof(MyEventPublisher) );
This will wire the first subscriber to the original event publisher. Anytime the event publisher fires an event,
(publisher.ClientMethodThatTriggersEvent1();) the first subscriber will handle the event, but the second
subscriber will not. This allows for selective subscription, regardless of the original prototype definition.
5.12.5. Event notification from IApplicationContext
Event handling in the IApplicationContext is provided through the IApplicationListener interface
that contains the single method void OnApplicationEvent( object source, ApplicationEventArgs
applicationEventArgs ). Classes that implement the IApplicationListener interface are automatically
registered as a listener with the IApplicationContext. Publishing an event is done via the context's
PublishEvent( ApplicationEventArgs eventArgs ) method. This implementation is based on the traditional
Observer design pattern.
The event argument type, ApplicationEventArgs, adds the time of the event firing as a property. The derived
class ContextEventArgs is used to notify observers on the lifecycle events of the application context. It
contains a property ContextEvent Event that returns the enumeration Refreshed or Closed.. The Refreshed
enumeration value indicated that the IApplicationContext was either initialized or refreshed. Initialized here
means that all objects are loaded, singletons are pre-instantiated and the IApplicationContext is ready for
use. The Closed is published when the IApplicationContext is closed using the Dispose() method on the
IConfigurableApplicationContext interface. Closed here means that singletons are destroyed.
Implementing custom events can be done as well. Simply call the PublishEvent method on the
IApplicationContext, specifying a parameter which is an instance of your custom event argument subclass.
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Let's have a look at an example. First, the IApplicationContext:
<object id="emailer" type="Example.EmailObject">
<property name="blackList">
<list>
<value>[email protected]</value>
<value>[email protected]</value>
<value>[email protected]</value>
</list>
</property>
</object>
<object id="blackListListener" type="Example.BlackListNotifier">
<property name="notificationAddress">
<value>[email protected]</value>
</property>
</object>
and then, the actual objects:
public class EmailObject : IApplicationContextAware {
// the blacklist
private IList blackList;
public IList BlackList
{
set { this.blackList = value; }
}
public IApplicationContext ApplicationContext
{
set { this.ctx = value; }
}
public void SendEmail(string address, string text) {
if (blackList.contains(address))
{
BlackListEvent evt = new BlackListEvent(address, text);
ctx.publishEvent(evt);
return;
}
// send email...
}
}
public class BlackListNotifier : IApplicationListener
{
// notification address
private string notificationAddress;
public string NotificationAddress
{
set { this.notificationAddress = value; }
}
public void OnApplicationEvent(ApplicationEvent evt)
{
if (evt instanceof BlackListEvent)
{
// notify appropriate person
}
}
}
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5.13. Customized behavior in the ApplicationContext
The IObjectFactory already offers a number of mechanisms to control the lifecycle of objects deployed in
it (such as marker interfaces like IInitializingObject and System.IDisposable, their configuration only
equivalents such as init-method and destroy-method) attributes in an XmlObjectFactory configuration, and
object post-processors. In an IApplicationContext, all of these still work, but additional mechanisms are added
for customizing behavior of objects and the container.
5.13.1. The IApplicationContextAware marker interface
All marker interfaces available with ObjectFactories still work. The IApplicationContext does add one extra
marker interface which objects may implement, IApplicationContextAware. An object which implements this
interface and is deployed into the context will be called back on creation of the object, using the interface's
ApplicationContext property, and provided with a reference to the context, which may be stored for later
interaction with the context.
5.13.2. The IObjectPostProcessor
Object
post-processors
are
classes
which
implement
the
Spring.Objects.Factory.Config.IObjectPostProcessor interface, have already been mentioned. It is worth
mentioning again here though, that post-processors are much more convenient to use in IApplicationContexts
than in plain IObjectFactory instances. In an IApplicationContext, any deployed object which implements
the above marker interface is automatically detected and registered as an object post-processor, to be called
appropriately at creation time for each object in the factory.
5.13.3. The IObjectFactoryPostProcessor
Object
factory
post-processors
are
classes
which
implement
the
Spring.Objects.Factory.Config.IObjectFactoryPostProcessor interface, have already been mentioned. It
is worth mentioning again here though, that object factory post-processors are much more convenient to use in
IApplicationContexts. In an IApplicationContext, any deployed object which implements the above marker
interface is automatically detected as an object factory post-processor, to be called at the appropriate time.
5.13.4. The PropertyPlaceholderConfigurer
The PropertyPlaceholderConfigurer has already been described in the context of its use within an
IObjectFactory. It is worth mentioning here though, that it is generally more convenient to use it with
an IApplicationContext, since the context will automatically recognize and apply any object factory postprocessors, such as this one, when they are simply deployed into it like any other object. There is no need for
a manual step to execute it.
5.14. Configuration of ApplicationContext without using XML
The class GenericApplicationContext can be used as a basis for creating an IApplicationContext implementation
that read the container metadata from sources other than XML. This could be by scanning objects in a .DLL
for known attributes or a scripting language that leverages a DSL to create terse IObjectDefinitions. There is a
class, Spring.Objects.Factory.Support.ObjectDefinitionBuilder offers some convenience methods for creating an
IObjectDefinition in a less verbose manner than using the RootObjectDefinition API. The following shows how
to configure the GenericApplicationContext to read from XML, just so show familiar API usage
GenericApplicationContext ctx = new GenericApplicationContext();
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XmlObjectDefinitionReader reader = new XmlObjectDefinitionReader(ctx);
reader.LoadObjectDefinitions("assembly://Spring.Core.Tests/Spring.Context.Support/contextB.xml");
reader.LoadObjectDefinitions("assembly://Spring.Core.Tests/Spring.Context.Support/contextC.xml");
reader.LoadObjectDefinitions("assembly://Spring.Core.Tests/Spring.Context.Support/contextA.xml");
ctx.Refresh();
The implementation of IObjectDefinitionReader is responsible for creating the configuration metadata, i.e.,
implementations of RootObjectDefinition, etc. Note a web version of this application class has not yet been
implemented.
An example, with a yet to be created DLL scanner, that would get configuration metadata from the .dll named
MyAssembly.dll located in the runtime path, would look something like this
GenericApplicationContext ctx = new GenericApplicationContext();
ObjectDefinitionScanner scanner = new ObjectDefinitionScanner(ctx);
scanner.scan("MyAssembly.dll");
ctx.refresh();
Refer to the Spring API documentation for more information.
5.15. Service Locator access
The majority of the code inside an application is best written in a Dependency Injection (Inversion of Control)
style, where that code is served out of an IObjectFactory or IApplicationContext container, has its own
dependencies supplied by the container when it is created, and is completely unaware of the container.
However, there is sometimes a need for singleton (or quasi-singleton) style access to an IObjectFactory or
IApplicationContext. For example, third party code may try to construct a new object directly without the ability
to force it to get these objects out of the IObjectFactory. Similarly, nested user control components in a WinForms
application are created inside the generated code in InitializeComponent. If this user control would like to obtain
references to objects contained in the container it can use the service locator style approach and 'reach out' from
inside the code to obtain the object it requires. (Note support for DI in WinForms is under development.)
The Spring.Context.Support.ContextRegistry class allows you to obtain a reference to an
IApplicationContext via a static locator method. The ContextRegistry is initialized when creating
an IApplicationContext through use of the ContextHandler discussed previously. The simple static
method GetContext() can then be used to retrieve the context. Alternatively, if you create an
IApplicationContext though other means you can register it with the ContextRegistry via the method void
RegisterContext(IApplicationContext context) in the start-up code of your application. Hierarchical context
retrieval is also supported though the use of the GetContext(string name) method, for example:
IApplicationContex ctx = ContextRegistry.GetContext("mySubContext");
This would retrieve the nested context for the context configuration shown previously.
<spring>
<context>
<resource uri="assembly://MyAssembly/MyProject/root-objects.xml"/>
<context name="mySubContext">
<resource uri="file://objects.xml"/>
</context>
</context>
</spring>
Do not call ContextRegistry.GetContext within a constructor as it will result in and endless recursion. (This is
scheduled to be fixed in 1.1.1) In this case it is quite likely you can use the IApplicationContextAware interface
and then retrieve other objects in a service locator style inside an initialization method.
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The ContextRegistry.Clear() method will remove all contexts. On .NET 2.0, this will also call the
ConfigurationManager's RefreshSection method so that the Spring context configuration section will be reread
from disk when it is retrieved again. Note that in a web application RefeshSection will not work as advertised
and you will need to touch the web.config files to reload a configuration.
5.16. Stereotype attributes
Beginning with Spring 1.2, the [Repository] attribute was introduced as a marker for any class that fulfills the role
or stereotype of a repository (a.k.a. Data Access Object or DAO). Among the possibilities for leveraging such a
marker is the automatic translation of exceptions as described in Exception Translation.
Spring 1.2 introduces further stereotype annotations: [Component] and [Service]. [Component] serves as a generic
stereotype for any Spring-managed component; whereas, [Repository] and [Service] serve as specializations of
[Component] for more specific use cases (e.g., in the persistence and service layers, respectively). The ASP.NET
MVC [Controller] attribute will serve this purpose for the controller layer. What this means is that you can
annotate your component classes with [Component], but by annotating them with [Repository] or [Service] your
classes are more properly suited for processing by tools or associating with aspects. For example, these stereotype
annotations make ideal targets for pointcuts. Of course, it is also possible that [Repository] and [Service] may
carry additional semantics in future releases of the Spring Framework. Thus, if you are making a decision between
using [Component] or [Service] for your service layer, [Service] is clearly the better choice. Similarly, as stated
above, [Repository] is already supported as a marker for automatic exception translation in your persistence layer.
The next version of Spring will use the [Component] attribute to perform attribute based autowiring by-type as
in the Spring Java Framework.
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Chapter 6. The IObjectWrapper and Type
conversion
6.1. Introduction
The concepts encapsulated by the IObjectWrapper interface are fundamental to the workings of the core
Spring.NET libraries The typical application developer most probably will not ever have the need to use the
IObjectWrapper directly... because this is reference documentation however, we felt that some explanation of
this core interface might be right. The IObjectWrapper is explained in this chapter since if you were going to
use it at all, you would probably do that when trying to bind data to objects, which, nicely enough, is precisely
the area that the IObjectWrapper addresses.
6.2. Manipulating objects using the IObjectWrapper
One quite important concept of the Spring.Objects namespace is encapsulated in the definition IObjectWrapper
interface and its corresponding implementation, the ObjectWrapper class. The functionality offered by the
IObjectWrapper includes methods to set and get property values (either individually or in bulk), get property
descriptors (instances of the System.Reflection.PropertyInfo class), and to query the readability and
writability of properties. The IObjectWrapper also offers support for nested properties, enabling the setting of
properties on subproperties to an unlimited depth. The IObjectWrapper usually isn't used by application code
directly, but by framework classes such as the various IObjectFactory implementations.
The way the IObjectWrapper works is partly indicated by its name: it wraps an object to perform actions on a
wrapped object instance... such actions would include the setting and getting of properties exposed on the wrapped
object.
Note: the concepts explained in this section are not important to you if you're not planning to work with the
IObjectWrapper directly.
6.2.1. Setting and getting basic and nested properties
Setting and getting properties is done using the SetPropertyValue() and GetPropertyValue() methods, for
which there are a couple of overloaded variants. The details of the various overloads (including return values and
method parameters) are all described in the extensive API documentation supplied as a part of the Spring.NET
distribution.
The aforementioned SetPropertyValue() and GetPropertyValue() methods have a number of conventions for
indicating the path of a property. A property path is an expression that implementations of the IObjectWrapper
interface can use to look up the properties of the wrapped object; some examples of property paths include...
Table 6.1. Examples of property paths
Path
Explanation
name
Indicates the name property of the wrapped object.
account.name
Indicates the nested property name of the account property of the wrapped
object.
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Path
Explanation
account[2]
Indicates the third element of the account property of the wrapped
object. Indexed properties are typically collections such as lists and
dictionaries, but can be any class that exposes an indexer.
Below you'll find some examples of working with the IObjectWrapper to get and set properties. Consider the
following two classes:
[C#]
public class Company
{
private string name;
private Employee managingDirector;
public string Name
{
get { return this.name; }
set { this.name = value; }
}
public Employee ManagingDirector
{
get { return this.managingDirector; }
set { this.managingDirector = value; }
}
}
[C#]
public class Employee
{
private string name;
private float salary;
public string Name
{
get { return this.name; }
set { this.name = value; }
}
public float Salary
{
get { return salary; }
set { this.salary = value; }
}
}
The following code snippets show some examples of how to retrieve and manipulate some of the properties of
IObjectWrapper-wrapped Company and Employee instances.
[C#]
Company c = new Company();
IObjectWrapper owComp = new ObjectWrapper(c);
// setting the company name...
owComp.SetPropertyValue("name", "Salina Inc.");
// can also be done like this...
PropertyValue v = new PropertyValue("name", "Salina Inc.");
owComp.SetPropertyValue(v);
// ok, let's create the director and bind it to the company...
Employee don = new Employee();
IObjectWrapper owDon = new ObjectWrapper(don);
owDon.SetPropertyValue("name", "Don Fabrizio");
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owComp.SetPropertyValue("managingDirector", don);
// retrieving the salary of the ManagingDirector through the company
float salary = (float)owComp.GetPropertyValue("managingDirector.salary");
Note that since the various Spring.NET libraries are compliant with the Common Language Specification (CLS),
the resolution of arbitrary strings to properties, events, classes and such is performed in a case-insensitive fashion.
The previous examples were all written in the C# language, which is a case-sensitive language, and yet the Name
property of the Employee class was set using the all-lowercase 'name' string identifier. The following example
(using the classes defined previously) should serve to illustrate this...
[C#]
// ok, let's create the director and bind it to the company...
Employee don = new Employee();
IObjectWrapper owDon = new ObjectWrapper(don);
owDon.SetPropertyValue("naMe", "Don Fabrizio");
owDon.GetPropertyValue("nAmE"); // gets "Don Fabrizio"
IObjectWrapper owComp = new ObjectWrapper(new Company());
owComp.SetPropertyValue("ManaGINGdirecToR", don);
owComp.SetPropertyValue("mANaGiNgdirector.salARY", 80000);
Console.WriteLine(don.Salary); // puts 80000
The case-insensitivity of the various Spring.NET libraries (dictated by the CLS) is not usually an issue... if you
happen to have a class that has a number of properties, events, or methods that differ only by their case, then you
might want to consider refactoring your code, since this is generally regarded as poor programming practice.
6.2.2. Other features worth mentioning
In addition to the features described in the preceding sections there a number of features that might be interesting
to you, though not worth an entire section.
• determining readability and writability: using the IsReadable() and IsWritable() methods, you can
determine whether or not a property is readable or writable.
• retrieving PropertyInfo instances: using GetPropertyInfo(string) and GetPropertyInfos() you can
retrieve instances of the System.Reflection.PropertyInfo class, that might come in handy sometimes when
you need access to the property metadata specific to the object being wrapped.
6.3. Type conversion
If you associate a TypeConverter with the definition of a custom Type using the standard .NET mechanism (see
the example code below), Spring.NET will use the associated TypeConverter to do the conversion.
[C#]
[TypeConverter (typeof (FooTypeConverter))]
public class Foo
{
}
The TypeConverter class from the System.ComponentModel namespace of the .NET BCL is used extensively by
the various classes in the Spring.Core library, as said class “... provides a unified way of converting types of
values to other types, as well as for accessing standard values and subproperties.” 1
1
More information about creating custom TypeConverter implementations can be found online at Microsoft's MSDN website, by searching
for Implementing a Type Converter.
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For example, a date can be represented in a human readable format (such as 30th August 1984), while we're
still able to convert the human readable form to the original date format or (even better) to an instance of the
System.DateTime class. This behavior can be achieved by using the standard .NET idiom of decorating a class
with the TypeConverterAttribute. Spring.NET also offers another means of associating a TypeConverters with
a class. You might want to do this to achieve a conversion that is not possible using standard idiom... for example,
the Spring.Core library contains a custom TypeConverter that converts comma-delimited strings to String array
instances. Registering custom converters on an IObjectWrapper instance gives the wrapper the knowledge of
how to convert properties to the desired Type.
An example of where property conversion is used in Spring.NET is the setting of properties on objects,
accomplished using the aforementioned TypeConverters. When mentioning System.String as the value of a
property of some object (declared in an XML file for instance), Spring.NET will (if the type of the associated
property is System.Type) use the RuntimeTypeConverter class to try to resolve the property value to a Type
object. The example below demonstrates this automatic conversion of the Example.Xml.SAXParser (a string) into
the corresponding Type instance for use in this factory-style class.
<objects xmlns="http://www.springframework.net">
<object id="parserFactory" type="Example.XmlParserFactory, ExamplesLibrary"
destroy-method="Close">
<property name="ParserClass" value="Example.Xml.SAXParser, ExamplesLibrary"/>
</object>
</objects>
[C#]
public class XmlParserFactory
{
private Type parserClass;
public Type ParserClass
{
get { return this.parserClass; }
set { this.parserClass = value; }
}
public XmlParser GetParser ()
{
return Activator.CreateInstance (ParserClass);
}
}
6.3.1. Type Conversion for Enumerations
The default type converter for enumerations is the System.ComponentModel.EnumConverter class. To specify
the value for an enumerated property, simply use the name of the property. For example the TestObject class
has a property of the enumerated type FileMode. One of the values for this enumeration is named Create. The
following XML fragment shows how to configure this property
<object id="rod" type="Spring.Objects.TestObject, Spring.Core.Tests">
<property name="name" value="Rod"/>
<property name="FileMode" value="Create"/>
</object>
6.4. Built-in TypeConverters
Spring.NET has a number of built-in TypeConverters to make life easy. Each of those is listed below and they
are all located in the Spring.Objects.TypeConverters namespace of the Spring.Core library.
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Table 6.2. Built-in TypeConverters
Type
Explanation
RuntimeTypeConverter
Parses strings representing System.Types to actual System.Types
and the other way around.
FileInfoConverter
Capable of resolving strings to a System.IO.FileInfo object.
StringArrayConverter
Capable of resolving a comma-delimited list of strings to a stringarray and vice versa.
UriConverter
Capable of resolving a string representation of a URI to an actual
Uri-object.
FileInfoConverter
Capable of resolving a string representation of a FileInfo to an actual
FileInfo-object.
StreamConverter
Capable of resolving Spring IResource URI (string) to its
corresponding InputStream-object.
ResourceConverter
Capable of resolving Spring IResource URI (string) to an IResource
object.
ResourceManagerConverter
Capable of resolving a two part string (resource name, assembly
name) to a System.Resources.ResourceManager object.
RgbColorConverter
Capable of resolving a comma separated list of Red, Green, Blue
integer values to a System.Drawing.Color structure.
RegexConverter
Converts string representation of regular expression into an instance
of System.Text.RegularExpressions.Regex
Spring.NET uses the standard .NET mechanisms for the resolution of System.Types, including, but not limited to
checking any configuration files associated with your application, checking the Global Assembly Cache (GAC),
and assembly probing.
6.4.1. Custom type converters
You can register a custom type converter either Programatically using the class TypeConverterRegistry or through
configuration of Spring's container and described in the section Registering Type Converters.
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Chapter 7. Resources
7.1. Introduction
The IResource interface contained in the Spring.Core.IO namespace provides a common interface to describe
and access data from diverse resource locations. This abstraction lets you treat the InputStream from a file
and from a URL in a polymorphic and protocol-independent manner... the .NET BCL does not provide such
an abstraction. The IResource interface inherits from IInputStream that provides a single property Stream
InputStream. The IResource interface adds descriptive information about the resource via a number of additional
properties. Several implementations for common resource locations, i.e. file, assembly, uri, are provided and you
may also register custom IResource implementations.
7.2. The IResource interface
The IResource interface is shown below
public interface IResource : IInputStreamSource
{
bool IsOpen { get; }
Uri Uri { get; }
FileInfo File { get; }
string Description { get; }
bool Exists { get; }
IResource CreateRelative(string relativePath);
}
Table 7.1. IResource Properties
Property
Explanation
InputStream
Inherited from IInputStream. Opens and returns a System.IO.Stream. It is
expected that each invocation returns a fresh Stream. It is the responsibility of
the caller to close the stream.
Exists
returns a boolean indicating whether this resource actually exists in physical
form.
IsOpen
returns a boolean indicating whether this resource represents a handle with an
open stream. If true, the InputStream cannot be read multiple times, and must
be read once only and then closed to avoid resource leaks. Will be false for all
usual resource implementations, with the exception of InputStreamResource.
Description
Returns a description of the resource, such as the fully qualified file name or
the actual URL.
Uri
The Uri representation of the resource.
File
Returns a System.IO.FileInfo for this resource if it can be resolved to an
absolute file path.
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and the methods
Table 7.2. IResource Methods
Method
IResource
Explanation
CreateRelative
(string relativePath)
Creates a resource relative to this resource using relative path like notation (./
and ../).
You can obtain an actual URL or File object representing the resource if the underlying implementation is
compatible and supports that functionality.
The Resource abstraction is used extensively in Spring itself, as an argument type in many method signatures
when a resource is needed. Other methods in some Spring APIs (such as the constructors to various
IApplicationContext implementations), take a String which is used to create a Resource appropriate to that
context implementation
While the Resource interface is used a lot with Spring and by Spring, it's actually very useful to use as a general
utility class by itself in your own code, for access to resources, even when your code doesn't know or care about
any other parts of Spring. While this couples your code to Spring, it really only couples it to this small set of
utility classes and can be considered equivalent to any other library you would use for this purpose
7.3. Built-in IResource implementations
The resource implementations provided are
• AssemblyResource accesses data stored as .NET resources inside an assembly. Uri syntax is assembly://
<AssemblyName>/<NameSpace>/<ResourceName>
• ConfigSectionResource accesses Spring.NET configuration data stored in a custom configuration section in
the .NET application configuration file (i.e. App.config). Uri syntax is config://<path to section>
• FileSystemResource accesses file system data. Uri syntax is file://<filename>
• InputStreamResource a wrapper around a raw System.IO.Stream . Uri syntax is not supported.
• UriResource accesses data from the standard System.Uri protocols such as http and https. In .NET 2.0 you can
use this also for the ftp protocol. Standard Uri syntax is supported.
Refer to the MSDN documentation for more information on supported Uri scheme types.
7.3.1. Registering custom IResource implementations
The configuration section handler, ResourceHandlersSectionHandler, is used to register any custom
IResource implementations you have created. In the configuration section you list the type of
IResource implementation and the protocol prefix. Your custom IResource implementation must provide
a constructor that takes a string as it's sole argument that represents the URI string. Refer to the
SDK documentation for ResourceHandlersSectionHandler for more information. An example of the
ResourceHandlersSectionHandler is shown below for a fictional IResource implementation that interfaces with
a database.
<configuration>
<configSections>
<sectionGroup name="spring">
<section name='context' type='Spring.Context.Support.ContextHandler, Spring.Core'/>
<section name="resourceHandlers"
type="Spring.Context.Support.ResourceHandlersSectionHandler, Spring.Core"/>
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</sectionGroup>
</configSections>
<spring>
<resourceHandlers>
<handler protocol="db" type="MyCompany.MyApp.Resources.MyDbResource, MyAssembly"/>
</resourceHandlers>
<context>
<resource uri="db://user:[email protected]/MyDefinitionsTable"/>
</context>
</spring>
</configuration>
7.4. The IResourceLoader
To load resources given their Uri syntax, an implementation of the IResourceLoader is used. The default
implementation is ConfigurableResourceLoader. Typically you will not need to access this class directly since
the IApplicationContext implements the IResourceLoader interface that contains the single method IResource
GetResource(string location). The provided implementations of IApplicationContext delegate this method
to an instance of ConfigurableResourceLoader which supports the Uri protocols/schemes listed previously. If
you do not specify a protocol then the file protocol is used. The following shows some sample usage.
IResource resource = appContext.GetResource("http://www.springframework.net/license.html");
resource = appContext.GetResource("assembly://Spring.Core.Tests/Spring/TestResource.txt");
resource = appContext.GetResource("https://sourceforge.net/");
resource = appContext.GetResource("file:///C:/WINDOWS/ODBC.INI");
StreamReader reader = new StreamReader(resource.InputStream);
Console.WriteLine(reader.ReadToEnd());
Other protocols can be registered along with a new implementations of an IResource that must correctly parse a Uri
string in its constructor. An example of this can be seen in the Spring.Web namespace that uses Server.MapPath
to resolve the filename of a resource.
The CreateRelative method allows you to easily load resources based on a relative path name. In the case of
relative assembly resources, the relative path navigates the namespace within an assembly. For example:
IResource res = new AssemblyResource("assembly://Spring.Core.Tests/Spring/TestResource.txt");
IResource res2 = res.CreateRelative("./IO/TestIOResource.txt");
This loads the resource TestResource.txt and then navigates to the Spring.Core.IO namespace and loads the
resource TestIOResource.txt
7.5. The IResourceLoaderAware interface
The IResourceLoaderAware interface is a special marker interface, identifying objects that expect to be provided
with a IResourceLoader reference.
public interface IResourceLoaderAware
{
IResourceLoader ResourceLoader
{
set;
get;
}
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}
When a class implements IResourceLoaderAware and is deployed into an application context (as a Springmanaged object), it is recognized as IResourceLoaderAware by the application context. The application context
will then invoke the ResourceLoader property, supplying itself as the argument (remember, all application
contexts in Spring implement the IResourceLoader interface).
Of course, since an IApplicationContext is a IResourceLoader, the object could also implement the
IApplicationContextAware interface and use the supplied application context directly to load resources, but in
general, it's better to use the specialized IResourceLoader interface if that's all that's needed. The code would
just be coupled to the resource loading interface, which can be considered a utility interface, and not the whole
Spring IApplicationContext interface.
7.6. Application contexts and IResource paths
An application context constructor (for a specific application context type) generally takes a string or array of
strings as the location path(s) of the resource(s) such as XML files that make up the definition of the context. For
example, you can create an XmlApplicationContext from two resources as follows:
IApplicationContext context = new XmlApplicationContext(
"file://objects.xml", "assembly://MyAssembly/MyProject/objects-dal-layer.xml");
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Chapter 8. Threading and Concurrency
Support
8.1. Introduction
The purpose of the Spring.Threading namespace is to provide a place to keep useful concurrency abstractions
that augment those in the BCL. Since Doug Lea has provided a wealth of mature public domain concurrency
abstractions in his Java based 'EDU.oswego.cs.dl.util.concurrent' libraries we decided to port a few of his
abstractions to .NET. So far, we've only ported three classes, the minimum necessary to provide basic object
pooling functionality to support an AOP based pooling aspect and to provide a Semaphore class that was
mistakenly not included in .NET 1.0/1.1.
There is also an important abstraction, IThreadStorage, for performing thread local storage.
8.2. Thread Local Storage
Depending on your runtime environment there are different strategies to use for storing objects in thread
local storage. If you are in web applications a single Request may be executed on different threads.
As such, the location to store thread local objects is in HttpContext.Current. For other environments
System.Runtime.Remoting.Messaging.CallContext is used. For more background information on the
motivation behind these choices, say as compared to the attribute [ThreadStatic] refer to "Piers7"'s blog and this
forum post. The interface IThreadStorage serves as the basis for the thread local storage abstraction and various
implementations can be selected from depending on your runtime requirements. Configuring the implementation
of IThreadStorage makes it easier to have more portability across runtime environments.
The API is quite simple and shown below
public interface IThreadStorage
{
object GetData(string name)
void SetData(string name, object value)
void FreeNamedDataSlot(string name)
}
The methods GetData and SetData are responsible for retrieving and setting the object that is to be bound to
thread local storage and associating it with a name. Clearing the thread local storage is done via the method
FreeNamedDataSlot.
In Spring.Core is the implementation, CallContextStorage, that directly uses CallContext and also
the implementation LogicalThreadContext which by default uses CallContextStorage but can be
configured via the static method SetStorage(IThreadStorage). The methods on CallContextStorage and
LogicalThreadContext are static.
In Spring.Web is the implementation HttpContextStorage which uses the HttpContext to store thread local data
and HybridContextStorage that uses HttpContext if within a web environment, i.e. HttpContext.Current !
= null, and CallContext otherwise.
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Spring internally uses LogicalThreadContext as this doesn't require a coupling to the System.Web namespace.
In the case of Spring based web applications, Spring's WebSupportModule sets the storage strategy of
LogicalThreadContext to be HybridContextStorage.
8.3. Synchronization Primitives
When you take a look at these synchronization classes, you'll wonder why it's even necessary when
System.Threading provides plenty of synchronization options. Although System.Threading provides great
synchronization classes, it doesn't provide well-factored abstractions and interfaces for us. Without these
abstractions, we will tend to code at a low-level. With enough experience, you'll eventually come up with some
abstractions that work well. Doug Lea has already done a lot of that research and has a class library that we can
take advantage of.
8.3.1. ISync
is the central interface for all classes that control access to resources from multiple threads. It's a simple
interface which has two basic use cases. The first case is to block indefinitely until a condition is met:
ISync
void ConcurrentRun(ISync lock) {
lock.Acquire(); // block until condition met
try {
// ... access shared resources
}
finally {
lock.Release();
}
}
The other case is to specify a maximum amount of time to block before the condition is met:
void ImpatientConcurrentRun(ISync lock) {
// block for at most 10 milliseconds for condition
if ( lock.Attempt(10) ) {
try {
// ... access shared resources
}
finally {
lock.Release();
}
} else {
// complain of time out
}
}
8.3.2. SyncHolder
The SyncHolder class implements the System.IDisposable interface and so provides a way to use an ISync with
the using C# keyword: the ISync will be automatically Acquired and then Released on exiting from the block.
This should simplify the programming model for code using (!) an ISync:
ISync sync = ...
...
using (new SyncHolder(sync))
{
// ... code to be executed
// holding the ISync lock
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}
There is also the timed version, a little more cumbersome as you must deal with timeouts:
ISync sync = ...
long msecs = 100;
...
// try to acquire the ISync for msecs milliseconds
try
{
using (new SyncHolder(sync, msecs))
{
// ... code to be executed
// holding the ISync lock
}
}
catch (TimeoutException)
{
// deal with failed lock acquisition
}
8.3.3. Latch
The Latch class implements the ISync interface and provides an implementation of a latch. A latch is a boolean
condition that is set at most once, ever. Once a single release is issued, all acquires will pass. It is similar to a
ManualResetEvent initialized unsignalled (Reset) and can only be Set(). A typical use is to act as a start signal
for a group of worker threads.
class Boss {
Latch _startPermit;
void Worker() {
// very slow worker initialization ...
// ... attach to messaging system
// ... connect to database
_startPermit.Acquire();
// ... use resources initialized in Mush
// ... do real work
}
void Mush() {
_startPermit = new Latch();
for (int i=0; i<10; ++i) {
new Thread(new ThreadStart(Worker)).Start();
}
// very slow main initialization ...
// ... parse configuration
// ... initialize other resources used by workers
_startPermit.Release();
}
}
8.3.4. Semaphore
The Semaphore class implements the ISync interface and provides an implementation of a semaphore.
Conceptually, a semaphore maintains a set of permits. Each Acquire() blocks if necessary until a permit is
available, and then takes it. Each Release() adds a permit. However, no actual permit objects are used; the
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Semaphore just keeps a count of the number available and acts accordingly. A typical use is to control access
to a pool of shared objects.
class LimitedConcurrentUploader {
// ensure we don't exceed maxUpload simultaneous uploads
Semaphore _available;
public LimitedConcurrentUploader(maxUploads) {
_available = new Semaphore(maxUploads);
}
// no matter how many threads call this method no more
// than maxUploads concurrent uploads will occur.
public Upload(IDataTransfer upload) {
_available.Acquire();
try {
upload.TransferData();
}
finally {
_available.Release();
}
}
}
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Chapter 9. Object Pooling
9.1. Introduction
The Spring.Pool namespace contains a generic API for implementing pools of objects. Object pooling is a well
known technique to minimize the creation of objects that can take a significant amount of time. Common examples
are to create a pool of database connections such that each request to the database can reuse an existing connection
instead of creating one per client request. Threads are also another common candidate for pooling in order to
increase responsiveness of an application to multiple concurrent client requests.
.NET contains support for object pooling in these common scenarios. Support for database connection pools is
directly supported by ADO.NET data providers as a configuration option. Similarly, thread pooling is supported
via the System.ThreadPool class. Support for pooling of other objects can be done using the CLR managed API
to COM+ found in the System.EnterpriseServices namespace.
Despite this built-in support there are scenarios where you would like to use alternative pool implementations. This
may be because the default implementations, such as System.ThreadPool, do not meet your requirements. (For
a discussion on advanced ThreadPool usage see Smart Thread Pool by Ami Bar.) Alternatively, you may want
to pool classes that do not inherit from System.EnterpriseServices.ServicedComponent. Instead of making
changes to the object model to meet this inheritance requirement, Spring .NET provides similar support for
pooling, but for any object, by using AOP proxies and a generic pool API for managing object instances.
Note, that if you are concerned only with applying pooling to an existing object, the pooling APIs discussed
here are not very important. Instead the use and configuration of Spring.Aop.Target.SimplePoolTargetSource
is more relevant. Pooling of objects can either be done Programatically or through the XML configuration of
the Spring .NET container. Attribute support for pooling, similar to the ServicedComponent approach, will be
available in a future release of Spring.NET.
Chapter 33, IoC Quickstarts contains an example that shows the use of the pooling API independent of AOP
functionality.
9.2. Interfaces and Implementations
The Spring.Pool namespace provides two simple interfaces to manage pools of objects. The first
interface, IObjectPool describes how to take and put back an object from the pool. The second interface
IPoolableObjectFactory is meant to be used in conjunction with implementations of the IObjectPool to provide
guidance in calling various lifecycle events on the objects managed by the pool. These interfaces are based on the
Jakarta Commons Pool API. Spring.Pool.Support.SimplePool is a default implementation of IObjectPool and
Spring.Aop.Target.SimplePoolTargetSource is the implementation of IPoolableObjectFactory for use with
AOP. The current goal of the Spring.Pool namespace is not to provide a one-for-one replacement of the Jakarta
Commons Pool API, but rather to support basic object pooling needs for common AOP scenarios. Consequently,
other interfaces and base classes available in the Jakarta package are not available.
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Chapter 10. Spring.NET miscellanea
10.1. Introduction
This chapter contains miscellanea information on features, goodies, caveats that does not belong to any paricular
area.
10.2. PathMatcher
Note, Spring.Util.PathMatcher is currently only available in CVS, not the RC3 release. If you want to use these
feature please get the code from CVS (instructions) or from the download section of the Spring.NET website that
contains an .zip with the full CVS tree.
Spring.Util.PathMatcher
provides Ant/NAnt-like path name matching features.
To do the match, you use the method:
static bool Match(string pattern, string path)
If you want to decide if case is important or not use the method:
static bool Match(string pattern, string path, bool ignoreCase)
10.2.1. General rules
To build your pattern, you use the *, ? and ** building blocks:
• *: matches any number of non slash characters;
• ?: matches exactly 1 (one) non slash/dot character;
• **: matches any subdirectory, without taking care of the depth;
10.2.2. Matching filenames
A file name can be matched using the following notation:
foo?bar.*
matches:
fooAbar.txt
foo1bar.txt
foo_bar.txt
foo-bar.txt
does not match:
foo.bar.txt
foo/bar.txt
foo\bar.txt
The classical all files pattern:
*.*
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matches:
foo.db
.db
foo
foo.bar.db
foo.db.db
db.db.db
does not match:
c:/
c:/foo.db
c:/foo
c:/.db
c:/foo.foo.db
//server/foo
10.2.3. Matching subdirectories
A directory name can be matched at any depth level using the following notation:
**/db/**
That pattern matches the following paths:
/db
//server/db
c:/db
c:/spring/app/db/foo.db
//Program Files/App/spaced dir/db/foo.db
/home/spring/spaced dir/db/v1/foo.db
but does not match these:
c:/spring/app/db-v1/foo.db
/home/spring/spaced dir/db-v1/foo.db
You can compose subdirectories to match like this:
**/bin/**/tmp/**
That pattern matches the following paths:
c:/spring/foo/bin/bar/tmp/a
c:/spring/foo/bin/tmp/a/b.c
but does not match these:
c:/spring/foo/bin/bar/temp/a
c:/tmp/foo/bin/bar/a/b.c
You can use more advanced patterns:
**/.spring-assemblies*/**
matches:
c:/.spring-assemblies
c:/.spring-assembliesabcd73xs
c:/app/.spring-assembliesabcd73xs
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c:/app/.spring-assembliesabcd73xs/foo.dll
//server/app/.spring-assembliesabcd73xs
does not match:
c:/app/.spring-assemblie
10.2.4. Case does matter, slashes don't
.NET is expected to be a cross-platform development ... platform. So, PathMatcher will match taking care of the
case of the pattern and the case of the path. For example:
**/db/**/*.DB
matches:
c:/spring/service/deploy/app/db/foo.DB
but does not match:
c:/spring/service/deploy/app/DB/foo.DB
c:spring/service/deploy/app/spaced dir/DB/foo.DB
//server/share/service/deploy/app/DB/backup/foo.db
If you do not matter about case, you should explicitly tell the Pathmatcher.
Back and forward slashes, in the very same cross-platform spirit, are not important:
spring/foo.bar
matches all the following paths:
c:\spring\foo.bar
c:/spring\foo.bar
c:/spring/foo.bar
/spring/foo.bar
\spring\foo.bar
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Chapter 11. Expression Evaluation
11.1. Introduction
The Spring.Expressions namespace provides a powerful expression language for querying and manipulating an
object graph at runtime. The language supports setting and getting of property values, property assignment,
method invocation, accessing the context of arrays, collections and indexers, logical and arithmetic operators,
named variables, and retrieval of objects by name from Spring's IoC container. It also supports list projection and
selection, as well as common list aggregators.
The functionality provided in this namespace serves as the foundation for a variety of other features in Spring.NET
such as enhanced property evaluation in the XML based configuration of the IoC container, a Data Validation
framework, and a Data Binding framework for ASP.NET. You will likely find other cool uses for this library in
your own work where run-time evaluation of criteria based on an object's state is required. For those with a Java
background, the Spring.Expressions namespace provides functionality similar to the Java based Object Graph
Navigation Language, OGNL.
This chapter covers the features of the expression language using an Inventor and Inventor's Society class as the
target objects for expression evaluation. The class declarations and the data used to populate them are listed at
the end of the chapter in section Section 11.4, “Classes used in the examples”. These classes are blatantly taken
from the NUnit tests for the Expressions namespace which you can refer to for additional example usage.
11.2. Evaluating Expressions
The simplest, but not the most efficient way to perform expression evaluation is by using one of the static
convenience methods of the ExpressionEvaluator class:
public static object GetValue(object root, string expression);
public static object GetValue(object root, string expression, IDictionary variables)
public static void SetValue(object root, string expression, object newValue)
public static void SetValue(object root, string expression, IDictionary variables, object newValue)
The first argument is the 'root' object that the expression string (2nd argument) will be evaluated against. The
third argument is used to support variables in the expression and will be discussed later. Simple usage to get the
value of an object property is shown below using the Inventor class. You can find the class listing in section
Section 11.4, “Classes used in the examples”.
Inventor tesla = new Inventor("Nikola Tesla", new DateTime(1856, 7, 9), "Serbian");
tesla.PlaceOfBirth.City = "Smiljan";
string evaluatedName = (string) ExpressionEvaluator.GetValue(tesla, "Name");
string evaluatedCity = (string) ExpressionEvaluator.GetValue(tesla, "PlaceOfBirth.City"));
The value of 'evaluatedName' is 'Nikola Tesla' and that of 'evaluatedCity' is 'Smiljan'. A period is used to navigate
the nested properties of the object. Similarly to set the property of an object, say we want to rewrite history and
change Tesla's city of birth, we would simply add the following line
ExpressionEvaluator.SetValue(tesla, "PlaceOfBirth.City", "Novi Sad");
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A much better way to evaluate expressions is to parse them once and then evaluate as many times as you want
usingExpressionclass. Unlike ExpressionEvaluator, which parses expression every time you invoke one of its
methods, Expression class will cache the parsed expression for increased performance. The methods of this class
are listed below:
public static IExpression Parse(string expression)
public override object Get(object context, IDictionary variables)
public override void Set(object context, IDictionary variables, object newValue)
The retrieval of the Name property in the previous example using the Expression class is shown below
IExpression exp = Expression.Parse("Name");
string evaluatedName = (string) exp.GetValue(tesla, null);
The difference in performance between the two approaches, when evaluating the same expression many times,
is several orders of magnitude, so you should only use convenience methods of the ExpressionEvaluator class
when you are doing one-off expression evaluations. In all other cases you should parse the expression first and
then evaluate it as many times as you need.
There are a few exception classes to be aware of when using the ExpressionEvaluator. These are
InvalidPropertyException, when you refer to a property that doesn't exist, NullValueInNestedPathException,
when a null value is encountered when traversing through the nested property list, and ArgumentException and
NotSupportedException when you pass in values that are in error in some other manner.
The expression language is based on a grammar and uses ANTLR to construct the lexer and parser. Errors relating
to bad syntax of the language will be caught at this level of the language implementation. For those interested in the
digging deeper into the implementation, the grammar file is named Expression.g and is located in the src directory
of the namespace. As a side note, the release version of the ANTLR DLL included with Spring.NET was signed
with the Spring.NET key, which means that you should always use the included version of antlr.runtime.dll
within your application. Upcoming releases of ANTLR will provide strongly signed assemblies, which will
remove this requirement.
11.3. Language Reference
11.3.1. Literal expressions
The types of literal expressions supported are strings, dates, numeric values (int, real, and hex), boolean and null.
String are delimited by single quotes. To put a single quote itself in a string use the backslash character. The
following listing shows simple usage of literals. Typically they would not be used in isolation like this, but as part
of a more complex expression, for example using a literal on one side of a logical comparison operator.
string helloWorld = (string) ExpressionEvaluator.GetValue(null, "'Hello World'"); // evals to "Hello World"
string tonyPizza
= (string) ExpressionEvaluator.GetValue(null, "'Tony\\'s Pizza'"); // evals to "Tony's Pizza"
double avogadrosNumber = (double) ExpressionEvaluator.GetValue(null, "6.0221415E+23");
int maxValue = (int)
ExpressionEvaluator.GetValue(null, "0x7FFFFFFF");
// evals to 2147483647
DateTime birthday = (DateTime) ExpressionEvaluator.GetValue(null, "date('1974/08/24')");
DateTime exactBirthday =
(DateTime) ExpressionEvaluator.GetValue(null, " date('19740824T131030', 'yyyyMMddTHHmmss')");
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bool trueValue = (bool) ExpressionEvaluator.GetValue(null, "true");
object nullValue = ExpressionEvaluator.GetValue(null, "null");
Note that the extra backslash character in Tony's Pizza is to satisfy C# escape syntax. Numbers support
the use of the negative sign, exponential notation, and decimal points. By default real numbers are parsed
using Double.Parse unless the format character "M" or "F" is supplied, in which case Decimal.Parse and
Single.Parse would be used respectfully. As shown above, if two arguments are given to the date literal then
DateTime.ParseExact will be used. Note that all parse methods of classes that are used internally reference the
CultureInfo.InvariantCulture.
11.3.2. Properties, Arrays, Lists, Dictionaries, Indexers
As shown in the previous example in Section 11.2, “Evaluating Expressions”, navigating through properties is
easy, just use a period to indicate a nested property value. The instances of Inventor class, pupin and tesla, were
populated with data listed in section Section 11.4, “Classes used in the examples”. To navigate "down" and get
Tesla's year of birth and Pupin's city of birth the following expressions are used
int year = (int) ExpressionEvaluator.GetValue(tesla, "DOB.Year"));
// 1856
string city = (string) ExpressionEvaluator.GetValue(pupin, "PlaCeOfBirTh.CiTy");
// "Idvor"
For the sharp-eyed, that isn't a typo in the property name for place of birth. The expression uses mixed cases to
demonstrate that the evaluation is case insensitive.
The contents of arrays and lists are obtained using square bracket notation.
// Inventions Array
string invention = (string) ExpressionEvaluator.GetValue(tesla, "Inventions[3]"); // "Induction motor"
// Members List
string name = (string) ExpressionEvaluator.GetValue(ieee, "Members[0].Name"); // "Nikola Tesla"
// List and Array navigation
string invention = (string) ExpressionEvaluator.GetValue(ieee, "Members[0].Inventions[6]") // "Wireless communic
The contents of dictionaries are obtained by specifying the literal key value within the brackets. In this case,
because keys for the Officers dictionary are strings, we can specify string literal.
// Officer's Dictionary
Inventor pupin = (Inventor) ExpressionEvaluator.GetValue(ieee, "Officers['president']";
string city = (string) ExpressionEvaluator.GetValue(ieee, "Officers['president'].PlaceOfBirth.City"); // "Idvor"
ExpressionEvaluator.SetValue(ieee, "Officers['advisors'][0].PlaceOfBirth.Country", "Croatia");
You may also specify non literal values in place of the quoted literal values by using another expression inside the
square brackets such as variable names or static properties/methods on other types. These features are discussed
in other sections.
Indexers are similarly referenced using square brackets. The following is a small example that shows the use of
indexers. Multidimensional indexers are also supported.
public class Bar
{
private int[] numbers = new int[] {1, 2, 3};
public int this[int index]
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{
get { return numbers[index];}
set { numbers[index] = value; }
}
}
Bar b = new Bar();
int val = (int) ExpressionEvaluator.GetValue(bar, "[1]") // evaluated to 2
ExpressionEvaluator.SetValue(bar, "[1]", 3);
// set value to 3
11.3.2.1. Defining Arrays, Lists and Dictionaries Inline
In addition to accessing arrays, lists and dictionaries by navigating the graph for the context object, Spring.NET
Expression Language allows you to define them inline, within the expression. Inline lists are defined by simply
enclosing a comma separated list of items with curly brackets:
{1, 2, 3, 4, 5}
{'abc', 'xyz'}
If you want to ensure that a strongly typed array is initialized instead of a weakly typed list, you can use array
initializer instead:
new int[] {1, 2, 3, 4, 5}
new string[] {'abc', 'xyz'}
Dictionary definition syntax is a bit different: you need to use a # prefix to tell expression parser to expect key/
value pairs within the brackets and to specify a comma separated list of key/value pairs within the brackets:
#{'key1' : 'Value 1', 'today' : DateTime.Today}
#{1 : 'January', 2 : 'February', 3 : 'March', ...}
Arrays, lists and dictionaries created this way can be used anywhere where arrays, lists and dictionaries obtained
from the object graph can be used, which we will see later in the examples.
Keep in mind that even though examples above use literals as array/list elements and dictionary keys and values,
that's only to simplify the examples -- you can use any valid expression wherever literals are used.
11.3.3. Methods
Methods are invoked using typical C# programming syntax. You may also invoke methods on literals.
//string literal
char[] chars = (char[]) ExpressionEvaluator.GetValue(null, "'test'.ToCharArray(1, 2)"))
// 't','e'
//date literal
int year = (int) ExpressionEvaluator.GetValue(null, "date('1974/08/24').AddYears(31).Year") // 2005
// object usage, calculate age of tesla navigating from the IEEE society.
ExpressionEvaluator.GetValue(ieee, "Members[0].GetAge(date('2005-01-01')") // 149 (eww..a big anniversary is com
11.3.4. Operators
11.3.4.1. Relational operators
The relational operators; equal, not equal, less than, less than or equal, greater than, and greater than or equal
are supported using standard operator notation. These operators take into account if the object implements the
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interface. Enumerations are also supported but you will need to register the enumeration type, as
described in Section Section 11.3.8, “Type Registration”, in order to use an enumeration value in an expression
if it is not contained in the mscorlib.
IComparable
ExpressionEvaluator.GetValue(null, "2 == 2")
// true
ExpressionEvaluator.GetValue(null, "date('1974-08-24') != DateTime.Today")
// true
ExpressionEvaluator.GetValue(null, "2 < -5.0") // false
ExpressionEvaluator.GetValue(null, "DateTime.Today <= date('1974-08-24')") // false
ExpressionEvaluator.GetValue(null, "'Test' >= 'test'") // true
Enumerations can be evaluated as shown below
FooColor fColor = new FooColor();
ExpressionEvaluator.SetValue(fColor, "Color", KnownColor.Blue);
bool trueValue = (bool) ExpressionEvaluator.GetValue(fColor, "Color == KnownColor.Blue"); //true
Where FooColor is the following class.
public class FooColor
{
private KnownColor knownColor;
public KnownColor Color
{
get { return knownColor;}
set { knownColor = value; }
}
}
In addition to standard relational operators, Spring.NET Expression Language supports some additional, very
useful operators that were "borrowed" from SQL, such as in, like and between, as well as is and matches operators,
which allow you to test if object is of a specific type or if the value matches a regular expression.
ExpressionEvaluator.GetValue(null, "3 in {1, 2, 3, 4, 5}")
// true
ExpressionEvaluator.GetValue(null, "'Abc' like '[A-Z]b*'")
// true
ExpressionEvaluator.GetValue(null, "'Abc' like '?'")
// false
ExpressionEvaluator.GetValue(null, "1 between {1, 5}")
// true
ExpressionEvaluator.GetValue(null, "'efg' between {'abc', 'xyz'}")
ExpressionEvaluator.GetValue(null, "'xyz' is int")
// true
// false
ExpressionEvaluator.GetValue(null, "{1, 2, 3, 4, 5} is IList")
// true
ExpressionEvaluator.GetValue(null, "'5.0067' matches '^-?\\d+(\\.\\d{2})?$'"))
ExpressionEvaluator.GetValue(null, @"'5.00' matches '^-?\d+(\.\d{2})?$'")
// false
// true
Note that the Visual Basic and not SQL syntax is used for the like operator pattern string.
11.3.4.2. Logical operators
The logical operators that are supported are and, or, and not. Their use is demonstrated below
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// AND
bool falseValue = (bool) ExpressionEvaluator.GetValue(null, "true and false"); //false
string expression = @"IsMember('Nikola Tesla') and IsMember('Mihajlo Pupin')";
bool trueValue = (bool) ExpressionEvaluator.GetValue(ieee, expression); //true
// OR
bool trueValue = (bool) ExpressionEvaluator.GetValue(null, "true or false");
//true
string expression = @"IsMember('Nikola Tesla') or IsMember('Albert Einstien')";
bool trueValue = (bool) ExpressionEvaluator.GetValue(ieee, expression); // true
// NOT
bool falseValue = (bool) ExpressionEvaluator.GetValue(null, "!true");
// AND and NOT
string expression = @"IsMember('Nikola Tesla') and !IsMember('Mihajlo Pupin')";
bool falseValue = (bool) ExpressionEvaluator.GetValue(ieee, expression);
11.3.4.3. Mathematical operators
The addition operator can be used on numbers, strings and dates. Subtraction can be used on numbers and dates.
Multiplication and division can be used only on numbers. Other mathematical operators supported are modulus
(%) and exponential power (^). Standard operator precedence is enforced. These operators are demonstrated below
// Addition
int two = (int)ExpressionEvaluator.GetValue(null, "1 + 1"); // 2
String testString = (String)ExpressionEvaluator.GetValue(null, "'test' + ' ' + 'string'"); //'test string'
DateTime dt = (DateTime)ExpressionEvaluator.GetValue(null, "date('1974-08-24') + 5"); // 8/29/1974
// Subtraction
int four = (int) ExpressionEvaluator.GetValue(null, "1 - -3"); //4
Decimal dec = (Decimal) ExpressionEvaluator.GetValue(null, "1000.00m - 1e4"); // 9000.00
TimeSpan ts = (TimeSpan) ExpressionEvaluator.GetValue(null, "date('2004-08-14') - date('1974-08-24')"); //10948.
// Multiplication
int six = (int) ExpressionEvaluator.GetValue(null, "-2 * -3"); // 6
int twentyFour = (int) ExpressionEvaluator.GetValue(null, "2.0 * 3e0 * 4"); // 24
// Division
int minusTwo = (int) ExpressionEvaluator.GetValue(null, "6 / -3"); // -2
int one = (int) ExpressionEvaluator.GetValue(null, "8.0 / 4e0 / 2"); // 1
// Modulus
int three = (int) ExpressionEvaluator.GetValue(null, "7 % 4"); // 3
int one = (int) ExpressionEvaluator.GetValue(null, "8.0 % 5e0 % 2"); // 1
// Exponent
int sixteen = (int) ExpressionEvaluator.GetValue(null, "-2 ^ 4"); // 16
// Operator precedence
int minusFortyFive = (int) ExpressionEvaluator.GetValue(null, "1+2-3*8^2/2/2"); // -45
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11.3.5. Assignment
Setting of a property is done by using the assignment operator. This would typically be done within a call
to GetValue since in the simple case SetValue offers the same functionality. Assignment in this manner is
useful when combining multiple operators in an expression list, discussed in the next section. Some examples
of assignment are shown below
Inventor inventor = new Inventor();
String aleks = (String) ExpressionEvaluator.GetValue(inventor, "Name = 'Aleksandar Seovic'");
DateTime dt = (DateTime) ExpressionEvaluator.GetValue(inventor, "DOB = date('1974-08-24')");
//Set the vice president of the society
Inventor tesla = (Inventor) ExpressionEvaluator.GetValue(ieee, "Officers['vp'] = Members[0]");
11.3.6. Expression lists
Multiple expressions can be evaluated against the same context object by separating them with a semicolon and
enclosing the entire expression within parentheses. The value returned is the value of the last expression in the
list. Examples of this are shown below
//Perform property assignments and then return Name property.
String pupin = (String) ExpressionEvaluator.GetValue(ieee.Members,
"( [1].PlaceOfBirth.City = 'Beograd'; [1].PlaceOfBirth.Country = 'Serbia'; [1].Name )"));
// pupin = "Mihajlo Pupin"
11.3.7. Types
In many cases, you can reference types by simply specifying type name:
ExpressionEvaluator.GetValue(null, "1 is int")
ExpressionEvaluator.GetValue(null, "DateTime.Today")
ExpressionEvaluator.GetValue(null, "new string[] {'abc', 'efg'}")
This is possible for all standard types from mscorlib, as well as for any other type that is registered with the
TypeRegistry as described in the next section.
For all other types, you need to use special T(typeName) expression:
Type dateType = (Type) ExpressionEvaluator.GetValue(null, "T(System.DateTime)")
Type evalType = (Type) ExpressionEvaluator.GetValue(null, "T(Spring.Expressions.ExpressionEvaluator, Spring.Core
bool trueValue = (bool) ExpressionEvaluator.GetValue(tesla, "T(System.DateTime) == DOB.GetType()")
Note
The implementation delegates to Spring's ObjectUtils.ResolveType method for the actual type
resolution, which means that the types used within expressions are resolved in the exactly the same
way as the types specified in Spring configuration files.
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11.3.8. Type Registration
To refer to a type within an expression that is not in the mscorlib you need to register it with the TypeRegistry.
This will allow you to refer to a shorthand name of the type within your expressions. This is commonly used in
expression that use the new operator or refer to a static properties of an object. Example usage is shown below.
TypeRegistry.RegisterType("Society", typeof(Society));
Inventor pupin = (Inventor) ExpressionEvaluator.GetValue(ieee, "Officers[Society.President]");
Alternatively, you can register types using typeAliases configuration section.
11.3.9. Constructors
Constructors can be invoked using the new operator. For classes outside mscorlib you will need to register your
types so they can be resolved. Examples of using constructors are shown below:
// simple ctor
DateTime dt = (DateTime) ExpressionEvaluator.GetValue(null, "new DateTime(1974, 8, 24)");
// Register Inventor type then create new inventor instance within Add method inside an expression list.
// Then return the new count of the Members collection.
TypeRegistry.RegisterType(typeof(Inventor));
int three = (int) ExpressionEvaluator.GetValue(ieee.Members, "{ Add(new Inventor('Aleksandar Seovic', date('1974
As a convenience, Spring.NET also allows you to define named constructor arguments, which are used to set
object's properties after instantiation, similar to the way standard .NET attributes work. For example, you could
create an instance of the Inventor class and set its Inventions property in a single statement:
Inventor aleks = (Inventor) ExpressionEvaluator.GetValue(null, "new Inventor('Aleksandar Seovic', date('1974-08-
The only rule you have to follow is that named arguments should be specified after standard constructor
arguments, just like in the .NET attributes.
While we are on the subject, Spring.NET Expression Language also provides a convenient syntax for .NET
attribute instance creation. Instead of using standard constructor syntax, you can use a somewhat shorter and more
familiar syntax to create an instance of a .NET attribute class:
WebMethodAttribute webMethod = (WebMethodAttribute) ExpressionEvaluator.GetValue(null, "@[WebMethod(true, CacheD
As you can see, with the exception of the @ prefix, syntax is exactly the same as in C#.
Slightly different syntax is not the only thing that differentiates an attribute expression from a standard constructor
invocation expression. In addition to that, attribute expression uses slightly different type resolution mechanism
and will attempt to load both the specified type name and the specified type name with an Attribute suffix, just
like the C# compiler.
11.3.10. Variables
Variables can referenced in the expression using the syntax #variableName. The variables are passed in and out
of the expression using the dictionary parameter in ExpressionEvaluator's GetValue or SetValue methods.
public static object GetValue(object root, string expression, IDictionary variables)
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public static void SetValue(object root, string expression, IDictionary variables, object newValue)
The variable name is the key value of the dictionary. Example usage is shown below;
IDictionary vars = new Hashtable();
vars["newName"] = "Mike Tesla";
ExpressionEvaluator.GetValue(tesla, "Name = #newName", vars));
You can also use the dictionary as a place to store values of the object as they are evaluated inside the expression.
For example to change Tesla's first name back again and keep the old value;
ExpressionEvaluator.GetValue(tesla, "{ #oldName = Name; Name = 'Nikola Tesla' }", vars);
String oldName = (String)vars["oldName"]; // Mike Tesla
Variable names can also be used inside indexers or maps instead of literal values. For example;
vars["prez"] = "president";
Inventor pupin = (Inventor) ExpressionEvaluator.GetValue(ieee, "Officers[#prez]", vars);
11.3.10.1. The '#this' and '#root' variables
There are two special variables that are always defined and can be references within the expression: #this and
#root.
The #this variable can be used to explicitly refer to the context for the node that is currently being evaluated:
// sets the name of the president and returns its instance
ExpressionEvaluator.GetValue(ieee, "Officers['president'].( #this.Name = 'Nikola Tesla'; #this )")
Similarly, the #root variable allows you to refer to the root context for the expression:
// removes president from the Officers dictionary and returns removed instance
ExpressionEvaluator.GetValue(ieee, "Officers['president'].( #root.Officers.Remove('president'); #this )")
11.3.11. Ternary Operator (If-Then-Else)
You can use the ternary operator for performing if-then-else conditional logic inside the expression. A minimal
example is;
String aTrueString
= (String) ExpressionEvaluator.GetValue(null, "false ? 'trueExp' : 'falseExp'") // trueExp
In this case, the boolean false results in returning the string value 'trueExp'. A less artificial example is shown
below
ExpressionEvaluator.SetValue(ieee, "Name", "IEEE");
IDictionary vars = new Hashtable();
vars["queryName"] = "Nikola Tesla";
string expression = @"IsMember(#queryName)
? #queryName + ' is a member of the ' + Name + ' Society'
: #queryName + ' is not a member of the ' + Name + ' Society'";
String queryResultString = (String) ExpressionEvaluator.GetValue(ieee, expression, vars));
// queryResultString = "Nikola Tesla is a member of the IEEE Society"
11.3.12. List Projection and Selection
List projection and selection are very powerful expression language features that allow you to transform the
source list into another list by either projecting across its "columns", or selecting from its "rows". In other
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words, projection can be thought of as a column selector in a SQL SELECT statement, while selection would
be comparable to the WHERE clause.
For example, let's say that we need a list of the cities where our inventors were born. This could be easily obtained
by projecting on the PlaceOfBirth.City property:
IList placesOfBirth = (IList) ExpressionEvaluator.GetValue(ieee, "Members.!{PlaceOfBirth.City}")
// { 'Smiljan'
Or we can get the list of officers' names:
IList officersNames = (IList) ExpressionEvaluator.GetValue(ieee, "Officers.Values.!{Name}")
// { 'Nikola Tesla'
As you can see from the examples, projection uses !{projectionExpression} syntax and will return a new list of
the same length as the original list but typically with the elements of a different type.
On the other hand, selection, which uses ?{projectionExpression} syntax, will filter the list and return a new
list containing a subset of the original element list. For example, selection would allow us to easily get a list of
Serbian inventors:
IList serbianInventors = (IList) ExpressionEvaluator.GetValue(ieee, "Members.?{Nationality == 'Serbian'}")
// {
Or to get a list of inventors that invented sonar:
IList sonarInventors = (IList) ExpressionEvaluator.GetValue(ieee, "Members.?{'Sonar' in Inventions}")
// { pupi
Or we can combine selection and projection to get a list of sonar inventors' names:
IList sonarInventorsNames = (IList) ExpressionEvaluator.GetValue(ieee, "Members.?{'Sonar' in Inventions}.!{Name}
As a convenience, Spring.NET Expression Language also supports a special syntax for selecting the first or
last match. Unlike regular selection, which will return an empty list if no matches are found, first or last match
selection expression will either return an instance of the matched element, or null if no matching elements were
found. In order to return a first match you should prefix your selection expression with ^{ instead of ?{, and to
return last match you should use ${ prefix:
ExpressionEvaluator.GetValue(ieee, "Members.^{Nationality == 'Serbian'}.Name")
ExpressionEvaluator.GetValue(ieee, "Members.${Nationality == 'Serbian'}.Name")
// 'Nikola Tesla'
// 'Mihajlo Pupin'
Notice that we access the Name property directly on the selection result, because an actual matched instance is
returned by the first and last match expression instead of a filtered list.
11.3.13. Collection Processors and Aggregators
In addition to list projection and selection, Spring.NET Expression Language also supports several collection
processors, such as distinct, nonNull and sort, as well as a number of commonly used aggregators, such as
max, min, count, sum and average.
The difference between processors and aggregators is that processors return a new or transformed collection,
while aggregators return a single value. Other than that, they are very similar -- both processors and aggregators
are invoked on a collection node using standard method invocation expression syntax, which makes them very
simple to use and allows easy chaining of multiple processors.
11.3.13.1. Count Aggregator
The count aggregator is a safe way to obtain a number of items in a collection. It can be applied to a collection
of any type, including arrays, which helps eliminate the decision on whether to use Count or Length property
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depending on the context. Unlike its standard .NET counterparts, count aggregator can also be invoked on the
null context without throwing a NullReferenceException. It will simply return zero in this case, which makes
it much safer than standard .NET properties within larger expression.
ExpressionEvaluator.GetValue(null, "{1, 5, -3}.count()")
ExpressionEvaluator.GetValue(null, "count()") // 0
// 3
11.3.13.2. Sum Aggregator
The sum aggregator can be used to calculate a total for the list of numeric values. If numbers within the list
are not of the same type or precision, it will automatically perform necessary conversion and the result will
be the highest precision type. If any of the collection elements is not a number, this aggregator will throw an
InvalidArgumentException.
ExpressionEvaluator.GetValue(null, "{1, 5, -3, 10}.sum()") // 13 (int)
ExpressionEvaluator.GetValue(null, "{5, 5.8, 12.2, 1}.sum()") // 24.0 (double)
11.3.13.3. Average Aggregator
The average aggregator will return the average for the collection of numbers. It will use the same type coercion
rules, as the sum aggregator in order to be as precise as possible. Just like the sum aggregator, if any of the
collection elements is not a number, it will throw an InvalidArgumentException.
ExpressionEvaluator.GetValue(null, "{1, 5, -4, 10}.average()")
ExpressionEvaluator.GetValue(null, "{1, 5, -2, 10}.average()")
// 3
// 3.5
11.3.13.4. Minimum Aggregator
The minimum aggregator will return the smallest item in the list. In order to determine what "the smallest"
actually means, this aggregator relies on the assumption that the collection items are of the uniform type
and that they implement the IComparable interface. If that is not the case, this aggregator will throw an
InvalidArgumentException.
ExpressionEvaluator.GetValue(null, "{1, 5, -3, 10}.min()") // -3
ExpressionEvaluator.GetValue(null, "{'abc', 'efg', 'xyz'}.min()")
// 'abc'
11.3.13.5. Maximum Aggregator
The maximum aggregator will return the largest item in the list. In order to determine what "the largest"
actually means, this aggregator relies on the assumption that the collection items are of the uniform type
and that they implement IComparable interface. If that is not the case, this aggregator will throw an
InvalidArgumentException.
ExpressionEvaluator.GetValue(null, "{1, 5, -3, 10}.max()") // 10
ExpressionEvaluator.GetValue(null, "{'abc', 'efg', 'xyz'}.max()")
// 'xyz'
11.3.13.6. Non-null Processor
A non-null processor is a very simple collection processor that eliminates all null values from the collection.
ExpressionEvaluator.GetValue(null, "{ 'abc', 'xyz', null, 'abc', 'def', null}.nonNull()") // { 'abc', 'xyz', 'a
ExpressionEvaluator.GetValue(null, "{ 'abc', 'xyz', null, 'abc', 'def', null}.nonNull().distinct().sort()") //
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11.3.13.7. Distinct Processor
A distinct processor is very useful when you want to ensure that you don't have duplicate items in the collection.
It can also accept an optional Boolean argument that will determine whether null values should be included in
the results. The default is false, which means that they will not be included.
ExpressionEvaluator.GetValue(null, "{ 'abc', 'xyz', 'abc', 'def', null, 'def' }.distinct(true).sort()") // { nu
ExpressionEvaluator.GetValue(null, "{ 'abc', 'xyz', 'abc', 'def', null, 'def' }.distinct(false).sort()") // { '
11.3.13.8. Sort Processor
The sort processor can be used to sort uniform collections of elements that implement IComparable.
ExpressionEvaluator.GetValue(null, "{1.2, 5.5, -3.3}.sort()") // { -3.3, 1.2, 5.5 }
ExpressionEvaluator.GetValue(null, "{ 'abc', 'xyz', 'abc', 'def', null, 'def' }.sort()")
// { null, 'abc', 'abc
The sort processor also accepts a boolean value as an argument to determine sort order, sort(false) will sort the
collection in decending order.
11.3.13.9. Type Conversion Processor
The convert processor can be used to convert a collection of elements to a given Type.
object[] arr = new object[] { "0", 1, 1.1m, "1.1", 1.1f };
decimal[] result = (decimal[]) ExpressionEvaluator.GetValue(arr, "convert(decimal)");
11.3.13.10. Reverse Processor
The reverse processor returns the reverse order of elements in the list
object[] arr = new object[] { "0", 1, 2.1m, "3", 4.1f };
object[] result = new ArrayList( (ICollection) ExpressionEvaluator.GetValue(arr, "reverse()") ).ToArray(); // {
11.3.13.11. OrderBy Processor
Collections can be ordered in three ways, an expression, a SpEL lamda expreression, or a delegate.
// orderBy expression
IExpression exp = Expression.Parse("orderBy('ToString()')");
object[] input = new object[] { 'b', 1, 2.0, "a" };
object[] ordered = exp.GetValue(input); // { 1, 2.0, "a", 'b' }
// SpEL lambda expressions
IExpression exp = Expression.Parse("orderBy({|a,b| $a.ToString().CompareTo($b.ToString())})");
object[] input = new object[] { 'b', 1, 2.0, "a" };
object[] ordered = exp.GetValue(input); // { 1, 2.0, "a", 'b' }
Hashtable vars = new Hashtable();
Expression.RegisterFunction( "compare", "{|a,b| $a.ToString().CompareTo($b.ToString())}", vars);
exp = Expression.Parse("orderBy(#compare)");
ordered = exp.GetValue(input, vars); // { 1, 2.0, "a", 'b' }
// .NET delegate
private delegate int CompareCallback(object x, object y);
private int CompareObjects(object x, object y)
{
if (x == y) return 0;
return x.ToString().CompareTo(""+y);
}
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Hashtable vars = new Hashtable();
vars["compare"] = new CompareCallback(CompareObjects);
IExpression exp = Expression.Parse("orderBy(#compare)");
object[] input = new object[] { 'b', 1, 2.0, "a" };
object[] ordered = exp.GetValue(input); // { 1, 2.0, "a", 'b' }
11.3.13.12. User Defined Collection Processor
You can register your own collection processor for use in evaluation a collection. Here is an example of a
ICollectionProcessor implementation that sums only the even numbers of an integer list
public class IntEvenSumCollectionProcessor : ICollectionProcessor
{
public object Process(ICollection source, object[] args)
{
object total = 0d;
foreach (object item in source)
{
if (item != null)
{
if (NumberUtils.IsInteger(item))
{
if ((int)item % 2 == 0)
{
total = NumberUtils.Add(total, item);
}
}
else
{
throw new ArgumentException("Sum can only be calculated for a collection of numeric
}
}
}
return total;
}
}
public void DoWork()
{
Hashtable vars = new Hashtable();
vars["EvenSum"] = new IntEvenSumCollectionProcessor();
int result = (int)ExpressionEvaluator.GetValue(null, "{1, 2, 3, 4}.EvenSum()", vars));
}
// 6
11.3.14. Spring Object References
Expressions can refer to objects that are declared in Spring's application context using the
syntax @(contextName:objectName). If no contextName is specified the default root context name
(Spring.RootContext) is used. Using the application context defined in the MovieFinder example from
Chapter 33, IoC Quickstarts, the following expression returns the number of movies directed by Roberto Benigni.
public static void Main()
{
. . .
// Retrieve context defined in the spring/context section of
// the standard .NET configuration file.
IApplicationContext ctx = ContextRegistry.GetContext();
int numMovies = (int) ExpressionEvaluator.GetValue(null,
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"@(MyMovieLister).MoviesDirectedBy('Roberto Benigni').Length");
. . .
}
The variable numMovies is evaluated to 2 in this example.
11.3.15. Lambda Expressions
A somewhat advanced, but a very powerful feature of Spring.NET Expression Language are lambda expressions.
Lambda expressions allow you to define inline functions, which can then be used within your expressions just
like any other function or method. You may also use .NET delegates as described in the next section.
The syntax for defining lambda expressions is:
#functionName = {|argList|
functionBody }
For example, you could define a max function and call it like this:
ExpressionEvaluator.GetValue(null, "(#max = {|x,y| $x > $y ? $x : $y }; #max(5,25))", new Hashtable())
// 25
As you can see, any arguments defined for the expression can be referenced within the function body using a local
variable syntax, $varName. Invocation of the function defined using lambda expression is as simple as specifying
the comma-separated list of function arguments in parentheses, after the function name.
Lambda expressions can be recursive, which means that you can invoke the function within its own body:
ExpressionEvaluator.GetValue(null, "(#fact = {|n| $n <= 1 ? 1 : $n * #fact($n-1) }; #fact(5))", new Hashtable())
Notice that in both examples above we had to specify a variables parameter for the GetValue method. This
is because lambda expressions are actually nothing more than parameterized variables and we need variables
dictionary in order to store them. If you don't specify a valid IDictionary instance for the variables parameter,
you will get a runtime exception.
Also, in both examples above we used an expression list in order to define and invoke a function in a single
expression. However, more likely than not, you will want to define your functions once and then use them within
as many expressions as you need. Spring.NET provides an easy way to pre-register your lambda expressions by
exposing a static Expression.RegisterFunction method, which takes function name, lambda expression and
variables dictionary to register function in as parameters:
IDictionary vars = new Hashtable();
Expression.RegisterFunction("sqrt", "{|n| Math.Sqrt($n)}", vars);
Expression.RegisterFunction("fact", "{|n| $n <= 1 ? 1 : $n * #fact($n-1)}", vars);
Once the function registration is done, you can simply evaluate an expression that uses these functions, making
sure that the vars dictionary is passed as a parameter to expression evaluation engine:
ExpressionEvaluator.GetValue(null, "#fact(5)", vars)
ExpressionEvaluator.GetValue(null, "#sqrt(9)", vars)
// 120
// 3
Finally, because lambda expressions are treated as variables, they can be assigned to other variables or passed
as parameters to other lambda expressions. In the following example we are defining a delegate function that
accepts function f as the first argument and parameter n that will be passed to function f as the second. Then we
invoke the functions registered in the previous example, as well as the lambda expression defined inline, through
our delegate:
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Expression.RegisterFunction("delegate", "{|f, n| $f($n) }", vars);
ExpressionEvaluator.GetValue(null, "#delegate(#sqrt, 4)", vars) // 2
ExpressionEvaluator.GetValue(null, "#delegate(#fact, 5)", vars) // 120
ExpressionEvaluator.GetValue(null, "#delegate({|n| $n ^ 2 }, 5)", vars)
// 25
While this particular example is not particularly useful, it does demonstrate that lambda expressions are indeed
treated as nothing more than parameterized variables, which is important to remember.
11.3.16. Delegate Expressions
Delegate expressions allow you to refer to .NET delegates which can then be used within your expressions just
like any other function or method.
For example, you can define a max delegate and call it like this
private delegate double DoubleFunctionTwoArgs(double arg1, double arg2);
private double Max(double arg1, double arg2)
{
return Math.Max(arg1, arg2);
}
public void DoWork()
{
Hashtable vars = new Hashtable();
vars["max"] = new DoubleFunctionTwoArgs(Max);
double result = (double) ExpressionEvaluator.GetValue(null, "#max(5,25)", vars);
}
// 25
11.3.17. Null Context
If you do not specify a root object, i.e. pass in null, then the expressions evaluated either have to be
literal values, i.e. ExpressionEvaluator.GetValue(null, "2 + 3.14"), refer to classes that have static methods
or properties, i.e. ExpressionEvaluator.GetValue(null, "DateTime.Today"), create new instances of objects, i.e.
ExpressionEvaluator.GetValue(null, "new DateTime(2004, 8, 14)") or refer to other objects such as those in the
variable dictionary or in the IoC container. The latter two usages will be discussed later.
11.4. Classes used in the examples
The following simple classes are used to demonstrate the functionality of the expression language.
public class Inventor
{
public string Name;
public string Nationality;
public string[] Inventions;
private DateTime dob;
private Place pob;
public Inventor() : this(null, DateTime.MinValue, null)
{}
public Inventor(string name, DateTime dateOfBirth, string nationality)
{
this.Name = name;
this.dob = dateOfBirth;
this.Nationality = nationality;
this.pob = new Place();
}
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public DateTime DOB
{
get { return dob; }
set { dob = value; }
}
public Place PlaceOfBirth
{
get { return pob; }
}
public int GetAge(DateTime on)
{
// not very accurate, but it will do the job ;-)
return on.Year - dob.Year;
}
}
public class Place
{
public string City;
public string Country;
}
public class Society
{
public string Name;
public static string Advisors = "advisors";
public static string President = "president";
private IList members = new ArrayList();
private IDictionary officers = new Hashtable();
public IList Members
{
get { return members; }
}
public IDictionary Officers
{
get { return officers; }
}
public bool IsMember(string name)
{
bool found = false;
foreach (Inventor inventor in members)
{
if (inventor.Name == name)
{
found = true;
break;
}
}
return found;
}
}
The code listings in this chapter use instances of the data populated with the following information.
Inventor tesla = new Inventor("Nikola Tesla", new DateTime(1856, 7, 9), "Serbian");
tesla.Inventions = new string[]
{
"Telephone repeater", "Rotating magnetic field principle",
"Polyphase alternating-current system", "Induction motor",
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"Alternating-current power transmission", "Tesla coil transformer",
"Wireless communication", "Radio", "Fluorescent lights"
};
tesla.PlaceOfBirth.City = "Smiljan";
Inventor pupin = new Inventor("Mihajlo Pupin", new DateTime(1854, 10, 9), "Serbian");
pupin.Inventions = new string[] {"Long distance telephony & telegraphy", "Secondary X-Ray radiation", "Sonar"};
pupin.PlaceOfBirth.City = "Idvor";
pupin.PlaceOfBirth.Country = "Serbia";
Society ieee = new Society();
ieee.Members.Add(tesla);
ieee.Members.Add(pupin);
ieee.Officers["president"] = pupin;
ieee.Officers["advisors"] = new Inventor[] {tesla, pupin};
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Chapter 12. Validation Framework
12.1. Introduction
Data validation is a very important part of any enterprise application. ASP.NET has a validation framework but it
is very limited in scope and starts falling apart as soon as you need to perform more complex validations. Problems
with the out of the box ASP.NET validation framework are well documented by Peter Blum on his web site, so
we are not going to repeat them here. Peter has also built a nice replacement for the standard ASP.NET validation
framework, which is worth looking into if you prefer the standard ASP.NET validation mechanism to the one
offered by Spring.NET for some reason. Both frameworks will allow you to perform very complex validations
but we designed the Spring.NET validation framework differently for the reasons described below.
On the Windows Forms side the situation is even worse. Out of the box data validation features are completely
inadequate as pointed out by Ian Griffiths in this article. One of the major problems we saw in most validation
frameworks available today, both open source and commercial, is that they are tied to a specific presentation
technology. The ASP.NET validation framework uses ASP.NET controls to define validation rules, so these rules
end up in the HTML markup of your pages. Peter Blum's framework uses the same approach. In our opinion,
validation is not applicable only to the presentation layer so there is no reason to tie it to any particular technology.
As such, the Spring.NET Validation Framework is designed in a way that enables data validation in different
application layers using the same validation rules.
The goals of the validation framework are the following:
1. Allow for the validation of any object, whether it is a UI control or a domain object.
2. Allow the same validation framework to be used in both Windows Forms and ASP.NET applications, as well
as in the service layer (to validate parameters passed to the service, for example).
3. Allow composition of the validation rules so arbitrarily complex validation rule sets can be constructed.
4. Allow validators to be conditional so they only execute if a specific condition is met.
The following sections will describe in more detail how these goals were achieved and show you how to use the
Spring.NET Validation Framework in your applications.
12.2. Example Usage
Decoupling validation from presentation was the major goal that significantly influenced design of the validation
framework. We wanted to be able to define a set of validation rules that are completely independent from the
presentation so we can reuse them (or at least have the ability to reuse them) in different application layers. This
meant that the approach taken by Microsoft ASP.NET team would not work and custom validation controls were
not an option. The approach taken was to configure validation rules just like any other object managed by Spring
- within the application context. However, due to possible complexity of the validation rules we decided not to
use the standard Spring.NET configuration schema for validator definitions but to instead provide a more specific
and easier to use custom configuration schema for validation. Note that the validation framework is not tied to
the use of XML, you can use its API Programatically. The following example shows validation rules defined for
the Trip object in the SpringAir sample application:
<objects xmlns="http://www.springframework.net" xmlns:v="http://www.springframework.net/validation">
<object type="TripForm.aspx" parent="standardPage">
<property name="TripValidator" ref="tripValidator" />
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</object>
<v:group id="tripValidator">
<v:required id="departureAirportValidator" test="StartingFrom.AirportCode">
<v:message id="error.departureAirport.required" providers="departureAirportErrors, validationSummary"/>
</v:required>
<v:group id="destinationAirportValidator">
<v:required test="ReturningFrom.AirportCode">
<v:message id="error.destinationAirport.required" providers="destinationAirportErrors, validationSumm
</v:required>
<v:condition test="ReturningFrom.AirportCode != StartingFrom.AirportCode" when="ReturningFrom.AirportCod
<v:message id="error.destinationAirport.sameAsDeparture" providers="destinationAirportErrors, validat
</v:condition>
</v:group>
<v:group id="departureDateValidator">
<v:required test="StartingFrom.Date">
<v:message id="error.departureDate.required" providers="departureDateErrors, validationSummary"/>
</v:required>
<v:condition test="StartingFrom.Date >= DateTime.Today" when="StartingFrom.Date != DateTime.MinValue">
<v:message id="error.departureDate.inThePast" providers="departureDateErrors, validationSummary"/>
</v:condition>
</v:group>
<v:group id="returnDateValidator" when="Mode == 'RoundTrip'">
<v:required test="ReturningFrom.Date">
<v:message id="error.returnDate.required" providers="returnDateErrors, validationSummary"/>
</v:required>
<v:condition test="ReturningFrom.Date >= StartingFrom.Date" when="ReturningFrom.Date != DateTime.MinValu
<v:message id="error.returnDate.beforeDeparture" providers="returnDateErrors, validationSummary"/>
</v:condition>
</v:group>
</v:group>
</objects>
There are a few things to note in the example above:
• You need to reference the validation schema by adding a xmlns:v="http://www.springframework.net/
validation" namespace declaration to the root element.
• You can mix standard object definitions and validator definitions in the same configuration file as long as both
schemas are referenced.
• The Validator defined in the configuration file is identified by and id attribute and can be referenced in the
standard Spring way, i.e. the injection of tripValidator into TripForm.aspx page definition in the first <object>
tag above.
• The validation framework uses Spring's powerful expression evaluation engine to evaluate both validation rules
and applicability conditions for the validator. As such, any valid Spring expression can be specified within the
test and when attributes of any validator.
The example above shows many of the features of the framework, so let's discuss them one by one in the following
sections.
12.3. Validator Groups
Validators can be grouped together. This is important for many reasons but the most typical usage scenario is to
group multiple validation rules that apply to the same value. In the example above there is a validator group for
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almost every property of the Trip instance. There is also a top-level group for the Trip object itself that groups
all other validators.
There are three types of validator groups each with a different behavior:
While the first type (AND) is definitely the most useful, the other two allow you to implement some specific
validation scenarios in a very simple way, so you should keep them in mind when designing your validation rules.
Table 12.1. Validator Groups
TypeXML Tag
Behavior
ANDgroup
Returns true only if all contained validators return true. This is the most commonly
used validator group.
OR any
Returns true if one or more of the contained validators return true.
XORexclusive
Returns true if only one of the contained validators return true.
One thing to remember is that a validator group is a validator like any other and can be used anywhere validator is
expected. You can nest groups within other groups and reference them using validator reference syntax (described
later), so they really allow you to structure your validation rules in the most reusable way.
12.4. Validators
Ultimately, you will have one or more validator definitions for each piece of data that you want to validate.
Spring.NET has several built-in validators that are sufficient for most validations, even fairly complex ones. The
framework is extensible so you can write your own custom validators and use them in the same way as the builtin ones.
12.4.1. Condition Validator
The condition validator evaluates any logical expression that is supported by Spring's evaluation engine. The
syntax is
<v:condition id="id" test="testCondition" when="applicabilityCondition" parent="parentValidator">
actions
</v:condition>
An example is shown below
<v:condition test="StartingFrom.Date >= DateTime.Today" when="StartingFrom.Date != DateTime.MinValue">
<v:message id="error.departureDate.inThePast" providers="departureDateErrors, validationSummary"/>
</v:condition>
In this example the StartingFrom property of the Trip object is compared to see if it is later than the current
date, i.e. DateTime but only when the date has been set (the initial value of StartingFrom.Date was set to
DateTime.MinValue).
The condition validator could be considered "the mother of all validators". You can use it to achieve almost
anything that can be achieved by using other validator types, but in some cases the test expression might be very
complex, which is why you should use more specific validator type if possible. However, condition validator is
still your best bet if you need to check whether particular value belongs to a particular range, or perform a similar
test, as those conditions are fairly easy to write.
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Note
Keep in mind that Spring.NET Validation Framework typically works with domain objects. This is
after data binding from the controls has been performed so that the object being validated is strongly
typed. This means that you can easily compare numbers and dates without having to worry if the
string representation is comparable.
12.4.2. Required Validator
This validator ensures that the specified test value is not empty. The syntax is
<v:required id="id" test="requiredValue" when="applicabilityCondition" parent="parentValidator">
actions
</v:required>
An example is shown below
<v:required test="ReturningFrom.AirportCode">
<v:message id="error.destinationAirport.required" providers="destinationAirportErrors, validationSummary"/>
</v:required>
The specific tests done to determine if the required value is set is listed below
Table 12.2. Rules to determine if required value is valid
System.Type
Test
System.Type
Type exists
System.String
not null or an empty string
system.DateTime
Not System.DateTime.MinValue and not system.DateTime.MaxV
One of the number types.
System.Char
not zero
Not System.Char.MinValue or whitespace.
Any reference type other than System.String
not null
Required validator is also one of the most commonly used ones, and it is much more powerful than the ASP.NET
Required validator, because it works with many other data types other than strings. For example, it will allow
you to validate DateTime instances (both MinValue and MaxValue return false), integer and decimal numbers, as
well as any reference type, in which case it returns true for a non-null value and false for {{null}}s.
The test attribute for the required validator will typically specify an expression that resolves to a property of a
domain object, but it could be any valid expression that returns a value, including a method call.
12.4.3. Regular Expression Validator
The syntax is
<v:regex id="id" test="valueToEvaluate" when="applicabilityCondition" parent="parentValidator">
<v:property name="Expression" value="regularExpressionToMatch"/>
<v:property name="Options" value="regexOptions"/>
actions
</v:regex>
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An example is shown below
<v:regex test="ReturningFrom.AirportCode">
<v:property name="Expression" value="[A-Z][A-Z][A-Z]"/>
<v:message id="error.destinationAirport.threeCharacters" providers="destinationAirportErrors, validationSumma
</v:regex>
Regular expression validator is very useful when validating values that need to conform to some predefined
format, such as telephone numbers, email addresses, URLs, etc.
One major difference of the regular expression validator compared to other built-in validator types is that you
need to set a required Expression property to a regular expression to match against.
12.4.4. Generic Validator
The syntax is
<v:validator id="id" test="requiredValue" when="applicabilityCondition" type="validatorType" parent="parentValid
actions
</v:validator>
An example is shown below
<v:validator test="ReturningFrom.AirportCode" type="MyNamespace.MyAirportCodeValidator, MyAssembly">
<v:message id="error.destinationAirport.invalid" providers="destinationAirportErrors, validationSummary"/>
</v:required>
Generic validator allows you to plug in your custom validator by specifying its type name. Custom validators
are very simple to implement, because all you need to do is extend BaseValidator class and implement abstract
bool Validate(object objectToValidate) method. Your implementation simply needs to return true if it
determines that object is valid, or false otherwise
12.4.5. Conditional Validator Execution
As you can see from the examples above, each validator (and validator group) allows you to define its applicability
condition by specifying a logical expression as the value of the when attribute. This feature is very useful and
is one of the major deficiencies in the standard ASP.NET validation framework, because in many cases specific
validators need to be turned on or off based on the values of the object being validated.
For example, when validating a Trip object we need to validate return date only if the Trip.Mode property is set
to the TripMode.RoundTrip enum value. In order to achieve that we created following validator definition:
<v:group id="returnDateValidator" when="Mode == 'RoundTrip'">
// nested validators
</v:group>
Validators within this group will only be evaluated for round trips.
Note
You should also note that you can compare enums using the string value of the enumeration. You
can also use fully qualified enum name, such as:
Mode == TripMode.RoundTrip
However, in this case you need to make sure that alias for the TripMode enum type is registered using
Spring's standard type aliasing mechanism.
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12.5. Validator Actions
Validation actions are executed every time the containing validator is executed. They allow you to do anything
you want based on the result of the validation. By far the most common use of the validation action is to add
validation error message to the errors collection, but theoretically you could do anything you want. Because adding
validation error messages to the errors collection is such a common scenario, Spring.NET validation schema
defines a separate XML tag for this type of validation action.
12.5.1. Error Message Action
The syntax is
<v:message id="messageId" providers="errorProviderList" when="messageApplicabilityCondition">
<v:param value="paramExpression"/>
</v:message>
An example is shown below
<v:message id="error.departureDate.inThePast" providers="departureDateErrors, validationSummary">
<v:param value="StartingFrom.Date.ToString('D')"/>
<v:param value="DateTime.Today.ToString('D')"/>
</v:message>
There are several things that you have to be aware of when dealing with error messages:
• id is used to look up the error message in the appropriate Spring.NET message source.
• providers specifies a comma separated list of "error buckets" particular error message should be added to.
These "buckets" will later be used by the particular presentation technology in order to display error messages
as necessary.
• a message can have zero or more parameters. Each parameter is an expression that will be resolved using
current validation context and the resolved values will be passed as parameters to IMessageSource.GetMessage
method, which will return the fully resolved message.
12.5.2. Generic Actions
The syntax is
<v:action type="actionType" when="actionApplicabilityCondition">
properties
</v:action>
An example is shown below
<v:action type="Spring.Validation.Actions.ExpressionAction, Spring.Core" when="#page != null">
<v:property name="Valid" value="#page.myPanel.Visible = true"/>
<v:property name="Invalid" value="#page.myPanel.Visible = false"/>
</v:action>
Generic actions can be used to perform all kinds of validation actions. In simple cases, such as in the example
above where we turn control's visibility on or off depending on the validation result, you can use the built-in
ExpressionAction class and simply specify expressions to be evaluated based on the validator result.
In other situations you may want to create your own action implementation, which is fairly simple thing to do –
all you need to do is implement IValidationAction interface:
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public interface IValidationAction
{
/// <summary>
/// Executes the action.
/// </summary>
/// <param name="isValid">Whether associated validator is valid or not.</param>
/// <param name="validationContext">Validation context.</param>
/// <param name="contextParams">Additional context parameters.</param>
/// <param name="errors">Validation errors container.</param>
void Execute(bool isValid, object validationContext, IDictionary contextParams, ValidationErrors errors);
}
12.6. Validator References
Sometimes it is not possible (or desirable) to nest all the validation rules within a single top-level validator group.
For example, if you have an object graph where both ObjectA and ObjectB have a reference to ObjectC, you
might want to set up validation rules for ObjectC only once and reference them from the validation rules for both
ObjectA and ObjectB, instead of duplicating them within both definitions.
The syntax is shown below
<v:ref name="referencedValidatorId" context="validationContextForTheReferencedValidator"/>
An example is shown below
<v:group id="objectA.validator">
<v:ref name="objectC.validator" context="MyObjectC"/>
// other validators for ObjectA
</v:group>
<v:group id="objectB.validator">
<v:ref name="objectC.validator" context="ObjectCProperty"/>
// other validators for ObjectB
</v:group>
<v:group id="objectC.Validator">
// validators for ObjectC
</v:group>
It is as simple as that — you define validation rules for ObjectC separately and reference them from within other
validation groups. Important thing to realize that in most cases you will also want to "narrow" the context for the
referenced validator, typically by specifying the name of the property that holds referenced object. In the example
above, ObjectA.MyObjectC and ObjectB.ObjectCProperty are both of type ObjectC, which objectC.validator
expects to receive as the validation context.
12.7. Progammatic usage
You can also create Validators programmatically using the API. An example is shown below
UserInfo userInfo = new UserInfo();
// has Name and Password props
ValidatorGroup userInfoValidator = new ValidatorGroup();
userInfoValidator.Validators
.Add(new RequiredValidator("Name", null));
userInfoValidator.Validators
.Add(new RequiredValidator("Password", null));
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ValidationErrors errors = new ValidationErrors();
bool userInfoIsValid = userInfoValidator.Validate(userInfo, errors);
No matter if you create your validators programmatically or declaratively, you can invoke them in service side
code via the 'Validate' method shown above and then handle error conditions. Spring provides AOP parameter
validation advice as part of ithe aspect library which may also be useful for performing server-side validation.
12.8. Usage tips within ASP.NET
Now that you know how to configure validation rules, let's see what it takes to evaluate those rules within your
typical ASP.NET application and to display error messages.
The first thing you need to do is inject validators you want to use into your ASP.NET page, as shown in the
example below:
<objects xmlns="http://www.springframework.net" xmlns:v="http://www.springframework.net/validation">
<object type="TripForm.aspx" parent="standardPage">
<property name="TripValidator" ref="tripValidator" />
</object>
<v:group id="tripValidator">
// our validation rules
</v:group>
</objects>
Once that's done, you need to perform validation in one or more of the page event handlers, which typically looks
similar to this:
public void SearchForFlights(object sender, EventArgs e)
{
if (Validate(Controller.Trip, tripValidator))
{
Process.SetView(Controller.SearchForFlights());
}
}
Note
Keep in mind that your ASP.NET page needs to extend Spring.Web.UI.Page in order for the code
above to work.
Finally, you need to define where validation errors should be displayed by adding one or more
<spring:validationError/> and <spring:validationSummary/> controls to the ASP.NET form:
<%@ Page Language="c#" MasterPageFile="~/Web/StandardTemplate.master" Inherits="TripForm" CodeFile="TripForm.asp
<%@ Register TagPrefix="spring" Namespace="Spring.Web.UI.Controls" Assembly="Spring.Web" %>
<asp:Content ID="head" ContentPlaceHolderID="head" runat="server">
<script language="javascript" type="text/javascript">
<!-function showReturnCalendar(isVisible)
{
document.getElementById('<%= returningOnDate.ClientID %>').style.visibility = isVisible? '': 'hidden';
document.getElementById('returningOnCalendar').style.visibility = isVisible? '': 'hidden';
}
-->
</script>
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</asp:Content>
<asp:Content ID="body" ContentPlaceHolderID="body" runat="server">
<div style="text-align: center">
<h4><asp:Label ID="caption" runat="server"></asp:Label></h4>
<spring:ValidationSummary ID="validationSummary" runat="server" />
<table>
<tr class="formLabel">
<td>&nbsp;</td>
<td colspan="3">
<spring:RadioButtonGroup ID="tripMode" runat="server">
<asp:RadioButton ID="OneWay" onclick="showReturnCalendar(false);" runat="server" />
<asp:RadioButton ID="RoundTrip" onclick="showReturnCalendar(true);" runat="server" />
</spring:RadioButtonGroup>
</td>
</tr>
<tr>
<td class="formLabel" align="right">
<asp:Label ID="leavingFrom" runat="server" /></td>
<td nowrap="nowrap">
<asp:DropDownList ID="leavingFromAirportCode" AutoCallBack="true" runat="server" />
<spring:ValidationError id="departureAirportErrors" runat="server" />
</td>
<td class="formLabel" align="right">
<asp:Label ID="goingTo" runat="server" /></td>
<td nowrap="nowrap">
<asp:DropDownList ID="goingToAirportCode" AutoCallBack="true" runat="server" />
<spring:ValidationError id="destinationAirportErrors" runat="server" />
</td>
</tr>
<tr>
<td class="formLabel" align="right">
<asp:Label ID="leavingOn" runat="server" /></td>
<td nowrap="nowrap">
<spring:Calendar ID="leavingFromDate" runat="server" Width="75px" AllowEditing="true" Skin="
<spring:ValidationError id="departureDateErrors" runat="server" />
</td>
<td class="formLabel" align="right">
<asp:Label ID="returningOn" runat="server" /></td>
<td nowrap="nowrap">
<div id="returningOnCalendar">
<spring:Calendar ID="returningOnDate" runat="server" Width="75px" AllowEditing="true" Sk
<spring:ValidationError id="returnDateErrors" runat="server" />
</div>
</td>
</tr>
<tr>
<td class="buttonBar" colspan="4">
<br/>
<asp:Button ID="findFlights" runat="server"/></td>
</tr>
</table>
</div>
<script language="javascript" type="text/javascript">
if (document.getElementById('<%= tripMode.ClientID %>').value == 'OneWay')
showReturnCalendar(false);
else
showReturnCalendar(true);
</script>
</asp:Content>
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12.8.1. Rendering Validation Errors
Spring.NET allows you to render validation errors within the page in several different ways, and if none
of them suits your needs you can implement your own validation errors renderer. Implementations of the
Spring.Web.Validation.IValidationErrorsRenderer that ship with the framework are:
Table 12.3. Validation Renderers
Name
Class
Description
Block Spring.Web.Validation.DivValidationErrorsRenderer
Renders validation errors as list items within a <div> tag. Default
renderer for <spring:validationSummary> control.
Inline Spring.Web.Validation.SpanValidationErrorsRenderer
Renders validation errors within a <span> tag. Default renderer for
<spring:validationError> control.
Icon
Spring.Web.Validation.IconValidationErrorsRenderer
Renders validation errors as error icon, with error messages displayed
in a tooltip. Best option when saving screen real estate is important.
These three error renderers should be sufficient for most applications, but in case you want
to display errors in some other way you can write your own renderer by implementing
Spring.Web.Validation.IValidationErrorsRenderer interface:
namespace Spring.Web.Validation
{
/// <summary>
/// This interface should be implemented by all validation errors renderers.
/// </summary>
/// <remarks>
/// <para>
/// Validation errors renderers are used to decouple rendering behavior from the
/// validation errors controls such as <see cref="ValidationError"/> and
/// <see cref="ValidationSummary"/>.
/// </para>
/// <para>
/// This allows users to change how validation errors are rendered by simply plugging in
/// appropriate renderer implementation into the validation errors controls using
/// Spring.NET dependency injection.
/// </para>
/// </remarks>
public interface IValidationErrorsRenderer
{
/// <summary>
/// Renders validation errors using specified <see cref="HtmlTextWriter"/>.
/// </summary>
/// <param name="page">Web form instance.</param>
/// <param name="writer">An HTML writer to use.</param>
/// <param name="errors">The list of validation errors.</param>
void RenderErrors(Page page, HtmlTextWriter writer, IList errors);
}
}
12.8.1.1. Configuring which Error Renderer to use.
The best part of the errors renderer mechanism is that you can easily change it across the application by modifying
configuration templates for <spring:validationSummary> and <spring:validationError> controls:
<!-- Validation errors renderer configuration -->
<object id="Spring.Web.UI.Controls.ValidationError" abstract="true">
<property name="Renderer">
<object type="Spring.Web.Validation.IconValidationErrorsRenderer, Spring.Web">
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<property name="IconSrc" value="validation-error.gif"/>
</object>
</property>
</object>
<object id="Spring.Web.UI.Controls.ValidationSummary" abstract="true">
<property name="Renderer">
<object type="Spring.Web.Validation.DivValidationErrorsRenderer, Spring.Web">
<property name="CssClass" value="validationError"/>
</object>
</property>
</object>
It's as simple as that!
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Chapter 13. Aspect Oriented
Programming with Spring.NET
13.1. Introduction
Aspect-Oriented Programming (AOP) complements OOP by providing another way of thinking about program
structure. Whereas OO decomposes applications into a hierarchy of objects, AOP decomposes programs into
aspects or concerns. This enables the modularization of concerns such as transaction management that would
otherwise cut across multiple objects (such concerns are often termed crosscutting concerns).
One of the key components of Spring.NET is the AOP framework. While the Spring.NET IoC container does not
depend on AOP, meaning you don't need to use AOP if you don't want to, AOP complements Spring.NET IoC
to provide a very capable middleware solution.
AOP is used in Spring.NET:
• To provide declarative enterprise services, especially as a replacement for COM+ declarative services. The
most important such service is declarative transaction management, which builds on Spring.NET's transaction
abstraction. This functionality is planed for an upcoming release of Spring.NET
• To allow users to implement custom aspects, complementing their use of OOP with AOP.
Thus you can view Spring.NET AOP as either an enabling technology that allows Spring.NET to provide
declarative transaction management without COM+; or use the full power of the Spring.NET AOP framework
to implement custom aspects.
For those who would like to hit the ground running and start exploring how to use Spring's AOP functionality,
head on over to Chapter 34, AOP Guide.
13.1.1. AOP concepts
Let us begin by defining some central AOP concepts. These terms are not Spring.NET-specific. Unfortunately,
AOP terminology is not particularly intuitive. However, it would be even more confusing if Spring.NET used
its own terminology.
• Aspect: A modularization of a concern for which the implementation might otherwise cut across multiple
objects. Transaction management is a good example of a crosscutting concern in enterprise applications.
Aspects are implemented using Spring.NET as Advisors or interceptors.
• Joinpoint: Point during the execution of a program, such as a method invocation or a particular exception being
thrown.
• Advice: Action taken by the AOP framework at a particular joinpoint. Different types of advice include
"around," "before" and "throws" advice. Advice types are discussed below. Many AOP frameworks, including
Spring.NET, model an advice as an interceptor, maintaining a chain of interceptors "around" the joinpoint.
• Pointcut: A set of joinpoints specifying when an advice should fire. An AOP framework must allow developers
to specify pointcuts: for example, using regular expressions.
• Introduction: Adding methods or fields to an advised class. Spring.NET allows you to introduce new interfaces
to any advised object. For example, you could use an introduction to make any object implement an IAuditable
interface, to simplify the tracking of changes to an object's state.
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• Target object: Object containing the joinpoint. Also referred to as advised or proxied object.
• AOP proxy: Object created by the AOP framework, including advice. In Spring.NET, an AOP proxy is a
dynamic proxy that uses IL code generated at runtime.
• Weaving: Assembling aspects to create an advised object. This can be done at compile time (using the GripperLoom.NET compiler, for example), or at runtime. Spring.NET performs weaving at runtime.
Different advice types include:
• Around advice: Advice that surrounds a joinpoint such as a method invocation. This is the most powerful kind
of advice. Around advice will perform custom behaviour before and after the method invocation. They are
responsible for choosing whether to proceed to the joinpoint or to shortcut executing by returning their own
return value or throwing an exception.
• Before advice: Advice that executes before a joinpoint, but which does not have the ability to prevent execution
flow proceeding to the joinpoint (unless it throws an exception).
• Throws advice: Advice to be executed if a method throws an exception. Spring.NET provides strongly typed
throws advice, so you can write code that catches the exception (and subclasses) you're interested in, without
needing to cast from Exception.
• After returning advice: Advice to be executed after a joinpoint completes normally: for example, if a method
returns without throwing an exception.
Spring.NET provides a full range of advice types. We recommend that you use the least powerful advice type
that can implement the required behaviour. For example, if you need only to update a cache with the return value
of a method, you are better off implementing an after returning advice than an around advice, although an around
advice can accomplish the same thing. Using the most specific advice type provides a simpler programming
model with less potential for errors. For example, you don't need to invoke the proceed() method on the
IMethodInvocation used for around advice, and hence can't fail to invoke it.
The pointcut concept is the key to AOP, distinguishing AOP from older technologies offering interception.
Pointcuts enable advice to be targeted independently of the OO hierarchy. For example, an around advice
providing declarative transaction management can be applied to a set of methods spanning multiple objects. Thus
pointcuts provide the structural element of AOP.
13.1.2. Spring.NET AOP capabilities
Spring.NET AOP is implemented in pure C#. There is no need for a special compilation process - all weaving is
done at runtime. Spring.NET AOP does not need to control or modify the way in which assemblies are loaded,
nor does it rely on unmanaged APIs, and is thus suitable for use in any CLR environment.
Spring.NET currently supports interception of method invocations. Field interception is not implemented,
although support for field interception could be added without breaking the core Spring.NET AOP APIs.
Field interception arguably violates OO encapsulation. We don't believe it is wise in application development.
Spring.NET provides classes to represent pointcuts and different advice types. Spring.NET uses the term advisor
for an object representing an aspect, including both an advice and a pointcut targeting it to specific joinpoints.
Different advice types are IMethodInterceptor (from the AOP Alliance interception API); and the advice
interfaces defined in the Spring.Aop namespace. All advices must implement the AopAlliance.Aop.IAdvice
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tag interface. Advices supported out the box are IMethodInterceptor ; IThrowsAdvice; IBeforeAdvice; and
IAfterReturningAdvice. We'll discuss advice types in detail below.
Spring.NET provides a .NET translation of the Java interfaces defined by the AOP Alliance . Around advice must
implement the AOP Alliance AopAlliance.Interceptr.IMethodInterceptor interface. Whilst there is wide
support for the AOP Alliance in Java, Spring.NET is currently the only .NET AOP framework that makes use of
these interfaces. In the short term, this will provide a consistent programming model for those doing development
in both .NET and Java, and in the longer term, we hope to see more .NET projects adopt the AOP Alliance
interfaces.
The aim of Spring.NET AOP support is not to provide a comprehensive AOP implementation on par with the
functionality available in AspectJ. However, Spring.NET AOP provides an excellent solution to most problems
in .NET applications that are amenable to AOP.
Thus, it is common to see Spring.NET's AOP functionality used in conjunction with a Spring.NET IoC container.
AOP advice is specified using normal object definition syntax (although this allows powerful "autoproxying"
capabilities); advice and pointcuts are themselves managed by Spring.NET IoC.
13.1.3. AOP Proxies in Spring.NET
Spring.NET generates AOP proxies at runtime using classes from the System.Reflection.Emit namespace to
create necessary IL code for the proxy class. This results in proxies that are very efficient and do not impose any
restrictions on the inheritance hierarchy.
Another common approach to AOP proxy implementation in .NET is to use ContextBoundObject and the .NET
remoting infrastructure as an interception mechanism. We are not very fond of ContextBoundObject approach
because it requires classes that need to be proxied to inherit from the ContextBoundObject either directly or
indirectly. In our opinion this an unnecessary restriction that influences how you should design your object model
and also excludes applying AOP to "3rd party" classes that are not under your direct control. Context-bound
proxies are also an order of magnitude slower than IL-generated proxies, due to the overhead of the context
switching and .NET remoting infrastructure.
Spring.NET AOP proxies are also "smart" - in that because proxy configuration is known during proxy generation,
the generated proxy can be optimized to invoke target methods via reflection only when necessary (i.e. when
there are advices applied to the target method). In all other cases the target method will be called directly, thus
avoiding performance hit caused by the reflective invocation.
Finally, Spring.NET AOP proxies will never return a raw reference to a target object. Whenever a target method
returns a raw reference to a target object (i.e. "return this;"), AOP proxy will recognize what happened and will
replace the return value with a reference to itself instead.
The current implementation of the AOP proxy generator uses object composition to delegate calls from the proxy
to a target object, similar to how you would implement a classic Decorator pattern. This means that classes that
need to be proxied have to implement one or more interfaces, which is in our opinion not only a less-intruding
requirement than ContextBoundObject inheritance requirements, but also a good practice that should be followed
anyway for the service classes that are most common targets for AOP proxies.
In a future release we will implement proxies using inheritance, which will allow you to proxy classes without
interfaces as well and will remove some of the remaining raw reference issues that cannot be solved using
composition-based proxies.
13.2. Pointcut API in Spring.NET
Let's look at how Spring.NET handles the crucial pointcut concept.
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13.2.1. Concepts
Spring.NET's pointcut model enables pointcut reuse independent of advice types. It's possible to target different
advice using the same pointcut.
The Spring.Aop.IPointcut interface is the central interface, used to target advices to particular types and
methods. The complete interface is shown below:
public interface IPointcut
{
ITypeFilter TypeFilter { get; }
IMethodMatcher MethodMatcher { get; }
}
Splitting the IPointcut interface into two parts allows reuse of type and method matching parts, and fine-grained
composition operations (such as performing a "union" with another method matcher).
The ITypeFilter interface is used to restrict the pointcut to a given set of target classes. If the Matches() method
always returns true, all target types will be matched:
public interface ITypeFilter
{
bool Matches(Type type);
}
The IMethodMatcher interface is normally more important. The complete interface is shown below:
public interface IMethodMatcher
{
bool IsRuntime { get; }
bool Matches(MethodInfo method, Type targetType);
bool Matches(MethodInfo method, Type targetType, object[] args);
}
The Matches(MethodInfo, Type) method is used to test whether this pointcut will ever match a given method
on a target type. This evaluation can be performed when an AOP proxy is created, to avoid the need for a test on
every method invocation. If the 2-argument matches method returns true for a given method, and the IsRuntime
property for the IMethodMatcher returns true, the 3-argument matches method will be invoked on every method
invocation. This enables a pointcut to look at the arguments passed to the method invocation immediately before
the target advice is to execute.
Most IMethodMatchers are static, meaning that their IsRuntime property returns false. In this case, the 3-argument
Matches method will never be invoked.
Whenever possible, try to make pointcuts static... this allows the AOP framework to cache the results of pointcut
evaluation when an AOP proxy is created.
13.2.2. Operations on pointcuts
Spring.NET supports operations on pointcuts: notably, union and intersection.
Union means the methods that either pointcut matches.
Intersection means the methods that both pointcuts match.
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Union is usually more useful.
Pointcuts can be composed using the static methods in the Spring.Aop.Support.Pointcuts class, or using the
ComposablePointcut class in the same namespace.
13.2.3. Convenience pointcut implementations
Spring.NET provides several convenient pointcut implementations. Some can be used out of the box; others are
intended to be subclassed in application-specific pointcuts.
13.2.3.1. Static pointcuts
Static pointcuts are based on method and target class, and cannot take into account the method's arguments. Static
pointcuts are sufficient--and best--for most usages. It's possible for Spring.NET to evaluate a static pointcut only
once, when a method is first invoked: after that, there is no need to evaluate the pointcut again with each method
invocation.
Let's consider some static pointcut implementations included with Spring.NET.
13.2.3.1.1. Regular expression pointcuts
One obvious way to specify static pointcuts is using regular expressions. Several AOP frameworks besides
Spring.NET make this possible. The Spring.Aop.Support.SdkRegularExpressionMethodPointcut class is a
generic regular expression pointcut, that uses the regular expression classes from the .NET BCL.
Using this class, you can provide a list of pattern Strings. If any of these is a match, the pointcut will evaluate to
true (so the result is effectively the union of these pointcuts.). The matching is done against the full class name
so you can use this pointcut if you would like to apply advice to all the classes in a particular namespace.
The usage is shown below:
<object id="settersAndAbsquatulatePointcut"
type="Spring.Aop.Support.SdkRegularExpressionMethodPointcut, Spring.Aop">
<property name="patterns">
<list>
<value>.*set.*</value>
<value>.*absquatulate</value>
</list>
</property>
</object>
As a convenience, Spring provides the RegularExpressionMethodPointcutAdvisor class that allows us to
reference an IAdvice instance as well as defining the pointcut rules (remember that an IAdvice instance can be
an interceptor, before advice, throws advice etc.) This simplifies wiring, as the one object serves as both pointcut
and advisor, as shown below:
<object id="settersAndAbsquatulateAdvisor"
type="Spring.Aop.Support.RegularExpressionMethodPointcutAdvisor, Spring.Aop">
<property name="advice">
<ref local="objectNameOfAopAllianceInterceptor"/>
</property>
<property name="patterns">
<list>
<value>.*set.*</value>
<value>.*absquatulate</value>
</list>
</property>
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</object>
The RegularExpressionMethodPointcutAdvisor class can be used with any Advice type.
If you only have one pattern you can use the property name pattern and specify a single value instead of using
the property name patterns and specifying a list.
You may also specify a Regex object from the System.Text.RegularExpressions namespace. The built in
RegexConverter class will perform the conversion. See Section 6.4, “Built-in TypeConverters” for more
information on Spring's build in type converters. The Regex object is created as any other object within the IoC
container. Using an inner-object definition for the Regex object is a handy way to keep the definition close to the
PointcutAdvisor declaration. Note that the class SdkRegularExpressionMethodPointcut has a DefaultOptions
property to set the regular expression options if they are not explicitly specified in the constructor.
13.2.3.1.2. Attribute pointcuts
Pointcuts can be specified by matching an attribute type that is associated with a method. Advice associated
with this pointcut can then read the metadata associated with the attribute to configure itself. The class
AttributeMatchMethodPointcut provides this functionality. Sample usage that will match all methods that have
the attribute Spring.Attributes.CacheAttribute is shown below.
<object id="cachePointcut" type="Spring.Aop.Support.AttributeMatchMethodPointcut, Spring.Aop">
<property name="Attribute" value="Spring.Attributes.CacheAttribute, Spring.Core"/>
</object>
This can be used with a DefaultPointcutAdvisor as shown below
<object id="cacheAspect" type="Spring.Aop.Support.DefaultPointcutAdvisor, Spring.Aop">
<property name="Pointcut">
<object type="Spring.Aop.Support.AttributeMatchMethodPointcut, Spring.Aop">
<property name="Attribute" value="Spring.Attributes.CacheAttribute, Spring.Core"/>
</object>
</property>
<property name="Advice" ref="aspNetCacheAdvice"/>
</object>
where aspNetCacheAdvice is an implementation of an IMethodInterceptor that caches method return values.
See the SDK docs for Spring.Aop.Advice.CacheAdvice for more information on this particular advice.
As a convenience the class AttributeMatchMethodPointcutAdvisor is provided to defining an attribute based
Advisor as a somewhat shorter alternative to using the generic DefaultPointcutAdvisor. An example is shown
below.
<object id="AspNetCacheAdvice" type="Spring.Aop.Support.AttributeMatchMethodPointcutAdvisor, Spring.Aop">
<property name="advice">
<object type="Aspect.AspNetCacheAdvice, Aspect"/>
</property>
<property name="attribute" value="Framework.AspNetCacheAttribute, Framework" />
</object>
13.2.3.2. Dynamic Pointcuts
Dynamic pointcuts are costlier to evaluate than static pointcuts. They take into account method arguments, as
well as static information. This means that they must be evaluated with every method invocation; the result cannot
be cached, as arguments will vary.
The main example is the control flow pointcut.
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13.2.3.2.1. Control Flow Pointcuts
Spring.NET control flow pointcuts are conceptually similar to AspectJ cflow pointcuts, although less powerful.
(There is currently no way to specify that a pointcut executes below another pointcut.). A control flow pointcut
is dynamic because it is evaluated against the current call stack for each method invocation. For example, if
method ClassA.A() calls ClassB.B() then the execution of ClassB.B() has occurred in ClassA.A()'s control flow. A
control flow pointcut allows advice to be applied to the method ClassA.A() but only when called from ClassB.B()
and not when ClassA.A() is executed from another call stack. Control flow pointcuts are specified using the
Spring.Aop.Support.ControlFlowPointcut class.
Note
Control flow pointcuts are significantly more expensive to evaluate at runtime than even other
dynamic pointcuts.
When using control flow point cuts some attention should be paid to the fact that at runtime the JIT compiler
can inline the methods, typically for increased performance, but with the consequence that the method no longer
appears in the current call stack. This is because inlining takes the callee's IL code and inserts it into the caller's
IL code effectively removing the method call. The information returned from System.Diagnostics.StackTrace,
used in the implementation of ControlFlowPointcut is subject to these optimizations and therefore a control
flow pointcut will not match if the method has been inlined.
Generally speaking, a method will be a candidate for inlining when its code is 'small', just a few lines of
code (less than 32 bytes of IL). For some interesting reading on this process read David Notario's blog entries
(JIT Optimizations I and JIT Optimizations II). Additionally, when an assembly is compiled with a Release
configuration the assembly metadata instructs the CLR to enable JIT optimizations. When compiled with a Debug
configuration the CLR will disable (some?) these optimizations. Empirically, method inlining is turned off in a
Debug configuration.
The way to ensure that your control flow pointcut will not be overlooked because of method
inlining is to apply the System.Runtime.CompilerServices.MethodImplAttribute attribute with the value
MethodImplOptions.NoInlining. In this (somewhat artificial) simple example, if the code is compiled in release
mode it will not match a control flow pointcut for the method "GetAge".
public int GetAge(IPerson person)
{
return person.GetAge();
}
However, applying the attributes as shown below will prevent the method from being inlined even in a release
build.
[MethodImpl(MethodImplOptions.NoInlining)]
public int GetAge(IPerson person)
{
return person.GetAge();
}
13.2.4. Custom pointcuts
Because pointcuts in Spring.NET are .NET types, rather than language features (as in AspectJ) it is possible
to declare custom pointcuts, whether static or dynamic. However, there is no support out of the box for the
sophisticated pointcut expressions that can be coded in the AspectJ syntax. However, custom pointcuts in
Spring.NET can be as arbitrarily complex as any object model.
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Spring.NET provides useful pointcut superclasses to help you to implement your own pointcuts.
Because static pointcuts are the most common and generally useful pointcut type, you'll probably subclass
StaticMethodMatcherPointcut, as shown below. This requires you to implement just one abstract method
(although it is possible to override other methods to customize behaviour):
public class TestStaticPointcut : StaticMethodMatcherPointcut {
public override bool Matches(MethodInfo method, Type targetType) {
// return true if custom criteria match
}
}
13.3. Advice API in Spring.NET
Let's now look at how Spring.NET AOP handles advice.
13.3.1. Advice Lifecycle
Spring.NET advices can be shared across all advised objects, or unique to each advised object. This corresponds
to per-class or per-instance advice.
Per-class advice is used most often. It is appropriate for generic advice such as transaction advisors. These do not
depend on the state of the proxied object or add new state; they merely act on the method and arguments.
Per-instance advice is appropriate for introductions, to support mixins. In this case, the advice adds state to the
proxied object.
It's possible to use a mix of shared and per-instance advice in the same AOP proxy.
13.3.2. Advice types
Spring.NET provides several advice types out of the box, and is extensible to support arbitrary advice types. Let
us look at the basic concepts and standard advice types.
13.3.2.1. Interception Around Advice
The most fundamental advice type in Spring.NET is interception around advice.
Spring.NET is compliant with the AOP Alliance interface for around advice using method interception. Around
advice is implemented using the following interface:
public interface IMethodInterceptor : IInterceptor
{
object Invoke(IMethodInvocation invocation);
}
The IMethodInvocation argument to the Invoke() method exposes the method being invoked; the target
joinpoint; the AOP proxy; and the arguments to the method. The Invoke() method should return the invocation's
result: the return value of the joinpoint.
A simple IMethodInterceptor implementation looks as follows:
public class DebugInterceptor : IMethodInterceptor {
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public object Invoke(IMethodInvocation invocation) {
Console.WriteLine("Before: invocation=[{0}]", invocation);
object rval = invocation.Proceed();
Console.WriteLine("Invocation returned");
return rval;
}
}
Note the call to the IMethodInvocation's Proceed() method. This proceeds down the interceptor chain towards the
joinpoint. Most interceptors will invoke this method, and return its return value. However, an IMethodInterceptor,
like any around advice, can return a different value or throw an exception rather than invoke the Proceed()
method. However, you don't want to do this without good reason!
13.3.2.2. Before advice
A simpler advice type is a before advice. This does not need an IMethodInvocation object, since it will only
be called before entering the method.
The main advantage of a before advice is that there is no need to invoke the Proceed()method, and therefore no
possibility of inadvertently failing to proceed down the interceptor chain.
The IMethodBeforeAdvice interface is shown below.
public interface IMethodBeforeAdvice : IBeforeAdvice
{
void Before(MethodInfo method, object[] args, object target);
}
Note the return type is void. Before advice can insert custom behaviour before the joinpoint executes, but cannot
change the return value. If a before advice throws an exception, this will abort further execution of the interceptor
chain. The exception will propagate back up the interceptor chain. If it is unchecked, or on the signature of the
invoked method, it will be passed directly to the client; otherwise it will be wrapped in an unchecked exception
by the AOP proxy.
An example of a before advice in Spring.NET, which counts all methods that return normally:
public class CountingBeforeAdvice : IMethodBeforeAdvice {
private int count;
public void Before(MethodInfo method, object[] args, object target) {
++count;
}
public int Count {
get { return count; }
}
}
Before advice can be used with any pointcut.
13.3.2.3. Throws advice
Throws advice is invoked after the return of the joinpoint if the joinpoint threw an exception. The
Spring.Aop.IThrowsAdvice interface does not contain any methods: it is a tag interface identifying that the
implementing advice object implements one or more typed throws advice methods. These throws advice methods
must be of the form:
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AfterThrowing([MethodInfo method, Object[] args, Object target], Exception subclass)
Throws-advice methods must be named 'AfterThrowing'. The return value will be ignored by the Spring.NET
AOP framework, so it is typically void. With regard to the method arguments, only the last argument is required.
Thus there are exactly one or four arguments, depending on whether the advice method is interested in the method,
method arguments and the target object.
The following method snippets show examples of throws advice.
This advice will be invoked if a RemotingException is thrown (including subclasses):
public class RemoteThrowsAdvice : IThrowsAdvice {
public void AfterThrowing(RemotingException ex) {
// Do something with remoting exception
}
}
The following advice is invoked if a SqlException is thrown. Unlike the above advice, it declares 4 arguments,
so that it has access to the invoked method, method arguments and target object:
public class SqlExceptionThrowsAdviceWithArguments : IThrowsAdvice {
public void AfterThrowing(MethodInfo method, object[] args, object target, SqlException ex) {
// Do something will all arguments
}
}
The final example illustrates how these two methods could be used in a single class, which handles both
RemotingException and SqlException. Any number of throws advice methods can be combined in a single class,
as can be seen in the following example.
public class CombinedThrowsAdvice : IThrowsAdvice {
public void AfterThrowing(RemotingException ex)
// Do something with remoting exception
}
{
public void AfterThrowing(MethodInfo method, object[] args, object target, SqlException ex) {
// Do something will all arguments
}
}
Finally, it is worth stating that throws advice is only applied to the actual exception being thrown.
What does this mean? Well, it means that if you have defined some throws advice that handles
RemotingExceptions, the applicable AfterThrowing method will only be invoked if the type of the thrown
exception is RemotingException... if a RemotingException has been thrown and subsequently wrapped
inside another exception before the exception bubbles up to the throws advice interceptor, then the throws
advice that handles RemotingExceptions will never be called. Consider a business method that is advised
by throws advice that handles RemotingExceptions; if during the course of a method invocation said
business method throws a RemoteException... and subsequently wraps said RemotingException inside a
business-specific BadConnectionException (see the code snippet below) before throwing the exception,
then the throws advice will never be able to respond to the RemotingException... because all the throws
advice sees is a BadConnectionException. The fact that the RemotingException is wrapped up inside the
BadConnectionException is immaterial.
public void BusinessMethod()
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{
try
{
// do some business operation...
}
catch (RemotingException ex)
{
throw new BadConnectionException("Couldn't connect.", ex);
}
}
Note
Please note that throws advice can be used with any pointcut.
13.3.2.4. After Returning advice
An after returning advice in Spring.NET must implement the Spring.Aop.IAfterReturningAdvice interface,
shown below:
public interface IAfterReturningAdvice : IAdvice
{
void AfterReturning(object returnValue, MethodBase method, object[] args, object target);
}
An after returning advice has access to the return value (which it cannot modify), invoked method, methods
arguments and target.
The following after returning advice counts all successful method invocations that have not thrown exceptions:
public class CountingAfterReturningAdvice : IAfterReturningAdvice {
private int count;
public void AfterReturning(object returnValue, MethodBase m, object[] args, object target) {
++count;
}
public int Count {
get { return count; }
}
}
This advice doesn't change the execution path. If it throws an exception, this will be thrown up the interceptor
chain instead of the return value.
Note
Please note that after-returning advice can be used with any pointcut.
13.3.2.5. Advice Ordering
When multiple pieces of advice want to run on the same joinpoint the precedence is determined by having the
advice implement the IOrdered interface or by specifying order information on an advisor.
13.3.2.6. Introduction advice
Spring.NET allows you to add new methods and properties to an advised class. This would typically be done
when the functionality you wish to add is a crosscutting concern and want to introduce this functionality as a
change to the static structure of the class hierarchy. For example, you may want to cast objects to the introduction
interface in your code. Introductions are also a means to emulate multiple inheritance.
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Introduction advice is defined by using a normal interface declaration that implements the tag interface IAdvice.
Note
The need for implementing this marker interface will likely be removed in future versions.
As an example, consider the interface IAuditable that describes the last modified time of an object.
public interface IAuditable : IAdvice
{
DateTime LastModifiedDate
{
get;
set;
}
}
where
public interface IAdvice
{
}
Access to the advised object can be obtained by implementing the interface ITargetAware
public interface ITargetAware
{
IAopProxy TargetProxy
{
set;
}
}
with the IAopProxy reference providing a layer of indirection through which the advised object can be accessed.
public interface IAopProxy
{
object GetProxy();
}
A simple class that demonstrates this functionality is shown below.
public interface IAuditable : IAdvice, ITargetAware
{
DateTime LastModifiedDate
{
get;
set;
}
}
A class that implements this interface is shown below.
public class AuditableMixin : IAuditable
{
private DateTime date;
private IAopProxy targetProxy;
public AuditableMixin()
{
date = new DateTime();
}
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public DateTime LastModifiedDate
{
get { return date; }
set { date = value; }
}
public IAopProxy TargetProxy
{
set { targetProxy = value; }
}
}
Introduction advice is not associated with a pointcut, since it applies at the class and not the method level. As
such, introductions use their own subclass of the interface IAdvisor, namely IIntroductionAdvisor, to specify
the types that the introduction can be applied to.
public interface IIntroductionAdvisor : IAdvisor
{
ITypeFilter TypeFilter { get; }
Type[] Interfaces { get; }
void ValidateInterfaces();
}
The TypeFilter property returns the filter that determines which target classes this introduction should apply to.
The Interfaces property returns the interfaces introduced by this advisor.
The ValidateInterfaces() method is used internally to see if the introduced interfaces can be implemented by
the introduction advice.
Spring.NET provides a default implementation of this interface (the DefaultIntroductionAdvisor class) that
should be sufficient for the majority of situations when you need to use introductions. The most simple
implementation of an introduction advisor is a subclass that simply passes a new instance the base constructor.
Passing a new instance is important since we want a new instance of the mixin classed used for each advised object.
public class AuditableAdvisor : DefaultIntroductionAdvisor
{
public AuditableAdvisor() : base(new AuditableMixin())
{
}
}
Other constructors let you explicitly specify the interfaces of the class that will be introduced. See the SDK
documentation for more details.
We can apply this advisor Programatically, using the IAdvised.AddIntroduction(), method, or (the
recommended way) in XML configuration using the IntroductionNames property on ProxyFactoryObject,
which will be discussed later.
Unlike the AOP implementation in the Spring Framework for Java, introduction advice in Spring.NET is not
implemented as a specialized type of interception advice. The advantage of this approach is that introductions
are not kept in the interceptor chain, which allows some significant performance optimizations. When a method
is called that has no interceptors, a direct call is used instead of reflection regardless of whether the target
method is on the target object itself or one of the introductions. This means that introduced methods perform
the same as target object methods, which could be useful for adding introductions to fine grained objects. The
disadvantage is that if the mixin functionality would benefit from having access to the calling stack, it is not
available. Introductions with this functionality will be addressed in a future version of Spring.NET AOP.
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13.4. Advisor API in Spring.NET
In Spring.NET, an advisor is a modularization of an aspect. Advisors typically incorporate both an advice and
a pointcut.
Apart from the special case of introductions, any advisor can be used with any advice. The
Spring.Aop.Support.DefaultPointcutAdvisor class is the most commonly used advisor implementation. For
example, it can be used with a IMethodInterceptor, IBeforeAdvice or IThrowsAdvice and any pointcut
definition.
Other convenience implementations provided are: AttributeMatchMethodPointcutAdvisor shown in
usage previously in Section 13.2.3.1.2, “Attribute pointcuts” for use with attribute based pointcuts.
RegularExpressionMethodPointcutAdvisor that will apply pointcuts based on the matching a regular expression
to method names.
It is possible to mix advisor and advice types in Spring.NET in the same AOP proxy. For example, you could
use a interception around advice, throws advice and before advice in one proxy configuration: Spring.NET will
automatically create the necessary interceptor chain.
13.5. Using the ProxyFactoryObject to create AOP proxies
If you're using the Spring.NET IoC container for your business objects - generally a good idea - you will want
to use one of Spring.NET's AOP-specific IFactoryObject implementations (remember that a factory object
introduces a layer of indirection, enabling it to create objects of a different type - Section 5.3.9, “Setting a reference
using the members of other objects and classes.”).
The basic way to create an AOP proxy in Spring.NET is to use the Spring.Aop.Framework.ProxyFactoryObject
class. This gives complete control over ordering and application of the pointcuts and advice that will apply to
your business objects. However, there are simpler options that are preferable if you don't need such control.
13.5.1. Basics
The ProxyFactoryObject, like other Spring.NET IFactoryObject implementations, introduces a level of
indirection. If you define a ProxyFactoryObject with name foo, what objects referencing foo see is not the
ProxyFactoryObject instance itself, but an object created by the ProxyFactoryObject's implementation of the
GetObject() method. This method will create an AOP proxy wrapping a target object.
One of the most important benefits of using a ProxyFactoryObject or other IoC-aware classes that create AOP
proxies, is that it means that advice and pointcuts can also be managed by IoC. This is a powerful feature, enabling
certain approaches that are hard to achieve with other AOP frameworks. For example, an advice may itself
reference application objects (besides the target, which should be available in any AOP framework), benefiting
from all the pluggability provided by Dependency Injection.
13.5.2. ProxyFactoryObject Properties
Like most IFactoryObject implementations provided with Spring.NET, the ProxyFactoryObject is itself a
Spring.NET configurable object. Its properties are used to:
• Specify the target object that is to be proxied.
• Specify the advice that is to be applied to the proxy.
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Some key properties are inherited from the Spring.Aop.Framework.ProxyConfig class: this class is the superclass
for all AOP proxy factories in Spring.NET. Some of the key properties include:
• ProxyTargetType: a boolean value that should be set to true if the target class is to be proxied directly, as
opposed to just proxying the interfaces exposed on the target class.
• Optimize: whether to apply aggressive optimization to created proxies. Don't use this setting unless you
understand how the relevant AOP proxy handles optimization. The exact meaning of this flag will differ
between proxy implementations and will generally result in a trade off between proxy creation time and runtime
performance. Optimizations may be ignored by certain proxy implementations and may be disabled silently
based on the value of other properties such as ExposeProxy.
• IsFrozen: whether advice changes should be disallowed once the proxy factory has been configured. The
default is false.
• ExposeProxy: whether the current proxy should be exposed via the AopContext so that it can be accessed by
the target. (It's available via the IMethodInvocation without the need for the AopContext.) If a target needs to
obtain the proxy and ExposeProxy is true, the target can use the AopContext.CurrentProxy property.
• AopProxyFactory: the implementation of IAopProxyFactory to use when generating a proxy. Offers a way
of customizing whether to use remoting proxies, IL generation or any other proxy strategy. The default
implementation will use IL generation to create composition-based proxies.
Other properties specific to the ProxyFactoryObject class include:
• ProxyInterfaces: the array of string interface names we're proxying.
• InterceptorNames: string array of IAdvisor, interceptor or other advice names to apply. Ordering is
significant... first come, first served that is. The first interceptor in the list will be the first to be able to interceptor
the invocation (assuming it concerns a regular MethodInterceptor or BeforeAdvice).
The names are object names in the current container, including objectnames from container hierarchies. You
can't mention object references here since doing so would result in the ProxyFactoryObject ignoring the
singleton setting of the advise.
• IntroductionNames: The names of objects in the container that will be used as introductions to the target
object. If the object referred to by name does not implement the IIntroductionAdvisor it will be passed to the
default constructor of DefaultIntroductionAdvisor and all of the objects interfaces will be added to the target
object. Objects that implement the IIntroductionAdvisor interface will be used as is, giving you a finer level
of control over what interfaces you may want to expose and the types for which they will be matched against.
• IsSingleton: whether or not the factory should return a single proxy object, no matter how often the
GetObject() method is called. Several IFactoryObject implementations offer such a method. The default
value is true. If you would like to be able to apply advice on a per-proxy object basis, use a IsSingleton value
of false and a IsFrozen value of false. If you want to use stateful advice--for example, for stateful mixins-use prototype advices along with a IsSingleton value of false.
13.5.3. Proxying Interfaces
Let's look at a simple example of ProxyFactoryObject in action. This example involves:
• A target object that will be proxied. This is the "personTarget" object definition in the example below.
• An IAdvisor and an IInterceptor used to provide advice.
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• An AOP proxy object definition specifying the target object (the personTarget object) and the interfaces to
proxy, along with the advices to apply.
<object id="personTarget" type="MyCompany.MyApp.Person, MyCompany">
<property name="name" value="Tony"/>
<property name="age" value="51"/>
</object>
<object id="myCustomInterceptor" type="MyCompany.MyApp.MyCustomInterceptor, MyCompany">
<property name="customProperty" value="configuration string"/>
</object>
<object id="debugInterceptor" type="Spring.Aop.Advice.DebugAdvice, Spring.Aop">
</object>
<object id="person" type="Spring.Aop.Framework.ProxyFactoryObject, Spring.Aop">
<property name="proxyInterfaces" value="MyCompany.MyApp.IPerson"/>
<property name="target" ref="personTarget"/>
<property name="interceptorNames">
<list>
<value>debugInterceptor</value>
<value>myCustomInterceptor</value>
</list>
</property>
</object>
Note that the InterceptorNames property takes a list of strings: the object names of the interceptor or advisors
in the current context. Advisors, interceptors, before, after returning and throws advice objects can be used. The
ordering of advisors is significant.
You might be wondering why the list doesn't hold object references. The reason for this is that if the
ProxyFactoryObject's singleton property is set to false, it must be able to return independent proxy instances.
If any of the advisors is itself a prototype, an independent instance would need to be returned, so it's necessary
to be able to obtain an instance of the prototype from the context; holding a reference isn't sufficient.
The "person" object definition above can be used in place of an IPerson implementation, as follows:
IPerson person = (IPerson) factory.GetObject("person");
Other objects in the same IoC context can express a strongly typed dependency on it, as with an ordinary .NET
object:
<object id="personUser" type="MyCompany.MyApp.PersonUser, MyCompany">
<property name="person" ref="person"/>
</object>
The PersonUser class in this example would expose a property of type IPerson. As far as it's concerned, the AOP
proxy can be used transparently in place of a "real" person implementation. However, its type would be a proxy
type. It would be possible to cast it to the IAdvised interface (discussed below).
It's possible to conceal the distinction between target and proxy using an anonymous inline object, as follows.
(for more information on inline objects see Section 5.3.2.3, “Inline objects”.) Only the ProxyFactoryObject
definition is different; the advice is included only for completeness:
<object id="myCustomInterceptor" type="MyCompany.MyApp.MyCustomInterceptor, MyCompany">
<property name="customProperty" value="configuration string"/>
</object>
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<object id="debugInterceptor" type="Spring.Aop.Advice.DebugAdvice, Spring.Aop">
</object>
<object id="person" type="Spring.Aop.Framework.ProxyFactoryObject, Spring.Aop">
<property name="proxyInterfaces" value="MyCompany.MyApp.IPerson"/>
<property name="target">
<!-- Instead of using a reference to target, just use an inline object -->
<object type="MyCompany.MyApp.Person, MyCompany">
<property name="name" value="Tony"/>
<property name="age" value="51"/>
</object>
</property>
<property name="interceptorNames">
<list>
<value>debugInterceptor</value>
<value>myCustomInterceptor</value>
</list>
</property>
</object>
This has the advantage that there's only one object of type Person: useful if we want to prevent users of the
application context obtaining a reference to the un-advised object, or need to avoid any ambiguity with Spring
IoC autowiring. There's also arguably an advantage in that the ProxyFactoryObject definition is self-contained.
However, there are times when being able to obtain the un-advised target from the factory might actually be an
advantage: for example, in certain test scenarios.
13.5.1. Applying advice on a per-proxy basis.
Let's look at an example of configuring the proxy objects retrieved from ProxyFactoryObject.
<!-- create the object to reference -->
<object id="RealObjectTarget" type="MyRealObject" singleton="false"/>
<!-- create the proxied object for everyone to use-->
<object id="MyObject" type="Spring.Aop.Framework.ProxyFactoryObject, Spring.Aop">
<property name="proxyInterfaces" value="MyInterface" />
<property name="isSingleton" value="false"/>
<property name="targetName" value="RealObjectTarget" />
</object>
If you are using a prototype as the target you must set the TargetName property with the name/object id of your
object and not use the property Target with a reference to that object. This will then allow a new proxy to be
created around a new prototype target instance.
Consider the above Spring.Net object configuration. Notice that the IsSingleton property of the
ProxyFactoryObject instance is set to false. This means that each proxy object will be unique. Thus, you can
configure each proxy object with its' own individual advice(s) using the following syntax
// Will return un-advised instance of proxy object
MyInterface myProxyObject1 = (MyInterface)ctx.GetObject("MyObject");
// myProxyObject1 instance now has an advice attached to it.
IAdvised advised = (IAdvised)myProxyObject1;
advised.AddAdvice( new DebugAdvice() );
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// Will return a new, un-advised instance of proxy object
MyInterface myProxyObject2 = (MyInterface)ctx.GetObject("MyObject");
13.5.4. Proxying Classes
What if you need to proxy a class, rather than one or more interfaces?
Imagine that in our example above, there was no IPerson interface, rather we needed to advise a class called
Person that didn't implement any business interface. In this case the ProxyFactoryObject will proxy all public
virtual methods and properties if no interfaces are explicitly specified or if no interfaces are found to be present
on the target object. One can configure Spring.NET to force the use of class proxies, rather than interface proxies,
by setting the ProxyTargetType property on the ProxyFactoryObject above to true.
Class proxying works by generating a subclass of the target class at runtime. Spring.NET configures this generated
subclass to delegate method calls to the original target: the subclass is used to implement the Decorator pattern,
weaving in the advice.
Class proxying should generally be transparent to users. However, there is an important issue to consider:
Non-virtual methods can't be advised, as they can't be overridden. This may be a limiting factor when using
existing code as it has been common practice not to declare methods as virtual by default.
13.5.5. Concise proxy definitions
Especially when defining transactional proxies, if you do not make use of the transaction namespace, you may
end up with many similar proxy definitions. The use of parent and child object definitions, along with inner object
definitions, can result in much cleaner and more concise proxy definitions.
First a parent, template, object definition is created for the proxy:
<object id="txProxyTemplate" abstract="true"
type="Spring.Transaction.Interceptor.TransactionProxyFactoryObject, Spring.Data">
<property name="PlatformTransactionManager" ref="adoTransactionManager"/>
<property name="TransactionAttributes">
<name-values>
<add key="*" value="PROPAGATION_REQUIRED"/>
</name-values>
</property>
</object>
This will never be instantiated itself, so may actually be incomplete. Then each proxy which needs to be created
is just a child object definition, which wraps the target of the proxy as an inner object definition, since the target
will never be used on its own anyway.
<object name="testObjectManager" parent="txProxyTemplate">
<property name="Target">
<object type="Spring.Data.TestObjectManager, Spring.Data.Integration.Tests">
<property name="TestObjectDao" ref="testObjectDao"/>
</object>
</property>
</object>
It is of course possible to override properties from the parent template, such as in this case, the transaction
propagation settings:
<object name="testObjectManager" parent="txProxyTemplate">
<property name="Target">
<object type="Spring.Data.TestObjectManager, Spring.Data.Integration.Tests">
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<property name="TestObjectDao" ref="testObjectDao"/>
</object>
</property>
<property name="TransactionAttributes">
<name-values>
<add key="Save*" value="PROPAGATION_REQUIRED"/>
<add key="Delete*" value="PROPAGATION_REQUIRED"/>
<add key="Find*" value="PROPAGATION_REQUIRED,readonly"/>
</name-values>
</property>
</object>
Note that in the example above, we have explicitly marked the parent object definition as abstract by using the
abstract attribute, as described previously, so that it may not actually ever be instantiated. Application contexts
(but not simple object factories) will by default pre-instantiate all singletons. It is therefore important (at least
for singleton object) that if you have a (parent) object definition which you intend to use only as a template, and
this definition specifies a class, you must make sure to set the abstract attribute to true, otherwise the application
context will actually try to pre-instantiate it.
13.6. Proxying mechanisms
Spring creates AOP proxies built at runtime through the use of the TypeBuilder API.
Two types of proxies can be created, composition based or inheritance based. If the target object implements at
least one interface then a composition based proxy will be created, otherwise an inheritance based proxy will
be created.
The composition based proxy is implemented by creating a type that implements all the interfaces specified on the
target object. The actual class name of this dynamic type is 'GUID' like. A private field holds the target object and
the dynamic type implementation will first execute any advice before or after making the target object method
call on the target object.
The inheritance based mechanism creates a dynamic type where that inherits from the target type. This lets you
downcast to the target type if needed. Please note that in both cases a target method implementation that calls
other methods on the target object will not be advised. To force inheritance based proxies you should either set
the ProxyTargetType to true property of a ProxyFactory or set the XML namespace element proxy-target-type
= true when using an AOP schema based configuration.
Note
An important alternative approach to inheritance based proxies is disucssed in the next section.
In .NET 2.0 you can define the assembly level attribute, InternalsVisibleTo, to allow access of internal
interfaces/classes to specified 'friend' assemblies. If you need to create an AOP proxy on an internal
class/interface add the following code, [assembly: InternalsVisibleTo("Spring.Proxy")] and [assembly:
InternalsVisibleTo("Spring.DynamicReflection")] to your to AssemblyInfo file.
13.6.1. InheritanceBasedAopConfigurer
There is an important limitation in the inheritance based proxy as described above, all methods that manipulate
the state of the object should be declared as virtual. Otherwise some method invocations get directed to the private
'target' field member and others to the base class. Winform object are an example of case where this approach
does not apply. To address this limitation, a new post-processing mechanism was introduced in version 1.2 that
creates a proxy type without the private 'target' field. Interception advice is added directly in the method body
before invoking the base class method.
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To use this new inheritance based proxy described in the note above, declare an instance of the
InheritanceBasedAopConfigurer, and IObjectFactoryPostProcessor, in yoru configuraiton file. Here is an
example.
<object type="Spring.Aop.Framework.AutoProxy.InheritanceBasedAopConfigurer, Spring.Aop">
<property name="ObjectNames">
<list>
<value>Form*</value>
<value>Control*</value>
</list>
</property>
<property name="InterceptorNames">
<list>
<value>debugInterceptor</value>
</list>
</property>
</object>
<object id="debugInterceptor" type="AopPlay.DebugInterceptor, AopPlay"/>
This configuraiton style is similar to the autoproxy by name approach described here and is particuarly appropriate
when you want to apply advice to WinForm classes.
13.7. Creating AOP Proxies Programatically with the
ProxyFactory
It's easy to create AOP proxies Programatically using Spring.NET. This enables you to use Spring.NET AOP
without dependency on Spring.NET IoC.
The following listing shows creation of a proxy for a target object, with one interceptor and one advisor. The
interfaces implemented by the target object will automatically be proxied:
ProxyFactory factory = new ProxyFactory(myBusinessInterfaceImpl);
factory.AddAdvice(myMethodInterceptor);
factory.AddAdvisor(myAdvisor);
IBusinessInterface tb = (IBusinessInterface) factory.GetProxy();
The first step is to construct an object of type Spring.Aop.Framework.ProxyFactory. You can create this with a
target object, as in the above example, or specify the interfaces to be proxied in an alternate constructor.
You can add interceptors or advisors, and manipulate them for the life of the ProxyFactory.
There are also convenience methods on ProxyFactory (inherited from AdvisedSupport) allowing you to add
other advice types such as before and throws advice. AdvisedSupport is the superclass of both ProxyFactory
and ProxyFactoryObject.
Note
Integrating AOP proxy creation with the IoC framework is best practice in most applications. We
recommend that you externalize configuration from .NET code with AOP, as in general.
13.8. Manipulating Advised Objects
However you create AOP proxies, you can manipulate them using the Spring.Aop.Framework.IAdvised
interface. Any AOP proxy can be cast to this interface, whatever other interfaces it implements. This interface
includes the following methods and properties:
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public interface IAdvised
{
IAdvisor[] Advisors { get; }
IIntroductionAdvisor[] Introductions { get; }
void
AddInterceptor(IInterceptor interceptor);
void
AddInterceptor(int pos, IInterceptor interceptor);
void
AddAdvisor(IAdvisor advisor);
void
AddAdvisor(int pos, IAdvisor advisor);
void
AddIntroduction(IIntroductionAdvisor advisor);
void
AddIntroduction(int pos, IIntroductionAdvisor advisor);
int IndexOf(IAdvisor advisor);
int IndexOf(IIntroductionAdvisor advisor);
bool RemoveAdvisor(IAdvisor advisor);
void RemoveAdvisor(int index);
bool RemoveInterceptor(IInterceptor interceptor);
bool RemoveIntroduction(IIntroductionAdvisor advisor);
void RemoveIntroduction(int index);
void ReplaceIntroduction(int index, IIntroductionAdvisor advisor);
bool ReplaceAdvisor(IAdvisor a, IAdvisor b);
}
The Advisors property will return an IAdvisor for every advisor, interceptor or other advice type that has been
added to the factory. If you added an IAdvisor, the returned advisor at this index will be the object that you
added. If you added an interceptor or other advice type, Spring.NET will have wrapped this in an advisor with
a IPointcut that always returns true. Thus if you added an IMethodInterceptor, the advisor returned for this
index will be a DefaultPointcutAdvisor returning your IMethodInterceptor and an IPointcut that matches
all types and methods.
The AddAdvisor() methods can be used to add any IAdvisor. Usually this will be the generic
DefaultPointcutAdvisor, which can be used with any advice or pointcut (but not for introduction).
By default, it's possible to add or remove advisors or interceptors even once a proxy has been created. The only
restriction is that it's impossible to add or remove an introduction advisor, as existing proxies from the factory
will not show the interface change. (You can obtain a new proxy from the factory to avoid this problem.)
It's questionable whether it's advisable (no pun intended) to modify advice on a business object in production,
although there are no doubt legitimate usage cases. However, it can be very useful in development: for example,
in tests. I have sometimes found it very useful to be able to add test code in the form of an interceptor or other
advice, getting inside a method invocation I want to test. (For example, the advice can get inside a transaction
created for that method: for example, to run SQL to check that a database was correctly updated, before marking
the transaction for roll back.)
Depending on how you created the proxy, you can usually set a Frozen flag, in which case the IAdvised IsFrozen
property will return true, and any attempts to modify advice through addition or removal will result in an
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AopConfigException.
The ability to freeze the state of an advised object is useful in some cases: For example,
to prevent calling code removing a security interceptor.
13.9. Using the "autoproxy" facility
So far we've considered explicit creation of AOP proxies using a ProxyFactoryObject or similar factory objects.
For applications that would like create many AOP proxies, say across all the classes in a service layer, this
approach can lead to a lengthy configuration file. To simplify the creation of many AOP proxies Spring provides
"autoproxy" capabilities that will automatically proxy object definitions based on higher level criteria that will
group together multiple objects as candidates to be proxied.
This functionality is built on Spring "object post-processor" infrastructure, which enables modification of any
object definition as the container loads. Refer to Section 5.9.1, “Customizing objects with IObjectPostProcessors”
for general information on object post-processors.
In this model, you set up some special object definitions in your XML object definition file configuring the auto
proxy infrastructure. This allows you just to declare the targets eligible for autoproxying: you don't need to use
ProxyFactoryObject.
• Using an autoproxy creator that refers to specific objects in the current context.
• A special case of autoproxy creation that deserves to be considered separately; autoproxy creation driven by
source-level attributes.
Autoproxying in general has the advantage of making it impossible for callers or dependencies to obtain an unadvised object. Calling GetObject("MyBusinessObject1") on an ApplicationContext will return an AOP proxy,
not the target business object. The "inline object" idiom shown earlier in Section 13.5.3, “Proxying Interfaces”
also offers this benefit.)
13.9.1. Autoproxy object definitions
The namespace Spring.Aop.Framework.AutoProxy provides generic autoproxy infrastructure, should you
choose to write your own autoproxy implementations, as well as several out-of-the-box implementations. Two
implementations are provided, ObjectNameAutoProxyCreator and DefaultAdvisorAutoProxyCreator. These
are discussed in the following sections.
13.9.1.1. ObjectNameAutoProxyCreator
The ObjectNameAutoProxyCreator automatically creates AOP proxies for object with names matching literal
values or wildcards. The pattern matching expressions supported are of the form "*name", "name*", and "*name*"
and exact name matching, i.e. "name". The following simple classes are used to demonstrate this autoproxy
functionality.
public enum Language
{
English = 1,
Portuguese = 2,
Italian = 3
}
public interface IHelloWorldSpeaker
{
void SayHello();
}
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public class HelloWorldSpeaker : IHelloWorldSpeaker
{
private Language language;
public Language Language
{
set { language = value; }
get { return language; }
}
public void SayHello()
{
switch (language)
{
case Language.English:
Console.WriteLine("Hello World!");
break;
case Language.Portuguese:
Console.WriteLine("Oi Mundo!");
break;
case Language.Italian:
Console.WriteLine("Ciao Mondo!");
break;
}
}
}
public class DebugInterceptor : IMethodInterceptor
{
public object Invoke(IMethodInvocation invocation)
{
Console.WriteLine("Before: " + invocation.Method.ToString());
object rval = invocation.Proceed();
Console.WriteLine("After: " + invocation.Method.ToString());
return rval;
}
}
The following XML is used to automatically create an AOP proxy and apply a Debug interceptor to object
definitions whose names match "English*" and "PortugueseSpeaker".
<object id="ProxyCreator" type="Spring.Aop.Framework.AutoProxy.ObjectNameAutoProxyCreator, Spring.Aop">
<property name="ObjectNames">
<list>
<value>English*</value>
<value>PortugeseSpeaker</value>
</list>
</property>
<property name="InterceptorNames">
<list>
<value>debugInterceptor</value>
</list>
</property>
</object>
<object id="debugInterceptor" type="AopPlay.DebugInterceptor, AopPlay"/>
<object id="EnglishSpeakerOne" type="AopPlay.HelloWorldSpeaker, AopPlay">
<property name="Language" value="English"/>
</object>
<object id="EnglishSpeakerTwo" type="AopPlay.HelloWorldSpeaker, AopPlay">
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<property name="Language" value="English"/>
</object>
<object id="PortugeseSpeaker" type="AopPlay.HelloWorldSpeaker, AopPlay">
<property name="Language" value="Portuguese"/>
</object>
<object id="ItalianSpeakerOne" type="AopPlay.HelloWorldSpeaker, AopPlay">
<property name="Language" value="Italian"/>
</object>
As with ProxyFactoryObject, there is an InterceptorNames property rather than a list of interceptors, to allow
correct behavior for prototype advisors. Named "interceptors" can be advisors or any advice type.
The same advice will be applied to all matching objects. Note that if advisors are used (rather than the interceptor
in the above example), the pointcuts may apply differently to different objects.
Running the following simple program demonstrates the application of the AOP interceptor.
IApplicationContext ctx = ContextRegistry.GetContext();
IDictionary speakerDictionary = ctx.GetObjectsOfType(typeof(IHelloWorldSpeaker));
foreach (DictionaryEntry entry in speakerDictionary)
{
string name = (string)entry.Key;
IHelloWorldSpeaker worldSpeaker = (IHelloWorldSpeaker)entry.Value;
Console.Write(name + " says; ");
worldSpeaker.SayHello();
}
The output is shown below
ItalianSpeakerOne says; Ciao Mondo!
EnglishSpeakerTwo says; Before: Void SayHello()
Hello World!
After: Void SayHello()
PortugeseSpeaker says; Before: Void SayHello()
Oi Mundo!
After: Void SayHello()
EnglishSpeakerOne says; Before: Void SayHello()
Hello World!
After: Void SayHello()
13.9.1.2. DefaultAdvisorAutoProxyCreator
A more general and extremely powerful auto proxy creator is DefaultAdvisorAutoProxyCreator. This will
automatically apply eligible advisors in the current application context, without the need to include specific
object names in the autoproxy advisor's object definition. It offers the same merit of consistent configuration and
avoidance of duplication as ObjectNameAutoProxyCreator.
Using this mechanism involves:
• Specifying a DefaultAdvisorAutoProxyCreator object definition
• Specifying any number of Advisors in the same or related contexts. Note that these must be Advisors, not
just interceptors or other advices. This is necessary because there must be a pointcut to evaluate, to check the
eligibility of each advice to candidate object definitions.
The DefaultAdvisorAutoProxyCreator will automatically evaluate the pointcut contained in each advisor, to
see what (if any) advice it should apply to each object defined in the application context.
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This means that any number of advisors can be applied automatically to each business object. If no pointcut in
any of the advisors matches any method in a business object, the object will not be proxied.
The DefaultAdvisorAutoProxyCreator is very useful if you want to apply the same advice consistently to many
business objects. Once the infrastructure definitions are in place, you can simply add new business objects without
including specific proxy configuration. You can also drop in additional aspects very easily--for example, tracing
or performance monitoring aspects--with minimal change to configuration.
The following example demonstrates the use of DefaultAdvisorAutoProxyCreator. Expanding on the previous
example code used to demonstrate ObjectNameAutoProxyCreator we will add a new class, SpeakerDao, that acts
as a Data Access Object to find and store IHelloWorldSpeaker objects.
public interface ISpeakerDao
{
IList FindAll();
IHelloWorldSpeaker Save(IHelloWorldSpeaker speaker);
}
public class SpeakerDao : ISpeakerDao
{
public System.Collections.IList FindAll()
{
Console.WriteLine("Finding speakers...");
// just a demo...fake the retrieval.
Thread.Sleep(10000);
HelloWorldSpeaker speaker = new HelloWorldSpeaker();
speaker.Language = Language.Portuguese;
IList list = new ArrayList();
list.Add(speaker);
return list;
}
public IHelloWorldSpeaker Save(IHelloWorldSpeaker speaker)
{
Console.WriteLine("Saving speaker...");
// just a demo...not really saving...
return speaker;
}
}
The XML configuration specifies two Advisors, that is, the combination of advice (the behavior to add) and a
pointcut (where the behavior should be applied). A RegularExpressionMethodPointcutAdvisor is used as a
convenience to specify the pointcut as a regular expression that matches methods names. Other pointcuts of your
own creation could be used, in which case a DefaultPointcutAdvisor would be used to define the Advisor. The
object definitions for these advisors, advice, and SpeakerDao object are shown below
<object id="SpeachAdvisor" type="Spring.Aop.Support.RegularExpressionMethodPointcutAdvisor, Spring.Aop">
<property name="advice" ref="debugInterceptor"/>
<property name="patterns">
<list>
<value>.*Say.*</value>
</list>
</property>
</object>
<object id="AdoAdvisor" type="Spring.Aop.Support.RegularExpressionMethodPointcutAdvisor, Spring.Aop">
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<property name="advice" ref="timingInterceptor"/>
<property name="patterns">
<list>
<value>.*Find.*</value>
</list>
</property>
</object>
// Advice
<object id="debugInterceptor" type="AopPlay.DebugInterceptor, AopPlay"/>
<object id="timingInterceptor" type="AopPlay.TimingInterceptor, AopPlay"/>
// Speaker DAO Object - has 'FindAll' Method.
<object id="speakerDao" type="AopPlay.SpeakerDao, AopPlay"/>
// HelloWorldSpeaker objects as previously listed.
Adding an instance of DefaultAdvisorAutoProxyCreator to the configuration file
<object id="ProxyCreator" type="Spring.Aop.Framework.AutoProxy.DefaultAdvisorAutoProxyCreator, Spring.Aop"/>
will apply the debug interceptor on all objects in the context that have a method that contains the text "Say" and
apply the timing interceptor on objects in the context that have a method that contains the text "Find". Running
the following code demonstrates this behavior. Note that the "Save" method of SpeakerDao does not have any
advice applied to it.
IApplicationContext ctx = ContextRegistry.GetContext();
IDictionary speakerDictionary = ctx.GetObjectsOfType(typeof(IHelloWorldSpeaker));
foreach (DictionaryEntry entry in speakerDictionary)
{
string name = (string)entry.Key;
IHelloWorldSpeaker worldSpeaker = (IHelloWorldSpeaker)entry.Value;
Console.Write(name + " says; ");
worldSpeaker.SayHello();
}
ISpeakerDao dao = (ISpeakerDao)ctx.GetObject("speakerDao");
IList speakerList = dao.FindAll();
IHelloWorldSpeaker speaker = dao.Save(new HelloWorldSpeaker());
This produces the following output
ItalianSpeakerOne says; Before: Void SayHello()
Ciao Mondo!
After: Void SayHello()
EnglishSpeakerTwo says; Before: Void SayHello()
Hello World!
After: Void SayHello()
PortugeseSpeaker says; Before: Void SayHello()
Oi Mundo!
After: Void SayHello()
EnglishSpeakerOne says; Before: Void SayHello()
Hello World!
After: Void SayHello()
Finding speakers...
Elapsed time = 00:00:10.0154745
Saving speaker...
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The DefaultAdvisorAutoProxyCreator offers support for filtering (using a naming convention so that only certain
advisors are evaluated, allowing use of multiple, differently configured, AdvisorAutoProxyCreators in the same
factory) and ordering. Advisors can implement the Spring.Core.IOrdered interface to ensure correct ordering
if this is an issue. The default is unordered.
13.9.1.3. PointcutFilteringAutoProxyCreator
An AutoProxyCreator that identified objects to proxy by matching a specified IPointcut.
13.9.1.4. TypeNameAutoProxyCreator
An AutoProxyCreator that identifies objects to proxy by matching their Type.FullName against a list of patterns.
13.9.1.5. AttributeAutoProxyCreator
An AutoProxyCreator, that identifies objects to be proxied by checking any System.Attribute defined on a given
type and that types interfaces.
13.9.1.6. AbstractFilteringAutoProxyCreator
The base class for AutoProxyCreator implementations that mark objects eligible for proxying based on arbitrary
criteria.
13.9.1.7. AbstractAutoProxyCreator
This is the superclass of DefaultAdvisorAutoProxyCreator. You can create your own autoproxy creators by
subclassing this class, in the unlikely event that advisor definitions offer insufficient customization to the behavior
of the framework DefaultAdvisorAutoProxyCreator.
13.9.2. Using attribute-driven auto-proxying
A particularly important type of autoproxying is driven by attributes. The programming model is similar to using
Enterprise Services with ServicedComponents.
In this case, you use the DefaultAdvisorAutoProxyCreator, in combination with Advisors that understand
attributes. The Advisor pointcut is identified by the presence of .NET attribute in the source code and it is
configured via the data and/or methods of the attribute. This is a powerful alternative to identifying the advisor
pointcut and advice configuration through traditional property configuration, either programmatic or through
XML based configuration.
Several of the aspect provided with Spring use attribute driven autoproxying. The most prominent example is
Transaction support.
13.10. Using AOP Namespace
The AOP namespace allows you to define an advisor, i.e pointcut + 1 piece of advice, in a more declarative
manner. Under the covers the DefaultAdvisorAutoProxyCreator is being used. Here is an example,
<objects xmlns="http://www.springframework.net"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:aop="http://www.springframework.net/aop">
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<aop:config>
<aop:advisor id="getDescriptionAdvisor" pointcut-ref="getDescriptionCalls" advice-ref="getDescriptionCounter"/
</aop:config>
<object id="getDescriptionCalls"
type="Spring.Aop.Support.SdkRegularExpressionMethodPointcut, Spring.Aop">
<property name="patterns">
<list>
<value>.*GetDescription.*</value>
</list>
</property>
</object>
<object id="getDescriptionCounter" type="Spring.Aop.Framework.CountingBeforeAdvice, Spring.Aop.Tests"/>
<object name="testObject" type="Spring.Objects.TestObject, Spring.Core.Tests"/>
</objects>
In this example, the TestObject, which implements the interface ITestObject, is having AOP advice applied to
it. The method GetDescription() is specified as a regular expression pointcut. The aop:config tag and subsequent
child tag, aop:advisor, brings together the pointcut with the advice.
In order to have Spring.NET recognise the aop namespace, you need to declare the namespace parser in the main
Spring.NET configuration section. For convenience this is shown below. Please refer to the section titled context
configuration for more extensive information..
<configuration>
<configSections>
<sectionGroup name="spring">
<section name="context" type="Spring.Context.Support.ContextHandler, Spring.Core"/>
<section name="objects" type="Spring.Context.Support.DefaultSectionHandler, Spring.Core" />
<section name="parsers" type="Spring.Context.Support.NamespaceParsersSectionHandler, Spring.Core"/>
</sectionGroup>
</configSections>
<spring>
<parsers>
<parser type="Spring.Aop.Config.AopNamespaceParser, Spring.Aop" />
</parsers>
<context>
<resource uri="config://spring/objects"/>
</context>
<objects xmlns="http://www.springframework.net">
...
</objects>
</spring>
</configuration>
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13.11. Using TargetSources
Spring.NET offers the concept of a TargetSource, expressed in the Spring.Aop.ITargetSource interface.
This interface is responsible for returning the "target object" implementing the joinpoint. The TargetSource
implementation is asked for a target instance each time the AOP proxy handles a method invocation.
Developers using Spring.NET AOP don't normally need to work directly with TargetSources, but this provides
a powerful means of supporting pooling, hot swappable and other sophisticated targets. For example, a pooling
TargetSource can return a different target instance for each invocation, using a pool to manage instances.
If you do not specify a TargetSource, a default implementation is used that wraps a local object. The same target
is returned for each invocation (as you would expect).
Let's look at the standard target sources provided with Spring.NET, and how you can use them.
When using a custom target source, your target will usually need to be a prototype rather than a singleton object
definition. This allows Spring.NET to create a new target instance when required.
13.11.1. Hot swappable target sources
The org.Spring.NETframework.aop.target.HotSwappableTargetSource exists to allow the target of an AOP
proxy to be switched while allowing callers to keep their references to it.
Changing the target source's target takes effect immediately. The HotSwappableTargetSource is thread safe.
You can change the target via the swap() method on HotSwappableTargetSource as follows:
HotSwappableTargetSource swapper =
(HotSwappableTargetSource) objectFactory.GetObject("swapper");
object oldTarget = swapper.swap(newTarget);
The XML definitions required look as follows:
<object id="initialTarget" type="MyCompany.OldTarget, MyCompany">
</object>
<object id="swapper"
type="Spring.Aop.Target.HotSwappableTargetSource, Spring.Aop">
<constructor-arg><ref local="initialTarget"/></constructor-arg>
</object>
<object id="swappable"
type="Spring.Aop.Framework.ProxyFactoryObject, Spring.Aop"
>
<property name="targetSource">
<ref local="swapper"/>
</property>
</object>
The above swap() call changes the target of the swappable object. Clients who hold a reference to that object will
be unaware of the change, but will immediately start hitting the new target.
Although this example doesn't add any advice--and it's not necessary to add advice to use a TargetSource--of
course any TargetSource can be used in conjunction with arbitrary advice.
13.11.2. Pooling target sources
Using a pooling target source provides a programming model in which a pool of identical instances is maintained,
with method invocations going to free objects in the pool.
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A crucial difference between Spring.NET pooling and pooling in .NET Enterprise Services pooling is that
Spring.NET pooling can be applied to any PONO. (Plain old .NET object). As with Spring.NET in general, this
service can be applied in a non-invasive way.
Spring.NET provides out-of-the-box support using a pooling implementation based on Jakarta Commons
Pool 1.1, which provides a fairly efficient pooling implementation. It's also possible to subclass
Spring.Aop.Target.AbstractPoolingTargetSource to support any other pooling API.
Sample configuration is shown below:
<object id="businessObjectTarget" type="MyCompany.MyBusinessObject, MyCompany" singleton="false">
... properties omitted
</object>
<object id="poolTargetSource" type="Spring.Aop.Target.SimplePoolTargetSource, Spring.Aop">
<property name="targetObjectName" value="businessObjectTarget"/>
<property name="maxSize" value="25"/>
</object>
<object id="businessObject" type="Spring.Aop.Framework.ProxyFactoryObject, Spring.Aop">
<property name="targetSource" ref="poolTargetSource"/>
<property name="interceptorNames" value="myInterceptor"/>
</object>
Note that the target object--"businessObjectTarget" in the example--must be a prototype. This allows the
PoolingTargetSource implementation to create new instances of the target to grow the pool as necessary.
See the SDK documentation for AbstractPoolingTargetSource and the concrete subclass you wish to use for
information about it's properties: maxSize is the most basic, and always guaranteed to be present.
In this case, "myInterceptor" is the name of an interceptor that would need to be defined in the same IoC context.
However, it isn't necessary to specify interceptors to use pooling. If you want only pooling, and no other advice,
don't set the interceptorNames property at all.
It's possible to configure Spring.NET so as to be able to cast any pooled object to the
Spring.Aop.Target.PoolingConfig interface, which exposes information about the configuration and current
size of the pool through an introduction. You'll need to define an advisor like this:
<object id="poolConfigAdvisor"
type="Spring.Object.Factory.Config.MethodInvokingFactoryObject, Spring.Aop">
<property name="target" ref="poolTargetSource" />
<property name="targetMethod" value="getPoolingConfigMixin" />
</object>
This advisor is obtained by calling a convenience method on the AbstractPoolingTargetSource class, hence the
use of MethodInvokingFactoryObject. This advisor's name ('poolConfigAdvisor' here) must be in the list of
interceptor names in the ProxyFactoryObject exposing the pooled object.
The cast will look as follows:
PoolingConfig conf = (PoolingConfig) objectFactory.GetObject("businessObject");
Console.WriteLine("Max pool size is " + conf.getMaxSize());
Pooling stateless service objects is not usually necessary. We don't believe it should be the default choice, as most
stateless objects are naturally threadsafe, and instance pooling is problematic if resources are cached.
Simpler pooling is available using autoproxying. It's possible to set the TargetSources used by any autoproxy
creator.
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13.11.3. Prototype target sources
Setting up a "prototype" target source is similar to a pooling TargetSource. In this case, a new instance of the
target will be created on every method invocation. Although the cost of creating a new object may not be high,
the cost of wiring up the new object (satisfying its IoC dependencies) may be more expensive. Thus you shouldn't
use this approach without very good reason.
To do this, you could modify the poolTargetSource definition shown above as follows. (the name of the definition
has also been changed, for clarity.)
<object id="prototypeTargetSource"
type="Spring.Aop.Target.PrototypeTargetSource, Spring.Aop">
<property name="targetObjectName" value="businessObject" />
</object>
There is only one property: the name of the target object. Inheritance is used in the TargetSource implementations
to ensure consistent naming. As with the pooling target source, the target object must be a prototype object
definition, the singleton property of the target should be set to false.
13.11.4. ThreadLocal target sources
ThreadLocal target sources are useful if you need an object to be created for each incoming request (per thread that
is). The concept of a ThreadLocal provides a facility to transparently store resource alongside a thread. Setting
up a ThreadLocalTargetSource is pretty much the same as was explained for the other types of target source:
<object id="threadlocalTargetSource"
type="Spring.Aop.Target.ThreadLocalTargetSource, Spring.Aop">
<property name="targetObjectName" value="businessObject" />
</object>
13.12. Defining new Advice types
Spring.NET AOP is designed to be extensible. While the interception implementation strategy is presently used
internally, it is possible to support arbitrary advice types in addition to interception around, before, throws, and
after returning advice, which are supported out of the box.
The Spring.Aop.Framework.Adapter package is an SPI (Service Provider Interface) package allowing support
for new custom advice types to be added without changing the core framework. The only constraint on a custom
Advice type is that it must implement the AopAlliance.Aop.IAdvice tag interface.
Please refer to the Spring.Aop.Framework.Adapter namespace documentation for further information.
13.13. Further reading and resources
The Spring.NET team recommends the excellent AspectJ in Action by Ramnivas Laddad (Manning, 2003) for
an introduction to AOP.
If you are interested in more advanced capabilities of Spring.NET AOP, take a look at the test suite as it illustrates
advanced features not discussed in this document.
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Chapter 14. Aspect Library
14.1. Introduction
Spring provides several aspects in the distribution. The most popular of which is transactional advice, located in
the Spring.Data module. However, the aspects that are documented in this section are those contained within the
Spring.Aop module itself. The aspects in within Spring.Aop.dll are Caching, Exception Handling, Logging, Retry,
and Parameter Validation. Other traditional advice types such as validation, security, and thread management,
will be included in a future release.
14.2. Caching
Caching the return value of a method or the value of a method parameter is a common approach to increase
application performance. Application performance is increased with effective use of caching since layers in the
application that are closer to the user can return information within their own layer as compared to making more
expensive calls to retrieve that information from a lower, and more slow, layer such as a database or a web service.
Caching also can help in terms of application scalability, which is generally the more important concern.
The caching support in Spring.NET consists of base cache interfaces that can be used to specify a specific storage
implementation of the cache and also an aspect that determines where to apply the caching functionality and its
configuration.
The base cache interface that any cache implementation should implement is Spring.Caching.ICache
located in Spring.Core. Two implementations are provided, Spring.Caching.AspNetCache located in
Spring.Web which stores cache entries within an ASP.NET cache and a simple implementation,
Spring.Caching.NonExpiringCache that stores cache entries in memory and never expires these entries. Custom
implementations based on 3rd party implementations, such as Oracle Coherence, or memcached, can be used by
implementing the ICache interface.
The cache aspect is Spring.Aspects.Cache.CacheAspect located in Spring.Aop. It consists of three pieces of
functionality, the ability to cache return values, method parameters, and explicit eviction of an item from the
cache. The aspect currently relies on using attributes to specify the pointcut as well as the behavior, much like
the transactional aspect. Future versions will allow for external configuration of the behavior so you can apply
caching to a code base without needing to use attributes in the code.
The following attributes are available
• CacheResult - used to cache the return value
• CacheResultItems - used when returning a collection as a return value
• CacheParameter - used to cache a method parameter
• InvalidateCache - used to indicate one or more cache items should be invalidated.
Each CacheResult, CacheResultItems, and CacheParameter attributes define the following properties.
• CacheName - the name of the cache implementation to use
• Key - a string representing a Spring Expression Language (SpEL) expression used as the key in the cache.
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• Condition - a SpEL expression that should be evaluated in order to determine whether the item should be
cached.
• TimeToLive - The amount of time an object should remain in the cache (in seconds).
The InvalidateCache attribute has properties for the CacheName, the Key as well as the Condition, with the
same meanings as listed previously.
Each ICache implementation will have properties that are specific to a caching technology. In the case of
AspNetCache, the two important properties to configure are:
• SlidingExperation - If this property value is set to true, every time the marked object is accessed it's
TimeToLive value is reset to its original value
• Priority - the cache item priority controlling how likely an object is to be removed from an associated cache
when the cache is being purged.
• TimeToLive - The amount of time an object should remain in the cache (in seconds).
The values of the Priority enumeration are
• Low - low likelihood of deletion when cache is purged.
• Normal - default priority for deletion when cache is purged.
• High - high likelihood of deletion when cache is purged.
• NotRemovable - cache item not deleted when cache is purged.
An important element of the applying these attributes is the use of the expression language that allows for calling
context information to drive the caching actions. Here is an example taken from the Spring Air sample application
of the AirportDao implementation that implements an interface with the method GetAirport(long id).
[CacheResult("AspNetCache", "'Airport.Id=' + #id", TimeToLive = "0:1:0")]
public Airport GetAirport(long id)
{
// implementation not shown...
}
The first parameter is the cache name. The second string parameter is the cache key and is a string expression that
incorporates the argument passed into the method, the id. The method parameter names are exposed as variables
to the key expression. If you do not specify a key, then all the parameter values will be used to cache the returned
value. The expression may also call out to other objects in the Spring container allowing for a more complex
key algorithm to be encapsulated. The end result is that the Airport object is cached by id for 60 seconds in a
cache named AspNetCache. The TimetoLive property could also have been specified on the configuration of the
AspNetCache object.
The configuration to enable the caching aspect is shown below
<object" id="CacheAspect" type="Spring.Aspects.Cache.CacheAspect, Spring.Aop"/>
<object id="AspNetCache" type="Spring.Caching.AspNetCache, Spring.Web">
<property name="SlidingExpiration" value="true"/>
<property name="Priority" value="Low"/>
<property name="TimeToLive" value="00:02:00"/>
</object>
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<!-- Apply aspects to DAOs -->
<object type="Spring.Aop.Framework.AutoProxy.ObjectNameAutoProxyCreator, Spring.Aop">
<property name="ObjectNames">
<list>
<value>*Dao</value>
</list>
</property>
<property name="InterceptorNames">
<list>
<value>CacheAspect</value>
</list>
</property>
</object>
in this example an ObjectNameAutoProxyCreator was used to apply the cache aspect to objects that have Dao
in their name. The AspNetCache setting for TimeToLive will override the TimeToLive value set at the method
level via the attribute.
14.3. Exception Handling
In some cases existing code can be easily adopted to a simple error handling strategy that can perform one of
the following actions
• translations - either wrap the thrown exception inside a new one or replace it with a new exception type (no
inner exception is set).
• return value - the exception is ignored and a return value for the method is provided instead
• swallow - the exception is ignored.
• execute - Execute an abritrary Spring Expression Language (SpEL expression)
The applicability of general exception handling advice depends greatly on how tangled the code is regarding
access to local variables that may form part of the exception. Once you get familiar with the feature set of Spring
declarative exception handling advice you should evaluate where it may be effectively applied in your code base.
It is worth noting that you can still chain together multiple pieces of exception handling advice allowing you to mix
the declarative approach shown in this section with the traditional inheritance based approach, i.e. implementing
IThrowsAdvice or IMethodInterceptor.
Declarative exception handling is expressed in the form of a mini-language relevant to the domain at hand,
exception handling. This could be referred to as a Domain Specific Language (DSL). Here is a simple example,
which should hopefully be self explanatory.
<object name="exceptionHandlingAdvice" type="Spring.Aspects.Exceptions.ExceptionHandlerAdvice, Spring.Aop">
<property name="exceptionHandlers">
<list>
<value>on exception name ArithmeticException wrap System.InvalidOperationException</value>
</list>
</property>
</object>
What this is instructing the advice to do is the following bit of code when an ArithmeticException is thrown,
throw new System.InvalidOperationException("Wrapped ArithmeticException", e), where e is the original
ArithmeticException. The default message, "Wrapped ArithmethicException" is automatically appended. You
may however specify the message used in the newly thrown exception as shown below
on exception name ArithmeticException wrap System.InvalidOperationException 'My Message'
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Similarly, if you would rather replace the exception, that is do not nest one inside the other, you can use the
following syntax
on exception name ArithmeticException replace System.InvalidOperationException
or
on exception name ArithmeticException replace System.InvalidOperationException 'My Message'
Both wrap and replace are special cases of the more general translate action. An example of a translate expression
is shown below
on exception name ArithmeticException translate new System.InvalidOperationException('My Message, Method Name '
What we see here after the translate keyword is text that will be passed into Spring's expression language (SpEL)
for evaluation. Refer to the chapter on the expression language for more details. One important feature of the
expression evaluation is the availability of variables relating to the calling context when the exception was thrown.
These are
• method - the MethodInfo object corresponding to the method that threw the exception
• args - the argument array to the method that threw the exception, signature is object[]
• target - the AOP target object instance.
• e - the thrown exception
You can invoke methods on these variables, prefixed by a '#' in the expression. This gives you the flexibility to
call special purpose constructors that can have any piece of information accessible via the above variables, or
even other external data through the use of SpEL's ability to reference objects within the Spring container.
You may also choose to 'swallow' the exception or to return a specific return value, for example
on exception name ArithmeticException swallow
or
on exception name ArithmeticException return 12
You may also simply log the exception
on exception name ArithmeticException,ArgumentException log 'My Message, Method Name ' + #method.Name
Here we see that a comma delimited list of exception names can be specified.
The logging is performed using the Commons.Logging library that provides an abstraction over the underlying
logging implementation. Logging is currently at the debug level with a logger name of "LogExceptionHandler"
The ability to specify these values will be a future enhancement and likely via a syntax resembling a constructor
for the action, i.e. log(Debug,"LoggerName").
Multiple exception handling statements can be specified within the list shown above. The processing flow is
on exception, the name of the exception listed in the statement is compared to the thrown exception to see if
there is a match. A comma separated list of exceptions can be used to group together the same action taken for
different exception names. If the action to take is logging, then the logging action is performed and the search
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for other matching exception names continues. For all other actions, namely translate, wrap, replace, swallow,
return, once an exception handler is matched, those in the chain are no longer evaluated. Note, do not confuse
this handler chain with the general advice AOP advice chain. For translate, wrap, and replace actions a SpEL
expression is created and used to instantiate a new exception (in addition to any other processing that may occur
when evaluating the expression) which is then thrown.
The exception handling DSL also supports the ability to provide a SpEL boolean expression to determine if the
advice will apply instead of just filtering by the expression name. For example, the following is the equivalent to
the first example based on exception names but compares the specific type of the exception thrown
on exception (#e is T(System.ArithmeticException)) wrap System.InvalidOperationException
The syntax use is 'on exception (SpEL boolean expression)' and inside the expression you have access to the
variables of the calling context listed before, i.e. method, args, target, and e. This can be useful to implement
a small amount of conditional logic, such as checking for a specific error number in an exception, i.e. (#e is
T(System.Data.SqlException) && #e.Errors[0].Number in {156,170,207,208}), to catch and translate bad
grammar codes in a SqlException.
While the examples given above are toy examples, they could just as easily be changed to convert your application
specific exceptions. If you find yourself pushing the limits of using SpEL expressions, you will likely be better
off creating your own custom aspect class instead of a scripting approach.
You can also configure the each of the Handlers individually based on the action keyword. For example, to
configure the logging properties on the LogExceptionHandler.
<object name="logExceptionHandler" type="Spring.Aspects.Exceptions.LogExceptionHandler, Spring.Aop">
<property name="LogName" value="Cms.Session.ExceptionHandler" />
<property name="LogLevel" value="Debug"/>
<property name="LogMessageOnly" value="true"/>
</object>
<object name="exceptionHandlingAdvice" type="Spring.Aspects.Exceptions.ExceptionHandlerAdvice, Spring.Aop">
<property name="ExceptionHandlerDictionary">
<dictionary>
<entry key="log" ref="logExceptionHandler"/>
</dictionary>
</property>
<property name="ExceptionHandlers">
<list>
<value>on exception name ArithmeticException,ArgumentException log 'My Message, Method Name ' + #method.Na
</list>
</property>
</object>
You can also configure ExceptionHandlerAdvice to use an instance of IExceptionHandler by specifing it as
an entry in the ExceptionHandlers list. This gives you complete control over all properties of the handler but
you must set ConstraintExpressionText and ActionExpressionText which are normally parsed for you from the
string. To use the case of configuring the LogExceptionHandler, this approach also lets you specify advanced
logging functionality, but at a cost of some additional complexity. For example setting the logging level and pass
the exception into the logging subsystem
<object name="exceptionHandlingAdvice" type="Spring.Aspects.Exceptions.ExceptionHandlerAdvice, Spring.Aop">
<property name="exceptionHandlers">
<list>
<object type="Spring.Aspects.Exceptions.LogExceptionHandler">
<property name="LogName" value="Cms.Session.ExceptionHandler" />
<property name="ConstraintExpressionText" value="#e is T(System.Threading.ThreadAbortException)" />
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<property name="ActionExpressionText" value="#log.Fatal('Request Timeout occured', #e)" />
</object>
</list>
</property>
</object>
The configuration of the logger name, level, and weather or not to pass the thrown exception as the second
argument to the log method will be supported in the DSL style in a future release.
14.3.1. Language Reference
The general syntax of the language is
on exception name [ExceptionName1,ExceptionName2,...] [action] [SpEL expression]
or
on exception (SpEL boolean expression) [action] [SpEL expression]
The exception names are required as well as the action. The valid actions are
• log
• translate
• wrap
• replace
• return
• swallow
• execute
The form of the expression depends on the action. For logging, the entire string is taken as the SpEL expression
to log. Translate expects an exception to be returned from evaluation the SpEL expression. Wrap and replace are
shorthand for the translate action. For wrap and replace you specify the exception name and the message to pass
into the standard exception constructors (string, exception) and (string). The exception name can be a partial or
fully qualified name. Spring will attempt to resolve the typename across all referenced assemblies. You may also
register type aliases for use with SpEL in the standard manner with Spring.NET and those will be accessible from
within the exception handling expression.
14.4. Logging
The logging advice lets you log the information on method entry, exit and thrown exception (if any). The
implementation is based on the logging library, Common.Logging, that provides portability across different
logging libraries. There are a number of configuration options available, listed below
• LogUniqueIdentifier
• LogExecutionTime
• LogMethodArguments
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• LogReturnValue
• Separator
• LogLevel
You declare the logging advice in IoC container with the following XML fragment. Alternatively, you can use
the class SimpleLoggingAdvice programatically.
<object name="loggingAdvice" type="Spring.Aspects.Logging.SimpleLoggingAdvice, Spring.Aop">
<property name="logUniqueIdentifier" value="true"/>
<property name="logExecutionTime"
value="true"/>
<property name="logMethodArguments" value="true"/>
<property name="LogReturnValue"
value="true"/>
<property name="Separator"
<property name="LogLevel"
value=";"/>
value="Info"/>
<property name="HideProxyTypeNames"
<property name="UseDynamicLogger"
</object>
value="true"/>
value="true"/>
The default values for LogUniqueIdentifier, LogExecutionTime, LogMethodArguments and LogReturnValue are
false. The default separator value is ", " and the default log level is Common.Logging's LogLevel.Trace.
You can set the name of the logger with the property LoggerName, for example "DataAccessLayer" for a logging
advice that would be applied across the all the classes in the data access layer. That works well when using
a 'category' style of logging. If you do not set the LoggerName property, then the type name of the logging
advice is used as the logging name. Another approach to logging is to log based on the type of the object
being called, the target type. Since often this is a proxy class with a relatively meaningless name, the property
HideProxyTypeNames can be set to true to show the true target type and not the proxy type.
To further extend the functionality of the SimpleLoggingAdvice you can subclass SimpleLoggingAdvice and
override the methods
• string GetEntryMessage(IMethodInvocation invocation, string idString)
• string
GetExceptionMessage(IMethodInvocation
invocation,
Exception
e,
TimeSpan
returnValue,
TimeSpan
executionTimeSpan, string idString)
• string
GetExitMessage(IMethodInvocation
invocation,
object
executionTimeSpan, string idString)
The default implementation to calculate a unique identifier is to use a GUID. You
can alter this behavior by overriding the method string
CreateUniqueIdentifier(). The
SimpleLoggingAdvice class inherits from AbstractLoggingAdvice, which has the abstract method object
InvokeUnderLog(IMethodInvocation invocation, ILog log) and you can also override the method ILog
GetLoggerForInvocation(IMethodInvocation invocation) to customize the logger instance used for logging.
Refer to the SDK documentation for more details on subclassing AbstractLoggingAdvice.
As an example of the Logging advice's output, adding the advice to the method
public int Bark(string message, int[] luckyNumbers)
{
return 4;
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}
And calling Bark("hello", new int[]{1, 2, 3} ), results in the following output
Entering Bark, 5d2bad47-62cd-435b-8de7-91f12b7f433e, message=hello; luckyNumbers=System.Int32[]
Exiting Bark, 5d2bad47-62cd-435b-8de7-91f12b7f433e, 30453.125 ms, return=4
The method parameters values are obtained using the ToString() method. If you would like to
have an alternate implementation, say to view some values in an array, override the method string
GetMethodArgumentAsString(IMethodInvocation invocation).
The Spring 1.2 release will have an additional logging advice implementation that leverages the Spring Expression
Language to further customize the content of the logging messages via simple configuration using similar syntax
to the retry and exception handling advice.
14.5. Retry
When making a distributed call it is often a common requirement to be able to retry the method invocation if there
was an exception. Typically the exception will be due to a communication issue that is intermittent and retrying
over a period of time will likely result in a successful invocation. When applying retry advice it is important to
know if making two calls to the remote service will cause side effects. Generally speaking, the method being
invoked should be idempotent, that is, it is safe to call multiple times.
The retry advice is specified using a little language, i.e a DSL. A simple example is shown below
on exception name ArithmeticException retry 3x delay 1s
The meaning is: when an exception that has 'ArithmeticException' in its type name is thrown, retry the invocation
up to 3 times and delay for 1 second between each retry event.
You can also provide a SpEL (Spring Expression Language) expression that calculates the time interval to sleep
between each retry event. The syntax for this is shown below
on exception name ArithmeticException retry 3x rate (1*#n + 0.5)
As with the exception handling advice, you may also specify a boolean SpEL that must evaluate to true in order
for the advice to apply. For example
on exception (#e is T(System.ArithmeticException)) retry 3x delay 1s
on exception (#e is T(System.ArithmeticException)) retry 3x rate (1*#n + 0.5)
The time specified after the delay keyword is converted to a TimeSpan object using Spring's TimeSpanConverter.
This supports setting the time as an integer + time unit. Time units are (d, h, m, s, ms) representing (days, hours,
minutes, seconds, and milliseconds). For example; 1d = 1day, 5h = 5 hours etc. You can not specify a string such
as '1d 5h'. The value that is calculated from the expression after the rate keyword is interpreted as a number of
seconds. The power of using SpEL for the rate expression is that you can easily specify some exponential retry
rate (a bigger delay for each retry attempt) or call out to a custom function developed for this purpose.
When using a SpEL expression for the filter condition or for the rate expression, the following variable are
available
• method - the MethodInfo object corresponding to the method that threw the exception
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• args - the argument array to the method that threw the exception, signature is object[]
• target - the AOP target object instance.
• e - the thrown exception
You declare the advice in IoC container with the following XML fragment. Alternatively, you can use the
RetryAdvice class programatically.
<object name="exceptionHandlingAdvice" type="Spring.Aspects.RetryAdvice, Spring.Aop">
<property name="retryExpression" value="on exception name ArithmeticException retry 3x delay 1s"/>
</object>
14.5.1. Language Reference
The general syntax of the language is
on exception name [ExceptionName1,ExceptionName2,...] retry [number of times]x [delay|rate]
[delay time|SpEL rate expression]
or
on exception (SpEL boolean expression) retry [number of times]x [delay|rate] [delay time|
SpELrate expression]
14.6. Transactions
The transaction aspect is more fully described in the section on transaction management.
14.7. Parameter Validation
Spring provides a UI-agnostic validation framework in which you can declare validation rules, both
progammatically and declaratively, and have those rules evaluated against an arbitrary .NET object. Spring
provides additional support for the rendering of validation errors within Spring's ASP.NET framework. (See the
section on ASP.NET usage tips for more information.) However, validation is not confined to the UI tier. It is a
common task that occurs across most, if not all, applications layers. Validation that is performed in the UI layer is
often repeated in the service layer, in order to be proactive in case non UI-based clients invoke the service layer.
Validation rules completely different from those used in the UI layer may also be used on the server side.
To address some of the common needs for validation on the server side, Spring provides parameter validation
advice so that applies Spring's validation rules to the method parameters. The class ParameterValidationAdvice
is used in conjunction with the Validated attribute to specify which validation rules are applied to method
parameters. For example, to apply parameter validation to the method SuggestFlights in the BookingAgent class
used in the SpringAir sample application, you would apply the Validated attribute to the method parameters as
shown below.
public FlightSuggestions SuggestFlights( [Validated("tripValidator")] Trip trip)
{
// unmodified implementation goes here
}
The Validated attribute takes a string name that specifies the name of the validation rule, i.e. the name of
the IValidator object in the Spring application context. The Validated attribute is located in the namespace
Spring.Validation of the Spring.Core assembly.
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Aspect Library
The configuration of the advice is to simply define the an instance of the ParameterValidationAdvice class and
apply the advice, for example based on object names using an ObjectNameAutoProxyCreator, as shown below,
<object id="validationAdvice" type="Spring.Aspects.Validation.ParameterValidationAdvice, Spring.Aop"/>
<object type="Spring.Aop.Framework.AutoProxy.ObjectNameAutoProxyCreator, Spring.Aop">
<property name="ObjectNames">
<list>
<value>bookingAgent</value>
</list>
</property>
<property name="InterceptorNames">
<list>
<value>validationAdvice</value>
</list>
</property>
</object>
When the advised method is invoked first the validation of each method parameter is performed. If all validation
succeeds, then the method body is executed. If validation fails an exception of the type ValidationException is
thrown and you can retrieve errors information from its property ValidationErrors. See the SDK documentation
for details.
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Chapter 15. Common Logging
15.1. Introduction
Spring uses a simple logging abstraction in order to provide a layer of indirection between logging calls made
by Spring and the specific logging library used in your application (log4net, EntLib logging, NLog). The library
is available for .NET 1.0, 1.1, and 2.0 with both debug and strongly signed assemblies. Since this need is not
specific to Spring, the logging library was moved out of the Spring project and into a more general open source
project called Common Infrastructure Libraries for .NET. The logging abstraction within the project is known as
Common.Logging. Note that it is not the intention of this library to be a replacement for the many fine logging
libraries that are out there. The API is incredibly minimal and will very likely stay that way. Please note that this
library is intended only for use where the paramount requirement is portability and you will generally be better
served by using a specific logging implementation so that you can leverage its advanced features and extended
APIs to your advantage.
You can find online documentation on how to configure Common.Logging is available in HTML , PDF, and
HTML Help formats.
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Chapter 16. Testing
16.1. Introduction
The Spring team considers developer testing to be an absolutely integral part of enterprise software development.
A thorough treatment of testing in the enterprise is beyond the scope of this chapter; rather, the focus here is on
the value add that the adoption of the IoC principle can bring to unit testing; and on the benefits that the Spring
Framework provides in integration testing.
16.2. Unit testing
One of the main benefits of Dependency Injection is that your code is much less likely to have any hidden
dependencies on the runtime environment or other configuration subsystems. This allows for unit tests to be
written in a manner such that the object under test can be simply instantiated with the new operator and have its
dependences set in the unit test code. You can use mock objects (in conjunction with many other valuable testing
techniques) to test your code in isolation. If you follow the architecture recommendations around Spring you
will find that the resulting clean layering and componentization of your codebase will naturally faciliate easier
unit testing. For example, you will be able to test service layer objects by stubbing or mocking DAO interfaces,
without any need to access persistent data while running unit tests.
True unit tests typically will run extremely quickly, as there is no runtime infrastructure to set up, i.e., database,
ORM tool, or whatever. Thus emphasizing true unit tests as part of your development methodology will boost
your productivity. The upshot of this is that you do not need this section of the testing chapter to help you write
effective unit tests for your IoC-based applications.
16.3. Integration testing
However, it is also important to be able to perform some integration testing enabling you to test things such as:
• The correct wiring of your Spring IoC container contexts.
• Data access using ADO.NET or an ORM tool. This would include such things such as the correctness of SQL
statements / or NHibernate XML mapping files.
The Spring Framework provides first class support for integration testing in the form of the classes that are
packaged in the Spring.Testing.NUnit.dll library. Please note that these test classes are NUnit-specific.
Support for mbUnit and VSTS are under consideration for future versions.
Note
The Spring.Testing.NUnit.dll library is compiled against NUnit 2.4.1. At the time of this writing the
latest version of NUnit is 2.4.6. Note that add-in have their own versions of NUnit they use. For
example, ReSharper 3.0 uses 2.2.8. If you are using the GUI-runner that comes with NUnit then you
should add the following to your .config file, (in the form of MyAssembly.dll.config)
<runtime>
<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
<dependentAssembly>
<assemblyIdentity name="nunit.framework"
publicKeyToken="96d09a1eb7f44a77"
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culture="neutral"/>
<bindingRedirect oldVersion="0.0.0.0-65535.65535.65535.65535
newVersion="2.4.6.0"/>
</dependentAssembly>
</assemblyBinding>
</runtime>
The Spring.Testing.NUnit namespace provides valuable NUnit TestCase superclasses for integration testing
using a Spring container. Note that as of NUnit 2.4 these can be rewritten in terms of custom attributes via NUnit's
new extensibility mechanism. This will be an additional option in an upcoming release of Spring.NET and is
already present in the Java version of the Spring framework.
These superclasses provide the following functionality:
• Spring IoC container caching between test case execution.
• The pretty-much-transparent Dependency Injection of test fixture instances (this is nice).
• Transaction management appropriate to integration testing (this is even nicer).
• A number of Spring-specific inherited instance variables that are really useful when integration testing.
16.3.1. Context management and caching
The Spring.Testing.NUnit package provides support for consistent loading of Spring contexts, and caching of loaded
contexts. Support for the caching of loaded contexts is important, because if you are working on a large project,
startup time may become an issue - not because of the overhead of Spring itself, but because the objects instantiated
by the Spring container will themselves take time to instantiate. For example, a project with 50-100 NHibernate
mapping files might take 10-20 seconds to load the mapping files, and incurring that cost before running every
single test case in every single test fixture will lead to slower overall test runs that could reduce productivity.
To address this issue, the AbstractDependencyInjectionSpringContextTests has an protected property that
subclasses must implement to provide the location of context definition files:
protected abstract string[] ConfigLocations { get; }
Implementations of this method must provide an array containing the IResource locations of XML configuration
metadata used to configure the application. This will be the same, or nearly the same, as the list of configuration
locations specified in App.config/Web.config or other deployment configuration.
By default, once loaded, the configuration file set will be reused for each test case. Thus the setup cost
will be incurred only once (per test fixture), and subsequent test execution will be much faster. In the
unlikely case that a test may 'dirty' the config location, requiring reloading - for example, by changing
an object definition or the state of an application object - you can call the SetDirty() method on
AbstractDependencyInjectionSpringContextTests to cause the test fixture to reload the configurations and
rebuild the application context before executing the next test case.
16.3.2. Dependency Injection of test fixtures
When AbstractDependencyInjectionSpringContextTests (and subclasses) load your application context, they
can optionally configure instances of your test classes by Setter Injection. All you need to do is to define instance
variables and the corresponding setters. AbstractDependencyInjectionSpringContextTests will automatically
locate the corresponding object in the set of configuration files specified in the ConfigLocations property.
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Consider the scenario where we have a class, HibernateTitleDao, that performs data access logic for say, the
Title domain object. We want to write integration tests that test all of the following areas:
• The Spring configuration; basically, is everything related to the configuration of the HibernateTitleDao object
correct and present?
• The Hibernate mapping file configuration; is everything mapped correctly and are the correct lazy-loading
settings in place?
• The logic of the HibernateTitleDao; does the configured instance of this class perform as anticipated?
Let's look at the test class itself (we will look at the configuration immediately afterwards).
[TestFixture]
public class HibernateTitleDaoTests : AbstractDependencyInjectionSpringContextTests
{
// this instance will be (automatically) dependency injected
private HibernateTitleDao titleDao;
// a setter method to enable DI of the 'titleDao' instance variable
public HibernateTitleDao HibernateTitleDao {
set { titleDao = value; }
}
[Test]
public void LoadTitle() {
Title title = this.titleDao.LoadTitle(10);
Assert.IsNotNull(title);
}
// specifies the Spring configuration to load for this test fixture
protected override string[] ConfigLocations {
return new String[] { "assembly://MyAssembly/MyNamespace/daos.xml" };
}
}
The file referenced by the ConfigLocations method ('classpath:com/foo/daos.xml') looks like this:
<?xml version="1.0" encoding="utf-8" ?>
<objects xmlns="http://www.springframework.net">
<!-- this object will be injected into the HibernateTitleDaoTests class -->
<object id="titleDao" type="Spring.Samples.HibernateTitleDao, Spring.Samples">
<property name="sessionFactory" ref="sessionFactory"/>
</object>
<object id="sessionFactory" type="Spring.Data.NHibernate.LocalSessionFactoryObject, Spring.Data.NHibernate">
<!-- dependencies elided for clarity -->
</object>
</objects>
The AbstractDependencyInjectionSpringContextTests classes uses autowire by type. Thus if you have
multiple object definitions of the same type, you cannot rely on this approach for those particular object. In that
case, you can use the inherited applicationContext instance variable, and explicit lookup using (for example)
an explicit call to applicationContext.GetObject("titleDao").
If you don't want dependency injection applied to your test cases, simply don't declare any set properties.
Alternatively, you can extend the AbstractSpringContextTests - the root of the class hierarchy in the
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namespace. It merely contains convenience methods to load Spring contexts, and
performs no Dependency Injection of the test fixture.
Spring.Testing.NUnit
16.3.2.1. Field level injection
If, for whatever reason, you don't fancy having setter properties in your test fixtures, Spring can (in this one case)
inject dependencies into protected fields. Find below a reworking of the previous example to use field level
injection (the Spring XML configuration does not need to change, merely the test fixture).
[TestFixture]
public class HibernateTitleDaoTests : AbstractDependencyInjectionSpringContextTests{
public HibernateTitleDaoTests() {
// switch on field level injection
PopulateProtectedVariables = true;
}
// this instance will be (automatically) dependency injected
protected HibernateTitleDao titleDao;
[Test]
public void LoadTitle() {
Title title = this.titleDao.LoadTitle(10);
Assert.IsNotNull(title);
}
// specifies the Spring configuration to load for this test fixture
protected override string[] ConfigLocations {
return new String[] { "assembly://MyAssembly/MyNamespace/daos.xml" };
}
}
In the case of field injection, there is no autowiring going on: the name of your protected instances variable(s)
are used as the lookup object name in the configured Spring container.
16.3.3. Transaction management
One common issue in tests that access a real database is their effect on the state of the persistence store. Even
when you're using a development database, changes to the state may affect future tests. Also, many operations such as inserting to or modifying persistent data - cannot be done (or verified) outside a transaction.
The AbstractTransactionalDbProviderSpringContextTests superclass (and subclasses) exist to meet this
need. By default, they create and roll back a transaction for each test. You simply write code that can assume
the existence of a transaction. If you call transactionally proxied objects in your tests, they will behave correctly,
according to their transactional semantics.
depends on a IPlatformTransactionManager object being
defined in the application context. The name doesn't matter, due to the use of autowire by type.
AbstractTransactionalSpringContextTests
Typically you will extend the subclass, AbstractTransactionalDbProviderSpringContextTests. This also
requires that a DbProvider object definition - again, with any name - be present in the configurations. It creates
an AdoTemplate instance variable that is useful for convenient querying, and provides handy methods to delete
the contents of selected tables (remember that the transaction will roll back by default, so this is safe to do).
If you want a transaction to commit - unusual, but occasionally useful when you want a
particular test to populate the database - you can call the SetComplete() method inherited from
AbstractTransactionalSpringContextTests. This will cause the transaction to commit instead of roll back.
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There is also convenient ability to end a transaction before the test case ends, through calling the
EndTransaction() method. This will roll back the transaction by default, and commit it only if SetComplete()
had previously been called. This functionality is useful if you want to test the behavior of 'disconnected' data
objects, such as Hibernate-mapped objects that will be used in a web or remoting tier outside a transaction. Often,
lazy loading errors are discovered only through UI testing; if you call EndTransaction() you can ensure correct
operation of the UI through your NUnit test suite.
16.3.4. Convenience variables
When you extend the AbstractTransactionalDbProviderSpringContextTests class you will have access to
the following protected instance variables:
• applicationContext
(a
IConfigurableApplicationContext):
AbstractDependencyInjectionSpringContextTests
inherited
from
the
superclass. Use this to perform explicit object lookup,
or test the state of the context as a whole.
• adoTemplate: inherited from AbstractTransactionalDbProviderSpringContextTests. Useful for querying
to confirm state. For example, you might query before and after testing application code that creates an object
and persists it using an ORM tool, to verify that the data appears in the database. (Spring will ensure that the
query runs in the scope of the same transaction.) You will need to tell your ORM tool to 'flush' its changes for
this to work correctly, for example using the Flush() method on NHibernate's ISession interface.
Often you will provide an application-wide superclass for integration tests that provides further useful instance
variables used in many tests
16.4. Further Resources
This section contains links to further resources about testing in general.
• The NUnit homepage. The Spring Framework's unit test suite is written using NUnit as the testing framework.
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Part II. Middle Tier Data Access
This part of the reference documentation is concerned with othe middle tier, and specifically the data access
responsibilities of said tier.
Spring's comprehensive transaction management support is covered in some detail, followed by thorough
coverage of the various middle tier data access frameworks and technologies that the Spring Framework integrates
with.
• Chapter 17, Transaction management
• Chapter 18, DAO support
• Chapter 19, DbProvider
• Chapter 20, Data access using ADO.NET
• Chapter 21, Object Relational Mapping (ORM) data access
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Chapter 17. Transaction management
17.1. Introduction
Spring.NET provides a consistent abstraction for transaction management that provides the following benefits
• Provides a consistent programming model across different transaction APIs such as ADO.NET, Enterprise
Services, System.Transactions, and NHibernate.
• Support for declarative transaction management with any of the above data access technologies
• Provides a simple API for programmatic transaction management
• Integrates with Spring's high level persistence integration APIs such as AdoTemplate.
This chapter is divided up into a number of sections, each detailing one of the value-adds or technologies of the
Spring Framework's transaction support. The chapter closes with some discussion of best practices surrounding
transaction management.
• The first section, entitled Motivations describes why one would want to use the Spring Framework's transaction
abstraction as opposed to using System.Transactions or a specific data access technology transaction API.
• The second section, entitled Key Abstractions outline the core classes as well as how to configure them.
• Th third section, entitled Declarative transaction management, covers support for declarative transaction
management.
• The fourth section, entitled Programmatic transaction management, covers support for programmatic
transaction management.
17.2. Motivations
The data access technology landscape is a broad one, within the .NET BCL there are three APIs for performing
transaction management, namely ADO.NET, Enterprise Services, and System.Transactions. Other data access
technologies such as object relational mappers and result-set mapping libraries are also gaining in popularity
and each come with their own APIs for transaction management. As such, code is often directly tied to a
particular transaction API which means you must make an up-front decision which API to use in your application.
Furthermore, if the need arises to change your approach, it quite often will not be a simple refactoring. Using
Spring's transaction API you can keep the same API across different data access technologies. Changing
the underlying transaction implementation that is used is a simple matter of configuration or a centralized
programmatic change as compared to a major overhauling.
Hand in hand with the variety of options available is the establishment generally agreed upon best practices
for data access. Martin Fowler's book, Patterns of Enterprise Application Architecture, is an excellent source of
approaches to data access that have been successful in the real world. One approach that is quite common is to
introduce a data access layer into your architecture. The data access layer is concerned not only with providing
some portability between different data access technologies and databases but its scope is strictly related to data
access. A simple data access layer would be not much more than data access objects (DAOs) with 'Create/Retrieve/
Update/Delete' (CRUD) methods devoid of any business logic. Business logic resides in another application layer,
the business service layer, in which business logic will call one or more DAOs to fulfill a higher level end-user
function.
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In order to perform this end-user function with all-or-nothing transactional semantics, the transaction context
is controlled by the business service layer (or other 'higher' layers). In such a common scenario, an important
implementation detail is how to make the DAO objects aware of the 'outer' transaction started in another layer.
A simplistic implementation of a DAO would perform its own connection and transaction management, but this
would not allow grouping of DAO operations with the same transaction as the DAO is doing its own transaction/
resource management. As such there needs to be a means to transfer the connection/transaction pair managed
in the business service layer to the DAOs. There are a variety of ways to do this, the most invasive being the
explicitly pass a connection/transaction object as method arguments to your DAOs. Another way is to store the
connection/transaction pair in thread local storage. In either case, if you are using ADO.NET you must invent
some infrastructure code to perform this task.
But wait, doesn't Enterprise Services solve this problem - and what about the functionality in the
System.Transactions namespace? The answer is yes...and no. Enterprise Services lets you use the 'raw' ADO.NET
API within a transaction context such that multiple DAO operations are grouped within the same transaction.
The downside to Enterprise Services is that it always uses distributed (global) transactions via the Microsoft
Distributed Transaction Coordinator (MS-DTC). For most applications this is overkill just to get this functionality
as global transactions are significantly less performant than local ADO.NET transactions.
There are similar issues with using the 'using TransactionScope' construct within the new System.Transactions
namespace. The goal with TransactionScope is to define a, well - transaction scope - within a using statement.
Plain ADO.NET code within that using block will then be a local ADO.NET based transaction if only a single
transactional resource is accessed. However, the 'magic' of System.Transactions (and the database) is that local
transactions will be promoted to distributed transactions when a second transaction resource is detected. The name
that this goes by is Promotable Single Phase Enlistment (PSPE). However, there is a big caveat - opening up a
second IDbConnection object to the same database with the same database string will trigger promotion from
local to global transactions. As such, if your DAOs are performing their own connection management you will
end up being bumped up to a distributed transaction. In order to avoid this situation for the common case of an
application using a single database, you must pass around a connection object to your DAOs. It is also worth
to note that many database providers (Oracle for sure) do not yet support PSPE and as such will always use a
distributed transaction even if there is only a single database.
Last but not least is the ability to use declarative transaction management. Not many topics in database transactionland give developers as much 'bang-for-the-buck' as declarative transactions since the noisy tedious bits of
transactional API code in your application are pushed to the edges, usually in the form of class/method attributes.
Only Enterprise Services offers this feature in the BCL. Spring fills the gap - it provides declarative transaction
management if you are using local ADO.NET or System.Transactions (the most popular) or other data access
technologies. Enterprise Services is not without it small warts as well, such as the need to separate your query/
retrieve operations from your create/update/delete operations if you want to use different isolation levels since
declarative transaction metadata can only be applied at the class level. Nevertheless, all in all, Enterprise Services,
in particular with the new 'Services Without Components' implementation for XP SP2/Server 2003, and hosted
within the same process as your application code is as good as it gets out of the .NET box. Despite these positive
points, it hasn't gained a significant mindshare in the development community.
Spring's transaction support aims to relieve these 'pain-points' using the data access technologies within the BCL
- and for other third party data access technologies as well. It provides declarative transaction management with
a configurable means to obtain transaction option metadata - out of the box attributes and XML within Spring's
IoC configuration file are supported.
Finally, Spring's transaction support lets you mix data access technologies within a single transaction - for example
ADO.NET and NHibernate operations.
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With this long winded touchy/feely motivational section behind us, lets move on to see the code.
17.3. Key Abstractions
The key to the Spring transaction management abstraction is the notion of a transaction strategy. A transaction
strategy is defined by the Spring.Transaction.IPlatformTransactionManager interface, shown below:
public interface IPlatformTransactionManager {
ITransactionStatus GetTransaction( ITransactionDefinition definition );
void Commit( ITransactionStatus transactionStatus );
void Rollback( ITransactionStatus transactionStatus );
}
This is primarily a 'SPI' (Service Provider Interface), although it can be used Programatically. Note that in keeping
with the Spring Framework's philosophy, IPlatformTransactionManager is an interface, and can thus be easily
mocked or stubbed as necessary. IPlatformTransactionManager implementations are defined like any other
object in the IoC container. The following implementations are provided
• AdoPlatformTransactionManager - local ADO.NET based transactions
• ServiceDomainPlatformTransactionManager - distributed transaction manager from Enterprise Services
• TxScopePlatformTransactionManager - local/distributed transaction manager from System.Transactions.
• HibernatePlatformTransactionManager - local transaction manager for use with NHibernate or mixed
ADO.NET/NHibernate data access operations.
Under the covers, the following API calls are made. For the AdoPlatformTransactionManager,
Transaction.Begin(), Commit(), Rollback(). ServiceDomainPlatformTransactionManager uses the
'Services without Components' update so that your objects do not need to inherit from
ServicedComponent or directly call the Enterprise Services API ServiceDomain.Enter(), Leave;
ContextUtil.SetAbort(). TxScopePlatformTransactionManager calls; new TransactionScope(); .Complete(),
Dispose(), Transaction.Current.Rollback(). Configuration properties for each transaction manager are specific to
the data access technology used. Refer to the API docs for comprehensive information but the examples should
give you a good basis for getting started. The HibernatePlatformTransactionManager is described more in the
following section .
The
method returns a ITransactionStatus object, depending on a
parameters. The returned ITransactionStatus might represent a new or existing
transaction (if there was a matching transaction in the current call stack - with the implication being that a
ITransactionStatus is associated with a logical thread of execution.
GetTransaction(..)
ITransactionDefinition
The ITransactionDefinition interface specified
• Isolation: the degree of isolation this transaction has from the work of other transactions. For example, can this
transaction see uncommitted writes from other transactions?
• Propagation: normally all code executed within a transaction scope will run in that transaction. However, there
are several options specifying behavior if a transactional method is executed when a transaction context already
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exists: for example, simply continue running in the existing transaction (the common case); or suspending the
existing transaction and creating a new transaction.
• Timeout: how long this transaction may run before timing out (and automatically being rolled back by the
underlying transaction infrastructure).
• Read-only status: a read-only transaction does not modify any data. Read-only transactions can be a useful
optimization in some cases (such as when using NHibernate).
These settings reflect standard transactional concepts. If necessary, please refer to a resource discussing
transaction isolation levels and other core transaction concepts because understanding such core concepts is
essential to using the Spring Framework or indeed any other transaction management solution.
The ITransactionStatus interface provides a simple way for transactional code to control transaction execution
and query transaction status.
Regardless of whether you opt for declarative or programmatic transaction management in Spring, defining
the correct IPlatformTransactionManager implementation is absolutely essential. In good Spring fashion, this
important definition typically is made using via Dependency Injection.
implementations normally require knowledge of the environment in which
they work, ADO.NET, NHibernate, etc. The following example shows how a standard ADO.NET based
IPlatformTransactionManager can be defined.
IPlatformTransactionManager
We must define a Spring IDbProvider and then use Spring's AdoPlatformTransactionManager, giving it a
reference to the IDbProvider. For more information on the IDbProvider abstraction refer to the next chapter.
<objects xmlns='http://www.springframework.net'
xmlns:db="http://www.springframework.net/database">
<db:provider id="DbProvider"
provider="SqlServer-1.1"
connectionString="Data Source=(local);Database=Spring;User ID=springqa;Password=springqa;Trusted
<object id="TransactionManager"
type="Spring.Data.AdoPlatformTransactionManager, Spring.Data">
<property name="DbProvider" ref="DbProvider"/>
</object>
. . . other object definitions . . .
</objects>
We can also use a transaction manager based on System.Transactions just as easily, as shown in the following
example
<object id="TransactionManager"
type="Spring.Data.TxScopeTransactionManager, Spring.Data">
</object>
Similarly for the HibernateTransactionManager as shown in the section on ORM transaction management.
Note that in all these cases, application code will not need to change at all since, dependency injection is a perfect
companion to using the strategy pattern. We can now change how transactions are managed merely by changing
configuration, even if that change means moving from local to global transactions or vice versa.
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17.4. Resource synchronization with transactions
How does application code participate with the resources (i.e. Connection/Transactions/Sessions) that are created/
reused/cleanedup via the different transaction managers? There are two approaches - a high-level and a low-level
approach
17.4.1. High-level approach
The preferred approach is to use Spring's high level persistence integration APIs. These do not replace native
APIs, but internally handle resource creation/reuse, cleanup, and optional transaction synchronization (i.e. event
notification) of the resources and exception mapping so that user data access code doesn't have to worry about
these concerns at all, but can concentrate purely on non-boilerplate persistence logic. Generally, the same
inversion of control approach is used for all persistence APIs. In this approach the API has a callback method or
delegate that presents the user code with the relevant resource ready to use - i.e. a DbCommand with its Connection
and Transaction properties set based on the transaction option metadata. These classes go by the naming scheme
'template', examples of which are AdoTemplate and HibernateTemplate. Convenient 'one-liner' helper methods
in these template classes build upon the core callback/IoC design by providing specific implementations of the
callback interface.
17.4.2. Low-level approach
A utility class can be used to directly obtain a connection/transaction pair that is aware of the transactional
calling context and returns a pair suitable for that context. The class ConnectionUtils contains the static method
ConnectionTxPair GetConnectionTxPair(IDbProvider provider) which serves this purpose.
17.5. Declarative transaction management
Most Spring users choose declarative transaction management. It is the option with the least impact on application
code, and hence is most consistent with the ideals of a non-invasive lightweight container.
Spring's declarative transaction management is made possible with Spring AOP, although, as the transactional
aspects code comes with Spring and may be used in a boilerplate fashion, AOP concepts do not generally have
to be understood to make effective use of this code.
The basic approach is to specify transaction behavior (or lack of it) down to the individual method level. It is also
possible to mark a transaction for rollback by setting the 'RollbackOnly' property on the ITransactionStatus object
returned from the IPlatformTransactionManager within a transaction context if necessary. Some of the highlights
of Spring's declarative transaction management are:
• Declarative Transaction management works in any environment. It can work with ADO.NET,
System.Transactions, NHibernate etc, with configuration changes only.
• Enables declarative transaction management to be applied to any class, not merely special classes such as those
that inherit from ServicedComponent or other infrastructure related base classes.
• Declarative rollback rules. Rollback rules can be control declaratively and allow for only specified exceptions
thrown within a transactional context to trigger a rollback
• Spring gives you an opportunity to customize transactional behavior, using AOP. For example if you want to
insert custom behavior in the case of a transaction rollback, you can. You can also add arbitrary advice, along
with the transactional advice.
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• Spring does not support propagation of transaction context across remote calls.
Note rollback rules as configured from XML are still under development.
The concept of rollback rules is important: they enable us to specify which exceptions should cause automatic
roll back. We specify this declaratively, in configuration, not in code. So, while we can still set RollbackOnly on
the ITransactionStatus object to roll the current transaction back Programatically, most often we can specify a
rule that MyApplicationException must always result in rollback. This has the significant advantage that business
objects don't need to depend on the transaction infrastructure. For example, they typically don't need to import
any Spring APIs, transaction or other. If you would like to rollback the transaction programmatically and you are
using declarative transaction management, use the utility method
TransactionInterceptor.CurrentTransactionStatus.SetRollbackOnly();
Note
Prior
to
Spring.NET
1.2
RC1
the
API
call
would
be
TransactionInterceptor.CurrentTransactionStatus.RollbackOnly = true;
17.5.1. Understanding Spring's declarative transaction implementation
The aim of this section is to dispel the mystique that is sometimes associated with the use of declarative
transactions. It is all very well for this reference documentation to simply tell you to annotate your classes with the
Transaction attribute and add some boilerplate XML to your IoC configuration, and then expect you to understand
how it all works. This section will explain the inner workings of Spring's declarative transaction infrastructure to
help you navigate your way back upstream to calmer waters in the event of transaction-related issues.
Note
Looking at the Spring source code is a good way to get a real understanding of Spring's transaction
support. You should find the API documentation informative and complete. We suggest turning the
logging level to 'DEBUG' in your Spring-enabled application(s) during development to better see
what goes on under the hood.
The most important concepts to grasp with regard to Spring's declarative transaction support are that this
support is enabled via AOP proxies, and that the transactional advice is driven by metadata (currently XMLor attribute-based). The combination of a proxy with transactional metadata yields an AOP proxy that uses a
TransactionInterceptor in conjunction with an appropriate IPlatformTransactionManager implementation
to drive transactions around method invocations.
Note
Although knowledge of AOP (and specifically Spring AOP) is not required in order to use Spring's
declarative transaction support, it can help. Spring AOP is thoroughly covered in the AOP chapter.
Conceptually, calling a method on a transactional proxy looks like this.
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The flow of events is the following. First the set of objects you would like to apply AOP transactional advice to
are identified. There are a variety of ways to configure the Spring IoC container to create proxies for the defined
object definitions. The standard Spring AOP based options are
• ProxyFactoryObject. The common properties to set are the reference to the object to proxy (the target object)
and a reference to the transaction advice. See Section 13.5, “Using the ProxyFactoryObject to create AOP
proxies” for more details.
• AutoProxy - Defines criteria to select a collection of objects to create a transactional AOP proxy.
The AutoProxy options are
• ObjectNameAutoProxyCreator which specifies a collection of object names based on wildcard matching of
object names. See Section 13.9.1.1, “ObjectNameAutoProxyCreator”
• DefaultAdvisorAutoProxyCreator which specifies one or more "advisors" i.e an object representing an
aspect, including both an advice and a pointcut targeting it to specific joinpoints. See Section 13.9.1.2,
“DefaultAdvisorAutoProxyCreator”
There is also a convenience subclass of ProxyFactoryObject, namely TransactionProxyFactoryObject, that
sets some common default values for the specific case of applying transactional advice.
The DefaultAdvisorAutoProxyCreator is very powerful and is the means by which Spring can be configured
to use attributes to identify the pointcuts where transaction advice should be applied. The advisor that performs
that task is TransactionAttributeSourceAdvisor.
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Note
Note, think of the word 'Attribute' in this class name not as the .NET attribute but as the transaction
'options' you want to specify. This name is inherited from the Java version and the name will be
changed in the RC1 release to avoid confusion since a common naming convention when creating
classes are .NET attributes is to put the word 'Attribute' in the name.
Which one of the many options available should you choose for your development? That depends, each one has
it own set of pro's and con's which will be discussed in turn in the following sections.
With the transactional AOP proxy now created we can discuss the flow of events in the code as proxied methods
are invoked. When the method is invoked, before calling the target object's method, a transaction is created if one
hasn't already been created. Then the target method is invoked. If there was an exception throw, the transaction
is typically rolled back, but it can also be committed if the exception type specified in the transaction option,
NoRollbackFor, matches the thrown exception. If no exception was thrown, that is taken as a sign of success and
the transaction is committed.
When using other AOP advice with the transactional advice you can set the order of the 'interceptor chain' so that,
for example, performance monitoring advice always precede the transactional advice.
17.5.2. A First Example
Consider the following interface. The intent is to convey the concepts to you so you can concentrate on the
transaction usage and not have to worry about domain specific details. The ITestObjectManager is a poor-mans
business service layer - the implementation of which will make two DAO calls. Clearly this example is overly
simplistic from the service layer perspective as there isn't any business logic at all!. The 'service' interface is
shown below.
public interface ITestObjectManager
{
void SaveTwoTestObjects(TestObject to1, TestObject to2);
void DeleteTwoTestObjects(string name1, string name2);
}
The implementation of ITestObjectManager is shown below
public class TestObjectManager : ITestObjectManager
{
// Fields/Properties ommited
[Transaction()]
public void SaveTwoTestObjects(TestObject to1, TestObject to2)
{
TestObjectDao.Create(to1.Name, to1.Age);
TestObjectDao.Create(to2.Name, to1.Age);
}
[Transaction()]
public void DeleteTwoTestObjects(string name1, string name2)
{
TestObjectDao.Delete(name1);
TestObjectDao.Delete(name2);
}
}
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Note the Transaction attribute on the methods. Other options such as isolation level can also be specified but in
this example the default settings are used. However, please note that the mere presence of the Transaction attribute
is not enough to actually turn on the transactional behavior - the Transaction attribute is simply metadata that can
be consumed by something that is Transaction attribute-aware and that can use the said metadata to configure the
appropriate objects with transactional behavior.
The TestObjectDao property has basic create update delete and find method for the 'domain' object TestObject.
TestObject in turn has simple properties like name and age.
public interface ITestObjectDao
{
void Create(string name, int age);
void Update(TestObject to);
void Delete(string name);
TestObject FindByName(string name);
IList FindAll();
}
The Create and Delete method implementation is shown below. Note that this uses the AdoTemplate class
discussed in the following chapter. Refer to Section 17.4, “Resource synchronization with transactions”
for information on the interaction between Spring's high level persistence integration APIs and transaction
management features.
public class TestObjectDao : AdoDaoSupport, ITestObjectDao
{
public void Create(string name, int age)
{
AdoTemplate.ExecuteNonQuery(CommandType.Text,
String.Format("insert into TestObjects(Age, Name) VALUES ({0}, '{1}')",
age, name));
}
public void Delete(string name)
{
AdoTemplate.ExecuteNonQuery(CommandType.Text,
String.Format("delete from TestObjects where Name = '{0}'",
name));
}
}
The TestObjectManager is configured with the DAO objects by standard dependency injection techniques. The
client code, which in this case directly asks the Spring IoC container for an instance of ITestObjectManager,
will receive a transaction proxy with transaction options based on the attribute metadata. Note that typically the
ITestObjectManager would be set on yet another higher level object via dependency injection, for example a
web service.
The client calling code is shown below
IApplicationContext ctx =
new XmlApplicationContext("assembly://Spring.Data.Integration.Tests/Spring.Data/autoDeclarativeServices.xml")
ITestObjectManager mgr = ctx["testObjectManager"] as ITestObjectManager;
TestObject to1 = new TestObject();
to1.Name = "Jack";
to1.Age = 7;
TestObject to2 = new TestObject();
to2.Name = "Jill";
to2.Age = 8;
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mgr.SaveTwoTestObjects(to1, to2);
mgr.DeleteTwoTestObjects("Jack", "Jill");
The configuration of the object definitions of the DAO and manager classes is shown below.
<objects xmlns='http://www.springframework.net'
xmlns:db="http://www.springframework.net/database">
<db:provider id="DbProvider"
provider="SqlServer-1.1"
connectionString="Data Source=(local);Database=Spring;User ID=springqa;Password=springqa;Trust
<object id="transactionManager"
type="Spring.Data.AdoPlatformTransactionManager, Spring.Data">
<property name="DbProvider" ref="DbProvider"/>
</object>
<object id="adoTemplate" type="Spring.Data.AdoTemplate, Spring.Data">
<property name="DbProvider" ref="DbProvider"/>
</object>
<object id="testObjectDao" type="Spring.Data.TestObjectDao, Spring.Data.Integration.Tests">
<property name="AdoTemplate" ref="adoTemplate"/>
</object>
<!-- The object that performs multiple data access operations -->
<object id="testObjectManager"
type="Spring.Data.TestObjectManager, Spring.Data.Integration.Tests">
<property name="TestObjectDao" ref="testObjectDao"/>
</object>
</objects>
This is standard Spring configuration and as such provides you with the flexibility to parameterize your connection
string and to easily switch implementations of your DAO objects. The configuration to create a transactional
proxy for the manager class is shown below.
<!-- The rest of the config file is common no matter how many objects you add -->
<!-- that you would like to have declarative tx management applied to -->
<object id="autoProxyCreator"
type="Spring.Aop.Framework.AutoProxy.DefaultAdvisorAutoProxyCreator, Spring.Aop">
</object>
<object id="transactionAdvisor"
type="Spring.Transaction.Interceptor.TransactionAttributeSourceAdvisor, Spring.Data">
<property name="TransactionInterceptor" ref="transactionInterceptor"/>
</object>
<!-- Transaction Interceptor -->
<object id="transactionInterceptor"
type="Spring.Transaction.Interceptor.TransactionInterceptor, Spring.Data">
<property name="TransactionManager" ref="transactionManager"/>
<property name="TransactionAttributeSource" ref="attributeTransactionAttributeSource"/>
</object>
<object id="attributeTransactionAttributeSource"
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type="Spring.Transaction.Interceptor.AttributesTransactionAttributeSource, Spring.Data">
</object>
Granted this is a bit verbose and hard to grok at first sight - however you only need to grok this once as it is 'boiler
plate' XML you can reuse across multiple projects. What these object definitions are doing is to instruct Spring's
to look for all objects within the IoC configuration that have the [Transaction] attribute and then apply the AOP
transaction interceptor to them based on the transaction options contained in the attribute. The attribute serves
both as a pointcut and as the declaration of transactional option information.
Since this XML fragment is not tied to any specific object references it can be included in its own file and
then imported via the <import> element. In examples and test code this XML configuration fragment is named
autoDeclarativeServices.xml See Section 5.2.2.1, “Composing XML-based configuration metadata” for more
information.
The classes and their roles in this configuration fragment are listed below
• TransactionInterceptor is the AOP advice responsible for performing transaction management functionality.
• TransactionAttributeSourceAdvisor is an AOP Advisor that holds the TransactionInterceptor, which is the
advice, and a pointcut (where to apply the advice), in the form of a TransactionAttributeSource.
• AttributesTransactionAttributeSource is an implementation of the ITransactionAttributeSource
interface that defines where to get the transaction metadata defining the transaction
semantics (isolation level, propagation behavior, etc) that should be applied to specific
methods of specific classes. The transaction metadata is specified via implementations
of the ITransactionAttributeSource interface. This example shows the use of the
implementation Spring.Transaction.Interceptor.AttributesTransactionAttributeSource to obtain
that information from standard .NET attributes. By the very nature of using standard .NET
attributes, the attribute serves double duty in identifying the methods where the
transaction semantics apply. Alternative implementations of ITransactionAttributeSource
available are MatchAlwaysTransactionAttributeSource, NameMatchTransactionAttributeSource, or
MethodMapTransactionAttributeSource.
• MatchAlwaysTransactionAttributeSource is configured with a ITransactionAttribute instance that is
applied to all methods. The shorthand string representation, i.e. PROPAGATION_REQUIRED can be used
• AttributesTransactionAttributeSource : Use a standard. .NET attributes to specify the transactional
information. See TransactionAttribute class for more information.
• NameMatchTransactionAttributeSource allows ITransactionAttributes to be matched by method name.
The NameMap IDictionary property is used to specify the mapping. For example
<object name="nameMatchTxAttributeSource" type="Spring.Transaction.Interceptor.NameMatchTransactionAttribute
<property name="NameMap">
<dictionary>
<entry key="Execute" value="PROPAGATION_REQUIRES_NEW, -ApplicationException"/>
<entry key="HandleData" value="PROPAGATION_REQUIRED, -DataHandlerException"/>
<entry key="Find*" value="ISOLATION_READUNCOMMITTED, -DataHandlerException"/>
</dictionary>
</property>
</object>
Key values can be prefixed and/or suffixed with wildcards as well as include the full namespace of the
containing class.
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• MethodMapTransactionAttributeSource : Similar to NameMatchTransactionAttributeSource but specifies
that only fully qualified method names (i.e. type.method, assembly) and wildcards can be used at the start
or end of the method name for matching multiple methods.
• DefaultAdvisorAutoProxyCreator: looks for Advisors in the context, and automatically creates proxy objects
which are the transactional wrappers
Refer to the following section for a more convenient way to achieve the same goal of declarative transaction
management using attributes.
17.5.3. Declarative transactions using the transaction namespace
Spring provides a custom XML schema to simplify the configuration of declarative transaction management. If
you would like to perform attribute driven transaction management you first need to register the custom namespace
parser for the transaction namespace. This can be done in the application configuration file as shown below
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<configSections>
<sectionGroup name="spring">
<section name="parsers" type="Spring.Context.Support.NamespaceParsersSectionHandler, Spring.Core" />
<!-- other spring config sections like context, typeAliases, etc not shown for brevity -->
</sectionGroup>
</configSections>
<spring>
<parsers>
<parser type="Spring.Data.Config.DatabaseNamespaceParser, Spring.Data" />
<parser type="Spring.Transaction.Config.TxNamespaceParser, Spring.Data" />
<parser type="Spring.Aop.Config.AopNamespaceParser, Spring.Aop" />
</parsers>
</spring>
</configSections>
Instead of using the XML configuration listed at the end of the previous section (declarativeServices.xml you can
use the following. Note that the schemaLocation in the objects element is needed only if you have not installed
Spring's schema into the proper VS.NET 2005 location. See the chapter on VS.NET integration for more details.
<objects xmlns="http://www.springframework.net"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:tx="http://www.springframework.net/tx"
xmlns:db="http://www.springframework.net/database"
xsi:schemaLocation="http://www.springframework.net http://www.springframework.net/schema/objects/spring
http://www.springframework.net/schema/tx http://www.springframework.net/schema/tx/spring-tx-1.1.xsd"
http://www.springframework.net/schema/db http://www.springframework.net/schema/db/spring-database.xsd">
<db:provider id="DbProvider"
provider="SqlServer-1.1"
connectionString="Data Source=(local);Database=Spring;User ID=springqa;Password=springqa;Trust
<object id="transactionManager"
type="Spring.Data.AdoPlatformTransactionManager, Spring.Data">
<property name="DbProvider" ref="DbProvider"/>
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</object>
<object id="adoTemplate" type="Spring.Data.AdoTemplate, Spring.Data">
<property name="DbProvider" ref="DbProvider"/>
</object>
<object id="testObjectDao" type="Spring.Data.TestObjectDao, Spring.Data.Integration.Tests">
<property name="AdoTemplate" ref="adoTemplate"/>
</object>
<!-- The object that performs multiple data access operations -->
<object id="testObjectManager"
type="Spring.Data.TestObjectManager, Spring.Data.Integration.Tests">
<property name="TestObjectDao" ref="testObjectDao"/>
</object>
<tx:attribute-driven transaction-manager="transactionManager"/>
</objects>
Tip
You can actually omit the 'transaction-manager' attribute in the <tx:attribute-driven/> tag
if the object name of the IPlatformTransactionManager that you want to wire in has the name
'transactionManager'. If the PlatformTransactionManager object that you want to dependency
inject has any other name, then you have to be explicit and use the 'transaction-manager' attribute
as in the example above.
The various optional elements of the <tx:attribute-driven/> tag are summarised in the following table
Table 17.1. <tx:annotation-driven/> settings
Attribute
Required?
Default
Description
transaction-manager
No
transactionManager
The name of transaction
manager to use. Only
required if the name of
the transaction manager is
not transactionManager,
as in the example above.
proxy-target-type
No
Controls
what
type
of transactional proxies
are created for classes
annotated
with
the
[Transaction] attribute.
If "proxy-target-type"
attribute is set to "true",
then class-based proxies
will be created (proxy
inherits from target class,
however calls are still
delegated to target object
via composition. This
allows for casting to base
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Attribute
Required?
Default
Description
class. If "proxy-targettype" is "false" or if
the attribute is omitted,
then a pure composition
based proxy is created
and you can only cast
the proxy to implemented
interfaces. (See the section
entitled Section 13.6,
“Proxying mechanisms”
for a detailed examination
of the different proxy
types.)
No
order
Defines the order of
the transaction advice
that will be applied to
objects annotated with
[Transaction]. More on
the rules related to
ordering of AOP advice
can be found in the
AOP chapter (see section
Section 13.3.2.5, “Advice
Ordering”). Note that not
specifying any ordering
will leave the decision as
to what order advice is run
in to the AOP subsystem.
Note
The "proxy-target-type" attribute on the <tx:attribute-driven/> element controls what type of
transactional proxies are created for classes annotated with the Transaction attribute. If "proxytarget-type" attribute is set to "true", then inheritance-based proxies will be created. If "proxytarget-type" is "false" or if the attribute is omitted, then composition based proxies will be created.
(See the section entitled Section 13.6, “Proxying mechanisms” for a detailed examination of the
different proxy types.)
You can also define the transactional semantics you want to apply through the use of a <tx:advice> definition.
This lets you define the transaction metadata such as propagation and isolation level as well as the methods for
which that metadata applies external to the code unlike the case of using the transaction attribute. The <tx:advice>
definition creates an instance of a ITransactionAttributeSource during parsing time. Switching to use <tx:advice>
instead of <tx:attribute-driven/> in the example would look like the following
<tx:advice id="txAdvice" transaction-manager="transactionManager">
<tx:attributes>
<tx:method name="Save*"/>
<tx:method name="Delete*"/>
</tx:attributes>
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</tx:advice>
This says that all methods that start with Save and Delete would have associated with them the default settings
of transaction metadata. These default values are listed below..
Here is an example using other elements of the <tx:method/> definition
<!-- the transactional advice (i.e. what 'happens'; see the <aop:advisor/> object below) -->
<tx:advice id="txAdvice" transaction-manager="transactionManager">
<!-- the transactional semantics... -->
<tx:attributes>
<!-- all methods starting with 'get' are read-only -->
<tx:method name="Get*" read-only="true"/>
<!-- other methods use the default transaction settings (see below) -->
<tx:method name="*"/>
</tx:attributes>
</tx:advice>
The <tx:advice/> definition reads as “... all methods on starting with 'Get' are to execute in the context of a readonly transaction, and all other methods are to execute with the default transaction semantics”. The 'transactionmanager' attribute of the <tx:advice/> tag is set to the name of the PlatformTransactionManager object that is
going to actually drive the transactions (in this case the 'transactionManager' object).
You can also use the AOP namespace <aop:advisor> element to tie together a pointcut and the above defined
advice as shown below.
<object id="serviceOperation" type="Spring.Aop.Support.SdkRegularExpressionMethodPointcut, Spring.Aop">
<property name="pattern" value="Spring.TxQuickStart.Services.*"/>
</object>
<aop:config>
<aop:advisor pointcut-ref="serviceOperation" advice-ref="txAdvice"/>
</aop:config>
This is assuming that the service layer class, TestObjectManager, in the namespace Spring.TxQuickStart.Services.
The <aop:config/> definition ensures that the transactional advice defined by the 'txAdvice' object actually
executes at the appropriate points in the program. First we define a pointcut that matches any operation defined
on classes in the Spring.TxQuickStart.Services (you can be more selective in your regular expression). Then we
associate the pointcut with the 'txAdvice' using an advisor. In the example, the result indicates that at the execution
of a 'SaveTwoTestObjects' and 'DeleteTwoTestObject', the advice defined by 'txAdvice' will be run.
The various transactional settings that can be specified using the <tx:advice/> tag. The default <tx:advice/>
settings are listed below and are the same as when you use the Transaction attribute.
• The propagation setting is TransactionPropagation.Required
• The isolation level is IsolationLevel.ReadCommitted
• The transaction is read/write
• The transaction timeout defaults to the default timeout of the underlying transaction system, or none if timeouts
are not supported
• EnterpriseServicesInteropOption (.NET 2.0 only with TxScopeTransactionManager) - options between
transaction created with System.Transactions and transactions created through COM+
• Any exception will trigger rollback.
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These default settings can be changed; the various attributes of the <tx:method/> tags that are nested within
<tx:advice/> and <tx:attributes/> tags are summarized below:
Table 17.2. <tx:method/> settings
Attribute
Required?
name
Yes
propagation
No
Required
The
transaction
propagation behavior
isolation
No
ReadCommitted
The transaction isolation
level
timeout
No
-1
The transaction timeout
value (in seconds)
read-only
No
false
Is this transaction readonly?
Description
None
Interoperability options
with COM+ transactions.
(.NET
2.0
and
TxScopeTransactionManager
only)
The method name(s) with
which the transaction
attributes are to be
associated. The wildcard
(*) character can be
used
to
associate
the same transaction
attribute settings with
a number of methods;
for example, 'Get*',
'Handle*', 'On*Event',
and so forth.
EnterpriseServicesInteropOption
No
rollback-for
Default
No
The Exception(s) that
will trigger rollback;
comma-delimited.
For
example,
'MyProduct.MyBusinessException,Va
no-rollback-for
No
The Exception(s) that
will not trigger rollback;
comma-delimited.
For
example,
'MyProduct.MyBusinessException,Va
17.5.4. Transaction attribute settings
The Transaction attribute is metadata that specifies that a class or method must have transactional semantics. The
default Transaction attribute settings are
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• The propagation setting is TransactionPropagation.Required
• The isolation level is IsolationLevel.ReadCommitted
• The transaction is read/write
• The transaction timeout defaults to the default timeout of the underlying transaction system, or none if timeouts
are not supported
• EnterpriseServicesInteropOption (.NET 2.0 only with TxScopeTransactionManager) - options between
transaction created with System.Transactions and transactions created through COM+
• Any exception will trigger rollback.
The default settings can, of course, be changed; the various properties of the Transaction attribute are summarised
in the following table
Table 17.3. Transaction attribute properties
Property
TransactionPropagation
Type
enumeration,
Description
optional propagation setting. Required,
RequiresNew,
NotSupported, Never, Nested
Spring.Transaction.TransactionPropagation
Supports,
Mandatory,
Isolation
System.Data.IsolationLevel
ReadOnly
boolean
optional isolation level
read/write vs. read-only transaction
EnterpriseServicesInteropOption enumeration
Options for interoperability with COM
System.Transactions.EnterpriseServicesInteropOption
+
transactions
(.NET
2.0
and
TxScopeTransactionManager only)
Timeout
int (in seconds granularity)
the transaction timeout
RollbackFor
an array of Type objects
an optional array of exception classes that
must cause rollback
NoRollbackFor
an array of Type objects
an optional array of exception classes that
must not cause rollback
Note that setting the TransactionPropagation to Nested will throw a NestedTransactionNotSupportedException
in a case where an actual nested transaction occurs, i.e. not in the case of applying the Nested propagation but in
fact no nested calls are made. This will be fixed for the Spring 1.2 release for SqlServer and Oracle which support
nested transactions. Also note, that changing of isolation levels on a per-method basis is also scheduled for the
Spring 1.2 release since it requires detailed command text metadata for each dbprovider. Please check the forums
for news on when this feature will be introduced into the nightly builds.
If you specify an exception type for 'NoRollbackFor' the action taken is to commit the work that has been done in
the database up to the point where the exception occurred. The exception is still propagated out to the calling code.
The ReadOnly boolean is a hint to the data access technology to enable read-only optimizations. This currently
has no effect in Spring's ADO.NET framework. If you would like to enable read-only optimizations in ADO.NET
this is generally done via the 'Mode=Read' or 'Mode=Read-Only" options in the connection string. Check your
database provider for more information. In the case of NHibernate the flush mode is set to Never when a new
Session is created for the transaction.
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Throwing exceptions to indicate failure and assuming success is an easier and less invasive programming model
than performing the same task Programatically - ContextUtil.MyTransactionVote or TransactionScope.Complete.
The rollback options are a means to influence the outcome of the transaction based on the exception type which
adds an extra degree of flexibility.
Having any exception trigger a rollback has similar behavior as applying the AutoComplete attribute available
when using .NET Enterprise Services. The difference with AutoComplete is that using AutoComplete is also
coupled to the lifetime of the ServicedComponent since it sets ContextUtil.DeactivateOnReturn to true. For a
stateless DAO layer this is not an issue but it could be in other scenarios. Spring's transactional aspect does not
affect the lifetime of your object.
17.5.5. Declarative Transactions using AutoProxy
if you choose not to use the transaction namespace for declarative transaction management then you can use
'lower level' object definitions to configure declarative transactions. This approach was shown in the first
example. The use of Spring's autoproxy functionality defines criteria to select a collection of objects to create
a transactional AOP proxy. There are two AutoProxy classes that you can use, ObjectNameAutoProxyCreator
and DefaultAdvisorAutoProxyCreator. If you are using the new transaction namespace support you do not need
to configure these objects as a DefaultAdvisorAutoProxyCreator is created 'under the covers' while parsing the
transaction namespace elements
17.5.5.1. Creating transactional proxies with ObjectNameAutoProxyCreator
The ObjectNameAutoProxyCreator is useful when you would like to create transactional proxies for many
objects. The definitions for the TransactionInterceptor and associated attributes is done once. When you add
new objects to your configuration file that need to be proxies you only need to add them to the list of object
referenced in the ObjectNameAutoProxyCreator. Here is an example showing its use. Look in the section that
use ProxyFactoryObject for the declaration of the transactionInterceptor.
<object name="autoProxyCreator"
type="Spring.Aop.Framework.AutoProxy.ObjectNameAutoProxyCreator, Spring.Aop">
<property name="InterceptorNames" value="transactionInterceptor"/>
<property name="ObjectNames">
<list>
<idref local="testObjectManager"/>
</list>
</property>
</object>
17.5.5.2. Creating transactional proxies with DefaultAdvisorAutoProxyCreator
This is a commonly used way to configure declarative transactions since it enables you to refer to the transaction
attribute as the pointcut to use for the transactional advice for any object definition defined in the IoC container.
An example of this configuration approach was shown in Chapter 5.
17.5.6. Declarative Transactions using TransactionProxyFactoryObject
The TransactionProxyFactoryObject is easier to use than a ProxyFactoryObject for most cases since the
transaction interceptor and transaction attributes are properties of this object. This removes the need to declare
them as separate objects. Also, unlike the case with the ProxyFactoryObject, you do not have to give fully qualified
method names, just the normal 'short' method name. Wild card matching on the method name is also allowed,
which in practice helps to enforce a common naming convention for the methods of your DAOs. The example
from chapter 5 is shown here using a TransactionProxyFactoryObject.
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<object id="testObjectManager"
type="Spring.Transaction.Interceptor.TransactionProxyFactoryObject, Spring.Data">
<property name="PlatformTransactionManager" ref="adoTransactionManager"/>
<property name="Target">
<object type="Spring.Data.TestObjectManager, Spring.Data.Integration.Tests">
<property name="TestObjectDao" ref="testObjectDao"/>
</object>
</property>
<property name="TransactionAttributes">
<name-values>
<add key="Save*" value="PROPAGATION_REQUIRED"/>
<add key="Delete*" value="PROPAGATION_REQUIRED"/>
</name-values>
</property>
</object>
Note the use of an inner object definition for the target which will make it impossible to obtain an unproxied
reference to the TestObjectManager.
As can be seen in the above definition, the TransactionAttributes property holds a collection of name/value pairs.
The key of each pair is a method or methods (a * wildcard ending is optional) to apply transactional semantics to.
Note that the method name is not qualified with a package name, but rather is considered relative to the class of
the target object being wrapped. The value portion of the name/value pair is the TransactionAttribute itself that
needs to be applied. When specifying it as a string value as in this example, it's in String format as defined by
TransactionAttributeConverter. This format is:
PROPAGATION_NAME,ISOLATION_NAME,readOnly,timeout_NNNN,+Exception1,-Exception2
Note that the only mandatory portion of the string is the propagation setting. The default transactions semantics
which apply are as follows:
• Exception Handling: All exceptions thrown trigger a rollback.
• Transactions are read/write
• Isolation Level: TransactionDefinition.ISOLATION_DEFAULT
• Timeout: TransactionDefinition.TIMEOUT_DEFAULT
Multiple rollback rules can be specified here, comma-separated. A - prefix forces rollback; a + prefix
specifies commit. Under the covers the IDictionary of name value pairs will be converted to an instance of
NameMatchTransactionAttributeSource
The
string
used
for
PROPAGATION_NAME
are
those
defined
on
the
Spring.Transaction.TransactionPropagation enumeration, namely Required, Supports, Mandatory, RequiresNew,
NotSupported, Never, Nested. The string used for ISOLATION_NAME are those defined on the
System.Data.IsolationLevel enumberateion, namely ReadCommitted, ReadUncommitted, RepeatableRead,
Serializable.
The TransactionProxyFactoryObject allows you to set optional "pre" and "post" advice, for additional interception
behavior, using the "PreInterceptors" and "PostInterceptors" properties. Any number of pre and post advices
can be set, and their type may be Advisor (in which case they can contain a pointcut), MethodInterceptor or
any advice type supported by the current Spring configuration (such as ThrowsAdvice, AfterReturningAdvice or
BeforeAdvice, which are supported by default.) These advices must support a shared-instance model. If you need
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transactional proxying with advanced AOP features such as stateful mixins, it's normally best to use the generic
ProxyFactoryObject, rather than the TransactionProxyFactoryObject convenience proxy creator.
17.5.7. Concise proxy definitions
Using abstract object definitions in conjunction with a TransactionProxyFactoryObject provides you a more
concise means to reuse common configuration information instead of duplicating it over and over again with a
definition of a TransactionProxyFactoryObject per object. Objects that are to be proxied typically have the same
pattern of method names, Save*, Find*, etc. This commonality can be placed in an abstract object definition,
which other object definitions refer to and change only the configuration information that is different. An abstract
object definition is shown below
<object id="txProxyTemplate" abstract="true"
type="Spring.Transaction.Interceptor.TransactionProxyFactoryObject, Spring.Data">
<property name="PlatformTransactionManager" ref="adoTransactionManager"/>
<property name="TransactionAttributes">
<name-values>
<add key="Save*" value="PROPAGATION_REQUIRED"/>
<add key="Delete*" value="PROPAGATION_REQUIRED"/>
</name-values>
</property>
</object>
Subsequent definitions can refer to this 'base' configuration as shown below
<object id="testObjectManager" parent="txProxyTemplate">
<property name="Target">
<object type="Spring.Data.TestObjectManager, Spring.Data.Integration.Tests">
<property name="TestObjectDao" ref="testObjectDao"/>
</object>
</property>
</object>
17.5.8. Declarative Transactions using ProxyFactoryObject
Using the general ProxyFactoryObject to declare transactions gives you a great deal of control over the proxy
created since you can specify additional advice, such as for logging or performance. Based on the example shown
previously a sample configuration using ProxyFactoryObject is shown below
<object id="testObjectManagerTarget" type="Spring.Data.TestObjectManager, Spring.Data.Integration.Tests">
<property name="TestObjectDao" ref="testObjectDao"/>
</object>
<object id="testObjectManager" type="Spring.Aop.Framework.ProxyFactoryObject, Spring.Aop">
<property name="Target" ref="testObjectManagerTarget"/>
<property name="ProxyInterfaces">
<value>Spring.Data.ITestObjectManager</value>
</property>
<property name="InterceptorNames">
<value>transactionInterceptor</value>
</property>
</object>
The ProxyFactoryObject will create a proxy for the Target, i.e. a TestObjectManager instance. An inner object
definition could also have been used such that it would make it impossible to obtain an unproxied object from the
container. The interceptor name refers to the following definition.
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<object id="transactionInterceptor" type="Spring.Transaction.Interceptor.TransactionInterceptor, Spring.Data
<property name="TransactionManager" ref="adoTransactionManager"/>
<!-- note do not have converter from string to this property type registered -->
<property name="TransactionAttributeSource" ref="methodMapTransactionAttributeSource"/>
</object>
<object name="methodMapTransactionAttributeSource"
type="Spring.Transaction.Interceptor.MethodMapTransactionAttributeSource, Spring.Data">
<property name="MethodMap">
<dictionary>
<entry key="Spring.Data.TestObjectManager.SaveTwoTestObjects, Spring.Data.Integration.Tests"
value="PROPAGATION_REQUIRED"/>
<entry key="Spring.Data.TestObjectManager.DeleteTwoTestObjects, Spring.Data.Integration.Tests"
value="PROPAGATION_REQUIRED"/>
</dictionary>
</property>
</object>
The transaction options for each method are specified using a dictionary containing the class name + method
name, assembly as the key and the value is of the form
• <Propagation Behavior>, <Isolation Level>, <ReadOnly>, -Exception, +Exception
All but the propagation behavior are optional. The + and - are used in front of the name of an exception. Minus
indicates to rollback if the exception is thrown, the Plus indicates to commit if the exception is thrown.
17.6. Programmatic transaction management
Spring provides two means of programmatic transaction management:
• Using the TransactionTemplate
• Using a IPlatformTransactionManager implementation directly
These are located in the Spring.Transaction.Support namespace. If you are going to use programmatic transaction
management, the Spring team generally recommends the first approach (i.e. Using the TransactionTemplate)
17.6.1. Using the TransactionTemplate
The TransactionTemplate adopts the same approach as other Spring templates such as AdoTemplate and
HibernateTemplate. It uses a callback approach, to free application code from having to do the boilerplate
acquisition and release of resources, and results in code that is intention driven, in that the code that is written
focuses solely on what the developer wants to do. Granted that the using construct of System.Transaction alleviates
much of this. One key difference with the approach taken with the TransactionTemplate is that a commit is
assumed - throwing an exception triggers a rollback instead of using the TransactionScope API to commit or
rollback. This also allows for the use of rollback rules, that is a commit can still occur for exceptions of certain
types.
Note
As you will immediately see in the examples that follow, using the TransactionTemplate absolutely
couples you to Spring's transaction infrastructure and APIs. Whether or not programmatic transaction
management is suitable for your development needs is a decision that you will have to make yourself.
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Application code that must execute in a transaction context looks like this. You, as an application developer, will
write a ITransactionCallback implementation (typically expressed as an anonymous delegate) that will contain
all of the code that you need to have execute in the context of a transaction. You will then pass an instance of
your custom ITransactionCallback to the Execute(..) method exposed on the TransactionTemplate. Note that the
ITransactionCallback can be used to return a value:
public class SimpleService : IService
{
private TransactionTemplate transactionTemplate;
public SimpleService(IPlatformTransactionManager transactionManager)
{
AssertUtils.ArgumentNotNull(transactionManager, "transactionManager");
transactionTemplate = new TransactionTemplate(transactionManager);
}
public object SomeServiceMethod()
{
return tt.Execute(delegate {
UpdateOperation(userId);
return ResultOfUpdateOperation2();
});
}
}
This code example is specific to .NET 2.0 since it uses anonymous delegates, which provides a particularly elegant
means to invoke a callback function as local variables can be referred to inside the delegate, i.e. userId. In this
case the ITransactionStatus was not exposed in the delegate (delegate can infer the signature to use), but one
could also obtain a reference to the ITransactionStatus instance and set the RollbackOnly property to trigger
a rollback - or alternatively throw an exception. This is shown below
tt.Execute(delegate(ITransactionStatus status)
{
try {
UpdateOperation1();
UpdateOperation2();
} catch (SomeBusinessException ex) {
status.RollbackOnly = true;
}
return null;
});
If you are using .NET 1.1 then you should provide a normal delegate reference or an instance of a class that
implements the ITransactionCallback interface. This is shown below
tt.Execute(new TransactionRollbackTxCallback(amount));
public class TransactionRollbackTxCallback : ITransactionCallback
{
private decimal amount;
public TransactionRollbackTxCallback(decimal amount)
{
this.amount = amount
}
public object DoInTransaction(ITransactionStatus status)
{
adoTemplate.ExecuteNonQuery(CommandType.Text, "insert into dbo.Debits (DebitAmount) VALUES (@amount
// decide you need to rollback...
status.RollbackOnly = true;
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return null;
}
}
Application
classes
wishing
to use the TransactionTemplate must have access to a
IPlatformTransactionManager (which will typically be supplied to the class via dependency injection). It is
easy to unit test such classes with a mock or stub IPlatformTransactionManager.
17.6.1.1. Specifying transaction settings
Transaction settings such as the propagation mode, the isolation level, the timeout, and so forth can be set on the
TransactionTemplate either programmatically or in configuration. TransactionTemplate instances by default
have the default transactional settings. Find below an example of programmatically customizing the transactional
settings for a specific TransactionTemplate.
public class SimpleService : IService
{
private TransactionTemplate transactionTemplate;
public SimpleService(IPlatformTransactionManager transactionManager)
{
AssertUtils.ArgumentNotNull(transactionManager, "transactionManager");
transactionTemplate = new TransactionTemplate(transactionManager);
// the transaction settings can be set here explicitly if so desired
transactionTemplate.TransactionIsolationLevel = IsolationLevel.ReadUncommitted;
transactionTemplate.TransactionTimeout = 30;
// and so forth...
}
. . .
}
Find below an example of defining a TransactionTemplate with some custom transactional settings, using Spring
XML configuration. The 'sharedTransactionTemplate' can then be injected into as many services as are required.
<object id="sharedTransactionTemplate"
type="Spring.Transaction.Support.TransactionTemplate, Sprng.Data">
<property name="TransactionIsolationLevel" value="IsolationLevel.ReadUncommitted"/>
<property name="TransactionTimeout" value="30"/>
</object>
Finally, instances of the TransactionTemplate class are threadsafe, in that instances do not maintain any
conversational state. TransactionTemplate instances do however maintain configuration state, so while a
number of classes may choose to share a single instance of a TransactionTemplate, if a class needed to
use a TransactionTemplate with different settings (for example, a different isolation level), then two distinct
TransactionTemplate instances would need to be created and used.
17.6.2. Using the PlatformTransactionManager
You can also use the PlatformTransactionManager directly to manage your transaction. Simply pass the
implementation of the PlatformTransactionManager you're using to your object via a object reference through
standard Dependency Injection techniques. Then, using the TransactionDefinition and ITransactionStatus objects,
you can initiate transactions, rollback and commit.
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DefaultTransactionDefinition def = new DefaultTransactionDefinition();
def.PropagationBehavior = TransactionPropagation.Required;
ITransactionStatus status = transactionManager.GetTransaction(def);
try
{
// execute your business logic here
} catch (Exception e)
{
transactionManager.Rollback(status);
throw;
}
transactionManager.Commit(status);
Note that a corresponding 'using TransactionManagerScope' class can be modeled to get similar API usage to
System.Transactions TransactionScope.
17.7. Choosing between programmatic and declarative
transaction management
Programmatic transaction management is usually a good idea only if you have a small number of transactional
operations. For example, if you have a web application that require transactions only for certain update operations,
you may not want to set up transactional proxies using Spring or any other technology. In this case, using the
TransactionTemplate may be a good approach. On the other hand, if your application has numerous transactional
operations, declarative transaction management is usually worthwhile. It keeps transaction management out of
business logic, and is not difficult to configure in Spring.
17.8. Transaction lifecycle and status information
You
can
query
the
status
of
the current Spring managed transaction with the class
TransactionSynchronizationManager. Typical application code should not need to rely on using this class but
in some cases it is convenient to receive events around the lifecycle of the transaction, i.e. before committing,
after committing. TransactionSynchronizationManager provides a method to register a callback object that is
informed on all significant stages in the transaction lifecycle. Note that you can register for lifecycle call back
information for any of the transaction managers you use, be it NHibernate or local ADO.NET transactions.
The method to register a callback with the TransactionSynchronizationManager is
public static void RegisterSynchronization( ITransactionSynchronization synchronization )
Please refer to the SDK docs for information on other methods in this class.
The ITransactionSynchronization interface is
public interface ITransactionSynchronization
{
// Typically used by Spring resource management code
void Suspend();
void Resume();
// Transaction lifeycyle callback methods
// Typically used by Spring resource management code but maybe useful in certain cases to application code
void BeforeCommit( bool readOnly );
void AfterCommit();
void BeforeCompletion();
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void AfterCompletion( TransactionSynchronizationStatus status );
}
The TransactionSynchronizationStatus is an enum with the values Committed, Rolledback, and Unknown.
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Chapter 18. DAO support
18.1. Introduction
Spring promotes the use of data access interfaces in your application architecture. These interfaces encapsulate
the storage and retrieval of data and objects specific to your business domain without reference to a specific
persistence API. Within a layered architecture, the service layer is typically responsible for coordinating responses
to a particular business request and it delegates any persistence related activities to objects that implement
these data access interfaces. These objects are commonly referred to as DAOs (Data Access Objects) and the
architectural layer as a DAL (Data Access Layer).
The benefits of using DAOs in your application are increased portability across persistence technology and ease
of testing. Testing is more easily facilitated because a mock or stub implementation of the data access interface
can be easily created in a NUnit test so that service layer functionality can be tested without any dependency on
the database. This is beneficial because tests that rely on the database are usually hard to set up and tear down
and also are impractical for testing exceptional behavior.
The Data Access Object (DAO) support in Spring is aimed at making it easy to work with data access technologies
like ADO.NET and NHibernate in a standardized way. Spring provides two central pieces of functionality to meet
this goal. The first is providing a common exception hierarchy across providers and the second is providing base
DAOs classes that raise the level of abstraction when performing common ADO.NET operations. This allows
one to switch between the aforementioned persistence technologies fairly easily and it also allows one to code
without worrying about catching exceptions that are specific to each technology.
18.2. Consistent exception hierarchy
Database exceptions in the ADO.NET API are not consistent across providers. The .NET 1.1 BCL did not provide
a common base class for ADO.NET exceptions. As such you were required to handle exceptions specific to each
provider such as System.Data.SqlClient.SqlException or System.Data.OracleClient.OracleException.
The .NET 2.0 BCL improved in this regard by introducing a common base class for exceptions,
System.Data.Common.DbException. However the common DbException is not very portable either as it provides
a vendor specific error code as the underlying piece of information as to what went wrong. This error code is
different across providers for the same conceptual error, such as a violation of data integrity or providing bad
SQL grammar.
To promote writing portable and descriptive exception handling code Spring provides a
convenient translation from technology specific exceptions like System.Data.SqlClient.SqlException
or System.Data.OracleClient.OracleException to its own exception hierarchy with the
Spring.Dao.DataAccessException as the root exception. These exceptions wrap the original exception so there
is never any risk that one might lose any information as to what might have gone wrong.
In addition to exceptions from ADO.NET providers, Spring can also wrap NHibernate-specific exceptions.. This
allows one to handle most persistence exceptions, which are non-recoverable, only in the appropriate layers,
without boilerplate using or catch and throw blocks, and exception declarations. As mentioned above, ADO.NET
exceptions (including database-specific dialects) are also converted to the same hierarchy, meaning that one can
perform some operations with ADO.NET within a consistent programming model. The above holds true for the
various template-based versions of the ORM access framework.
The exception hierarchy that Spring uses is outlined in the following image:
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(Please note that the class hierarchy detailed in the above image shows only a subset of the whole, rich,
DataAccessException hierarchy.)
The exception translation functionality is in the namespace Spring.Data.Support and is based on the interface
IAdoExceptionTranslator shown below.
public interface IAdoExceptionTranslator
{
DataAccessException Translate( string task, string sql, Exception exception );
}
The arguments to the translator are a task string providing a description of the task being attempted, the SQL query
or update that caused the problem, and the 'raw' exception thrown by the ADO.NET data provider. The additional
task and SQL arguments allow for very readable and clear error messages to be created when an exception occurs.
A default implementation, ErrorCodeExceptionTranslator, is provided that uses the error codes defined for each
data provider in the file dbproviders.xml. Refer to this file, an embedded resource in the Spring.Data assembly,
for the exact mappings of error codes to Spring DataAccessExceptions.
A common need is to modify the error codes that are map onto the exception hierarchy. There are several ways
to accomplish this task.
One approach is to override the error codes that are defined in assembly://Spring.Data/Spring.Data.Common/
dbproviders.xml. By default, the DbProviderFactory will look for additional metadata for the IoC container
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it uses internally to define and manage the DbProviders in a file named dbProviders.xml located in the root
runtime directory. (You can change this location, see the documentation on DbProvider for more information.)
This is a standard Spring application context so all features, such as ObjectFactoryPostProcessors are available
and will be automatically applied. Defining a PropertyOverrideConfigurer in this additional configuration file
will allow for you to override specific property values defined in the embedded resource file. As an example, the
additional dbProviders.xml file shown below will add the error code 2601 to the list of error codes that map to
a DataIntegrityViolationException.
<objects xmlns='http://www.springframework.net'>
<alias name='SqlServer-2.0' alias='SqlServer2005'/>
<object name="appConfigPropertyOverride" type="Spring.Objects.Factory.Config.PropertyOverrideConfigurer, Sprin
<property name="Properties">
<name-values>
<add key="SqlServer2005.DbMetadata.ErrorCodes.DataIntegrityViolationCodes"
value="544,2601,2627,8114,8115"/>
</name-values>
</property>
</object>
</objects>
The reason to define the alias is that PropertyOverrideConfigurer assumes a period (.) as the separator to pick
out the object name but the names of the objects in dbProviders.xml have periods in them (i.e. SqlServer-2.0 or
System.Data.SqlClient). Creating an alias that has no periods in the name is a workaround.
Another
subclass
way
to
customize
the
mappings
of
error
codes
to
ErrorCodeExceptionTranslator
and
override
the
method,
exceptions
is
to
DataAccessException
TranslateException(string task, string sql, string errorCode, Exception exception).
This will be
called before referencing the metadata to perform exception translation. The vendor specific error code provided
as a method argument has already been parsed out of the raw ADO.NET exception. If you create your own specific
subclass, then you should set the property ExceptionTranslator on AdoTemplate and HibernateTemplate/
HibernateTransactionManager to refer to your custom implementation (unless you are using autowiring).
The third way is to write an implementation of IAdoExceptionTranslator and set the property
FallbackTranslator'on ErrorCodeExceptionTranslator. In this case you are responsible for parsing our
the vendor specific error code from the raw ADO.NET exception. As with the case of subclassing
ErrorCodeExceptionTranslator, you will need to refer to this custom exception translator when using AdoTemplate
or HibernateTemplate/HibernateTransactionManager.
The ordering of the exception translation processing is as follows. The method TranslateException is called first,
then the standard exception translation logic, then the FallbackTranslator.
Note that you can use this API directly in your own Spring independent data layer. If you are using Spring's
ADO.NET abstraction class, AdoTemplate, or HibernateTemplate, the converted exceptions will be thrown
automatically. Somewhere in between these two cases is using Spring's declarative transaction management
features in .NET 2.0 with the raw ADO.NET APIs and using IAdoExceptionTranslator in your exception
handling layer (which might be implemented in AOP using Spring's exception translation aspect).
Some of the more common data access exceptions are described here. Please refer to the API documentation for
more details.
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Table 18.1. Common DataAccessExceptions
Exception
Description
BadSqlGrammarException
Exception thrown when SQL specified is invalid.
DataIntegrityViolationException
Exception thrown when an attempt to insert or update
data results in violation of an integrity constraint. For
example, inserting a duplicate key.
PermissionDeniedDataAccessException
Exception thrown when the underling resource denied
a permission to access a specific element, such as a
specific database table.
DataAccessResourceFailureException
Exception thrown when a resource fails completely, for
example, if we can't connect to a database.
ConcurrentyFailureException
Exception thrown when a concurrency error
occurs. OptimisticLockingFailureException and
PessimisticLockingFailureException are subclasses.
This is a useful exception to catch and to retry the
transaction again. See Spring's Retry Aspect for an
AOP based solution.
OptimisticLockingFailureException
Exception thrown when there an optimistic
locking
failure
occurs.
The
subclass
ObjectOptimisticLockingFailureException can be
used to examine the Type and the IDof the object that
failed the optimistic locking.
PessimisticLockingFailure
Exception
thrown
when
a
pessimistic
locking
failure
occures.
Subclasses
of
this exception are CannotAcquireLockException,
CannotSerializeTransactionException,
and
DeadlockLoserDataAccessException.
CannotAcquireLockException
Exception thrown when a lock can not be acquired, for
example during an update, i..e a select for update
CannotSerializeTransactionException
Exception thrown when a transaction can not be
serialized.
18.3. Consistent abstract classes for DAO support
To make it easier to work with a variety of data access technologies such as ADO.NET, NHibernate, and
iBatis.NET in a consistent way, Spring provides a set of abstract DAO classes that one can extend. These abstract
classes have methods for providing the data source and any other configuration settings that are specific to the
technology one is currently using.
DAO support classes:
• AdoDaoSupport - super class for ADO.NET data access objects. Requires a DbProvider to be provided; in turn,
this class provides a AdoTemplate instance initialized from the supplied DbProvider to subclasses. See the
documentation for AdoTemplate for more information.
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• HibernateDaoSupport - super class for NHibernate data access objects. Requires a ISessionFactory
to be provided; in turn, this class provides a HibernateTemplate instance initialized from the supplied
SessionFactory to subclasses. Can alternatively be initialized directly via a HibernateTemplate, to reuse the
latter's settings like SessionFactory, flush mode, exception translator, etc. This is contained in a download
separate from the main Spring.NET distribution.
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Chapter 19. DbProvider
19.1. Introduction
Spring provides a generic factory for creating ADO.NET API artifacts such as IDbConnection and IDbCommand. The
factory API is very similar to the one introduced in .NET 2.0 but adds extra metadata needed by Spring to support
features provided by its DAO/ADO.NET framework such as error code translation to a DAO exception hierarchy.
The factory itself is configured by using a standard Spring XML based configuration file though it is unlikely
you will need to modify those settings yourself, you only need be concerned with using the factory. Out of the
box several popular databases are supported and an extension mechanism is available for defining new database
providers or modifying existing ones. A custom database namespace for configuration aids in making terse XML
based declarations of Spring's database objects you wish to use.
The downside of Spring's factory as compared to the one in .NET 2.0 is that the types returned are lower
level interfaces and not the abstract base classes in System.Data.Common. However, there are still 'holes' in
the current .NET 2.0 provider classes that are 'plugged' with Spring's provider implementation. One of the most
prominent is the that the top level DbException exposes the HRESULT of the remote procedure call, which is
not what you are commonly looking for when things go wrong. As such Spring's provider factory exposes the
vendor sql error code and also maps that error code onto a consistent data access exception hierarchy. This makes
writing portable exception handlers much easier. In addition, the DbParameter class doesn't provide the most
common convenient methods you would expect as when using say the SqlServer provider. If you need to access
the BCL provider abstraction, you still can through Spring's provider class. Furthermore, a small wrapper around
the standard BCL provider abstraction allows for integration with Spring's transaction management facilities,
allowing you to create a DbCommand with its connection and transaction properties already set based on the
transaction calling context.
19.2. IDbProvider and DbProviderFactory
The IDbProvider API is shown below and should look familiar to anyone using .NET 2.0 data providers. Note that
Spring's DbProvider abstraction can be used on .NET 1.1 in addition to .NET 2.0
public interface IDbProvider
{
IDbCommand CreateCommand();
object CreateCommandBuilder();
IDbConnection CreateConnection();
IDbDataAdapter CreateDataAdapter();
IDbDataParameter CreateParameter();
string CreateParameterName(string name);
string CreateParameterNameForCollection(string name);
IDbMetadata DbMetadata
{
get;
}
string ConnectionString
{
set;
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get;
}
string ExtractError(Exception e);
bool IsDataAccessException(Exception e);
}
ExtractError is used to return an error string for translation into a DAO exception. On .NET 1.1 the method
IsDataAccessException is used to determine if the thrown exception is related to data access since in .NET 1.1
there isn't a common base class for database exceptions. CreateParameterName is used to create the string for
parameters used in a CommandText object while CreateParameterNameForCollection is used to create the string
for a IDataParameter.ParameterName, typically contained inside a IDataParameterCollection.
The class DbProviderFactory creates IDbProvider instances given a provider name. The connection string
property will be used to set the IDbConnection returned by the factory if present. The provider names, and
corresponding database, currently configured are listed below.
• SqlServer-1.1 - Microsoft SQL Server, provider V1.0.5000.0 in framework .NET V1.1
• SqlServer-2.0 (aliased to System.Data.SqlClient) - Microsoft SQL Server, provider V2.0.0.0 in
framework .NET V2.0
• SqlServerCe-3.1 - Microsoft SQL Server Compact Edition, provider V9.0.242.0
• SqlServerCe-3.5.1 (aliased to System.Data.SqlServerCe) - Microsoft SQL Server Compact Edition,
provider V3.5.1.0
• OleDb-1.1 - OleDb, provider V1.0.5000.0 in framework .NET V1.1
• OleDb-2.0 (aliased to System.Data.OleDb) - OleDb, provider V2.0.0.0 in framework .NET V2.0
• OracleClient-2.0 (aliased to System.Data.OracleClient) - Oracle, Microsoft provider V2.0.0.0
• OracleODP-2.0 (aliased to System.DataAccess.Client) - Oracle, Oracle provider V2.102.2.20
• MySql - MySQL, MySQL provider 1.0.10.1
• MySql-1.0.9 - MySQL, MySQL provider 1.0.9
• MySql-5.0 - MySQL, MySQL provider 5.0.7.0
• MySql-5.0.8.1 - MySQL, MySQL provider 5.0.8.1
• MySql-5.1 - MySQL, MySQL provider 5.1.2.2
• MySql-5.1.4 - MySQL, MySQL provider 5.1.2.2
• MySql-5.2.3 (aliased to MySql.Data.MySqlClient) MySQL, MySQL provider 5.2.3.0
• Npgsql-1.0 - Postgresql provider 1.0.0.0 (and 1.0.0.1 - were build with same version info)
• Npgsql-2.0-beta1 - Postgresql provider 1.98.1.0 beta 1
• Npgsql-2.0 - Postgresql provider 2.0.0.0
• DB2-9.0.0-1.1 - IBM DB2 Data Provider 9.0.0 for .NET Framework 1.1
• DB2-9.0.0-2.0 - (aliased to IBM.Data.DB2) - IBM DB2 Data Provider 9.0.0 for .NET Framework 2.0
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• DB2-9.1.0-1.1 - IBM DB2 Data Provider 9.1.0 for .NET Framework 1.1
• DB2-9.1.0.2 - (aliased to IBM.Data.DB2.9.1.0) - IBM DB2 Data Provider 9.1.0 for .NET Framework 2.0
• SQLite-1.0.43 SQLite provider 1.0.43 for .NET Framework 2.0
• SQLite-1.0.47 - (aliased to System.Data.SQLite) - SQLite provider 1.0.43 for .NET Framework 2.0
• SybaseAse-12 - Sybase ASE provider for ASE 12.x
• SybaseAse-15 - Sybase ASE provider for ASE 15.x
• SybaseAse-AdoNet2 - Sybase ADO.NET 2.0 provider for ASE 12.x and 15.x
• Odbc-1.1 - ODBC provider V1.0.5000.0 in framework .NET V1.1
• Odbc-2.0 - ODBC provider V2.0.0.0 in framework .NET V2
Note
If your exact version of the database provider is not listed, you can pick the general provider name,
i.e. MySql.Data.MySqlClient, and then perform an assembly redirect in App.config. This will often
be sufficient to upgrade to newer versions. As shown below
<runtime>
<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
<dependentAssembly>
<assemblyIdentity name="Npgsql"
publicKeyToken="5d8b90d52f46fda7"
culture="neutral"/>
<bindingRedirect oldVersion="0.0.0.0-65535.65535.65535.65535
newVersion="2.0.0.0"/>
</dependentAssembly>
</assemblyBinding>
</runtime>
An example using DbProviderFactory is shown below
IDbProvider dbProvider = DbProviderFactory.GetDbProvider("System.Data.SqlClient");
The default definitions of the providers are contained in the assembly resource assembly://Spring.Data/
Spring.Data.Common/dbproviders.xml. Future additions to round out the database coverage are
forthcoming. The current crude mechanism to add additional providers, or to apply any standard Spring
IApplicationContext functionality, such as applying AOP advice, is to set the public static property
DBPROVIDER_ADDITIONAL_RESOURCE_NAME in DbProviderFactory to a Spring resource location.
The default value is file://dbProviders.xml. (That isn't a typo, there is a difference in case with the name of the
embedded resource). This crude mechanism will eventually be replaced with one based on a custom configuration
section in App.config/Web.config.
It may happen that the version number of an assembly you have downloaded is different than the one listed above.
If it is a point release, i.e. the API hasn't changed in anyway that is material to your application, you should add
an assembly redirect of the form shown below.
<dependentAssembly>
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<assemblyIdentity name="MySql.Data"
publicKeyToken="c5687fc88969c44d"
culture="neutral"/>
<bindingRedirect oldVersion="0.0.0.0-65535.65535.65535.65535"
newVersion="1.0.10.1"/>
</dependentAssembly>
This redirects any reference to an older version of the assembly MySql.Data to the version 1.0.10.1.
19.3. XML based configuration
Creating a DbProvider in Spring's XML configuration file is shown below in the typical case of using it to specify
the DbProvider property on an AdoTemplate.
<objects xmlns='http://www.springframework.net'
xmlns:db="http://www.springframework.net/database">
<db:provider id="DbProvider"
provider="System.Data.SqlClient"
connectionString="Data Source=(local);Database=Spring;User ID=springqa;Password=springqa;Trusted_Connectio
<object id="adoTemplate" type="Spring.Data.AdoTemplate, Spring.Data">
<property name="DbProvider" ref="DbProvider"/>
</object>
</objects>
A custom namespace should be registered in the main application configuration file to use this syntax. This
configuration, only for the parsers, is shown below. Additional section handlers are needed to specify the rest of
the Spring configuration locations as described in previous chapters.
<configuration>
<configSections>
<sectionGroup name="spring">
<section name="parsers" type="Spring.Context.Support.NamespaceParsersSectionHandler, Spring.Core" />
</sectionGroup>
</configSections>
<spring>
<parsers>
<parser type="Spring.Data.Config.DatabaseNamespaceParser, Spring.Data" />
</parsers>
</spring>
</configuration>
19.4. Connection String management
There are a few options available to help manage your connection strings.
The first option is to leverage the Spring property replacement functionality, as described in Section 5.9.2.1,
“Example: The PropertyPlaceholderConfigurer”. This lets you insert variable names as placeholders for values in
a Spring configuration file. In the following example specific parts of a connection string have been parameterized
but you can also use a variable to set the entire connection string.
An example of such a setting is shown below
<configuration>
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<configSections>
<sectionGroup name="spring">
<section name='context' type='Spring.Context.Support.ContextHandler, Spring.Core'/>
</sectionGroup>
<section name="databaseSettings" type="System.Configuration.NameValueSectionHandler, System, Version=1.0.500
</configSections>
<spring>
<context>
<resource uri="Aspects.xml" />
<resource uri="Services.xml" />
<resource uri="Dao.xml" />
</context>
</spring>
<!-- These properties are referenced in Dao.xml -->
<databaseSettings>
<add key="db.datasource" value="(local)" />
<add key="db.user" value="springqa" />
<add key="db.password" value="springqa" />
<add key="db.database" value="Northwind" />
</databaseSettings>
</configuration>
Where Dao.xml has a connection string as shown below
<objects xmlns='http://www.springframework.net'
xmlns:db="http://www.springframework.net/database">
<db:provider id="DbProvider"
provider="System.Data.SqlClient"
connectionString="${db.datasource};Database=${db.database};User ID=${db.user};Password=${db.password};Trus
<object id="adoTemplate" type="Spring.Data.AdoTemplate, Spring.Data">
<property name="DbProvider" ref="DbProvider"/>
</object>
<!-- configuration of what values to substitute for ${ } variables listed above -->
<object name="appConfigPropertyHolder"
type="Spring.Objects.Factory.Config.PropertyPlaceholderConfigurer, Spring.Core">
<property name="configSections" value="DatabaseConfiguration"/>
</object>
</objects>
Please refer to the Section Section 5.9.2.1, “Example: The PropertyPlaceholderConfigurer” for more information.
19.5. Additional IDbProvider implementations
Spring provides some convenient implementations of the IDbProvider interface that add addtional behavior on
top of the standard implementation.
19.5.1. UserCredentialsDbProvider
This UserCredentialsDbProvider will allow you to change the username and password of a database connection
at runtime. The API contains the properties Username and Password which are used as the default strings
representing the user and password in the connection string. You can then change the value of these properties in
the connection string by calling the method SetCredentialsForCurrentThread and fall back to the default values
by calling the method RemoveCredentialsFromCurrentThread. You call the SetCredentialsForCurrentThread
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method at runtime, before any data access occurs, to determine which database user should be used for the current
user-case. Which user to select is up to you. You may retrieve the user information from an HTTP session for
example. Example configuration and usage is shown below
<object id="DbProvider" type="Spring.Data.Common.UserCredentialsDbProvider, Spring.Data">
<property name="TargetDbProvider" ref="targetDbProvider"/>
<property name="Username" value="User ID=defaultName"/>
<property name="Password" value="Password=defaultPass"/>
</object>
<db:provider id="targetDbProvider" provider="SqlServer-2.0"
connectionString="Data Source=MARKT60\SQL2005;Database=Spring;Trusted_Connection=False"/>
If you use dependency injection to configure a class with a property of the type IDbProvider, you will need to
downcast to the subtype or you can change your class to have a property of the type UserCredentialsDbProvider
instead of IDbProvider.
userCredentialsDbProvider.SetCredentialsForCurrentThread("User ID=springqa", "Password=springqa");
UserCredentialsDbProvider's has a base class, DelegatingDbProvider, and is intended for you to use in your
own implementations that delegate calls to a target IDbProvider instance. This class in meant to be subclassed
with subclasses overriding only those methods, such as CreateConnection(), that should not simply delegate
to the target IDbProvider.
19.5.2. MultiDelegatingDbProvider
There are use-cases in which there will need to be a runtime selection of the database to connect to among many
possible candidates. This is often the case where the same schema is installed in separate databases for different
clients. The MultiDelegatingDbProvider implements the IDbProvider interface and provides an abstraction
to the multiple databases and can be used in DAO layer such that the DAO layer is unaware of the switching
between databases. MultiDelegatingDbProvider does its job by looking into thread local storage under the key
dbProviderName. This storage location stores the name of the dbProvider that is to be used for processing the
request. MultiDelegatingDbProvider is configured using the dictionary property TargetDbProviders. The key
of this dictionary contains the name of a dbProvider and its value is a dbProvider object. (You can also provide
this dictionary as a constructor argument.)
During request processing, once you have determined which target dbProvider should be use, in this example
database1ProviderName, you should execute the following code is you are using Spring 1.2 M1 or later
// Spring 1.2 M1 or later
LogicalThreadContext.SetData(MultiDelegatingDbProvider.CURRENT_DBPROVIDER_SLOTNAME, "database1ProviderName")
and the following ocde if you are using earlier versions
// Prior to Spring 1.2 M1
LogicalThreadContext.SetData("dbProviderName", "database1ProviderName")
and then call the data access layer.
Here is a sample configuration to build up an object definition for MultiDelegatingDbProvider.
<db:provider id="CreditAndDebitsDbProvider"
provider="System.Data.SqlClient"
connectionString="Data Source=MARKT60\SQL2005;Initial Catalog=CreditsAndDebits;User ID=springqa; Password=sp
<db:provider id="CreditDbProvider"
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provider="System.Data.SqlClient"
connectionString="Data Source=MARKT60\SQL2005;Initial Catalog=Credits;User ID=springqa; Password=springqa"/>
<object id="dbProviderDictionary" type="Spring.Collections.SynchronizedHashtable, Spring.Core">
<property name="['DbProvider1']" ref="CreditAndDebitsDbProvider"/>
<property name="['DbProvider2']" ref="CreditDbProvider"/>
</object>
<object id="DbProvider" type="Spring.Data.MultiDelegatingDbProvider, Spring.Data">
<property name="TargetDbProviders" ref="dbProviderDictionary"/>
</object>
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Chapter 20. Data access using ADO.NET
20.1. Introduction
Spring provides an abstraction for data access via ADO.NET that provides the following benefits and features
• Consistent and comprehensive database provider interfaces for both .NET 1.1 and 2.0
• Integration with Spring's transaction management features.
• Template style use of DbCommand that removes the need to write typical ADO.NET boiler-plate code.
• 'One-liner' implementations for the most common database usage patterns lets you focus on the 'meat' of your
ADO.NET code.
• Easy database parameter creation/management
• Provider independent exceptions with database error codes and higher level DAO exception hierarchy.
• Centralized resource management for connections, commands, data readers, etc.
• Simple DataReader to Object mapping framework.
This chapter is divided up into a number of sections that describe the major areas of functionality within Spring's
ADO.NET support.
• Motivations - describes why one should consider using Spring's ADO.NET features as compared to using 'raw'
ADO.NET API.
• Provider Abstraction - a quick overview of Spring's provider abstraction.
• Approaches to ADO.NET Data Access - Discusses the two styles of Spring's ADO.NET data access classes
- template and object based.
• Introduction to AdoTemplate - Introduction to the design and core methods of the central class in Spring's
ADO.NET support.
• Exception Translation - Describes the features of Spring's data access exceptions
• Parameter Management - Convenience classes and methods for easy parameter management.
• Custom IDataReader implementations - Strategy for providing custom implementations of IDataReader. This
can be used to centralized and transparently map DBNull values to CLR types when accessing an IDataReader
or to provide extended mapping functionality in sub-interfaces.
• Basic data access operations - Usage of AdoTemplate for IDbCommand 'ExecuteScalar' and
'ExecuteNonScalar' functionality
• Queries and Lightweight Object Mapping - Using AdoTemplate to map result sets into objects
• DataSet and DataTable operations - Using AdoTemplate with DataSets and DataTables
• Modeling ADO.NET operations as .NET objects - An object-oriented approach to data access operations.
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. Motivations
There are a variety of motivations to create a higher level ADO.NET persistence API.
Encapsulation of common 'boiler plate' tasks when coding directly against the ADO.NET API. For example here
is a list of the tasks typically required to be coded for processing a result set query. Note that the code needed
when using Spring's ADO.NET framework is in italics.
1. Define connection parameters
2. Open the connection
3. Specify the command type and text
4. Prepare and execute the statement
5. Set up the loop to iterate through the results (if any)
6. Do the work for each iteration
7. Process any exception
8. Display or rollback on warnings
9. Handle transactions
10.Close the connection
Spring takes care of the low-level tasks and lets you focus on specifying the SQL and doing the real work of
extracting data. This standard boiler plate pattern is encapsulated in a class, AdoTemplate. The name 'Template'
is used because if you look at the typical code workflow for the above listing, you would essentially like to
'template' it, that is stick in the code that is doing the real work in the midst of the resource, transaction, exception
management.
Another very important motivation is to provide an easy means to group multiple ADO.NET operations within
a single transaction while at the same time adhering to a DAO style design in which transactions are initiated
outside the DAOs, typically in a business service layer. Using the 'raw' ADO.NET API to implement this design
often results in explicitly passing around of a Transaction/Connection pair to DAO objects. This infrastructure
task distracts from the main database task at hand and is frequently done in an ad-hoc manner. Integrating with
Spring's transaction management features provides an elegant means to achieve this common design goal. There
are many other benefits to integration with Spring's transaction management features, see Chapter 17, Transaction
management for more information.
Provider Independent Code: In .NET 1.1 writing provider independent code was difficult for a variety of reasons.
The most prominent was the lack of a lack of a central factory for creating interface based references to the
core ADO.NET classes such as IDbConnection, IDbCommand, DbParameter etc. In addition, the APIs exposed
by many of these interfaces were minimal or incomplete - making for tedious code that would otherwise be
more easily developed with provider specific subclasses. Lastly, there was no common base class for data access
exceptions across the providers. .NET 2.0 made many changes for the better in that regard across all these areas
of concern - and Spring only plugs smaller holes in that regard to help in the portability of your data access code.
Resource Management: The 'using' block is the heart of elegant resource management in .NET from the API
perspective. However, despite its elegance, writing 2-3 nested using statements for each data access method also
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starts to be tedious, which introduces the risk of forgetting to do the right thing all the time in terms of both direct
coding and 'cut-n-paste' errors. Spring centralizes this resource management in one spot so you never forget or
make a mistake and rely on it always being done correctly.
Parameter management: Frequently much of data access code is related to creating appropriate parameters. To
alleviate this boiler plate code Spring provides a parameter 'builder' class that allows for succinct creation of
parameter collections. Also, for the case of stored procedures, parameters can be derived from the database itself
which reduces parameter creation code to just one line.
Frequently result set data is converted into objects. Spring provides a simple framework to organize that mapping
task and allows you to reuse mapping artifacts across your application.
Exceptions: The standard course of action when an exception is thrown from ADO.NET code is to look up the
error code and then re-run the application to set a break point where the exception occurred so as to see what the
command text and data values were that caused the exception. Spring provides exceptions translation from these
error codes (across database vendors) to a Data Access Object exception hierarchy. This allows you to quickly
understand the category of the error that occurred and also the 'bad' data which lead to the exception.
Warnings: A common means to extract warning from the database, and to optionally treat those warnings as a
reason to rollback is not directly supported with the new System.Data.Common API
Portability: Where possible, increase the portability of code across database provider in the higher level API. The
need adding of a parameter prefix, i.e. @ for SqlServer or ':' for oracle is one such example of an area where a
higher level API can offer some help in making your code more portable.
Note that Spring's ADO.NET framework is just 'slightly' above the raw API. It does not try to compete with other
higher level persistence abstractions such as result set mappers (iBATIS.NET) or other ORM tools (NHibernate).
(Apologies if your favorite is left out of that short list). As always, pick and choose the appropriate level of
abstraction for the task at hand. As a side note, Spring does offer integration with higher level persistence
abstractions (currently NHibernate) providing such features as integration with Spring's transaction management
features as well as mixing orm/ado.net operations within the same transaction.
20.3. Provider Abstraction
Before you get started executing queries against the database you need to connect to it. Chapter 19, DbProvider
covers this topic in detail so we only discuss the basic idea of how to interact with the database in this section.
One important ingredient that increases the portability of writing ADO.NET applications is to refer to the base
ADO.NET interfaces, such as IDbCommand or IDbParameter in your code. However, In the .NET 1.1 BCL
the only means to obtain references to instances of these interfaces is to directly instantiate the classes, i.e. for
SqlServer this would be
IDbCommand command = new SqlCommand();
One of the classic creational patterns in the GoF Design Patterns book addresses this situation directly, the Abstract
Factory pattern. This approach was applied in the .NET BCL with the introduction of the DbProviderFactory
class which contains various factory methods that create the various objects used in ADO.NET programming. In
addition, .NET 2.0 introduced new abstract base classes that all ADO.NET providers must inherit from. These
base classes provide more core functionality and uniformity across the various providers as compared to the
original ADO.NET interfaces.
Spring's database provider abstraction has a similar API to that of .ADO.NET 2.0's DbProviderFactory. The
central interface is IDbProvider and it has factory methods that are analogous to those in the DbProviderFactory
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class except that they return references to the base ADO.NET interfaces. Note that in keeping with the Spring
Framework's philosophy, IDbProvider is an interface, and can thus be easily mocked or stubbed as necessary.
Another key element of this interface is the ConnectionString property that specifies the specific runtime
information necessary to connect to the provider. The interface also has a IDbMetadata property that contains
minimal database metadata information needed to support the functionality in rest of the Spring ADO.NET
framework. It is unlikely you will need to use the DatabaseMetadata class directly in your application.
For more information on configuring a Spring database provider refer to Chapter 19, DbProvider
20.3.1. Creating an instance of IDbProvider
Each database vendor is associated with a particular implementation of the IDbProvider interfaces. A variety of
implementations are provided with Spring such as SqlServer, Oracle and MySql. Refer to the documentation on
Spring's DbProvider for creating a configuration for database that is not yet provided. The programmatic way to
create an IDbProvider is shown below
IDbProvider dbProvider = DbProviderFactory.GetDbProvider("System.Data.SqlClient");
Please refer to the Chapter 19, DbProvider for information on how to create a IDbProvider in Spring's XML
configuration file.
20.4. Namespaces
The ADO.NET framework consists of a few namespaces, namely Spring.Data, Spring.Data.Generic,
Spring.Data.Common, Spring.Data.Support, and Spring.Data.Object.
The Spring.Data namespace contains the majority of the classes and interfaces you will deal with on a day to
day basis.
The Spring.Data.Generic namespaces add generic versions of some classes and interfaces and you will also likely
deal with this on a day to day basis if you are using .NET 2.0
The Spring.Data.Common namespaces contains Spring's DbProvider abstraction in addition to utility classes for
parameter creation.
The Spring.Data.Object namespaces contains classes that represent RDBMS queries, updates, and stored
procedures as thread safe, reusable objects.
Finally the Spring.Data.Support namespace is where you find the IAdoExceptionTransactor translation
functionality and some utility classes.
20.5. Approaches to Data Access
Spring provides two styles to interact with ADO.NET. The first is a 'template' based approach in which you
create an single instance of AdoTemplate to be used by all your DAO implementations. Your DAO methods are
frequently implemented as a single method call on the template class as described in detail in the following section.
The other approach a more object-oriented manner that models database operations as objects. For example, one
can encapsulate the functionality of a database query via an AdoQuery class and a create/update/delete operation
as a AdoNonQuery class. Stored procedures are also modelled in this manner via the class StoredProcedure. To
use these classes you inherit from them and define the details of the operation in the constructor and implement
an abstract method. This reads very cleanly when looking at DAO method implementation as you can generally
see all the details of what is going on.
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Generally speaking, experience has shown that the AdoTemplate approach reads very cleanly when looking at
DAO method implementation as you can generally see all the details of what is going on as compared to the object
based approach. The object based approach however, offers some advantages when calling stored procedures
since it acts as a cache of derived stored procedure arguments and can be invoked passing a variable length
argument list to the 'execute' method. As always, take a look at both approaches and use the approach that provides
you with the most benefit for a particular situation.
20.6. Introduction to AdoTemplate
The class AdoTemplate is at the heart of Spring's ADO.NET support. It is based on an Inversion of Control (i.e.
callback) design with the central method 'Execute' handing you a IDbCommand instance that has its Connection
and Transaction properties set based on the transaction context of the calling code. All resource management is
handled by the framework, you only need to focus on dealing with the IDbCommand object. The other methods in
this class build upon this central 'Execute' method to provide you a quick means to execute common data access
scenarios.
There are two implementations of AdoTemplate. The one that uses Generics and is in the namespace
Spring.Data.Generic and the other non-generic version in Spring.Data. In either case you create an instance of
an AdoTemplate by passing it a IDbProvider instance as shown below
AdoTemplate adoTemplate = new AdoTemplate(dbProvider);
is a thread-safe class and as such a single instance can be used for all data access operations in
you applications DAOs. AdoTemplate implements an IAdoOperations interface. Although the IAdoOperations
interface is more commonly used for testing scenarios you may prefer to code against it instead of the direct
class instance.
AdoTemplate
If you are using the generic version of AdoTemplate you can access the non-generic version via the property
ClassicAdoTemplate.
The following two sections show basic usage of the AdoTemplate 'Execute' API for .NET 1.1 and 2.0.
20.6.1. Execute Callback
The Execute method and its associated callback function/inteface is the basic method upon which all the other
methods in AdoTemplate delegate their work. If you can not find a suitable 'one-liner' method in AdoTemplate for
your purpose you can always fall back to the Execute method to perform any database operation while benefiting
from ADO.NET resource management and transaction enlistment. This is commonly the case when you are using
special provider specific features, such as XML or BLOB support.
20.6.2. Execute Callback in .NET 2.0
In this example a simple query against the 'Northwind' database is done to determine the number of customers
who have a particular postal code.
public int FindCountWithPostalCode(string postalCode)
{
return adoTemplate.Execute<int>(delegate(DbCommand command)
{
command.CommandText =
"select count(*) from Customers where PostalCode = @PostalCode";
DbParameter p = command.CreateParameter();
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p.ParameterName = "@PostalCode";
p.Value = postalCode;
command.Parameters.Add(p);
return (int)command.ExecuteScalar();
});
}
The DbCommand that is passed into the anonymous delegate is already has it Connection property set to the
corresponding value of the dbProvider instance used to create the template. Furthermore, the Transaction
property of the DbCommand is set based on the transactional calling context of the code as based on the use of
Spring's transaction management features. Also note the feature of anonymous delegates to access the variable
'postalCode' which is defined 'outside' the anonymous delegate implementation. The use of anonymous delegates
is a powerful approach since it allows you to write compact data access code. If you find that your callback
implementation is getting very long, it may improve code clarity to use an interface based version of the callback
function, i.e. an ICommandCallback shown below.
As you can see, only the most relevant portions of the data access task at hand need to be coded. (Note that in
this simple example you would be better off using AdoTemplate's ExecuteScalar method directly. This method
is described in the following sections). As mentioned before, the typical usage scenario for the Execute callback
would involve downcasting the passed in DbCommand object to access specific provider API features.
There is also an interface based version of the execute method. The signatures for the delegate and interface are
shown below
public delegate T CommandDelegate<T>(DbCommand command);
public interface ICommandCallback
{
T DoInCommand<T>(DbCommand command);
}
While the delegate version offers the most compact syntax, the interface version allows for reuse. The
corresponding method signatures on Spring.Data.Generic.AdoTemplate are shown below
public class AdoTemplate : AdoAccessor, IAdoOperations
{
...
T Execute<T>(ICommandCallback action);
T Execute<T>(CommandDelegate<T> del);
...
}
While it is common for .NET 2.0 ADO.NET provider implementations to inherit from the base class
System.Data.Common.DbCommand, that is not a requirement. To accommodate the few that don't, which as of
this writing are the latest Oracle (ODP) provider, Postgres, and DB2 for iSeries, two additional execute methods
are provided. The only difference is the use of callback and delegate implementations that have IDbCommand
and not DbCommand as callback arguments. The following listing shows these methods on AdoTemplate.
public class AdoTemplate : AdoAccessor, IAdoOperations
{
...
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T Execute<T>(IDbCommandCallback action);
T Execute<T>(IDbCommandDelegate<T> del);
...
}
where the signatures for the delegate and interface are shown below
public delegate T IDbCommandDelegate<T>(IDbCommand command);
public interface IDbCommandCallback<T>
{
T DoInCommand(IDbCommand command);
}
Internally the AdoTemplate implementation delegates to implementations of IDbCommandCallback so
that the 'lowest common denominator' API is used to have maximum portability. If you accidentally
call Execute<T>(ICommandCallback action)and the command does not inherit from DbCommand, an
InvalidDataAccessApiUsageException will be thrown.
Depending on how portable you would like your code to be, you can choose among the two callback styles. The
one based on DbCommand has the advantage of access to the more user friendly DbParameter class as compared
to IDbParameter obtained from IDbCommand.
20.6.3. Execute Callback in .NET 1.1
>
AdoTemplate differs from its .NET 2.0 generic counterpart in that it exposes the interface IDbCommand in
its 'Execute' callback methods and delegate as compared to the abstract base class DbProvider. Also, since
anonymous delegates are not available in .NET 1.1, the typical usage pattern requires you to create a explicitly
delegate and/or class that implements the ICommandCallback interface. Example code to query In .NET 1.1 the
'Northwind' database is done to determine the number of customers who have a particular postal code is shown
below.
public virtual int FindCountWithPostalCode(string postalCode)
{
return (int) AdoTemplate.Execute(new PostalCodeCommandCallback(postalCode));
}
and the callback implementation is
private class PostalCodeCommandCallback : ICommandCallback
{
private string cmdText = "select count(*) from Customer where PostalCode = @PostalCode";
private string postalCode;
public PostalCodeCommandCallback(string postalCode)
{
this.postalCode = postalCode;
}
public object DoInCommand(IDbCommand command)
{
command.CommandText = cmdText;
IDbDataParameter p = command.CreateParameter();
p.ParameterName = "@PostalCode";
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p.Value = postalCode;
command.Parameters.Add(p);
return command.ExecuteScalar();
}
}
Note that in this example, one could more easily use AdoTemplate's ExecuteScalar method.
The Execute method has interface and delegate overloads. The signatures for the delegate and interface are shown
below
public delegate object CommandDelegate(IDbCommand command);
public interface ICommandCallback
{
object DoInCommand(IDbCommand command);
}
The corresponding method signatures on Spring.Data.AdoTemplate are shown below
public class AdoTemplate : AdoAccessor, IAdoOperations
{
...
object Execute(CommandDelegate del);
object Execute(ICommandCallback action);
...
}
Note that you have to cast to the appropriate object type returned from the execute method.
20.6.4. Quick Guide to AdoTemplate Methods
There are many methods in AdoTemplate so it is easy to feel a bit overwhelmed when taking a look at the SDK
documentation. However, after a while you will hopefully find the class 'easy to navigate' with intellisense. Here is
a quick categorization of the method names and their associated data access operation. Each method is overloaded
to handle common cases of passing in parameter values.
The generic 'catch-all' method
• Execute - Allows you to perform any data access operation on a standard DbCommand object. The connection
and transaction properties of the DbCommand are already set based on the transactional calling context. There
is also an overloaded method that operates on a standard IDbCommand object. This is for those providers that
do not inherit from the base class DbCommand.
The following methods mirror those on the DbCommand object.
• ExecuteNonQuery - Executes the 'NonQuery' method on a DbCommand, applying provided parameters and
returning the number of rows affected.
• ExecuteScalar - Executes the 'Scalar' method on a DbCommand, applying provided parameters, and returning
the first column of the first row in the result set.
Mapping result sets to objects
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• QueryWithResultSetExtractor - Execute a query mapping a result set to an object with an implementation
of the IResultSetExtractor interface.
• QueryWithResultSetExtractorDelegate - Same as QueryWithResultSetExtractor
ResultSetExtractorDelegate to perform result set mapping.
but
using
a
• QueryWithRowCallback - Execute a query calling an implementation of IRowCallback for each row in the
result set.
• QueryWithRowCallbackDelegate - Same as QueryWithRowCallback but calling a RowCallbackDelegate for
each row.
• QueryWithRowMapper - Execute a query mapping a result set on a row by row basis with an implementation
of the IRowMapper interface.
• QueryWithRowMapperDelegate - Same as QueryWithRowMapper but using a RowMapperDelegate to perform
result set row to object mapping.
Mapping result set to a single object
• QueryForObject - Execute a query mapping the result set to an object using a IRowMapper. Exception is thrown
if the query does not return exactly one object.
Query with a callback to create the DbCommand object. These are generally used by the framework itself to
support other functionality, such as in the Spring.Data.Objects namespace.
• QueryWithCommandCreator - Execute a query with a callback to IDbCommandCreator to create a IDbCommand
object and using either a IRowMapper or IResultSetExtractor to map the result set to an object. One variation
lets multiple result set 'processors' be specified to act on multiple result sets and return output parameters.
DataTable and DataSet operations
• DataTableCreate - Create and Fill DataTables
• DataTableCreateWithParameters - Create and Fill DataTables using a parameter collection.
• DataTableFill - Fill a pre-existing DataTable.
• DataTableFillWithParameters - Fill a pre-existing DataTable using parameter collection.
• DataTableUpdate - Update the database using the provided DataTable, insert, update, delete SQL.
• DataTableUpdateWithCommandBuilder - Update the database using the provided DataTable, select SQL, and
parameters.
• DataSetCreate - Create and Fill DataSets
• DataSetCreateWithParameters - Create and Fill DataTables using a parameter collection.
• DataSetFill - Fill a pre-existing DataSet
• DataSetFillWithParameters - Fill a pre-existing DataTable using parameter collection.
• DataSetUpdate - Update the database using the provided DataSet, insert, update, delete SQL.
• DataSetUpdateWithCommandBuilder - Update the database using the provided DataSet, select SQL, and
parameters..
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Note
These methods are not currently in the generic version of AdoTemplate but accessible through the
property ClassicAdoTemplate.
Parameter Creation utility methods
• DeriveParameters - Derive the parameter collection for stored procedures.
In turn each method typically has four overloads, one with no parameters and three for providing parameters.
Aside from the DataTable/DataSet operations, the three parameter overloads are of the form shown below
• MethodName(CommandType cmdType, string cmdText, CallbackInterfaceOrDelegate, parameter setting
arguments)
The CallbackInterfaceOrDelegate is one of the three types listed previously. The parameters setting arguments
are of the form
• MethodName( ... string parameterName, Enum dbType, int size, object parameterValue)
• MethodName( ... IDbParameters parameters)
• MethodName( ... ICommandSetter commandSetter)
The first overload is a convenience method when you only have one parameter to set. The database enumeration
is the base class 'Enum' allowing you to pass in any of the provider specific enumerations as well as the common
DbType enumeration. This is a trade off of type-safety with provider portability. (Note generic version could be
improved to provide type safety...).
The second overload contains a collection of parameters. The data type is Spring's IDbParameters collection class
discussed in the following section.
The third overload is a callback interface allowing you to set the parameters (or other properties) of the
IDbCommand passed to you by the framework directly.
If you are using .NET 2.0 the delegate versions of the methods are very useful since very compact definitions
of database operations can be created that reference variables local to the DAO method. This removes some
of the tedium in passing parameters around with interface based versions of the callback functions since they
need to be passed into the constructor of the implementing class. The general guideline is to use the delegate
when available for functionality that does not need to be shared across multiple DAO classes or methods and
use interface based version to reuse the implementation in multiple places. The .NET 2.0 versions make use of
generics where appropriate and therefore enhance type-safety.
20.6.5. Quick Guide to AdoTemplate Properties
AdoTemplate has the following properties that you can configure
• LazyInit - Indicates if the IAdoExceptionTranslator should be created on first encounter of an exception
from the data provider or when AdoTemplate is created. Default is true, i.e. to lazily instantiate.
• ExceptionTranslator - Gets or sets the implementation of IAdoExceptionTranslator to use. If no custom
translator is provided, a default ErrorCodeExceptionTranslator is used.
• DbProvider - Gets or sets the IDbProvider instance to use.
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• DataReaderWrapperType - Gets or set the System.Type to use to create an instance of IDataReaderWrapper
for the purpose of providing extended mapping functionality. Spring provides an implementation to use as the
basis for a mapping strategy that will map DBNull values to default values based on the standard IDataReader
interface. See the section custom IDataReader implementations for more information.
• CommandTimeout - Gets or sets the command timeout for IDbCommands that this AdoTemplate executes.
Default is 0, indicating to use the database provider's default.
20.7. Transaction Management
The AdoTemplate is used in conjunction with an implementation of a IPlatformTransactionManager, which is
Spring's portable transaction management API. This section gives a brief overview of the transaction managers
you can use with AdoTemplate and the details of how you can retrieve the connection/transaction ADO.NET
objects that are bound to the thread when a transaction starts. Please refer to the section key abstractions in the
chapter on transactions for more comprehensive introduction to transaction management.
To use local transactions, those with only one transactional resource (i.e. the database) you will typically use
AdoPlatformTransactionManager. If you need to mix Hibernate and ADO.NET data access operations within
the same local transaction you should use HibernatePlatformTransaction manager which is described more in
the section on ORM transaction management.
While it is most common to use Spring's transaction management features to avoid the low level management of
ADO.NET connection and transaction objects, you can retrieve the connection/transaction pair that was created
at the start of a transaction and bound to the current thread. This may be useful for some integration with other
data access APIs. The can be done using the utility class ConnectionUtils as shown below.
IDbProvider dbProvider = DbProviderFactory.GetDbProvider("System.Data.SqlClient");
ConnectionTxPair connectionTxPairToUse = ConnectionUtils.GetConnectionTxPair(dbProvider);
IDbCommand command = DbProvider.CreateCommand();
command.Connection = connectionTxPairToUse.Connection;
command.Transaction = connectionTxPairToUse.Transaction;
It is possible to provide a wrapper around the standard .NET provider interfaces such that you can use the plain
ADO.NET API in conjunction with Spring's transaction management features.
If you are using ServiceDomainPlatformTransactionManager or TxScopePlatformTransactionManager then
you can retrieve the currently executing transaction object via the standard .NET APIs.
20.8. Exception Translation
AdoTemplate's methods throw exceptions within a Data Access Object (DAO) exception hierarchy described in
Chapter 18, DAO support. In addition, the command text and error code of the exception are extracted and logged.
This leads to easier to write provider independent exception handling layer since the exceptions thrown are not
tied to a specific persistence technology. Additionally, for ADO.NET code the error messages logged provide
information on the SQL and error code to better help diagnose the issue.
20.9. Parameter Management
A fair amount of the code in ADO.NET applications is related to the creation and population of parameters.
The BCL parameter interfaces are very minimal and do not have many convenience methods found in provider
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implementations such as SqlClient. Even still, with SqlClient, there is a fair amount of verbosity to creating and
populating a parameter collection. Spring provides two ways to make this mundane task easier and more portable
across providers.
20.9.1. IDbParametersBuilder
Instead of creating a parameter on one line of code, then setting its type on another and size on another, a
builder and parameter interface, IDbParametersBuilder and IDbParameter respectfully, are provided so that this
declaration process can be condensed. The IDbParameter support chaining calls to its methods, in effect a simple
language-constrained domain specific language, to be fancy about it. Here is an example of it in use.
IDbParametersBuilder builder = CreateDbParametersBuilder();
builder.Create().Name("Country").Type(DbType.String).Size(15).Value(country);
builder.Create().Name("City").Type(DbType.String).Size(15).Value(city);
// now get the IDbParameters collection for use in passing to AdoTemplate methods.
IDbParameters parameters = builder.GetParameters();
Please note that IDbParameters and IDbParameter are not part of the BCL, but part of the Spring.Data.Common
namespace. The IDbParameters collection is a frequent argument to the overloaded methods of AdoTemplate.
The parameter prefix, i.e. '@' in Sql Server, is not required to be added to the parameter name. The DbProvider
is aware of this metadata and AdoTemplate will add it automatically if required before execution.
An additional feature of the IDbParametersBuilder is to create a Spring FactoryObject that creates IDbParameters
for use in the XML configuration file of the IoC container. By leveraging Spring's expression evaluation language,
the above lines of code can be taken as text from the XML configuration file and executed. As a result you
can externalize your parameter definitions from your code. In combination with abstract object definitions and
importing of configuration files your increase the chances of having one code base support multiple database
providers just by a change in configuration files.
20.9.2. IDbParameters
This class is similar to the parameter collection class you find in provider specific implementations of
IDataParameterCollection. It contains a variety of convenience methods to build up a collection of parameters.
Here is an abbreviated listing of the common convenience methods.
• int Add(object parameterValue)
• void AddRange(Array values)
• IDbDataParameter AddWithValue(string name, object parameterValue)
• IDbDataParameter Add(string name, Enum parameterType)
• IDbDataParameter AddOut(string name, Enum parameterType)
• IDbDataParameter AddReturn(string name, Enum parameterType)
• void DeriveParameters(string storedProcedureName)
Here a simple usage example
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// inside method has has local variable country and city...
IDbParameters parameters = CreateDbParameters();
parameters.AddWithValue("Country", country).DbType = DbType.String;
parameters.Add("City", DbType.String).Value = city;
// now pass on to AdoTemplate methods.
The parameter prefix, i.e. '@' in Sql Server, is not required to be added to the parameter name. The DbProvider
is aware of this metadata and AdoTemplate will add it automatically if required before execution.
20.10. Custom IDataReader implementations
The passed in implementation of IDataReader can be customized. This lets you add a strategy for handling null
values to the standard methods in the IDataReader interface or to provide sub-interface of IDataReader that
contains extended functionality, for example support for default values. In callback code, i.e. IRowMapper and
associated delegate, you would downcast to the sub-interface to perform processing.
Spring provides a class to map DBNull values to default values. When reading from a IDataReader there is often the
need to map DBNull values to some default values, i.e. null or say a magic number such as -1. This is usually done
via a ternary operator which decreases readability and also increases the likelihood of mistakes. Spring provides
an IDataReaderWrapper interface (which inherits from the standard IDataReader) so that you can provide your
own implementation of a IDataReader that will perform DBNull mapping for you in a consistent and non invasive
manner to your result set reading code. A default implementation, NullMappingDataReader is provided which
you can subclass to customize or simply implement the IDataReaderWrapper interface directly. This interface
is shown below
public interface IDataReaderWrapper : IDataReader
{
IDataReader WrappedReader
{
get;
set;
}
}
All of AdoTemplates callback interfaces/delegates that have an IDataReader as an argument are wrapped with a
IDataReaderWrapper if the AdoTemplate has been configured with one via its DataReaderWrapperType property.
Your implementation should support a zero-arg constructor.
Frequently you will use a common mapper for DBNull across your application so only one instance of
AdoTemplate and IDataReaderWrapper in required. If you need to use multiple null mapping strategies you will
need to create multiple instances of AdoTemplate and configure them appropriately in the DAO objects.
20.11. Basic data access operations
The 'ExecuteNonQuery' and 'ExecuteScalar' methods of AdoTemplate have the same functionality as the same
named methods on the DbCommand object
20.11.1. ExecuteNonQuery
ExecuteNonQuery is used to perform create, update, and delete operations. It has four overloads listed below
reflecting different ways to set the parameters.
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An example of using this method is shown below
public void CreateCredit(float creditAmount)
{
AdoTemplate.ExecuteNonQuery(CommandType.Text,
String.Format("insert into Credits(creditAmount) VALUES ({0})",
creditAmount));
}
20.11.2. ExecuteScalar
An example of using this method is shown below
int iCount = (int)adoTemplate.ExecuteScalar(CommandType.Text, "SELECT COUNT(*) FROM TestObjects");
20.12. Queries and Lightweight Object Mapping
A common ADO.NET development task is reading in a result set and converting it to a collection of domain
objects. The family of QueryWith methods on AdoTemplate help in this task. The responsibility of performing
the mapping is given to one of three callback interfaces/delegates that you are responsible for developing. These
callback interfaces/delegates are:
• IResultSetExtractor / ResultSetExtractorDelegate - hands you a IDataReader object for you to iterate over and
return a result object.
• IRowCallback / RowCallbackDelegate - hands you a IDataReader to process the current row. Returns void and
as such is usually stateful in the case of IRowCallback implementations or uses a variable to collect a result
that is available to an anonymous delegate.
• IRowMapper / RowMapperDelegate - hands you a IDataReader to process the current row and return an object
corresponding to that row.
There are generic versions of the IResultSetExtractor and IRowMapper interfaces/delegates providing you with
additional type-safety as compared to the object based method signatures used in the .NET 1.1 implementation.
As usual with callback APIs in Spring.Data, your implementations of these interfaces/delegates are only
concerned with the core task at hand - mapping data - while the framework handles iteration of readers and
resource management.
Each 'QueryWith' method has 4 overloads to handle common ways to bind parameters to the command text.
The following sections describe in more detail how to use Spring's lightweight object mapping framework.
20.12.1. ResultSetExtractor
The ResultSetExtractor gives you control to iterate over the IDataReader returned from the query. You are
responsible for iterating through all the result sets and returning a corresponding result object. Implementations
of IResultSetExtractor are typically stateless and therefore reusable as long as the implementation doesn't access
stateful resources. The framework will close the IDataReader for you.
The interface and delegate signature for ResutSetExtractors is shown below for the generic version in the
Spring.Data.Generic namespace
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public interface IResultSetExtractor<T>
{
T ExtractData(IDataReader reader);
}
public delegate T ResultSetExtractorDelegate<T>(IDataReader reader);
The definition for the non-generic version is shown below
public interface IResultSetExtractor
{
object ExtractData(IDataReader reader);
}
public delegate object ResultSetExtractorDelegate(IDataReader reader);
Here is an example taken from the Spring.DataQuickStart. It is a method in a DAO class that inherits from
AdoDaoSupport, which has a convenience method 'CreateDbParametersBuilder()'.
public virtual IList<string> GetCustomerNameByCountryAndCityWithParamsBuilder(string country, string cit
{
IDbParametersBuilder builder = CreateDbParametersBuilder();
builder.Create().Name("Country").Type(DbType.String).Size(15).Value(country);
builder.Create().Name("City").Type(DbType.String).Size(15).Value(city);
return AdoTemplate.QueryWithResultSetExtractor(CommandType.Text,
customerByCountryAndCityCommandText,
new CustomerNameResultSetExtractor<List<string>>(),
builder.GetParameters());
}
The implementation of the ResultSetExtractor is shown below.
internal class CustomerNameResultSetExtractor<T> : IResultSetExtractor<T> where T : IList<string>, new()
{
public T ExtractData(IDataReader reader)
{
T customerList = new T();
while (reader.Read())
{
string contactName = reader.GetString(0);
customerList.Add(contactName);
}
return customerList;
}
}
Internally the implementation of the QueryWithRowCallback and QueryWithRowMapper methods are
specializations of the general ResultSetExtractor. For example, the QueryWithRowMapper implementation
iterates through the result set, calling the callback method 'MapRow' for each row and collecting the results
in an IList. If you have a specific case that is not covered by the QueryWithXXX methods you can subclass
AdoTemplate and follow the same implementation pattern to create a new QueryWithXXX method to suit your
needs.
20.12.2. RowCallback
The RowCallback is usually a stateful object itself or populates another stateful object that is accessible to the
calling code. Here is a sample take from the Data QuickStart
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public class RowCallbackDao : AdoDaoSupport
{
private string cmdText = "select ContactName, PostalCode from Customers";
public virtual IDictionary<string, IList<string>> GetPostalCodeCustomerMapping()
{
PostalCodeRowCallback statefullCallback = new PostalCodeRowCallback();
AdoTemplate.QueryWithRowCallback(CommandType.Text, cmdText,
statefullCallback);
// Do something with results in stateful callback...
return statefullCallback.PostalCodeMultimap;
}
}
The PostalCodeRowCallback builds up state which is then retrieved via the property PostalCodeMultimap. The
Callback implementation is shown below
internal class PostalCodeRowCallback : IRowCallback
{
private IDictionary<string, IList<string>> postalCodeMultimap =
new Dictionary<string, IList<string>>();
public IDictionary<string, IList<string>> PostalCodeMultimap
{
get { return postalCodeMultimap; }
}
public void ProcessRow(IDataReader reader)
{
string contactName = reader.GetString(0);
string postalCode = reader.GetString(1);
IList<string> contactNameList;
if (postalCodeMultimap.ContainsKey(postalCode))
{
contactNameList = postalCodeMultimap[postalCode];
}
else
{
postalCodeMultimap.Add(postalCode, contactNameList = new List<string>());
}
contactNameList.Add(contactName);
}
}
20.12.3. RowMapper
The RowMapper lets you focus on just the logic to map a row of your result set to an object. The creation of
a IList to store the results and iterating through the IDataReader is handled by the framework. Here is a simple
example taken from the Data QuickStart application
public class RowMapperDao : AdoDaoSupport
{
private string cmdText = "select Address, City, CompanyName, ContactName, " +
"ContactTitle, Country, Fax, CustomerID, Phone, PostalCode, " +
"Region from Customers";
public virtual IList<Customer> GetCustomers()
{
return AdoTemplate.QueryWithRowMapper<Customer>(CommandType.Text, cmdText,
new CustomerRowMapper<Customer>());
}
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}
where the implementation of the RowMapper is
public class CustomerRowMapper<T> : IRowMapper<T> where T : Customer, new()
{
public T MapRow(IDataReader dataReader, int rowNum)
{
T customer = new T();
customer.Address = dataReader.GetString(0);
customer.City = dataReader.GetString(1);
customer.CompanyName = dataReader.GetString(2);
customer.ContactName = dataReader.GetString(3);
customer.ContactTitle = dataReader.GetString(4);
customer.Country = dataReader.GetString(5);
customer.Fax = dataReader.GetString(6);
customer.Id = dataReader.GetString(7);
customer.Phone = dataReader.GetString(8);
customer.PostalCode = dataReader.GetString(9);
customer.Region = dataReader.GetString(10);
return customer;
}
}
You may also pass in a delegate, which is particularly convenient if the mapping logic is short and you need to
access local variables within the mapping logic.
public virtual IList<Customer> GetCustomersWithDelegate()
{
return AdoTemplate.QueryWithRowMapperDelegate<Customer>(CommandType.Text, cmdText,
delegate(IDataReader dataReader, int rowNum)
{
Customer customer = new Customer();
customer.Address = dataReader.GetString(0);
customer.City = dataReader.GetString(1);
customer.CompanyName = dataReader.GetString(2);
customer.ContactName = dataReader.GetString(3);
customer.ContactTitle = dataReader.GetString(4);
customer.Country = dataReader.GetString(5);
customer.Fax = dataReader.GetString(6);
customer.Id = dataReader.GetString(7);
customer.Phone = dataReader.GetString(8);
customer.PostalCode = dataReader.GetString(9);
customer.Region = dataReader.GetString(10);
return customer;
});
}
20.12.4. Query for a single object
The QueryForObject method is used when you expect there to be exactly one object returned from the mapping,
otherwise a Spring.Dao.IncorrectResultSizeDataAccessException will be thrown. Here is some sample usage
taken from the Data QuickStart.
public class QueryForObjectDao : AdoDaoSupport
{
private string cmdText = "select Address, City, CompanyName, ContactName, " +
"ContactTitle, Country, Fax, CustomerID, Phone, PostalCode, " +
"Region from Customers where ContactName = @ContactName";
public Customer GetCustomer(string contactName)
{
return AdoTemplate.QueryForObject(CommandType.Text, cmdText,
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new CustomerRowMapper<Customer>(),
"ContactName", DbType.String, 30, contactName);
}
}
20.12.5. Query using a CommandCreator
There is a family of overloaded methods that allows you to encapsulate and reuse a particular configuration
of a IDbCommand object. These methods also allow for access to returned out parameters as well as a method
that allows processing of multiple result sets. These methods are used internally to support the classes in the
Spring.Data.Objects namespace and you may find the API used in that namespace to be more convenient. The
family of methods is listed below.
• object QueryWithCommandCreator(IDbCommandCreator cc, IResultSetExtractor rse)
• void QueryWithCommandCreator(IDbCommandCreator cc, IRowCallback rowCallback)
• IList QueryWithCommandCreator(IDbCommandCreator cc, IRowMapper rowMapper)
There is also the same methods with an additional collecting parameter to obtain any output parameters. These are
• object QueryWithCommandCreator(IDbCommandCreator cc, IResultSetExtractor rse, IDictionary
returnedParameters)
• void QueryWithCommandCreator(IDbCommandCreator cc, IRowCallback rowCallback, IDictionary
returnedParameters)
• IList
QueryWithCommandCreator(IDbCommandCreator
cc,
IRowMapper
rowMapper,
IDictionary
returnedParameters)
The IDbCommandCreator callback interface is shown below
public interface IDbCommandCreator
{
IDbCommand CreateDbCommand();
}
The created IDbCommand object is used when performing the QueryWithCommandCreator method.
To process multiple result sets specify a list of named result set processors,( i.e. IResultSetExtractor,
IRowCallback, or IRowMapper). This method is shown below
• IDictionary QueryWithCommandCreator(IDbCommandCreator cc, IList namedResultSetProcessors)
The list must contain objects of the type Spring.Data.Support.NamedResultSetProcessor. This is the class
responsible for associating a name with a result set processor. The constructors are listed below.
public class NamedResultSetProcessor
{
public NamedResultSetProcessor(string name, IRowMapper rowMapper) { ... }
public NamedResultSetProcessor(string name, IRowCallback rowcallback)
{ ... }
public NamedResultSetProcessor(string name, IResultSetExtractor resultSetExtractor) { ... }
. . .
}
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The results of the RowMapper or ResultSetExtractor are retrieved by name from the dictionary that is returned.
RowCallbacks, being stateless, only have the placeholder text, "ResultSet returned was processed by an
IRowCallback" as a value for the name of the RowCallback used as a key. Output and InputOutput parameters
can be retrieved by name. If this parameter name is null, then the index of the parameter prefixed with the letter
'P' is a key name, i.e P2, P3, etc.
The namespace Spring.Data.Objects.Generic contains generic versions of these methods. These are listed below
• T QueryWithCommandCreator<T>(IDbCommandCreator cc, IResultSetExtractor<T> rse)
• IList<T> QueryWithCommandCreator<T>(IDbCommandCreator cc, IRowMapper<T> rowMapper)
and overloads that have an additional collecting parameter to obtain any output parameters.
• T QueryWithCommandCreator<T>(IDbCommandCreator cc, IResultSetExtractor<T> rse, IDictionary
returnedParameters)
• IList<T>
QueryWithCommandCreator<T>(IDbCommandCreator
cc,
IRowMapper<T>
rowMapper,
IDictionary returnedParameters)
When processing multiple result sets you can specify up to two type safe result set processors.
• IDictionary QueryWithCommandCreator<T>(IDbCommandCreator cc, IList namedResultSetProcessors)
• IDictionary
QueryWithCommandCreator<T,U>(IDbCommandCreator
cc,
IList
namedResultSetProcessors)
The
list
of
result
set
processors
contains
either
objects
of
the
type
Spring.Data.Generic.NamedResultSetProcessor<T> or Spring.Data.NamedResultSetProcessor. The generic
result set processors, NamedResultSetProcessor<T>, is used to process the first result set in the case of
using QueryWithCommandCreator<T> and to process the first and second result set in the case of using
QueryWithCommandCreator<T,U>. Additional Spring.Data.NamedResultSetProcessors that are listed can be
used to process additional result sets. If you specify a RowCallback with NamedResultSetProcessor<T>, you still
need to specify a type parameter (say string) because the RowCallback processor does not return any object. It is
up to subclasses of RowCallback to collect state due to processing the result set which is later queried.
20.13. DataTable and DataSet
AdoTemplate contains several 'families' of methods to help remove boilerplate code and reduce common
programming errors when using DataTables and DataSets. There are many methods in AdoTemplate so it is
easy to feel a bit overwhelmed when taking a look at the SDK documentation. However, after a while you will
hopefully find the class 'easy to navigate' with intellisense. Here is a quick categorization of the method names
and their associated data access operation. Each method is overloaded to handle common cases of passing in
parameter values.
The 'catch-all' Execute methods upon which other functionality is built up upon are shown below.
In Spring.Data.Core.AdoTemplate
• object Execute(IDataAdapterCallback dataAdapterCallback) - Execute ADO.NET operations on a
IDbDataAdapter object using an interface based callback.
Where IDataAdapterCallback is defined as
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public interface IDataAdapterCallback
{
object DoInDataAdapter(IDbDataAdapter dataAdapter);
}
The passed in IDbDataAdapter will have its SelectCommand property created and set with its Connection and
Transaction values based on the calling transaction context. The return value is the result of processing or null.
There are type-safe versions of this method in Spring.Data.Generic.AdoTemplate
• T Execute<T>(IDataAdapterCallback<T> dataAdapterCallback) - Execute ADO.NET operations on a
IDbDataAdapter object using an interface based callback.
• T Execute<T>(DataAdapterDelegate<T> del) - Execute ADO.NET operations on a IDbDataAdapter object
using an delegate based callback.
Where IDataAdapterCallback<T> and DataAdapterDelegate<T> are defined as
public interface IDataAdapterCallback<T>
{
T DoInDataAdapter(IDbDataAdapter dataAdapter);
}
public delegate T DataAdapterDelegate<T>(IDbDataAdapter dataAdapter);
20.13.1. DataTables
DataTable operations are available on the class Spring.Data.Core.AdoTemplate. If you are using the
generic version, Spring.Data.Generic.AdoTemplate, you can access these methods through the property
ClassicAdoTemplate, which returns the non-generic version of AdoTemplate. DataTable operations available fall
into the general family of methods with 3-5 overloads per method.
• DataTableCreate - Create and Fill DataTables
• DataTableCreateWithParameters - Create and Fill DataTables using a parameter collection.
• DataTableFill - Fill a pre-existing DataTable.
• DataTableFillWithParameters - Fill a pre-existing DataTable using a parameter collection.
• DataTableUpdate - Update the database using the provided DataTable, insert, update, delete SQL.
• DataTableUpdateWithCommandBuilder - Update the database using the provided DataTable, select SQL, and
parameters.
20.13.2. DataSets
DataSet operations are available on the class Spring.Data.Core.AdoTemplate. If you are using the
generic version, Spring.Data.Generic.AdoTemplate, you can access these methods through the property
ClassicAdoTemplate, which returns the non-generic version of AdoTemplate. DataSet operations available fall
into the following family of methods with 3-5 overloads per method.
• DataSetCreate - Create and Fill DataSets
• DataSetCreateWithParameters - Create and Fill DataTables using a parameter collection.
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• DataSetFill - Fill a pre-existing DataSet
• DataSetFillWithParameters - Fill a pre-existing DataTable using parameter collection.
• DataSetUpdate - Update the database using the provided DataSet, insert, update, delete SQL.
• DataSetUpdateWithCommandBuilder - Update the database using the provided DataSet, select SQL, and
parameters.
The following code snippets demonstrate the basic functionality of these methods using the Northwind database.
See the SDK documentation for more details on other overloaded methods.
public class DataSetDemo : AdoDaoSupport
{
private string selectAll = @"select Address, City, CompanyName, ContactName, " +
"ContactTitle, Country, Fax, CustomerID, Phone, PostalCode, " +
"Region from Customers";
public void DemoDataSetCreate()
{
DataSet customerDataSet = AdoTemplate.DataSetCreate(CommandType.Text, selectAll);
// customerDataSet has a table named 'Table' with 91 rows
customerDataSet = AdoTemplate.DataSetCreate(CommandType.Text, selectAll, new string[] { "Customers" });
// customerDataSet has a table named 'Customers' with 91 rows
}
public void DemoDataSetCreateWithParameters()
{
string selectLike = @"select Address, City, CompanyName, ContactName, " +
"ContactTitle, Country, Fax, CustomerID, Phone, PostalCode, " +
"Region from Customers where ContactName like @ContactName";
DbParameters dbParameters = CreateDbParameters();
dbParameters.Add("ContactName", DbType.String).Value = "M%';
DataSet customerLikeMDataSet = AdoTemplate.DataSetCreateWithParams(CommandType.Text, selectLike, dbParameter
// customerLikeMDataSet has a table named 'Table' with 12 rows
}
public void DemoDataSetFill()
{
DataSet dataSet = new DataSet();
dataSet.Locale = CultureInfo.InvariantCulture;
AdoTemplate.DataSetFill(dataSet, CommandType.Text, selectAll);
}
Updating a DataSet can be done using a CommandBuilder, automatically created from the specified select
command and select parameters, or by explicitly specifying the insert, update, delete commands and parameters.
Below is an example, refer to the SDK documentation for additional overloads
public class DataSetDemo : AdoDaoSupport
{
private string selectAll = @"select Address, City, CompanyName, ContactName, " +
"ContactTitle, Country, Fax, CustomerID, Phone, PostalCode, " +
"Region from Customers";
public void DemoDataSetUpdateWithCommandBuilder()
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{
DataSet dataSet = new DataSet();
dataSet.Locale = CultureInfo.InvariantCulture;
AdoTemplate.DataSetFill(dataSet, CommandType.Text, selectAll, new string[]{ "Customers" } );
AddAndEditRow(dataSet);.
AdoTemplate.DataSetUpdateWithCommandBuilder(dataSet, CommandType.Text, selectAll, null, "Customers");
}
public void DemoDataSetUpdateWithoutCommandBuilder()
{
DataSet dataSet = new DataSet();
dataSet.Locale = CultureInfo.InvariantCulture;
AdoTemplate.DataSetFill(dataSet, CommandType.Text, selectAll, new string[]{ "Customers" } );
AddAndEditRow(dataSet);.
string insertSql = @"INSERT Customers (CustomerID, CompanyName) VALUES (@CustomerId, @CompanyName)";
IDbParameters insertParams = CreateDbParameters();
insertParams.Add("CustomerId", DbType.String, 0, "CustomerId");
//.Value = "NewID";
insertParams.Add("CompanyName", DbType.String, 0, "CompanyName"); //.Value = "New Company Name";
string updateSql = @"update Customers SET [email protected] where CustomerId = @CustomerId";
IDbParameters updateParams = CreateDbParameters();
updateParams.Add("Phone", DbType.String, 0, "Phone");//.Value = "030-0074322"; // simple change, last digit
updateParams.Add("CustomerId", DbType.String, 0, "CustomerId");//.Value = "ALFKI";
AdoTemplate.DataSetUpdate(dataSet, "Customers",
CommandType.Text, insertSql, insertParams,
CommandType.Text, updateSql, updateParams,
CommandType.Text, null , null);
}
private static void AddAndEditRow(DataSet dataSet)
{
DataRow dataRow = dataSet.Tables["Customers"].NewRow();
dataRow["CustomerId"] = "NewID";
dataRow["CompanyName"] = "New Company Name";
dataRow["ContactName"] = "New Name";
dataRow["ContactTitle"] = "New Contact Title";
dataRow["Address"] = "New Address";
dataRow["City"] = "New City";
dataRow["Region"] = "NR";
dataRow["PostalCode"] = "New Code";
dataRow["Country"] = "New Country";
dataRow["Phone"] = "New Phone";
dataRow["Fax"] = "New Fax";
dataSet.Tables["Customers"].Rows.Add(dataRow);
DataRow alfkiDataRow = dataSet.Tables["Customers"].Rows[0];
alfkiDataRow["Phone"] = "030-0074322"; // simple change, last digit changed from 1 to 2.
}
}
In the case of needing to set parameter SourceColumn or SourceVersion properties it may be more convenient
to use IDbParameterBuilder.
20.14. TableAdapters and participation in transactional context
Typed DataSets need to have commands in their internal DataAdapters and command collections explicitly set
with a connection/transaction in order for them to correctly participate with a surrounding transactional context.
The reason for this is by default the code generated is explicitly managing the connections and transactions.
This issue is very well described in the article System.Transactions and ADO.NET 2.0 by ADO.NET guru
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Sahil Malik. Spring offers a convenience method that will use reflection to internally set the transaction
on the table adapter's internal command collection to the ambient transaction. This method on the class
Spring.Data.Support.TypedDataSetUtils and is named ApplyConnectionAndTx. Here is sample usage of a
DAO method that uses a VS.NET 2005 generated typed dataset for a PrintGroupMapping table.
public PrintGroupMappingDataSet FindAll()
{
PrintGroupMappingTableAdapter adapter = new PrintGroupMappingTableAdapter();
PrintGroupMappingDataSet printGroupMappingDataSet = new PrintGroupMappingDataSet();
printGroupMappingDataSet = AdoTemplate.Execute(delegate(IDbCommand command)
{
TypedDataSetUtils.ApplyConnectionAndTx(adapter, command);
adapter.Fill(printGroupMappingDataSet.PrintGroupMapping);
return printGroupMappingDataSet;
})
as PrintGroupMappingDataSet;
return printGroupMappingDataSet;
}
This DAO method may be combined with other DAO operations inside a transactional context and they will all
share the same connection/transaction objects.
There are two overloads of the method ApplyConnectionAndTx which differ in the second method argument,
one takes an IDbCommand and the other IDbProvider. These are listed below
public static void ApplyConnectionAndTx(object typedDataSetAdapter, IDbCommand sourceCommand)
public static void ApplyConnectionAndTx(object typedDataSetAdapter, IDbProvider dbProvider)
The method that takes IDbCommand is a convenience if you will be using AdoTemplate callback's as the passed in
command object will already have its connection and transaction properties set based on the current transactional
context. The method that takes an IDbProvider is convenient to use when you have data access logic that is not
contained within a single callback method but is instead spead among multiple classes. In this case passing the
transactionally aware IDbCommand object can be intrusive on the method signatures. Instead you can pass in
an instance of IDbProvider that can be obtained via standard dependency injection techniques or via a service
locator style lookup.
20.15. Database operations as Objects
The Spring.Data.Objects and Spring.Data.Objects.Generic namespaces contains classes that allow one to
access the database in a more object-oriented manner. By way of an example, one can execute queries and get
the results back as a list containing business objects with the relational column data mapped to the properties of
the business object. One can also execute stored procedures and run update, delete and insert statements.
Note
There is a view borne from experience acquired in the field amongst some of the Spring
developers that the various RDBMS operation classes described below (with the exception of the
StoredProcedure class) can often be replaced with straight AdoTemplate calls... often it is simpler to
use and plain easier to read a DAO method that simply calls a method on a AdoTemplate direct (as
opposed to encapsulating a query as a full-blown class).
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It must be stressed however that this is just a view... if you feel that you are getting measurable value
from using the RDBMS operation classes, feel free to continue using these classes.
20.15.1. AdoQuery
is a reusable, threadsafe class that encapsulates an SQL query. Subclasses must implement the
method to provide a IRowMapper instance that can create one object per row obtained from
iterating over the IDataReader that is created during the execution of the query. The AdoQuery class is rarely
used directly since the MappingAdoQuery subclass provides a much more convenient implementation for mapping
rows to .NET classes. Another implementations that extends AdoQuery is MappingadoQueryWithParameters (See
SDK docs for details).
AdoQuery
NewRowMapper(..)
The AdoNonQuery class encapsulates an IDbCommand 's ExecuteNonQuery method functionality. Like the
AdoQuery object, an AdoNonQuery object is reusable, and like all AdoOperation classes, an AdoNonQuery can have
parameters and is defined in SQL. This class provides two execute methods
• IDictionary ExecuteNonQuery(params object[] inParameterValues)
• IDictionary ExecuteNonQueryByNamedParam(IDictionary inParams)
This class is concrete. Although it can be subclassed (for example to add a custom update method) it can easily
be parameterized by setting SQL and declaring parameters.
An example of an AdoQuery subclass to encapsulate an insert statement for a 'TestObject' (consisting only name
and age columns) is shown below
public class CreateTestObjectNonQuery : AdoNonQuery
{
private static string sql = "insert into TestObjects(Age,Name) values (@Age,@Name)";
public CreateTestObjectNonQuery(IDbProvider dbProvider) : base(dbProvider, sql)
{
DeclaredParameters.Add("Age", DbType.Int32);
DeclaredParameters.Add("Name", SqlDbType.NVarChar, 16);
Compile();
}
public void Create(string name, int age)
{
ExecuteNonQuery(name, age);
}
}
20.15.2. MappingAdoQuery
is a reusable query in which concrete subclasses must implement the abstract MapRow(..)
method to convert each row of the supplied IDataReader into an object. Find below a brief example of a custom
query that maps the data from a relation to an instance of the Customer class.
MappingAdoQuery
public class TestObjectQuery : MappingAdoQuery
{
private static string sql = "select TestObjectNo, Age, Name from TestObjects";
public TestObjectQuery(IDbProvider dbProvider)
: base(dbProvider, sql)
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{
CommandType = CommandType.Text;
}
protected override object MapRow(IDataReader reader, int num)
{
TestObject to = new TestObject();
to.ObjectNumber = reader.GetInt32(0);
to.Age = reader.GetInt32(1);
to.Name = reader.GetString(2);
return to;
}
}
20.15.3. AdoNonQuery
The AdoNonQuery class encapsulates an IDbCommand 's ExecuteNonQuery method functionality. Like the
AdoQuery object, an AdoNonQuery object is reusable, and like all AdoOperation classes, an AdoNonQuery can have
parameters and is defined in SQL. This class provides two execute methods
• IDictionary ExecuteNonQuery(params object[] inParameterValues)
• IDictionary ExecuteNonQueryByNamedParam(IDictionary inParams)
This class is concrete. Although it can be subclassed (for example to add a custom update method) it can easily
be parameterized by setting SQL and declaring parameters.
public class CreateTestObjectNonQuery : AdoNonQuery
{
private static string sql = "insert into TestObjects(Age,Name) values (@Age,@Name)";
public CreateTestObjectNonQuery(IDbProvider dbProvider) : base(dbProvider, sql)
{
DeclaredParameters.Add("Age", DbType.Int32);
DeclaredParameters.Add("Name", SqlDbType.NVarChar, 16);
Compile();
}
public void Create(string name, int age)
{
ExecuteNonQuery(name, age);
}
}
20.15.4. Stored Procedure
The StoredProcedure class is designed to make it as simple as possible to call a stored procedure. It takes advantage
of metadata present in the database to look up names of in and out parameters.. This means that you don't have
to explicitly declare parameters. You can of course still declare them if you prefer. There are two versions of the
StoredProcedure class, one that uses generics and one that doesn't. Using the StoredProcedure class consists of
two steps, first defining the in/out parameter and any object mappers and second executing the stored procedure.
The non-generic version of StoredProcedure is in the namespace Spring.Data.Objects. It contains the following
methods to execute a stored procedure
• IDictionary ExecuteScalar(params object[] inParameterValues)
• IDictionary ExecuteScalarByNamedParam(IDictionary inParams)
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• IDictionary ExecuteNonQuery(params object[] inParameterValues)
• IDictionary ExecuteNonQueryByNamedParam(IDictionary inParams)
• IDictionary Query(params object[] inParameterValues)
• IDictionary QueryByNamedParam(IDictionary inParams)
Each of these methods returns an IDictionary that contains the output parameters and/or any results from Spring's
object mapping framework. The arguments to these methods can be a variable length argument list, in which case
the order must match the parameter order of the stored procedure. If the argument is an IDictionary it contains
parameter key/value pairs. Return values from stored procedures are contained under the key "RETURN_VALUE".
The standard in/out parameters for the stored procedure can be set programmatically by adding to the parameter
collection exposed by the property DeclaredParameters. For each result sets that is returned by the stored
procedures you can registering either an IResultSetExtractor, IRowCallback, or IRowMapper by name, which
is used later to extract the mapped results from the returned IDictionary.
Lets take a look at an example. The following stored procedure class will call the CustOrdersDetail stored
procedure in the Northwind database, passing in the OrderID as a stored procedure argument and returning a
collection of OrderDetails business objects.
public class CustOrdersDetailStoredProc : StoredProcedure
{
private static string procedureName = "CustOrdersDetail";
public CustOrdersDetailStoredProc(IDbProvider dbProvider) : base(dbProvider, procedureName)
{
DeriveParameters();
AddRowMapper("orderDetailRowMapper", new OrderDetailRowMapper() );
Compile();
}
public virtual IList GetOrderDetails(int orderid)
{
IDictionary outParams = Query(orderid);
return outParams["orderDetailRowMapper"] as IList;
}
}
The 'DeriveParameters' method saves you the trouble of having to declare each parameter explicitly. When using
DeriveParameters is it often common to use the Query method that takes a variable length list of arguments. This
assumes additional knowledge on the order of the stored procedure arguments. If you do not want to follow this
loose shorthand convention, you can call the method QueryByNamesParameters instead passing in a IDictionary
of parameter key/value pairs.
Note
If you would like to have the return value of the stored procedure included in the returned dictionary,
pass in true as a method parameter to DeriveParameters().
The StoredProcedure class is threadsafe once 'compiled', an act which is usually done in the constructor. This
sets up the cache of database parameters that can be used on each call to Query or QueryByNamedParam.
The implementation of IRowMapper that is used to extract the business objects is 'registered' with the class
and then later retrieved by name as a fictional output parameter. You may also register IRowCallback and
IResultSetExtractor callback interfaces via the AddRowCallback and AddResultSetExtractor methods.
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The generic version of StoredProcedure is in the namespace Spring.Data.Objects.Generic. It allows you to define
up to two generic type parameters that will be used to process result sets returned from the stored procedure. An
example is shown below
public class CustOrdersDetailStoredProc : StoredProcedure
{
private static string procedureName = "CustOrdersDetail";
public CustOrdersDetailStoredProc(IDbProvider dbProvider) : base(dbProvider, procedureName)
{
DeriveParameters();
AddRowMapper("orderDetailRowMapper", new OrderDetailRowMapper<OrderDetails>() );
Compile();
}
public virtual List<OrderDetails> GetOrderDetails(int orderid)
{
IDictionary outParams = Query<OrderDetails>(orderid);
return outParams["orderDetailRowMapper"] as List<OrderDetails>;
}
}
You can find ready to run code demonstrating the StoredProcedure class in the example 'Data Access' that is part
of the Spring.NET distribution.
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Chapter 21. Object Relational Mapping
(ORM) data access
21.1. Introduction
The Spring Framework provides integration with NHibernate in terms of resource management, DAO
implementation support, and transaction strategies. For example for NHibernate, there is first-class support with
lots of IoC convenience features, addressing many typical NHibernate integration issues. All of these support
packages for O/R (Object Relational) mappers comply with Spring's generic transaction and DAO exception
hierarchies. There are usually two integration styles: either using Spring's DAO 'templates' or coding DAOs
against the 'plain' NHibernate APIs. In both cases, DAOs can be configured through Dependency Injection and
participate in Spring's resource and transaction management.
You can use Spring's support for NHibernate without needing to use Spring IoC or transaction management
functionality. The NHibernate support classes can be used in typical 3rd party library style. However, usage inside
a Spring IoC container does provide additional benefits in terms of ease of configuration and deployment; as such,
most examples in this section show configuration inside a Spring container.
Some of the benefits of using the Spring Framework to create your ORM DAOs include:
• Ease of testing. Spring's IoC approach makes it easy to swap the implementations and config locations of
Hibernate SessionFactory instances, ADO.NET DbProvider instances, transaction managers, and mapper
object implementations (if needed). This makes it much easier to isolate and test each piece of persistencerelated code in isolation.
• Common data access exceptions. Spring can wrap exceptions from your O/R mapping tool of choice, converting
them from proprietary exceptions to a common runtime DataAccessException hierarchy. You can still trap
and handle exceptions anywhere you need to. Remember that ADO.NET exceptions (including DB specific
dialects) are also converted to the same hierarchy, meaning that you can perform some operations with
ADO.NET within a consistent programming model.
• General resource management. Spring application contexts can handle the location and configuration of
Hibernate ISessionFactory instances, ADO.NET DbProvider instances and other related resources. This
makes these values easy to manage and change. Spring offers efficient, easy and safe handling of persistence
resources. For example: related code using NHibernate generally needs to use the same NHibernate Session for
efficiency and proper transaction handling. Spring makes it easy to transparently create and bind a Session to
the current thread, either by using an explicit 'template' wrapper class at the code level or by exposing a current
Session through the Hibernate SessionFactory (for DAOs based on plain Hibernate 1.2 API). Thus Spring
solves many of the issues that repeatedly arise from typical NHibernate usage, for any transaction environment
(local or distributed).
• Integrated transaction management. Spring allows you to wrap your O/R mapping code with either a
declarative, AOP style method interceptor, or an explicit 'template' wrapper class at the code level. In either
case, transaction semantics are handled for you, and proper transaction handling (rollback, etc) in case of
exceptions is taken care of. As discussed below, you also get the benefit of being able to use and swap various
transaction managers, without your Hibernate/ADO.NET related code being affected: for example, between
local transactions and distributed, with the same full services (such as declarative transactions) available in
both scenarios. As an additional benefit, ADO.NET-related code can fully integrate transactionally with the
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code you use to do O/R mapping. This is useful for data access that's not suitable for O/R mapping which still
needs to share common transactions with ORM operations.
The NHibernate Northwind example in the Spring distribution shows a NHibernate implementation of a
persistence-technology agnostic DAO interfaces. (In the upcoming RC1 release the SpringAir example will
demonstrate an ADO.NET and NHibernate based implementation of technology agnostic DAO interfaces.) The
NHibernate Northwind example serves as a working sample application that illustrates the use of NHibernate in a
Spring web application. It also leverages declarative transaction demarcation with different transaction strategies.
Both NHibernate 1.0 and NHibernate 1.2 are supported. Differences relate to the use of generics and new features
such as contextual sessions. For information on the latter, refer to the section Implementing DAOs based on the
plain NHibernate API. The NHibernate 1.0 support is in the assembly Spring.Data.NHibernate and the 1.2 support
is in the assembly Spring.Data.NHibernate12
At the moment the only ORM supported in NHibernate, but others can be integrated with Spring (in as much as
makes sense) to offer the same value proposition.
21.2. NHibernate
We will start with a coverage of NHibernate in a Spring environment, using it to demonstrate the approach that
Spring takes towards integrating O/R mappers. This section will cover many issues in detail and show different
variations of DAO implementations and transaction demarcations. Most of these patterns can be directly translated
to all other supported O/R mapping tools.
The following discussion focuses on Hibernate 1.0.4, the major differences with NHibernate 1.2 being the ability
to participate in Spring transaction/session management via the normal NHibernate API instead of the 'template'
approach. Spring supports both NHibernate 1.0 and NHibernate 1.2 via separate .dlls with the same internal
namespace.
21.2.1. Resource management
Typical business applications are often cluttered with repetitive resource management code. Many projects try
to invent their own solutions for this issue, sometimes sacrificing proper handling of failures for programming
convenience. Spring advocates strikingly simple solutions for proper resource handling, namely IoC via
templating; for example infrastructure classes with callback interfaces, or applying AOP interceptors. The
infrastructure cares for proper resource handling, and for appropriate conversion of specific API exceptions to
a common infrastructure exception hierarchy. Spring introduces a DAO exception hierarchy, applicable to any
data access strategy. For direct ADO.NET, the AdoTemplate class mentioned in a previous section cares for
connection handling, and for proper conversion of ADO.NET data access exceptions (not even singly rooted
in .NET 1.1) to Spring's DataAccessException hierarchy, including translation of database-specific SQL error
codes to meaningful exception classes. It supports both distributed and local transactions, via respective Spring
transaction managers.
Spring also offers Hibernate support, consisting of a HibernateTemplate analogous to AdoTemplate, a
HibernateInterceptor, and a Hibernate transaction manager. The major goal is to allow for clear application
layering, with any data access and transaction technology, and for loose coupling of application objects. No more
business service dependencies on the data access or transaction strategy, no more hard-coded resource lookups, no
more hard-to-replace singletons, no more custom service registries. One simple and consistent approach to wiring
up application objects, keeping them as reusable as possible. All the individual data access features are usable
on their own but integrate nicely with Spring's application context concept, providing XML-based configuration
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and cross-referencing of plain object instances that don't need to be Spring-aware. In a typical Spring application,
many important objects are plain .NET objects: data access templates, data access objects (that use the templates),
transaction managers, business services (that use the data access objects and transaction managers), ASP.NET
web pages (that use the business services),and so on.
21.2.2. Transaction Management
While NHibernate offers an API for transaction management you will quite likely find the benefits of using
Spring's generic transaction management features to be more compelling to use, typically for use of a declarative
programming model for transaction demarcation and easily mixing ADO.NET and NHibernate operations within
a single transaction. See the chapter on transaction management for more information on Spring's transaction
management features. There are two choices for transaction management strategies, one based on the NHibernate
API and the other the .NET 2.0 TransactionScope API.
The first strategy is encapsulated in the class Spring.Data.NHibernate.HibernateTransactionManager in
both the Spring.Data.NHibernate namespace. This strategy is preferred when you are using a single database.
ADO.NET operations can also participate in the same transaction, either by using AdoTemplate or by retrieving
the ADO.NET connection/transaction object pair stored in thread local storage when the transaction begins.
Refer to the documentation of Spring's ADO.NET framework for more information on retrieving and using
the connection/transaction pair without using AdoTemplate. You can use the HibernateTransactionManager and
associated classes such as SessionFactory, HibernateTemplate directly as you would any third party API, however
they are most commonly used through Spring's XML configuration file to gain the benefits of easy configuration
for a particular runtime environment and as the basis for the configuration of a data access layer also configured
using XML. An XML fragment showing the declaration of HibernateTransactionManager is shown below.
<object id="HibernateTransactionManager"
type="Spring.Data.NHibernate.HibernateTransactionManager, Spring.Data.NHibernate">
<property name="DbProvider" ref="DbProvider"/>
<property name="SessionFactory" ref="MySessionFactory"/>
</object>
The important property of HibernateTransactionManager are the references to the DbProvider and the Hibernate
ISessionFactory. For more information on the DbProvider, refer to the chapter DbProvider and the following
section on SessionFactory set up.
The second strategy is to use the class Sping.Data.TxScopeTransactionManager that uses .NET 2.0
System.Transaction namespace and its corresponding TransactionScope API. This is preferred when you are
using multiple transactional resources, such as multiple databases.
Both strategies associate one Hibernate Session for the scope of the transaction (scope in the general demarcation
sense, not System.Transaction sense). If there is no transaction then a new Session will be opened for each
operation. The exception to this rule is when using the OpenSessionInViewModule in a web application in single
session mode (see Section 21.2.10, “Web Session Management”). In this case the session will be created on the
start of the web request and closed on the end of the request. Note that the session's flush mode will be set to
FlushMode.NEVER at the start of the request. If a non-readonly transaction is performed, then during the scope of
that transaction processing the flush mode will be changed to AUTO, and then set back to NEVER at the end
of the transaction scope so that any changes to objects associated with the session during rendering will not be
persisted back to the database when the session is closed at the end of the web request.
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21.2.3. SessionFactory set up in a Spring container
To avoid tying application objects to hard-coded resource lookups, Spring allows you to define resources like a
DbProvider or a Hibernate SessionFactory as objects in an application context. Application objects that need to
access resources just receive references to such pre-defined instances via object references (the DAO definition
in the next section illustrates this). The following excerpt from an XML application context definition shows how
to set up Spring's ADO.NET DbProvider and a Hibernate SessionFactory on top of it:
<objects xmlns="http://www.springframework.net"
xmlns:db="http://www.springframework.net/database">
<!-- Property placeholder configurer for database settings -->
<object type="Spring.Objects.Factory.Config.PropertyPlaceholderConfigurer, Spring.Core">
<property name="ConfigSections" value="databaseSettings"/>
</object>
<!-- Database and NHibernate Configuration -->
<db:provider id="DbProvider"
provider="SqlServer-1.1"
connectionString="Integrated Security=false; Data Source=(local);Integrated Security=true;Dat
<object id="MySessionFactory" type="Spring.Data.NHibernate.LocalSessionFactoryObject, Spring.Data.NHibernate">
<property name="DbProvider" ref="DbProvider"/>
<property name="MappingAssemblies">
<list>
<value>Spring.Northwind.Dao.NHibernate</value>
</list>
</property>
<property name="HibernateProperties">
<dictionary>
<entry key="hibernate.connection.provider"
value="NHibernate.Connection.DriverConnectionProvider"/>
<entry key="hibernate.dialect"
value="NHibernate.Dialect.MsSql2000Dialect"/>
<entry key="hibernate.connection.driver_class"
value="NHibernate.Driver.SqlClientDriver"/>
</dictionary>
</property>
</object>
</objects>
Many of the properties on LocalSessionFactoryObject are those you will commonly configure, for example
the property MappingAssemblies specifies a list of assemblies to seach for hibernate mapping files. The property
HibernateProperies are the familiar NHibernate properties used to set typical options such as dialect and driver
class. The location of NHibernate mapping information can also be specified using Spring's IResource abstraction
via the property MappingResources. The IResource abstraction supports opening an input stream from assemblies,
file system, and http(s) based on a Uri syntax. You can also leverage the extensibility of IResource and thereby
allow NHibernate to obtain its configuration information from locations such as a database or LDAP.For other
properties you can configure them as you normal using the file hibernate.cfg.xml and refer to it via the property
ConfigFileNames. This property is a string array so multiple configuration files are supported.
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There are other properties in LocalSessionFactoryObject that relate to the integration of Spring with
NHibernate. The property ExposeTransactionAwareSessionFactory is discussed below and allows you to use
Spring's declarative transaction demarcation functionality with the standard NHibernate API (as compared to
using HibernateTemplate).
The property DbProvider is used to infer two NHibernate configurations options.
• Infer the connection string, typically done via the hibernate property "hibernate.connection.connection_string".
• Delegate to the DbProvider itself as the NHibernate connection provider instead of listing it via property
hibernate.connection.provider via HibernateProperties.
If you specify both the property hibernate.connection.provider and DbProvider (as shown above) the configuration
of the property hibernate.connection.provider is used and a warning level message is logged. If you use
Spring's DbProvider as the NHibernate connection provider then you can take advantage of IDbProvider
implementations that will let you change the connection string at runtime such as UserCredentialsDbProvider
and MultiDelegatingDbProvider.
Note
UserCredentialsDbProvider and MultiDelegatingDbProvider only change the connection string at
runtime based on values in thread local storage and do not clear out the Hibernate cache that is
unique to each ISessionFactory instance. As such, they are only useful for selecting at runtime
a single database instance. Cleaning up an existing session factory when switching to a new
database is left to user code. Creating a new session factory per connection string (assuming
the same mapping files can be used across all databases connections) is not currently supported.
To support this functionality, you can subclass LocalSessionFactoryObject and override the
method ISessionFactory NewSessionFactory(Configuration config) so that it returns an
implementation of ISessionFactory that selects among multiple instances based on values in thread
local storage, much like the implementation of MultiDelegatingDbProvider.
21.2.4. The HibernateTemplate
The basic programming model for templating looks as follows for methods that can be part of any custom data
access object or business service. There are no restrictions on the implementation of the surrounding object at
all, it just needs to provide a Hibernate SessionFactory. It can get the latter from anywhere, but preferably as
an object reference from a Spring IoC container - via a simple SessionFactory property setter. The following
snippets show a DAO definition in a Spring container, referencing the above defined SessionFactory, and an
example for a DAO method implementation.
<objects>
<object id="CustomerDao" type="Spring.Northwind.Dao.NHibernate.HibernateCustomerDao, Spring.Northwind.Dao.NHib
<property name="SessionFactory" ref="MySessionFactory"/>
</object>
</objects>
public class HibernateCustomerDao : ICustomerDao {
private HibernateTemplate hibernateTemplate;
public ISessionFactory SessionFactory
{
set { hibernateTemplate = new HibernateTemplate(value); }
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}
public Customer SaveOrUpdate(Customer customer)
{
hibernateTemplate.SaveOrUpdate(customer);
return customer;
}
}
The HibernateTemplate class provides many methods that mirror the methods exposed on the Hibernate Session
interface, in addition to a number of convenience methods such as the one shown above. If you need access to
the Session to invoke methods that are not exposed on the HibernateTemplate, you can always drop down to
a callback-based approach like so.
public class HibernateCustomerDao : ICustomerDao {
private HibernateTemplate hibernateTemplate;
public ISessionFactory SessionFactory
{
set { hibernateTemplate = new HibernateTemplate(value); }
}
public Customer SaveOrUpdate(Customer customer)
{
return HibernateTemplate.Execute(
delegate(ISession session)
{
// do whatever you want with the session....
session.SaveOrUpdate(customer);
return customer;
}) as Customer;
}
}
Using the anonymous delegate is particularly convenient when you would otherwise be passing various method
parameter calls to the interface based version of this callback. Furthermore, when using generics, you can avoid
the typecast and write code like the following
IList<Supplier> suppliers = HibernateTemplate.ExecuteFind<Supplier>(
delegate(ISession session)
{
return session.CreateQuery("from Supplier s were s.Code = ?")
.SetParameter(0, code)
.List<Supplier>();
});
where code is a variable in the surrounding block, accessible inside the anonymous delegate implementation.
A callback implementation effectively can be used for any Hibernate data access. HibernateTemplate will ensure
that Session instances are properly opened and closed, and automatically participate in transactions. The template
instances are thread-safe and reusable, they can thus be kept as instance variables of the surrounding class. For
simple single step actions like a single Find, Load, SaveOrUpdate, or Delete call, HibernateTemplate offers
alternative convenience methods that can replace such one line callback implementations. Furthermore, Spring
provides a convenient HibernateDaoSupport base class that provides a SessionFactory property for receiving
a SessionFactory and for use by subclasses. In combination, this allows for very simple DAO implementations
for typical requirements:
public class HibernateCustomerDao : HibernateDaoSupport, ICustomerDao
{
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public Customer SaveOrUpdate(Customer customer)
{
HibernateTemplate.SaveOrUpdate(customer);
return customer;
}
}
21.2.5. Implementing Spring-based DAOs without callbacks
As an alternative to using Spring's HibernateTemplate to implement DAOs, data access code can also be written
in a more traditional fashion, without wrapping the Hibernate access code in a callback, while still respecting and
participating in Spring's generic DataAccessException hierarchy. The HibernateDaoSupport base class offers
methods to access the current transactional Session and to convert exceptions in such a scenario; similar methods
are also available as static helpers on the SessionFactoryUtils class. Note that such code will usually pass 'false'
as the value of the DoGetSession(..) method's 'allowCreate' argument, to enforce running within a transaction
(which avoids the need to close the returned Session, as its lifecycle is managed by the transaction). Asking for the
public class HibernateProductDao : HibernateDaoSupport, IProductDao {
public Customer SaveOrUpdate(Customer customer)
{
ISession session = DoGetSession(false);
session.SaveOrUpdate(customer);
return customer;
}
}
}
This code will not translate the Hibernate exception to a generic DataAccessException.
21.2.6. Implementing DAOs based on plain Hibernate 1.2/2.0 API
Hibernate 1.2 introduced a feature called "contextual Sessions", where Hibernate itself manages one current
ISession per transaction. This is roughly equivalent to Spring's synchronization of one Hibernate Session per
transaction. A corresponding DAO implementation looks like as follows, based on the plain Hibernate API:
public class ProductDaoImpl implements IProductDao {
private SessionFactory sessionFactory;
public ISessionFactory SessionFactory
{
get { return sessionFactory; }
set { sessionFactory = value; }
}
public IList<Product> LoadProductsByCategory(String category) {
return SessionFactory.GetCurrentSession()
.CreateQuery("from test.Product product where product.category=?")
.SetParameter(0, category)
.List<Product>();
}
}
public class HibernateCustomerDao : ICustomerDao {
private ISessionFactory sessionFactory;
public ISessionFactory SessionFactory
{
set { sessionFactory = value; }
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}
public Customer SaveOrUpdate(Customer customer)
{
sessionFactory.GetCurrentSession().SaveOrUpdate(customer);
return customer;
}
}
The above DAO follows the Dependency Injection pattern: it fits nicely into a Spring IoC container, just like it
would if coded against Spring's HibernateTemplate. Of course, such a DAO can also be set up in plain C# (for
example, in unit tests): simply instantiate it and call SessionFactory property with the desired factory reference.
As a Spring object definition, it would look as follows:
<objects>
<object id="CustomerDao" type="Spring.Northwind.Dao.NHibernate.HibernateCustomerDao, Spring.Northwind.Dao.NHib
<property name="sessionFactory" ref="MySessionFactory"/>
</object>
</objects>
The SessionFactory configuration to support this programming model can be done two ways,
both via configuration of Spring's LocalSessionFactoryObject. You can enable the use of Spring's
implementation of the NHibernate extension interface, ICurrentSessionContext, by setting the property
'ExposeTransactionAwareSessionFactory' to true on LocalSessionFactoryObject. This is just a short-cut for
setting the NHibernate property current_session_context_class with the name of the implementation class to use.
The first way is shown below
<object id="sessionFactory" type="Spring.Data.NHibernate.LocalSessionFactoryObject, Spring.Data.NHibernate12">
<property name="ExposeTransactionAwareSessionFactory" value="true" />
<!-- other configuration settings omitted -->
</object>
Which is simply a shortcut for the following configuration
<object id="sessionFactory" type="Spring.Data.NHibernate.LocalSessionFactoryObject, Spring.Data.NHibernate12">
<!-- other configuration settings omitted -->
<property name="HibernateProperties">
<dictionary>
<!-- other dictionary entries omitted -->
<entry key="hibernate.current_session_context_class"
value="Spring.Data.NHibernate.SpringSessionContext, Spring.Data.NHibernate12"/>
</dictionary>
</property>
</object>
The main advantage of this DAO style is that it depends on the Hibernate API only; no import of any Spring
class is required. This is of course appealing from a non-invasiveness perspective, and will no doubt feel more
natural to Hibernate developers.
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21.2.6.1. Exception Translation
However, the DAO implemenation as shown throws plain HibernateException which means that callers can only
treat exceptions as generally fatal - unless they want to depend on Hibernate's own exception hierarchy. Catching
specific causes such as an optimistic locking failure is not possible without tying the caller to the implementation
strategy. This trade off might be acceptable to applications that are strongly Hibernate-based and/or do not need
any special exception treatment. As an alternative you can use Spring's exception translation advice to convert
the NHibernate exception to Spring's DataAccessException hierarchy.
Spring offers a solution allowing exception translation to be applied transparently through the [Repository]
attribute:
[Repository]
public class HibernateCustomerDao : ICustomerDao {
// class body here
}
and register an exception translation post processor.
<objects>
<!-- configure session factory (omittied for brevity) -->
<!-- Exception translation object post processor -->
<object type="Spring.Dao.Attributes.PersistenceExceptionTranslationPostProcessor, Spring.Data"/>
<!-- Same DAO configuration as before -->
<object id="CustomerDao" type="Spring.Northwind.Dao.NHibernate.HibernateCustomerDao, Spring.Northwind.Dao.NHib
<property name="sessionFactory" ref="MySessionFactory"/>
</object>
</objects>
The postprocessor will automatically look for all exception translators (implementations of the
IPersistenceExceptionTranslator interface) and advise all object marked with the [Repository] attribute
so that the discovered translators can intercept and apply the appropriate translation on the thrown exceptions.
Spring's LocalSessionFactory object implements the IPersistenceExceptionTranslator interface and
performs the same exception translation as was done when using HibernateTemplate.
The [Repository] attribute is definedin the Spring.Data assembly, however it is used as a 'marker' attribute, and
you can provide your own if you would like to avoid coupling your DAO implementation to a Spring attribute. This
is done by setting PersistenceExceptionTranslationPostProcessor's property RepositoryAttributeType
to your own attribute type.
Note
In summary: DAOs can be implemented based on the plain Hibernate 1.2/2.0 API, while still being
able to participate in Spring-managed transactions and exception translation.
21.2.7. Programmatic transaction demarcation
Transactions can be demarcated in a higher level of the application, on top of such lower-level data access services
spanning any number of operations. There are no restrictions on the implementation of the surrounding business
service here as well, it just needs a Spring PlatformTransactionManager. Again, the latter can come from
anywhere, but preferably as an object reference via a TransactionManager property - just like the productDAO
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should be set via a setProductDao(..) method. The following snippets show a transaction manager and a
business service definition in a Spring application context, and an example for a business method implementation.
<objects>
<object id="HibernateTransactionManager"
type="Spring.Data.NHibernate.HibernateTransactionManager, Spring.Data.NHibernate">
<property name="DbProvider" ref="DbProvider"/>
<property name="SessionFactory" ref="MySessionFactory"/>
</object>
<!-- DAO definition not listed, see above for an example. -->
<object id="FulfillmentService" type="Spring.Northwind.Service.FulfillmentService, Spring.Northwind.Service">
<property name="CustomerDao" ref="CustomerDao"/>
<property name="OrderDao" ref="OrderDao"/>
<property name="ShippingService" ref="ShippingService"/>
<property name="TransactionManager" ref="HibernateTransactionManager"/>
</object>
</objects>
public class FulfillmentService : IFulfillmentService
private TransactionTemplate transactionTemplate;
private IProductDao productDao;
private ICustomerDao customerDao;
private IOrderDao orderDao;
private IShippingService shippingService;
public TransactionManager TransactionManager
{
set { transactionTemplate = new TransactionTemplate(value);
}
public void ProcessCustomer(string customerId)
{
tt.Execute(delegate(ITransactionStatus status)
{
//Find all orders for customer
Customer customer = CustomerDao.FindById(customerId);
foreach (Order order in customer.Orders)
{
//Validate Order
Validate(order);
//Ship with external shipping service
ShippingService.ShipOrder(order);
//Update shipping date
order.ShippedDate = DateTime.Now;
//Update shipment date
OrderDao.SaveOrUpdate(order);
//Other operations...Decrease product quantity... etc
}
return null;
});
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}
}
21.2.8. Declarative transaction demarcation
Alternatively, one can use Spring's declarative transaction support, which essentially enables you to replace
explicit transaction demarcation API calls in your C# code with an AOP transaction interceptor configured in a
Spring container. You can either externalize the transaction semantics (like propagation behavior and isolation
level ) in a configuration file or use the Transaction attribute on the service method to set the transaction semantics.
An example showing attribute driven transaction is shown below
<objects>
<object id="HibernateTransactionManager"
type="Spring.Data.NHibernate.HibernateTransactionManager, Spring.Data.NHibernate">
<property name="DbProvider" ref="DbProvider"/>
<property name="SessionFactory" ref="MySessionFactory"/>
</object>
<!-- DAO definition not listed, see above for an example. -->
<object id="FulfillmentService" type="Spring.Northwind.Service.FulfillmentService, Spring.Northwind.Service">
<property name="CustomerDao" ref="CustomerDao"/>
<property name="OrderDao" ref="OrderDao"/>
<property name="ShippingService" ref="ShippingService"/>
</object>
<!-- Import 'standard xml' configuration for attribute driven declarative tx management -->
<import resource="DeclarativeServicesAttributeDriven.xml"/>
</objects>
Note that with the new transaction namespace, you can replace the importing of
DeclarativeServicesAttributeDriven.xml with the following single line, <tx:attribute-driven/> that more
clearly expresses the intent as compared to the contents of DeclarativeServicesAttributeDriven.xml.
<objects xmlns="http://www.springframework.net"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:tx="http://www.springframework.net/schema/tx"
xsi:schemaLocation="http://www.springframework.net http://www.springframework.net/schema/objects/spring
http://www.springframework.net/schema/tx http://www.springframework.net/schema/tx/spring-tx-1.1.xsd">
<object id="HibernateTransactionManager"
type="Spring.Data.NHibernate.HibernateTransactionManager, Spring.Data.NHibernate">
<property name="DbProvider" ref="DbProvider"/>
<property name="SessionFactory" ref="MySessionFactory"/>
</object>
<!-- DAO definition not listed, see above for an example. -->
<object id="FulfillmentService" type="Spring.Northwind.Service.FulfillmentService, Spring.Northwind.Service">
<property name="CustomerDao" ref="CustomerDao"/>
<property name="OrderDao" ref="OrderDao"/>
<property name="ShippingService" ref="ShippingService"/>
</object>
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<tx:attribute-driven/>
</objects>
The placement of the transaction attribute in the service layer method is shown below.
public class FulfillmentService : IFulfillmentService
{
// fields and properties for dao object omitted, see above
[Transaction(ReadOnly=false)]
public void ProcessCustomer(string customerId)
{
//Find all orders for customer
Customer customer = CustomerDao.FindById(customerId);
foreach (Order order in customer.Orders)
{
//Validate Order
Validate(order);
//Ship with external shipping service
ShippingService.ShipOrder(order);
//Update shipping date
order.ShippedDate = DateTime.Now;
//Update shipment date
OrderDao.SaveOrUpdate(order);
//Other operations...Decrease product quantity... etc
}
}
}
If you prefer to not use attribute to demarcate your transaction boundaries, you can import a configuration file
with the following XML instead of using <tx:attribute-driven/>
<object id="TxProxyConfigurationTemplate" abstract="true"
type="Spring.Transaction.Interceptor.TransactionProxyFactoryObject, Spring.Data">
<property name="PlatformTransactionManager" ref="HibernateTransactionManager"/>
<property name="TransactionAttributes">
<name-values>
<!-- Add common methods across your services here -->
<add key="Process*" value="PROPAGATION_REQUIRED"/>
</name-values>
</property>
</object>
Refer to the documentation on Spring Transaction management for configuration of other features, such as
rollback rules.
21.2.9. Transaction management strategies
Both TransactionTemplate and TransactionInterceptor (not yet seen explicitly in above configuration,
TransactionProxyFactoryObject uses a TransactionInterceptor, you would have to specify it explicitly
if you were using an ordinary ProxyFactoryObject.) delegate the actual transaction handling to a
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instance, which can be a HibernateTransactionManager (for a single
Hibernate SessionFactory, using a ThreadLocal Session under the hood) or a TxScopeTransactionManager
(delegating to MS-DTC for distributed transaction) for Hibernate applications. You could even use a custom
PlatformTransactionManager implementation. So switching from native Hibernate transaction management to
TxScopeTransactionManager, such as when facing distributed transaction requirements for certain deployments
of your application, is just a matter of configuration. Simply replace the Hibernate transaction manager with
Spring's TxScopeTransactionManager implementation. Both transaction demarcation and data access code will
work without changes, as they just use the generic transaction management APIs.
PlatformTransactionManager
For
distributed
transactions across multiple Hibernate session factories, simply combine
TxScopeTransactionManager as a transaction strategy with multiple LocalSessionFactoryObject definitions.
Each of your DAOs then gets one specific SessionFactory reference passed into it's respective object property.
TO BE DONE
can export the ADO.NET Transaction used by Hibernate to plain ADO.NET
access code, for a specific DbProvider. (matching connection string). This allows for high-level transaction
demarcation with mixed Hibernate/ADO.NET data access!
HibernateTransactionManager
21.2.10. Web Session Management
The open session in view pattern keeps the hibernate session open during page rendering so lazily loaded hibernate
objects can be displayed. You configure its use by adding an additional custom HTTP module declaration as
shown below
<system.web>
<httpModules>
<add name="OpenSessionInView" type="Spring.Data.NHibernate.Support.OpenSessionInViewModule, Spring.Data.NH
</httpModules>
...
</system.web>
You can configure which SessionFactory the OpenSessionInViewModule will use by setting 'global' application
key-value pairs as shown below. (this will change in future releases)
<appSettings>
<add key="Spring.Data.NHibernate.Support.OpenSessionInViewModule.SessionFactoryObjectName" value="SessionFac
</appSettings>
The default behavior of the module is that a single session is currently used for
the life of the request. Refer to the earlier section on Transaction Management in this
chapter for more information on how sessions are managed in the OpenSessionInViewModule.
You can also configure in the application setting the EntityInterceptorObjectName using the
key Spring.Data.NHibernate.Support.OpenSessionInViewModule.EntityInterceptorObjectName and if
SingleSession
mode
is
used
via
the
key
Spring.Data.NHibernate.Support.OpenSessionInViewModule.SingleSession. If SingleSession is set to
false, referred to as 'deferred close mode', then each transaction scope will use a new Session and kept open until
the end of the web request. This has the drawback that the first level cache is not reused across transactions and
that objects are required to be unique across all sessions. Problems can arise if the same object is associated with
more than one hibernate session.
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Important
By default, OSIV applies FlushMode.NEVER on every session it creates. This is because if OSIV
flushed pending changes during "EndRequest" and an error occurs, all response has already been sent
to the client. There would be no way of telling the client about the error.
By default this means you MUST explicitly demarcate transaction boundaries around nonreadonly statements when using OSIV. For configuring transactions see Section 21.2.8, “Declarative
transaction demarcation” or the Spring.Data.NHibernate.Northwind example application.
21.2.11. Session Scope
The class Spring.Data.NHibernate.Support.SessionScope allows for you to use a single NHibernate session across
multiple transactions. The usage is shown below
using (new SessionScope())
{
... do multiple operations with a single session, possibly in multiple transactions.
}
At the end of the using block the session is automatically closed. All transactions within the scope use the
same session, if you are using Spring's HibernateTemplate or using Spring's implementation of NHibernate
1.2's ICurrentSessionContext interface. See other sections in this chapter for further information on those usage
scenarios.
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Part III. The Web
This part of the reference documentation covers the Spring Framework's support for the presentation tier,
specifically web-based presentation tiers.
• Chapter 22, Spring.NET Web Framework
• Chapter 23, ASP.NET AJAX
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Chapter 22. Spring.NET Web Framework
22.1. Introduction
Spring.NET's web application framework aims to increase your productivity writing ASP.NET WebForms
applications. It offers a unique value proposition to creating ASP.NET applications not found in other .NET web
frameworks.
The goal of the framework is to make it easy to write 'thin and clean' web applications. By thin, what is meant
is that the WebForm's responsibility is to act as adapter between the HTML based world of the web and the oo
world of your application. The application layer your web form communicates with is where the business logic
resides, not in the web tier. By 'clean' what is meant that the web framework should have a good separation of
concerns, leading ideally to an event-handler that does not contain any reference to UI elements. This makes
it possible to test your event handler code in integration style tests. Last but not least, Spring's web framework
reduces the incidental complexity of common tasks in the web tier, for example the conversion of HTML control
data to objects and then vice-versa after the request has been processed by the application layer.
Highlights of Spring's Web framework are
• Dependency Injection for all ASP.NET artifacts. This includes pages and user controls but also modules,
providers and HTTP handlers. Your pages, controls, etc., do not have any Spring dependencies in order to be
configured via dependency injection.
• Bi-directional data binding. This allows you to declaratively define the data that will be marshaled out of your
html/user controls and into a data model that in turn is generally submitted to the application layer. After the data
model is updated in the application layer, those changes are automatically reflected in the html/user controls
on post back. This removes large amounts of tedious, error prone boilerplate code.
• Web object scopes. Object definitions can be defined at the application, session or request scope. This makes
it easy to inject, say a session scoped shopping cart, into your page without having to do any lower level
programming.
• Data Model Management. While ASP.NET managed the view state of your form, it does not offer facilities
to manage the data model that you build up to submit to the application layer. Spring provides a mechanism
similar to view state to help manage your data model.
• UI agnostic validation framework. Declaratively define complex validation rules, for example that take into
account complex relationships in your data model. Error controls are provided to easily render validation failure.
This allows you to centralize your validation logic and also reuse it on the server side, for example using
parameter validation advice described in the aspect library chapter
• Externalized page navigation through 'result mapping'. Instead of hard coding urls and data to direct where a
page should go next, result mappings are externally defined and configured that associate logical names and a
URL (+ data). This also allows for the encryption of values that are sent via Response.Redirect.
• Improved localization and master page support - Advanced localization features (including image localization)
as well as declarative configuration of what mater page to apply to different parts of your web application are
easy to perform.
All you know about ASP.NET development still applies, Spring's approach is to 'embrace and extend' the basic
ASP.NET programming model so you can be as productive as possible.
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Note
Support for ASP.NET MVC is planned for Spring.NET 2.0 and previews of our integration with the
MVC framework will be mode available when the final MVC framework ships.
What follows is a more detailed background and motivation of features and most importantly the detailed reference
manual for using Spring's web framework. One of the great things about the framework is that it is not an all
or nothing solution. If you choose to use only dependency injection and bi-directional data binding, that is just
fine. You can incrementally adopt the web framework, addressing problems areas in your current web application
with a specific feature. There is no need to go 'whole hog' into using all parts of the framework everywhere in
your application.
The Spring.NET distribution ships with a number of Web QuickStarts and a complete reference application,
SpringAir. Web QuickStarts are the best way to learn each Spring.Web feature by following simple examples,
and the SpringAir reference application has a Spring.Web-enabled frontend which uses many best practices for
Spring.NET web applications, so please do refer to it as you are reading this (reference) material (see Chapter 37,
SpringAir - Reference Application).
22.2. Background
One of the objections many developers have to the ASP.NET programming model is that it is not a "true
MVC" (Model-View-Controller) implementation, because controller-type logic within the page is too tightly
coupled to the view. A good example of this are event handlers within the page class, which typically have
references to view elements, such as input controls, all over the place. Without getting into academic discussion
of what "true MVC" is, and whether it is even appropriate to try to fit form-based technology such as ASP.NET
into traditionally request-based MVC pattern when MVP (Model-View-Presenter) or Presentation Model might
be more appropriate, we'd like to agree with the critics on the most important point they are making: controllertype logic, such as the code within page event handlers in ASP.NET, should not depend on the view elements.
Having said that, there are good things about ASP.NET. Server-side forms and controls make developers
significantly more productive and allow us to significantly simplify page markup. They also make cross-browser
issues easier to deal with, as each control can make sure that it renders correct markup based on the user's browser.
The ability to hook custom logic into the lifecycle of the page, as well as to customize HTTP processing pipeline
are also very powerful features. Finally, being able to interact with the strongly typed server-side controls instead
of manipulating string-based HTTP request collections, such as Form and QueryString, is a much needed layer
of abstraction in web development.
For these reasons, we decided that instead of developing a new, "pure and true MVC" web framework as part
of Spring.NET, we should take a more pragmatic approach and extend ASP.NET in such a way that most, if not
all of its shortcomings are eliminated. It should be noted that with the introduction of a 'true MVC framework'
being added to .NET, with extension points for IoC containers such as Spring, Spring will continue to play a role
within a MVC based model once that functionality is available from Microsoft. It is worth noting that Spring Java
has a very popular MVC framework and much of that experience and added value can be transliterated to help
developers be more productive when using the upcoming ASP.NET MVC support.
Spring.Web also adds support for applying the dependency injection principle to one's ASP.NET Pages and
Controls as well as http modules and custom provider modules. This means that application developers can easily
inject service dependencies into web controllers by leveraging the power of the Spring.NET IoC container. See
Dependency Injection for ASP.NET Pages for more information.
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As we said earlier, event handlers in code-behind classes really should not have to deal with ASP.NET UI controls
directly. Such event handlers should rather work with the presentation model of the page, represented either as a
hierarchy of domain objects or an ADO.NET DataSet. It is for that reason that the Spring.NET team implemented
bidirectional data binding framework to handle the mapping of values to and from the controls on a page to the
underlying data model. The data binding framework also transparently takes care of data type conversion and
formatting, enabling application developers to work with fully typed data (domain) objects in the event handlers
of code-behind files. See Bidirectional Data Binding and Model Management for more information.
The flow of control through an application is another area of concern that is addressed by Spring.NET Web
Framework. Typical ASP.NET applications will use Response.Redirect or Server.Transfer calls within Page
logic to navigate to an appropriate page after an action is executed. This typically leads to hard-coded target URLs
in the Page, which is never a good thing. Result mapping solves this problem by allowing application developers
to specify aliases for action results that map to target URLs based on information in an external configuration
file that can easily be edited. Under consideration for future releases of Spring.NET is a process management
framework, which will take this approach to another level, allowing you to control complex page flows in a very
simple way. See Result Mapping for more information.
Standard localization support is also limited in versions of ASP.NET prior to ASP.NET 2.0. Even though Visual
Studio 2003 generates a local resource file for each ASP.NET Page and user control, those resources are never
used by the ASP.NET infrastructure. This means that application developers have to deal directly with resource
managers whenever they need access to localized resources, which in the opinion of the Spring.NET team
should not be the case. Spring.NET's Web Framework (hereafter referred to as Spring.Web) adds comprehensive
support for localization using both local resource files and global resources that are configured within and for a
Spring.NET container. See Localization and Message Sources for more information.
In addition to the aforementioned features that can be considered to be the 'core' features of the Spring.Web
framework, Spring.Web also ships with a number of other lesser features that might be useful to a large number of
application developers. Some of these additional features include back-ports of ASP.NET 2.0 features that can be
used with ASP.NET 1.1, such as Master Page support. See Master Pages in ASP.NET 1.1 for more information.
In order to implement some of the above mentioned features the Spring.NET team had to extend (as in the objectoriented sense) the standard ASP.NET Page and UserControl classes. This means that in order to take advantage
of the full feature stack of Spring.Web (most notably bidirectional data binding, localization and result mapping),
your code-behind classes will have to extend Spring.Web specific base classes such as Spring.Web.UI.Page;
however, some very powerful features such as dependency injection for ASP.NET Pages, Controls, and providers
can be leveraged without having to extend Spring.Web-specific base classes. It is worth stating that by taking
advantage of some of the more useful features offered by Spring.Web you will be coupling the presentation tier
of your application(s) to Spring.Web. The choice of whether or not this is appropriate is, of course, left to you.
22.3. Automatic context loading and hierarchical contexts
22.3.1. Configuration
Unsurprisingly, Spring.Web builds on top of the Spring.NET IoC container, and makes heavy use (internally)
of the easy pluggability and standardized configuration afforded by the IoC container. This also means that all
of the controllers (ASP.NET Pages) that make up a typical Spring.Web enabled application will be configured
using the same standard Spring.NET XML configuration syntax. Spring.Web uses a custom PageHandlerFactory
implementation to load and configure a Spring.NET IoC container, which is in turn used to locate an appropriate
Page to handle a HTTP request. The WebSupportModule configures miscellaneous Spring infrastructure classes
for use in a web environment, for example setting the storage strategy of LogicalThreadContext to be
HybridContextStorage.
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The instantiation and configuration of the Spring.NET IoC container by the Spring.Web infrastructure is wholly
transparent to application developers, who will typically never have to explicitly instantiate and configure an IoC
container manually (by for example using the new operator in C#). In order to effect the transparent bootstrapping
of the IoC container, the Spring.Web infrastructure requires the insertion of the following configuration snippet
into each and every Spring.Web-enabled web application's root Web.config file (the verb and path properties
can of course be changed from the values that are shown below):
<system.web>
<httpHandlers>
<add verb="*" path="*.aspx" type="Spring.Web.Support.PageHandlerFactory, Spring.Web"/>
</httpHandlers>
<httpModules>
<add name="Spring" type="Spring.Context.Support.WebSupportModule, Spring.Web"/>
</httpModules>
...
</system.web>
Please note that this snippet of standard ASP.NET configuration is only required to be present in the root directory
of each Spring.Web web application (i.e. in the web.config file present in the top level virtual directory of an
ASP.NET web application).
The above XML configuration snippet will direct the ASP.NET infrastructure to use Spring.NET's page factory,
which will in turn create instances of the appropriate .aspx Page, (possibly) inject dependencies into said Page
(as required), and then forward the handling of the request to said Page.
After the Spring.Web page factory is configured, you will also need to define a root application context by adding
a Spring.NET configuration section to that same web.config file. The final configuration file should look a little
like this (your exact configuration will no doubt vary in particulars)...
<?xml version="1.0" encoding="utf-8"?>
<configuration>
<configSections>
<sectionGroup name="spring">
<section name="context" type="Spring.Context.Support.WebContextHandler, Spring.Web"/>
</sectionGroup>
</configSections>
<spring>
<context>
<resource uri="~/Config/CommonObjects.xml"/>
<resource uri="~/Config/CommonPages.xml"/>
<!-- TEST CONFIGURATION -->
<!-<resource uri="~/Config/Test/Services.xml"/>
<resource uri="~/Config/Test/Dao.xml"/>
-->
<!-- PRODUCTION CONFIGURATION -->
<resource uri="~/Config/Production/Services.xml"/>
<resource uri="~/Config/Production/Dao.xml"/>
</context>
</spring>
<system.web>
<httpHandlers>
<add verb="*" path="*.aspx" type="Spring.Web.Support.PageHandlerFactory, Spring.Web"/>
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</httpHandlers>
<httpModules>
<add name="Spring" type="Spring.Context.Support.WebSupportModule, Spring.Web"/>
</httpModules>
</system.web>
</configuration>
There are a few important points that need to be noted with regard to the above configuration:
1. You must define a custom configuration section handler for the spring/context element. If you use
Spring.NET for many applications on the same web server, it might be easier to move the whole definition of
the Spring.NET section group to your machine.config file.
2. The custom configuration section handler is of the type Spring.Context.Support.WebContextHandler which
will in turn instantiate an IoC container of the type Spring.Context.Support.WebApplicationContext. This
will ensure that all of the features provided by Spring.Web are handled properly (such as request and sessionscoped object definitions).
3. Within the <spring> element you need to define a root context, and resource locations that contain the object
definitions that will be used within the web application (such as service or business tier objects) then need to
be specified as child elements within the <context> element. Object definition resources can be fully-qualified
paths or URLs, or non-qualified, as in the example above. Non-qualified resources will be loaded using the
default resource type for the context, which for the WebApplicationContext is the WebResource type.
4. Please note that the object definition resources do not all have to be the same resource type (e.g. all file://, all
http://, all assembly://, etc). This means that you can load some object definitions from resources embedded
directly within application assemblies (assembly://), while continuing to load other object definitions from
web resources that can be more easily edited.
22.3.1.1. Configuration for IIS7
The configuration for IIS7 is shown below
<system.webServer>
<validation validateIntegratedModeConfiguration="false"/>
<modules>
<add name="Spring" type="Spring.Context.Support.WebSupportModule, Spring.Web"/>
</modules>
<handlers>
<add name="SpringPageHandler" verb="*" path="*.aspx" type="Spring.Web.Support.PageHandlerFactory, Spring.Web
<add name="SpringContextMonitor" verb="*" path="ContextMonitor.ashx" type="Spring.Web.Support.ContextMonitor
</handlers>
</system.webServer>
22.3.2. Context Hierarchy
ASP.NET provides a hierarchical configuration mechanism by allowing application developers to override
configuration settings specified at a higher level in the web application directory hierarchy with configuration
settings specified at the lower level.
For example, a web application's root Web.config file overrides settings from the (lower level) machine.config
file. In the same fashion, settings specified within the web.config file within a subdirectory of a web application
will override settings from the root Web.config and so on. Lower level Web.config files can also add settings of
their own that were not previously defined anywhere.
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Spring.Web leverages this ASP.NET feature to provide support for a context hierarchy. Your lower level
Web.config files can be used to add new object definitions or to override existing ones per virtual directory.
What this means to application developers is that one can easily componentize an application by creating a
virtual directory per component and creating a custom context for each component that contains the necessary
configuration info for that particular context. The configuration for a lower level component will generally contain
only those definitions for the pages that the component consists of and (possibly) overrides for some of the
definitions from the root context (for example, menus).
Because each such lower level component will usually contain only a few object definitions, application
developers are encouraged to embed those object definitions directly into the Web.config for the lower level
context instead of relying on an external resource containing object definitions. This is easily accomplished by
creating a component Web.config similar to the following one:
<?xml version="1.0" encoding="utf-8"?>
<configuration>
<configSections>
<sectionGroup name="spring">
<section name="objects" type="Spring.Context.Support.DefaultSectionHandler, Spring.Core"/>
</sectionGroup>
</configSections>
<spring>
<context type="Spring.Context.Support.WebApplicationContext, Spring.Web">
<resource uri="config://spring/objects"/>
</context>
<objects xmlns="http://www.springframework.net">
<object type="MyPage.aspx" parent="basePage">
<property name="MyRootService" ref="myServiceDefinedInRootContext"/>
<property name="MyLocalService" ref="myServiceDefinedLocally"/>
<property name="Results">
<!-- ... -->
</property>
</object>
<object id="myServiceDefinedLocally" type="MyCompany.MyProject.Services.MyServiceImpl, MyAssembly"/>
</objects>
</spring>
</configuration>
The <context/> element seen above (contained within the <spring/> element) simply tells the Spring.NET
infrastructure code to load (its) object definitions from the spring/objects section of the configuration file.
You can (and should) avoid the need to specify <configSections/> element by moving the configuration
handler definition for the <objects> element to a higher level (root) Web.config file, or even to the level of the
machine.config file if Spring.NET is to be used for multiple applications on the same server.
A very important point to be aware of is that this component-level context can reference definitions from its
parent context(s). Basically, if a referenced object definition is not found in the current context, Spring.NET will
search all the ancestor contexts in the context hierarchy until it finds said object definition (or ultimately fails
and throws an exception).
22.4. Dependency Injection for ASP.NET Pages
Spring.Web builds on top of the feature set and capabilities of ASP.NET; one example of this can be seen the way
that Spring.Web has used the code-behind class of the Page mechanism to satisfy the Controller portion of the
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MVC architectural pattern. In MVC-based (web) applications, the Controller is typically a thin wrapper around
one or more service objects. In the specific case of Spring.Web, the Spring.NET team realized that it was very
important that service object dependencies be easily injected into Page Controllers. Accordingly, Spring.Web
provides first class support for dependency injection in ASP.NET Pages. This allows application developers
to inject any required service object dependencies (and indeed any other dependencies) into their Pages using
standard Spring.NET configuration instead of having to rely on custom service locators or manual object lookups
in a Spring.NET application context.
Once an application developer has configured the Spring.NET web application context, said developer can easily
create object definitions for the pages that compose that web application:
<objects xmlns="http://www.springframework.net">
<object name="basePage" abstract="true">
<property name="MasterPageFile" value="~/Web/StandardTemplate.master"/>
</object>
<object type="Login.aspx">
<property name="Authenticator" ref="authenticationService"/>
</object>
<object type="Default.aspx" parent="basePage"/>
</objects>
This example contains three definitions:
1. The first definition is an abstract definition for the base page that many other pages in the application will
inherit from. In this case, the definition simply specifies which page is to be referenced as the master page,
but it will typically also configure localization-related dependencies and root folders for images, scripts and
CSS stylesheets.
2. The second definition defines a login page that neither inherits from the base page nor references the
master page. What it does show is how to inject a service object dependency into a page instance (the
authenticationService is defined elsewhere).
3. The final definition defines a default application page. In this case it simply inherits from the base page in
order to inherit the master page dependency, but apart from that it doesn't need any additional dependency
injection configuration.
One thing that slightly differentiates the configuration of ASP.NET pages from the configuration of other .NET
classes is in the value passed to the type attribute. As can be seen in the above configuration snippet the type
name is actually the path to the .aspx file for the Page, relative to the directory context it is defined in. In the case
of the above example, those definitions are in the root context so Login.aspx and Default.aspx also must be in
the root of the web application's virtual directory. The master page is defined using an absolute path because it
could conceivably be referenced from child contexts that are defined within subdirectories of the web application.
The astute reader may have noticed that the definitions for the Login and Default pages don't specify either of
the id and name attributes. This is in marked contrast to typical object definitions in Spring.NET, where the id
or name attributes are typically mandatory (although not always, as in the case of inner object definitions). This
is actually intentional, because in the case of Spring.Web Page Controller instances one typically wants to use
the name of the .aspx file name as the identifier. If an id is not specified, the Spring.Web infrastructure will
simply use the name of the .aspx file as the object identifier (minus any leading path information, and minus
the file extension too).
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Nothing prevents an application developer from specifying an id or name value explicitly; one use case when
the explicit naming might be useful is when one wants to expose the same page multiple times using a slightly
different configuration (Add / Edit pages for example). If you would like to use abstract object definitions and
have your page inherit from them, the use of the name attribute should be used instead of the id attribute on the
abstract object definition.
22.4.1. Injecting Dependencies into Controls
Spring.Web also allows application developers to inject dependencies into controls (both user controls and
standard controls) that are contained within a page. This can be accomplished globally for all controls of a
particular Type by using the location of the .ascx as the object type identifier. This is similar to injecting into
.aspx pages shown above.
<object type="~/controls/MyControl.ascx" abstract="true">
<!-- inject dependencies here... -->
</object>
In either case, be sure to mark the object definition as abstract (by adding abstract="true" to the attribute
list of the <object/> element).
22.4.2. Injecting dependencies into custom HTTP modules
You can perform dependency injection on custom HTTP modules through the use of the class
Spring.Context.Support.HttpApplicationConfigurer. You register your custom HTTP module as you would
normally, for example a module of the type HtmlCommentAppenderModule, taken from the Web Quickstart,
appends additional comments into the http response. It is registered as shown below
<httpModules>
<add name="HtmlCommentAppender" type="HtmlCommentAppenderModule"/>
</httpModules>
To configure this module, naming conventions are used to identify the module name with configuration
instructions in the Spring configuration file. The ModuleTemplates property of HttpApplicationConfigurer is
a dictionary that takes as a key the name of the HTTP module, HtmlCommentAppender, and as a value the
configuration instructions as you would normally use for configuring an object with Spring. An example is shown
below. HttpApplicationConfigurer' ModuleTemplates property.
<object name="HttpApplicationConfigurer" type="Spring.Context.Support.HttpApplicationConfigurer, Spring.Web">
<property name="ModuleTemplates">
<dictionary>
<entry key="HtmlCommentAppender"> <!-- this name must match the module name -->
<object>
<!-- select "view source" in your browser on any page to see the appended html comment -->
<property name="AppendText" value="My configured comment!" />
</object>
</entry>
</dictionary>
</property>
</object>
You can see this example in action in the Web Quickstart.
22.4.3. Injecting dependencies into HTTP handlers and handler factories
You can perform dependency injection on IHttpHandlers and IHttpHandlerFactory. This effectively
allows for a fully Spring-managed <httpHandlers> configuration section. To configure an IHttpHandler or
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you should register Spring's MappingHandlerFactory with a specific path or wildcard
string (i.e. *.aspx) using the standard configuration of an <httpHandler> in web.config. This is shown below
IHttpHandlerFactory
<system.web>
<httpHandlers>
<!-the lines below map *any* request ending with *.ashx or *.whatever
to the global(!) MappingHandlerFactory. Further "specialication"
of which handler to map to is done within MappingHandlerFactory's configuration use MappingHandlerFactoryConfigurer for this (see below)
-->
<add verb="*" path="*.ashx" type="Spring.Web.Support.MappingHandlerFactory, Spring.Web" validate="true"/>
<add verb="*" path="*.whatever" type="Spring.Web.Support.MappingHandlerFactory, Spring.Web" validate="false"
</httpHandlers>
</system.web>
The specialization of which specific handler is mapped to the path is done by configuration of Spring's
MappingHandlerFactoryConfigurer class. The MappingHandlerFactoryConfigurer is configured by specifying
a dictionary of key value paris, the key value is a regular expression that will match the request URL and the
value is an instance of an IHttpHandler or IHttpHandlerFactory configured via dependency injection.
the configuration of MappingHandlerFactoryConfigurer is shown below
<objects xmlns="http://www.springframework.net">
<!-- configures the global GenericHandlerFactory instance -->
<object name="mappingHandlerFactoryConfigurer" type="Spring.Web.Support.MappingHandlerFactoryConfigurer, Spr
<property name="HandlerMap">
<dictionary>
<!-- map any request ending with *.whatever to NoOpHandler -->
<entry key="\.whatever$" value="myCustomHandler" />
<entry key="\.ashx$" value="standardHandlerFactory" />
</dictionary>
</property>
</object>
<object name="standardHandlerFactory" type="Spring.Web.Support.DefaultHandlerFactory, Spring.Web" />
<!-- defines a standard singleton that will handle *.whatever requests -->
<object name="myCustomHandler" type="MyCustomHttpHandler, App_Code">
<property name="MessageText" value="This text is injected via Spring" />
</object>
<!-used for configuring ~/DemoHandler.ashx custom handler
note, that this is an abstract definition because 'type' is not specified
-->
<object name="DemoHandler.ashx">
<property name="OutputText">
<value>This text is injected via Spring</value>
</property>
</object>
</objects>
Spring's DefaultHandlerFactory will use the .NET class System.Web.UI.SimpleHandlerFactory to create
handler instaces and will configure each instances used an object definition whose name matches the request
url's filename. The abstract object definition of DemoHandler.ashx is an example of this approach. You may also
configure standard classes that implment the IHttpHandler interface as demonstrated in the example above for
the class MyCustomHttpHandler.
Please refer to the Web Quickstart application too see this in action.
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22.4.4. Injecting dependencies into custom providers
Custom providers can be configured with Spring. The approach to configuration is a family of adapters that
correspond 1-to-1 with the standard ASP.NET providers that are registered using the standard ASP.NET
mechanism. The adapters inherit from their correspondingly named provider class in the BCL.
• MembershipProviderAdapter
• ProfileProviderAdapter
• RoleProviderAdapter
• SiteMapProviderAdapter
Here is an example of how to register the adapter for membership providers.
<membership defaultProvider="mySqlMembershipProvider">
<providers>
<clear/>
<add connectionStringName="" name="mySqlMembershipProvider" type="Spring.Web.Providers.Membershi
</providers>
</membership>
The name of the provider must match the name of the object in the spring configuration that will serve as the actual
provider implementation. For convenience there are configurable versions of the providers found in ASP.NET so
that you can use the full functionality of spring to configure these standard provider implementations, for example
using property place holders, etc. These are
• ConfigurableActiveDirectoryMembershipProvider
• ConfigurableSqlMembershipProvider
• ConfigurableSqlProfileProvider
• ConfigurableSqlRoleProvider
• ConfigurableXmlSiteMapProvider
Here is an example configuration taken from the Web Quickstart that simply sets the description property and
connection string.
<object id="mySqlMembershipProvider" type="Spring.Web.Providers.ConfigurableSqlMembershipProvider">
<property name="connectionStringName" value="MyLocalSQLServer" />
<property name="parameters">
<name-values>
<add key="description" value="membershipprovider description" />
</name-values>
</property>
</object>
Your own custom providers of course will contain additional configuration specific to your implementation.
22.4.5. Customizing control dependency injection
There might be situations where it is necessary to customize Spring.Web's dependency injection processing. In
particular when using GridViews, which create a large number of child controls, dependency injection can slow
down your page. To overcome this problem, you may tell Spring to handle the dependency injection process
yourself by implementing the interface ISupportsWebDependencyInjection as shown below:
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[C#]
class MyControl : Control, ISupportsWebDependencyInjection
{
private IApplicationContext _defaultApplicationContext;
public IApplicationContext DefaultApplicationContext
{
get { return _defaultApplicationContext; }
set { _defaultApplicationContext = value; }
}
override protected AddedControl( Control control, int index )
{
// handle DI for children ourselves // defaults to a call to InjectDependenciesRecursive
WebUtils.InjectDependenciesRecursive( _defaultApplicationContext, control );
base.AddedControl( control, index );
}
}
There is a Spring server control, Panel, that provides an easier way to turn of dependency injection for parts of
your page. Example use is shown below
<spring:Panel runat="server"
suppressDependencyInjection="true"
renderContainerTag="false">
.. put your heavy controls here - they won't be touched by DI
</spring:Panel>
By wrapping the performance sensitive parts of your page within this panel, you can easily turn off DI using the
attribute suppressDependencyInjection. By default <spring:Panel/> won't render a container tag (<div>, <span>,
etc.). You can modify this behavior by setting the attribute "renderContainerTag" accordingly.
22.5. Web object scopes
Spring.NET web applications support an additional attribute within object definition elements that allows you to
control the scope of an object:
<object id="myObject" type="MyType, MyAssembly" scope="application | session | request"/>
As you can see, there are three possible values for the scope attribute -- application, session or request. Application
scope is the default, and will be used for all objects that don't have scope attribute defined. As its name says, it will
result in a single instance of an object being created for the duration of the application, so it works exactly like the
standard singleton objects in non-web applications. Session scope allows you to define objects in such a way that
an instance is created for each HttpSession. This is the ideal scope for objects that you want bound to a single user
such as user profile, shopping cart, etc. Request scope will result in a creation of an instance per HTTP request.
Unlike with prototype objects, calls to IApplicationContext.GetObject will return the same instance of the
request-scoped object during a single HTTP request. This allows you, for example, to inject the same requestscoped object into multiple pages and then use server-side transfer to move from one page to another. As all the
pages are executed within the single HTTP request in this case, they will share the same instance of the injected
object.
One thing to keep in mind is that objects can only reference other objects that are in the same or broader scope.
This means that application-scoped objects can only reference other application-scoped, session-scoped objects
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can reference both session and application-scoped objects, and finally, request-scoped objects can reference other
request, session or application-scoped objects. Also, prototype objects (and that includes all ASP.NET web pages
defined within Spring.NET context) can reference singleton objects from any scope, as well as other prototype
objects.
22.6. Master Pages in ASP.NET 1.1
Support for ASP.NET 1.1 master pages in Spring.Web is very similar to the support for master pages in ASP.NET
2.0.
The idea is that a web developer can define a layout template for the site as a master page and specify content
place holders that other pages can then reference and populate. A sample master page (MasterLayout.ascx) could
look like this:
<%@ Control language="c#" Codebehind="MasterLayout.ascx.cs" AutoEventWireup="false" Inherits="MyApp.Web.UI.Maste
<%@ Register TagPrefix="spring" Namespace="Spring.Web.UI.Controls" Assembly="Spring.Web" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
<html>
<head>
<title>Master Page</title>
<link rel="stylesheet" type="text/css" href="<%= Context.Request.ApplicationPath %>/css/styles.css">
<spring:ContentPlaceHolder id="head" runat="server"/>
</head>
<body>
<form runat="server">
<table cellPadding="3" width="100%" border="1">
<tr>
<td colspan="2">
<spring:ContentPlaceHolder id="title" runat="server">
<!-- default title content -->
</spring:ContentPlaceHolder>
</td>
</tr>
<tr>
<td>
<spring:ContentPlaceHolder id="leftSidebar" runat="server">
<!-- default left side content -->
</spring:ContentPlaceHolder>
</td>
<td>
<spring:ContentPlaceHolder id="main" runat="server">
<!-- default main area content -->
</spring:ContentPlaceHolder>
</td>
</tr>
</table>
</form>
</body>
</html>
As you can see from the above code, the master page defines the overall layout for the page, in addition to four
content placeholders that other pages can override. The master page can also include default content within the
placeholder that will be displayed if a derived page does not override the placeholder.
A page (Child.aspx) that uses this master page might look like this:
<%@ Register TagPrefix="spring" Namespace="Spring.Web.UI.Controls" Assembly="Spring.Web" %>
<%@ Page language="c#" Codebehind="Child.aspx.cs" AutoEventWireup="false" Inherits="ArtFair.Web.UI.Forms.Child"
<html>
<body>
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<spring:Content id="leftSidebarContent" contentPlaceholderId="leftSidebar" runat="server">
<!-- left sidebar content -->
</spring:Content>
<spring:Content id="mainContent" contentPlaceholderId="main" runat="server">
<!-- main area content -->
</spring:Content>
</body>
</html>
The <spring:Content/> control in the above example uses the contentPlaceholderId attribute (property) to
specify exactly which placeholder from the master page is to be overridden. Because this particular page does
not define content elements for the head and title place holders, they will be displayed using the default content
supplied in the master page.
Both the ContentPlaceHolder and Content controls can contain any valid ASP.NET markup: HTML, standard
ASP.NET controls, user controls, etc.
VS.NET 2003 issue
Technically, the <html> and <body> tags from the previous example are not strictly necessary because
they are already defined in the master page. However, if these tags are omitted, then Visual Studio
2003 will complain about a schema and intellisense won't work, so it's much easier to work in the
HTML view if those tags are included. They will be ignored when the page is rendered.
22.6.1. Linking child pages to their master
The Spring.Web.UI.Page class exposes a property called MasterPageFile, which can be used to specify the
master page.
The recommended way to do this is by leveraging the Spring.NET IoC container and creating definitions similar
to the following:
<?xml version="1.0" encoding="utf-8" ?>
<objects xmlns="http://www.springframework.net">
<object name="basePage" abstract="true">
<property name="MasterPageFile" value="~/MasterLayout.ascx"/>
</object>
<object type="Child.aspx" parent="basePage">
<!-- inject other objects that page needs -->
</object>
</objects>
This approach allows application developers to change the master page being used for a number of pages within a
web application. Of course, the master page can still be overridden on a per context or per page basis by creating
a new abstract page definition within a child context, or by specifying the MasterPageFile property directly.
22.7. Bidirectional Data Binding and Model Management
A problem with the existing data binding support in ASP.NET is that it is one-way only. It allows application
developers to bind page controls to the data model and display information from said data model, but it
doesn't allow for the extraction of values from the controls when the form is submitted. Spring.Web adds such
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bidirectional data binding to ASP.NET by allowing developers to specify data binding rules for their page, and
by automatically evaluating configured data binding rules at the appropriate time in the page's lifecycle.
ASP.NET also doesn't provide any support for model management within the postbacks. Sure, it has a ViewState
management, but that takes care of the control state only and not of the state of any presentation model objects
these controls might be bound to. In order to manage model within ASP.NET, developers will typically use HTTP
Session object to store the model between the postbacks. This results in a decent amount of boilerplate code
that can and should be eliminated, which is exactly what Spring.Web does by providing a simple set of model
management methods.
Please note that in order to take advantage of the bidirectional data binding and model management support
provided by Spring.Web, you will have to couple your presentation layer to Spring.Web; this is because features
requires you to extend a Spring.Web.UI.Page instead of the usual System.Web.UI.Page class.
Spring.Web data binding is very easy to use. Application developers simply need to override the protected
InitializeDataBindings method and configure data binding rules for the page. They also need to override three
model management methods: InitializeModel, LoadModel and SaveModel. This is perhaps best illustrated by
an example from the SpringAir reference application. First, let's take a look at the page markup:
<%@ Page Language="c#" Inherits="TripForm" CodeFile="TripForm.aspx.cs" %>
<asp:Content ID="body" ContentPlaceHolderID="body" runat="server">
<div style="text-align: center">
<h4><asp:Label ID="caption" runat="server"></asp:Label></h4>
<table>
<tr class="formLabel">
<td>&nbsp;</td>
<td colspan="3">
<spring:RadioButtonGroup ID="tripMode" runat="server">
<asp:RadioButton ID="OneWay" runat="server" />
<asp:RadioButton ID="RoundTrip" runat="server" />
</spring:RadioButtonGroup>
</td>
</tr>
<tr>
<td class="formLabel" align="right">
<asp:Label ID="leavingFrom" runat="server" /></td>
<td nowrap="nowrap">
<asp:DropDownList ID="leavingFromAirportCode" runat="server" />
</td>
<td class="formLabel" align="right">
<asp:Label ID="goingTo" runat="server" /></td>
<td nowrap="nowrap">
<asp:DropDownList ID="goingToAirportCode" runat="server" />
</td>
</tr>
<tr>
<td class="formLabel" align="right">
<asp:Label ID="leavingOn" runat="server" /></td>
<td nowrap="nowrap">
<spring:Calendar ID="departureDate" runat="server" Width="75px" AllowEditing="true" Skin="sy
</td>
<td class="formLabel" align="right">
<asp:Label ID="returningOn" runat="server" /></td>
<td nowrap="nowrap">
<div id="returningOnCalendar">
<spring:Calendar ID="returnDate" runat="server" Width="75px" AllowEditing="true" Skin="s
</div>
</td>
</tr>
<tr>
<td class="buttonBar" colspan="4">
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<br/>
<asp:Button ID="findFlights" runat="server"/></td>
</tr>
</table>
</div>
</asp:Content>
Ignore for the moment the fact that none of the label controls have text defined, which will be described later
when we discuss localization in Spring.NET. What is important for the purposes of our current discussion,
is that we have a number of input controls defined: tripMode radio group, leavingFromAirportCode and
goingToAirportCode dropdowns, as well as two Spring.NET Calendar controls, departureDate and returnDate.
Next, let's take a look at the model we will be binding this form to:
namespace SpringAir.Domain
{
[Serializable]
public class Trip
{
// fields
private TripMode mode;
private TripPoint startingFrom;
private TripPoint returningFrom;
// constructors
public Trip()
{
this.mode = TripMode.RoundTrip;
this.startingFrom = new TripPoint();
this.returningFrom = new TripPoint();
}
public Trip(TripMode mode, TripPoint startingFrom, TripPoint returningFrom)
{
this.mode = mode;
this.startingFrom = startingFrom;
this.returningFrom = returningFrom;
}
// properties
public TripMode Mode
{
get { return this.mode; }
set { this.mode = value; }
}
public TripPoint StartingFrom
{
get { return this.startingFrom; }
set { this.startingFrom = value; }
}
public TripPoint ReturningFrom
{
get { return this.returningFrom; }
set { this.returningFrom = value; }
}
}
[Serializable]
public class TripPoint
{
// fields
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private string airportCode;
private DateTime date;
// constructors
public TripPoint()
{}
public TripPoint(string airportCode, DateTime date)
{
this.airportCode = airportCode;
this.date = date;
}
// properties
public string AirportCode
{
get { return this.airportCode; }
set { this.airportCode = value; }
}
public DateTime Date
{
get { return this.date; }
set { this.date = value; }
}
}
[Serializable]
public enum TripMode
{
OneWay,
RoundTrip
}
}
As you can see, Trip class uses the TripPoint class to represent departure and return, which are exposed as
StartingFrom and ReturningFrom properties. It also uses TripMode enumeration to specify whether the trip is
one way or return trip, which is exposed as Mode property.
Finally, let's see the code-behind class that ties everything together:
public class TripForm : Spring.Web.UI.Page
{
// model
private Trip trip;
public Trip Trip
{
get { return trip; }
set { trip = value; }
}
// service dependency, injected by Spring IoC container
private IBookingAgent bookingAgent;
public IBookingAgent BookingAgent
{
set { bookingAgent = value; }
}
// model management methods
protected override void InitializeModel()
{
trip = new Trip();
trip.Mode = TripMode.RoundTrip;
trip.StartingFrom.Date = DateTime.Today;
trip.ReturningFrom.Date = DateTime.Today.AddDays(1);
}
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protected override void LoadModel(object savedModel)
{
trip = (Trip) savedModel;
}
protected override object SaveModel()
{
return trip;
}
// data binding rules
protected override void InitializeDataBindings()
{
BindingManager.AddBinding("tripMode.Value", "Trip.Mode");
BindingManager.AddBinding("leavingFromAirportCode.SelectedValue", "Trip.StartingFrom.AirportCode");
BindingManager.AddBinding("goingToAirportCode.SelectedValue", "Trip.ReturningFrom.AirportCode");
BindingManager.AddBinding("departureDate.SelectedDate", "Trip.StartingFrom.Date");
BindingManager.AddBinding("returnDate.SelectedDate", "Trip.ReturningFrom.Date");
}
// event handler for findFlights button, uses injected 'bookingAgent'
// service and model 'trip' object to find flights
private void SearchForFlights(object sender, EventArgs e)
{
FlightSuggestions suggestions = bookingAgent.SuggestFlights(trip);
if (suggestions.HasOutboundFlights)
{
// redirect to SuggestedFlights page
}
}
}
There are quite a few things that are happening in this relatively simple piece of code, so it's worth that we spend
some time on each one:
1. When the page is initially loaded (IsPostback == false), the InitializeModel() method is called which
initializes the trip object by creating a new instance and setting its properties to desired values. Right before
the page is rendered, the SaveModel() method will be invoked and whatever the value it returns will be stored
within the HTTP Session. Finally, on each postback, the LoadModel() method will be called and the value
returned by the previous call to SaveModel will be passed to it as an argument.
In this particular case the implementation is very simple because our whole model is just the trip object.
As such, SaveModel() simply returns the trip object and LoadModel() casts the savedModel() argument to
Trip and assigns it to the trip field within the page. In the more complex scenarios, you will typically
return a dictionary containing your model objects from the SaveModel() method, and read the values from that
dictionary within the LoadModel().
2. InitializeDataBindings method defines the binding rules for all five input controls on our form. It does so
by invoking AddBinding method on the BindingManager exposed by the page. AddBinding method is heavily
overloaded and it allows you to specify a binding direction and a formatter to use in addition to the source and
target binding expressions that are used above. We'll discuss these optional parameters shortly, but for now
let's focus on the source and target expressions.
The Data Binding framework uses Spring.NET Expression Language to define binding expressions. In most
cases, like in the example above, both source and target expression will evaluate to a property or a field within
one of the controls or a data model. This is always the case when you are setting a bi-directional binding, as both
binding expressions need to be "settable". What is important to remember about InitializeDataBindings
method is that it is executed only once per page type. Basically, all of the binding expressions are parsed the
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first time the page is instantiated, and are the cached and used by all instances of that same page type that
are created at a later time. This is done for performance reasons, as data binding expression parsing on every
postback is unnecessary and would add a significant overhead to the overall page processing time.
3. If you look at the SearchForFlights event handler, you will notice that it has no dependencies on the view
elements. It simply uses the injected bookingAgent service and a trip object that in order to obtain a list of
suggested flights. Furthermore, if you make any modifications to the trip object within your event handler,
bound controls will be updated accordingly just before the page is rendered.
This accomplishes one of the major goals we set out to achieve, allowing developers to remove view element
references from the page event handlers and decouple controller-type methods from the view.
Now that you have a solid high-level picture of how Spring.NET data binding and model management are typically
used in web applications, let's take a look at the details and see how data binding is actually implemented under
the hood, what the extension points are, and what are some additional features that make data binding framework
usable in real-world applications.
22.7.1. Data Binding Under the Hood
Spring.NET Data Binding framework revolves around two main interfaces: IBinding and IBindingContainer.
The IBinding interface is definitely the more important one of the two, as it has to be implemented by all binding
types. This interface defines several methods, with some of them being overloaded for convenience:
public interface IBinding
{
void BindSourceToTarget(object source, object target, ValidationErrors validationErrors);
void BindSourceToTarget(object source, object target, ValidationErrors validationErrors,
IDictionary variables);
void BindTargetToSource(object source, object target, ValidationErrors validationErrors);
void BindTargetToSource(object source, object target, ValidationErrors validationErrors,
IDictionary variables);
void SetErrorMessage(string messageId, params string[] errorProviders);
}
As their names imply, BindSourceToTarget method is used to extract and copy bound values from the source
object to the target object, while BindTargetToSource does the opposite. Both method names and parameter types
are very generic for a good reason -- data binding framework can indeed be used to bind any two objects. Using
it to bind web forms to model objects is just one of its possible uses, although a very common one and tightly
integrated into the Spring.NET Web Framework.
The validationErrors parameter requires further explanation. While the data binding framework is not in any
way coupled to the data validation framework, they are in some ways related. For example, while the data
validation framework is best suited to validate the populated model according to the business rules, the data
binding framework is in a better position to validate data types during the binding process. However, regardless of
where specific validation is performed, all error messages should be presented to the user in a consistent manner.
In order to accomplish this, Spring.NET Web Framework passes the same ValidationErrors instance to binding
methods and to any validators that might be executed within your event handlers. This ensures that all error
messages are stored together and are displayed consistently to the end user, using Spring.NET validation error
controls.
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The last method in the IBinding interface, SetErrorMessage, enables this by allowing you to specify the resource
id of the error message to be displayed in the case of binding error, as well as the list of error providers that
messages should be displayed in. We will see an example of the SetErrorMessage usage shortly.
The IBindingContainer interface extends the IBinding interface and adds the following members:
public interface IBindingContainer : IBinding
{
bool HasBindings { get; }
IBinding
IBinding
IBinding
IBinding
IBinding
AddBinding(IBinding binding);
AddBinding(string sourceExpression,
AddBinding(string sourceExpression,
AddBinding(string sourceExpression,
AddBinding(string sourceExpression,
IFormatter formatter);
string
string
string
string
targetExpression);
targetExpression, BindingDirection direction);
targetExpression, IFormatter formatter);
targetExpression, BindingDirection direction,
}
As you can see, this interface has a number of overloaded AddBinding methods. The first one,
AddBinding(IBinding binding) is the most generic one, as it can be used to add any binding type to the container.
The other four are convenience methods that provide a simple way to add the most commonly used binding type,
SimpleExpressionBinding. The SimpleExpressionBinding is what we used in the example at the beginning of
this section to bind our web form to a Trip instance. It uses Spring.NET Expression Language to extract and to
set values within source and target objects. We discussed sourceExpression and targetExpression arguments
earlier, so let's focus on the remaining ones.
22.7.1.1. Binding Direction
The direction argument determines whether the binding is bidirectional or unidirectional. By default, all data
bindings are bidirectional unless the direction argument is set to either BindingDirection.SourceToTarget or
BindingDirection.TargetToSource. If one of these two values is specified, binding will be evaluated only when
the appropriate BindDirection method is invoked, and will be completely ignored in the other direction. This is
very useful when you want to bind some information from the model into non-input controls, such as labels.
However, unidirectional data bindings are also useful when your form doesn't have a simple one-to-one mapping
to presentation model. In our earlier trip form example, the presentation model was intentionally designed to
allow for simple one-to-one mappings. For the sake of discussion, let's add the Airport class and modify our
TripPoint class like this:
namespace SpringAir.Domain
{
[Serializable]
public class TripPoint
{
// fields
private Airport airport;
private DateTime date;
// constructors
public TripPoint()
{}
public TripPoint(Airport airport, DateTime date)
{
this.airport = airport;
this.date = date;
}
// properties
public Airport Airport
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{
get { return this.airport; }
set { this.airport = value; }
}
public DateTime Date
{
get { return this.date; }
set { this.date = value; }
}
}
[Serializable]
public class Airport
{
// fields
private string code;
private string name;
// properties
public string Code
{
get { return this.code; }
set { this.code = value; }
}
public string Name
{
get { return this.name; }
set { this.name = value; }
}
}
}
Instead of the string property AirportCode, our TripPoint class now exposes an Airport property of type
Airport, which is defined above. Now we have a problem: what used to be a simple string to string binding,
with the airport code selected in a dropdown being copied directly into the TripPoint.AirportCode property and
vice versa, now becomes a not so simple string to Airport binding, so let's see how we can solve this mismatch
problem.
First of all, binding from the model to the control is still very straight forward. We just need to set up one-way
bindings from the model to controls:
protected override void InitializeDataBindings()
{
BindingManager.AddBinding("leavingFromAirportCode.SelectedValue", "Trip.StartingFrom.Airport.Code", Bind
BindingManager.AddBinding("goingToAirportCode.SelectedValue", "Trip.ReturningFrom.Airport.Code", Binding
...
}
All we need to do is extract airport code value from the Trip.StartingFrom.Airport.Code instead of
Trip.StartingFrom.AirportCode. Unfortunately, binding from the control to the model the same way won't
work: we might be able to set Code property of the Airport object, but that will likely make the Airport.Name
property invalid. What we really want do is find an instance of the Airport class based on the airport code
and set the TripPoint.Airport property to it. Fortunately, this is very simple to do with Spring.NET data
binding, especially because we already have airportDao object defined in the Spring context, which has
GetAirport(string airportCode) finder method. All we need to do is set up data bindings from source to target
that will invoke this finder method when evaluating the source expression. Our complete set of bindings for these
two drop down lists will then look like this:
protected override void InitializeDataBindings()
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{
BindingManager.AddBinding("@(airportDao).GetAirport(leavingFromAirportCode.SelectedValue)", "Trip.Starti
BindingManager.AddBinding("leavingFromAirportCode.SelectedValue", "Trip.StartingFrom.Airport.Code", Bind
BindingManager.AddBinding("@(airportDao).GetAirport(goingToAirportCode.SelectedValue)", "Trip.ReturningF
BindingManager.AddBinding("goingToAirportCode.SelectedValue", "Trip.ReturningFrom.Airport.Code", Binding
...
}
That's it -- by using two unidirectional bindings with different expressions and by leveraging the fact that
expressions can reference objects defined in the Spring context, we were able to solve this non-trivial data binding
problem.
22.7.1.2. Formatters
The last argument to AddBinding method that we need to discuss is a formatter argument. This argument allows
you to specify a formatter that should be used to parse string value from the typical input control before it is bound
to the model, and to format strongly typed model value before it is bound to the control.
You will typically use one of the formatters provided in the Spring.Globalization.Formatters namespace, but if
you have requirements that cannot be satisfied by one of the standard formatters it is easy enough to write your
own -- all you need to do is implement a very simple IFormatter interface:
public interface IFormatter
{
string Format(object value);
object Parse(string value);
}
Standard formatters provided with Spring.NET are: CurrencyFormatter, DateTimeFormatter, FloatFormatter,
IntegerFormatter, NumberFormatter and PercentFormatter, which should be sufficient for most usage
scenarios.
22.7.1.3. Type Conversion
Because the data binding framework uses the same expression evaluation engine as the Spring.NET IoC container,
it will use any registered type converters to perform data binding. Many type converters are included with
Spring.NET (take a look at the classes in Spring.Objects.TypeConverters namespace) and automatically registered
for you, but you can implement your own custom converters and register them using standard Spring.NET type
converter registration mechanisms.
22.7.1.4. Data Binding Events
Spring.Web's base Page class adds two events to the standard .NET page lifecycle - DataBound and DataUnbound.
The DataUnbound event is fired after the data model has been updated using values from the controls. It is fired
right after the Load event and only on postbacks, because it doesn't make sense to update the data model using
the controls' initial values.
The DataBound is fired after controls have been updated using values from the data model. This happens right
before the PreRender event.
The fact that data model is updated immediately after the Load event and that controls are updated right before
the PreRender event means that your event handlers will be able to work with a correctly updated data model, as
they execute after the Load event, and that any changes you make to the data model within event handlers will be
reflected in the controls immediately afterwards, as they (the controls) are updated prior to the actual rendering.
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22.7.1.5. Rendering Binding Errors
If there are errors in the databinding, for example, trying to bind a string 'hello' to an integer property on the
model, you can specify how those fundamental binding errors should be rendered. An example of this shown
below taken from the WebQuickStart 'RobustEmployeeInfo' example.
[Default.aspx.cs]
protected override void InitializeDataBindings()
{
// collect txtId.Text binding errors in "id.errors" collection
BindingManager.AddBinding("txtId.Text", "Employee.Id").SetErrorMessage("ID has to be an integer", "id.errors")
...
[Default.aspx]
...
<asp:TextBox ID="txtId" runat="server" />
<!-- output validation errors from "id.errors" collection -->
<spring:ValidationError Provider="id.errors" runat="server" />
...
The SetErrorMessage specifies the message text or resource id of the error message to be displayed followed by
a variable length list of strings that specify the collection of error providers message where the message should
be displayed. In the above case the error provider will be rendered in Spring's ValidationError User Control. See
22.7.1.6. HttpRequestListBindingContainer
HttpRequestListBindingContainer extracts posted raw values from the request and populates the specified IList
by creating objects of the type specified and populating each of these objects according to the requestBindings
collection.
Please checkout the WebQuickStart sample's demo of HttpRequestListBindingContainer. Below
protected override void InitializeDataBindings()
{
// HttpRequestListBindingContainer unbinds specified values from Request -> Productlist
HttpRequestListBindingContainer requestBindings =
new HttpRequestListBindingContainer("sku,name,quantity,price", "Products", typeof(ProductInfo));
requestBindings.AddBinding("sku", "Sku");
requestBindings.AddBinding("name", "Name");
requestBindings.AddBinding("quantity", "Quantity", quantityFormatter);
requestBindings.AddBinding("price", "Price", priceFormatter);
BindingManager.AddBinding(requestBindings);
}
Note
Due to the fact, that browsers don't send the values of unchecked checkboxes, you can't use
HttpRequestListBindingContainer with <input type="checkbox" > html controls.
22.7.2. Using DataBindingPanel
To simplify use of Spring's Data Binding feature on web pages and controls, Spring.Web provides a special
DataBindingPanel container control. A DataBindingPanel does not render any html code itself, but allows for
specifying additional, data binding related attributes to its child controls:
<%@ Page Language="C#" CodeFile="Default.aspx.cs" Inherits="DataBinding_EasyEmployeeInfo_Default" %>
<%@ Register TagPrefix="spring" Namespace="Spring.Web.UI.Controls" Assembly="Spring.Web" %>
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<html>
<body>
<spring:DataBindingPanel ID="ctlDataBindingPanel" runat="server">
<table cellpadding="3" cellspacing="3" border="0">
<tr>
<td>Employee ID:</td>
<td>
<asp:TextBox ID="txtId" runat="server" BindingTarget="Employee.Id" />
</td>
</tr>
<tr>
<td>First Name:</td>
<td><asp:TextBox ID="txtFirstName" runat="server" BindingTarget="Employee.FirstName" /></td>
</tr>
</table>
</spring.DataBindingPanel>
</body>
</html>
Using DataBindingPanel the binding information can be specified directly on the control declaration. The
following attributes are recognized by a DataBindingPanel:
• BindingTarget
corresponds to the target expression used in IBindingContainer.AddBinding()
• BindingSource
corresponds to the source expression used in IBindingContainer.AddBinding(). For standard controls you don't
need to specify the source expression. If you are binding to some custom control, of course you must specific
this attribute.
• BindingDirection
one of the values of the BindingDirection enumeration
• BindingFormatter
if you need a custom formatter, you can specific the object name of a formatter here. The formatter instance
will be obtained by a call to IApplicationContext.GetObject() each time it is needed.
• BindingType
In case you need a completely customized binding, specify its type here. Note that a custom binding type must
implement the following constructor signature:
ctor(string source,string target, BindingDirection, IFormatter)
Note
The Visual Studio Web Form Editor will of course complain about binding attributes because it
doesn't know them. You can safely ignore those warnings.
22.7.3. Customizing Model Persistence
As was already mentioned in the introduction to this chapter, model management needs an application developer
to override InitializeModel(), SaveModel() and LoadModel() for storing model information between requests
in the user's session. On web farms this of course storing information in a user's session is not a good
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strategy. Thus it is possible to choose another persistence strategy by setting a Spring.Web.UI.Page's resp.
Spring.Web.UI.UserControl's ModelPersistenceMedium property:
<object id="modelPersister" type="Sample.DatabaseModelPersistenceMedium, MyCode"/>
<object type="UserRegistration.aspx">
<property name="ModelPersistenceMedium" ref="modelPersister"/>
</object>
To implement any arbitrary persistence strategy, one simply needs to implement the IModelPersistenceMedium
interface:
public interface IModelPersistenceMedium
{
// Load the model for the specified control context.
object LoadFromMedium( Control context );
// Save the specified model object.
void SaveToMedium( Control context, object modelToSave );
}
22.8. Localization and Message Sources
While recognizing that the .NET framework has excellent support for localization, the support within ASP.NET
1.x is somewhat incomplete.
Every .aspx page in an ASP.NET project has a resource file associated with it, but those resources are never used
(by the current ASP.NET infrastructure). ASP.NET 2.0 will change that and allow application developers to use
local resources for pages. In the meantime, the Spring.NET team built support for using local pages resources into
Spring.Web thus allowing application developers to start using ASP.NET 2.0-like page resources immediately.
Spring.Web supports several different approaches to localization within a web application, which can be mixed
and matched as appropriate. Both push and pull mechanisms are supported, as well as the fallback to globally
defined resources when a local resource cannot be found. Spring.Web also provides support for user culture
management and image localization, which are described in the later sections.
Tip
Introductory material covering ASP.NET Globalization and Localization can be found at the
following URLs; Globalization Architecture for ASP.NET and Localization Practices for ASP.NET
2.0 by Michele Leroux Bustamante.
22.8.1. Automatic Localization Using Localizers ("Push" Localization)
The central idea behind 'push' localization is that an application developer should be able to specify localization
resources in the resource file for the page and have those resources automatically applied to the user
controls on the page by the framework. For example, an application developer could define a page such as
UserRegistration.aspx...
<%@ Register TagPrefix="spring" Namespace="Spring.Web.UI.Controls" Assembly="Spring.Web" %>
<%@ Page language="c#" Codebehind="UserRegistration.aspx.cs"
AutoEventWireup="false" Inherits="ArtFair.Web.UI.Forms.UserRegistration" %>
<html>
<body>
<spring:Content id="mainContent" contentPlaceholderId="main" runat="server">
<div align="right">
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<asp:LinkButton ID="english" Runat="server" CommandArgument="en-US">English</asp:LinkButton>&nbs
<asp:LinkButton ID="serbian" Runat="server" CommandArgument="sr-SP-Latn">Srpski</asp:LinkButton>
</div>
<table>
<tr>
<td><asp:Label id="emailLabel" Runat="server"/></td>
<td><asp:TextBox id="email" Runat="server" Width="150px"/></td>
</tr>
<tr>
<td><asp:Label id="passwordLabel" Runat="server"/></td>
<td><asp:TextBox id="password" Runat="server" Width="150px"/></td>
</tr>
<tr>
<td><asp:Label id="passwordConfirmationLabel" Runat="server"/></td>
<td><asp:TextBox id="passwordConfirmation" Runat="server" Width="150px"/></td>
</tr>
<tr>
<td><asp:Label id="nameLabel" Runat="server"/></td>
<td><asp:TextBox id="name" Runat="server" Width="150px"/></td>
</tr>
...
<tr>
<td colspan="2">
<asp:Button id="saveButton" Runat="server"/>&nbsp;
<asp:Button id="cancelButton" Runat="server"/>
</td>
</tr>
</table>
</spring:Content>
</body>
</html>
A close inspection of the above .aspx code reveals that none of the Label or Button controls have had a value
assigned to the Text property. The values of the Text property for these controls are stored in the local resource
file (of the page) using the following convention to identify the resource (string).
$this.controlId.propertyName
The corresponding local resource file, UserRegistration.aspx.resx, is shown below.
<root>
<data name="$this.emailLabel.Text">
<value>Email:</value>
</data>
<data name="$this.passwordLabel.Text">
<value>Password:</value>
</data>
<data name="$this.passwordConfirmationLabel.Text">
<value>Confirm password:</value>
</data>
<data name="$this.nameLabel.Text">
<value>Full name:</value>
</data>
...
<data name="$this.countryLabel.Text">
<value>Country:</value>
</data>
<data name="$this.saveButton.Text">
<value>$messageSource.save</value>
</data>
<data name="$this.cancelButton.Text">
<value>$messageSource.cancel</value>
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</data>
</root>
VS2003
To view the .resx file for a page, you may need to enable "Project/Show All Files" in Visual Studio.
When "Show All Files" is enabled, the .resx file appears like a "child" of the code-behind page.
When Visual Studio creates the .resx file, it will include a xds:schema element and several reshead
elements. Your data elements will follow the reshead elements. When working with the .resx files,
you may want to choose "Open With" from the context menu and select the "Source Code" text editor.
VS2005
To create a resource file in VS2005, open your control or page in design mode and select "Tools/
Generate local resource" from the menu
Finally a localizer must be configured for the page to enable automatic localization:
<object id="localizer" type="Spring.Globalization.Localizers.ResourceSetLocalizer, Spring.Core"/>
<object type="UserRegistration.aspx">
<property name="Localizer" ref="localizer"/>
</object>
For more information on configuring localizers see Section 22.8.3, “Working with Localizers”
22.8.2. Global Message Sources
The last two resource definitions from the previous section require some additional explanation:
<data name="$this.saveButton.Text">
<value>$messageSource.save</value>
</data>
<data name="$this.cancelButton.Text">
<value>$messageSource.cancel</value>
</data>
In some cases it makes sense to apply a resource that is defined globally as opposed to locally. In this example,
it makes better sense to define values for the Save and Cancel buttons globally as they will probably be used
throughout the application.
The above example demonstrates how one can achieve that by defining a resource redirection expression as the
value of a local resource by prefixing a global resource name with the following string.
$messageSource.
Taking the case of the above example, this will tell the localizer to use the save and cancel portions of the resource
key as lookup keys to retrieve the actual values from a global message source. The important thing to remember
is that one need only define a resource redirect once, typically in the invariant resource file – any lookup for a
resource redirect will simply fall back to the invariant culture, and result in a global message source lookup using
the correct culture.
Global resources are (on a per-context basis) defined as a plain vanilla object definition using the reserved name
of 'messageSource', which one can add to one's Spring.NET configuration file as shown below.
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<object id="messageSource" type="Spring.Context.Support.ResourceSetMessageSource, Spring.Core">
<property name="ResourceManagers">
<list>
<value>MyApp.Web.Resources.Strings, MyApp.Web</value>
</list>
</property>
</object>
NET 2.0
To use resources from your App_GlobalResources folder, specify App_GlobalResources as assembly
name (see the SpringAir example application for more):
<value>Resources.Strings, App_GlobalResources</value>
The global resources are cached within the Spring.NET IApplicationContext and are accessible through the
Spring.NET IMessageSource interface.
The Spring.Web Page and UserControl classes have a reference to their owning IApplicationContext and it's
associated IMessageSource. As such, they will automatically redirect resource lookups to a global message source
if a local resource cannot be found.
Currently, the ResourceSetMessageSource is the only message source implementation that ships with
Spring.NET.
22.8.3. Working with Localizers
In order to apply resources automatically, a localizer needs to be injected into all pages requiring this feature
(typically accomplished using a base page definition that other pages will inherit from). The injected localizer will
inspect the resource file when the page is first requested, cache the resources that start with the '$this' marker
string value, and apply the values to the controls that populate the page prior to the page being rendered.
A localizer is simply an object that implements the Spring.Globalization.ILocalizer interface.
Spring.Globalization.AbstractLocalizer is provided as a convenient base class for localization: this class
has one abstract method, LoadResources. This method must load and return a list of all the resources that must
be automatically applied from the resource store.
Spring.NET
ships
with
one
concrete
implementation
of
a
localizer,
Spring.Globalization.Localizers.ResourceSetLocalizer, that retrieves a list of resources to apply from the
local resource file. Future releases of Spring.NET may provide other localizers that read resources from an XML
file or even a flat text file that contains resource name-value pairs which will allow application developers to store
resources within the files in a web application instead of as embedded resources in an assembly. Of course, if an
application developer would rather store such resources in a database, he or she can write their own ILocalizer
implementation that will load a list of resources to apply from a database.
As mentioned previously, one would typically configure the localizer to be used within an abstract base definition
for those pages that require localization as shown below.
<object id="localizer" type="Spring.Globalization.Localizers.ResourceSetLocalizer, Spring.Core"/>
<object name="basePage" abstract="true">
<description>
Pages that reference this definition as their parent
(see examples below) will automatically inherit following properties.
</description>
<property name="Localizer" ref="localizer"/>
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</object>
Of course, nothing prevents an application developer from defining a different localizer for each page in the
application; in any case, one can always override the localizer defined in a base (page) definition. Alternatively,
if one does want any resources to be applied automatically one can completely omit the localizer definition.
One last thing to note is that Spring.NET UserControl instances will (by default) inherit the localizer and other
localization settings from the page that they are contained within, but one can similarly also override that behavior
using explicit dependency injection.
22.8.4. Applying Resources Manually ("Pull" Localization)
While automatic localization as described above works great for many form-like pages, it doesn't work nearly as
well for the controls defined within any iterative controls because the IDs for such iterative controls are not fixed.
It also doesn't work well in those cases where one needs to display the same resource multiple times within the
same page. For example, think of the header columns for outgoing and return flights tables within the SpringAir
application (see Chapter 37, SpringAir - Reference Application).
In these situations, one should use a pull-style mechanism for localization, which boils down to a simple
GetMessage call as shown below.
<asp:Repeater id="outboundFlightList" Runat="server">
<HeaderTemplate>
<table border="0" width="90%" cellpadding="0" cellspacing="0" align="center" class="suggestedTable">
<thead>
<tr class="suggestedTableCaption">
<th colspan="6">
<%= GetMessage("outboundFlights") %>
</th>
</tr>
<tr class="suggestedTableColnames">
<th><%= GetMessage("flightNumber") %></th>
<th><%= GetMessage("departureDate") %></th>
<th><%= GetMessage("departureAirport") %></th>
<th><%= GetMessage("destinationAirport") %></th>
<th><%= GetMessage("aircraft") %></th>
<th><%= GetMessage("seatPlan") %></th>
</tr>
</thead>
<tbody>
</HeaderTemplate>
The GetMessage method is available within both the Spring.Web.UI.Page and Spring.Web.UI.UserControl
classes, and it will automatically fall back to a global message source lookup if a local resource is not found.
22.8.5. Localizing Images within a Web Application
Spring.Web provides an easy (and consistent) way to localize images within a web application. Unlike text
resources, which can be stored within embedded resource files, XML files, or even a database, images in a typical
web application are usually stored as files on the file system. Using a combination of directory naming conventions
and a custom ASP.NET control, Spring.Web allows application developers to localize images within the page
as easily as text resources.
The Spring.Web Page class exposes the ImagesRoot property, which is used to define the root directory where
images are stored. The default value is 'Images', which means that the localizer expects to find an 'Images' directory
within the application root, but one can set it to any value in the definition of the page.
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In order to localize images, one needs to create a directory for each localized culture under the ImagesRoot
directory as shown below.
/MyApp
/Images
/en
/en-US
/fr
/fr-CA
/sr-SP-Cyrl
/sr-SP-Latn
...
Once an appropriate folder hierarchy is in place all one need do is put the localized images in the appropriate
directories and make sure that different translations of the same image are named the same. In order to place a
localized image on a page, one needs to use the <spring:LocalizedImage> as shown below.
<%@ Page language="c#" Codebehind="StandardTemplate.aspx.cs"
AutoEventWireup="false" Inherits="SpringAir.Web.StandardTemplate" %>
<%@ Register TagPrefix="spring" Namespace="Spring.Web.UI.Controls" Assembly="Spring.Web" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
<html>
<body>
<spring:LocalizedImage id="logoImage" imageName="spring-air-logo.jpg" borderWidth="0" runat="server" />
</body>
</html>
This control will find the most specific directory that contains an image with the specified name using standard
localization fallback rules and the user's culture. For example, if the user's culture is 'en-US', the localizer will
look for the spring-air-logo.jpg file in Images/en-US, then in Images/en and finally, if the image file has still
not been found, in the root Images directory (which for all practical purposes serves as an invariant culture folder).
22.8.6. User Culture Management
In addition to global and local resource management, Spring.Web also adds support for user culture management
by exposing the current CultureInfo through the UserCulture property on the Page and UserControl classes.
The
simply delegate culture resolution to an implementation of
Spring.Globalization.ICultureResolver interface. One can specify exactly which culture resolver to use by
configuring the CultureResolver property of the Page class in the relevant object definition as shown below.
UserCulture
property
will
<object name="BasePage" abstract="true">
<property name="CultureResolver">
<object type="Spring.Globalization.Resolvers.CookieCultureResolver, Spring.Web"/>
</property>
</object>
Several useful implementations of ICultureResolver ship as part of Spring.Web, so it is unlikely that application
developers will have to implement their own culture resolver. However, if one does have such a requirement, the
resulting implementation should be fairly straightforward as there are only two methods that one need implement.
The following sections discuss each available implementation of the ICultureResolver interface.
22.8.6.1. DefaultWebCultureResolver
This is default culture resolver implementation. It will be used if one does not specify a culture resolver for a
page, or if one explicitly injects a DefaultWebCultureResolver into a page definition explicitly. The latter case
(explicit injection) is sometimes useful because it allows one to specify a culture that should always be used by
providing a value to the DefaultCulture property on the resolver.
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The DefaultWebCultureResolver will first look at the DefaultCulture property and return its value if said
property value is not null. If it is null, the DefaultWebCultureResolver will fall back to request header inspection,
and finally, if no 'Accept-Lang' request headers are present it will return the UI culture of the currently executing
thread.
22.8.6.2. RequestCultureResolver
This resolver works in a similar way to the DefaultWebCultureResolver with the exception that it always checks
request headers first, and only then falls back to the value of the DefaultCulture property or the culture code
of the current thread.
22.8.6.3. SessionCultureResolver
This resolver will look for culture information in the user's session and return it if it finds one. If not, it will fall
back to the behavior of the DefaultWebCultureResolver.
22.8.6.4. CookieCultureResolver
This resolver will look for culture information in a cookie, and return it if it finds one. If not, it will fall back to
the behavior of the DefaultWebCultureResolver.
Warning
CookieCultureResolver will not work if your application uses localhost as the server URL, which
is a typical setting in a development environment.
In order to work around this limitation you should use SessionCultureResolver during development
and switch to CookieCultureResolver before you deploy the application in a production. This is
easily accomplished in Spring.Web (simply change the config file) but is something that you should
be aware of.
22.8.7. Changing Cultures
In order to be able to change the culture application developers will need to use one of the culture resolvers that
support culture changes, such as SessionCultureResolver or CookieCultureResolver. One could also write a
custom ICultureResolver that will persist culture information in a database, as part of a user's profile.
Once that requirement is satisfied, all that one need do is to set the UserCulture property to a new CultureInfo
object before the page is rendered. In the following .aspx example, there are two link buttons that can be used
to change the user's culture. In the code-behind, this is all one need do to set the new culture. A code snippet for
the code-behind file (UserRegistration.aspx.cs) is shown below.
protected override void OnInit(EventArgs e)
{
InitializeComponent();
this.english.Command += new CommandEventHandler(this.SetLanguage);
this.serbian.Command += new CommandEventHandler(this.SetLanguage);
base.OnInit(e);
}
private void SetLanguage(object sender, CommandEventArgs e)
{
this.UserCulture = new CultureInfo((string) e.CommandArgument);
}
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22.9. Result Mapping
One of the problems evident in many ASP.NET applications is that there is no built-in way to externalize
the flow of an application. The most common way of defining application flow is by hardcoding calls to the
Response.Redirect and Server.Transfer methods within event handlers.
This approach is problematic because any changes to the flow of an application necessitates code changes (with
the attendant recompilation, testing, redeployment, etc). A much better way, and one that has been proven to work
successfully in many MVC ( Model-View-Controller) web frameworks is to provide the means to externalize the
mapping of action results to target pages.
Spring.Web adds this functionality to ASP.NET by allowing one to define result mappings within the definition
of a page, and to then simply use logical result names within event handlers to control application flow.
In Spring.Web, a logical result is encapsulated and defined by the Result class; because of this one can configure
results just like any other object:
<objects xmlns="http://www.springframework.net">
<object id="homePageResult" type="Spring.Web.Support.Result, Spring.Web">
<property name="TargetPage" value="~/Default.aspx"/>
<property name="Mode" value="Transfer"/>
<property name="Parameters">
<dictionary>
<entry key="literal" value="My Text"/>
<entry key="name" value="%{UserInfo.FullName}"/>
<entry key="host" value="%{Request.UserHostName}"/>
</dictionary>
</property>
</object>
<object id="loginPageResult" type="Spring.Web.Support.Result, Spring.Web">
<property name="TargetPage" value="Login.aspx"/>
<property name="Mode" value="Redirect"/>
</object>
<object type="UserRegistration.aspx" parent="basePage">
<property name="UserManager" ref="userManager"/>
<property name="Results">
<dictionary>
<entry key="userSaved" value-ref="homePageResult"/>
<entry key="cancel" value-ref="loginPageResult"/>
</dictionary>
</property>
</object>
</objects>
The only property that you must supply a value for each and every result is the TargetPage property. The value
of the Mode property can be either Transfer, TransferNoPreserve, Redirect, and defaults to Transfer if none
is specified. TransferNoPreserve issues a server-side transfer with 'preserveForm=false', so that QueryString and
Form data are not preserved.
If one's target page requires parameters, one can define them using the Parameters dictionary property. One
simply specifies either literal values or object navigation expressions for such parameter values; if one specifies
an expression, this expression will be evaluated in the context of the page in which the result is being referenced...
in the specific case of the above example, this means that any page that uses the homePageResult needs to expose
a UserInfo property on the page class itself.
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Note
In Spring 1.1.0 and before the prefix used to indicate an object navigation expression in the
Parameters dictionary property was the dollar sign, i.e. ${UserInfo.FullName}.This conflicted
with the prefix used to perform property replacement, the dollar sign, as described in the section
PropertyPlaceholderConfigurer. As a workaround you can change the prefix and suffix used
in PropertyPlaceholderConfigurer to be different, for example prefix = $${ and suffix = }. In
Spring 1.1.1 a new prefix character, the percent sign (i.e.%{UserInfo.FullName}.) can be used
in the Parameters dictionary to avoid this conflict so you can keep the familiar NAnt style
PropertyPlaceholderConfigurer defaults.
Parameters will be handled differently depending on the result mode. For redirect results, every parameter will
be converted to a string, then URL encoded, and finally appended to a redirect query string. On the other hand,
parameters for transfer results will be added to the HttpContext.Items collection before the request is transferred
to the target page. This means that transfers are more flexible because any object can be passed as a parameter
between pages. They are also more efficient because they don't require a round-trip to the client and back to the
server, so transfer mode is recommended as the preferred result mode (it is also the current default).
Tip
If you should need to customize how to a redirect request is generate, for example to encrypt the
request parameters, subclass the Request object and override one or more protected methods, for
example string BuildUrl( string resolvedPath, IDictionary resolvedParameters ). See
the API documentation for additional information.
The above example shows independent result object definitions, which are useful for global results such as a
home- and login- page. Result definitions that are only going to be used by one page should be simply embedded
within the definition of a page, either as inner object definitions or using a special shortcut notation for defining
a result definition:
<object type="~/UI/Forms/UserRegistration.aspx" parent="basePage">
<property name="UserManager">
<ref object="userManager"/>
</property>
<property name="Results">
<dictionary>
<entry key="userSaved" value="redirect:UserRegistered.aspx?status=Registration Successful,user=${UserInfo}
<entry key="cancel" value-ref="homePageResult"/>
</dictionary>
</property>
</object>
The short notation for the result must adhere to the following format...
[<mode>:]<targetPage>[?param1,param2,...,paramN]
There are three possible values for the mode value referred to in the above notation snippet; they are:
• redirect
• transfer
• TransferNoPreserve
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They correspond to the values of the ResultMode enumeration. One thing to notice is that a comma is used instead
of an ampersand to separate parameters; this is done so as to avoid the need for laborious ampersand escaping
within an XML object definition. The use of the ampersand character is still supported if required, but one will
then have to specify it using the well known & entity reference.
Once one has defined one's results, it is very simple to use them within the event handlers of one's pages
(UserRegistration.apsx.cs)...
private void SaveUser(object sender, EventArgs e)
{
UserManager.SaveUser(UserInfo);
SetResult("userSaved");
}
public void Cancel(object sender, EventArgs e)
{
SetResult("cancel");
}
protected override void OnInit(EventArgs e)
{
InitializeComponent();
this.saveButton.Click += new EventHandler(this.SaveUser);
this.cancelButton.Click += new EventHandler(this.Cancel);
base.OnInit(e);
}
One could of course further refactor the above example and use defined constants. This would be a good thing to
do in the case of a logical result name such as "home" that is likely to be referenced by many pages.
22.9.1. Registering user defined transfer modes
You may also register a custom interpreter that can parse the short-hand string representation that creates a Result
object.. The string representation can be broken down into two parts shown below
<resultmode>:<textual result representation>
The interface IResultFactory is responsible for creating an IResult object from these two pieces, as shown below
public interface IResultFactory
{
IResult CreateResult( string resultMode, string resultText );
}
A ResultFactoryRegistry is used to associate a given resultmode string with an IResultFactory
implementation. Here is an example
class MySpecialResultLogic : IResult
{
...
}
class MySpecialResultLogicFactory : IResultFactory
{
IResult Create( string mode, string expression ) {
/* ... convert 'expression' into MySpecialResultLogic */
}
}
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// register with global factory
ResultFactoryRegistry.RegisterResultFactory( "mySpecialMode", new MySpecialResultLogicFactory );
You would then use the custom 'continue' mode in your page as shown below
// configure your Results
<object type="mypage.aspx">
<property name="Results">
<dictionary>
<entry key="continue" value="mySpecialMode:<some MySpecialResultLogic string representation>" />
</dictionary>
</property>
</object>
The result redirection is done as before, by calling myPage.SetResult("continue");
22.10. Client-Side Scripting
ASP.NET has decent support for client-side scripting through the use of the Page.RegisterClientScriptBlock
and Page.RegisterStartupScript methods.
However, neither of these two methods allows you to output a registered script markup within a <head> section
of a page, which is (in many cases) exactly what you would like to do.
22.10.1. Registering Scripts within the head HTML section
Spring.Web adds several methods to enhance client-side scripting to the base Spring.Web.UI.Page class:
RegisterHeadScriptBlock and RegisterHeadScriptFile, each with a few overrides. You can call these methods
from your custom pages and controls in order to register script blocks and script files that must be included in
the <head> section of the final HTML page.
The only additional thing that is required to make this work is that you use the <spring:Head> server-side control
to define your <head> section instead of using the standard HTML <head> element. This is shown below.
<%@ Page language="c#" Codebehind="StandardTemplate.aspx.cs"
AutoEventWireup="false" Inherits="SpringAir.Web.StandardTemplate" %>
<%@ Register TagPrefix="spring" Namespace="Spring.Web.UI.Controls" Assembly="Spring.Web" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
<html>
<spring:Head runat="server" id="Head1">
<title>
<spring:ContentPlaceHolder id="title" runat="server">
<%= GetMessage("default.title") %>
</spring:ContentPlaceHolder>
</title>
<LINK href="<%= CssRoot %>/default.css" type="text/css" rel="stylesheet">
<spring:ContentPlaceHolder id="head" runat="server"></spring:ContentPlaceHolder>
</spring:Head>
<body>
...
</body>
</html>
The example above shows you how you would typically set-up a <head> section within a master page template
in order to be able to change the title value and to add additional elements to the <head> section from the child
pages using <spring:ContentPlaceholder> controls. However, only the <spring:Head> declaration is required
in order for Spring.NET Register* scripts to work properly.
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22.10.2. Adding CSS Definitions to the head Section
In a similar fashion, you can add references to CSS files, or even specific styles, directly to the <head> HTML
section using Page.RegisterStyle and Page.RegisterStyleFile methods. The latter one simply allows you to
include a reference to an external CSS file, while the former one allows you to define embedded style definitions
by specifying the style name and definition as the parameters. The final list of style definitions registered this
way will be rendered within the single embedded style section of the final HTML document.
22.10.3. Well-Known Directories
In order to make the manual inclusion of client-side scripts, CSS files and images easier, the Spring.Web Page
class exposes several properties that help you reference such artifacts using absolute paths. This affords web
application developers a great deal of convenience functionality straight out of the box if they stick to common
conventions such as a web application (directory) structure..
These properties are ScriptsRoot, CssRoot and ImagesRoot. They have default values of Scripts, CSS and
Images, which will work just fine if you create and use these directories in your web application root. However,
if you prefer to place them somewhere else, you can always override default values by injecting new values into
your page definitions (you will typically inject these values only in the base page definition, as they are normally
shared by all the pages in the application). An example of such configuration is shown below:
<object name="basePage" abstract="true">
<description>
Convenience base page definition for all the pages.
Pages that reference this definition as their parent (see the examples below)
will automatically inherit the following properties....
</description>
<property name="CssRoot" value="Web/CSS"/>
<property name="ImagesRoot" value="Web/Images"/>
</object>
22.11. Spring User Controls
Spring provides several custom user controls that are located in the Spring.Web.UI.Controls namespace. This
section primarily lists the controls and points to other documentation to provide additional information. There are
a few other controls not documented here, please check the SDK docs for their descriptions.
22.11.1. Validation Controls
The location in the web page where validation errors are to be rendered can be specifies by using the
ValidationSummary and ValidationError controls. There are two controls since they have different defaults
for how errors are rendered. ValidationSummary is used to display potentially multiple errors identified by the
validation framework. ValidationError is used to display field-level validation errors. Please refer to the section
ASP.NET usage tips in the chapter on the Validation Framework more information.
22.11.2. Databinding Controls
Some standard controls are not easy to use with Spring's databinding support. Examples are check boxes and
ratio button groups. In this case you should use the CheckBoxList and RadioButtonGroup controls. Databinding
itself can be done using the DataBindingPanel instead of the using the BindingManager API within the code
behind page.
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22.11.3. Calendar Control
A pop-up DHTML calendar control is provided. It is a slightly modified version of the Dynarch.com DHTML
Calendar control written by Mihai Bazon.
22.11.4. Panel Control
You can suppress dependency injection for controls inside your ASP.NET by using the Panel control. See the
section Customizing control dependency injection for more information.
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Chapter 23. ASP.NET AJAX
23.1. Introduction
Spring's ASP.NET AJAX integration allows for a plain .NET object (PONO), that is one that doesn't have any
attributes or special base classes, to be exported as a web service, configured via dependency injection, 'decorated'
by applying AOP, and then exposed to client side JavaScript.
23.2. Web Services
Spring.NET, and particularly Spring.Web, improved support for web services in .NET with the
WebServiceExporter. Exporting of an ordinary plain .NET object as a web service is achieved by registering a
custom implementation of the WebServiceHandlerFactory class as the HTTP handler for *.asmx requests.
Microsoft
ASP.NET
AJAX
introduced
a
new
HTTP
handler
System.Web.Script.Services.ScriptHandlerFactory to allow a Web Service to be invoked from the browser
by using JavaScript.
Spring's integration allows for both Spring.Web and ASP.NET AJAX functionality to be used together by creating
a new HTTP handler.
23.2.1. Exposing Web Services
The WebServiceExporter combined with the new HTTP handler exposes PONOs as Web Services in your
ASP.NET AJAX application.
In order for a Web service to be accessed from script, the WebServiceExporter should decorate the Web
Service class with the ScriptServiceAttribute. The code below is taken from the sample application
Spring.Web.Extensions.Sample, aka the 'AJAX' shortcut in the installation. :
<object id="ContactWebService" type="Spring.Web.Services.WebServiceExporter, Spring.Web">
<property name="TargetName" value="ContactService"/>
<property name="Namespace" value="http://Spring.Examples.Atlas/ContactService"/>
<property name="Description" value="Contact Web Services"/>
<property name="TypeAttributes">
<list>
<object type="System.Web.Script.Services.ScriptServiceAttribute, System.Web.Extensions"/>
</list>
</property>
</object>
All that one needs to do in order to use the WebServiceExporter is:
1. Configure the Web.config file of your ASP.NET AJAX application as a Spring.Web application.
<sectionGroup name="spring">
<section name="context" type="Spring.Context.Support.WebContextHandler, Spring.Web"/>
</sectionGroup>
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<spring>
<context>
<resource uri="~/Spring.config"/>
</context>
</spring>
2. Register the HTTP handler and the Spring HttpModule under the system.web section.
<httpHandlers>
<remove verb="*" path="*.asmx"/>
<add verb="*" path="*.asmx" validate="false" type="Spring.Web.Script.Services.ScriptHandlerFactory, Spring.Web
<add verb="*" path="*_AppService.axd" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory,
<add verb="GET,HEAD" path="ScriptResource.axd" type="System.Web.Handlers.ScriptResourceHandler, System.Web.Ext
</httpHandlers>
<httpModules>
<add name="ScriptModule" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=1.0.61025.0, C
<add name="SpringModule" type="Spring.Context.Support.WebSupportModule, Spring.Web"/>
</httpModules>
3. Register the HTTP handler and the Spring HttpModule under system.webServer section.
<modules>
<add name="ScriptModule" preCondition="integratedMode" type="System.Web.Handlers.ScriptModule, System.Web.Exte
<add name="SpringModule" type="Spring.Context.Support.WebSupportModule, Spring.Web"/>
</modules>
<handlers>
<remove name="WebServiceHandlerFactory-Integrated" />
<add name="ScriptHandlerFactory" verb="*" path="*.asmx" preCondition="integratedMode"
type="Spring.Web.Script.Services.ScriptHandlerFactory, Spring.Web.Extensions"/>
<add name="ScriptHandlerFactoryAppServices" verb="*" path="*_AppService.axd" preCondition="integratedMode"
type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=1.0.61025.0, Cultur
<add name="ScriptResource" preCondition="integratedMode" verb="GET,HEAD" path="ScriptResource.axd" type="Syste
</handlers>
You can find a full Web.config file in the example that comes with this integration.
23.2.2. Calling Web Services by using JavaScript
A proxy class is generated for each Web Service. Calls to Web Services methods are made by using this proxy
class. When using the WebServiceExporter, the name of the proxy class is equal to the WebServiceExporter's id.
// This function calls the Contact Web service method
// passing simple type parameters and the callback function
function GetEmails(prefix, count)
{
ContactWebService.GetEmails(prefix, count, GetEmailsOnSucceeded);
}
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Part IV. Services
This part of the reference documentation covers the Spring Framework's integration with .NET distributed
technologies such as .NET Remoting, Enterprise Services, Web Services. Integration with WCF Services is
forthcoming. Please refer to the introduction chapter for more details.
• Chapter 24, Introduction to Spring Services
• Chapter 25, .NET Remoting
• Chapter 26, .NET Enterprise Services
• Chapter 27, Web Services
• Chapter 28, Windows Communication Foundation (WCF)
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Chapter 24. Introduction to Spring
Services
24.1. Introduction
The goal of Spring's integration with distributed technologies is to adapt plain .NET objects so they can be used
with a specific distributed technology. This integration is designed to be as non-intrusive as possible. If you need
to expose an object to a remote process then you can define an exporter for that object. Similarly, on the client
side you define an corresponding endpoint accessor. Of course, the object's methods still need to be suitable for
remoting, i.e. coarse grained, to avoid making unnecessary and expensive remote calls.
Since these exporters and client side endpoint accessors are defined using meta data for Spring IoC container,
you can easily use dependency injection on them to set initial state and to 'wire up' the presentation tier, such as
web forms, to the service layer. In addition, you may apply AOP aspects to the exported classes and/or service
endpoints to apply behavior such as logging, security, or other custom behavior that may not be provided by
the target distributed technology. The Spring specific terminology for this approach to object distribution is
known as Portable Service Abstractions (PSA). As a result of this approach, you can decide much later in the
development process the technical details of how you will distribute your objects as compared to traditional code
centric approaches. Changing of the implementation is done though configuration of the IoC container and not
by recompilation. Of course, you may choose to not use the IoC container to manage these objects and use the
exporter and service endpoints programatically.
The diagram shown below is a useful way to demonstrate the key abstractions in the Spring tool chest and their
interrelationships. The four key concepts are; plain .NET objects, Dependency Injection, AOP, and Portable
Service Abstractions. At the heart sits the plain .NET object that can be instantiated and configured using
dependency injection. Then, optionally, the plain object can be adapted to a specific distributed technology. Lastly,
additional behavior can be applied to objects. This behavior is typically that which can not be easily address by
traditional OO approaches such as inheritance. In the case of service layer, common requirements such as 'the
service layer must be transactional' are implemented in a manner that naturally expresses that intention in a single
place, as compared to scattered code across the service layer.
Spring implements this exporter functionality by creating a proxy at runtime that meets the implementation
requirements of a specific distributed technology. In the case of .NET Remoting the proxy will inherit from
MarshalByRef, for EnterpriseServices it will inherit from ServicedComponent and for aspx web services,
WebMethod attributes will be added to methods. Client side functionality is often implemented by a thin layer
over the client access mechanism of the underlying distributed technology, though in some cases such as client
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side access to web services, you have the option to create a proxy on the fly from the .wsdl definition, much like
you would have done using the command line tools.
The common implementation theme for you as a provider of these service objects is to implement an interface.
This is generally considered a best practice in its own right, you will see most pure WCF examples following this
practice, and also lends itself to a straightforward approach to unit testing business functionality as stub or mock
implementations may be defined for testing purposes.
The assembly Spring.Services.dll contains support for .NET Remoting, Enterprise Services and ASMX Web
Services. Support for WCF services is planned for Spring 1.2 and is currently in the CVS repository if you care
to take an early look.
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Chapter 25. .NET Remoting
25.1. Introduction
Spring's .NET Remoting support allows you to export a 'plain .NET object' as a .NET Remoted object. By
"plain .NET object" we mean classes that do not inherit from a specific infrastructure base class such as
MarshalByRefObject. On the server side, Spring's .NET Remoting exporters will automatically create a proxy that
implements MarshalByRefObject. You register SAO types as either SingleCall or Singleton and also configure
on a per-object basis lifetime and leasing parameters. On the client side you can obtain CAO references to server
proxy objects in a manner that promotes interface based design best practices when developing .NET remoting
applications. The current implementation requires that your plain .NET objects implements a business service
interface. Additionally you can add AOP advice to both SAO and CAO objects.
You can leverage the IoC container to configure the exporter and service endpoints. A remoting specific xmlschema is provided to simplify the remoting configuration but you can still use the standard reflection-like
property based configuration schema. You may also opt to not use the IoC container to configure the objects and
use Spring's .NET Remoting classes Programatically, as you would with any third party library.
A sample application, often referred to in this documentation, is in the distribution under the directory "examples
\Spring\Spring.Calculator" and may also be found via the start menu by selecting the 'Calculator' item.
25.2. Publishing SAOs on the Server
Exposing a Singleton SAO service can be done in two ways. The first is through programmatic or administrative
type registration that makes calls to RemotingConfiguration.RegisterWellKnownServiceType. This method has
the limitation that you must use a default constructor and you can not easily configure the singleton state at runtime
since it is created on demand. The second way is to publish an object instance using RemotingServices.Marshal.
This method overcomes the limitations of the first method. Example server side code for publishing an SAO
singleton object with a predefined state is shown below
AdvancedMBRCalculator calc = new AdvancedMBRCalculator(217);
RemotingServices.Marshal(calc, "MyRemotedCalculator");
The class AdvancedMBRCalculator used above inherits from MarshalByRefObject.
If your design calls for configuring a singleton SAO, or using a non-default constructor, you can use the Spring
IoC container to create the SAO instance, configure it, and register it with the .NET remoting infrastructure. The
SaoExporter class performs this task and most importantly, will automatically create a proxy class that inherits
from MarshalbyRefObject if your business object does not already do so. The following XML taken from the
Remoting QuickStart demonstrates its usage to an SAO Singleton object
25.2.1. SAO Singleton
<object id="singletonCalculator" type="Spring.Calculator.Services.AdvancedCalculator, Spring.Calculator.Services
<constructor-arg type="int" value="217"/>
</object>
<!-- Registers the calculator service as a SAO in 'Singleton' mode. -->
<object name="saoSingletonCalculator" type="Spring.Remoting.SaoExporter, Spring.Services">
<property name="TargetName" value="singletonCalculator" />
<property name="ServiceName" value="RemotedSaoSingletonCalculator" />
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</object>
This XML fragment shows how an existing object "singletonCalculator" defined in the Spring context
is exposed under the url-path name "RemotedSaoSingletonCalculator". (The fully qualified url is tcp://
localhost:8005/RemotedSaoSingleCallCalculator using the standard .NET channel configuration shown further
below.) AdvancedCalculator class implements the business interface IAdvancedCalculator. The current proxy
implementation requires that your business objects implement an interface. The interfaces' methods will be the
ones exposed in the generated .NET remoting proxy. The initial memory of the calculator is set to 217 via
the constructor. The class AdvancedCalculator does not inherit from MarshalByRefObject. Also note that the
exporter sets the lifetime of the SAO Singleton to infinite so that the singleton will not be garbage collected after 5
minutes (the .NET default lease time). If you would like to vary the lifetime properties, they are InitialLeaseTime,
RenewOnCallTime, and SponsorshipTimeout.
A custom schema is provided to make the object declaration even easier and with intellisense support for the
attributes. This is shown below
<objects xmlns="http://www.springframework.net"
xmlns:r="http://www.springframework.net/remoting">
<r:saoExporter targetName="singletonCalculator"
serviceName="RemotedSaoSingletonCalculator" />
... other object definitions
</objects>
Refer to the end of this chapter for more information on Spring's .NET custom schema.
25.2.2. SAO SingleCall
The following XML fragment shows how to expose the calculator service in SAO 'SingleCall' mode.
<object id="prototypeCalculator" type="Spring.Calculator.Services.AdvancedCalculator, Spring.Calculator.Services
singleton="false">
<constructor-arg type="int" value="217"/>
</object>
<object name="saoSingleCallCalculator" type="Spring.Remoting.SaoExporter, Spring.Services">
<property name="TargetName" value="prototypeCalculator" />
<property name="ServiceName" value="RemotedSaoSingleCallCalculator" />
</object>
Note that we change the singleton attribute of the plain .NET object as configured by Spring in the <object>
definition and not an attribute on the SaoExporter. The object referred to in the TargetName parameter can be an
AOP proxy to a business object. For example, if we were to apply some simple logging advice to the singleton
calculator, the following standard AOP configuration is used to create the target for the SaoExporter
<object id="singletonCalculatorWeaved" type="Spring.Aop.Framework.ProxyFactoryObject, Spring.Aop">
<property name="target" ref="singletonCalculator"/>
<property name="interceptorNames">
<list>
<value>Log4NetLoggingAroundAdvice</value>
</list>
</property>
</object>
<object name="saoSingletonCalculatorWeaved" type="Spring.Remoting.SaoExporter, Spring.Services">
<property name="TargetName" value="singletonCalculatorWeaved" />
<property name="ServiceName" value="RemotedSaoSingletonCalculatorWeaved" />
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</object>
Note
As generally required with a .NET Remoting application, the arguments to your service methods
should be Serializable.
25.2.1. Console Application Configuration
When using SaoExporter you can still use the standard remoting administration section in the application
configuration file to register the channel. ChannelServices as shown below
<system.runtime.remoting>
<application>
<channels>
<channel ref="tcp" port="8005" />
</channels>
</application>
</system.runtime.remoting>
A console application that will host this Remoted object needs to initialize the .NET Remoting infrastructure with
a call to RemotingConfiguration (since we are using the .config file for channel registration) and then start the
Spring application context. This is shown below
RemotingConfiguration.Configure("RemoteApp.exe.config");
IApplicationContext ctx = ContextRegistry.GetContext();
Console.Out.WriteLine("Server listening...");
Console.ReadLine();
You can also put in the configuration file an instance of the object Spring.Remoting.RemotingConfigurer to
make the RemotingConfiguration call show above on your behalf during initialization of the IoC container.
The RemotingConfigurer implements the IObjectFactoryPostProcessor interface, which gets called after all
object definitions have been loaded but before they have been instantiated, (SeeSection 5.9.2, “Customizing
configuration metadata with ObjectFactoryPostProcessors” for more information). The RemotingConfigurer has
two properties you can configure. Filename, that specifies the filename to load the .NET remoting configuration
from (if null the default file name is used) and EnsureSecurity which makes sure the channel in encrypted
(available only on .NET 2.0). As a convenience, the custom Spring remoting schema can be used to define an
instance of this class as shown below, taken from the Remoting QuickStart
<objects xmlns="http://www.springframework.net"
xmlns:r="http://www.springframework.net/remoting">
<r:configurer filename="Spring.Calculator.RemoteApp.exe.config" />
</objects>
The ReadLine prevents the console application from exiting. You can refer to the code in RemoteApp in the
Remoting QuickStart to see this code in action.
25.2.3. IIS Application Configuration
If you are deploying a .NET remoting application inside IIS there is a sample project that demonstrates the
necessary configuration using Spring.Web.
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Spring.Web ensures the application context is initialized, but if you don't use Spring.Web the idea is to start the
initialization of the Spring IoC container inside the application start method defined in Global.asax, as shown
below
void Application_Start(object sender, EventArgs e)
{
// Code that runs on application startup
// Ensure Spring has loaded configuration registering context
Spring.Context.IApplicationContext ctx = new Spring.Context.Support.XmlApplicationContext(
HttpContext.Current.Server.MapPath("Spring.Config"));
Spring.Context.Support.ContextRegistry.RegisterContext(ctx);
}
In this example, the Spring configuration file is named Spring.Config. Inside Web.config you add a standard
<system.runtime.remoting> section. Note that you do not need to specify the port number of your channels as
they will use the port number of your web site. Ambiguous results have been reported if you do specify the port
number. Also, in order for IIS to recognize the remoting request, you should add the suffix '.rem' or '.soap' to the
target name of your exported remote object so that the correct IIS handler can be invoked.
25.3. Accessing a SAO on the Client
Administrative type registration on the client side lets you easily obtain a reference to a SAO object. When a type is
registered on the client, using the new operator or using the reflection API will return a proxy to the remote object
instead of a local reference. Administrative type registration on the client for a SAO object is performed using
the wellknown element in the client configuration section. However, this approach requires that you expose the
implementation of the class on the client side. Practically speaking this would mean linking in the server assembly
to the client application, a generally recognized bad practice. This dependency can be removed by developing
remote services based on a business interface. Aside from remoting considerations, the separation of interface and
implementation is considered a good practice when designing OO systems. In the context of remoting, this means
that the client can obtain a proxy to a specific implementation with only a reference to the interface assembly.
To achieve the decoupling of client and server, a separate assembly containing the interface definitions is created
and shared between the client and server applications.
There is a simple means for following this design when the remote object is a SAO object. A call to
Activator.GetObject will instantiate a SAO proxy on the client. For CAO objects another mechanism is used
and is discussed later. The code to obtain the SAO proxy is shown below
ICalculator calc = (ICalculator)Activator.GetObject (
typeof (ICalculator),
"tcp://localhost:8005/MyRemotedCalculator");
To obtain a reference to a SAO proxy within the IoC container, you can use the object factory SaoFactoryObject
in the Spring configuration file. The following XML taken from the Remoting QuickStart demonstrates its usage.
<object id="calculatorService" type="Spring.Remoting.SaoFactoryObject, Spring.Services">
<property name="ServiceInterface" value="Spring.Calculator.Interfaces.IAdvancedCalculator, Spring.Calculator.C
<property name="ServiceUrl" value="tcp://localhost:8005/RemotedSaoSingletonCalculator" />
</object>
The ServiceInterface property specifies the type of proxy to create while the ServiceUrl property creates a proxy
bound to the specified server and published object name.
Other objects in the IoC container that depend on an implementation of the interface ICalculator can now
refer to the object "calculatorService", thereby using a remote implementation of this interface. The exposure of
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dependencies among objects within the IoC container lets you easily switch the implementation of ICalculator.
By using the IoC container changing the application to use a local instead of remote implementation is a
configuration file change, not a code change. By promoting interface based programing, the ability to switch
implementation makes it easier to unit test the client application, since unit testing can be done with a mock
implementation of the interface. Similarly, development of the client can proceed independent of the server
implementation. This increases productivity when there are separate client and server development teams. The
two teams agree on interfaces before starting development. The client team can quickly create a simple, but
functional implementation and then integrate with the server implementation when it is ready.
25.4. CAO best practices
Creating a client activated object (CAO) is typically done by administrative type registration, either
Programatically or via the standard .NET remoting configuration section. The registration process allows you to
use the 'new' operator to create the remote object and requires that the implementation of the object be distributed
to the client. As mentioned before, this is not a desirable approach to developing distributed systems. The best
practice approach that avoids this problem is to create an SAO based factory class on the server that will return
CAO references to the client. In a manner similar to how Spring's generic object factory can be used as a
replacement creating a factory per class, we can create a generic SAO object factory to return CAO references
to objects defined in Spring's application context. This functionality is encapsulated in Spring's CaoExporter
class. On the client side a reference is obtained using CaoFactoryObject. The client side factory object supports
creation of the CAO object using constructor arguments. In addition to reducing the clutter and tedium around
creating factory classes specific to each object type you wish to expose in this manner, this approach has the
additional benefit of not requiring any type registration on the client or server side. This is because the act of
returning an instance of a class that inherits from MarshalByRefObject across a remoting boundary automatically
returns a CAO object reference. For more information on this best-practice, refer to the last section, Section 25.8,
“Additional Resources”, for some links to additional resources.
25.5. Registering a CAO object on the Server
To expose an object as a CAO on the server you should declare an object in the standard Spring configuration that
is a 'prototype', that is the singleton property is set to false. This results in a new object being created each time
it is retrieved from Spring's IoC container. An implementation of ICaoRemoteFactory is what is exported via a
call to RemotingServices.Marshal. This implementation uses Spring's IoC container to create objects and then
dynamically create a .NET remoting proxy for the retrieved object. Note that the default lifetime of the remote
object is set to infinite (null is returned from the implementation of InitializeLifetimeService()).
This is best shown using an example from the Remoting Quickstart application. Here is the definition of a simple
calculator object,
<object id="prototypeCalculator" type="Spring.Calculator.Services.AdvancedCalculator, Spring.Calculator.Services
singleton="false">
<constructor-arg type="int" value="217" />
</object>
To export this as a CAO object we can declare the CaoExporter object directly in the server's XML configuration
file, as shown below
<object id="caoCalculator" type="Spring.Remoting.CaoExporter, Spring.Services">
<property name="TargetName" value="prototypeCalculator" />
<property name="Infinite" value="false" />
<property name="InitialLeaseTime" value="2m" />
<property name="RenewOnCallTime" value="1m" />
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</object>
Note the property 'TargetName' is set to the name, not the reference, of the non-singleton declaration of the
'AdvancedCalculator' class.
Alternatively, you can use the remoting schema and declare the CAO object as shown below
<r:caoExporter targetName="prototypeCalculator" infinite="false">
<r:lifeTime initialLeaseTime="2m" renewOnCallTime="1m" />
</r:caoExporter>
25.5.1. Applying AOP advice to exported CAO objects
Applying AOP advice to exported CAO objects is done by referencing the adviced object name to the CAO
exporter. Again, taking an example from the Remoting QuickStart, a calculator with logging around advice is
defined as shown below.
<object id="prototypeCalculatorWeaved" type="Spring.Aop.Framework.ProxyFactoryObject, Spring.Aop">
<property name="targetSource">
<object type="Spring.Aop.Target.PrototypeTargetSource, Spring.Aop">
<property name="TargetObjectName" value="prototypeCalculator" />
</object>
</property>
<property name="interceptorNames">
<list>
<value>ConsoleLoggingAroundAdvice</value>
</list>
</property>
</object>
If this declaration is unfamiliar to you, please refer to Chapter 13, Aspect Oriented Programming with Spring.NET
for more information. The CAO exporter then references with the name 'prototypeCalculatorWeaved' as shown
below.
<r:caoExporter targetName="prototypeCalculatorWeaved" infinite="false">
<r:lifeTime initialLeaseTime="2m" renewOnCallTime="1m" />
</r:caoExporter>
25.6. Accessing a CAO on the Client
On the client side a CAO reference is obtained by using the CaoFactoryObject as shown below
<object id="calculatorService" type="Spring.Remoting.CaoFactoryObject, Spring.Services">
<property name="RemoteTargetName" value="prototypeCalculator" />
<property name="ServiceUrl" value="tcp://localhost:8005" />
</object>
This definition corresponds to the exported calculator from the previous section. The property
'RemoteTargetName' identifies the object on the server side. Using this approach the client can obtain an reference
though standard DI techniques to a remote object that implements the IAdvancedCalculator interface. (As
always, that doesn't mean the client should treat the object as if it was an in-process object).
Alternatively, you can use the Remoting schema to shorten this definition and provide intellisense code
completion
<r:caoFactory id="calculatorService"
remoteTargetName="prototypeCalculator"
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serviceUrl="tcp://localhost:8005" />
25.6.1. Applying AOP advice to client side CAO objects.
Applying AOP advice to a client side CAO object is done just like any other object. Simply use the id of the
object created by the CaoFactoryObject as the AOP target, i.e. 'calculatorService' in the previous example.
25.7. XML Schema for configuration
Please install the XSD schemas into VS.NET as described in Chapter 32, Visual Studio.NET Integration. XML
intellisense for the attributes of the saoExporter, caoExporter and caoFactory should be self explanatory as they
mimic the standard property names used to configure .NET remote objects.
25.8. Additional Resources
Two articles that describe the process of creating a standard SAO factory for returning CAO objects are
Implementing Broker with .NET Remoting Using Client-Activated Objects on MSDN and Step by Step guide to
CAO creation through SAO class factories on Glacial Components website.
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Chapter 26. .NET Enterprise Services
26.1. Introduction
Spring's .NET Enterprise Services support allows you to export a 'plain .NET object' as a .NET Remoted object.
By "plain .NET object" we mean classes that do not inherit from a specific infrastructure base class such as
ServicedComponent..
You can leverage the IoC container to configure the exporter and service endpoints. You may also opt to not use
the IoC container to configure the objects and use Spring's .NET Enterprise Services classes Programatically, as
you would with any third party library.
26.2. Serviced Components
Services components in .NET are able to use COM+ services such as declarative and distributed transactions,
role based security, object pooling messaging. To access these services your class needs to derive from the class
System.EnterpriseServices.ServicedComponent, adorn your class and assemblies with relevant attributes,
and configure your application by registering your serviced components with the COM+ catalog. The overall
landscape of accessing and using COM+ services within .NET goes by the name .NET Enterprise Services.
Many of these services can be provided without the need to derive from a ServicedComponent though the use
of Spring's Aspect-Oriented Programming functionality. Nevertheless, you may be interested in exporting your
class as a serviced component and having client access that component in a location transparent manner. By using
Spring's ServicedComponentExporter, EnterpriseServicesExporter and ServicedComponentFactory you can
easily create and consume serviced components without having your class inherit from ServicedComponent and
automate the manual deployment process that involves strongly signing your assembly and using the regsvcs
utility.
Note that the following sections do not delve into the details of programming .NET Enterprise Services. An
excellent reference for such information is Christian Nagel's "Enterprise Services with the .NET Framework"
Spring.NET includes an example of using these classes, the 'calculator' example. More information can be found
in the section, .NET Enterprise Services example.
26.3. Server Side
One of the main challenges for the exporting of a serviced component to the host is the need for them to be
contained within a physical assembly on the file system in order to be registered with the COM+ Services. To
make things more complicated, this assembly has to be strongly named before it can be successfully registered.
Spring provides two classes that allow all of this to happen.
• Spring.Enterprise.ServicedComponentExporter is responsible for exporting a single component and
making sure that it derives from ServicedComponent class. It also allows you to specify class-level and methodlevel attributes for the component in order to define things such as transactional behavior, queuing, etc.
• Spring.Enterprise.EnterpriseServicesExporter corresponds to a COM+ application, and it allows you to
specify list of components that should be included in the application, as well as the application name and other
assembly-level attributes
Let's say that we have a simple service interface and implementation class, such as these:
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namespace MyApp.Services
{
public interface IUserManager
{
User GetUser(int userId);
void SaveUser(User user);
}
public class SimpleUserManager : IUserManager
{
private IUserDao userDao;
public IUserDao UserDao
{
get { return userDao; }
set { userDao = value; }
}
public User GetUser(int userId)
{
return UserDao.FindUser(userId);
}
public void SaveUser(User user)
{
if (user.IsValid)
{
UserDao.SaveUser(user);
}
}
}
}
And the corresponding object definition for it in the application context config file:
<object id="userManager" type="MyApp.Services.SimpleUserManager">
<property name="UserDao" ref="userDao"/>
</object>
Let's say that we want to expose user manager as a serviced component so we can leverage its support for
transactions. First we need to export our service using the exporter ServicedComponentExporter as shown below
<object id="MyApp.EnterpriseServices.UserManager" type="Spring.Enterprise.ServicedComponentExporter, Spring.Serv
<property name="TargetName" value="userManager"/>
<property name="TypeAttributes">
<list>
<object type="System.EnterpriseServices.TransactionAttribute, System.EnterpriseServices"/>
</list>
</property>
<property name="MemberAttributes">
<dictionary>
<entry key="*">
<list>
<object type="System.EnterpriseServices.AutoCompleteAttribute, System.EnterpriseServices"/>
</list>
</entry>
</dictionary>
</property>
</object>
The exporter defined above will create a composition proxy for our SimpleUserManager class that extends
ServicedComponent and delegates method calls to SimpleUserManager instance. It will also adorn the proxy
class with a TransactionAtribute and all methods with an AutoCompleteAttribute.
The next thing we need to do is configure an exporter for the COM+ application that will host our new component:
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<object id="MyComponentExporter" type="Spring.Enterprise.EnterpriseServicesExporter, Spring.Services">
<property name="ApplicationName" value="My COM+ Application"/>
<property name="Description" value="My enterprise services application."/>
<property name="AccessControl">
<object type="System.EnterpriseServices.ApplicationAccessControlAttribute, System.EnterpriseServices">
<property name="AccessChecksLevel" value="ApplicationComponent"/>
</object>
</property>
<property name="Roles">
<list>
<value>Admin : Administrator role</value>
<value>User : User role</value>
<value>Manager : Administrator role</value>
</list>
</property>
<property name="Components">
<list>
<ref object="MyApp.EnterpriseServices.UserManager"/>
</list>
</property>
<property name="Assembly" value="MyComPlusApp"/>
</object>
This exporter will put all proxy classes for the specified list of components into the specified assembly, sign the
assembly, and register it with the specified COM+ application name. If application does not exist it will create it
and configure it using values specified for Description, AccessControl and Roles properties.
26.4. Client Side
Because serviced component classes are dynamically generated and registered, you cannot instantiate them in
your code using the new operator. Instead, you need to use Spring.Enterprise.ServicedComponentFactory
definition, which also allows you to specify the configuration template for the component as well as the name of
the remote server the component is running on, if necessary. An example is shown below
<object id="enterpriseUserManager" type="Spring.Enterprise.ServicedComponentFactory, Spring.Services">
<property name="Name" value="MyApp.EnterpriseServices.UserManager"/>
<property name="Template" value="userManager"/>
</object>
You can then inject this instance of the IUserManager into a client class and use it just like you would use original
SimpleUserManager implementation. As you can see, by coding your services as plain .Net objects, against well
defined service interfaces, you gain easy pluggability for your service implementation though this configuration,
while keeping the core business logic in a technology agnostic PONO, i.e. Plain Ordinary .Net Object.
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Chapter 27. Web Services
27.1. Introduction
While the out-of-the-box support for web services in .NET is excellent, there are a few areas that the Spring.NET
thought could use some improvement. Spring adds the ability to perform dependency injection on standard asmx
web services. Spring's .NET Web Services support also allows you to export a 'plain .NET object' as a .NET
web service By "plain .NET object" we mean classes that do not contain infrastructure specific attributes, such as
WebMethod. On the server side, Spring's .NET web service exporters will automatically create a proxy that adds
web service attributes. On the client side you can use Spring IoC container to configure a client side proxy that
you generated with standard command line tools. Additionally, Spring provides the functionality to create the
web service proxy dynamically at runtime (much like running the command line tools but at runtime and without
some of the tools quirks) and use dependency injection to configure the resulting proxy class. On both the server
and client side, you can apply AOP advice to add behavior such as logging, exception handling, etc. that is not
easily encapsulated within an inheritance hierarchy across the application.
27.2. Server-side
One thing that the Spring.NET team didn't like much is that we had to have all these .asmx files lying around
when all said files did was specify which class to instantiate to handle web service requests.
Second, the Spring.NET team also wanted to be able to use the Spring.NET IoC container to inject dependencies
into our web service instances. Typically, a web service will rely on other objects, service objects for example,
so being able to configure which service object implementation to use is very useful.
Last, but not least, the Spring.NET team did not like the fact that creating a web service is an implementation task.
Most (although not all) services are best implemented as normal classes that use coarse-grained service interfaces,
and the decision as to whether a particular service should be exposed as a remote object, web service, or even an
enterprise (COM+) component, should only be a matter of configuration, and not implementation.
An example using the web service exporter can be found in quickstart example named 'calculator'. More
information can be found here 'Web Services example'.
27.2.1. Removing the need for .asmx files
Unlike web pages, which use .aspx files to store presentation code, and code-behind classes for the logic, web
services are completely implemented within the code-behind class. This means that .asmx files serve no useful
purpose, and as such they should neither be necessary nor indeed required at all.
Spring.NET allows application developers to expose existing web services easily by registering a custom
implementation of the WebServiceHandlerFactory class and by creating a standard Spring.NET object definition
for the service.
By way of an example, consider the following web service...
namespace MyComany.MyApp.Services
{
[WebService(Namespace="http://myCompany/services")]
public class HelloWorldService
{
[WebMethod]
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public string HelloWorld()
{
return "Hello World!";
}
}
}
This is just a standard class that has methods decorated with the WebMethod attribute and (at the class-level) the
WebService attribute. Application developers can create this web service within Visual Studio just like any other
class.
All that one need to do in order to publish this web service is:
1. Register the Spring.Web.Services.WebServiceFactoryHandler as the HTTP handler for *.asmx requests
within one's web.config file.
<system.web>
<httpHandlers>
<add verb="*" path="*.asmx" type="Spring.Web.Services.WebServiceHandlerFactory, Spring.Web"/>
</httpHandlers>
</system.web>
Of course, one can register any other extension as well, but typically there is no need as Spring.NET's handler
factory will behave exactly the same as a standard handler factory if said handler factory cannot find the object
definition for the specified service name. In that case the handler factory will simply look for an .asmx file.
If you are using IIS7 the following configuration is needed
<system.webServer>
<validation validateIntegratedModeConfiguration="false"/>
<handlers>
<add name="SpringWebServiceSupport" verb="*" path="*.asmx" type="Spring.Web.Services.WebServiceHandlerFactor
</handlers>
</system.webServer>
2. Create an object definition for one's web service.
<object name="HelloWorld" type="MyComany.MyApp.Services.HelloWorldService, MyAssembly" abstract="true"/>
Note that one is not absolutely required to make the web service object definition abstract (via the
abstract="true" attribute), but this is a recommended best practice in order to avoid creating an unnecessary
instance of the service. Because the .NET infrastructure creates instances of the target service object internally
for each request, all Spring.NET needs to provide is the System.Type of the service class, which can be retrieved
from the object definition even if it is marked as abstract.
That's pretty much it as we can access this web service using the value specified for the name attribute of the
object definition as the service name:
http://localhost/MyWebApp/HelloWorld.asmx
27.2.2. Injecting dependencies into web services
For arguments sake, let's say that we want to change the implementation of the HelloWorld method to make the
returned message configurable.
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One way to do it would be to use some kind of message locator to retrieve an appropriate message, but that
locator needs to implemented. Also, it would certainly be an odd architecture that used dependency injection
throughout the application to configure objects, but that resorted to the service locator approach when dealing
with web services.
Ideally, one should be able to define a property for the message within one's web service class and have
Spring.NET inject the message value into it:
namespace MyApp.Services
{
public interface IHelloWorld
{
string HelloWorld();
}
[WebService(Namespace="http://myCompany/services")]
public class HelloWorldService : IHelloWorld
{
private string message;
public string Message
{
set { message = value; }
}
[WebMethod]
public string HelloWorld()
{
return this.message;
}
}
}
The problem with standard Spring.NET DI usage in this case is that Spring.NET does not control the instantiation
of the web service. This happens deep in the internals of the .NET framework, thus making it quite difficult to
plug in the code that will perform the configuration.
The solution is to create a dynamic server-side proxy that will wrap the web service and configure it. That way,
the .NET framework gets a reference to a proxy type from Spring.NET and instantiates it. The proxy then asks a
Spring.NET application context for the actual web service instance that will process requests.
This
proxying
requires
that
one
export
the
web
service
explicitly
using
the
Spring.Web.Services.WebServiceExporter class; in the specific case of this example, one must also not forget
to configure the Message property for said service:
<object id="HelloWorld" type="MyApp.Services.HelloWorldService, MyApp">
<property name="Message" value="Hello, World!"/>
</object>
<object id="HelloWorldExporter" type="Spring.Web.Services.WebServiceExporter, Spring.Web">
<property name="TargetName" value="HelloWorld"/>
</object>
The WebServiceExporter copies the existing web service and method attribute values to the proxy
implementation (if indeed any are defined). Please note however that existing values can be overridden by setting
properties on the WebServiceExporter.
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Interface Requirements
In order to support some advanced usage scenarios, such as the ability to expose an AOP proxy as
a web service (allowing the addition of AOP advices to web service methods), Spring.NET requires
those objects that need to be exported as web services to implement a (service) interface.
Only methods that belong to an interface will be exported by the WebServiceExporter.
27.2.3. Exposing PONOs as Web Services
Now that we are generating a server-side proxy for the service, there is really no need for it to have all the attributes
that web services need to have, such as WebMethod. Because .NET infrastructure code never really sees the "real"
service, those attributes are redundant as the proxy needs to have them on its methods, because that's what .NET
deals with, but they are not necessary on the target service's methods.
This means that we can safely remove the WebService and WebMethod attribute declarations from the service
implementation, and what we are left with is a plain old .NET object (a PONO). The example above would still
work, because the proxy generator will automatically add WebMethod attributes to all methods of the exported
interfaces.
However, that is still not the ideal solution. You would lose information that the optional WebService and
WebMethod attributes provide, such as service namespace, description, transaction mode, etc. One way to keep
those values is to leave them within the service class and the proxy generator will simply copy them to the proxy
class instead of creating empty ones, but that really does defeat the purpose.
To add specific attributes to the exported web service, you can set all the necessary values within the definition
of the service exporter, like so...
<object id="HelloWorldExporter" type="Spring.Web.Services.WebServiceExporter, Spring.Web">
<property name="TargetName" value="HelloWorld"/>
<property name="Namespace" value="http://myCompany/services"/>
<property name="Description" value="My exported HelloWorld web service"/>
<property name="MemberAttributes">
<dictionary>
<entry key="HelloWorld">
<object type="System.Web.Services.WebMethodAttribute, System.Web.Services">
<property name="Description" value="My Spring-configured HelloWorld method."/>
<property name="MessageName" value="ZdravoSvete"/>
</object>
</entry>
</dictionary>
</property>
</object>
// or, once configuration improvements are implemented...
<web:service targetName="HelloWorld" namespace="http://myCompany/services">
<description>My exported HelloWorld web service.</description>
<methods>
<method name="HelloWorld" messageName="ZdravoSvete">
<description>My Spring-configured HelloWorld method.</description>
</method>
</methods>
</web:service>
Based on the configuration above, Spring.NET will generate a web service proxy for all the interfaces
implemented by a target and add attributes as necessary. This accomplishes the same goal while at the same
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time moving web service metadata from implementation class to configuration, which allows one to export pretty
much any class as a web service.
The WebServiceExporter also has a TypeAttributes IList property for applying attributes at the type level.
Note
The attribute to confirms to the WSI basic profile 1.1 is not added by default. This will
be added in a future release. In the meantime use the TypeAttributes IList property to add
[WebServiceBinding(ConformsTo=WsiProfiles.BasicProfile1_1)] to the generated proxy.
One can also export only certain interfaces that a service class implements by setting the Interfaces property
of the WebServiceExporter.
Distributed Objects Warning
Distributed Objects Warning
Just because you can export any object as a web service, doesn't mean that you should. Distributed
computing principles still apply and you need to make sure that your services are not chatty and that
arguments and return values are Serializable.
You still need to exercise common sense when deciding whether to use web services (or remoting in
general) at all, or if local service objects are all you need.
27.2.4. Exporting an AOP Proxy as a Web Service
It is often useful to be able to export an AOP proxy as a web service. For example, consider the case where you
have a service that is wrapped with an AOP proxy that you want to access both locally and remotely (as a web
service). The local client would simply obtain a reference to an AOP proxy directly, but any remote client needs
to obtain a reference to an exported web service proxy, that delegates calls to an AOP proxy, that in turn delegates
them to a target object while applying any configured AOP advice.
Effecting this setup is actually fairly straightforward; because an AOP proxy is an object just like any other object,
all you need to do is set the WebServiceExporter's TargetName property to the id (or indeed the name or alias)
of the AOP proxy. The following code snippets show how to do this...
<object id="DebugAdvice" type="MyApp.AOP.DebugAdvice, MyApp"/>
<object id="TimerAdvice" type="MyApp.AOP.TimerAdvice, MyApp"/>
<object id="MyService" type="MyApp.Services.MyService, MyApp"/>
<object id="MyServiceProxy" type="Spring.Aop.Framework.ProxyFactoryObject, Spring.Aop">
<property name="TargetName" value="MyService"/>
<property name="IsSingleton" value="true"/>
<property name="InterceptorNames">
<list>
<value>DebugAdvice</value>
<value>TimerAdvice</value>
</list>
</property>
</object>
<object id="MyServiceExporter" type="Spring.Web.Services.WebServiceExporter, Spring.Web">
<property name="TargetName" value="MyServiceProxy"/>
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<property name="Name" value="MyService"/>
<property name="Namespace" value="http://myApp/webservices"/>
<property name="Description" value="My web service"/>
</object>
That's it as every call to the methods of the exported web service will be intercepted by the target AOP proxy,
which in turn will apply the configured debugging and timing advice to it.
27.3. Client-side
On the client side, the main objection the Spring.NET team has is that client code becomes tied to a proxy class,
and not to a service interface. Unless you make the proxy class implement the service interface manually, as
described by Juval Lowy in his book "Programming .NET Components", application code will be less flexible
and it becomes very difficult to plug in different service implementation in the case when one decides to use a
new and improved web service implementation or a local service instead of a web service.
The goal for Spring.NET's web services support is to enable the easy generation of client-side proxies that
implement a specific service interface.
27.3.1. Using VS.NET generated proxy
The problem with the web-service proxy classes that are generated by VS.NET or the WSDL command line utility
is that they don't implement a service interface. This tightly couples client code with web services and makes it
impossible to change the implementation at a later date without modifying and recompiling the client.
Spring.NET provides a simple IFactoryObject implementation that will generate a "proxy for proxy" (however
obtuse that may sound). Basically, the Spring.Web.Services.WebServiceProxyFactory class will create a proxy
for the VS.NET- / WSDL-generated proxy that implements a specified service interface (thus solving the problem
with the web-service proxy classes mentioned in the preceding paragraph).
At this point, an example may well be more illustrative in conveying what is happening; consider the following
interface definition that we wish to expose as a web service...
namespace MyCompany.Services
{
public interface IHelloWorld
{
string HelloWorld();
}
}
In order to be able to reference a web service endpoint through this interface, you need to add a definition similar
to the example shown below to your client's application context:
<object id="HelloWorld" type="Spring.Web.Services.WebServiceProxyFactory, Spring.Services">
<property name="ProxyType" value="MyCompany.WebServices.HelloWorld, MyClientApp"/>
<property name="ServiceInterface" value="MyCompany.Services.IHelloWorld, MyServices"/>
</object>
What is important to notice is that the underlying implementation class for the web service does not have to
implement the same IHelloWorld service interface... so long as matching methods with compliant signatures
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exist (a kind of duck typing), Spring.NET will be able to create a proxy and delegate method calls appropriately.
If a matching method cannot be found, the Spring.NET infrastructure code will throw an exception.
That said, if you control both the client and the server it is probably a good idea to make sure that the web service
class on the server implements the service interface, especially if you plan on exporting it using Spring.NET's
WebServiceExporter, which requires an interface in order to work.
27.3.2. Generating proxies dynamically
The WebServiceProxyFactory can also dynamically generate a web-service proxy. The XML object definition
for this factory object is shown below
<object id="calculatorService" type="Spring.Web.Services.WebServiceProxyFactory, Spring.Services">
<property name="ServiceUri" value="http://myServer/Calculator/calculatorService.asmx"/>
<!--<property name="ServiceUri" value="file://~/calculatorService.wsdl"/>-->
<property name="ServiceInterface" value="Spring.Calculator.Interfaces.IAdvancedCalculator, Spring.Calc
<!-- Dependency injection on Factory's product : the proxy instance of type SoapHttpClientProtocol -->
<property name="ProductTemplate">
<object>
<property name="Timeout" value="10000" /> <!-- 10s -->
</object>
</property>
</object>
One use-case where this proxy is very useful is when dealing with typed data sets through a web service. Leaving
the pros and cons of this approach aside, the current behavior of the proxy generator in .NET is to create wrapper
types for the typed dataset. This not only pollutes the solution with extraneous classes but also results in multiple
wrapper types being created, one for each web service that uses the typed dataset. This can quickly get confusing.
The proxy created by Spring allows you to reference you typed datasets directly, avoiding the above mentioned
issues.
27.3.3. Configuring the proxy instance
The
implements
the
interface,
Spring.Objects.Factory.IConfigurableFactoryObject, allowing to specify configuration for the product
that the WebServiceProxyFactory creates. This is done by specifying the ProductTemplate property. This is
particularly useful for securing the web service. An example is shown below.
WebServiceProxyFactory
also
<object id="PublicarAltasWebService" type="Spring.Web.Services.WebServiceProxyFactory, Spring.Services">
<property name="ProxyType" value="My.WebService" />
<property name="ServiceInterface" value="My.IWebServiceInterface" />
<property name="ProductTemplate">
<object>
<!-- Configure the web service URL -->
<property name="Url" value="https://localhost/MyApp/webservice.jws" />
<!-- Configure the Username and password for the web service -->
<property name="Credentials">
<object type="System.Net.NetworkCredential, System">
<property name="UserName" value="user"/>
<property name="Password" value="password"/>
</object>
</property>
<!-- Configure client certificate for the web service -->
<property name="ClientCertificates">
<list>
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<object id="MyCertificate" type="System.Security.Cryptography.X509Certificates.X509Certificate2, Sys
<constructor-arg name="fileName" value="Certificate.p12" />
<constructor-arg name="password" value="notgoingtotellyou" />
</object>
</list>
</property>
</object>
</property>
</object>
For an example of how using SOAP headers for authentication using the WebServiceExporter and
WebServiceProxyFactory, refer to this solution on our wiki.
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Chapter 28. Windows Communication
Foundation (WCF)
28.1. Introduction
Spring's WCF support allows you to configure your WCF services via dependency injection and add additional
behavior to them using Aspect-Oriented programming (AOP).
For those who would like to get their feet wet right way, check out the WcfQuickStart application in the examples
directory.
28.2. Configuring WCF services via Dependency Injection
The technical approach used to perform dependency injection is based on dynamically creating an implementation
of your service interface (a dynamic proxy) that retrieves a configured instance of your service type from the
Spring container. This dynamic proxy is then the final service type that is hosted.
Note
An alternative implementation approach that uses extensibility points in WCF to delegate to
Spring to create and configure your WCF service was tried but proved to be limited in its range
of applicability. This approach was first taken (afaik) by Oran Dennison on his blog [http://
orand.blogspot.com/2006/10/wcf-service-dependency-injection.html] and several other folks on the
web since then. The issue in using this approach is that if the service is configured to be a singleton,
for example using [ServiceBehavior(InstanceContextMode=InstanceContextMode.Single)]
then the invocation of the IInstanceProvider is short-circuited. See the notes
on the MSDN class documentation here [http://msdn.microsoft.com/en-us/library/
system.servicemodel.dispatcher.iinstanceprovider.aspx]. While this would be the preferred approach,
no acceptable work around was found.
28.2.1. Dependency Injection
In this approach you develop your WCF services as you would normally do. For example here is a sample service
type taken from the quickstart example.
[ServiceContract(Namespace = "http://Spring.WcfQuickStart")]
public interface ICalculator
{
[OperationContract]
double Add(double n1, double n2);
[OperationContract]
double Subtract(double n1, double n2);
[OperationContract]
double Multiply(double n1, double n2);
[OperationContract]
double Divide(double n1, double n2);
[OperationContract]
string GetName();
}
The implementation for the methods is fairly obvious but an additional property, SleepInSeconds, is present.
This is the property we will configure via dependency injection. Here is a partial listing of the implementation
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public class CalculatorService : ICalculator
{
private int sleepInSeconds;
public int SleepInSeconds
{
get { return sleepInSeconds; }
set { sleepInSeconds = value; }
}
public double Add(double n1, double n2)
{
Thread.Sleep(sleepInSeconds*1000);
return n1 + n2;
}
//
additional implementation not shown for brevity
}
To configure this object with Spring, provide the XML configuration metadata as shown below as you would
with any Spring managed object.
<object id="calculator" singleton="false" type="Spring.WcfQuickStart.CalculatorService, Spring.WcfQuickSta
<property name="SleepInSeconds" value="1"/>
</object>
Note
The object must be declared as a 'prototype' object, i.e. not a singleton, in order to interact correctly
with WCF instancing.
To
host
this
service
type
in
a
standalone
application
define
an
instance
of
a
Spring.ServiceModel.Activation.ServiceHostFactoryObject and set is property TargetName to the id value
of the previously defined service type. ServiceHostFactoryObject is a Spring IFactoryObject implementation.
(See here for more information on IFactoryObjects and their interaction with the container.) The
ServiceHostFactoryObject will create an instance of Spring.ServiceModel.Activation.SpringServiceHost
that will be the ServiceHost instance associated with your service type. This configuration for this step is shown
below.
<object id="calculatorServiceHost" type="Spring.ServiceModel.Activation.ServiceHostFactoryObject, Spring.S
<property name="TargetName" value="calculator" />
</object>
Additional service configuration can be done declaratively in the standard App.config file as shown below
<system.serviceModel>
<services>
<service name="calculator" behaviorConfiguration="DefaultBehavior">
<host> ... </host>
<endpoint> ... </endpoint>
</service>
...
</services>
</system.serviceModel>
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Note
It is important that the name of the service in the WCF declarative configuration section match the
name of the Spring object definition
is where the dynamic proxy for your service type is
generated. This dynamic proxy will implement a single 'WCF' interface, the same on that your service type
implements. The implementation of the service interface methods on the proxy will delegate to a wrapped
'target' object which is the object instance retrieved by name from the Spring container using the Spring API,
ApplicationContext.GetObject(name). Since the object retrieved in this manner is fully configured, your WCF
service is as well.
Spring.ServiceModel.Activation.SpringServiceHost
Outside
of
a
standalone
application
you
can
also
use
the
class
Spring.ServiceModel.Activation.ServiceHostFactory
(which
inherits
from
System.ServiceModel.Activation.ServiceHostFactory) to host your services so that they can be configured
via dependency injection. To use the dynamic proxy approached described here you should still refer to the name
of the service as the name of the object definition used to configure the service type in the Spring container.
There are not many disadvantages to this approach other than the need to specify the service name as the name
of the object definition in the Spring container and to ensure that singleton=false is used in the object definition.
You can also use Spring.ServiceModel.Activation.ServiceHostFactory to host your service inside IIS but
should still refer to the service by the name of the object in the Spring container.
28.3. Apply AOP advice to WCF services
In either approach to performing dependency injection you can apply additional AOP advice to your WCF services
in the same way as you have always done in Spring. The following configuration shows how to apply some simple
performance monitoring advice to all services in the Spring.WcfQuickStart namespace and is taken from the
QuickStart example.
<object id="serviceOperation" type="Spring.Aop.Support.SdkRegularExpressionMethodPointcut, Spring.Aop">
<property name="pattern" value="Spring.WcfQuickStart.*"/>
</object>
<object id="perfAdvice" type="Spring.WcfQuickStart.SimplePerformanceInterceptor, Spring.WcfQuickStart.Serv
<property name="Prefix" value="Service Layer Performance"/>
</object>
<aop:config>
<aop:advisor pointcut-ref="serviceOperation" advice-ref="perfAdvice"/>
</aop:config>
The aop:config section implicitly uses Spring's autoproxying features to add additional behavior to any objects
defined in the container that match the pointcut criteria.
28.4. Creating client side proxies declaratively
To create a client side proxy based on the use of ChannelFactory<T>, you can use this rather ugly 'boiler plate'
XML snippit that takes uses Spring's support for calling factory methods on object instances.
<!-- returns ChannelFactory<ICalculator>("calculatorEndpoint").CreateChannel() -->
<object id="serverAppCalculator" type="Spring.WcfQuickStart.ICalculator, Spring.WcfQuickStart.ClientApp"
factory-object="serverAppCalculatorChannelFactory"
factory-method="CreateChannel" />
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<object id="serverAppCalculatorChannelFactory"
type="System.ServiceModel.ChannelFactory&lt;Spring.WcfQuickStart.ICalculator>, System.ServiceModel">
<constructor-arg name="endpointConfigurationName" value="serverAppCalculatorEndpoint" />
</object>
Note
This will be shortened using a custom namespce in a future release
The value 'serverAppCalculatorEndpoint' refers to the name of an enpoints in the <client> section of the standard
WCF configuration inside of App.config.
28.5. Exporting PONOs as WCF Services
Much like the approach taken for .asmx web services Spring provides an exporter that will add
[ServiceContract] and [OperationContract] attributes by default to all public interface methods on a given
(PONO) class. The exporter class is Spring.ServiceModel.ServiceExporter and has various options to finetune what interfaces are exported and the specific attributes that get applied to each method and on that class.
Here is a simple example
<object id="HelloWorldExporter" type="Spring.ServiceModel.ServiceExporter, Spring.Services">
<property name="TargetName" value="HelloWorld"/>
<property name="MemberAttributes">
<dictionary>
<entry key="SayHelloWorld">
<object type="System.ServiceModel.OperationContractAttribute, System.ServiceModel">
<property name="IsOneWay" value="false"/>
<!-- configure any other OperationContractAttribute properties here -->
</object>
</entry>
</dictionary>
</property>
</object>
Spring does not provide any means to add [DataContract] or [DataMember] attributes to method arguments
of your service operations. As such, either you will do that yourself or you may choose to use a serializer other
than DataContractSerializer, for example one that relies on method arguments that implement the ISerializable
interface, having the [Serializable] attribute, or are serializable via the XmlSerializer. Use the latter serializers
is a good way to migrate from an existing RCP based approach, such as using .NET remoting, to WCF in order to
take advantage of the WCF runtime and avoid editing much existing code. You can then incrementally refactor
and/or create new operations that use DataContractSerializer.
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Part V. Integration
This part of the reference documentation covers the Spring Framework's integration with a number of related
enterprise .NET technologies.
• Chapter 29, Message Oriented Middleware - Apache ActiveMQ
• Chapter 30, Message Oriented Middleware - MSMQ
• Chapter 31, Scheduling and Thread Pooling
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Chapter 29. Message Oriented
Middleware - Apache ActiveMQ
29.1. Introduction
The goal of Spring's messaging is to increase your productiviity when writing an enterprise strength messaging
middleware applications. Spring achieves these goals in several ways. First it provides several helper classes
that remove from the developer the incidental complexity and resource management issues that arise when using
messaging APIs. Second, the design of these messaging helper classes promote best practices in designing a
messaging application by promoting a clear separation between the messaging middleware specific code and
business processing that is technology agnostic. This is generally referred to a "plain old .NET object" (or PONO)
programming model.
This chapter discusses Spring's messaging support for providers whose API was modeled after the Java Message
Service (JMS) API. Vendors who provide a JMS inspired API include Apache, TIBCO, IBM, and Progress
Software. If you are using Microsoft's Message Queue, please refer to the specific MSMQ section.
As there is no de facto-standard common API across messaging vendors, Spring provides an implementation
of its helper classes for each of the major messaging middleware vendors. The naming of the classes you will
interact with most frequently will either be identical for each provider, but located in a different namespace, or
have their prefix change to be the three-letter-acronym commonly associated with the message provider. The list
of providers supported by Spring is show below along with their namespace and prefix.
1. Apache ActiveMQ (NMS) in namespace Spring.Messaging.Nms. 'Nms' is sometimes used as the class prefix
2. TIBCO EMS in namespace Spring.Messaging.Ems. 'Ems' is sometimes used as the class prefix (to
becommerically available )
3. SonicMQ in namespace Spring.Messaging.Sonic, 'Jms' is sometimes used as the class prefix. (to be
commercially available)
4. Websphere MQ in namespace Spring.Messaging.Xms, 'Xms' is sometimes used as the class prefix (to be
commerically available)
JMS can be roughly divided into two areas of functionality, namely the production and consumption of messages.
For message production and the synchronous consumption of messages the a template class, named NmsTemplate,
EmsTemplate (etc.) is used. Asynchronous message consumption is performed though a multi-threaded message
listener container, SimpleMessageListenerContainer. This message listener container is used to create MessageDriven PONOs (MDPs) which refer to a messaging callback class that consists of just 'plain .NET object's and is
devoid of any specific messaging types or other artifacts. The IMessageConverter interface is used by both the
template class and the message listener container to convert between provider message types and PONOs.
The namespace Spring.Messaging.<Vendor>.Core contains the messing template class (e.g. NmsTemplate). The
template class simplifies the use of the messaging APIs by handling the creation and release of resources, much
like the AdoTemplate does for ADO.NET. The JMS inspired APIs are low-level API, much like ADO.NET. As
such, even the simplest of operations requires 10s of lines of code with the bulk of that code related to resource
management of intermediate API objects Spring's messaging support, both in Java and .NET, addresses the errorprone boiler plate coding style one needs when using these APIs.
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The design principle common to Spring template classes is to provide helper methods to perform common
operations and for more sophisticated usage, delegate the essence of the processing task to user implemented
callback interfaces. The messaging template follows the same design. The message template class offer various
convenience methods for the sending of messages, consuming a message synchronously, and exposing the
message Session and MessageProducer to the user.
The namespace Spring.Messaging.<VendorAcronym>.Support.Converter provides a IMessageConverter
abstraction
to
convert
between
.NET
objects
and
messages.
The
namespace
Spring.Messaging.<VendorAcronym>.Support.Destinations provides various strategies for managing
destinations, such as providing a service locater for destinations stored in a directory service.
Finally, the namespace Spring.Messaging.<VendorAcronym>.Connections provides an implementations of the
ConnectionFactory suitable for use in standalone applications.
The rest of the sections in this chapter discusses each of the major helper classes in detail. Please refer to the
sample application that ships with Spring for additional hands-on usage.
Note
To simplify documenting features that are common across all provider implementations of Spring's
helper classes a specific provider, Apache ActiveMQ, was selected. As such when you see
'NmsTemplate' in the documentation, it also refers to EmsTemplate, XmsTemplate, etc. unless
specifically documented otherwise. The provider specific API classes are typically named after
their JMS counterparts with the possible exception of a leading 'I' in front of interfaces in order
to follow .NET naming conventions. In the documentation these API artifacts are referred to as
'ConnectionFactory', 'Session', 'Message', etc. without the leading 'I'.
29.1.1. Separation of Concerns
The use of MessageConverters and a PONO programming model promote messaging best practices by applying
the principal of Separation of Concerns to messaging based architectures. The infrastructure concern of publishing
and consuming messages is separated from the concern of business processing. These two concerns are reflected
in the architecture as two distinct layers, a message processing layer and a business processing layer. The
benefit of this approach is that your business processing is decoupled from the messaging technology, making
it more likely to survive technological changes over time and also easier to test. Spring's MessageConverters
provides support for mapping messaging data types to PONOs. Aside from being the link between the two layers,
MessageConverters provide a pluggable strategy to help support the evolution of a loosely coupled architecture
over time. Message formats will change over time, typically by the addition of new fields. MessageConverters can
be implemented to detect different versions of messages and perform the appropriate mapping logic to PONOs
such so that multiple versions of a message can be supported simultaneously, a common requirement in enterprise
messaging architectures.
29.1.2. Interoperability and provider portability
Messaging is a traditional area of Interoperability across heterogeneous systems with messaging vendors
providing support on multiple operating systems (Windows, UNIX, Mainframes OS's) as well as multiple
language bindings (C, C++, Java, .NET, Perl, etc.). In 199x the Java Community Process came up with a
specification to provide a common API across messaging providers as well as define some common messaging
functionality. This specification is know as the Java Message Service. From the API perspective, it can roughly be
thought of as the messaging counterpart to the ADO.NET or JDBC APIs that provide portability across different
database providers.
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Given this history, when messaging vendors created their .NET APIs, many did so by creating their own JMS
inspired API in .NET. There is no de facto-standard common API across messaging vendors. As such, portability
across vendors using Spring's helper classes is done by changing the configuration schema in your configuration
to a particular vendor and doing a 'search-and-replace' on the code base, changing the namespace and a few class
names. While not ideal ,using Spring will push you in the direction of isolating the messaging specific classes in
its own layer and therefore will reduce the impact of the changes you make to the code when switch providers.
You business logic classes called into via Spring's messaging infrastructure will remain the same.
The NMS project from Apache addresses the lack of a common API across .NET messaging providers by
providing an abstract interface based API for messaging and several implementations for different providers. At
the time of this writing, the project is close to releasing a 1.0 version that supports ApacheMQ, MSMQ, and
TIBCO EMS. There are a few outstanding issues at the moment that prevent one using NMS as a common API
for all messaging providers but hopefully these issues will be resolved. Note, that NMS serves 'double' duty as
the preferred API for messaging with ActiveMQ as well as a providing portability across different messaging
providers.
29.1.3. The role of Messaging API in a 'WCF world'
Windows Communication Foundation (WCF) also supports message oriented middleware. Not surprisingly, a
Microsoft Message Queuing (MSMQ) binding is provided as part of WCF. The WCF programming model is
higher level than the traditional messaging APIs such as JMS and NMS since you are programing to a service
interface and use metadata (either XML or attributes) to configure the messaging behavior. If you prefer to use this
service-oriented, RPC style approach, then look to see if a vendor provides a WCF binding for your messaging
provider. Note that even with the option of using WCF, many people prefer to sit 'closer to the metal' when using
messaging middleware, to access specific features and functionality not available in WCF, or simply because they
are more comfortable with that programming model.
A WCF binding for Apache NMS is being developed as a separate project under the Spring Extensions [http://
www.springframework.org/extensions/faq] umbrella project. Stay tuned for details.
29.2. Using Spring Messaging
29.2.1. Messaging Template overview
Code that uses the messaging template classes (NmsTemplate, EmsTemplate, etc) only needs to implement callback
interfaces giving them a clearly defined contract. The IMessageCreator callback interface creates a message
given a Session provided by the calling code in NmsTemplate. In order to allow for more complex usage of the
provider messaging API, the callback ISessionCallback provides the user with the provider specific messaging
Session and the callback IProducerCallback exposes a provider specific Session and MessageProducer pair.
Provider messaging APIs typically expose two types of send methods, one that takes delivery mode, priority, and
time-to-live as quality of service (QOS) parameters and one that takes no QOS parameters which uses default
values. Since there are many higher level send methods in NmsTemplate, the setting of the QOS parameters have
been exposed as properties on the template class to avoid duplication in the number of send methods. Similarly,
the timeout value for synchronous receive calls is set using the property ReceiveTimeout.
Note
Instances of the NmsTemplate class are thread-safe once configured. This is important because it
means that you can configure a single instance of a NmsTemplate and then safely inject this shared
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reference into multiple collaborators. To be clear, the NmsTemplate is stateful, in that it maintains a
reference to a ConnectionFactory, but this state is not conversational state.
29.2.2. Connections
The NmsTemplate requires a reference to a ConnectionFactory. The ConnectionFactory serves as the entry point
for working with the provider's messaging API. It is used by the client application as a factory to create connections
to the messaging server and encapsulates various configuration parameters, many of which are vendor specific
such as SSL configuration options.
29.2.3. Caching Messaging Resources
The standard API usage of NMS and other JMS inspired APIs involves creating many intermediate objects. To
send a message the following 'API' walk is performed
IConnectionFactory->IConnection->ISession->IMessageProducer->Send
Between the ConnectionFactory and the Send operation there are three intermediate objects that are created and
destroyed. To optimise the resource usage and increase performance two implementations of IConnectionFactory
are provided.
29.2.3.1. SingleConnectionFactory
Spring.Messaging.Nms.Connections.SingleConnectionFactory
will return the same connection on all calls
to CreateConnection and ignore calls to Close.
29.2.3.2. CachingConnectionFactory
extends
the
functionality
SingleConnectionFactory and adds the caching of Sessions, MessageProducers, and MessageConsumers.
Spring.Messaging.Nms.Connections.CachingConnectionFactory
of
The initial cache size is set to 1, use the property SessionCacheSize to increase the number of cached sessions.
Note that the number of actual cached sessions will be more than that number as sessions are cached based on their
acknowledgment mode, so there can be up to 4 cached session instances when SessionCacheSize is set to one,
one for each AcknowledgementMode. MessageProducers and MessageConsumers are cached within their owning
session and also take into account the unique properties of the producers and consumers when caching.
MessageProducers are cached based on their destination. MessageConsumers are cached based on a key composed
of the destination, selector, noLocal delivery flag, and the durable subscription name (if creating durable
consumers).
29.2.4. Destination Management
In Java implementations of JMS, Connections and Destinations are 'administered objects' accessible though
JNDI - a directory service much like ActiveDirectory. In .NET each vendor has selected a different approach to
destination management. Some are JNDI inspired, allowing you to retrieve Connections and Destinations that
were configured administratively. You can use these vendor specific APIs to perform dependency injection on
references to JMS Destination objects in Spring's XML configuration file by creating am implementation of
IObjectFactory or alternatively configuring the specific concrete class implementation for a messaging provider.
However, this approach of administered objects can be quite cumbersome if there are a large number of
destinations in the application or if there are advanced destination management features unique to the messaging
provider. Examples of such advanced destination management would be the creation of dynamic destinations or
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support for a hierarchical namespace of destinations. The NmsTemplate delegates the resolution of a destination
name to a destination object by delegating to an implementation of the interface IDestinationResolver.
DynamicDestinationResolver is the default implementation used by NmsTemplate and accommodates resolving
dynamic destinations.
Quite often the destinations used in a messaging application are only known at runtime and therefore cannot be
administratively created when the application is deployed. This is often because there is shared application logic
between interacting system components that create destinations at runtime according to a well-known naming
convention. Even though the creation of dynamic destinations are not part of the original JMS specification,
most vendors have provided this functionality. Dynamic destinations are created with a name defined by the
user which differentiates them from temporary destinations and are often not registered in a directory service.
The API used to create dynamic destinations varies from provider to provider since the properties associated
with the destination are vendor specific. However, a simple implementation choice that is sometimes made by
vendors is to use the TopicSession method CreateTopic(string topicName) or the QueueSession method
CreateQueue(string queueName) to create a new destination with default destination properties. Depending on
the vendor implementation, DynamicDestinationResolver may then also create a physical destination instead
of only resolving one.
The boolean property PubSubDomain is used to configure the NmsTemplate with knowledge of what messaging
'domain' is being used. By default the value of this property is false, indicating that the point-to-point domain,
Queues, will be used. This property is infrequently used as the provider messaging APIs are now largely
agnostic as to which messaging 'domain' is used, referring to 'Destinations' rather than 'Queues' or 'Topics'.
However, this property does influence the behavior of dynamic destination resolution via implementations of the
IDestinationResolver interface.
You can also configure the NmsTemplate with a default destination via the property DefaultDestination. The
default destination will be used with send and receive operations that do not refer to a specific destination.
29.2.5. Message Listener Containers
One of the most common uses of JMS is to concurrently process messages delivered asynchronously. A message
listener container is used to receive messages from a message queue and drive the IMessageListener that is
injected into it. The listener container is responsible for all threading of message reception and dispatches into
the listener for processing. A message listener container is the intermediary between an Message-Driven PONO
(MDP) and a messaging provider, and takes care of registering to receive messages, resource acquisition and
release, exception conversion and suchlike. This allows you as an application developer to write the (possibly
complex) business logic associated with receiving a message (and possibly responding to it), and delegates
boilerplate messaging infrastructure concerns to the framework.
A subclass of AbstractMessageListenerContainer is used to receive messages from JMS and
drive the Message-Driven PONOs (MDPs) that are injected into it. There are one subclasses of
AbstractMessageListenerContainer packaged with Spring - SimpleMessageListenerContainer. Additional
subclasses, in particular to participate in distributed transactions (if the provider supports it), will be provided
in future releases. SimpleMessageListenerContainer creates a fixed number of JMS sessions at startup and uses
them throughout the lifespan of the container.
29.2.6. Transaction Management
Spring provides a NmsTransactionManager that manages transactions for a single ConnectionFactory. This allows
messaging applications to leverage the managed transaction features of Spring as described in Chapter 17,
Transaction management. The NmsTransactionManager performs local resource transactions, binding a
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Connection/Session pair from the specified ConnectionFactory to the thread. NmsTemplate automatically detects
such transactional resources and operates on them accordingly.
Using Spring's SingleConnectionFactory will result in a shared Connection, with each transaction having its
own independent Session.
29.3. Sending a Message
The NmsTemplate contains three convenience methods to send a message. The methods are listed below.
• void Send(IDestination destination, IMessageCreator messageCreator)
• void Send(string destinationName, IMessageCreator messageCreator)
• void Send(IMessageCreator messageCreator)
The method differ in how the destination is specified. In first case the JMS Destination object is specified
directly. The second case specifies the destination using a string that is then resolved to a messaging Destination
object using the IDestinationResolver associated with the template. The last method sends the message to the
destination specified by NmsTemplate''s DefaultDestination property.
All methods take as an argument an instance of IMessageCreator which defines the API contract for you to create
the JMS message. The interface is show below
public interface IMessageCreator {
IMessage CreateMessage(ISession session);
}
Intermediate Sessions and MessageProducers needed to send the message are managed by NmsTemplate. The
session passed in to the method is never null. There is a similar set methods that use a delegate instead of the
interface, which can be convenient when writing small implementation in .NET 2.0 using anonymous delegates.
Larger, more complex implementations of the method 'CreateMessage' are better suited to an interface based
implementation.
• void
SendWithDelegate(IDestination
destination,
MessageCreatorDelegate
messageCreatorDelegate)
• void SendWithDelegate(string destinationName, MessageCreatorDelegate messageCreatorDelegate)
• void SendWithDelegate(MessageCreatorDelegate messageCreatorDelegate)
The declaration of the delegate is
public delegate IMessage MessageCreatorDelegate(ISession session);
The following class shows how to use the SendWithDelegate method with an anonymous delegate to create a
MapMessage from the supplied Session object. The use of the anonymous delegate allows for very terse syntax
and easy access to local variables. The NmsTemplate is constructed by passing a reference to a ConnectionFactory.
public class SimplePublisher
{
private NmsTemplate template;
public SimplePublisher()
{
template = new NmsTemplate(new ConnectionFactory("tcp://localhost:61616"));
}
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public void Publish(string ticker, double price)
{
template.SendWithDelegate("APP.STOCK.MARKETDATA",
delegate(ISession session)
{
IMapMessage message = session.CreateMapMessage();
message.Body.SetString("TICKER", ticker);
message.Body.SetDouble("PRICE", price);
message.NMSPriority = 2;
return message;
});
}
}
A zero argument constructor and ConnectionFactory property are also provided. Alternatively consider deriving
from Spring's NmsGatewaySupport convenience base class which provides a ConnectionFactory property that will
instantiate a NmsTemplate instance that is made available via the property NmsTemplate.
29.3.1. Using MessageConverters
In order to facilitate the sending of domain model objects, the NmsTemplate has various send methods that
take a .NET object as an argument for a message's data content. The overloaded methods ConvertAndSend and
ReceiveAndConvert in NmsTemplate delegate the conversion process to an instance of the IMessageConverter
interface. This interface defines a simple contract to convert between .NET objects and JMS messages. The
default implementation SimpleMessageConverter supports conversion between String and TextMessage, byte[]
and BytesMesssage, and System.Collections.IDictionary and MapMessage. By using the converter, you and your
application code can focus on the business object that is being sent or received via messaging and not be concerned
with the details of how it is represented as a JMS message. There is also an XmlMessageConverter that converts
objects to an XML string and vice-versa for sending via a TextMessage.
The family of ConvertAndSend messages are similar to that of the Send method with the additional argument of
type IMessagePostProcessor. These methods are listed below.
• void ConvertAndSend(object message)
• void ConvertAndSend(object message, IMessagePostProcessor postProcessor)
• void ConvertAndSend(string destinationName, object message)
• void
ConvertAndSend(string
destinationName,
object
message,
IMessagePostProcessor
postProcessor);
• void ConvertAndSend(Destination destination, object message)
• void
ConvertAndSend(Destination
destination,
object
message,
IMessagePostProcessor
postProcessor)
The example below uses the default message converter to send a Hashtable as a message to the destination
"APP.STOCK".
public void PublishUsingDict(string ticker, double price)
{
IDictionary marketData = new Hashtable();
marketData.Add("TICKER", ticker);
marketData.Add("PRICE", price);
template.ConvertAndSend("APP.STOCK.MARKETDATA", marketData);
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}
To accommodate the setting of message's properties, headers, and body that can not be generally encapsulated
inside a converter class, the IMessageConverterPostProcessor interface gives you access to the message after
it has been converted but before it is sent. The example below demonstrates how to modify a message header
and a property after a Hashtable is converted to a message using the IMessagePostProcessor. The methods
ConvertAndSendUsingDelegate allow for the use of a delegate to perform message post processing. This family
of methods is listed below
• void ConvertAndSendWithDelegate(object message, MessagePostProcessorDelegate postProcessor)
• void
ConvertAndSendWithDelegate(IDestination
destination,
object
message,
MessagePostProcessorDelegate postProcessor)
• void
ConvertAndSendWithDelegate(string
destinationName,
object
message,
MessagePostProcessorDelegate postProcessor)
The declaration of the delegate is
public delegate IMessage MessagePostProcessorDelegate(IMessage message);
The following code shows this in action.
public void PublishUsingDict(string ticker, double price)
{
IDictionary marketData = new Hashtable();
marketData.Add("TICKER", ticker);
marketData.Add("PRICE", price);
template.ConvertAndSendWithDelegate("APP.STOCK.MARKETDATA", marketData,
delegate(IMessage message)
{
message.NMSPriority = 2;
message.NMSCorrelationID = new Guid().ToString();
return message;
});
}
29.4. Session and Producer Callback
While the send operations cover many common usage scenarios, there are cases when you want to perform
multiple operations on a JMS Session or MessageProducer. The SessionCallback and ProducerCallback expose
the Session and Session / MessageProducer pair respectfully. The Execute() methods on NmsTemplate execute
these callback methods.
• public object Execute(IProducerCallback action)
• public object Execute(ProducerDelegate action)
• public object Execute(ISessionCallback action)
• public object Execute(SessionDelegate action)
Where ISessionCallback and IProducerCallback are
public interface IProducerCallback
{
object DoInJms(Session session, MessageProducer producer);
}
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and
public interface ISessionCallback
{
object DoInJms(Session session);
}
The delegate signatures are listed below and mirror the interface method signature
public delegate object SessionDelegate(ISession session);
public delegate object ProducerDelegate(ISession session, IMessageProducer producer);
29.5. Receiving a message
29.5.1. Synchronous Reception
While messaging middleware is typically associated with asynchronous processing, it is possible to consume
messages synchronously. The overloaded Receive(..) methods on NmsTemplate provide this functionality.
During a synchronous receive, the calling thread blocks until a message becomes available. This can
be a dangerous operation since the calling thread can potentially be blocked indefinitely. The property
ReceiveTimeout on NmsTemplate specifies how long the receiver should wait before giving up waiting for a
message.
The Receive methods are listed below
• public Message Receive()
• public Message Receive(Destination destination)
• public Message Receive(string destinationName)
• public Message ReceiveSelected(string messageSelector)
• public Message ReceiveSelected(string destinationName, string messageSelector)
• public Message ReceiveSelected(Destination destination, string messageSelector)
The Receive method without arguments will use the DefaultDestination. The ReceiveSelected methods apply
the provided message selector string to the MessageConsumer that is created.
The ReceiveAndConvert methods apply the template's message converter when receiving a message. The message
converter to use is set using the property MessageConverter and is the SimpleMessageConverter implementation
by default. These methods are listed below.
• public object ReceiveAndConvert()
• public object ReceiveAndConvert(Destination destination)
• public object ReceiveAndConvert(string destinationName)
• public object ReceiveSelectedAndConvert(string messageSelector)
• public object ReceiveSelectedAndConvert(string destinationName, string messageSelector)
• public object ReceiveSelectedAndConvert(Destination destination, string messageSelector)
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29.5.2. Asynchronous Reception
Asynchronous reception of messages occurs by the messaging provider invoking a callback function. This is
commonly an interface such as the IMessageListener interface shown below, taken from the TIBCO EMS
provider.
public interface IMessageListener
{
void OnMessage(Message message);
}
Other vendors may provide a delegate based version of this callback or even both a delegate and interface options.
Apache ActiveMQ supports the use of delegates for message reception callbacks. As a programming convenience
in Spring.Messaging.Nms.Core is an interface IMessageListener that can be used with NMS.
Below is a simple implementation of the IMessageListener interface that processes a message.
using Spring.Messaging.Nms.Core;
using Apache.NMS;
using Common.Logging;
namespace MyApp
{
public class SimpleMessageListener : IMessageListener
{
private static readonly ILog LOG = LogManager.GetLogger(typeof(SimpleMessageListener));
private int messageCount;
public int MessageCount
{
get { return messageCount; }
}
public void OnMessage(IMessage message)
{
messageCount++;
LOG.Debug("Message listener count = " + messageCount);
ITextMessage textMessage = message as ITextMessage;
if (textMessage != null)
{
LOG.Info("Message Text = " + textMessage.Text);
} else
{
LOG.Warn("Can not process message of type " message.GetType());
}
}
}
Once you've implemented your message listener, it's time to create a message listener container.
You register you listener with a message listener container that specifies various messaging configuration
parameters, such as the ConnectionFactory, and the number of concurrent consumers to create. There
is an abstract base class for message listener containers, AbstractMessageListenerContainer, and one
concrete implementation, SimpleMessageListenerContainer. SimpleMessageListenerContainer creates a
fixed number of JMS Sessions/MessageConsumer pairs as set by the property ConcurrentConsumers. Here is a
sample configuration
<object id="ConnectionFactory" type="Apache.NMS.ActiveMQ.ConnectionFactory, Apache.NMS.ActiveMQ">
<constructor-arg index="0" value="tcp://localhost:61616"/>
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</object>
<object id="MyMessageListener" type="MyApp.SimpleMessageListener, MyApp"/>
<object id="MessageListenerContainer" type="Spring.Messaging.Nms.Listener.SimpleMessageListenerContainer, Spri
<property name="ConnectionFactory" ref="ConnectionFactory"/>
<property name="DestinationName" value="APP.REQUEST"/>
<property name="ConcurrentConsumers" value="10"/>
<property name="MessageListener" ref="MyMessageListener"/>
</object>
The above configuration will create 10 threads that process messages off of the queue named "APP.REQUEST".
The threads are those owned by the messaging provider as a result of creating a MessageConsumer. Other
important properties are ClientID, used to set the ClientID of the Connection and MessageSelector to specify the
'sql-like' message selector string. Durable subscriptions are supported via the properties SubscriptionDurable and
DurableSubscriptionName. You may also register an exception listener using the property ExceptionListener.
A custom schema to create the SimpleMessageListener container is also provided. Using this schema the
configuration above looks like the following
<objects xmlns="http://www.springframework.net"
xmlns:nms="http://www.springframework.net/nms">
<!-- other object definitions -->
<nms:listener-container connection-factory="ConnectionFactory" concurrency="10">
<nms:listener ref="MyMessageListener" destination="APP.STOCK.REQUEST" />
</nms:listener-container>
</objects>
Exceptions that are thrown during message processing can be passed to an implementation of IExceptionHandler
and registered with the container via the property ExceptionListener. The registered IExceptionHandler will
be invoked if the exception is of the type NMSException (or the equivalent root exception type for other providers).
The SimpleMessageListenerContainer will logs the exception at error level and not propagate the exception to
the provider. All handling of acknowledgement and/or transactions is done by the listener container. You can
override the method HandleListenerException to change this behavior.
Please refer to the Spring SDK documentation for additional description of the features and properties of
SimpleMessageListenerContainer.
29.5.3. The ISessionAwareMessageListener interface
The ISessionAwareMessageListener interface is a Spring-specific interface that provides a similar contract to
the messaging provider's IMessageListener interface or Listener delegate/event, but also provides the message
handling method with access to the Session from which the Message was received.
public interface ISessionAwareMessageListener
{
void OnMessage(IMessage message, ISession session);
}
You can also choose to implement this interface and register it with the message listener container
29.5.4. MessageListenerAdapater
The MessageListenerAdapter class is the final component in Spring's asynchronous messaging support: in a
nutshell, it allows you to expose almost any class to be invoked as a messaging callback (there are of course
some constraints).
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Consider the following interface definition. Notice that although the interface extends neither the
IMessageListener nor ISessionAwareMessageListener interfaces, it can still be used as a Message-Driven
PONOs (MDP) via the use of the MessageListenerAdapter class. Notice also how the various message handling
methods are strongly typed according to the contents of the various Message types that they can receive and
handle.
public interface MessageHandler {
void HandleMessage(string message);
void HandleMessage(Hashtable message);
void HandleMessage(byte[] message);
}
and a class that implements this interface...
public class DefaultMessageHandler : IMessageHandler {
// stub implementations elided for bevity...
}
In particular, note how the above implementation of the IMessageHandler interface (the above
DefaultMessageHandler class) has no messaging provider API dependencies at all. It truly is a PONO that we
will make into an MDP via the following configuration.
<object id="MessagleHandler" type="MyApp.DefaultMessageHandler, MyApp"/>
<object id="MessageListenerAdapter" type="Spring.Messaging.Nms.Listener.Adapter.MessageListenerAdapter, Spring.M
<property name="HandlerObject" ref="MessagleHandler"/>
</object>
<object id="MessageListenerContainer" type="Spring.Messaging.Nms.Listener.SimpleMessageListenerContainer, Spring
<property name="ConnectionFactory" ref="ConnectionFactory"/>
<property name="DestinationName" value="APP.REQUEST"/>
<property name="MessageListener" ref="MessageListenerAdapter"/>
</object>
The previous examples relies on the fact that the default IMessageConverter implementation of the
MessageListenerAdapter is SimpleMessageConverter that can convert from messages to strings, byte[], and
hashtables and object from a ITextMessage, IBytesMessage, IMapMessage, and IObjectMessage respectfully.
Below is an example of another MDP that can only handle the receiving of NMS ITextMessage messages. Notice
how the message handling method is actually called 'Receive' (the name of the message handling method in a
MessageListenerAdapter defaults to 'HandleMessage'), but it is configurable (as you will see below). Notice also
how the 'Receive(..)' method is strongly typed to receive and respond only to NMS ITextMessage messages.
public interface TextMessageHandler {
void Receive(ITextMessage message);
}
public class TextMessageHandler implements ITextMessageHandler {
// implementation elided for clarity...
}
The configuration of the attendant MessageListenerAdapter would look like this
<object id="MessagleHandler" type="MyApp.DefaultMessageHandler, MyApp"/>
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<object id="MessageListenerAdapter" type="Spring.Messaging.Nms.Listener.Adapter.MessageListenerAdapter, Spring.M
<property name="HandlerObject" ref="TextMessagleHandler"/>
<property name="DefaultHandlerMethod" value="Receive"/>
<!-- we don't want automatic message context extraction -->
<property name="MessageConverter">
<null/>
</property>
</object>
Please note that if the above 'MessageListener' receives a Message of a type other than ITextMessage, a
ListenerExecutionFailedException will be thrown (and subsequently handled by the container by logging the
exception).
If your IMessageConverter implementation will return multiple object types, overloading the handler method is
perfectly acceptable, the most specific matching method will be used. A method with an object signature would
be consider a 'catch-all' method of last resort. For example, you can have an handler interface as shown below.
public interface IMyHandler
{
void DoWork(string text);
void DoWork(OrderRequest orderRequest);
void DoWork(InvoiceRequest invoiceRequest);
void DoWork(object obj);
}
Another of the capabilities of the MessageListenerAdapter class is the ability to automatically send back a
response Message if a handler method returns a non-void value. The adapter's message converter will be
used to convert the methods return value to a message. The resulting message will then be sent to the
Destination defined in the JMS Reply-To property of the original Message (if one exists) , or the default
Destination set on the MessageListenerAdapter (if one has been configured). If no Destination is found then an
InvalidDestinationException will be thrown (and please note that this exception will not be swallowed and
will propagate up the call stack).
An interface that is typical when used with a message converter that supports multiple object types and has return
values is shown below.
public interface IMyHandler
{
string DoWork(string text);
OrderResponse DoWork(OrderRequest orderRequest);
InvoiceResponse DoWork(InvoiceRequest invoiceRequest);
void DoWork(object obj);
}
29.5.5. Processing messages within a messaging transaction
Invoking a message listener within a transaction only requires reconfiguration of the listener container. Local
message transactions can be activated by setting the property SessionAcknowledgeMode which for NMS is of the
enum type AcknowledgementMode, to AcknowledgementMode.Transactional. Each message listener invocation
will then operate within an active messaging transaction, with message reception rolled back in case of listener
execution failure.
Sending a response message (via ISessionAwareMessageListener) will be part of the same local transaction, but
any other resource operations (such as database access) will operate independently. This usually requires duplicate
message detection in the listener implementation, covering the case where database processing has committed but
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message processing failed to commit. See the discussion on the ActiveMQ web site here for more information
combining local database and messaging transactions.
29.5.6. Messaging Namespace support
To use the NMS namespace elements you will need to reference the NMS schema. For information on how to set
this up refer to Section A.2.6, “The nms messaging schema”. The namespace consists of one top level elements:
<listener-container/> which can contain one or more <listener/> child elements. Here is an example of a basic
configuration for two listeners.
<nms:listener-container>
<nms:listener destination="queue.orders" ref="OrderService" method="PlaceOrder"/>
<nms:listener destination="queue.confirmations" ref="ConfirmationLogger" method="Log"/>
</nms:listener-container>
The example above is equivalent to creating two distinct listener container object definitions and two
distinct MessageListenerAdapter object definitions as demonstrated in the section entitled Section 29.5.4,
“MessageListenerAdapater”. In addition to the attributes shown above, the listener element may contain several
optional ones. The following table describes all available attributes:
Table 29.1. Attributes of the NMS <listener> element
Attribute
Description
id
A object name for the hosting listener container. If not specified, a object
name will be automatically generated.
destination (required)
The destination name for this listener, resolved through the
IDestinationResolver strategy.
ref (required)
The object name of the handler object.
method
The name of the handler method to invoke. If the ref points to
a IMessageListener or Spring ISessionAwareMessageListener, this
attribute may be omitted.
response-destination
The name of the default response destination to send response messages
to. This will be applied in case of a request message that does not carry
a "NMSReplyTo" field. The type of this destination will be determined
by the listener-container's "destination-type" attribute. Note: This only
applies to a listener method with a return value, for which each result
object will be converted into a response message.
subscription
The name of the durable subscription, if any.
selector
An optional message selector for this listener.
pubsub-domain
An optional boolean value. Set to true for the publish-subscribe domain
(Topics) or false (the default) for point-to-point domain (Queues). This is
useful when using the default implementation for destination resolvers.
The <listener-container/> element also accepts several optional attributes. This allows for customization of the
various strategies (for example, DestinationResolver) as well as basic messaging settings and resource references.
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Using these attributes, it is possible to define highly-customized listener containers while still benefiting from
the convenience of the namespace.
<jms:listener-container connection-factory="MyConnectionFactory"
destination-resolver="MyDestinationResolver"
concurrency="10">
<jms:listener destination="queue.orders" ref="OrderService" method="PlaceOrder"/>
<jms:listener destination="queue.confirmations" ref="ConfirmationLogger" method="Log"/>
</jms:listener-container>
The following table describes all available attributes. Consult the class-level SDK documentation of the
AbstractMessageListenerContainer and its subclass SimpleMessageListenerContainer for more detail on the
individual properties.
Table 29.2. Attributes of the NMS <listener-container> element
Attribute
Description
connection-factory
A reference to the NMS ConnectionFactory object (the default object
name is 'ConnectionFactory').
destination-resolver
A reference to the IDestinationResolver strategy for resolving JMS
Destinations.
message-converter
A reference to the IMessageConverter strategy for converting
NMS Messages to listener method arguments. Default is a
SimpleMessageConverter.
destination-type
The NMS destination type for this listener: queue, topic or
durableTopic. The default is queue.
client-id
The NMS client id for this listener container. Needs to be specified when
using durable subscriptions.
acknowledge
The native NMS acknowledge mode: auto, client, dups-ok or
transacted. A value of transacted activates a locally transacted
Session. As an alternative, specify the transaction-manager attribute
described below. Default is auto.
concurrency
The number of concurrent sessions/consumers to start for each listener.
Default is 1; keep concurrency limited to 1 in case of a topic listener or if
queue ordering is important; consider raising it for general queues.
recovery-interval
The time interval between connection recovery attempts. The default is 5
seconds. Specify as a TimeSpan value using Spring's TimeSpanConverter
(e.g. 10s, 10m, 3h, etc)
max-recovery-time
The maximum time try reconnection attempts. The default is 10 minutes.
Specify as a TimeSpan value using Spring's TimeSpanConverter (e.g. 10s,
10m, 3h, etc)
auto-startup
Set whether to automatically start the listeners after initialization. Default
is true, optionally set to false.
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Chapter 30. Message Oriented
Middleware - MSMQ
30.1. Introduction
The goals of Spring's MSMQ 3.0 messaging support is to raise the level of abstraction when writing MSMQ
applications. The System.Messaging API is a low-level API that provides the basis for creating a messaging
application. However, 'Out-of-the-box', System.Messaging leaves the act of creating sophisticated multi-threaded
messaging servers and clients as an infrastructure activity for the developer. Spring fills this gap by proving easy
to use helper classes that makes creating an enterprise messaging application easy. These helper classes take into
account the nuances of the System.Messaging API, such as its lack of thread-safety in many cases, the handling
of so-called 'poison messages' (messages that are endlessly redelivered due to an unrecoverable exception during
message processing), and combining database transactions with message transactions. Other goals of Spring's
MSMQ messaging support are to support messaging best practices, in particular encouraging a clean architectural
layering that separates the messaging middleware specifics from the core business processing.
Spring's approach to distributed computing has always been to promote a plain old .NET object approach or a
PONO programming model. In this approach plain .NET objects are those that are devoid of any reference to
a particular middleware technology. Spring provides the 'adapter' classes that converts between the middleware
world, in this case MSMQ, and the oo-world of your business processing. This is done through the use of Spring's
MessageListenerAdapter class and IMessageConverters.
The namespace Spring.Messaging provides the core functionality for messaging. It contains the class
MessageQueueTemplate that simplifies the use of System.Messaging.MessageQueue by handling the lack
of thread-safety in most of System.Messaging.MessageQueue's methods (for example Send). A single
instance of MessageQueueTemplate can be used throughout your application and Spring will ensure that
a different instance of a MessageQueue class is used per thread when using MessageQueueTemplate's
methods. This per-thread instance of a System.Messaging.MessageQueue is also available via its
property MessageQueue. The MessageQueueTemplate class is also aware of the presence of either
an 'ambient' System.Transaction's transaction or a local System.Messaging.MessageQueueTransaction.
As such if you use MessageQueueTemplate's send and receive methods, unlike with plain use of
System.Messaging.MessageQueue, you do not need to keep track of this information yourself and call the correct
overloaded System.Messaging.MessageQueue method for a specific transaction environment. When using a
System.Messaging.MessageQueueTransaction this would usually require you as a developer to come up with
your own mechanism for passing around a MessageQueueTransaction to multiple classes and layers in your
application. MessageQueueTemplate manages this for you, so you don't have to do so yourself. These resource
management and transaction features of MessageQueueTemplate are quite analogous to the transactional features
of Spring's AdoTemplate in case you are already familiar with that functionality.
For asynchronous reception Spring provides several multi-threaded message listener containers. You can pick
and configure the container that matches your message transactional processing needs and configure poisonmessage handling policies. The message listener container leverages Spring's support for managing transactions.
Both DTC, local messaging transactions, and local database transactions are supported. In particular, you can
easily coordinate the commit and rollback of a local MessageQueueTransaction and a local database transaction
when they are used together.
From a programming perspective, Spring's MSMQ support involves you configuring message listener containers
and writing a callback function for message processing. On the sending side, it involves you learning
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how to use MessageQueueTemplate. In both cases you will quite likely want to take advantage of using
MessageListenerConverters so you can better structure the translation from the System.Messaging.Message
data structure to your business objects. After the initial learning hurdle, you should find that you will be much
more productive leveraging Spring's helper classes to write enterprise MSMQ applications than rolling your own
infrastructure. Feedback and new feature requests are always welcome.
The Spring.MsmqQuickstart application located in the examples directory of the distribution shows this
functionality in action.
30.2. A quick tour for the impatient
Here is a quick example of how to use Spring's MSMQ support to create a client that sends a message and a
multi-threaded server application that receives the message. (The client code could also be used as-is in a multithreaded environment but this is not demonstrated).
On the client side you create an instance of the MessageQueueTemplate class and configure it to use a
MessageQueue. This can be done programmatically but it is common to use dependency injection and Spring's
XML configuration file to configure your client class as shown below.
<object id='questionTxQueue' type='Spring.Messaging.Support.MessageQueueFactoryObject, Spring.Messaging'>
<property name='Path' value='.\Private$\questionTxQueue'/>
<property name='MessageReadPropertyFilterSetAll' value='true'/>
</object>
<object id="messageQueueTemplate" type="Spring.Messaging.Core.MessageQueueTemplate, Spring.Messaging">
<property name="MessageQueueObjectName" value="questionTxQueue"/>
</object>
<!-- Class you write -->
<object id="questionService" type="MyNamespace.QuestionService, MyAssembly">
<property name="MessageQueueTemplate" ref="messageQueueTemplate"/>
<object>
The MessageQueue object is created via an instance of MessageQueueFactoryObject and the
MessageQueueTemplate refers to this factory object by name and not by reference. The SimpleSender class looks
like this
public class QuestionService : IQuestionService
{
private MessageQueueTemplate messageQueueTemplate;
public MessageQueueTemplate {
get { return messageQueueTemplate; }
set { messageQueueTemplate = value; }
}
public void SendQuestion(string question)
{
MessageQueueTemplate.ConvertAndSend(question);
}
}
This class can be shared across multiple threads and the MessageQueueTemplate will take care of managing thread
local access to a System.Messaging.MessageQueue as well as any System.Messaging.IMessageFormatter
instances.
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Furthermore, since this is a transactional queue (only the name gives it away), the message will be sent using
a single local messaging transaction. The conversion from the string to the underling message is managed by
an instance of the IMessageConverter class. By default an implementation that uses an XmlMessageFormatter
with a TargetType of System.String is used. You can configure the MessageQueueTemplate to use other
IMessageConveter implementations that do conversions above and beyond what the 'stock' IMessageFormatters
do. See the section on MessageConverters for more details.
On the receiving side we would like to consume the messages transactionally from the queue.
Since no other database operations are being performed in our server side processing, we select the
TransactionMessageListenerContainer and configure it to use the MessageQueueTransactionManager. The
MessageQueueTransactionManager an implementation of Spring's IPlatformTransactionManager abstraction
that provides a uniform API on top of various transaction manager (ADO.NET,NHibernate, MSMQ, etc).
Spring's MessageQueueTransactionManager is responsible for createing, committing, and rolling back a MSMQ
MessageQueueTransaction.
While you can create the message listener container programmatically, we will show the declarative configuration
approach below
<!-- Queue to receive from -->
<object id='questionTxQueue' type='Spring.Messaging.Support.MessageQueueFactoryObject, Spring.Messaging'>
<property name='Path' value='.\Private$\questionTxQueue'/>
<property name='MessageReadPropertyFilterSetAll' value='true'/>
</object>
<!-- MSMQ Transaction Manager -->
<object id="messageQueueTransactionManager" type="Spring.Messaging.Core.MessageQueueTransactionManager, Spring
<!-- Message Listener Container that uses MSMQ transactional for receives -->
<object id="transactionalMessageListenerContainer" type="Spring.Messaging.Listener.TransactionalMessageListene
<property name="MessageQueueObjectName" value="questionTxQueue"/>
<property name="PlatformTransactionManager" ref="messageQueueTransactionManager"/>
<property name="MaxConcurrentListeners" value="10"/>
<property name="MessageListener" ref="messageListenerAdapter"/>
</object>
<!-- Adapter to call a PONO as a messaging callback -->
<object id="messageListenerAdapter" type="Spring.Messaging.Listener.MessageListenerAdapter, Spring.Messaging">
<property name="HandlerObject" ref="questionHandler"/>
</object>
<!-- The PONO class that you write -->
<object id="questionHandler" type="MyNamespace.QuestionHandler, MyAssembly"/>
We have specified the queue to listen, that we want to consume the messages transactionally, process messages
from the queue using 10 threads, and that our plain object that will handle the business processing is of the type
QuestionHandler. The only class you need to write, QuestionHandler, looks like
public class QuestionHandler : IQuestionHandler
{
public void HandleObject(string question)
{
// perform message processing here
Console.WriteLine("Received question: " + question);
// use an instance of MessageQueueTemplate and have other MSQM send operations
// partake in the same local message transaction used to receive
}
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}
That is general idea. You write the sender class using MessageQueueTemplate and the consumer class which does
not refer to any messaging specific class. The rest is configuration of Spring provided helper classes.
Note that if the HandleObject method has returned a string value a reply message would be sent to a response
queue. The response queue would be taken from the Message's own ResponseQueue property or can be specified
explicitly using MessageListenerAdapter's DefaultResponseQueueName property.
If an exception is thrown inside the QuestionHandler, then the MSMQ transaction is rolled back, putting the
message back on the queue for redelivery. If the exception is not due to a transient error in the system, but a logical
processing exception, then one would get endless redelivery of the message - clearly not a desirable situation.
These messages are so called 'poison messages' and a strategy needs to be developed to deal with them. This is left
as a development task if you when using the System.Messaging APIs but Spring provides a strategy for handling
poison messages, both for DTC based message reception as well as for local messaging transactions.
In the last part this 'quick tour' we will configure the message listener container to handle poison messages. This
is done by creating an instance of SendToQueueExceptionHandler and setting the property MaxRetry to be the
number of exceptions or retry attempts we are willing to tolerate before taking corrective actions. In this case, the
corrective action is to send the message to another queue. We can then create other message listener containers to
read from those queues and handle the messages appropriately or perhaps you will avoid automated processing
of these messages and take manual corrective actions.
<!-- The 'error' queue to send poison messages -->
<object id='errorQuestionTxQueue' type='Spring.Messaging.Support.MessageQueueFactoryObject, Spring.Messaging'>
<property name='Path' value='.\Private$\errorQuestionTxQueue'/>
<property name='MessageReadPropertyFilterSetAll' value='true'/>
</object>
<!-- Message Listener Container that uses MSMQ transactional for receives -->
<object id="transactionalMessageListenerContainer" type="Spring.Messaging.Listener.TransactionalMessageListene
<!-- as before but adding -->
<property name="MessageTransactionExceptionHandler" ref="messageTransactionExceptionHandler"/>
</object>
<!-- Poison message handling policy -->
<object id="messageTransactionExceptionHandler" type="Spring.Messaging.Listener.SendToQueueExceptionHandler, S
<property name="MaxRetry" value="5"/>
<property name="MessageQueueObjectName" value="errorQuestionTxQueue"/>
</object>
In the event of an exception while processing the message, the message transaction will be rolled back
(putting the message back on the queue questionTxQueue for redelivery). If the same message causes an
exception in processing 5 times ,then it will be sent transactionally to the errorQuestionTxQueue and the
message transaction will commit (removing it from the queue questionTxQueue). You can also specify that
certain exceptions should commit the transaction (remove from the queue) but this is not shown here ,see
below for more informatio non this functionality The SendToQueueExceptionHandler implements the interface
IMessageTransactionExceptionHandler (discussed below) so you can write your own implementations should
the provided ones not meet your needs.
That's the quick tour folks. Hopefully you got a general feel for how things work, what requires configuration,
and what is the code you need to write. The following sections describe each of Spring's helper classes in more
detail. The sample application that ships with Spring is also a good place to get started.
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30.3. Using Spring MSMQ
30.3.1. MessageQueueTemplate
The MessageQueueTemplate is used for synchronously sending and receiving messages. A single instance
can be shared across multiple threads, unlike the standard System.Messaging.MessageQueue class. (One less
resource management issue to worry about!) A thread-local instance of the MessageQueue class is available via
MessageQueueTemplate's property MessageQueue. A MessageQueueTemplate is created by passing a reference
to the name of a MessageQueueFactoryObject, you can think of it as a friendly name for your MessagingQueue
and the recipe of how to create an instance of it. See the following section on MessageQueueFactoryObject for
more information.
The MessageQueueTemplate also provides several convenience methods for sending and receiving messages.
A family of overloaded ConvertAndSend and ReceiveAndConvert methods allow you to send and receive an
object. The default message queue to send and receive from is specified using the MessageQueueTemplate's
property MessageQueueObjectName. The responsibility of converting the object to a Message and vice versa
is given to the template's associated IMessageConverter implementation. This can be set using the property
MessageConverter. The default implementation, XmlMessageConverter, uses an XmlMessageFormatter with its
TargetType set to System.String. Note that System.Messaging.IMessageFormatter classes are also not thread
safe, so MessageQueueTemplate ensures that thread-local instances of IMessageConverter are used (as they
generally wrap IMessageFormatter's that are not thread-safe).
You can use the MessageQueueTemplate to send messages to other MessageQueues by specifying their queue
'object name', the name of the MessageQueueFactoryObject.
The family of overloaded ConvertAndSend and ReceiveAndConvert methods are shown below
void ConvertAndSend(object obj);
void ConvertAndSend(object obj, MessagePostProcessorDelegate messagePostProcessorDelegate);
void ConvertAndSend(string messageQueueObjectName, object message);
void ConvertAndSend(string messageQueueObjectName, object obj, MessagePostProcessorDelegate messagePostProcessor
object ReceiveAndConvert();
object ReceiveAndConvert(string messageQueueObjectName);
The transactional settings of the underlying overloaded System.Messaging.MessageQueue Send method that are
used are based on the following algorithm.
1. If the message queue is transactional and there is an ambient MessageQueueTransaction in
thread local storage (put there via the use of Spring's MessageQueueTransactionManager or
TransactionalMessageListenerContainer), the message will be sent transactionally using the
MessageQueueTransaction object in thread local storage.
Note
This lets you group together multiple messaging operations within the same transaction without
having to explicitly pass around the MessageQueueTransaction object.
2. f the message queue is transactional but there is no ambient MessageQueueTransaction, then a single message
transaction is created on each messaging operation. (MessageQueueTransactionType = Single).
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3. If there is an ambient System.Transactions transaction then that transaction will be used
(MessageQueueTransactionType = Automatic).
4. If the queue is not transactional, then a non-transactional send (MessageQueueTransactionType = None) is
used.
The delegate MessagePostProcessorDelegate has the following signature
public delegate Message MessagePostProcessorDelegate(Message message);
This lets you modify the message after it has been converted from and object to a message using the
IMessageConverter but before it is sent. This is useful for setting Message properties (e.g. CorrelationId,
AppSpecific, TimeToReachQueue). Using anonymous delegates in .NET 2.0 makes this a very succinct coding
task. If you have elaborate properties that need to be set, perhaps creating a custom IMessageConverter would
be appropriate.
Overloaded Send and Receive operations that use the algorithm listed above to set transactional delivery options
are also available. These are listed below
Message Receive();
Message Receive(string messageQueueObjectName);
void Send(Message message);
void Send(string messageQueueObjectName, Message message);
void Send(MessageQueue messageQueue, Message message);
Note that in the last Send method that takes a MessageQueue instance, it is the callers responsibility to ensure
that this instance is not accessed from multiple threads. This Send method is commonly used when getting the
MessageQueue from the ResponseQueue property of a Message during an asynchronous receive process. The
receive timeout of the Receive operations is set using the ReceiveTimeout property of MessageQueueTemplate.
The default value is MessageQueue.InfiniteTimeout (which is actually ~3 months).
The XML configuration snippit for defining a MessageQueueTemplate is shown in the previous section and also
is located in the MSMQ quickstart application configuraiton file Messaging.xml
30.3.2. MessageQueueFactoryObject
The MessageQueueFactoryObject is responsible for creating MessageQueue instances. You configure the factory
with some basic information, namely the constructor parameters you are familiar with already when creating a
standard MessageQueue instance, and then setting MessageQueue properties, such a Label etc. Some configuration
tasks of a MessageQueue involve calling methods, for example to set which properties of the message to read.
These available as properties to set on the MessageQueueFactoryObject. An example declarative configuration
is shown below
<object id='testqueue' type='Spring.Messaging.Support.MessageQueueFactoryObject, Spring.Messaging'>
<!-- propeties passed to the MessageQueue constructor -->
<property name='Path' value='.\Private$\testqueue'/>
<property name='DenySharedReceive' value='true'/>
<property name='AccessMode' value='Receive'/>
<property name='EnableCache' value='true'/>
<!-- properties that call configuration methods on the MessageQueue -->
<property name='MessageReadPropertyFilterSetAll' value='true'/>
<property name='ProductTemplate'>
<object>
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<property name='Label' value='MyLabel'/>
<!-- other MessageQueue properties can be set here -->
</object>
</property>
</object>
Whenever an object reference is made to 'testqueue' an new instance of the MessageQueue class is created. This
Spring's so-called 'prototype' model, which differs from 'singleton' mode. In the singleton creation mode whenever
an object reference is made to a 'testqueue' the same MessageQueue instance would be used. So that a new
instance can be retrieved based on need, the message listener containers take as an argument the name of the
MessageQueueFactoryObject and not a reference. (i.e. use of 'value' instead of 'ref' in the XML).
Note
The MessageQueueFactoryObject class is an ideal candidate for use of a custom namespace. This
will be provided in the future. This will allow you to use VS.NET IntelliSense to configure this
commonly used object. An example of the potential syntax is shown below
<mq:messageQueue id="testqueue" path=".\Private$\testqueue" MessageReadPropertyFilterSetAll="true">
<mq:properties label="MyLabel"/>
</mq:messageQueue>
30.3.3. MessageQueue and IMessageConverter resource management
and IMessageFormatters (commonly used in IMessageConverter implementations) are
not thread-safe. For example, only the following methods on MessageQueue are thread-safe, BeginPeek,
BeginReceive, EndPeek, EndReceive, GetAllMessages, Peek, and Receive.
MessageQueues
To isolate the creation logic of these classes, the factory interface IMessageQueueFactory is used. The interface
is shown below
public interface IMessageQueueFactory
{
MessageQueue CreateMessageQueue(string messageQueueObjectName);
IMessageConverter CreateMessageConverter(string messageConverterObjectName);
}
A provided implementation, DefaultMessageQueueFactory will create an instance of each class perthread. It delegates the creation of the MessageQueue instance to the Spring container. The argument,
messageConverterObjectName, must be the id/name of a MessageQueueFactoryObject defined in the Spring
container.
DefaultMessageQueueFactory
leverages Spring's local thread storage support so it will work correctly in stand
alone and web applications.
You can use the DefaultMessageQueueFactory independent of the rest of Spring's MSMQ support should
you need only the functionality it offers. MessageQueueTemplate and the listener containers create an instance
of DefaultMessageQueueFactory by default. Should you want to share the same instance across these two
classes, or provide your own custom implementation, use the property MessageQueueFactory on either
MessageQueueTemplate or the message listener classe.s
30.3.4. Message Listener Containers
One of the most common uses of MSMQ is to concurrently process messages delivered asynchronously. This
support is provided in Spring by message listener containers. A message listener container is the intermediary
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between an IMessageListener and a MessageQueue. (Note, message listener containers are conceptually different
than Spring's Inversion of Control container, though it integrates and leverages the IoC container.) The message
listener container takes care of registering to receive messages, participating in transactions, resource acquisition
and release, exception conversion and suchlike. This allows you as an application developer to write the (possibly
complex) business logic associated with receiving a message (and possibly responding to it), and delegate
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