The J2EE Tutorial - telecharger des cours et des livres d

The J2EETM Tutorial
Stephanie Bodoff
Dale Green
Kim Haase
Eric Jendrock
Monica Pawlan
Beth Stearns
January 24, 2002
Copyright © 2002 by Sun Microsystems, Inc.
901 San Antonio Road, Palo Alto, California 94303 U.S.A.
All rights reserved.
RESTRICTED RIGHTS LEGEND: Use, duplication, or disclosure by the United States Government is
subject to the restrictions set forth in DFARS 252.227-7013(c)(1)(iii) and FAR 52.227-19.
The release described in this book may be protected by one or more U.S. patents, foreign patents, or
pending applications.
Sun, Sun Microsystems, Sun Microsystems Computer Corporation, the Sun logo, the Sun Microsystems
Computer Corporation logo, Java, JavaSoft, Java Software, JavaScript, JDBC, JDBC Compliant, JavaOS, JavaBeans, Enterprise JavaBeans, JavaServer Pages, J2EE, J2SE, JavaMail, Java Naming and
Directory Interface, EJB, and JSP are trademarks or registered trademarks of Sun Microsystems, Inc.
UNIX® is a registered trademark in the United States and other countries, exclusively licensed through
X/Open Company, Ltd. All other product names mentioned herein are the trademarks of their respective
owners.
THIS PUBLICATION IS PROVIDED “AS IS” WITHOUT WARRANTY OF ANY KIND, EITHER
EXPRESS OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT.
THIS PUBLICATION COULD INCLUDE TECHNICAL INACCURACIES OR TYPOGRAPHICAL
ERRORS. CHANGES ARE PERIODICALLY ADDED TO THE INFORMATION HEREIN; THESE
CHANGES WILL BE INCORPORATED IN NEW EDITIONS OF THE PUBLICATION. SUN
MICROSYSTEMS, INC. MAY MAKE IMPROVEMENTS AND/OR CHANGES IN THE PRODUCT(S) AND/OR THE PROGRAM(S) DESCRIBED IN THIS PUBLICATION AT ANY TIME.
Contents
Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xxi
Chapter 1:
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Distributed Multitiered Applications
J2EE Components
J2EE Clients
Web Components
Business Components
Enterprise Information System Tier
J2EE Containers
Container Services
Container Types
Packaging
Development Roles
J2EE Product Provider
Tool Provider
Application Component Provider
Application Assembler
Application Deployer and Administrator
Reference Implementation Software
Database Access
J2EE APIs
Simplified Systems Integration
Tools
2
3
4
6
7
8
8
8
10
10
11
12
12
12
13
14
14
15
15
18
19
v
vi
CONTENTS
Chapter 2:
Getting Started . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
Setting Up
Getting the Example Code
Getting the Build Tool (ant)
Checking the Environment Variables
Starting the J2EE™ Server
Starting the deploytool
Creating the J2EE™ Application
Creating the Enterprise Bean
Coding the Enterprise Bean
Compiling the Source Files
Packaging the Enterprise Bean
Creating the J2EE™ Application Client
Coding the J2EE Application Client
Compiling the Application Client
Packaging the J2EE Application Client
Specifying the Application Client’s Enterprise Bean Reference
Creating the Web Client
Coding the Web Client
Compiling the Web Client
Packaging the Web Client
Specifying the Web Client’s Enterprise Bean Reference
Specifying the JNDI Names
Deploying the J2EE™ Application
Running the J2EE™ Application Client
Running the Web Client
Modifying the J2EE™ Application
Modifying a Class File
Adding a File
Modifying the Web Client
Modifying a Deployment Setting
Common Problems and Their Solutions
Cannot Start the J2EE Server
Compilation Errors
Deployment Errors
J2EE Application Client Runtime Errors
Web Client Runtime Errors
Detecting Problems With the Verifier Tool
Comparing Your EAR Files with Ours
When All Else Fails
22
22
22
23
23
23
24
24
24
26
26
28
28
31
31
32
32
32
34
34
35
35
37
37
38
39
39
40
40
40
41
41
42
43
43
45
45
46
46
vii
CONTENTS
Chapter 3:
Enterprise Beans . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
What Is an Enterprise Bean?
48
Benefits of Enterprise Beans
48
When to Use Enterprise Beans
49
Types of Enterprise Beans
49
What Is a Session Bean?
49
State Management Modes
50
When to Use Session Beans
51
What Is an Entity Bean?
51
What Makes Entity Beans Different from Session Beans?
52
Container-Managed Persistence
53
When to Use Entity Beans
56
What Is a Message-Driven Bean?
56
What Makes Message-Driven Beans Different from Session and Entity
Beans?
57
When to Use Message-Driven Beans
57
Defining Client Access with Interfaces
58
Remote Access
58
Local Access
59
Local Interfaces and Container-Managed Relationships
59
Deciding on Remote or Local Access
60
Performance and Access
61
Method Parameters and Access
61
The Contents of an Enterprise Bean
62
Naming Conventions for Enterprise Beans
63
The Life Cycles of Enterprise Beans
63
The Life Cycle of a Stateful Session Bean
64
The Life Cycle of a Stateless Session Bean
65
The Life Cycle of an Entity Bean
65
The Life Cycle of a Message-Driven Bean
67
Chapter 4:
A Session Bean Example . . . . . . . . . . . . . . . . . . . . . 69
The CartEJB Example
Session Bean Class
Home Interface
Remote Interface
Helper Classes
Running the CartEJB Example
Other Enterprise Bean Features
Accessing Environment Entries
Comparing Enterprise Beans
Passing an Enterprise Bean’s Object Reference
70
70
75
76
76
76
78
78
80
80
viii
CONTENTS
Chapter 5:
Bean-Managed Persistence Examples. . . . . . . . . .83
The SavingsAccountEJB Example
Entity Bean Class
Home Interface
Remote Interface
Running the SavingsAccountEJB Example
deploytool Tips for Entity Beans With Bean-Managed Persistence
Mapping Table Relationships for Bean-Managed Persistence
One-to-One Relationships
One-to-Many Relationships
Many-to-Many Relationships
Primary Keys for Bean-Managed Persistence
The Primary Key Class
Primary Keys in the Entity Bean Class
Getting the Primary Key
Handling Exceptions
Chapter 6:
84
85
94
96
97
99
99
99
103
110
113
113
114
115
116
Container-Managed Persistence Examples. . . . .119
Overview of the RosterApp Application
120
The PlayerEJB Code
121
Entity Bean Class
122
Local Home Interface
126
Local Interface
128
A Guided Tour of the RosterApp Settings
128
RosterApp
128
RosterClient
130
RosterJAR
130
TeamJAR
131
Method Invocations in RosterApp
137
Creating a Player
137
Adding a Player to a Team
138
Removing a Player
140
Dropping a Player from a Team
140
Getting the Players of a Team
141
Getting a Copy of a Team’s Players
143
Finding the Players by Position
145
Getting the Sports of a Player
146
Running the RosterApp Example
147
Setting Up
147
Deploying the Application
148
Running the Client
148
deploytool Tips for Entity Beans With Container-Managed Persistence
ix
CONTENTS
148
Specifying the Bean’s Type
Selecting the Persistent Fields and Abstract Schema Name
Defining EJB QL Queries for Finder and Select Methods
Generating SQL and Specifying Table Creation
Specifying the Database JNDI Name, User Name, and Password
Defining Relationships
Primary Keys for Container-Managed Persistence
The Primary Key Class
Primary Keys in the Entity Bean Class
Generating Primary Key Values
Chapter 7:
149
149
149
150
150
151
151
151
152
153
A Message-Driven Bean Example . . . . . . . . . . . . 155
Example Application Overview
The J2EE™ Application Client
The Message-Driven Bean Class
The onMessage Method
The ejbCreate and ejbRemove Methods
Running the SimpleMessageEJB Example
Starting the J2EE Server
Creating the Queue
Deploying the Application
Running the Client
deploytool Tips for Message-Driven Beans
Specifying the Bean’s Type and Transaction Management
Setting the Message-Driven Bean’s Characteristics
deploytool Tips for JMS Clients
Setting the Resource References
Setting the Resource Environment References
Specifying the JNDI Names
156
157
158
158
159
159
159
159
159
160
160
161
161
162
163
163
163
Chapter 8: Enterprise JavaBeans™
Query Language165
Terminology
Simplified Syntax
Example Queries
Simple Finder Queries
Finder Queries That Navigate to Related Beans
Finder Queries with Other Conditional Expressions
Select Queries
166
167
167
167
169
170
172
x
CONTENTS
Full Syntax
BNF Grammar of EJB QL
BNF Symbols
FROM Clause
Path Expressions
WHERE Clause
SELECT Clause
EJB QL Restrictions
Chapter 9:
173
173
176
176
179
182
190
191
Web Clients and Components. . . . . . . . . . . . . . . .193
Web Client Life Cycle
Web Application Archives
Creating a WAR File
Adding a WAR File to an EAR File
Adding a Web Component to a WAR File
Configuring Web Clients
Application-Level Configuration
WAR-Level Configuration
Component-Level Configuration
Deploying Web Clients
Running Web Clients
Updating Web Clients
Internationalizing Web Clients
194
196
197
198
198
200
200
200
202
203
204
204
206
Chapter 10: Java Servlet Technology . . . . . . . . . . . . . . . . . . . .209
What Is a Servlet?
The Example Servlets
Troubleshooting
Servlet Life Cycle
Handling Servlet Life-Cycle Events
Handling Errors
Sharing Information
Using Scope Objects
Controlling Concurrent Access to Shared Resources
Accessing Databases
Initializing a Servlet
Writing Service Methods
Getting Information from Requests
Constructing Responses
210
211
215
216
216
218
218
219
220
221
222
223
223
225
xi
CONTENTS
Filtering Requests and Responses
Programming Filters
Programming Customized Requests and Responses
Specifying Filter Mappings
Invoking Other Web Resources
Including Other Resources in the Response
Transferring Control to Another Web Component
Accessing the Web Context
Maintaining Client State
Accessing a Session
Associating Attributes with a Session
Session Management
Session Tracking
Finalizing a Servlet
Tracking Service Requests
Notifying Methods to Shut Down
Creating Polite Long-Running Methods
228
229
231
233
235
235
237
238
239
239
239
240
241
242
242
243
244
Chapter 11: JavaServer Pages™ Technology . . . . . . . . . . . . . 245
What Is a JSP Page?
The Example JSP Pages
The Life Cycle of a JSP Page
Translation and Compilation
Execution
Initializing and Finalizing a JSP Page
Creating Static Content
Creating Dynamic Content
Using Objects within JSP Pages
JSP Scripting Elements
Including Content in a JSP Page
Transferring Control to Another Web Component
Param Element
Including an Applet
Extending the JSP Language
246
249
253
253
254
256
257
257
257
260
263
264
265
265
267
Chapter 12: JavaBeans™ Components in JSP™ Pages . . . . . 269
JavaBeans Component Design Conventions
Why Use a JavaBeans Component?
Creating and Using a JavaBeans Component
Setting JavaBeans Component Properties
Retrieving JavaBeans Component Properties
270
271
272
273
275
xii
CONTENTS
Chapter 13: Custom Tags in JSP™ Pages. . . . . . . . . . . . . . . . . .279
What is a Custom Tag?
The Example JSP Pages
Using Tags
Declaring Tag Libraries
Types of Tags
Defining Tags
Tag Handlers
Tag Library Descriptors
Simple Tags
Tags with Attributes
Tags With Bodies
Tags That Define Scripting Variables
Cooperating Tags
Examples
An Iteration Tag
A Template Tag Library
How Is a Tag Handler Invoked?
280
281
285
285
286
289
289
290
293
294
296
298
302
304
304
308
313
Chapter 14: Transactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .315
What Is a Transaction?
Container-Managed Transactions
Transaction Attributes
Rolling Back a Container-Managed Transaction
Synchronizing a Session Bean’s Instance Variables
Methods Not Allowed in Container-Managed Transactions
Bean-Managed Transactions
JDBC Transactions
JTA Transactions
Returning without Committing
Methods Not Allowed in Bean-Managed Transactions
Summary of Transaction Options for Enterprise Beans
Transaction Timeouts
Isolation Levels
Updating Multiple Databases
Transactions in Web Components
316
316
317
321
322
323
323
324
325
326
327
327
328
329
329
331
Chapter 15: Security. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .333
Overview
334
xiii
CONTENTS
Security Roles
Declaring and Linking Role References
Mapping Roles to J2EE Users and Groups
Web-Tier Security
Protecting Web Resources
Controlling Access to Web Resources
Authenticating Users of Web Resources
Using Programmatic Security in the Web Tier
Unprotected Web Resources
EJB-Tier Security
Declaring Method Permissions
Using Programmatic Security in the EJB Tier
Unprotected EJB-Tier Resources
Application Client-Tier Security
Specifying the Application Client’s Callback Handler
EIS-Tier Security
Configuring Sign-On
Container-Managed Sign-On
Component-Managed Sign-On
Configuring Resource Adapter Security
Propagating Security Identity
Configuring a Component’s Propagated Security Identity
Configuring Client Authentication
J2EE Users, Realms, and Groups
Managing J2EE Users and Groups
Setting Up a Server Certificate
335
335
337
337
337
338
338
340
340
341
341
341
342
342
343
343
344
344
344
345
346
347
347
348
349
350
Chapter 16: Resource Connections. . . . . . . . . . . . . . . . . . . . . . 353
JNDI Names and Resource References
deploytool Tips for Resource References
Database Connections for Enterprise Beans
Coded Connections
Connection Pooling
Mail Session Connections
Running the ConfirmerEJB Example
URL Connections
Running the HTMLReaderEJB Example
353
354
356
357
359
359
361
362
363
xiv
CONTENTS
Chapter 17: J2EE™ Connector Architecture . . . . . . . . . . . . . . .365
About Resource Adapters
Resource Adapter Contracts
Administering Resource Adapters
The Black Box Resource Adapters
Transaction Levels
Properties
Configuring JDBC™ Drivers
Resource Adapter Tutorial
Setting Up
Deploying the Resource Adapter
Testing the Resource Adapter
Common Client Interface
Overview of the CCI
Programming with the CCI
Writing a CCI Client
CCI Tutorial
366
366
368
369
369
370
371
372
372
372
373
375
375
377
386
386
Chapter 18: The Duke’s Bank Application . . . . . . . . . . . . . . . . .391
Enterprise Beans
Session Beans
CustomerControllerEJB
TxControllerEJB
Entity Beans
Helper Classes
Database Tables
Protecting the Enterprise Beans
Application Client
The Classes and Their Relationships
BankAdmin Class
EventHandle Class
DataModel Class
Web Client
Design Strategies
Web Client Life Cycle
Protecting the Web Resources
Internationalization
393
394
396
396
397
397
398
400
400
402
403
404
406
409
410
411
415
415
xv
CONTENTS
Building, Packaging, Deploying, and Running the Application
Adding Groups and Users to the Realm
Starting the J2EE Server, deploytool, and Database
Compiling the Enterprise Beans
Packaging the Enterprise Beans
Compiling the Web Client
Packaging the Web Client
Compiling the J2EE Application Client
Packaging the J2EE Application Client
Packaging the Enterprise Archive File
Opening the Enterprise Archive File
Reviewing JNDI Names
Mapping the Security Roles to Groups
Deploying the Duke’s Bank Application
Creating the Bank Database
Running the J2EE Application Client
Running the Web Client
417
417
418
419
419
420
420
420
421
421
421
423
425
426
426
427
428
Appendix A: HTTP Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431
HTTP Requests
HTTP Responses
432
432
Appendix B: J2EE™ SDK Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . 433
J2EE Administration Tool
Cleanup Tool
Cloudscape Server
Starting Cloudscape
Stopping Cloudscape
Running the Interactive SQL Tool
Cloudscape Server Configuration
Deployment Tool
J2EE Server
Key Tool
Packager Tool
EJB JAR File
Web Application WAR File
Application Client JAR File
J2EE Application EAR File
Specifying the Runtime Deployment Descriptor
Resource Adapter RAR File
434
435
435
436
436
436
437
438
439
439
440
440
441
441
442
442
443
xvi
CONTENTS
Realm Tool
Examples
runclient Script
Syntax
Example
Accessing a Remote Server
Preventing the User Name and Password Prompts
Verifier Tool
Command-Line Verifier
Stand-Alone GUI Verifier
444
444
445
445
446
446
447
447
447
448
Appendix C: Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .449
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .453
Biographies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .477
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .479
Foreword
I joined Sun—actually, a small Sun spin-off called FirstPerson—in August
1993. I knew about the company because a few of my favorite coworkers had
left NeXT to work at FirstPerson. But my main reason for joining was that I
loved the cartoony user interfaces FirstPerson was developing interfaces that
featured a character nicknamed Duke.1
Figure 1 Duke, the Unofficial Mascot of the Java Platform
FirstPerson’s first demo, called Star 7, was a household remote control with a
small touchscreen. By the time I arrived, they were working on a demo for video
on demand.
The wonderfully loony animation for the video-on-demand demo was created by
a San Francisco studio called Colossal Pictures (where, incidentally, my husband
had gotten his start in the animation industry). Both demos were written using a
programming language that was then called Oak.
My first task was to help the creator of the Oak language, James Gosling, write
the language specification. What I really wanted to do, though, was to write taskoriented documentation aimed at ordinary programmers.
1
You can get more information about Duke in the article “It’s Duke’s Birthday, Too!”:
http://java.sun.com/features/1999/05/duke.html.
xvii
xviii
FOREWORD
By July 1994, FirstPerson was in turmoil, having failed to convince cable companies that their video-on-demand solution was what customers needed. I stayed
at the company only because I was about to go on maternity leave.
Programming for the Internet
When I returned to work in the fall of 1994, the company’s dynamic and vision
had completely changed. They had decided that the Oak language—with its ability to produce platform-independent, secure, easily transported code—was ideal
for the Internet. And they were creating a Web browser called WebRunner that
showcased the ability to deliver Oak code, packaged in a form they called
applets, over the Internet.
I set to work writing a guide to help people write and use applets. When the
WebRunner browser was first released in early 1995, the guide was part of the
small set of documentation included with the browser. That guide was the granddaddy of The J2EE™ Tutorial.
The guide was the first documentation to include applets. It looked somewhat
similar to The Java™ Tutorial, and in fact The Java Tutorial probably still has
some of the text originally published in the guide. Because we had no HTML
tools, however, I had to generate the guide completely by hand. Let me tell you,
hand coding navigation links for a document in progress is not fun, even for a
small document. Much less painful was making name changes: The language
name changed from Oak to Java, and the name of the browser from WebRunner
to HotJava.
Mary Enters the Picture
In early 1995, we hired a contract writer named Mary Campione. She and I knew
of each other from her time in NeXT developer support. Mary’s job was to help
programmers use platform features such as threads. We soon realized that our
work was too similar for us to do it separately, and we started working together
on a programmer’s guide for the Java platform.
On May 18, 1995, Mary Campione and I released the first version of our guide,
which we called The Java Programmer’s Guide. It was an incomplete first
draft—nothing pretty—but it provided people with the information they needed
to get started programming for the Java platform.
FOREWORD
The next week, Sun officially announced the Java platform at a show called SunWorld. The best part of the show for us was the announcement that Netscape had
agreed (just hours before) to support applets in their Web browser.
In the following months, Mary and I continued to add to and refine our programmer’s guide. 1We worked together closely, sharing the same office and even the
same train commute from San Francisco to Palo Alto. By coincidence, we even
got pregnant within days of each other.
By late 1995, the first wave of books in The Java Series was being developed.
The Java Series was a group of books published by Addison-Wesley and written
mainly by employees of what used to be FirstPerson. By that time, FirstPerson
had been absorbed back into Sun, in the form of a division called JavaSoft. The
Series Editor was JavaSoft technical publications manager Lisa Friendly.2
Our programmer’s guide was slated to be one of the books in The Java Series,
but the publisher wanted it to have a less intimidating name. So we changed its
name to The Java Tutorial. There we were, two increasingly large women working insanely long hours to finish the book before the babies arrived in mid-1996.
We managed—just barely—to get the book to our publisher in time. We couldn’t
have done it without the help of yet another ex-NeXTer, Randy Nelson, who
took care of all the final details of the book and Web site.
The Tutorial Team Grows
When Mary and I returned from maternity leave, we felt completely overwhelmed. Our book and Web site covered the 1.0 version of the Java platform
(JDK 1.0), but JDK 1.1 was scheduled to be released soon and work had already
started on JDK 1.2 (which would be renamed to the Java 2 Platform, Standard
Edition, Version 1.2—J2SE v 1.2, for short). We would be able to update our
existing documentation to 1.1, but for 1.2 we’d need help.
Help arrived in the form of guest authors and Alison Huml. The guest authors
were writers and engineers on the teams developing the new 1.2 features. Alison
was a postgraduate student with experience in both software and publishing. She
did whatever was necessary to make the Tutorial succeed, ranging from producing camera-ready copy for books to writing text and examples.
1
2
By looking at http://java.sun.com/docs/books/tutorial/information/his
tory.html, you can see what was in each of our updates.
Lisa has some great anecdotes about the early days of FirstPerson. You can read some of
them at http://java.sun.com/features/1998/05/birthday.html.
xix
xx
FOREWORD
Between 1998 and 2000, the Tutorial team updated the Web site many times and
produced two completely new books, as well as two major revisions of the original book. In mid-2000, Mary retired from paid work. Alison and I still work on
The Java Tutorial, in both its Web and book forms. Although we rely on guest
authors from time to time, the rate of change has become less frantic as the J2SE
platform matures.
The J2EE Tutorial
Now there’s a new platform—and a new tutorial—in town. The success of the
Java 2 Platform, Enterprise Edition has been phenomenal. Developers are clamoring for information about how to write applications using this new Java platform for the server. And this book helps, continuing the tradition of The Java
Tutorial, but this time for the J2EE platform. Like the original Tutorial, this is an
example-filled, easy-to-use entry point and quick reference for programming
with the J2EE platform. And I’m sure, like the original tutorial team, Stephanie,
Dale, Eric, Kim, and Beth all have stories to tell about the time they’ve spent
working on the J2EE platform and bringing you this book.
Just a note—Because the J2EE platform sits on top of the J2SE platform, you
need to be comfortable writing programs for the J2SE platform before you can
make full use of this book. If you’re not comfortable with the J2SE platform, go
to The Java Tutorial1 and learn!
Then come back here, so you can find out all about developing and deploying
applications for the J2EE platform.
Kathy Walrath
Sun Microsystems
San Francisco, CA
December 21, 2001
1
On the Web at http://java.sun.com/docs/books/tutorial/, or in book form as
The Java Tutorial: A Short Course on the Basics.
Preface
THE Java Tutorial has been an indispensable resource for many programmers
learning the Java programming language. This tutorial hopes to serve the same
role for developers encountering the Java™ 2 Platform, Enterprise Edition
(J2EE™) for the first time. It follows an example-oriented focus similar to the
Java Tutorial.
Who Should Use This Tutorial
This tutorial is intended for programmers interested in developing and deploying
J2EE applications. It covers the main component technologies comprising the
J2EE platform and describes how to develop J2EE components and deploy them
on the J2EE Software Development Kit (SDK).
This tutorial is not intended for J2EE server or tool vendors. It does not explain
how to implement the J2EE architecture, nor does it explain the internals of the
J2EE SDK. The J2EE specifications describe the J2EE architecture and can be
downloaded from
http://java.sun.com/j2ee/docs.html#specs
About the Examples
This tutorial includes many complete, working examples. See
Examples, page (449) for a list of the examples and the chapters where they
appear.
xxii
PREFACE
Prerequisites for the Examples
To understand the examples, you will need a good knowledge of the Java programming language, SQL, and relational database concepts. The topics in the
Java Tutorial listed in Table 1 are particularly relevant:
Table 1 Prerequisite Topics
Topic
Java Tutorial
JDBC™
http://java.sun.com/docs/books/tutorial/jdbc
Threads
http://java.sun.com/docs/books/tutorial/essential/threads
JavaBeans™
http://java.sun.com/docs/books/tutorial/javabeans
Security
http://java.sun.com/docs/books/tutorial/security1.2
Downloading the Examples
If you are viewing this online and you want to build and run the examples, you
need to download the tutorial bundle from
http://java.sun.com/j2ee/download.html#tutorial
Once you have installed the bundle, the example source code is in the
j2eetutorial/examples/src directory, with subdirectories ejb for enterprise
bean technology examples, web for Web technology examples, and connector
for connector technology examples. For most of the examples, the bundle also
includes J2EE application Enterprise Archive EAR files, which are located in the
j2eetutorial/examples/ears directory.
How to Build and Run the Examples
This tutorial documents the J2EE SDK version 1.3. To build, deploy, and run the
examples you need a copy of the J2EE SDK 1.3 and the Java 2 Platform, Standard Edition (J2SE™) SDK 1.3.1 (earlier versions were called JDK). You can
download the J2EE SDK from
http://java.sun.com/j2ee/download.html#sdk
PREFACE
xxiii
and the J2SE 1.3.1 from:
http://java.sun.com/j2se/1.3/
The examples are distributed with a configuration file for version 1.3 of ant a
portable make tool. The ant utility is hosted by the Jakarta project at the Apache
Software Foundation. You can download ant from
http://jakarta.apache.org/builds/jakartaant/release/v1.3/bin
To build the tutorial examples:
1. Download and install the J2SE SDK 1.3.1, J2EE SDK 1.3, and ant.
2. The installation instructions for the J2SE SDK, J2EE SDK, and ant
explain how to set the required environment variables. Verify that the
environment variables have been set to the values noted in the Table 1.
Table 1 Settings for Environment Variables
Environment Variable
Value
JAVA_HOME
The location of the J2SE SDK installation.
J2EE_HOME
The location of the J2EE SDK installation.
ANT_HOME
The location of the ant installation.
PATH
Should include the bin directories of the J2EE SDK, J2SE SDK,
and ant installations.
3. Go to the j2eetutorial/examples directory.
4. Execute ant target. For example, to build all the examples, execute ant
all; to build the Web layer examples, execute ant web. The build process
deposits the output into the directory j2eetutorial/examples/build.
xxiv
PREFACE
Related Information
This tutorial provides a concise overview of how to use the central component
technologies in the J2EE platform. For more information about these technologies, see the Web sites listed in Table 2
Table 2 Information Sources
Component Technology
Web Site
Enterprise JavaBeans™ (EJB™)
http://java.sun.com/products/ejb
Java Servlet
http://java.sun.com/products/servlets
JavaServer Pages™ (JSP™)
http://java.sun.com/products/jsp
The J2EE platform includes a wide variety of APIs that this tutorial only briefly
touches on. Some of these technologies have their own tutorials, which are listed
in Table 3.
Table 3 Other Tutorials
API
Tutorial
Java Message Service (JMS)
http://java.sun.com/products/jms/tutorial/
Java Naming and Directory
Interface™ (JNDI)
http://java.sun.com/products/jndi/tutorial/
Java API for XML Processing
(JAXP)
http://java.sun.com/xml/jaxp/dist/1.1/docs/
tutorial/index.html
PREFACE
For complete information on these topics, see the Web sites listed in Table 4.
Table 4 Other Web sites
API
Web Site
J2EE Connector
http://java.sun.com/j2ee/connector
JAXP
http://java.sun.com/products/jaxp
JavaMail™
http://java.sun.com/products/javamail
JMS
http://java.sun.com/products/jms
JNDI
http://java.sun.com/products/jndi
JDBC™
http://java.sun.com/products/jdbc
Once you have become familiar with the J2EE technologies described in this
tutorial, you may be interested in guidelines for architecting J2EE applications.
The J2EE BluePrints illustrate best practices for developing and deploying J2EE
applications. You can obtain the J2EE BluePrints from
http://java.sun.com/blueprints
How to Print This Tutorial
To print this tutorial, follow these steps:
1. Ensure that Adobe Acrobat Reader is installed on your system.
2. Download the PDF version of this book from
http://java.sun.com/j2ee/download.html#tutorial.
3. Click the printer icon in Adobe Acrobat Reader.
xxv
xxvi
PREFACE
Typographical Conventions
Table 5 lists the typographical conventions used in this tutorial.
Table 5 Typographical Conventions
Font Style
Uses
Italic
Emphasis, titles, first occurrence of terms
Monospace
URLs, code examples, file names, command
names, programming language keywords
Italic monospace
Programming variables, variable file names
Menu selections indicated with the right-arrow character →, for example,
First→Second, should be interpreted as: select the First menu, then choose Second from the First submenu.
Acknowledgments
The J2EE tutorial team would like to thank the J2EE SDK team for their technical advice.
We are extremely grateful to the many internal and external reviewers who provided feedback on the tutorial. This helped us to improve the presentation, correct errors, and eliminate bugs.
We would also like to thank our manager, Jim Inscore, for his support and
steadying influence.
The chapters on Web components use an example and some material that first
appeared in the servlet trail of the Java Tutorial. The chapters on custom tags and
the Duke’s Bank application use a template tag library that first appeared in the
J2EE BluePrints.
1
Overview
Monica Pawlan
TODAY, more and more developers want to write distributed transactional
applications for the enterprise and leverage the speed, security, and reliability of
server-side technology. If you are already working in this area, you know that in
today’s fast-moving and demanding world of e-commerce and information technology, enterprise applications have to be designed, built, and produced for less
money, with greater speed, and with fewer resources than ever before.
To reduce costs and fast-track enterprise application design and development,
the Java™ 2 Platform, Enterprise Edition (J2EE™) technology provides a component-based approach to the design, development, assembly, and deployment of
enterprise applications. The J2EE platform offers a multitiered distributed application model, the ability to reuse components, integrated Extensible Markup
Language (XML)-based data interchange, a unified security model, and flexible
transaction control. Not only can you deliver innovative customer solutions to
market faster than ever, but your platform-independent J2EE component-based
solutions are not tied to the products and application programming interfaces
(APIs) of any one vendor. Vendors and customers enjoy the freedom to choose
the products and components that best meet their business and technological
requirements.
This tutorial takes an examples-based approach to describing the features and
functionalities available in J2EE Software Development Kit (SDK) version 1.3.
Whether you are a new or an experienced enterprise developer, you should find
the examples and accompanying text a valuable and accessible knowledge base
for creating your own enterprise solutions.
1
2
OVERVIEW
If you are new to J2EE applications development, this chapter is a good place to
start. Here you will learn the J2EE architecture, become acquainted with important terms and concepts, and find out how to approach J2EE application programming, assembly, and deployment.
In This Chapter
Distributed Multitiered Applications 2
J2EE Components 3
J2EE Clients 4
Web Components 6
Business Components 7
Enterprise Information System Tier 8
J2EE Containers 8
Container Services 8
Container Types 10
Packaging 10
Development Roles 11
J2EE Product Provider 12
Tool Provider 12
Application Component Provider 12
Application Assembler 13
Application Deployer and Administrator 14
Reference Implementation Software 14
Database Access 15
J2EE APIs 15
Simplified Systems Integration 18
Tools 19
Distributed Multitiered Applications
The J2EE platform uses a multitiered distributed application model. Application
logic is divided into components according to function, and the various application components that make up a J2EE application are installed on different
machines depending on the tier in the multitiered J2EE environment to which the
application component belongs. Figure 1–1 shows two multitiered J2EE applications divided into the tiers described in the following list. The J2EE application
parts shown in Figure 1–1 are presented in J2EE Components, page (3).
• Client-tier components run on the client machine.
• Web-tier components run on the J2EE server.
• Business-tier components run on the J2EE server.
DISTRIBUTED MULTITIERED APPLICATIONS
• Enterprise information system (EIS)-tier software runs on the EIS server.
Although a J2EE application can consist of the three or four tiers shown in Figure 1–1, J2EE multitiered applications are generally considered to be three-tiered
applications because they are distributed over three different locations: client
machines, the J2EE server machine, and the database or legacy machines at the
back end. Three-tiered applications that run in this way extend the standard twotiered client and server model by placing a multithreaded application server
between the client application and back-end storage.
Figure 1–1 Multitiered Applications
J2EE Components
J2EE applications are made up of components. A J2EE component is a self-contained functional software unit that is assembled into a J2EE application with its
related classes and files and that communicates with other components. The
J2EE specification defines the following J2EE components:
• Application clients and applets are components that run on the client.
• Java Servlet and JavaServer Pages™ (JSP™) technology components are
Web components that run on the server.
3
4
OVERVIEW
• Enterprise JavaBeans™ (EJB™) components (enterprise beans) are business components that run on the server.
J2EE components are written in the Java programming language and are compiled in the same way as any program in the language. The difference between
J2EE components and “standard” Java classes is that J2EE components are
assembled into a J2EE application, verified to be well formed and in compliance
with the J2EE specification, and deployed to production, where they are run and
managed by the J2EE server.
J2EE Clients
A J2EE client can be a Web client or an application client.
Web Clients
A Web client consists of two parts: dynamic Web pages containing various types
of markup language (HTML, XML, and so on), which are generated by Web
components running in the Web tier, and a Web browser, which renders the
pages received from the server.
A Web client is sometimes called a thin client. Thin clients usually do not do
things like query databases, execute complex business rules, or connect to legacy
applications. When you use a thin client, heavyweight operations like these are
off-loaded to enterprise beans executing on the J2EE server where they can
leverage the security, speed, services, and reliability of J2EE server-side technologies.
Applets
A Web page received from the Web tier can include an embedded applet. An
applet is a small client application written in the Java programming language
that executes in the Java virtual machine installed in the Web browser. However,
client systems will likely need the Java Plug-in and possibly a security policy file
in order for the applet to successfully execute in the Web browser.
Web components are the preferred API for creating a Web client program
because no plug-ins or security policy files are needed on the client systems.
Also, Web components enable cleaner and more modular application design
because they provide a way to separate applications programming from Web
page design. Personnel involved in Web page design thus do not need to understand Java programming language syntax to do their jobs.
DISTRIBUTED MULTITIERED APPLICATIONS
Application Clients
A J2EE application client runs on a client machine and provides a way for users
to handle tasks that require a richer user interface than can be provided by a
markup language. It typically has a graphical user interface (GUI) created from
Swing or Abstract Window Toolkit (AWT) APIs, but a command-line interface
is certainly possible.
Application clients directly access enterprise beans running in the business tier.
However, if application requirements warrant it, a J2EE application client can
open an HTTP connection to establish communication with a servlet running in
the Web tier.
JavaBeans™ Component Architecture
The server and client tiers might also include components based on the JavaBeans component architecture (JavaBeans component) to manage the data flow
between an application client or applet and components running on the J2EE
server or between server components and a database. JavaBeans components are
not considered J2EE components by the J2EE specification.
JavaBeans components have instance variables and get and set methods for
accessing the data in the instance variables. JavaBeans components used in this
way are typically simple in design and implementation, but should conform to
the naming and design conventions outlined in the JavaBeans component architecture.
J2EE Server Communications
Figure 1–2 shows the various elements that can make up the client tier. The client communicates with the business tier running on the J2EE server either
directly or, as in the case of a client running in a browser, by going through JSP
pages or servlets running in the Web tier.
Your J2EE application uses a thin browser-based client or thick application client. In deciding which one to use, you should be aware of the trade-offs between
keeping functionality on the client and close to the user (thick client) and offloading as much functionality as possible to the server (thin client). The more
functionality you off-load to the server, the easier it is to distribute, deploy, and
manage the application; however, keeping more functionality on the client can
make for a better perceived user experience.
5
6
OVERVIEW
Figure 1–2 Server Communications
Web Components
J2EE Web components can be either servlets or JSP pages. Servlets are Java programming language classes that dynamically process requests and construct
responses. JSP pages are text-based documents that execute as servlets but allow
a more natural approach to creating static content.
Static HTML pages and applets are bundled with Web components during application assembly, but are not considered Web components by the J2EE specification. Server-side utility classes can also be bundled with Web components and,
like HTML pages, are not considered Web components.
Like the client tier and as shown in Figure 1–3, the Web tier might include a JavaBeans component to manage the user input and send that input to enterprise
beans running in the business tier for processing.
DISTRIBUTED MULTITIERED APPLICATIONS
Figure 1–3 Web Tier and J2EE Application
Business Components
Business code, which is logic that solves or meets the needs of a particular business domain such as banking, retail, or finance, is handled by enterprise beans
running in the business tier. Figure 1–4 shows how an enterprise bean receives
data from client programs, processes it (if necessary), and sends it to the enterprise information system tier for storage. An enterprise bean also retrieves data
from storage, processes it (if necessary), and sends it back to the client program.
Figure 1–4 Business and EIS Tiers
7
8
OVERVIEW
There are three kinds of enterprise beans: session beans, entity beans, and message-driven beans. A session bean represents a transient conversation with a client. When the client finishes executing, the session bean and its data are gone. In
contrast, an entity bean represents persistent data stored in one row of a database
table. If the client terminates or if the server shuts down, the underlying services
ensure that the entity bean data is saved.
A message-driven bean combines features of a session bean and a Java Message
Service (JMS) message listener, allowing a business component to receive JMS
messages asynchronously. This tutorial describes entity beans and session beans.
For information on message-driven beans, see the Java Message Service Tutorial, available at
http://java.sun.com/products/jms/tutorial/index.html
Enterprise Information System Tier
The enterprise information system tier handles enterprise information system
software and includes enterprise infrastructure systems such as enterprise
resource planning (ERP), mainframe transaction processing, database systems,
and other legacy information systems. J2EE application components might need
access to enterprise information systems for database connectivity, for example.
J2EE Containers
Normally, thin-client multitiered applications are hard to write because they
involve many lines of intricate code to handle transaction and state management,
multithreading, resource pooling, and other complex low-level details. The component-based and platform-independent J2EE architecture makes J2EE applications easy to write because business logic is organized into reusable components.
In addition, the J2EE server provides underlying services in the form of a container for every component type. Because you do not have to develop these services yourself, you are free to concentrate on solving the business problem at
hand.
Container Services
Containers are the interface between a component and the low-level platformspecific functionality that supports the component. Before a Web, enterprise
bean, or application client component can be executed, it must be assembled into
a J2EE application and deployed into its container.
J2EE CONTAINERS
The assembly process involves specifying container settings for each component
in the J2EE application and for the J2EE application itself. Container settings
customize the underlying support provided by the J2EE server, which includes
services such as security, transaction management, Java Naming and Directory
Interface™ (JNDI) lookups, and remote connectivity. Here are some of the highlights:
• The J2EE security model lets you configure a Web component or enterprise bean so that system resources are accessed only by authorized users.
• The J2EE transaction model lets you specify relationships among methods
that make up a single transaction so that all methods in one transaction are
treated as a single unit.
• JNDI lookup services provide a unified interface to multiple naming and
directory services in the enterprise so that application components can
access naming and directory services.
• The J2EE remote connectivity model manages low-level communications
between clients and enterprise beans. After an enterprise bean is created,
a client invokes methods on it as if it were in the same virtual machine.
The fact that the J2EE architecture provides configurable services means that
application components within the same J2EE application can behave differently
based on where they are deployed. For example, an enterprise bean can have
security settings that allow it a certain level of access to database data in one production environment and another level of database access in another production
environment.
The container also manages nonconfigurable services such as enterprise bean
and servlet life cycles, database connection resource pooling, data persistence,
and access to the J2EE platform APIs described in the section J2EE
APIs, page (15). Although data persistence is a nonconfigurable service, the
J2EE architecture lets you override container-managed persistence by including
the appropriate code in your enterprise bean implementation when you want
more control than the default container-managed persistence provides. For
example, you might use bean-managed persistence to implement your own
finder (search) methods or to create a customized database cache.
9
10
OVERVIEW
Container Types
The deployment process installs J2EE application components in the J2EE containers illustrated in Figure 1–5.
• J2EE server: Is the runtime portion of a J2EE product. A J2EE server provides EJB and Web containers.
• Enterprise JavaBeans (EJB) container: Manages the execution of enterprise beans for J2EE applications. Enterprise beans and their container run
on the J2EE server.
• Web container: Manages the execution of JSP page and servlet components for J2EE applications. Web components and their container run on
the J2EE server.
• Application client container: Manages the execution of application client
components. Application clients and their container run on the client.
• Applet container: Manages the execution of applets. Consists of a Web
browser and Java Plug-in running on the client together.
Figure 1–5 J2EE Server and Containers
Packaging
J2EE components are packaged separately and bundled into a J2EE application
for deployment. Each component, its related files such as GIF and HTML files
DEVELOPMENT ROLES
or server-side utility classes, and a deployment descriptor are assembled into a
module and added to the J2EE application. A J2EE application is composed of
one or more enterprise bean, Web, or application client component modules. The
final enterprise solution can use one J2EE application or be made up of two or
more J2EE applications, depending on design requirements.
A J2EE application and each of its modules has its own deployment descriptor.
A deployment descriptor is an XML document with an .xml extension that
describes a component’s deployment settings. An enterprise bean module
deployment descriptor, for example, declares transaction attributes and security
authorizations for an enterprise bean. Because deployment descriptor information is declarative, it can be changed without modifying the bean source code. At
run time, the J2EE server reads the deployment descriptor and acts upon the
component accordingly.
A J2EE application with all of its modules is delivered in an Enterprise ARchive
(EAR) file. An EAR file is a standard Java Archive (JAR) file with an .ear
extension. In the GUI version of the J2EE SDK application deployment tool, you
create an EAR file first and add JAR and Web Archive (WAR) files to the EAR.
If you use the command line packager tools, however, you create the JAR and
WAR files first and then create the EAR. The J2EE SDK tools are described in
the section Tools, page (19).
• Each EJB JAR file contains a deployment descriptor, the enterprise bean
files, and related files.
• Each application client JAR file contains a deployment descriptor, the
class files for the application client, and related files.
• Each WAR file contains a deployment descriptor, the Web component
files, and related resources.
Using modules and EAR files makes it possible to assemble a number of different J2EE applications using some of the same components. No extra coding is
needed; it is just a matter of assembling various J2EE modules into J2EE EAR
files.
Development Roles
Reusable modules make it possible to divide the application development and
deployment process into distinct roles so that different people or companies can
perform different parts of the process.
11
12
OVERVIEW
The first two roles involve purchasing and installing the J2EE product and tools.
Once software is purchased and installed, J2EE components can be developed by
application component providers, assembled by application assemblers, and
deployed by application deployers. In a large organization, each of these roles
might be executed by different individuals or teams. This division of labor works
because each of the earlier roles outputs a portable file that is the input for a subsequent role. For example, in the application component development phase, an
enterprise bean software developer delivers EJB JAR files. In the application
assembly role, another developer combines these EJB JAR files into a J2EE
application and saves it in an EAR file. In the application deployment role, a system administrator at the customer site uses the EAR file to install the J2EE application into a J2EE server.
The different roles are not always executed by different people. If you work for a
small company, for example, or if you are prototyping a sample application, you
might perform the tasks in every phase.
J2EE Product Provider
The J2EE product provider is the company that designs and makes available for
purchase the J2EE platform, APIs, and other features defined in the J2EE specification. Product providers are typically operating system, database system,
application server, or Web server vendors who implement the J2EE platform
according to the Java 2 Platform, Enterprise Edition Specification.
Tool Provider
The tool provider is the company or person who creates development, assembly,
and packaging tools used by component providers, assemblers, and deployers.
See the section Tools, page (19) for information on the tools available with J2EE
SDK version 1.3.
Application Component Provider
The application component provider is the company or person who creates Web
components, enterprise beans, applets, or application clients for use in J2EE
applications.
DEVELOPMENT ROLES
Enterprise Bean Developer
An enterprise bean developer performs the following tasks to deliver an EJB
JAR file that contains the enterprise bean:
• Writes and compiles the source code
• Specifies the deployment descriptor
• Bundles the .class files and deployment descriptor into an EJB JAR file
Web Component Developer
A Web component developer performs the following tasks to deliver a WAR file
containing the Web component:
•
•
•
•
Writes and compiles servlet source code
Writes JSP and HTML files
Specifies the deployment descriptor for the Web component
Bundles the .class, .jsp, .html, and deployment descriptor files in the
WAR file
J2EE Application Client Developer
An application client developer performs the following tasks to deliver a JAR
file containing the J2EE application client:
• Writes and compiles the source code
• Specifies the deployment descriptor for the client
• Bundles the .class files and deployment descriptor into the JAR file
Application Assembler
The application assembler is the company or person who receives application
component JAR files from component providers and assembles them into a J2EE
application EAR file. The assembler or deployer can edit the deployment
descriptor directly or use tools that correctly add XML tags according to interactive selections. A software developer performs the following tasks to deliver an
EAR file containing the J2EE application:
• Assembles EJB JAR and WAR files created in the previous phases into a
J2EE application (EAR) file.
• Specifies the deployment descriptor for the J2EE application
13
14
OVERVIEW
• Verifies that the contents of the EAR file are well formed and comply with
the J2EE specification
Application Deployer and Administrator
The application deployer and administrator is the company or person who configures and deploys the J2EE application, administers the computing and networking infrastructure where J2EE applications run, and oversees the runtime
environment. Duties include such things as setting transaction controls and security attributes and specifying connections to databases.
During configuration, the deployer follows instructions supplied by the application component provider to resolve external dependencies, specify security settings, and assign transaction attributes. During installation, the deployer moves
the application components to the server and generates the container-specific
classes and interfaces.
A deployer/system administrator performs the following tasks to install and configure a J2EE application:
• Adds the J2EE application (EAR) file created in the preceding phase to the
J2EE server
• Configures the J2EE application for the operational environment by modifying the deployment descriptor of the J2EE application
• Verifies that the contents of the EAR file are well formed and comply with
the J2EE specification
• Deploys (installs) the J2EE application EAR file into the J2EE server
Reference Implementation Software
The J2EE SDK is a noncommercial operational definition of the J2EE platform
and specification made freely available by Sun Microsystems for demonstrations, prototyping, and educational use. It comes with the J2EE application
server, Web server, relational database, J2EE APIs, and complete set of development and deployment tools. You can download the J2EE SDK from the Web
http://java.sun.com/j2ee/download.html#sdk
The purpose of the J2EE SDK is to allow product providers to determine what
their implementations must do under a given set of application conditions, and to
run the J2EE Compatibility Test Suite to test that their J2EE products fully com-
REFERENCE IMPLEMENTATION SOFTWARE
ply with the specification. It also allows application component developers to
run their J2EE applications on the J2EE SDK to verify that applications are fully
portable across all J2EE products and tools.
Database Access
The relational database provides persistent storage for application data. A J2EE
implementation is not required to support a particular type of database, which
means that the database supported by different J2EE products can vary. See the
Release Notes included with the J2EE SDK download for a list of the databases
currently supported by the reference implementation.
J2EE APIs
The Java 2 Platform, Standard Edition (J2SE™) SDK is required to run the J2EE
SDK and provides core APIs for writing J2EE components, core development
tools, and the Java virtual machine. The J2EE SDK provides the following APIs
to be used in J2EE applications.
Enterprise JavaBeans Technology 2.0
An enterprise bean is a body of code with fields and methods to implement modules of business logic. You can think of an enterprise bean as a building block
that can be used alone or with other enterprise beans to execute business logic on
the J2EE server.
There are three kinds of enterprise beans: session beans, entity beans, and message-driven beans. Enterprise beans often interact with databases. One of the
benefits of entity beans is that you do not have to write any SQL code or use the
JDBC™ API directly to perform database access operations; the EJB container
handles this for you. However, if you override the default container-managed
persistence for any reason, you will need to use the JDBC API. Also, if you
choose to have a session bean access the database, you have to use the JDBC
API.
JDBC API 2.0
The JDBC API lets you invoke SQL commands from Java programing language
methods. You use the JDBC API in an enterprise bean when you override the
default container-managed persistence or have a session bean access the database. With container-managed persistence, database access operations are handled by the container, and your enterprise bean implementation contains no
JDBC code or SQL commands. You can also use the JDBC API from a servlet or
15
16
OVERVIEW
JSP page to access the database directly without going through an enterprise
bean.
The JDBC API has two parts: an application-level interface used by the application components to access a database, and a service provider interface to attach a
JDBC driver to the J2EE platform.
Java Servlet Technology 2.3
Java Servlet technology lets you define HTTP-specific servlet classes. A servlet
class extends the capabilities of servers that host applications accessed by way of
a request-response programming model. Although servlets can respond to any
type of request, they are commonly used to extend the applications hosted by
Web servers.
JavaServer Pages Technology 1.2
JavaServer Pages technology lets you put snippets of servlet code directly into a
text-based document. A JSP page is a text-based document that contains two
types of text: static template data, which can be expressed in any text-based format such as HTML, WML, and XML, and JSP elements, which determine how
the page constructs dynamic content.
Java Message Service 1.0
The JMS is a messaging standard that allows J2EE application components to
create, send, receive, and read messages. It enables distributed communication
that is loosely coupled, reliable, and asynchronous. For more information on
JMS, see the online Java Message Service Tutorial:
http://java.sun.com/products/jms/tutorial/index.html
Java Naming and Directory Interface 1.2
The JNDI provides naming and directory functionality. It provides applications
with methods for performing standard directory operations, such as associating
attributes with objects and searching for objects using their attributes. Using
JNDI, a J2EE application can store and retrieve any type of named Java object.
Because JNDI is independent of any specific implementations, applications can
use JNDI to access multiple naming and directory services, including existing
naming and directory services such as LDAP, NDS, DNS, and NIS. This allows
J2EE applications to coexist with legacy applications and systems. For more
information on JNDI, see the online JNDI Tutorial:
REFERENCE IMPLEMENTATION SOFTWARE
http://java.sun.com/products/jndi/tutorial/index.html
Java Transaction API 1.0
The Java Transaction API (JTA) provides a standard interface for demarcating
transactions. The J2EE architecture provides a default auto commit to handle
transaction commits and rollbacks. An auto commit means that any other applications viewing data will see the updated data after each database read or write
operation. However, if your application performs two separate database access
operations that depend on each other, you will want to use the JTA API to
demarcate where the entire transaction, including both operations, begins, rolls
back, and commits.
JavaMail™ API 1.2
J2EE applications can use the JavaMail API to send e-mail notifications. The
JavaMail API has two parts: an application-level interface used by the application components to send mail, and a service provider interface. The J2EE platform includes JavaMail with a service provider that allows application
components to send Internet mail.
JavaBeans Activation Framework 1.0
The JavaBeans Activation Framework (JAF) is included because JavaMail uses
it. It provides standard services to determine the type of an arbitrary piece of
data, encapsulate access to it, discover the operations available on it, and create
the appropriate JavaBeans component to perform those operations.
Java API for XML Processing 1.1
XML is a language for representing text-based data so the data can be read and
handled by any program or tool. Programs and tools can generate XML documents that other programs and tools can read and handle. Java API for XML
Processing (JAXP) supports processing of XML documents using DOM, SAX,
and XSLT. JAXP enables applications to parse and transform XML documents
independent of a particular XML processing implementation.
For example, a J2EE application can use XML to produce reports, and different
companies that receive the reports can handle the data in a way that best suits
their needs. One company might put the XML data through a program to translate the XML to HTML so it can post the reports to the Web, another company
might put the XML data through a tool to create a marketing presentation, and
yet another company might read the XML data into its J2EE application for processing.
17
18
OVERVIEW
J2EE Connector Architecture 1.0
The J2EE Connector Architecture is used by J2EE tools vendors and system
integrators to create resource adapters that support access to enterprise information systems that can be plugged into any J2EE product. A resource adapter is a
software component that allows J2EE application components to access and
interact with the underlying resource manager. Because a resource adapter is
specific to its resource manager, there is typically a different resource adapter for
each type of database or enterprise information system.
Java Authentication and Authorization Service 1.0
The Java Authentication and Authorization Service (JAAS) provides a way for a
J2EE application to authenticate and authorize a specific user or group of users
to run it.
JAAS is a Java programing language version of the standard Pluggable Authentication Module (PAM) framework that extends the Java 2 Platform security
architecture to support user-based authorization.
Simplified Systems Integration
The J2EE platform is a platform-independent, full systems integration solution
that creates an open marketplace in which every vendor can sell to every customer. Such a marketplace encourages vendors to compete, not by trying to lock
customers into their technologies but by trying to outdo each other by providing
products and services that benefit customers, such as better performance, better
tools, or better customer support.
The J2EE APIs enable systems and applications integration through the following:
•
•
•
•
•
•
•
Unified application model across tiers with enterprise beans
Simplified response and request mechanism with JSP pages and servlets
Reliable security model with JAAS
XML-based data interchange integration with JAXP
Simplified interoperability with the J2EE Connector Architecture
Easy database connectivity with the JDBC API
Enterprise application integration with message-driven beans and JMS,
JTA, and JNDI
You can learn more about using the J2EE platform to build integrated business
systems by reading J2EE Technology in Practice:
REFERENCE IMPLEMENTATION SOFTWARE
http://java.sun.com/j2ee/inpractice/aboutthebook.html
Tools
The J2EE reference implementation provides an application deployment tool
and an array of scripts for assembling, verifying, and deploying J2EE applications and managing your development and production environments. See
Appendix B for a discussion of the tools.
Application Deployment Tool
The J2EE reference implementation provides an application deployment tool
(deploytool) for assembling, verifying, and deploying J2EE applications. There
are two versions: command line and GUI.
The GUI tool includes wizards for
•
•
•
•
•
Packaging, configuring, and deploying J2EE applications
Packaging and configuring enterprise beans
Packaging and configuring Web components
Packaging and configuring application clients
Packaging and configuring resource adaptors
In addition, configuration information can be set for each component and module type in the tabbed inspector panes.
Scripts
Table 1–1 lists the scripts included with the J2EE reference implementation that
let you perform operations from the command line.
Table 1–1 J2EE Scripts
Script
Description
j2ee
Start and stop the J2EE server
cloudscape
Start and stop the default database
j2eeadmin
Add JDBC drivers, JMS destinations, and connection factories for various
resources
keytool
Create public and private keys and generate X509 self-signed certificate.
19
20
OVERVIEW
Table 1–1 J2EE Scripts (Continued)
Script
Description
realmtool
Import certificate files. Add J2EE users to and remove J2EE users from the
authentication and authorization list for a J2EE application
packager
Package J2EE application components into EAR, EJB JAR, application client JAR, and WAR files
verifier
Verify that EAR, EJB JAR, application client JAR, and WAR files are wellformed and comply with the J2EE specification
runclient
Run a J2EE application client
cleanup
Remove all deployed applications from the J2EE server
2
Getting Started
Dale Green
T
HIS chapter shows how to develop, deploy, and run a simple client-server
application that consists of a currency conversion enterprise bean and two clients: a J2EE™ application client and a Web client that consists of a JSP page.
In This Chapter
Setting Up 22
Getting the Example Code 22
Getting the Build Tool (ant) 22
Checking the Environment Variables 23
Starting the J2EE™ Server 23
Starting the deploytool 23
Creating the J2EE™ Application 24
Creating the Enterprise Bean 24
Coding the Enterprise Bean 24
Compiling the Source Files 26
Packaging the Enterprise Bean 27
Creating the J2EE™ Application Client 28
Coding the J2EE Application Client 28
Compiling the Application Client 31
Packaging the J2EE Application Client 31
Specifying the Application Client’s Enterprise Bean Reference 32
Creating the Web Client 32
Coding the Web Client 33
Compiling the Web Client 34
Packaging the Web Client 34
Specifying the Web Client’s Enterprise Bean Reference 35
21
22
GETTING STARTED
Specifying the JNDI Names 36
Deploying the J2EE™ Application 37
Running the J2EE™ Application Client 38
Running the Web Client 38
Modifying the J2EE™ Application 39
Modifying a Class File 39
Adding a File 40
Modifying the Web Client 40
Modifying a Deployment Setting 41
Common Problems and Their Solutions 41
Cannot Start the J2EE Server 41
Compilation Errors 42
Deployment Errors 43
J2EE Application Client Runtime Errors 44
Web Client Runtime Errors 45
Detecting Problems With the Verifier Tool 46
Comparing Your EAR Files with Ours 46
When All Else Fails 46
Setting Up
Before you start developing the example application, you should follow the
instructions in this section.
Getting the Example Code
The source code for the components is in j2eetutorial/exam
ples/src/ejb/converter, a directory that is created when you unzip the tutorial bundle. If you are viewing this tutorial online, you need to download the
tutorial bundle from
http://java.sun.com/j2ee/download.html#tutorial
Getting the Build Tool (ant)
To build the example code, you’ll need installations of the J2EE SDK and ant, a
portable make tool. For more information, see the section How to Build and Run
the Examples, page (xxii).
SETTING UP
Checking the Environment Variables
The installation instructions for the J2EE SDK and ant explain how to set the
required environment variables. Verify that the environment variables have been
set to the values noted in Table 2–1.
Table 2–1 Required Environment Variables
Environment Variable
Value
JAVA_HOME
The location of the J2SE™ SDK installation.
J2EE_HOME
The location of the J2EE™ SDK installation.
ANT_HOME
The location of the ant installation.
PATH
Should include the bin directories of the J2EE SDK, J2SE, and
ant installations.
Starting the J2EE™ Server
To launch the J2EE server, open a terminal window and type this command:
j2ee verbose
Although not required, the verbose option is useful for debugging.
To stop the server, type the following command:
j2ee stop
Starting the deploytool
The deploytool utility has two modes: command line and GUI. The instructions
in this chapter refer to the GUI version. To start the deploytool GUI, open a terminal window and type this command:
deploytool
To view the tool’s context-sensitive help, press the F1 key.
23
24
GETTING STARTED
Creating the J2EE™ Application
The sample application contains three J2EE components: an enterprise bean, a
J2EE application client, and a Web component. Before building these components, you will create a new J2EE application called ConverterApp and will
store it in an EAR file named ConverterApp.ear.
1. In deploytool, select File→New→Application.
2. Click Browse.
3. In the file chooser, navigate to j2eetutorial/examples/src/ejb/con
verter.
4. In the File Name field, enter ConverterApp.ear.
5. Click New Application.
6. Click OK.
Creating the Enterprise Bean
An enterprise bean is a server-side component that contains the business logic of
an application. At runtime, the application clients execute the business logic by
invoking the enterprise bean’s methods. The enterprise bean in our example is a
stateless session bean called ConverterEJB. The source code for ConverterEJB
is in the j2eetutorial/examples/src/ejb/converter directory.
Coding the Enterprise Bean
The enterprise bean in this example requires the following code:
• Remote interface
• Home interface
• Enterprise bean class
Coding the Remote Interface
A remote interface defines the business methods that a client may call. The business methods are implemented in the enterprise bean code. The source code for
the Converter remote interface follows.
import javax.ejb.EJBObject;
import java.rmi.RemoteException;
import java.math.*;
CREATING THE ENTERPRISE BEAN
public interface Converter extends EJBObject {
}
public BigDecimal dollarToYen(BigDecimal dollars)
throws RemoteException;
public BigDecimal yenToEuro(BigDecimal yen)
throws RemoteException;
Coding the Home Interface
A home interface defines the methods that allow a client to create, find, or
remove an enterprise bean. The ConverterHome interface contains a single create method, which returns an object of the remote interface type. Here is the
source code for the ConverterHome interface:
import
import
import
import
java.io.Serializable;
java.rmi.RemoteException;
javax.ejb.CreateException;
javax.ejb.EJBHome;
public interface ConverterHome extends EJBHome {
}
Converter create() throws RemoteException, CreateException;
Coding the Enterprise Bean Class
The enterprise bean class for this example is called ConverterBean. This class
implements the two business methods, dollarToYen and yenToEuro, that the
Converter remote interface defines. The source code for the ConverterBean
class follows.
import
import
import
import
java.rmi.RemoteException;
javax.ejb.SessionBean;
javax.ejb.SessionContext;
java.math.*;
public class ConverterBean implements SessionBean {
BigDecimal yenRate = new BigDecimal("121.6000");
BigDecimal euroRate = new BigDecimal("0.0077");
public BigDecimal dollarToYen(BigDecimal dollars) {
BigDecimal result = dollars.multiply(yenRate);
return result.setScale(2,BigDecimal.ROUND_UP);
}
25
26
GETTING STARTED
public BigDecimal yenToEuro(BigDecimal yen) {
BigDecimal result = yen.multiply(euroRate);
return result.setScale(2,BigDecimal.ROUND_UP);
}
}
public
public
public
public
public
public
ConverterBean() {}
void ejbCreate() {}
void ejbRemove() {}
void ejbActivate() {}
void ejbPassivate() {}
void setSessionContext(SessionContext sc) {}
Compiling the Source Files
Now you are ready to compile the remote interface (Converter.java), home
interface (ConverterHome.java), and the enterprise bean class (Converter
Bean.java):
1. In a terminal window, go to the j2eetutorial/examples directory.
2. Type the following command:
ant converter
This command compiles the source files for the enterprise bean and the J2EE
application client. It places the resulting class files in the j2eetutorial/exam
ples/build/ejb/converter directory (not the src directory). For more information about ant, see How to Build and Run the Examples, page (xxii).
Note: When compiling the code, the preceding ant task includes the j2ee.jar file
in the classpath. This file resides in the lib directory of your J2EE SDK installation.
If you plan on using other tools to compile the source code for J2EE components,
make sure that the classpath includes the j2ee.jar file.
Packaging the Enterprise Bean
To package an enteprise bean, you run the New Enterprise Bean wizard of the
deploytool utility. During this process, the wizard performs the following tasks.
• Creates the bean’s deployment descriptor
• Packages the deployment descriptor and the bean’s classes in an EJB JAR
file
• Inserts the EJB JAR file into the application’s ConverterApp.ear file
CREATING THE ENTERPRISE BEAN
During the packaging process, you can view the deployment descriptor by
selecting Tools→Descriptor Viewer.
To start the New Enterprise Bean wizard, select File→New→Enterprise Bean.
The wizard displays the following dialog boxes.
1. Introduction dialog box
a. Read the explanatory text for an overview of the wizard’s features.
b. Click Next.
2. EJB JAR dialog box
a. Select the Create New JAR File In Application button.
b. In the combo box, select ConverterApp.
c. In the JAR Display Name field, enter ConverterJAR.
d. Click Edit.
e. In the tree under Available Files, locate the j2eetutorial/exam
ples/build/ejb/converter directory. (If the converter directory is
many levels down in the tree, you can simplify the tree view by entering all or part of the converter directory’s path name in the Starting
Directory field.)
f. Select the following classes from the Available Files tree and click
Add: Converter.class, ConverterBean.class, and Converter
Home.class. (You may also drag and drop these class files to the Contents text area.)
g. Click OK.
h. Click Next.
3. General dialog box
a. Under Bean Type, select the Session radio button.
b. Select the Stateless radio button.
c. In the Enterprise Bean Class combo box, select ConverterBean.
d. In the Enterprise Bean Name field, enter ConverterEJB.
e. In the Remote Home Interface combo box, select ConverterHome.
f. In the Remote Interface combo box, select Converter.
g. Click Next.
4. Transaction Management dialog box
Because you may skip the remaining dialog boxes, click Finish.
27
28
GETTING STARTED
Creating the J2EE™ Application Client
A J2EE application client is a program written in the Java™ programming language. At runtime, the client program executes in a different virtual machine
than the J2EE server.
The J2EE application client in this example requires two different JAR files. The
first JAR file is for the J2EE component of the client. This JAR file contains the
client’s deployment descriptor and its class files. When you run the New Application Client wizard, the deploytool utility automatically creates the JAR file
and stores it in the application’s EAR file. Defined by the J2EE Specification,
the JAR file is portable across all compliant J2EE servers.
The second JAR file contains stub classes that are required by the client program
at run time. These stub classes enable the client to access the enterprise beans
that are running in the J2EE server. Because this second JAR file is not covered
by the J2EE Specification, it is implementation specific, intended only for the
J2EE SDK.
The J2EE application client source code is in j2eetutorial/exam
ples/src/ejb/converter/ConverterClient.java. You already compiled this
code along with the enterprise bean code in the section Compiling the Source
Files, page (26).
Coding the J2EE Application Client
The ConverterClient.java source code illustrates the basic tasks performed
by the client of an enterprise bean:
• Locating the home interface
• Creating an enterprise bean instance
• Invoking a business method
Locating the Home Interface
The ConverterHome interface defines life-cycle methods such as create. Before
the ConverterClient can invoke the create method, it must locate and instantiate an object whose type is ConverterHome. This is a four-step process.
1. Create an initial naming context.
Context initial = new InitialContext();
CREATING THE J2EE™ APPLICATION CLIENT
The Context interface is part of the Java Naming and Directory Interface
(JNDI). A naming context is a set of name-to-object bindings. A name
that is bound within a context is the JNDI name of the object.
An InitialContext object, which implements the Context interface,
provides the starting point for the resolution of names. All naming operations are relative to a context.
2. Obtain the environment naming context of the application client.
Context myEnv = (Context)initial.lookup("java:comp/env");
The java:comp/env name is bound to the environment naming context of
the ConverterClient component.
3. Retrieve the object bound to the name ejb/SimpleConverter.
Object objref = myEnv.lookup("ejb/SimpleConverter");
The ejb/SimpleConverter name is bound to an enterprise bean reference, a logical name for the home of an enterprise bean. In this case, the
ejb/SimpleConverter name refers to the ConverterHome object. The
names of enterprise beans should reside in the java:com/env/ejb subcontext.
4. Narrow the reference to a ConverterHome object.
ConverterHome home =
(ConverterHome) PortableRemoteObject.narrow(objref,
ConverterHome.class);
Creating an Enterprise Bean Instance
To create the bean instance, the client invokes the create method on the Con
verterHome object. The create method returns an object whose type is Con
verter. The remote Converter interface defines the business methods of the
bean that the client may call. When the client invokes the create method, the
EJB container instantiates the bean and then invokes the ConverterBean.ejb
Create method. The client invokes the create method as follows:
Converter currencyConverter = home.create();
29
30
GETTING STARTED
Invoking a Business Method
Calling a business method is easy—you simply invoke the method on the Con
verter object. The EJB container will invoke the corresponding method on the
ConverterEJB instance that is running on the server. The client invokes the dol
larToYen business method in the following lines of code.
BigDecimal param = new BigDecimal ("100.00");
BigDecimal amount = currencyConverter.dollarToYen(param);
ConverterClient Source Code
The full source code for the ConverterClient program follows.
import
import
import
import
javax.naming.Context;
javax.naming.InitialContext;
javax.rmi.PortableRemoteObject;
java.math.BigDecimal;
import Converter;
import ConverterHome;
public class ConverterClient {
public static void main(String[] args) {
try {
Context initial = new InitialContext();
Object objref = initial.lookup
("java:comp/env/ejb/SimpleConverter");
ConverterHome home =
(ConverterHome)PortableRemoteObject.narrow(objref,
ConverterHome.class);
Converter currencyConverter = home.create();
BigDecimal param = new BigDecimal ("100.00");
BigDecimal amount =
currencyConverter.dollarToYen(param);
System.out.println(amount);
amount = currencyConverter.yenToEuro(param);
System.out.println(amount);
System.exit(0);
} catch (Exception ex) {
System.err.println("Caught an unexpected exception!");
CREATING THE J2EE™ APPLICATION CLIENT
}
}
}
ex.printStackTrace();
Compiling the Application Client
The application client files are compiled at the same time as the enterprise bean
files, as described in Compiling the Source Files, page (26).
Packaging the J2EE Application Client
To package an application client component, you run the New Application Client
wizard of the deploytool. During this process the wizard performs the following tasks.
• Creates the application client’s deployment descriptor
• Puts the deployment descriptor and client files into a JAR file
• Adds the JAR file to the application’s ConverterApp.ear file
During the packaging process you can view the deployment descriptor by selecting Tools→Descriptor Viewer.
To start the New Application Client wizard, select File→New→Application Client. The wizard displays the following dialog boxes.
1. Introduction dialog box
a. Read the explanatory text for an overview of the wizard’s features.
b. Click Next.
2. JAR File Contents dialog box
a. In the combo box, select ConverterApp.
b. Click Edit.
c. In the tree under Available Files, locate the j2eetutorial/exam
ples/build/ejb/converter directory.
d. Select the ConverterClient.class file and click Add.
e. Click OK.
f. Click Next.
3. General dialog box
a. In the Main Class combo box, select ConverterClient.
b. Verify that the entry in the Display Name field is ConverterClient.
31
32
GETTING STARTED
c. In the Callback Handler Class combo box, select container-managed
authentication.
d. Click Next.
e. Click Finish.
Specifying the Application Client’s Enterprise Bean
Reference
When it invokes the lookup method, the ConverterClient refers to the home of
an enterprise bean:
Object objref = myEnv.lookup("ejb/SimpleConverter");
You specify this reference as follows.
1.
2.
3.
4.
5.
6.
7.
8.
In the tree, select ConverterClient.
Select the EJB Refs tab.
Click Add.
In the Coded Name column, enter ejb/SimpleConverter.
In the Type column, select Session.
In the Interfaces column, select Remote.
In the Home Interface column, enter ConverterHome.
In the Local/Remote Interface column, enter Converter.
Creating the Web Client
The Web client is contained in the JSP page j2eetutorial/exam
ples/src/ejb/converter/index.jsp. A JSP page is a text-based document
that contains static template data, which can be expressed in any text-based format such as HTML, WML, and XML; and JSP elements, which construct
dynamic content.
Coding the Web Client
The statements (in bold in the following code) for locating the home interface,
creating an enterprise bean instance, and invoking a business method are nearly
identical to those of the J2EE application client. The parameter of the lookup
method is the only difference; the motivation for using a different name is discussed in Specifying the JNDI Names, page (35).
CREATING THE WEB CLIENT
The classes needed by the client are declared with a JSP page directive (enclosed
within the <%@ %> characters). Because locating the home interface and creating
the enterprise bean are performed only once, this code appears in a JSP declaration (enclosed within the <%! %> characters) that contains the initialization
method, jspInit, of the JSP page. The declaration is followed by standard
HTML markup for creating a form with an input field. A scriptlet (enclosed
within the <% %> characters) retrieves a parameter from the request and converts
it to a double. Finally, JSP expressions (enclosed within <%= %> characters)
invoke the enterprise bean’s business methods and insert the result into the
stream of data returned to the client.
<%@ page import="Converter,ConverterHome,javax.ejb.*,
javax.naming.*, javax.rmi.PortableRemoteObject,
java.rmi.RemoteException" %>
<%!
private Converter converter = null;
public void jspInit() {
try {
InitialContext ic = new InitialContext();
Object objRef = ic.lookup("
java:comp/env/ejb/TheConverter");
ConverterHome home =
(ConverterHome)PortableRemoteObject.narrow(
objRef, ConverterHome.class);
converter = home.create();
} catch (RemoteException ex) {
...
}
}
...
%>
<html>
<head>
<title>Converter</title>
</head>
<body bgcolor="white">
<h1><center>Converter</center></h1>
<hr>
<p>Enter an amount to convert:</p>
<form method="get">
<input type="text" name="amount" size="25">
<br>
<p>
<input type="submit" value="Submit">
<input type="reset" value="Reset">
33
34
GETTING STARTED
</form>
<%
String amount = request.getParameter("amount");
if ( amount != null && amount.length() > 0 ) {
BigDecimal d = new BigDecimal (amount);
%>
<p><%= amount %> dollars are
<%= converter.dollarToYen(d) %> Yen.
<p><%= amount %> Yen are
<%= converter.yenToEuro(d) %> Euro.
<%
}
%>
</body>
</html>
Compiling the Web Client
The J2EE server automatically compiles Web clients that are JSP pages. If the
Web client were a servlet, you would have to compile it.
Packaging the Web Client
To package a Web client, you run the New Web Component wizard of the
deploytool utility. During this process the wizard performs the following tasks.
• Creates the Web application deployment descriptor
• Adds the component files to a WAR file
• Adds the WAR file to the application’s ConverterApp.ear file
During the packaging process, you can view the deployment descriptor by
selecting Tools→Descriptor Viewer.
To start the New Web Component wizard, select File→New→Web Component.
The wizard displays the following dialog boxes.
1. Introduction dialog box
a. Read the explanatory text for an overview of the wizard’s features.
b. Click Next.
2. WAR File dialog box
a. Select Create New WAR File In Application.
a. In the combo box, select ConverterApp.
b. In the WAR Display Name field, enter ConverterWAR.
SPECIFYING THE JNDI NAMES
c. Click Edit.
d. In the tree under Available Files, locate the j2eetutorial/exam
ples/build/ejb/converter directory.
e. Select index.jsp and click Add.
f. Click OK.
g. Click Next.
3. Choose Component Type dialog box
a. Select the JSP radio button.
b. Click Next.
4. Component General Properties dialog box
a. In the JSP Filename combo box, select index.jsp.
b. Click Finish.
Specifying the Web Client’s Enterprise Bean
Reference
When it invokes the lookup method, the Web client refers to the home of an
enterprise bean:
Object objRef = ic.lookup("java:comp/env/ejb/TheConverter");
You specify this reference as follows:
1.
2.
3.
4.
5.
6.
7.
8.
In the tree, select ConverterWAR.
Select the EJB Refs tab.
Click Add.
In the Coded Name column, enter ejb/TheConverter.
In the Type column, select Session.
In the Interfaces column, select Remote.
In the Home Interface column, enter ConverterHome.
In the Local/Remote Interface column, enter Converter.
Specifying the JNDI Names
Although the J2EE application client and the Web client access the same enterprise bean, their code refers to the bean’s home by different names. The J2EE
35
36
GETTING STARTED
application client refers to the bean’s home as ejb/SimpleConverter, but the
Web client refers to it as ejb/TheConverter. These references are in the parameters of the lookup calls. In order for the lookup method to retrieve the home
object, you must map the references in the code to the enterprise bean’s JNDI
name. Although this mapping adds a level of indirection, it decouples the clients
from the beans, making it easier to assemble applications from J2EE components.
To map the enterprise bean references in the clients to the JNDI name of the
bean, follow these steps.
1. In the tree, select ConverterApp.
2. Select the JNDI Names tab.
3. To specify a JNDI name for the bean, in the Application table locate the
ConverterEJB component and enter MyConverter in the JNDI Name column.
4. To map the references, in the References table enter MyConverter in the
JNDI Name for each row.
Figure 2–1 shows what the JNDI Names tab should look like after you’ve performed the preceding steps.
DEPLOYING THE J2EE™ APPLICATION
Figure 2–1 ConverterApp JNDI Names
Deploying the J2EE™ Application
Now that the J2EE application contains the components, it is ready for deployment.
1. Select the ConverterApp application.
2. Select Tools→Deploy.
3. In the Introduction dialog box, confirm that ConverterApp is shown for
the Object To Deploy and that localhost is shown for the Target Server.
4. Select the checkbox labeled Return Client Jar.
5. In the text field that appears, enter the full path name for the file Convert
erAppClient.jar so that it will reside in the j2eetutorial/exam
ples/src/ejb/converter subdirectory. The ConverterAppClient.jar
file contains the stub classes that enable remote access to ConverterEJB.
6. Click Next.
7. In the JNDI Names dialog box, verify the names you entered in the previous section.
8. Click Next.
9. In the WAR Context Root dialog box, enter converter in the Context
Root field. When you run the Web client, the converter context root will
be part of the URL.
10. Click Next.
11. In the Review dialog box, click Finish.
12. In the Deployment Progress dialog box, click OK when the deployment
completes.
Running the J2EE™ Application Client
To run the J2EE application client, perform the following steps.
1. In a terminal window, go to the j2eetutorial/examples/src/ejb/con
verter directory.
2. Verify that this directory contains the ConverterApp.ear and Convert
erAppClient.jar files.
3. Set the APPCPATH environment variable to ConverterAppClient.jar.
37
38
GETTING STARTED
4. Type the following command (on a single line):
runclient client ConverterApp.ear name ConverterClient
textauth
5. The client container prompts you to log in. Enter guest for the user name
and guest123 for the password.
6. In the terminal window, the client displays these lines:
Binding name:’java:comp/env/ejb/SimpleConverter’
12160.00
0.77
Unbinding name:’java:comp/env/ejb/SimpleConverter’
Running the Web Client
To run the Web client, point your browser at the following URL. Replace <host>
with the name of the host running the J2EE server. If your browser is running on
the same host as the J2EE server, you may replace <host> with localhost.
http://<host>:8000/converter
You should see the screen shown in Figure 2–2 after entering 100 in the input
field and clicking Submit.
MODIFYING THE J2EE™ APPLICATION
Figure 2–2 Converter Web Client
Modifying the J2EE™ Application
Since the J2EE SDK is intended for experimentation, it supports iterative development. Whenever you make a change to a J2EE application, you must redeploy
the application.
Modifying a Class File
To modify a class file in an enterprise bean, you change the source code, recompile it, and redeploy the application. For example, suppose that you want to
change the exchange rate in the dollarToYen business method of the Convert
erBean class:
Edit ConverterBean.java.
Recompile ConverterBean.java by typing ant converter.
In deploytool, select Tools→Update Files.
A dialog box appears reporting the changed file. Verify that Converter
Bean.class has been changed and then dismiss the dialog box.
5. Select Tools→Deploy. Make sure the checkbox labeled Save Object
Before Deploying is checked.
1.
2.
3.
4.
39
40
GETTING STARTED
You can also perform steps 4 and 5 by selecting Tools→Update And Redeploy.
The deploytool utility replaces the old JSP file in ConverterApp.ear with the
new one and then redeploys the application.
Adding a File
To add a file to the EJB JAR or WAR of the application, perform these steps:
1.
2.
3.
4.
5.
6.
Select the JAR or WAR.
Select the General tab.
Click Edit.
In the tree of the Available Files field, locate the file and click Add.
Click OK.
From the main toolbar, select Tools→Update And Redeploy.
Modifying the Web Client
To modify the Web client, follow these steps:
Edit index.jsp.
Execute ant converter to copy the modified file to the build directory.
In deploytool, select Tools→Update Files.
A dialog box appears reporting the changed file. Verify that index.jsp
has been changed and then dismiss the dialog box.
5. Select Tools→Deploy. Make sure the checkbox labeled Save Object
Before Deploying is checked.
1.
2.
3.
4.
You can also perform steps 4 and 5 by selecting Tools→Update And Redeploy.
The deploytool utility replaces the old JSP file in ConverterApp.ear with the
new one and then redeploys the application.
Modifying a Deployment Setting
To modify a deployment setting of ConverterApp, you edit the appropriate field
in a tabbed pane and redeploy the application. For example, to change the JNDI
name of the ConverterBean from ATypo to MyConverter, you would follow
these steps:
1. In deploytool, select ConverterApp in the tree.
2. Select the JNDI Names tab.
3. In the JNDI Name field, enter MyConverter.
COMMON PROBLEMS AND THEIR SOLUTIONS
4. From the main toolbar, select File→Save.
5. Select Tools→Update And Redeploy.
Common Problems and Their Solutions
Cannot Start the J2EE Server
Naming and Directory Service Port Conflict
Symptom: When you start the J2EE server with the verbose option, it displays
these lines:
J2EE server listen port: 1050
RuntimeException: Could not initialize server. . .
Solution: Another process is using port 1050. If the J2EE server is already running, you can stop it by typing j2ee stop. If some other program is using the
port, then you can change the default port number (1050) by editing the con
fig/orb.properties file of your J2EE SDK installation.
For more information about default port numbers, see the Configuration Guide
in the download bundle of the J2EE SDK.
Web Service Port Conflict
Symptom: When you start the J2EE server with the verbose option, it displays
these lines:
LifecycleException: HttpConnector[8000].open:
java.net.BindException: Address in use. . .
Solution: Another process is using port 8000. You can change the default port
number (8000) by editing the config/web.properties file of your J2EE SDK
installation.
Incorrect XML Parser
Symptom: When you start the J2EE server with the verbose option, it displays
these lines:
Exception in thread "main"
javax.xml.parsers.FactoryConfigurationError:
org.apache.xerces.jaxp.SAXParserFactoryImpl at . . .
41
42
GETTING STARTED
Solution: Remove the jre/lib/jaxp.properties file from your J2SE installation.
Compilation Errors
ant Cannot Locate the Build File
Symptom: When you type ant converter, these messages appear:
Buildfile: build.xml does not exist!
Build failed.
Solution: Before running ant, go to the j2eetutorial/examples/src directory.
If you want to run ant from your current directory, you must specify the build
file on the command line. For example, on Windows you would type this command on a single line:
ant buildfile C:\j2eetutorial\examples\src\build.xml
converter
The Compiler Cannot Resolve Symbols
Symptom: When you type ant converter, the compiler reports many errors,
including these:
cannot resolve symbol
. . .
BUILD FAILED
. . .
Compile failed, messages should have been provided
Solution: Make sure that you’ve set the J2EE_HOME environment variable correctly. See Checking the Environment Variables, page (23).
ant 1.4 Will Not Compile the Example after You Run the Client
Symptom: ant 1.4 displays this error:
The filename, directory name, or volume label syntax is
incorrect.
Solution: Use version 1.3 of ant. The 1.4 version of the ant.bat script and the
scripts of the J2EE SDK all use the JAVACMD environment variable. The SDK’s
COMMON PROBLEMS AND THEIR SOLUTIONS
runclient.bat script, for example, sets JAVACMD to a value that causes problems for ant.bat.
Deployment Errors
The Incorrect XML Parser Is in Your Classpath
Symptom: The error displayed has the following text:
. . .
[]java.rmi.RemoteException:Error saving/opening
Deployment Error:Bad mapping of key{0} class{1},
not found: com.sum.enterprise.deployment.xml.ApplicationNode
Solution: Remove the jaxp.jar file from the jre/lib/ext directory of your
J2SE installation. This JAR file contains XML parsing routines that are incompatible with the J2EE server. If you do not have a jaxp.jar file, then perhaps
your classpath refers to the XML routines of a Tomcat installation. In this case,
you should remove that reference from your classpath.
The Remote Home Interface Was Specified as a Local Home
Interface
Symptom: An error such as the following is displayed:
LocalHomeImpl must be declared abstract.
It does not define javax.ejb.HomeHandle getHomeHandle()
from interface javax.ejb.EJBHome.
Solution: Remove the enterprise bean from the EAR file (Edit→Delete) and create a new bean with the New Enterprise Bean wizard. In the General dialog box
of the wizard, select values from the Remote Home Interface and Remote Interface combo boxes.
J2EE Application Client Runtime Errors
The Client Throws a NoClassDefFoundError
Symptom: The client reports this exception:
java.lang.NoClassDefFoundError:converter.ConverterHome
43
44
GETTING STARTED
Solution: This error occurs if the client cannot find the classes in the Converter
AppClient.jar file. Make sure that you’ve correctly followed the steps outlined
in Running the J2EE™ Application Client, page (37).
The Client Cannot Find ConverterApp.ear
Symptom: The client reports this exception:
IOException: ConverterApp.ear does not exist
Solution: Ensure that the ConverterApp.ear file exists and that you’ve specified it with the client option:
runclient client ConverterApp.ear name ConverterClient
You created the ConverterApp.ear file in the section, Creating the J2EE™
Application, page (24). See also the section Running the J2EE™ Application
Client, page (37).
The Client Cannot Find the ConverterClient Component
Symptom: The client displays this line:
No application client descriptors defined for: . . .
Solution: Verify that you’ve created the ConverterClient component and that
you’ve specified it for the name option of the runclient command. You created the ConverterClient component in the section, Packaging the J2EE Application Client, page (31).
The Login Failed
Symptom: After you log in, the client displays this line:
Incorrect login and/or password
Solution: At the login prompts, enter guest as the user name and guest123 as
the password.
The J2EE Application Has Not Been Deployed
Symptom: The client reports the following exception:
NameNotFoundException. Root exception is org.omg.CosNaming. . .
COMMON PROBLEMS AND THEIR SOLUTIONS
Solution: Deploy the application. For instructions, see Deploying the J2EE™
Application, page (37).
The JNDI Name Is Incorrect
Symptom: The client reports the following exception:
NameNotFoundException. Root exception is org.omg.CosNaming. . .
Solution: In the JNDI Names tabbed pane of the ConverterApp, make sure that
the JNDI names for the ConverterBean and the ejb/SimpleConverter match.
Edit the appropriate JNDI Name field and then redeploy the application.
Web Client Runtime Errors
The Web Context in the URL Is Incorrect
Symptom: The browser reports that the page cannot be found (HTTP 404).
Solution: Verify that the Web context (converter) in the URL matches the one
you specified in the Component General Properties dialog box (See the section
Packaging the Web Client, page (34)). The case (upper or lower) of the Web context is significant.
The J2EE Application Has Not Been Deployed
Symptom: The browser reports that the page cannot be found (HTTP 404).
Solution: Deploy the application.
The JNDI Name Is Incorrect
Symptom: When you click Submit on the Web page, the browser reports
A Servlet Exception Has Occurred.
Solution: In the JNDI Names tabbed pane of the ConverterApp, make sure that
the JNDI names for the ConverterBean and the ConverterWAR match. Edit the
appropriate JNDI Name field and then redeploy the application.
Detecting Problems With the Verifier Tool
The verifier tool (verifier) can detect inconsistencies in deployment descriptors and method signatures. These inconsistencies often cause deployment or
runtime errors. From deploytool, you can run the GUI version of verifier by
45
46
GETTING STARTED
selecting Tools→Verifier. You can also run a stand-alone GUI or command-line
version of verifier. For more information, see Appendix B.
Comparing Your EAR Files with Ours
For most of the examples, the download bundle of the tutorial includes J2EE
application EAR files, which are located in the j2eetutorial/examples/ears
directory.
When All Else Fails
If none of these suggestions fixes the problem, you can uninstall the application
and clean out the server’s repository by running the cleanup script. You’ll also
need to shut down and restart the server:
j2ee stop
cleanup
j2ee verbose
3
Enterprise Beans
Dale Green
E
NTERPRISE beans are the J2EE™ components that implement Enterprise
JavaBeans™ (EJB™) technology. Enterprise beans run in the EJB container, a
runtime environment within the J2EE server (see Figure 1–5). Although transparent to the application developer, the EJB container provides system-level services such as transactions to its enterprise beans. These services enable you to
quickly build and deploy enterprise beans, which form the core of transactional
J2EE applications.
In This Chapter
What Is an Enterprise Bean? 48
Benefits of Enterprise Beans 48
When to Use Enterprise Beans 49
Types of Enterprise Beans 49
What Is a Session Bean? 49
State Management Modes 50
When to Use Session Beans 51
What Is an Entity Bean? 51
What Makes Entity Beans Different from Session Beans? 52
Container-Managed Persistence 53
When to Use Entity Beans 56
What Is a Message-Driven Bean? 56
What Makes Message-Driven Beans Different from Session and Entity
Beans? 57
When to Use Message-Driven Beans 57
47
48
ENTERPRISE BEANS
Defining Client Access with Interfaces 58
Remote Access 58
Local Access 59
Local Interfaces and Container-Managed Relationships 59
Deciding on Remote or Local Access 60
Performance and Access 61
Method Parameters and Access 61
The Contents of an Enterprise Bean 62
Naming Conventions for Enterprise Beans 63
The Life Cycles of Enterprise Beans 63
The Life Cycle of a Stateful Session Bean 64
The Life Cycle of a Stateless Session Bean 65
The Life Cycle of an Entity Bean 65
The Life Cycle of a Message-Driven Bean 67
What Is an Enterprise Bean?
Written in the Java™ programming language, an enterprise bean is a server-side
component that encapsulates the business logic of an application. The business
logic is the code that fulfills the purpose of the application. In an inventory control application, for example, the enterprise beans might implement the business
logic in methods called checkInventoryLevel and orderProduct. By invoking
these methods, remote clients can access the inventory services provided by the
application.
Benefits of Enterprise Beans
For several reasons, enterprise beans simplify the development of large, distributed applications. First, because the EJB container provides system-level services to enterprise beans, the bean developer can concentrate on solving business
problems. The EJB container—not the bean developer—is responsible for system-level services such as transaction management and security authorization.
Second, because the beans—and not the clients—contain the application’s business logic, the client developer can focus on the presentation of the client. The
client developer does not have to code the routines that implement business rules
or access databases. As a result, the clients are thinner, a benefit that is particularly important for clients that run on small devices.
Third, because enterprise beans are portable components, the application assembler can build new applications from existing beans. These applications can run
on any compliant J2EE server.
WHAT IS A SESSION BEAN?
When to Use Enterprise Beans
You should consider using enterprise beans if your application has any of the following requirements:
• The application must be scalable. To accommodate a growing number of
users, you may need to distribute an application’s components across multiple machines. Not only can the enterprise beans of an application run on
different machines, but their location will remain transparent to the clients.
• Transactions are required to ensure data integrity. Enterprise beans support transactions, the mechanisms that manage the concurrent access of
shared objects.
• The application will have a variety of clients. With just a few lines of code,
remote clients can easily locate enterprise beans. These clients can be thin,
various, and numerous.
Types of Enterprise Beans
Table 3–1 summarizes the three different types of enterprise beans. The following sections discuss each type in more detail.
Table 3–1 Summary of Enterprise Bean Types
Enterprise Bean Type
Purpose
Session
Performs a task for a client
Entity
Represents a business entity object that exists in persistent storage
Message-Driven
Acts as a listener for the Java™ Message Service API, processing
messages asynchronously
What Is a Session Bean?
A session bean represents a single client inside the J2EE server. To access an
application that is deployed on the server, the client invokes the session bean’s
methods. The session bean performs work for its client, shielding the client from
complexity by executing business tasks inside the server.
As its name suggests, a session bean is similar to an interactive session. A session bean is not shared—it may have just one client, in the same way that an
49
50
ENTERPRISE BEANS
interactive session may have just one user. Like an interactive session, a session
bean is not persistent. (That is, its data is not saved to a database.) When the client terminates, its session bean appears to terminate and is no longer associated
with the client.
For code samples, see Chapter 4.
State Management Modes
There are two types of session beans: stateful and stateless.
Stateful Session Beans
The state of an object consists of the values of its instance variables. In a stateful
session bean, the instance variables represent the state of a unique client-bean
session. Because the client interacts (“talks”) with its bean, this state is often
called the conversational state.
The state is retained for the duration of the client-bean session. If the client
removes the bean or terminates, the session ends and the state disappears. This
transient nature of the state is not a problem, however, because when the conversation between the client and the bean ends there is no need to retain the state.
Stateless Session Beans
A stateless session bean does not maintain a conversational state for a particular
client. When a client invokes the method of a stateless bean, the bean’s instance
variables may contain a state, but only for the duration of the invocation. When
the method is finished, the state is no longer retained. Except during method
invocation, all instances of a stateless bean are equivalent, allowing the EJB container to assign an instance to any client.
Because stateless session beans can support multiple clients, they can offer better
scalability for applications that require large numbers of clients. Typically, an
application requires fewer stateless session beans than stateful session beans to
support the same number of clients.
At times, the EJB container may write a stateful session bean to secondary storage. However, stateless session beans are never written to secondary storage.
Therefore, stateless beans may offer better performance than stateful beans.
WHAT IS AN ENTITY BEAN?
When to Use Session Beans
In general, you should use a session bean if the following circumstances hold:
• At any given time, only one client has access to the bean instance.
• The state of the bean is not persistent, existing only for a short period of
time (perhaps a few hours).
Stateful session beans are appropriate if any of the following conditions are true:
• The bean’s state represents the interaction between the bean and a specific
client.
• The bean needs to hold information about the client across method invocations.
• The bean mediates between the client and the other components of the
application, presenting a simplified view to the client.
• Behind the scenes, the bean manages the work flow of several enterprise
beans. For an example, see the AccountControllerEJB session bean in
Chapter 18.
To improve performance, you might choose a stateless session bean if it has any
of these traits:
• The bean’s state has no data for a specific client.
• In a single method invocation, the bean performs a generic task for all clients. For example, you might use a stateless session bean to send an e-mail
that confirms an online order.
• The bean fetches from a database a set of read-only data that is often used
by clients. Such a bean, for example, could retrieve the table rows that represent the products that are on sale this month.
What Is an Entity Bean?
An entity bean represents a business object in a persistent storage mechanism.
Some examples of business objects are customers, orders, and products. In the
J2EE SDK, the persistent storage mechanism is a relational database. Typically,
each entity bean has an underlying table in a relational database, and each
instance of the bean corresponds to a row in that table. For code examples of
entity beans, please refer to chapters 5 and 6.
51
52
ENTERPRISE BEANS
What Makes Entity Beans Different from Session
Beans?
Entity beans differ from session beans in several ways. Entity beans are persistent, allow shared access, have primary keys, and may participate in relationships with other entity beans.
Persistence
Because the state of an entity bean is saved in a storage mechanism, it is persistent. Persistence means that the entity bean’s state exists beyond the lifetime of
the application or the J2EE server process. If you’ve worked with databases,
you’re familiar with persistent data. The data in a database is persistent because
it still exists even after you shut down the database server or the applications it
services.
There are two types of persistence for entity beans: bean-managed and container-managed. With bean-managed persistence, the entity bean code that you
write contains the calls that access the database. If your bean has container-managed persistence, the EJB container automatically generates the necessary database access calls. The code that you write for the entity bean does not include
these calls. For additional information, see the section Container-Managed
Persistence, page (53).
Shared Access
Entity beans may be shared by multiple clients. Because the clients might want
to change the same data, it’s important that entity beans work within transactions. Typically, the EJB container provides transaction management. In this
case, you specify the transaction attributes in the bean’s deployment descriptor.
You do not have to code the transaction boundaries in the bean—the container
marks the boundaries for you. See Chapter 14 for more information.
Primary Key
Each entity bean has a unique object identifier. A customer entity bean, for
example, might be identified by a customer number. The unique identifier, or
primary key, enables the client to locate a particular entity bean. For more information see the section Primary Keys for Bean-Managed Persistence, page (113).
WHAT IS AN ENTITY BEAN?
Relationships
Like a table in a relational database, an entity bean may be related to other entity
beans. For example, in a college enrollment application, StudentEJB and Cour
seEJB would be related because students enroll in classes.
You implement relationships differently for entity beans with bean-managed persistence and those with container-managed persistence. With bean-managed persistence, the code that you write implements the relationships. But with
container-managed persistence, the EJB container takes care of the relationships
for you. For this reason, relationships in entity beans with container-managed
persistence are often referred to as container-managed relationships.
Container-Managed Persistence
The term container-managed persistence means that the EJB container handles
all database access required by the entity bean. The bean’s code contains no
database access (SQL) calls. As a result, the bean’s code is not tied to a specific
persistent storage mechanism (database). Because of this flexibility, even if you
redeploy the same entity bean on different J2EE servers that use different databases, you won’t need to modify or recompile the bean’s code. In short, your
entity beans are more portable.
In order to generate the data access calls, the container needs information that
you provide in the entity bean’s abstract schema.
Abstract Schema
Part of an entity bean’s deployment descriptor, the abstract schema defines the
bean’s persistent fields and relationships. The term abstract distinguishes this
schema from the physical schema of the underlying data store. In a relational
database, for example, the physical schema is made up of structures such as
tables and columns.
You specify the name of an abstract schema in the deployment descriptor. This
name is referenced by queries written in the Enterprise JavaBeans™ Query Language (EJB™ QL). For an entity bean with container-managed persistence, you
must define an EJB QL query for every finder method (except findByPrima
ryKey). The EJB QL query determines the query that is executed by the EJB
container when the finder method is invoked. To learn more about EJB QL, see
Chapter 8.
You’ll probably find it helpful to sketch the abstract schema before writing any
code. Figure 3–1 represents a simple abstract schema that describes the relation-
53
54
ENTERPRISE BEANS
ships between three entity beans. These relationships are discussed further in the
sections that follow.
Figure 3–1 A High-Level View of an Abstract Schema
Persistent Fields
The persistent fields of an entity bean are stored in the underlying data store.
Collectively, these fields constitute the state of the bean. At runtime, the EJB
container automatically synchronizes this state with the database. During
deployment, the container typically maps the entity bean to a database table and
maps the persistent fields to the table’s columns.
A CustomerEJB entity bean, for example, might have persistent fields such as
firstName, lastName, phone, and emailAddress. In container-managed persistence, these fields are virtual. You declare them in the abstract schema, but you
do not code them as instance variables in the entity bean class. Instead, the persistent fields are identified in the code by access methods (getters and setters).
Relationship Fields
A relationship field is like a foreign key in a database table—it identifies a
related bean. Like a persistent field, a relationship field is virtual and is defined
WHAT IS AN ENTITY BEAN?
in the enterprise bean class with access methods. But unlike a persistent field, a
relationship field does not represent the bean’s state. Relationship fields are discussed further in Direction in Container-Managed Relationships, page (55).
Multiplicity in Container-Managed Relationships
There are four types of multiplicities:
One-to-one: Each entity bean instance is related to a single instance of another
entity bean. For example, to model a physical warehouse in which each storage
bin contains a single widget, StorageBinEJB and WidgetEJB would have a oneto-one relationship.
One-to-many: An entity bean instance may be related to multiple instances of the
other entity bean. A sales order, for example, can have multiple line items. In the
order application, OrderEJB would have a one-to-many relationship with
LineItemEJB.
Many-to-one: Multiple instances of an entity bean may be related to a single
instance of the other entity bean. This multiplicity is the opposite of a one-tomany relationship. In the example mentioned in the previous item, from the perspective of LineItemEJB the relationship to OrderEJB is many-to-one.
Many-to-many: The entity bean instances may be related to multiple instances of
each other. For example, in college each course has many students, and every
student may take several courses. Therefore, in an enrollment application, Cour
seEJB and StudentEJB would have a many-to-many relationship.
Direction in Container-Managed Relationships
The direction of a relationship may be either bidirectional or unidirectional. In a
bidirectional relationship, each entity bean has a relationship field that refers to
the other bean. Through the relationship field, an entity bean’s code can access
its related object. If an entity bean has a relative field, then we often say that it
“knows” about its related object. For example, if OrderEJB knows what
LineItemEJB instances it has and if LineItemEJB knows what OrderEJB it
belongs to, then they have a bidirectional relationship.
In a unidirectional relationship, only one entity bean has a relationship field that
refers to the other. For example, LineItemEJB would have a relationship field
that identifies ProductEJB, but ProductEJB would not have a relationship field
for LineItemEJB. In other words, LineItemEJB knows about ProductEJB, but
ProductEJB doesn’t know which LineItemEJB instances refer to it.
55
56
ENTERPRISE BEANS
EJB QL queries often navigate across relationships. The direction of a relationship determines whether a query can navigate from one bean to another. For
example, a query can navigate from LineItemEJB to ProductEJB, but cannot
navigate in the opposite direction. For OrderEJB and LineItemEJB, a query
could navigate in both directions, since these two beans have a bidirectional relationship.
When to Use Entity Beans
You should probably use an entity bean under the following conditions:
• The bean represents a business entity, not a procedure. For example,
CreditCardEJB would be an entity bean, but CreditCardVerifierEJB
would probably be a session bean.
• The bean’s state must be persistent. If the bean instance terminates or if
the J2EE server is shut down, the bean’s state still exists in persistent storage (a database).
What Is a Message-Driven Bean?
Note: This section contains text from the Java™ Message Service Tutorial.
Because message-driven beans rely on Java Message Service (JMS) technology, to
fully understand how these beans work you should consult the tutorial at this URL:
http://java.sun.com/products/jms/tutorial/index.html
A message-driven bean is an enterprise bean that allows J2EE applications to
process messages asynchronously. It acts as a JMS message listener, which is
similar to an event listener except that it receives messages instead of events.
The messages may be sent by any J2EE component—an application client,
another enterprise bean, or a Web component—or by a JMS application or system that does not use J2EE technology.
Message-driven beans currently process only JMS messages, but in the future
they may be used to process other kinds of messages.
For a code sample, see Chapter 7.
WHAT IS A MESSAGE-DRIVEN BEAN?
What Makes Message-Driven Beans Different from
Session and Entity Beans?
The most visible difference between message-driven beans and session and
entity beans is that clients do not access message-driven beans through interfaces. Interfaces are described in the section Defining Client Access with
Interfaces, page (58). Unlike a session or entity bean, a message-driven bean has
only a bean class.
In several respects, a message-driven bean resembles a stateless session bean:
• A message-driven bean’s instances retain no data or conversational state
for a specific client.
• All instances of a message-driven bean are equivalent, allowing the EJB
container to assign a message to any message-driven bean instance. The
container can pool these instances to allow streams of messages to be processed concurrently.
• A single message-driven bean can process messages from multiple clients.
The instance variables of the message-driven bean instance can contain some
state across the handling of client messages—for example, a JMS API connection, an open database connection, or an object reference to an enterprise bean
object.
When a message arrives, the container calls the message-driven bean’s onMes
sage method to process the message. The onMessage method normally casts the
message to one of the five JMS message types and handles it in accordance with
the application’s business logic. The onMessage method may call helper methods, or it may invoke a session or entity bean to process the information in the
message or to store it in a database.
A message may be delivered to a message-driven bean within a transaction context, so that all operations within the onMessage method are part of a single
transaction. If message processing is rolled back, the message will be redelivered. For more information, see Chapter 7.
When to Use Message-Driven Beans
Session beans and entity beans allow you to send JMS messages and to receive
them synchronously, but not asynchronously. To avoid tying up server resources,
you may prefer not to use blocking synchronous receives in a server-side component. To receive messages asynchronously, use a message-driven bean.
57
58
ENTERPRISE BEANS
Defining Client Access with Interfaces
Note: The material in this section applies only to session and entity beans, not to
message-driven beans. Because they have a different programming model, message-driven beans do not have interfaces that define client access.
A client may access a session or an entity bean only through the methods defined
in the bean’s interfaces. These interfaces define the client’s view of a bean. All
other aspects of the bean—method implementations, deployment descriptor settings, abstract schemas, and database access calls—are hidden from the client.
Well-designed interfaces simplify the development and maintenance of J2EE
applications. Not only do clean interfaces shield the clients from any complexities in the EJB tier, but they also allow the beans to change internally without
affecting the clients. For example, even if you change your entity beans from
bean-managed to container-managed persistence, you won’t have to alter the client code. But if you were to change the method definitions in the interfaces, then
you might have to modify the client code as well. Therefore, to isolate your clients from possible changes in the beans, it is important that you design the interfaces carefully.
When you design a J2EE application, one of the first decisions you make is the
type of client access allowed by the enterprise beans: remote or local.
Remote Access
A remote client of an enterprise bean has the following traits:
• It may run on a different machine and a different Java™ 2 virtual machine
(JVM) than the enterprise bean it accesses. (It is not required to run on a
different JVM.)
• It can be a Web component, a J2EE application client, or another enterprise bean.
• To a remote client, the location of the enterprise bean is transparent.
To create an enterprise bean with remote access, you must code a remote interface and a home interface. The remote interface defines the business methods
that are specific to the bean. For example, the remote interface of a bean named
BankAccountEJB might have business methods named debit and credit. The
home interface defines the bean’s life cycle methods—create and remove. For
entity beans, the home interface also defines finder methods and home methods.
DEFINING CLIENT ACCESS WITH INTERFACES
Finder methods are used to locate entity beans. Home methods are business
methods that are invoked on all instances of an entity bean class. Figure 3–2
shows how the interfaces control the client’s view of an enterprise bean.
Figure 3–2 Interfaces for an Enterprise Bean With Remote Access
Local Access
A local client has these characteristics:
• It must run in the same JVM as the enterprise bean it accesses.
• It may be a Web component or another enterprise bean.
• To the local client, the location of the enterprise bean it accesses is not
transparent.
• It is often an entity bean that has a container-managed relationship with
another entity bean.
To build an enterprise bean that allows local access, you must code the local
interface and the local home interface. The local interface defines the bean’s
business methods, and the local home interface defines its life cycle and finder
methods.
Local Interfaces and Container-Managed
Relationships
If an entity bean is the target of a container-managed relationship, then it must
have local interfaces. The direction of the relationship determines whether or not
59
60
ENTERPRISE BEANS
a bean is the target. In Figure 3–1, for example, ProductEJB is the target of a
unidirectional relationship with LineItemEJB. Because LineItemEJB accesses
ProductEJB locally, ProductEJB must have the local interfaces. LineItemEJB
also needs local interfaces—not because of its relationship with ProductEJB—
but because it is the target of a relationship with OrderEJB. And because the relationship between LineItemEJB and OrderEJB is bidirectional, both beans must
have local interfaces.
Because they require local access, entity beans that participate in a containermanaged relationship must reside in the same EJB JAR file. The primary benefit
of this locality is increased performance—local calls are usually faster than
remote calls.
Deciding on Remote or Local Access
The decision regarding whether to allow local or remote access depends on the
following factors.
Container-managed relationships: If an entity bean is the target of a containermanaged relationship, it must use local access.
Tight or loose coupling of related beans: Tightly coupled beans depend on one
another. For example, a completed sales order must have one or more line items,
which cannot exist without the order to which they belong. The OrderEJB and
LineItemEJB entity beans that model this relationship are tightly coupled.
Tightly coupled beans are good candidates for local access. Since they fit
together as a logical unit, they probably call each other often and would benefit
from the increased performance that is possible with local access.
Type of client: If an enterprise bean is accessed by J2EE application clients, then
it should allow remote access. In a production environment, these clients almost
always run on different machines than the J2EE server. If an enterprise bean’s
clients are Web components or other enterprise beans, then the type of access
depends on how you want to distribute your components.
Component distribution: J2EE applications are scalable because their server-side
components can be distributed across multiple machines. In a distributed application, for example, the Web components may run on a different server than the
enterprise beans they access. In this distributed scenario, the enterprise beans
should allow remote access.
If you aren’t sure which type of access an enterprise bean should have, then
choose remote access. This decision gives you more flexibility—in the future
DEFINING CLIENT ACCESS WITH INTERFACES
you can distribute your components to accommodate growing demands on your
application.
Although uncommon, it is possible for an enterprise bean to allow both remote
and local access. Such a bean would require both remote and local interfaces.
Performance and Access
Because of factors such as network latency, remote calls may be slower than
local calls. On the other hand, if you distribute components among different
servers, you might improve the application’s overall performance. Both of these
statements are generalizations; actual performance can vary in different operational environments. Nevertheless, you should keep in mind how your application design might affect performance.
Method Parameters and Access
The type of access affects the parameters of the bean methods that are called by
clients. The following topics apply not only to method parameters, but also to
method return values.
Isolation
An argument in a remote call is passed by value; it is a copy of an object. But an
argument in a local call is passed by reference, just like a normal method call in
the Java programming language.
The parameters of remote calls are more isolated than those of local calls. With
remote calls, the client and bean operate on different copies of a parameter
object. If the client changes the value of the object, the value of the copy in the
bean does not change. This layer of isolation can help protect the bean if the client accidentally modifies the data.
In a local call, both the client and the bean may modify the same object. In general, you should not rely on this side effect of local calls. Perhaps some day you
will want to distribute your components, replacing the local calls with remote
ones.
Granularity of Accessed Data
Because remote calls are likely to be slower than local calls, the parameters in
remote methods should be relatively coarse-grained. Since a coarse-grained
object contains more data than a fine-grained one, fewer access calls are
required.
61
62
ENTERPRISE BEANS
For example, suppose that a CustomerEJB entity bean is accessed remotely. This
bean would have a single getter method that returns a CustomerDetails object,
which encapsulates all of the customer’s information. But if CustomerEJB is to
be accessed locally, it could have a getter method for each instance variable:
getFirstName, getLastName, getPhoneNumber, and so forth. Because local
calls are fast, the multiple calls to these finer-grained getter methods would not
significantly degrade performance.
The Contents of an Enterprise Bean
To develop an enterprise bean, you must provide the following files:
• Deployment descriptor: An XML file that specifies information about the
bean such as its persistence type and transaction attributes. The deploy
tool utility creates the deployment descriptor when you step through the
New Enterprise Bean wizard.
• Enterprise bean class: Implements the methods defined in the following
interfaces.
• Interfaces: The remote and home interfaces are required for remote access.
For local access, the local and local home interfaces are required. See the
section Defining Client Access with Interfaces, page (58). (Please note
that these interfaces are not used by message-driven beans.)
• Helper classes: Other classes needed by the enterprise bean class, such as
exception and utility classes.
You package the files in the preceding list into an EJB JAR file, the module that
stores the enterprise bean. An EJB JAR file is portable and may be used for different applications. To assemble a J2EE application, you package one or more
modules—such as EJB JAR files—into an EAR file, the archive file that holds
the application. When you deploy the EAR file that contains the bean’s EJB JAR
file, you also deploy the enterprise bean onto the J2EE server.
NAMING CONVENTIONS FOR ENTERPRISE BEANS
Naming Conventions for Enterprise Beans
Because enterprise beans are composed of multiple parts, it’s useful to follow a
naming convention for your applications. Table 3–2 summarizes the conventions
for the example beans of this tutorial.
Table 3–2 Naming Conventions for Enterprise Beans
Item
Syntax
Example
Enterprise bean name (DD)
<name>EJB
AccountEJB
EJB JAR display name (DD)
<name>JAR
AccountJAR
Enterprise bean class
<name>Bean
AccountBean
Home interface
<name>Home
AccountHome
Remote interface
<name>
Account
Local home interface
Local<name>Home
LocalAccountHome
Local interface
Local<name>
LocalAccount
Abstract schema (DD)
<name>
Account
DD means that the item is an element in the bean’s deployment descriptor.
The Life Cycles of Enterprise Beans
An enterprise bean goes through various stages during its lifetime, or life cycle.
Each type of enterprise bean—session, entity, or message-driven—has a different life cycle.
The descriptions that follow refer to methods that are explained along with the
code examples in the next two chapters. If you are new to enterprise beans, you
should skip this section and try out the code examples first.
63
64
ENTERPRISE BEANS
The Life Cycle of a Stateful Session Bean
Figure 3–3 illustrates the stages that a session bean passes through during its lifetime. The client initiates the life cycle by invoking the create method. The EJB
container instantiates the bean and then invokes the setSessionContext and
ejbCreate methods in the session bean. The bean is now ready to have its business methods invoked.
While in the ready stage, the EJB container may decide to deactivate, or passivate, the bean by moving it from memory to secondary storage. (Typically, the
EJB container uses a least-recently-used algorithm to select a bean for passivation.) The EJB container invokes the bean’s ejbPassivate method immediately
before passivating it. If a client invokes a business method on the bean while it is
in the passive stage, the EJB container activates the bean, moving it back to the
ready stage, and then calls the bean’s ejbActivate method.
Figure 3–3 Life Cycle of a Stateful Session Bean
At the end of the life cycle, the client invokes the remove method and the EJB
container calls the bean’s ejbRemove method. The bean’s instance is ready for
garbage collection.
Your code controls the invocation of only two life-cycle methods—the create
and remove methods in the client. All other methods in Figure 3–3 are invoked
by the EJB container. The ejbCreate method, for example, is inside the bean
class, allowing you to perform certain operations right after the bean is instanti-
THE LIFE CYCLES OF ENTERPRISE BEANS
ated. For instance, you may wish to connect to a database in the ejbCreate
method. See Chapter 16 for more information.
The Life Cycle of a Stateless Session Bean
Because a stateless session bean is never passivated, its life cycle has just two
stages: nonexistent and ready for the invocation of business methods. Figure 3–4
illustrates the stages of a stateless session bean.
Figure 3–4 Life Cycle of a Stateless Session Bean
The Life Cycle of an Entity Bean
Figure 3–5 shows the stages that an entity bean passes through during its lifetime. After the EJB container creates the instance, it calls the setEntityCon
text method of the entity bean class. The setEntityContext method passes the
entity context to the bean.
After instantiation, the entity bean moves to a pool of available instances. While
in the pooled stage, the instance is not associated with any particular EJB object
identity. All instances in the pool are identical. The EJB container assigns an
identity to an instance when moving it to the ready stage.
There are two paths from the pooled stage to the ready stage. On the first path,
the client invokes the create method, causing the EJB container to call the ejb
65
66
ENTERPRISE BEANS
Create and ejbPostCreate methods. On the second path, the EJB container
invokes the ejbActivate method. While in the ready stage, an entity bean’s
business methods may be invoked.
There are also two paths from the ready stage to the pooled stage. First, a client
may invoke the remove method, which causes the EJB container to call the
ejbRemove method. Second, the EJB container may invoke the ejbPassivate
method.
At the end of the life cycle, the EJB container removes the instance from the
pool and invokes the unsetEntityContext method.
Figure 3–5 Life Cycle of an Entity Bean
THE LIFE CYCLES OF ENTERPRISE BEANS
In the pooled state, an instance is not associated with any particular EJB object
identity. With bean-managed persistence, when the EJB container moves an
instance from the pooled state to the ready state, it does not automatically set the
primary key. Therefore, the ejbCreate and ejbActivate methods must set the
primary key. If the primary key is incorrect, the ejbLoad and ejbStore methods
cannot synchronize the instance variables with the database. In the The SavingsAccountEJB Example, page (84), the ejbCreate method assigns the primary key from one of the input parameters. The ejbActivate method sets the
primary key (id ) as follows:
id = (String)context.getPrimaryKey();
In the pooled state, the values of the instance variables are not needed. You can
make these instance variables eligible for garbage collection by setting them to
null in the ejbPasssivate method.
The Life Cycle of a Message-Driven Bean
Figure 3–6 illustrates the stages in the life cycle of a message-driven bean.
Figure 3–6 Life Cycle of a Message-Driven Bean
67
68
ENTERPRISE BEANS
The EJB container usually creates a pool of message-driven bean instances. For
each instance, the EJB container instantiates the bean and performs these tasks:
1. It calls the setMessageDrivenContext method to pass the context object
to the instance.
2. It calls the instance’s ejbCreate method.
Like a stateless session bean, a message-driven bean is never passivated, and it
has only two states: nonexistent and ready to receive messages.
At the end of the life cycle, the container calls the ejbRemove method. The
bean’s instance is then ready for garbage collection.
4
A Session Bean
Example
Dale Green
SESSION beans are powerful because they extend the reach of your clients into
remote servers—yet they’re easy to build. In Chapter 2, you built a stateless session bean named ConverterEJB. This chapter examines the source code of a
stateful session bean called CartEJB.
In This Chapter
The CartEJB Example 70
Session Bean Class 70
Home Interface 75
Remote Interface 76
Helper Classes 76
Running the CartEJB Example 76
Other Enterprise Bean Features 78
Accessing Environment Entries 78
Comparing Enterprise Beans 80
Passing an Enterprise Bean’s Object Reference 80
69
70
A SESSION BEAN EXAMPLE
The CartEJB Example
The CartEJB session bean represents a shopping cart in an online bookstore. The
bean’s client may add a book to the cart, remove a book, or retrieve the cart’s
contents. To construct CartEJB, you need the following code:
• Session bean class (CartBean)
• Home interface (CartHome)
• Remote interface (Cart)
All session beans require a session bean class. All enterprise beans that permit
remote access must have a home and remote interface. To meet the needs of a
specific application, an enterprise bean may also need some helper classes. The
CartEJB session bean uses two helper classes, BookException and IdVerifier,
which are discussed in the section Helper Classes, page (76).
The source code for this example is in the j2eetutorial/exam
ples/src/ejb/cart directory. To compile the code, go to the
j2eetutorial/examples directory and type ant cart. A sample CartApp.ear
file is in the j2eetutorial/examples/ears directory.
Session Bean Class
The session bean class for this example is called CartBean. Like any session
bean, the CartBean class must meet these requirements:
•
•
•
•
•
•
•
It implements the SessionBean interface.
The class is defined as public.
The class cannot be defined as abstract or final.
It implements one or more ejbCreate methods.
It implements the business methods.
It contains a public constructor with no parameters.
It must not define the finalize method.
The source code for the CartBean class follows.
import java.util.*;
import javax.ejb.*;
public class CartBean implements SessionBean {
String customerName;
THE CARTEJB EXAMPLE
String customerId;
Vector contents;
public void ejbCreate(String person) throws CreateException {
if (person == null) {
throw new CreateException("Null person not allowed.");
}
else {
customerName = person;
}
}
customerId = "0";
contents = new Vector();
public void ejbCreate(String person, String id)
throws CreateException {
if (person == null) {
throw new CreateException("Null person not allowed.");
}
else {
customerName = person;
}
IdVerifier idChecker = new IdVerifier();
if (idChecker.validate(id)) {
customerId = id;
}
else {
throw new CreateException("Invalid id: "+ id);
}
}
contents = new Vector();
public void addBook(String title) {
}
contents.addElement(title);
public void removeBook(String title) throws BookException {
boolean result = contents.removeElement(title);
if (result == false) {
throw new BookException(title + "not in cart.");
}
71
72
A SESSION BEAN EXAMPLE
}
public Vector getContents() {
return contents;
}
public
public
public
public
public
CartBean() {}
void ejbRemove() {}
void ejbActivate() {}
void ejbPassivate() {}
void setSessionContext(SessionContext sc) {}
}
The SessionBean Interface
The SessionBean interface extends the EnterpriseBean interface, which in
turn extends the Serializable interface. The SessionBean interface declares
the ejbRemove, ejbActivate , ejbPassivate, and setSessionContext methods. The CartBean class doesn’t use these methods, but it must implement them
because they’re declared in the SessionBean interface. Consequently, these
methods are empty in the CartBean class. Later sections explain when you
might use these methods.
The ejbCreate Methods
Because an enterprise bean runs inside an EJB container, a client cannot directly
instantiate the bean. Only the EJB container can instantiate an enterprise bean.
During instantiation, the example program performs the following steps.
1. The client invokes a create method on the home object:
Cart shoppingCart = home.create("Duke DeEarl","123");
2. The EJB container instantiates the enterprise bean.
3. The EJB container invokes the appropriate ejbCreate method in Cart
Bean:
public void ejbCreate(String person, String id)
throws CreateException {
if (person == null) {
throw new CreateException("Null person not allowed.");
}
else {
customerName = person;
THE CARTEJB EXAMPLE
}
IdVerifier idChecker = new IdVerifier();
if (idChecker.validate(id)) {
customerId = id;
}
else {
throw new CreateException("Invalid id: "+ id);
}
}
contents = new Vector();
Typically, an ejbCreate method initializes the state of the enterprise bean. The
preceding ejbCreate method, for example, initializes the customerName and
customerId variables with the arguments passed by the create method.
An enterprise bean must have one or more ejbCreate methods. The signatures
of the methods must meet the following requirements:
• The access control modifier must be public.
• The return type must be void .
• If the bean allows remote access, the arguments must be legal types for the
Java™ Remote Method Invocation (RMI) API.
• The modifier cannot be static or final.
The throws clause may include the javax.ejb.CreateException and other
exceptions that are specific to your application. The ejbCreate method usually
throws a CreateException if an input parameter is invalid.
Business Methods
The primary purpose of a session bean is to run business tasks for the client. The
client invokes business methods on the remote object reference that is returned
by the create method. From the client’s perspective, the business methods
appear to run locally, but they actually run remotely in the session bean. The following code snippet shows how the CartClient program invokes the business
methods:
Cart shoppingCart = home.create("Duke DeEarl", "123");
. . .
shoppingCart.addBook("The Martian Chronicles");
shoppingCart.removeBook("Alice In Wonderland");
bookList = shoppingCart.getContents();
73
74
A SESSION BEAN EXAMPLE
The CartBean class implements the business methods in the following code:
public void addBook(String title) {
}
contents.addElement(new String(title));
public void removeBook(String title) throws BookException {
}
boolean result = contents.removeElement(title);
if (result == false) {
throw new BookException(title + "not in cart.");
}
public Vector getContents() {
return contents;
}
The signature of a business method must conform to these rules:
• The method name must not conflict with one defined by the EJB architecture. For example, you cannot call a business method ejbCreate or
ejbActivate.
• The access control modifier must be public.
• If the bean allows remote access, the arguments and return types must be
legal types for the Java RMI API.
• The modifier must not be static or final.
The throws clause may include exceptions that you define for your application.
The removeBook method, for example, throws the BookException if the book is
not in the cart.
To indicate a system-level problem, such as the inability to connect to a database, a business method should throw the javax.ejb.EJBException. When a
business method throws an EJBException, the container wraps it in a Remote
Exception, which is caught by the client. The container will not wrap application exceptions such as BookException. Because EJBException is a subclass of
RuntimeException, you do not need to include it in the throws clause of the
business method.
THE CARTEJB EXAMPLE
Home Interface
A home interface extends the javax.ejb.EJBHome interface. For a session bean,
the purpose of the home interface is to define the create methods that a remote
client may invoke. The CartClient program, for example, invokes this create
method:
Cart shoppingCart = home.create("Duke DeEarl", "123”);
Every create method in the home interface corresponds to an ejbCreate
method in the bean class. The signatures of the ejbCreate methods in the Cart
Bean class follow:
public void ejbCreate(String person) throws CreateException
. . .
public void ejbCreate(String person, String id)
throws CreateException
Compare the ejbCreate signatures with those of the create methods in the
CartHome interface:
import
import
import
import
java.io.Serializable;
java.rmi.RemoteException;
javax.ejb.CreateException;
javax.ejb.EJBHome;
public interface CartHome extends EJBHome {
Cart create(String person) throws
RemoteException, CreateException;
Cart create(String person, String id) throws
RemoteException, CreateException;
}
The signatures of the ejbCreate and create methods are similar, but differ in
important ways. The rules for defining the signatures of the create methods of a
home interface follow.
• The number and types of arguments in a create method must match those
of its corresponding ejbCreate method.
• The arguments and return type of the create method must be valid RMI
types.
• A create method returns the remote interface type of the enterprise bean.
(But an ejbCreate method returns void.)
75
76
A SESSION BEAN EXAMPLE
• The throws clause of the create method must include the
java.rmi.RemoteException and the javax.ejb.CreateException.
Remote Interface
The remote interface, which extends javax.ejb.EJBObject, defines the business methods that a remote client may invoke. Here is the source code for the
Cart remote interface:
import java.util.*;
import javax.ejb.EJBObject;
import java.rmi.RemoteException;
public interface Cart extends EJBObject {
}
public void addBook(String title) throws RemoteException;
public void removeBook(String title) throws
BookException, RemoteException;
public Vector getContents() throws RemoteException;
The method definitions in a remote interface must follow these rules:
• Each method in the remote interface must match a method implemented
in the enterprise bean class.
• The signatures of the methods in the remote interface must be identical to
the signatures of the corresponding methods in the enterprise bean class.
• The arguments and return values must be valid RMI types.
• The throws clause must include the java.rmi.RemoteException.
Helper Classes
The CartEJB session bean has two helper classes: BookException and IdVeri
fier. The BookException is thrown by the removeBook method and the IdVer
ifier validates the customerId in one of the ejbCreate methods. Helper
classes must reside in the EJB JAR file that contains the enterprise bean class.
Running the CartEJB Example
1. Start the J2EE server and deploytool. For instructions, see the section
Setting Up, page (22).
THE CARTEJB EXAMPLE
2. In deploytool open the j2eetutorial/examples/ears/CartApp.ear
file (File→Open). You should see the application that is displayed in Figure 4–1.
3. Deploy the CartApp application (Tools→Deploy). In the Introduction dialog box, make sure that you select the Return Client JAR checkbox. For
detailed instructions, see Deploying the J2EE™ Application, page (37).
4. Run the application.
a. In a terminal window, go to the j2eetutorial/examples/ears directory.
b. Set the APPCPATH environment variable to CartAppClient.jar.
c. Type the following command:
runclient client CartApp.ear name CartClient textauth
d. At the login prompts, enter guest for the user name and guest123 for
the password.
Figure 4–1 General Tabbed Pane of the CartApp Application
77
78
A SESSION BEAN EXAMPLE
Other Enterprise Bean Features
The topics that follow apply to both session and entity beans.
Accessing Environment Entries
Stored in an enterprise bean’s deployment descriptor, an environment entry is a
name-value pair that allows you to customize the bean’s business logic without
changing its source code. An enterprise bean that calculates discounts, for example, might have an environment entry named Discount Percent. Before deploying the bean’s application, you could run deploytool and assign Discount
Percent a value of .05 on the Env. Entries tab. (See Figure 4–2.) When you run
the application, the enterprise bean fetches the .05 value from its environment.
Figure 4–2 Env. Entries Tab of CheckerBean
OTHER ENTERPRISE BEAN FEATURES
In the following code example, the applyDiscount method uses environment
entries to calculate a discount based on the purchase amount. First, the method
locates the environment naming context by invoking lookup with the
java:comp/env parameter. Then it calls lookup on the environment to get the
values for the Discount Level and Discount Percent names. For example, if
you assign a value of .05 to the Discount Percent name in deploytool, the
code will assign .05 to the discountPercent variable. The applyDiscount
method, which follows, is in the CheckerBean class. The source code for this
example is in j2eetotorial/examples/src/ejb/checker. A sample Checker
App.ear file is in the j2eetutorial/examples/ears directory.
public double applyDiscount(double amount) {
try {
double discount;
Context initial = new InitialContext();
Context environment =
(Context)initial.lookup("java:comp/env");
Double discountLevel =
(Double)environment.lookup("Discount Level");
Double discountPercent =
(Double)environment.lookup("Discount Percent");
if (amount >= discountLevel.doubleValue()) {
discount = discountPercent.doubleValue();
}
else {
discount = 0.00;
}
return amount * (1.00 discount);
}
} catch (NamingException ex) {
throw new EJBException("NamingException: "+
ex.getMessage());
}
79
80
A SESSION BEAN EXAMPLE
Comparing Enterprise Beans
A client can determine if two stateful session beans are identical by invoking the
isIdentical method:
bookCart = home.create("Bill Shakespeare");
videoCart = home.create("Lefty Lee");
...
if (bookCart.isIdentical(bookCart)) {
// true ... }
if (bookCart.isIdentical(videoCart)) {
// false ... }
Because stateless session beans have the same object identity, the isIdentical
method always returns true when used to compare them.
To determine if two entity beans are identical, the client can invoke the isIden
tical method, or it can fetch and compare the beans’s primary keys:
String key1 = (String)accta.getPrimaryKey();
String key2 = (String)acctb.getPrimaryKey();
if (key1.compareTo(key2) == 0)
System.out.println(“equal”);
Passing an Enterprise Bean’s Object Reference
Suppose that your enterprise bean needs to pass a reference to itself to another
bean. You might want to pass the reference, for example, so that the second bean
can call the first bean’s methods. You can’t pass the this reference because it
points to the bean’s instance, which is running in the EJB container. Only the
container may directly invoke methods on the bean’s instance. Clients access the
instance indirectly by invoking methods on the object whose type is the bean’s
remote interface. It is the reference to this object (the bean’s remote reference)
that the first bean would pass to the second bean.
A session bean obtains its remote reference by calling the getEJBObject method
of the SessionContext interface. An entity bean would call the getEJBObject
method of the EntityContext interface. These interfaces provide beans with
access to the instance contexts maintained by the EJB container. Typically, the
OTHER ENTERPRISE BEAN FEATURES
bean saves the context in the setSessionContext method. The following code
fragment shows how a session bean might use these methods.
public class WagonBean implements SessionBean {
SessionContext context;
...
public void setSessionContext(SessionContext sc) {
this.context = sc;
}
...
public void passItOn(Basket basket) {
...
basket.copyItems(context.getEJBObject());
}
...
81
82
A SESSION BEAN EXAMPLE
5
Bean-Managed
Persistence Examples
Dale Green
DATA is at the heart of most business applications. In J2EE™ applications,
entity beans represent the business objects that are stored in a database. For
entity beans with bean-managed persistence, you must write the code for the
database access calls. Although writing this code is an additional responsibility,
you will have more control over how the entity bean accesses a database.
This chapter discusses the coding techniques for entity beans with bean-managed persistence. For conceptual information on entity beans, please see What Is
an Entity Bean?, page (51).
In This Chapter
The SavingsAccountEJB Example 84
Entity Bean Class 85
Home Interface 94
Remote Interface 96
Running the SavingsAccountEJB Example 97
deploytool Tips for Entity Beans With Bean-Managed Persistence 99
Mapping Table Relationships for Bean-Managed Persistence 99
One-to-One Relationships 99
One-to-Many Relationships 103
Many-to-Many Relationships 110
83
84
BEAN-MANAGED PERSISTENCE EXAMPLES
Primary Keys for Bean-Managed Persistence 113
The Primary Key Class 113
Primary Keys in the Entity Bean Class 114
Getting the Primary Key 115
Handling Exceptions 116
The SavingsAccountEJB Example
The entity bean illustrated in this section represents a simple bank account. The
state of SavingsAccountEJB is stored in the savingsaccount table of a relational database. The savingsaccount table is created by the following SQL
statement:
CREATE TABLE savingsaccount
(id VARCHAR(3)
CONSTRAINT pk_savingsaccount PRIMARY KEY,
firstname VARCHAR(24),
lastname VARCHAR(24),
balance
NUMERIC(10,2));
The SavingsAccountEJB example requires the following code:
• Entity bean class (SavingsAccountBean)
• Home interface (SavingsAccountHome)
• Remote interface (SavingsAccount)
This example also makes use of the following classes:
• A utility class named InsufficientBalanceException
• A client class called SavingsAccountClient
The source code for this example is in the j2eetutorial/exam
ples/src/ejb/savingsaccount directory. To compile the code, go to the
j2eetutorial/examples directory and type ant savingsaccount. A sample
SavingsAccountApp.ear file is in the j2eetutorial/examples/ears directory.
THE SAVINGSACCOUNT EJB EXAMPLE
Entity Bean Class
The sample entity bean class is called SavingsAccountBean. As you look
through its code, note that it meets the requirements of any entity bean with
bean-managed persistence. First of all, it implements the following:
• EntityBean interface
• Zero or more ejbCreate and ejbPostCreate methods
• Finder methods
• Business methods
• Home methods
In addition, an entity bean class with bean-managed persistence has these
requirements:
•
•
•
•
The class is defined as public.
The class cannot be defined as abstract or final.
It contains an empty constructor.
It does not implement the finalize method.
The EntityBean Interface
The EntityBean interface extends the EnterpriseBean interface, which extends
the Serializable interface. The EntityBean interface declares a number of
methods, such as ejbActivate and ejbLoad, which you must implement in your
entity bean class. These methods are discussed in later sections.
The ejbCreate Method
When the client invokes a create method, the EJB container invokes the corresponding ejbCreate method. Typically, an ejbCreate method in an entity bean
performs the following tasks:
• Inserts the entity state into the database
• Initializes the instance variables
• Returns the primary key
The ejbCreate method of SavingsAccountBean inserts the entity state into the
database by invoking the private insertRow method, which issues the SQL
INSERT statement. Here is the source code for the ejbCreate method:
85
86
BEAN-MANAGED PERSISTENCE EXAMPLES
public String ejbCreate(String id, String firstName,
String lastName, BigDecimal balance)
throws CreateException {
if (balance.signum() == 1) {
throw new CreateException
("A negative initial balance is not allowed.");
}
try {
insertRow(id, firstName, lastName, balance);
} catch (Exception ex) {
throw new EJBException("ejbCreate: " +
ex.getMessage());
}
this.id = id;
this.firstName = firstName;
this.lastName = lastName;
this.balance = balance;
}
return id;
Although the SavingsAccountBean class has just one ejbCreate method, an
enterprise bean may contain multiple ejbCreate methods. For an example, see
the CartEJB.java source code in the j2eetutorial/examples/src/ejb/cart
directory.
When writing an ejbCreate method for an entity bean, be sure to follow these
rules:
•
•
•
•
The access control modifier must be public.
The return type must be the primary key.
The arguments must be legal types for the Java™ 2 RMI API.
The method modifier cannot be final or static.
The throws clause may include the javax.ejb.CreateException and exceptions that are specific to your application. An ejbCreate method usually throws
a CreateException if an input parameter is invalid. If an ejbCreate method
cannot create an entity because another entity with the same primary key already
exists, it should throw a javax.ejb.DuplicateKeyException (a subclass of
CreateException). If a client receives a CreateException or a Dupli
cateKeyException, it should assume that the entity was not created.
THE SAVINGSACCOUNT EJB EXAMPLE
The state of an entity bean may be directly inserted into the database by an application that is unknown to the J2EE server. For example, a SQL script might
insert a row into the savingsaccount table. Although the entity bean for this
row was not created by an ejbCreate method, the bean can be located by a client program.
The ejbPostCreate Method
For each ejbCreate method, you must write an ejbPostCreate method in the
entity bean class. The EJB container invokes ejbPostCreate immediately after
it calls ejbCreate. Unlike the ejbCreate method, the ejbPostCreate method
can invoke the getPrimaryKey and getEJBObject methods of the EntityCon
text interface. For more information on the getEJBObject method, see the section Passing an Enterprise Bean’s Object Reference, page (80). Often, your
ejbPostCreate methods will be empty.
The signature of an ejbPostCreate method must meet the following requirements:
• The number and types of arguments must match a corresponding ejbCre
ate method.
• The access control modifier must be public.
• The method modifier cannot be final or static.
• The return type must be void .
The throws clause may include the javax.ejb.CreateException and exceptions that are specific to your application.
The ejbRemove Method
A client deletes an entity bean by invoking the remove method. This invocation
causes the EJB container to call the ejbRemove method, which deletes the entity
state from the database. In the SavingsAccountBean class, the ejbRemove
method invokes a private method named deleteRow, which issues a SQL
DELETE statement. The ejbRemove method is short:
public void ejbRemove() {
try {
deleteRow(id);
catch (Exception ex) {
throw new EJBException("ejbRemove: " +
ex.getMessage());
}
}
87
88
BEAN-MANAGED PERSISTENCE EXAMPLES
If the ejbRemove method encounters a system problem, it should throw the
javax.ejb.EJBException. If it encounters an application error, it should throw
a javax.ejb.RemoveException. For a comparison of system and application
exceptions, see the section Handling Exceptions, page (116).
An entity bean may also be removed directly by a database deletion. For example, if a SQL script deletes a row that contains an entity bean state, then that
entity bean is removed.
The ejbLoad and ejbStore Methods
If the EJB container needs to synchronize the instance variables of an entity bean
with the corresponding values stored in a database, it invokes the ejbLoad and
ejbStore methods. The ejbLoad method refreshes the instance variables from
the database, and the ejbStore method writes the variables to the database. The
client may not call ejbLoad and ejbStore.
If a business method is associated with a transaction, the container invokes ejb
Load before the business method executes. Immediately after the business
method executes, the container calls ejbStore. Because the container invokes
ejbLoad and ejbStore, you do not have to refresh and store the instance variables in your business methods. The SavingsAccountBean class relies on the
container to synchronize the instance variables with the database. Therefore, the
business methods of SavingsAccountBean should be associated with transactions.
If the ejbLoad and ejbStore methods cannot locate an entity in the underlying
database, they should throw the javax.ejb.NoSuchEntityException. This
exception is a subclass of EJBException. Because EJBException is a subclass
of RuntimeException, you do not have to include it in the throws clause. When
NoSuchEntityException is thrown, the EJB container wraps it in a RemoteEx
ception before returning it to the client.
In the SavingsAccountBean class, ejbLoad invokes the loadRow method, which
issues a SQL SELECT statement and assigns the retrieved data to the instance
variables. The ejbStore method calls the storeRow method, which stores the
instance variables in the database with a SQL UPDATE statement. Here is the code
for the ejbLoad and ejbStore methods:
public void ejbLoad() {
try {
loadRow();
} catch (Exception ex) {
THE SAVINGSACCOUNT EJB EXAMPLE
}
}
throw new EJBException("ejbLoad: " +
ex.getMessage());
public void ejbStore() {
}
try {
storeRow();
} catch (Exception ex) {
throw new EJBException("ejbStore: " +
ex.getMessage());
}
The Finder Methods
The finder methods allow clients to locate entity beans. The SavingsAccount
Client program locates entity beans with three finder methods:
SavingsAccount jones = home.findByPrimaryKey("836");
...
Collection c = home.findByLastName("Smith");
...
Collection c = home.findInRange(20.00, 99.00);
For every finder method available to a client, the entity bean class must implement a corresponding method that begins with the prefix ejbFind. The Sav
ingsAccountBean class, for example, implements the ejbFindByLastName
method as follows:
public Collection ejbFindByLastName(String lastName)
throws FinderException {
Collection result;
}
try {
result = selectByLastName(lastName);
} catch (Exception ex) {
throw new EJBException("ejbFindByLastName " +
ex.getMessage());
}
return result;
The finder methods that are specific to your application, such as ejbFindBy
LastName and ejbFindInRange, are optional—but the ejbFindByPrimaryKey
89
90
BEAN-MANAGED PERSISTENCE EXAMPLES
method is required. As its name implies, the ejbFindByPrimaryKey method
accepts as an argument the primary key, which it uses to locate an entity bean. In
the SavingsAccountBean class, the primary key is the id variable. Here is the
code for the ejbFindByPrimaryKey method:
public String ejbFindByPrimaryKey(String primaryKey)
throws FinderException {
boolean result;
try {
result = selectByPrimaryKey(primaryKey);
} catch (Exception ex) {
throw new EJBException("ejbFindByPrimaryKey: " +
ex.getMessage());
}
}
if (result) {
return primaryKey;
}
else {
throw new ObjectNotFoundException
("Row for id " + primaryKey + " not found.");
}
The ejbFindByPrimaryKey method may look strange to you, because it uses a
primary key for both the method argument and return value. However, remember
that the client does not call ejbFindByPrimaryKey directly. It is the EJB container that calls the ejbFindByPrimaryKey method. The client invokes the
findByPrimaryKey method, which is defined in the home interface.
The following list summarizes the rules for the finder methods that you implement in an entity bean class with bean-managed persistence:
The ejbFindByPrimaryKey method must be implemented.
A finder method name must start with the prefix ejbFind.
The access control modifier must be public.
The method modifier cannot be final or static.
The arguments and return type must be legal types for the Java 2 RMI API.
(This requirement applies only to methods defined in a remote—not
local—home interface.)
• The return type must be the primary key or a collection of primary keys.
•
•
•
•
•
THE SAVINGSACCOUNT EJB EXAMPLE
The throws clause may include the javax.ejb.FinderException and exceptions that are specific to your application. If a finder method returns a single primary key and the requested entity does not exist, the method should throw the
javax.ejb.ObjectNotFoundException (a subclass of FinderException). If a
finder method returns a collection of primary keys and it does not find any
objects, it should return an empty collection.
The Business Methods
The business methods contain the business logic that you want to encapsulate
within the entity bean. Usually, the business methods do not access the database,
allowing you to separate the business logic from the database access code. The
SavingsAccountBean class contains the following business methods:
public void debit(BigDecimal amount)
throws InsufficientBalanceException {
}
if (balance.compareTo(amount) == 1) {
throw new InsufficientBalanceException();
}
balance = balance.subtract(amount);
public void credit(BigDecimal amount) {
}
balance = balance.add(amount);
public String getFirstName() {
}
return firstName;
public String getLastName() {
}
return lastName;
public BigDecimal getBalance() {
}
return balance;
The SavingsAccountClient program invokes the business methods as follows:
91
92
BEAN-MANAGED PERSISTENCE EXAMPLES
BigDecimal zeroAmount = new BigDecimal("0.00");
SavingsAccount duke = home.create("123", "Duke", "Earl",
zeroAmount);
. . .
duke.credit(new BigDecimal("88.50"));
duke.debit(new BigDecimal("20.25"));
BigDecimal balance = duke.getBalance();
The requirements for the signature of a business method are the same for both
session and entity beans:
• The method name must not conflict with a method name defined by the
EJB architecture. For example, you cannot call a business method ejb
Create or ejbActivate.
• The access control modifier must be public.
• The method modifier cannot be final or static.
• The arguments and return types must be legal types for the Java 2 RMI
API. This requirement applies only to methods defined in a remote—not
local—home interface.
The throws clause may include the exceptions that you define for your application. The debit method, for example, throws the InsufficientBalanceExcep
tion. To indicate a system-level problem, a business method should throw the
javax.ejb.EJBException.
The Home Methods
A home method contains the business logic that applies to all entity beans of a
particular class. In contrast, the logic in a business method applies to a single
entity bean, an instance with a unique identity. During a home method invocation, the instance has neither a unique identity nor a state that represents a business object. Consequently, a home method must not access the bean’s
persistence state (instance variables). (For container-managed persistence, a
home method also must not access relationships.)
Typically, a home method locates a collection of bean instances and invokes
business methods as it iterates through the collection. This approach is taken by
the ejbHomeChargeForLowBalance method of the SavingsAccountBean class.
The ejbHomeChargeForLowBalance method applies a service charge to all savings accounts with balances less than a specified amount. The method locates
these accounts by invoking the findInRange method. As it iterates through the
collection of SavingsAccount instances, the ejbHomeChargeForLowBalance
THE SAVINGSACCOUNT EJB EXAMPLE
method checks the balance and invokes the debit business method. Here is the
source code of the ejbHomeChargeForLowBalance method:
public void ejbHomeChargeForLowBalance(
BigDecimal minimumBalance, BigDecimal charge)
throws InsufficientBalanceException {
try {
SavingsAccountHome home =
(SavingsAccountHome)context.getEJBHome();
Collection c = home.findInRange(new BigDecimal("0.00"),
minimumBalance.subtract(new BigDecimal("0.01")));
Iterator i = c.iterator();
while (i.hasNext()) {
SavingsAccount account = (SavingsAccount)i.next();
if (account.getBalance().compareTo(charge) == 1) {
account.debit(charge);
}
}
}
} catch (Exception ex) {
throw new EJBException("ejbHomeChargeForLowBalance: "
+ ex.getMessage());
}
The home interface defines a corresponding method named chargeForLowBal
ance (see Home Method Definitions, page (96)). Since the interface provides the
client view, the SavingsAccountClient program invokes the home method as
follows:
SavingsAccountHome home;
. . .
home.chargeForLowBalance(new BigDecimal("10.00"),
new BigDecimal("1.00"));
In the entity bean class, the implementation of a home method must adhere to
these rules:
• A home method name must start with the prefix ejbHome.
• The access control modifier must be public.
• The method modifier cannot be static.
93
94
BEAN-MANAGED PERSISTENCE EXAMPLES
The throws clause may include exceptions that are specific to your application;
it must not throw the java.rmi.RemoteException.
Database Calls
Table 5–1summarizes the database access calls in the SavingsAccountBean
class. The business methods of the SavingsAccountBean class are absent from
the preceding table because they do not access the database. Instead, these business methods update the instance variables, which are written to the database
when the EJB container calls ejbStore. Another developer might have chosen
to access the database in the business methods of the SavingsAccountBean
class. This choice is one of those design decisions that depend on the specific
needs of your application.
Table 5–1 SQL Statements in SavingsAccountBean
Method
SQL Statement
ejbCreate
INSERT
ejbFindByPrimaryKey
SELECT
ejbFindByLastName
SELECT
ejbFindInRange
SELECT
ejbLoad
SELECT
ejbRemove
DELETE
ejbStore
UPDATE
Before accessing a database, you must connect to it. For more information, see
Chapter 16.
Home Interface
The home interface defines the methods that allow a client to create and find an
entity bean. The SavingsAccountHome interface follows:
THE SAVINGSACCOUNT EJB EXAMPLE
import
import
import
import
java.util.Collection;
java.math.BigDecimal;
java.rmi.RemoteException;
javax.ejb.*;
public interface SavingsAccountHome extends EJBHome {
public SavingsAccount create(String id, String firstName,
String lastName, BigDecimal balance)
throws RemoteException, CreateException;
public SavingsAccount findByPrimaryKey(String id)
throws FinderException, RemoteException;
public Collection findByLastName(String lastName)
throws FinderException, RemoteException;
public Collection findInRange(BigDecimal low,
BigDecimal high)
throws FinderException, RemoteException;
}
public void chargeForLowBalance(BigDecimal minimumBalance,
BigDecimal charge)
throws InsufficientBalanceException, RemoteException;
create Method Definitions
Each create method in the home interface must conform to the following
requirements:
• It has the same number and types of arguments as its matching ejbCreate
method in the enterprise bean class.
• It returns the remote interface type of the enterprise bean.
• The throws clause includes the exceptions specified by the throws clause
of the corresponding ejbCreate and ejbPostCreate methods.
• The throws clause includes the javax.ejb.CreateException.
• If the method is defined in a remote—not local—home interface, then the
throws clause includes the java.rmi.RemoteException.
Finder Method Definitions
Every finder method in the home interface corresponds to a finder method in the
entity bean class. The name of a finder method in the home interface begins with
find, whereas the corresponding name in the entity bean class begins with
95
96
BEAN-MANAGED PERSISTENCE EXAMPLES
ejbFind. For example, the SavingsAccountHome class defines the findByLast
Name method, and the SavingsAccountBean class implements the ejbFindBy
LastName method. The rules for defining the signatures of the finder methods of
a home interface follow.
• The number and types of arguments must match those of the corresponding method in the entity bean class.
• The return type is the entity bean’s remote interface type, or a collection
of those types.
• The exceptions in the throws clause include those of the corresponding
method in the entity bean class.
• The throws clause contains the javax.ejb.FinderException.
• If the method is defined in a remote—not local—home interface, then the
throws clause includes the java.rmi.RemoteException.
Home Method Definitions
Each home method definition in the home interface corresponds to a method in
the entity bean class. In the home interface, the method name is arbitrary, provided that it does not begin with create or find. In the bean class, the matching
method name begins with ejbHome. For example, in the SavingsAccountBean
class the name is ejbChargeForLowBalance, but in the SavingsAccountHome
interface the name is chargeForLowBalance.
The home method signature must follow the same rules specified for finder
methods in the previous section (except that a home method does not throw a
FinderException).
Remote Interface
The remote interface extends javax.ejb.EJBObject and defines the business
methods that a remote client may invoke. Here is the SavingsAccount remote
interface:
import javax.ejb.EJBObject;
import java.rmi.RemoteException;
import java.math.BigDecimal;
public interface SavingsAccount extends EJBObject {
public void debit(BigDecimal amount)
throws InsufficientBalanceException, RemoteException;
THE SAVINGSACCOUNT EJB EXAMPLE
public void credit(BigDecimal amount)
throws RemoteException;
public String getFirstName()
throws RemoteException;
public String getLastName()
throws RemoteException;
}
public BigDecimal getBalance()
throws RemoteException;
The requirements for the method definitions in a remote interface are the same
for both session and entity beans:
• Each method in the remote interface must match a method in the enterprise
bean class.
• The signatures of the methods in the remote interface must be identical to
the signatures of the corresponding methods in the enterprise bean class.
• The arguments and return values must be valid RMI types.
• The throws clause must include java.rmi.RemoteException.
A local interface has the same requirements, with the following exceptions:
• The arguments and return values are not required to be valid RMI types.
• The throws clause does not include java.rmi.RemoteException.
Running the SavingsAccountEJB Example
Setting Up the Database
The instructions that follow explain how to use the SavingsAccountEJB example with a Cloudscape database. The Cloudscape software is included with the
J2EE SDK download bundle.
1. From the command-line prompt, run the Cloudscape database server by
typing cloudscape start. (When you are ready to shut down the
server, type cloudscape stop.)
2. Create the savingsaccount database table.
a. Go to the j2eetutorial/examples directory
b. Type ant createsavingsaccounttable.
97
98
BEAN-MANAGED PERSISTENCE EXAMPLES
You may also run this example with databases other than Cloudscape. (See the
Release Notes of the J2EE SDK for a list of supported databases.) If you are
using one of these other databases, you may run the j2eetutorial/exam
ples/sql/savingsaccount.sql script to create the savingsaccount table.
Deploying the Application
1. In deploytool, open the j2eetutorial/examples/ears/SavingsAc
countApp.ear file (File→Open).
2. Deploy the SavingsAccountApp application (Tools→Deploy). In the
Introduction dialog box, make sure that you select the Return Client JAR
checkbox. For detailed instructions, see Deploying the J2EE™
Application, page (37).
Running the Client
1. In a terminal window, go to the j2eetutorial/examples/ears directory.
2. Set the APPCPATH environment variable to SavingsAccountAppCli
ent.jar.
3. Type the following command on a single line:
runclient client SavingsAccountApp.ear name
SavingsAccountClient textauth
4. At the login prompts, enter guest for the user name and guest123 for the
password.
5. The client should display the following lines:
balance = 68.25
balance = 32.53
456: 44.77
730: 19.54
268: 100.07
836: 32.55
456: 44.77
4.00
7.00
DEPLOYTOOL
TIPS FOR ENTITY BEANS WITH BEAN-MANAGED PERSISTENCE
deploytool Tips for Entity Beans With BeanManaged Persistence
Chapter 4 gave step-by-step instructions for creating and packaging a session
bean. To build an entity bean, you follow the same procedures, but with the following exceptions.
1. In the New Enterprise Bean wizard, specify the bean’s type and persistent
management.
a. In the General dialog box, select the Entity radio button.
b. In the Entity Settings dialog box, select the radio button for Bean-Managed Persistence.
2. In the Resource Refs tab, specify the resource factories referenced by the
bean. These settings enable the bean to connect to the database. For
instructions, see the section deploytool Tips for Resource
References, page (354).
3. Before you deploy the bean, verify that the JNDI names are correct.
a. Select the application from the tree.
b. Select the JNDI Names tab.
Mapping Table Relationships for BeanManaged Persistence
In a relational database, tables can be related by common columns. The relationships between the tables affect the design of their corresponding entity beans.
The entity beans discussed in this section are backed up by tables with the following types of relationships:
• One-to-one
• One-to-many
• Many-to-many
One-to-One Relationships
In a one-to-one relationship, each row in a table is related to a single row in
another table. For example, in a warehouse application, a storagebin table
might have a one-to-one relationship with a widget table. This application
100
BEAN-MANAGED PERSISTENCE EXAMPLES
would model a physical warehouse in which each storage bin contains one type
of widget and each widget resides in one storage bin.
Figure 5–1 illustrates the storagebin and widget tables. Because the storage
binid uniquely identifies a row in the storagebin table, it is that table’s primary key. The widgetid is the primary key of the widget table. The two tables
are related because the widgetid is also a column in the storagebin table. By
referring to the primary key of the widget table, the widgetid in the storage
bin table identifies which widget resides in a particular storage bin in the warehouse. Because the widgetid of the storagebin table refers to the primary key
of another table, it is called a foreign key. (The figures in this chapter denote a
primary key with PK and a foreign key with FK.)
Figure 5–1 One-to-One Table Relationship
A dependent (child) table includes a foreign key that matches the primary key of
the referenced (parent) table. The values of the foreign keys in the storagebin
(child) table depend on the primary keys in the widget (parent) table. For example, if the storagebin table has a row with a widgetid of 344, then the widget
table should also have a row whose widgetid is 344.
When designing a database application, you may choose to enforce the dependency between the parent and child tables. There are two ways to enforce such a
dependency: by defining a referential constraint in the database or by performing
checks in the application code. The storagebin table has a referential constraint
named fk_widgetid:
CREATE TABLE storagebin
(storagebinid VARCHAR(3)
CONSTRAINT pk_storagebin PRIMARY KEY,
widgetid VARCHAR(3),
quantity INTEGER,
CONSTRAINT fk_widgetid
FOREIGN KEY (widgetid)
REFERENCES widget(widgetid));
MAPPING TABLE RELATIONSHIPS FOR BEAN-MANAGED PERSISTENCE101
The source code for the following example is in the j2eetutorial/exam
ples/src/ejb/storagebin directory. To compile the code, go to the
j2eetutorial/examples directory and type ant storagebin. A sample Stor
ageBinApp.ear file is in the j2eetutorial/examples/ears directory.
The StorageBinBean and WidgetBean classes illustrate the one-to-one relationship of the storagebin and widget tables. The StorageBean class contains
variables for each column in the storagebin table, including the foreign key,
widgetId:
private String storageBinId;
private String widgetId;
private int quantity;
The ejbFindByWidgetId method of the StorageBean class returns the stor
ageBinId that matches a given widgetId:
public String ejbFindByWidgetId(String widgetId)
throws FinderException {
String storageBinId;
try {
storageBinId = selectByWidgetId(widgetId);
} catch (Exception ex) {
throw new EJBException("ejbFindByWidgetId: " +
ex.getMessage());
}
}
if (storageBinId == null) {
throw new ObjectNotFoundException
("Row for widgetId " + widgetId + " not found.");
}
else {
return storageBinId;
}
The ejbFindByWidgetId method locates the widgetId by querying the database
in the selectByWidgetId method:
private String selectByWidgetId(String widgetId)
throws SQLException {
String storageBinId;
102
BEAN-MANAGED PERSISTENCE EXAMPLES
String selectStatement =
"select storagebinid " +
"from storagebin where widgetid = ? ";
PreparedStatement prepStmt =
con.prepareStatement(selectStatement);
prepStmt.setString(1, widgetId);
ResultSet rs = prepStmt.executeQuery();
if (rs.next()) {
storageBinId = rs.getString(1);
}
else {
storageBinId = null;
}
}
prepStmt.close();
return storageBinId;
To find out in which storage bin a widget resides, the StorageBinClient program calls the findByWidgetId method:
String widgetId = "777";
StorageBin storageBin =
storageBinHome.findByWidgetId(widgetId);
String storageBinId = (String)storageBin.getPrimaryKey();
int quantity = storageBin.getQuantity();
Running the StorageBinEJB Example
1. Create the storagebin database table.
a. Go to the j2eetutorial/examples directory.
b. Type ant createstoragebintable.
2. Deploy the StorageBinApp.ear file (located in the j2eetutorial/exam
ples/ears directory).
3. Run the client.
a. Go to the j2eetutorial/examples/ears directory.
b. Set the APPCPATH environment variable to StorageBinAppCli
ent.jar.
c. Type the following command on a single line:
MAPPING TABLE RELATIONSHIPS FOR BEAN-MANAGED PERSISTENCE103
runclient client StorageBinApp.ear name StorageBinClient
textauth
d. At the login prompts, enter guest for the user name and guest123 for
the password.
One-to-Many Relationships
If the primary key in a parent table matches multiple foreign keys in a child
table, then the relationship is one-to-many. This relationship is common in database applications. For example, an application for a sports league might access a
team table and a player table. Each team has multiple players, and each player
belongs to a single team. Every row in the child table (player) has a foreign key
identifying the player’s team. This foreign key matches the team table’s primary
key.
The sections that follow describe how you might implement one-to-many relationships in entity beans. When designing such entity beans, you must decide
whether both tables are represented by entity beans, or just one.
A Helper Class for the Child Table
Not every database table needs to be mapped to an entity bean. If a database
table doesn’t represent a business entity, or if it stores information that is contained in another entity, then the table should be represented with a helper class.
In an online shopping application, for example, each order submitted by a customer can have multiple line items. The application stores the information in the
database tables shown by Figure 5–2.
Figure 5–2 One-to-Many Relationship: Order and Line Items
104
BEAN-MANAGED PERSISTENCE EXAMPLES
Not only does a line item belong to an order, it also does not exist without the
order. Therefore, the lineitems table should be represented with a helper class
and not with an entity bean. Using a helper class in this case is not required, but
doing so might improve performance because a helper class uses fewer system
resources than an entity bean.
The source code for the following example is in the j2eetutorial/exam
ples/src/ejb/order
directory. To compile the code, go to the
j2eetutorial/examples directory and type ant order. A sample Order
App.ear file is in the j2eetutorial/examples/ears directory.
The LineItem and OrderBean classes show how to implement a one-to-many
relationship with a helper class (LineItem). The instance variables in the
LineItem class correspond to the columns in the lineitems table. The itemNo
variable matches the primary key for the lineitems table, and the orderId variable represents the table’s foreign key. Here is the source code for the LineItem
class:
public class LineItem implements java.io.Serializable {
String productId;
int quantity;
double unitPrice;
int itemNo;
String orderId;
public LineItem(String productId, int quantity,
double unitPrice, int itemNo, String orderId) {
}
this.productId = productId;
this.quantity = quantity;
this.unitPrice = unitPrice;
this.itemNo = itemNo;
this.orderId = orderId;
public String getProductId() {
return productId;
}
public int getQuantity() {
return quantity;
}
public double getUnitPrice() {
MAPPING TABLE RELATIONSHIPS FOR BEAN-MANAGED PERSISTENCE105
}
return unitPrice;
public int getItemNo() {
return itemNo;
}
}
public String getOrderId() {
return orderId;
}
The OrderBean class contains an ArrayList variable named lineItems. Each
element in the lineItems variable is a LineItem object. The lineItems variable is passed to the OrderBean class in the ejbCreate method. For every
LineItem object in the lineItems variable, the ejbCreate method inserts a row
into the lineitems table. It also inserts a single row into the orders table. The
code for the ejbCreate method follows:
public String ejbCreate(String orderId, String customerId,
String status, double totalPrice, ArrayList lineItems)
throws CreateException {
try {
insertOrder(orderId, customerId, status, totalPrice);
for (int i = 0; i < lineItems.size(); i++) {
LineItem item = (LineItem)lineItems.get(i);
insertItem(item);
}
} catch (Exception ex) {
throw new EJBException("ejbCreate: " +
ex.getMessage());
}
this.orderId = orderId;
this.customerId = customerId;
this.status = status;
this.totalPrice = totalPrice;
this.lineItems = lineItems ;
}
return orderId;
The OrderClient program creates and loads an ArrayList of LineItem objects.
The program passes this ArrayList to the entity bean when it invokes the cre
ate method:
106
BEAN-MANAGED PERSISTENCE EXAMPLES
ArrayList lineItems = new ArrayList();
lineItems.add(new LineItem("p23", 13, 12.00, 1, "123"));
lineItems.add(new LineItem("p67", 47, 89.00, 2, "123"));
lineItems.add(new LineItem("p11", 28, 41.00, 3, "123"));
. . .
Order duke = home.create("123", "c44", "open",
totalItems(lineItems), lineItems);
Other methods in the OrderBean class also access both database tables. The
ejbRemove method, for example, deletes not only a row from the orders table,
but also deletes all corresponding rows in the lineitems table. The ejbLoad and
ejbStore methods synchronize the state of an OrderEJB instance, including the
lineItems ArrayList, with the orders and lineitems tables.
The ejbFindByProductId method enables clients to locate all orders that have a
particular line item. This method queries the lineitems table for all rows with a
particular productId. The method returns a Collection of productId String
objects. The OrderClient program iterates through the Collection and prints
the primary key of each order:
Collection c = home.findByProductId("p67");
Iterator i=c.iterator();
while (i.hasNext()) {
Order order = (Order)i.next();
String id = (String)order.getPrimaryKey();
System.out.println(id);
}
Running the OrderEJB Example
1. Create the orders database table:.
a. Go to the j2eetutorial/examples/src directory.
b. Type ant createordertable.
2. Deploy the OrderApp.ear file (located in the j2eetutorial/exam
ples/ears directory).
3. Run the client.
a. Go to the j2eetutorial/examples/ears directory.
b. Set the APPCPATH environment variable to OrderAppClient.jar.
c. Type the following command on a single line:
runclient client OrderApp.ear name OrderClient
textauth
MAPPING TABLE RELATIONSHIPS FOR BEAN-MANAGED PERSISTENCE107
d. At the login prompts, enter guest for the user name and guest123 for
the password.
An Entity Bean for the Child Table
You should consider building an entity bean for a child table under the following
conditions:
• The information in the child table is not dependent on the parent table.
• The business entity of the child table could exist without that of the parent
table.
• The child table might be accessed by another application that does not
access the parent table.
These conditions exist in the following scenario. Suppose that each sales representative in a company has multiple customers and that each customer has only
one sales representative. The company tracks its sales force with a database
application. In the database, each row in the salesrep table (parent) matches
multiple rows in the customer table (child). Figure 5–3 illustrates this relationship.
.
Figure 5–3 One-to-Many Relationship: Sales Representative and Customers
The SalesRepBean and CustomerBean entity bean classes implement the one-tomany relationship of the sales and customer tables.
The source code for this example is in the j2eetutorial/exam
ples/src/ejb/salesrep directory. To compile the code, go to the
j2eetutorial/examples directory and type ant salesrep. A sample SalesRe
pApp.ear file is in the j2eetutorial/examples/ears directory.
The SalesRepBean class contains a variable named customerIds, which is an
ArrayList of String elements. These String elements identify which custom-
108
BEAN-MANAGED PERSISTENCE EXAMPLES
ers belong to the sales representative. Because the customerIds variable reflects
this relationship, the SalesRepBean class must keep the variable up to date.
The SalesRepBean class instantiates the customerIds variable in the setEnti
tyContext method, not in ejbCreate. The container invokes setEntityCon
text just once—when it creates the bean instance—ensuring that customerIds
is instantiated just once. Because the same bean instance can assume different
identities during its life cycle, instantiating customerIds in ejbCreate might
cause multiple and unnecessary instantiations. Therefore, the SalesRepBean
class instantiates the customerIds variable in setEntityContext:
public void setEntityContext(EntityContext context) {
this.context = context;
customerIds = new ArrayList();
try {
makeConnection();
Context initial = new InitialContext();
Object objref =
initial.lookup("java:comp/env/ejb/Customer");
}
customerHome =
(CustomerHome)PortableRemoteObject.narrow(objref,
CustomerHome.class);
} catch (Exception ex) {
throw new EJBException("setEntityContext: " +
ex.getMessage());
}
Invoked by the ejbLoad method, loadCustomerIds is a private method that
refreshes the customerIds variable. There are two approaches when coding a
method such as loadCustomerIds: fetch the identifiers from the customer database table or get them from the CustomerEJB entity bean. Fetching the identifiers from the database might be faster, but exposes the code in the SalesRepBean
class to the CustomerEJB bean’s underlying database table. In the future, if you
were to change the CustomerEJB bean’s table (or move the bean to a different
J2EE server), you might need to change the SalesRepBean code. But if the
SalesRepBean class gets the identifiers from the CustomerEJB entity bean, no
coding changes would be required. The two approaches present a trade-off: performance versus flexibility. The SalesRepEJB example opts for flexibility, loading the customerIds variable by calling the findSalesRep and getPrimaryKey
methods of CustomerEJB. Here is the code for the loadCustomerIds method:
MAPPING TABLE RELATIONSHIPS FOR BEAN-MANAGED PERSISTENCE109
private void loadCustomerIds() {
customerIds.clear();
try {
Collection c = customerHome.findBySalesRep(salesRepId);
Iterator i=c.iterator();
while (i.hasNext()) {
Customer customer = (Customer)i.next();
String id = (String)customer.getPrimaryKey();
customerIds.add(id);
}
}
} catch (Exception ex) {
throw new EJBException("Exception in loadCustomerIds: " +
ex.getMessage());
}
If a customer’s sales representative changes, the client program updates the database by calling the setSalesRepId method of the CustomerBean class. The next
time a business method of the SalesRepBean class is called, the ejbLoad method
invokes loadCustomerIds, which refreshes the customerIds variable. (To
ensure that ejbLoad is invoked before each business method, set the transaction
attributes of the business methods to Required.) For example, the SalesRepCli
ent program changes the salesRepId for a customer named Mary Jackson as
follows:
Customer mary = customerHome.findByPrimaryKey("987");
mary.setSalesRepId("543");
The salesRepId value 543 identifies a sales representative named Janice Martin. To list all of Janice’s customers, the SalesRepClient program invokes the
getCustomerIds method, iterates through the ArrayList of identifiers, and
locates each CustomerEJB entity bean by calling its findByPrimaryKey method:
SalesRep janice = salesHome.findByPrimaryKey("543");
ArrayList a = janice.getCustomerIds();
i = a.iterator();
while (i.hasNext()) {
String customerId = (String)i.next();
Customer customer =
110
BEAN-MANAGED PERSISTENCE EXAMPLES
customerHome.findByPrimaryKey(customerId);
String name = customer.getName();
System.out.println(customerId + ": " + name);
}
Running the SalesRepEJB Example
1. Create the database tables.
a. Go to the j2eetutorial/examples/src directory.
b. Type ant createsalesreptable.
2. Deploy the SalesRepApp.ear file (located in the j2eetutorial/exam
ples/ears directory).
3. Run the client.
a. Go to the j2eetutorial/examples/ears directory.
b. Set the APPCPATH environment variable to SalesRepAppClient.jar.
c. Type the following command on a single line:
runclient client SalesRepApp.ear name SalesRepClient
textauth
d. At the login prompts, enter guest for the user name and guest123 for
the password.
Many-to-Many Relationships
In a many-to-many relationship, each entity may be related to multiple occurrences of the other entity. For example, a college course has many students and
each student may take several courses. In a database, this relationship is represented by a cross reference table containing the foreign keys. In Figure 5–4, the
cross reference table is the enrollment table. These tables are accessed by the
StudentBean, CourseBean, and EnrollerBean classes.
MAPPING TABLE RELATIONSHIPS FOR BEAN-MANAGED PERSISTENCE111
Figure 5–4 Many-to-Many Relationship: Students and Courses
The source code for this example is in the j2eetutorial/exam
ples/src/ejb/enroller directory. To compile the code, go to the
j2eetutorial/examples directory and type ant enroller. A sample Enrol
lerApp.ear file is in the j2eetutorial/examples/ears directory.
The StudentBean and CourseBean classes are complementary. Each class contains an ArrayList of foreign keys. The StudentBean class, for example, contains an ArrayList named courseIds, which identifies the courses the student
is enrolled in. Likewise, the CourseBean class contains an ArrayList named
studentIds.
The ejbLoad method of the StudentBean class adds elements to the courseIds
ArrayList by calling loadCourseIds, a private method. The loadCourseIds
method gets the course identifiers from the EnrollerEJB session bean. The
source code for the loadCourseIds method follows:
private void loadCourseIds() {
courseIds.clear();
try {
112
BEAN-MANAGED PERSISTENCE EXAMPLES
Enroller enroller = enrollerHome.create();
ArrayList a = enroller.getCourseIds(studentId);
courseIds.addAll(a);
}
} catch (Exception ex) {
throw new EJBException("Exception in loadCourseIds: " +
ex.getMessage());
}
Invoked by the loadCourseIds method, the getCourses method of the Enrol
lerBean class queries the enrollment table:
select courseid from enrollment
where studentid = ?
Only the EnrollerBean class accesses the enrollment table. Therefore, the
EnrollerBean class manages the student-course relationship represented in the
enrollment table. If a student enrolls in a course, for example, the client calls
the enroll business method, which inserts a row:
insert into enrollment
values (studentid, courseid)
If a student drops a course, the unEnroll method deletes a row:
delete from enrollment
where studentid = ? and courseid = ?
And if a student leaves the school, the deleteStudent method deletes all rows
in the table for that student:
delete from enrollment
where student = ?
The EnrollerBean class does not delete the matching row from the student
table. That action is performed by the ejbRemove method of the StudentBean
class. To ensure that both deletes are executed as a single operation, they should
belong to the same transaction. See Chapter 14 for more information.
Running the EnrollerEJB Example
1. Create the database tables.
a. Go to the j2eetutorial/examples directory.
PRIMARY KEYS FOR BEAN-MANAGED PERSISTENCE
b. Type ant createenrollertable.
2. Deploy the EnrollerApp.ear file (located in the j2eetutorial/exam
ples/ears directory).
3. Run the client.
a. Go to the j2eetutorial/examples/ears directory.
b. Set the APPCPATH environment variable to EnrollerAppClient.jar.
c. Type the following command on a single line:
runclient client EnrollerApp.ear name EnrollerClient
textauth
d. At the login prompts, enter guest for the user name and guest123 for
the password.
Primary Keys for Bean-Managed
Persistence
You specify the primary key class in the entity bean’s deployment descriptor. In
most cases, your primary key class will be a String, an Integer, or some other
class that belongs to the J2SE or J2EE standard libraries. For some entity beans,
you will need to define your own primary key class. For example, if the bean has
a composite primary key (that is, one composed of multiple fields), then you
must create a primary key class.
The Primary Key Class
The following primary key class is a composite key—the productId and ven
dorId fields together uniquely identify an entity bean.
public class ItemKey implements java.io.Serializable {
public String productId;
public String vendorId;
public ItemKey() { };
public ItemKey(String productId, String vendorId) {
this.productId = productId;
this.vendorId = vendorId;
113
114
BEAN-MANAGED PERSISTENCE EXAMPLES
}
public String getProductId() {
}
return productId;
public String getVendorId() {
}
return vendorId;
public boolean equals(Object other) {
}
if (other instanceof ItemKey) {
return (productId.equals(((ItemKey)other).productId)
&& vendorId.equals(((ItemKey)other).vendorId));
}
return false;
public int hashCode() {
}
}
return productId.concat(vendorId).hashCode();
For bean-managed persistence, a primary key class must meet these requirements:
The access control modifier of the class is public.
All fields are declared as public.
The class has a public default constructor.
The class implements the hashCode() and equals(Object other) methods.
• The class is serializable.
•
•
•
•
Primary Keys in the Entity Bean Class
With bean-managed persistence, the ejbCreate method assigns the input parameters to instance variables and then returns the primary key class:
PRIMARY KEYS FOR BEAN-MANAGED PERSISTENCE
public ItemKey ejbCreate(String productId, String vendorId,
String description) throws CreateException {
if (productId == null || vendorId == null) {
throw new CreateException(
"The productId and vendorId are required.");
}
this.productId = productId;
this.vendorId = vendorId;
this.description = description;
}
return new ItemKey(productId, vendorId);
The ejbFindByPrimaryKey verifies the existence of the database row for the
given primary key:
public ItemKey ejbFindByPrimaryKey(ItemKey primaryKey)
throws FinderException {
}
try {
if (selectByPrimaryKey(primaryKey))
return primaryKey;
...
private boolean selectByPrimaryKey(ItemKey primaryKey)
throws SQLException {
}
String selectStatement =
"select productid " +
"from item where productid = ? and vendorid = ?";
PreparedStatement prepStmt =
con.prepareStatement(selectStatement);
prepStmt.setString(1, primaryKey.getProductId());
prepStmt.setString(2, primaryKey.getVendorId());
ResultSet rs = prepStmt.executeQuery();
boolean result = rs.next();
prepStmt.close();
return result;
Getting the Primary Key
A client can fetch the primary key of an entity bean by invoking the getPrima
ryKey method of the EJBObject class:
115
116
BEAN-MANAGED PERSISTENCE EXAMPLES
SavingsAccount account;
...
String id = (String)account.getPrimaryKey();
The entity bean retrieves its own primary key by calling the getPrimaryKey
method of the EntityContext class:
EntityContext context;
...
String id = (String) context.getPrimaryKey();
Handling Exceptions
The exceptions thrown by enterprise beans fall into two categories: system and
application.
A system exception indicates a problem with the services that support an application. Examples of these problems include the following: a database connection
cannot be obtained, a SQL insert fails because the database is full, or a lookup
method cannot find the desired object. If your enterprise bean encounters a system-level problem, it should throw a javax.ejb.EJBException. The container
will wrap the EJBException in a RemoteException, which it passes back to the
client. Because the EJBException is a subclass of the RuntimeException, you
do not have to specify it in the throws clause of the method declaration. If a system exception is thrown, the EJB container might destroy the bean instance.
Therefore, a system exception cannot be handled by the bean’s client program; it
requires intervention by a system administrator.
An application exception signals an error in the business logic of an enterprise
bean. There are two types of application exceptions: customized and predefined.
A customized exception is one that you’ve coded yourself, such as the Insuffi
centBalanceException thrown by the debit business method of the Sav
ingsAccountEJB example. The javax.ejb package includes several predefined
exceptions that are designed to handle common problems. For example, an ejb
Create method should throw a CreateException to indicate an invalid input
parameter. When an enterprise bean throws an application exception, the container does not wrap it in another exception. The client should be able to handle
any application exception it receives.
If a system exception occurs within a transaction, the EJB container rolls back
the transaction. However, if an application exception is thrown within a transaction, the container does not roll back the transaction.
117
HANDLING EXCEPTIONS
Table 5–2 summarizes the exceptions of the javax.ejb package. All of these
exceptions are application exceptions, except for the NoSuchEntityException
and the EJBException, which are system exceptions.
Table 5–2 Exceptions
Method Name
Exception It Throws
Reason for Throwing
ejbCreate
CreateException
An input parameter is
invalid.
ejbFindByPrimaryKey
(and other finder methods
that return a single object)
ObjectNotFoundException
(subclass of FinderException)
The database row for the
requested entity bean
cannot be found.
ejbRemove
RemoveException
The entity bean’s row
cannot be deleted from
the database.
ejbLoad
NoSuchEntityException
The database row to be
loaded cannot be found.
ejbStore
NoSuchEntityException
The database row to be
updated cannot be found.
(all methods)
EJBException
A system problem has
been encountered.
118
BEAN-MANAGED PERSISTENCE EXAMPLES
6
Container-Managed
Persistence Examples
Dale Green
AN entity bean with container-managed persistence offers important advantages to the bean developer. First, the EJB™ container handles all database storage and retrieval calls. Second, the container manages the relationships between
the entity beans. Because of these services, you don’t have to code the database
access calls in the entity bean. Instead, you specify settings in the bean’s deployment descriptor. Not only does this approach save you time, but it makes the
bean portable across various database servers.
This chapter focuses on the source code and deployment settings for an example
called RosterApp, an application that features entity beans with container-managed persistence. If you are unfamiliar with the terms and concepts mentioned in
this
chapter,
please
consult
the
section
Container-Managed
Persistence, page (53).
In This Chapter
Overview of the RosterApp Application 120
The PlayerEJB Code 121
Entity Bean Class 122
Local Home Interface 126
Local Interface 128
119
120
CONTAINER-MANAGED PERSISTENCE EXAMPLES
A Guided Tour of the RosterApp Settings 128
RosterApp 128
RosterClient 130
RosterJAR 130
TeamJAR 131
Method Invocations in RosterApp 136
Creating a Player 137
Adding a Player To a Team 138
Removing a Player 139
Dropping a Player From a Team 140
Getting the Players Of a Team 141
Getting a Copy of a Team’s Players 142
Finding the Players By Position 144
Getting the Sports of a Player 145
Running the RosterApp Example 147
Setting Up 147
Deploying the Application 147
Running the Client 147
Deploytool Tips for Entity Beans With Container-Managed Persistence 148
Specifying the Bean’s Type 148
Selecting the Persistent Fields and Abstract Schema Name 148
Defining EJB QL Queries for Finder and Select Methods 149
Generating SQL and Specifying Table Creation 149
Specifying the Database JNDI Name, User Name, and Password 150
Defining Relationships 150
Primary Keys for Container-Managed Persistence 150
The Primary Key Class 151
Primary Keys in the Entity Bean Class 152
Generating Primary Key Values 153
Overview of the RosterApp Application
The RosterApp application maintains the team rosters for players in sports
leagues. The application has five components. The RosterAppClient component is a J2EE™ application client that accesses the RosterEJB session bean
through the bean’s remote interfaces. RosterEJB accesses three entity beans—
PlayerEJB, TeamEJB, and LeagueEJB—through their local interfaces.
The entity beans use container-managed persistence and relationships. The
TeamEJB and PlayerEJB entity beans have a bidirectional, many-to-many relationship. In a bidirectional relationship, each bean has a relationship field whose
value identifies the related bean instance. The multiplicity of the TeamEJBPlay
THE PLAYEREJB CODE
erEJB relationship is many-to-many: Players who participate in more than one
sport belong to multiple teams, and each team has multiple players. The
LeagueEJB and TeamEJB entity beans also have a bidirectional relationship, but
the multiplicity is one-to-many: A league has many teams, but a team can belong
to just one league.
Figure 6–1 shows the components and relationships of the RosterApp application. The dotted lines represent the access gained through invocations of the
JNDI lookup method. The solid lines represent the container-managed relationships.
Figure 6–1 RosterApp J2EE™ Application
The PlayerEJB Code
The PlayerEJB entity bean represents a player in a sports league. Like any entity
bean with container-managed persistence, PlayerEJB needs the following code:
• Entity bean class (PlayerBean)
• Local home interface (LocalPlayerHome)
• Local interface (LocalPlayer)
The source code for this example is in the j2eetutorial/exam
ples/src/ejb/cmproster directory. To compile the code, go to the
121
122
CONTAINER-MANAGED PERSISTENCE EXAMPLES
j2eetutorial/examples directory and type ant cmproster. A sample Roster
App.ear file is in the j2eetutorial/examples/ears directory.
Entity Bean Class
For container-managed persistence, the code of the entity bean class must meet
the syntax requirements. First, the class must be defined as public and
abstract. Also, the class must implement the following:
• The EntityBean interface
• Zero or more ejbCreate and ejbPostCreate methods
• The get and set access methods, defined as abstract, for the persistent
and relationship fields
• Any select methods, defining them as abstract
• The home methods
• The business methods
The entity bean class must not implement these methods:
• The finder methods
• The finalize method
Differences between Container-Managed and BeanManaged Code
Because it contains no calls to access the database, an entity bean with containermanaged persistence requires a lot less code than one with bean-managed persistence. For example, the PlayerBean.java source file discussed in this chapter is
much smaller than the SavingsAccountBean.java code documented in
Chapter 5. Table 6–1 compares the code of the two types of entity beans.
Table 6–1 Coding Differences between Persistent Types
Difference
Container-Managed
Bean-Managed
Class definition
Abstract
Not abstract
Database access calls
Generated by tools
Coded by developers
Persistent state
Represented by virtual
persistent fields
Coded as instance
variables
123
THE PLAYEREJB CODE
Table 6–1 Coding Differences between Persistent Types (Continued)
Difference
Container-Managed
Bean-Managed
Access methods for persistent and relationship
fields
Required
None
Handled by container
Coded by developers
Customized finder methods
Handled by container, but the
developer must define the EJB
QL queries
Coded by developers
Select methods
Handled by container
None
Should be null
Must be the primary key
findByPrimaryKey
method
Return value of
ejbCreate
Note that for both types of persistence, the rules for implementing business and
home methods are the same. See the sections The Business Methods, page (91)
and The Home Methods, page (92) in Chapter 5 .
Access Methods
An entity bean with container-managed persistence has persistent and relationship fields. These fields are virtual, so you do not code them in the class as
instance variables. Instead, you specify them in the bean’s deployment descriptor. To permit access to the fields, you define abstract get and set methods in
the entity bean class.
Access Methods for Persistent Fields
The EJB container automatically performs the database storage and retrieval of
the bean’s persistent fields. The deployment descriptor of PlayerEJB specifies
the following persistent fields:
•
•
•
•
playerId (primary key)
name
position
salary
124
CONTAINER-MANAGED PERSISTENCE EXAMPLES
The PlayerBean class defines the access methods for the persistent fields as follows:
public abstract String getPlayerId();
public abstract void setPlayerId(String id);
public abstract String getName();
public abstract void setName(String name);
public abstract String getPosition();
public abstract void setPosition(String position);
public abstract double getSalary();
public abstract void setSalary(double salary);
The name of an access method begins with get or set, followed by the capitalized name of the persistent or relationship field. For example, the accessor methods for the salary field are getSalary and setSalary. This naming convention
is similar to that of JavaBeans™ components.
Access Methods for Relationship Fields
In the RosterApp application, since a player can belong to multiple teams, a
PlayerEJB instance may be related to many TeamEJB instances. To specify this
relationship, the deployment descriptor of PlayerEJB defines a relationship field
named teams. In the PlayerBean class, the access methods for the teams relationship field are as follows:
public abstract Collection getTeams();
public abstract void setTeams(Collection teams);
Select Methods
A select method is similar to a finder method in the following ways:
• A select method queries a database and returns objects.
• The deployment descriptor specifies an EJB QL query for a select method.
• The entity bean class does not implement the select method.
THE PLAYEREJB CODE
However, a select method differs significantly from a finder method:
• A select method can return persistent fields or the home interfaces of
related entity beans. A finder method can return only the home interface
(or a collection thereof) that defines it.
• Since it is not exposed in any of the local or remote interfaces, a select
method cannot be invoked by a client. It can be invoked only by the methods implemented within the entity bean class. A select method is usually
invoked by a business method.
• A select method is defined in the entity bean class. For bean-managed persistence, a finder method is defined in the entity bean class, but for container-managed persistence it is not.
The PlayerBean class defines these select methods:
public abstract Collection ejbSelectLeagues(LocalPlayer
player)
throws FinderException;
public abstract Collection ejbSelectSports(LocalPlayer player)
throws FinderException;
The signature for a select method must follow these rules:
•
•
•
•
The prefix of the method name must be ejbSelect.
The access control modifier must be public.
The method must be declared as abstract.
The throws clause must include the javax.ejb.FinderException.
Business Methods
Since clients cannot invoke select methods, the PlayerBean class wraps them in
the getLeagues and getSports business methods:
public Collection getLeagues() throws FinderException {
}
LocalPlayer player =
(team.LocalPlayer)context.getEJBLocalObject();
return ejbSelectLeagues(player);
public Collection getSports() throws FinderException {
125
126
CONTAINER-MANAGED PERSISTENCE EXAMPLES
}
LocalPlayer player =
(team.LocalPlayer)context.getEJBLocalObject();
return ejbSelectSports(player);
Entity Bean Methods
Because the container handles persistence, the life-cycle methods in the Player
Bean class are nearly empty.
The ejbCreate method initializes the bean instance by assigning the input arguments to the persistent fields. After the ejbCreate method completes, the container inserts a row into the database. Here is the source code for the ejbCreate
method:
public String ejbCreate (String id, String name,
String position, double salary) throws CreateException {
}
setPlayerId(id);
setName(name);
setPosition(position);
setSalary(salary);
return null;
Except for a debug statement, the ejbRemove method in the PlayerBean class is
empty. The container invokes ejbRemove right before it deletes the database row.
The ejbPostCreate method must have the same input parameters and return
type as the ejbCreate method. If you want to set a relationship field to initialize
the bean instance, you should do so in the ejbPostCreate method. You may not
set a relationship field in the ejbCreate method.
The container automatically synchronizes the state of the entity bean with the
database. After the container loads the bean’s state from the database, it invokes
the ejbLoad method. In like manner, before storing the state in the database, the
container invokes the ejbStore method.
Local Home Interface
The local home interface defines the create, finder, and home methods that may
be invoked by local clients.
THE PLAYEREJB CODE
The syntax rules for a create method follow:
• The name begins with create.
• It has the same number and types of arguments as its matching ejbCreate
method in the entity bean class.
• It returns the local interface type of the entity bean.
• The throws clause includes the exceptions specified by the throws clause
of the corresponding ejbCreate method.
• The throws clause contains the javax.ejb.CreateException .
These rules apply for a finder method:
• The name begins with find.
• The return type is the entity bean’s local interface type, or a collection of
those types.
• The throws clause contains the javax.ejb.FinderException .
• The findByPrimaryKey method must be defined.
An excerpt of the LocalPlayerHome interface follows.
package team;
import java.util.*;
import javax.ejb.*;
public interface LocalPlayerHome extends EJBLocalHome {
public LocalPlayer create (String id, String name,
String position, double salary)
throws CreateException;
public LocalPlayer findByPrimaryKey (String id)
throws FinderException;
}
public Collection findByPosition(String position)
throws FinderException;
. . .
public Collection findByLeague(LocalLeague league)
throws FinderException;
...
127
128
CONTAINER-MANAGED PERSISTENCE EXAMPLES
Local Interface
This interface defines the business and access methods that a local client may
invoke. The PlayerBean class implements two business methods: getLeagues
and getSports. It also defines several get and set access methods for the persistent and relationship fields. The set methods are hidden from the bean’s clients because they are not defined in the LocalPlayer interface. However, the
get methods are exposed to the clients by the interface:
package team;
import java.util.*;
import javax.ejb.*;
public interface LocalPlayer extends EJBLocalObject {
public
public
public
public
public
}
String getPlayerId();
String getName();
String getPosition();
double getSalary();
Collection getTeams();
public Collection getLeagues() throws FinderException;
public Collection getSports() throws FinderException;
A Guided Tour of the RosterApp Settings
This section introduces you to the settings of the deployment descriptors for
entity beans with container-managed persistence and relationships. As this tour
guides you through the deploytool screens, it discusses the highlights of the
tabs and dialog boxes that appear.
To begin our tour, please run deploytool and open the RosterApp.ear file,
which is in the j2eetutorial/examples/ears directory.
RosterApp
To view the deployment settings for the application, select the RosterApp node
in the tree view.
A GUIDED TOUR OF THE ROSTERAPP SETTINGS
General Tab (RosterApp)
The Contents field displays the files contained in the RosterApp.ear file,
including the two EJB JAR files (teamejb.jar, rosterejb.jar) and the
J2EE application client JAR file (rosterac.jar). See Figure 6–2.
Figure 6–2 General Tab of RosterApp
JNDI Names Tab (RosterApp)
The Application table lists the JNDI names for the enterprise beans in the Ros
terApp application.
The References table has two entries. The EJB Ref entry maps the coded name
(ejb/SimpleRoster) in the RosterClient to the JNDI name of the RosterEJB
session bean. The Resource entry specifies the JNDI name for the database that
is accessed by the entity beans contained in the TeamJAR module.
129
130
CONTAINER-MANAGED PERSISTENCE EXAMPLES
RosterClient
To view this client, expand the RosterApp node by clicking its adjacent key icon
in the tree view. Next, select RosterClient.
JAR File Tab (RosterClient)
The Contents field shows the files contained by the rosterac.jar file: two
XML files (the deployment descriptors) and a single class file (RosterCli
ent.class).
EJB Refs Tab (RosterClient)
The RosterClient accesses a single bean, the RosterEJB session bean. Because
this access is remote, the value in the Interfaces column is Remote and the value
for the Local/Remote Interface column is the bean’s remote interface (ros
ter.Roster).
RosterJAR
In the tree view, select RosterJAR. This JAR file contains the RosterEJB session
bean.
General Tab (RosterJAR)
The Contents field lists three packages of class files. The roster package contains the class files required for RosterEJB —the session bean class, remote
interface, and home interface. The team package includes the local interfaces for
the entity beans accessed by the RosterEJB session bean. The util package
holds the utility classes for this application.
RosterEJB
In the tree view, expand the RosterJAR node and select RosterEJB.
General Tab (RosterEJB)
This tab shows that RosterEJB is a stateful session bean with remote access.
Because it allows no local access, the Local Interfaces fields are empty.
EJB Refs Tab (RosterEJB)
The RosterEJB session bean accesses three entity beans: PlayerEJB, TeamEJB,
and LeagueEJB. Because this access is local, the entries in the Interfaces columns are defined as Local. The Home Interface column lists the local home
A GUIDED TOUR OF THE ROSTERAPP SETTINGS
interfaces of the entity beans. The Local/Remote Interfaces column displays the
local interfaces of the entity beans.
To view the runtime deployment settings, select a row in the table. For example,
when you select the row with the Coded Name of ejb/SimpleLeague, the
LeagueEJB name appears in the Enterprise Bean Name field. If a component references a local entity bean, then you must enter the name of the referenced bean
in the Enterprise Bean Name field.
TeamJAR
In the tree view, select the TeamJAR node. This JAR file contains the three related
entity beans: LeagueEJB, TeamEJB, and PlayerEJB.
General Tab (TeamJAR)
The Contents field shows two packages of class files: team and util. The team
package has the entity bean classes, local interfaces, and local home interfaces
for all three entity beans. The util package contains utility classes.
Relationships Tab (TeamJAR)
On this tab (Figure 6–3) you define the relationships between entity beans with
container-managed persistence.
131
132
CONTAINER-MANAGED PERSISTENCE EXAMPLES
Figure 6–3 Relationships Tab of TeamJAR
The Container Managed Relationships table summarizes two relationships:
TeamEJBPlayerEJB and LeagueEJBTeamEJB. In the TeamEJBPlayerEJB relationship, TeamEJB is designated as EJB A and PlayerEJB as EJB B. (This designation is arbitrary—we could have assigned PlayerEJB to EJB A and TeamEJB
to EJB B.)
Edit Relationship Dialog Box (TeamJAR)
To view the Edit Relationship dialog box (Figure 6–4), on the Relationships tab
select a row and click Edit. For example, to view the TeamEJBPlayerEJB relationship, select the row in which the EJB A value is Team and then click Edit.
A GUIDED TOUR OF THE ROSTERAPP SETTINGS
Figure 6–4 Edit Relationship Dialog Box of TeamJAR
TeamEJB-PlayerEJB Relationship
The Multiplicity combo box offers four choices. For this relationship, the Many
To Many choice should be selected because a team has many players and a
player can belong to more than one team.
The information in the Enterprise Bean A box defines TeamEJB side of the relationship. The Field Referencing Bean B combo box displays the relationship
field (players) in TeamEJB. This field corresponds to the relationship access
methods in the TeamBean.java source code:
public abstract Collection getPlayers();
public abstract void setPlayers(Collection players);
The selection of the Field Type combo box is java.util.Collection, which
matches the players type in the access methods. The players type is a multivalued object (Collection) because on the TeamEJB side of the relationship the
multiplicity is many.
The TeamEJBPlayerEJB relationship is bidirectional—each bean has a relationship field that identifies the related bean. If this relationship were unidirectional,
then one of the beans would not have a relationship field identifying the other
bean. For the bean without the relationship field, the value of the Field Referencing combo box would be <none>.
133
134
CONTAINER-MANAGED PERSISTENCE EXAMPLES
LeagueEJB-TeamEJB Relationship
In the Edit Relationship dialog box, the Multiplicity choice should be One to
Many. This choice indicates that a single league has multiple teams.
For LeagueEJB, the relationship field is teams and for TeamEJB it is league.
Because TeamEJB is on the multiple side of the relationship, the teams field is a
Collection. In contrast, since LeagueEJB is on the single side of the relationship, the league field is a single-valued object, a LocalLeague. The Team
Bean.java code defines the league relationship field with these access methods:
public abstract LocalLeague getLeague();
public abstract void setLeague(LocalLeague players);
For TeamEJB (Enterprise Bean B), the Delete When Bean A Is Deleted checkbox
is selected. Because of this selection, when a LeagueEJB instance is deleted the
related TeamEJB instances are automatically deleted. This type of deletion, in
which one deletion triggers another, is called a cascade delete. For LeagueEJB,
the corresponding checkbox is disabled: If you delete a team, you don’t want to
automatically delete the league, because there may be other teams in that league.
In general, if a bean is on the multiple side of a relationship, the other bean cannot be automatically deleted.
PlayerEJB
In the tree view, expand the TeamJAR node and select the PlayerEJB entity bean.
General Tab (PlayerEJB)
This tab shows the enterprise bean class and interfaces. Since the PlayerEJB
entity bean uses container-managed persistence, it has local interfaces. It does
not have remote interfaces because it does not allow remote access.
Entity Tab (PlayerEJB)
The radio buttons at the top of the tabbed page define the bean’s persistence type
(Figure 6–5). For PlayerEJB, this type is container-managed persistence, version 2.0. (Because version 1.0 did not support relationships, it is not recommended. These version numbers identify a particular release of the Enterprise
JavaBeans™ Specification, not the J2EE SDK software.)
A GUIDED TOUR OF THE ROSTERAPP SETTINGS
Figure 6–5 Entity Tab of PlayerEJB
The Fields To Be Persisted box lists the persistent and relationship fields defined
by the access methods in the PlayerBean.java code. The checkboxes for the
persistent fields must be selected, but those for the relationship fields must not
be selected. The PlayerEJB entity bean has one relationship field: teams.
The abstract schema name is Player, a name that represents the relationships
and persistent fields of the PlayerEJB entity bean. This abstract name is referenced in the PlayerEJB Enterprise JavaBeans™ Query Language (EJB™ QL)
queries. For more information on EJB QL, see Chapter 8.
Finder/Select Methods Dialog Box (PlayerEJB)
To open this dialog box, click Finder/Select Methods on the Entity tab. This dialog box(Figure 6–6) enables you to view and edit the EJB QL queries for a
bean’s finder and select methods. For example, to list the finder methods defined
in the LocalPlayerHome interface, select the Local Finders radio button. When
you select the finder method, its EJB QL query appears in an editable text field.
135
136
CONTAINER-MANAGED PERSISTENCE EXAMPLES
Figure 6–6 Finder/Select Methods Dialog Box of PlayerEJB
Entity Deployment Settings Dialog Box (PlayerEJB)
To view this dialog box, click Deployment Settings in the Entity tab. In this dialog box, you define the runtime settings of an entity bean with container-managed persistence. These runtime settings are specific to the J2EE™ SDK; other
implementations of the J2EE platform may take a different approach.
In the J2EE SDK, the bean’s persistent fields are stored in a relational database
table. In the checkboxes of the Database Table box, you specify whether or not
the server automatically creates or drops the table. If you want to save the data in
your table between deployments, then make sure that the Delete Table checkbox
is not selected. Otherwise, every time you undeploy the bean, the table will be
deleted.
The J2EE server accesses the database by issuing SQL calls. In an entity bean
with container-managed persistence, you do not code these calls. The deploy
tool utility creates the SQL calls automatically when you click the Generate
Default SQL button. To view the SQL statement for a finder method, for example, select the Local Finder radio button and then select an entry in the Method
list. You may modify a SQL statement by editing the text in the SQL Query field.
For the finder and select methods, the corresponding EJB QL query is also displayed. When you click Generate Default SQL, deploytool translates the EJB
QL queries into SQL calls. If you change an EJB QL query, you should click the
Generate Default SQL button again.
METHOD INVOCATIONS IN ROSTERAPP
To view the SQL CREATE TABLE statement, for example, click the Container
Methods radio button and then select the createTable entry in the Method list.
The CREATE TABLE statement defines column names for the bean’s persistent
fields and specifies a primary key constraint for playerId, the bean’s primary
key field.
When the EJB container creates a new PlayerEJB instance, it issues a SQL
INSERT statement. To examine this statement, select createRow from the Method
list. In the INSERT statement, the parameters in the values clause correspond to
the arguments of the create method that is defined in the LocalPlayerHome
interface:
public LocalPlayer create (String id, String name,
String position, double salary) throws CreateException;
Database Deployment Settings Dialog Box (PlayerEJB)
To access this dialog box, click Deployment Settings on the Entity tab. In the
Deployment Settings dialog box that appears, click Database Settings. The
Deployment Settings dialog box with the Database Settings label should appear.
It is important that you set the JNDI name of the database. (If it is not set, the
bean cannot connect to the database.) For this example, the Database JNDI
Name field should be jdbc/Cloudscape. The User Name and Password fields
are blank because they are not required for Cloudscape.
Method Invocations in RosterApp
To show how the various components interact, this section describes the
sequence of method invocations that occur for particular functions. The source
code for the components is in the j2eetutorial/examples/src/ejb/cmpros
ter directory.
Creating a Player
1. RosterClient
The RosterClient invokes the createPlayer business method of the Ros
terEJB session bean. In the following line of code, the type of the myRoster
object is Roster, the remote interface of RosterEJB. The argument of the cre
atePlayer method is a PlayerDetails object, which encapsulates information
about a particular player.
137
138
CONTAINER-MANAGED PERSISTENCE EXAMPLES
myRoster.createPlayer(new PlayerDetails("P1", "Phil Jones",
"goalkeeper", 100.00));
2. RosterEJB
The createPlayer method of the RosterEJB session bean creates a new
instance of the PlayerEJB entity bean. Because the access PlayerEJB is local,
the create method is defined in the local home interface, LocalPlayerHome.
The type of the playerHome object is LocalPlayerHome. Here is the source code
for the createPlayer method:
public void createPlayer(PlayerDetails details) {
try {
}
LocalPlayer player = playerHome.create(details.getId(),
details.getName(), details.getPosition(),
details.getSalary());
} catch (Exception ex) {
throw new EJBException(ex.getMessage());
}
3. PlayerEJB
The ejbCreate method assigns the input arguments to the bean’s persistent
fields by calling the set access methods. After invoking the ejbCreate method,
the container saves the persistent fields in the database by issuing a SQL INSERT
statement. The code for the ejbCreate method follows.
public String ejbCreate (String id, String name,
String position,double salary) throws CreateException {
}
setPlayerId(id);
setName(name);
setPosition(position);
setSalary(salary);
return id;
Adding a Player to a Team
1. RosterClient
The RosterClient calls the addPlayer business method of the RosterEJB session bean. The P1 and T1 parameters are the primary keys of the PlayerEJB and
TeamEJB instances, respectively.
METHOD INVOCATIONS IN ROSTERAPP
myRoster.addPlayer("P1", "T1");
2. RosterEJB
The addPlayer method performs two steps. First, it calls findByPrimaryKey to
locate the PlayerEJB and TeamEJB instances. Second, it invokes the addPlayer
business method of the TeamEJB entity bean. Here is the source code for the
addPlayer method of the RosterEJB session bean:
public void addPlayer(String playerId, String teamId) {
}
try {
LocalTeam team = teamHome.findByPrimaryKey(teamId);
LocalPlayer player =
playerHome.findByPrimaryKey(playerId);
team.addPlayer(player);
} catch (Exception ex) {
throw new EJBException(ex.getMessage());
}
3. TeamEJB
The TeamEJB entity bean has a relationship field named players, a Collection
that represents the players that belong to the team. The access methods for the
players relationship field are as follows:
public abstract Collection getPlayers();
public abstract void setPlayers(Collection players);
The addPlayer method of TeamEJB invokes the getPlayers access method to
fetch the Collection of related LocalPlayer objects. Next, the addPlayer
method invokes the add method of the Collection interface. Here is the source
code for the addPlayer method:
public void addPlayer(LocalPlayer player) {
try {
Collection players = getPlayers();
players.add(player);
} catch (Exception ex) {
throw new EJBException(ex.getMessage());
}
}
139
140
CONTAINER-MANAGED PERSISTENCE EXAMPLES
Removing a Player
1. RosterClient
To remove player P4, the client would invoke the removePlayer method of the
RosterEJB session bean:
myRoster.removePlayer("P4");
2. RosterEJB
The removePlayer method locates the PlayerEJB instance by calling findByP
rimaryKey and then invokes the remove method on the instance. This invocation
signals the container to delete the row in the database that corresponds to the
PlayerEJB instance. The container also removes the item for this instance from
the players relationship field in the TeamEJB entity bean. By this removal, the
container automatically updates the TeamEJBPlayerEJB relationship. Here is
the removePlayer method of the RosterEJB session bean:
public void removePlayer(String playerId) {
try {
LocalPlayer player =
playerHome.findByPrimaryKey(playerId);
player.remove();
} catch (Exception ex) {
throw new EJBException(ex.getMessage());
}
}
Dropping a Player from a Team
1. RosterClient
To drop player P2 from team T1, the client would call the dropPlayer method of
the RosterEJB session bean:
myRoster.dropPlayer("P2", "T1");
2. RosterEJB
The dropPlayer method retrieves the PlayerEJB and TeamEJB instances by calling their findByPrimaryKey methods. Next, it invokes the dropPlayer business
method of the TeamEJB entity bean. The dropPlayer method of the RosterEJB
session bean follows:
METHOD INVOCATIONS IN ROSTERAPP
public void dropPlayer(String playerId, String teamId) {
}
try {
LocalPlayer player =
playerHome.findByPrimaryKey(playerId);
LocalTeam team = teamHome.findByPrimaryKey(teamId);
team.dropPlayer(player);
} catch (Exception ex) {
throw new EJBException(ex.getMessage());
}
3. TeamEJB
The dropPlayer method updates the TeamEJBPlayerEJB relationship. First,
the method retrieves the Collection of LocalPlayer objects that correspond to
the players relationship field. Next, it drops the target player by calling the
remove method of the Collection interface. Here is the dropPlayer method of
the TeamEJB entity bean:
public void dropPlayer(LocalPlayer player) {
try {
}
Collection players = getPlayers();
players.remove(player);
} catch (Exception ex) {
throw new EJBException(ex.getMessage());
}
Getting the Players of a Team
1. RosterClient
The client can fetch a team’s players by calling the getPlayersOfTeam method
of the RosterEJB session bean. This method returns an ArrayList of PlayerDe
tails objects. A PlayersDetails object contains four variables—playerId,
name, position, and salary—which are copies of the PlayerEJB persistent
fields. The RosterClient calls the getPlayersOfTeam method as follows:
playerList = myRoster.getPlayersOfTeam("T2");
2. RosterEJB
The getPlayersOfTeam method of the RosterEJB session bean locates the
LocalTeam object of the target team by invoking the findByPrimaryKey
141
142
CONTAINER-MANAGED PERSISTENCE EXAMPLES
method. Next, the getPlayersOfTeam method calls the getPlayers method of
the TeamEJB entity bean. Here is the source code for the getPlayersOfTeam
method:
public ArrayList getPlayersOfTeam(String teamId) {
Collection players = null;
try {
LocalTeam team = teamHome.findByPrimaryKey(teamId);
players = team.getPlayers();
} catch (Exception ex) {
throw new EJBException(ex.getMessage());
}
}
return copyPlayersToDetails(players);
The getPlayersOfTeam method returns the ArrayList of PlayerDetails
objects that is generated by the copyPlayersToDetails method:
private ArrayList copyPlayersToDetails(Collection players) {
ArrayList detailsList = new ArrayList();
Iterator i = players.iterator();
while (i.hasNext()) {
LocalPlayer player = (LocalPlayer) i.next();
PlayerDetails details =
new PlayerDetails(player.getPlayerId(),
player.getName(), player.getPosition(),
player.getSalary());
detailsList.add(details);
}
}
return detailsList;
3. TeamEJB
The getPlayers method of the TeamEJB entity bean is an access method of the
players relationship field:
public abstract Collection getPlayers();
METHOD INVOCATIONS IN ROSTERAPP
This method is exposed to local clients because it is defined in the local interface, LocalTeam:
public Collection getPlayers();
When invoked by a local client, a get access method returns a reference to the
relationship field. If the local client alters the object returned by a get access
method, it also alters the value of the relationship field inside the entity bean. For
example, a local client of the TeamEJB entity bean could drop a player from a
team as follows:
LocalTeam team = teamHome.findByPrimaryKey(teamId);
Collection players = team.getPlayers();
players.remove(player);
If you want to prevent a local client from modifying a relationship field in this
manner, you should take the approach described in the next section.
Getting a Copy of a Team’s Players
In contrast to the methods discussed in the preceding section, the methods in this
section demonstrate the following techniques:
• Filtering the information passed back to the remote client
• Preventing the local client from directly modifying a relationship field
1. RosterClient
If you wanted to hide the salary of a player from a remote client, you would
require the client to call the getPlayersOfTeamCopy method of the RosterEJB
session bean. Like the getPlayersOfTeam method, the getPlayersOfTeamCopy
method returns an ArrayList of PlayerDetails objects. However, the objects
returned by getPlayersOfTeamCopy are different—their salary variables have
been set to zero. The RosterClient calls the getPlayersOfTeamCopy method
as follows:
playerList = myRoster.getPlayersOfTeamCopy("T5");
2. RosterEJB
Unlike the getPlayersOfTeam method, the getPlayersOfTeamCopy method
does not invoke the getPlayers access method that is exposed in the LocalTeam
interface. Instead, the getPlayersOfTeamCopy method retrieves a copy of the
player information by invoking the getCopyOfPlayers business method that is
143
144
CONTAINER-MANAGED PERSISTENCE EXAMPLES
defined in the LocalTeam interface. As a result, the getPlayersOfTeamCopy
method cannot modify the players relationship field of TeamEJB. Here is the
source code for the getPlayersOfTeamCopy method of RosterEJB:
public ArrayList getPlayersOfTeamCopy(String teamId) {
ArrayList playersList = null;
try {
LocalTeam team = teamHome.findByPrimaryKey(teamId);
playersList = team.getCopyOfPlayers();
} catch (Exception ex) {
throw new EJBException(ex.getMessage());
}
}
return playersList;
3. TeamEJB
The getCopyOfPlayers method of TeamEJB returns an ArrayList of PlayerDe
tails objects. To create this ArrayList, the method iterates through the Col
lection of related LocalPlayer objects and copies information to the variables
of the PlayerDetails objects. The method copies the values of PlayerEJB persistent fields—except for the salary field, which it sets to zero. As a result, a
player’s salary is hidden from a client that invokes the getPlayersOfTeamCopy
method. The source code for the getCopyOfPlayers of TeamEJB follows.
public ArrayList getCopyOfPlayers() {
ArrayList playerList = new ArrayList();
Collection players = getPlayers();
Iterator i = players.iterator();
while (i.hasNext()) {
LocalPlayer player = (LocalPlayer) i.next();
PlayerDetails details =
new PlayerDetails(player.getPlayerId(),
player.getName(), player.getPosition(), 0.00);
playerList.add(details);
}
}
return playerList;
METHOD INVOCATIONS IN ROSTERAPP
Finding the Players by Position
1. RosterClient
The client starts the procedure by invoking the getPlayersByPosition method
of the RosterEJB session bean:
playerList = myRoster.getPlayersByPosition("defender");
2. RosterEJB
The getPlayersByPosition method retrieves the players list by invoking the
findByPosition method of the PlayerEJB entity bean:
public ArrayList getPlayersByPosition(String position) {
Collection players = null;
try {
players = playerHome.findByPosition(position);
} catch (Exception ex) {
throw new EJBException(ex.getMessage());
}
}
return copyPlayersToDetails(players);
3. PlayerEJB
The LocalPlayerHome interface defines the findByPosition method:
public Collection findByPosition(String posistion)
throws FinderException;
Because the PlayerEJB entity bean uses container-managed persistence, the
entity bean class (PlayerBean) does not implement its finder methods. To specify the queries associated with the finder methods, EJB QL queries must be
defined in the bean’s deployment descriptor. For example, the findByPosition
method has this EJB QL query:
SELECT DISTINCT OBJECT(p) FROM Player p
WHERE p.position = ?1
The deploytool utility translates the EJB QL query into a SQL SELECT statement. At runtime, when the container invokes the findByPosition method, it
will execute the SQL SELECT statement.
145
146
CONTAINER-MANAGED PERSISTENCE EXAMPLES
For details about EJB QL, please refer to Chapter 8. To learn how to view and
edit an EJB QL query in deploytool, see the section Finder/Select Methods
Dialog Box (PlayerEJB), page (135).
Getting the Sports of a Player
1. RosterClient
The client invokes the getSportsOfPlayer method of the RosterEJB session
bean:
sportList = myRoster.getSportsOfPlayer("P28");
2. RosterEJB
The getSportsOfPlayer method returns an ArrayList of String objects that
represent the sports of the specified player. It constructs the ArrayList from a
Collection returned by the getSports business method of the PlayerEJB
entity bean. Here is the source code for the getSportsOfPlayer method of the
RosterEJB session bean:
public ArrayList getSportsOfPlayer(String playerId) {
ArrayList sportsList = new ArrayList();
Collection sports = null;
try {
LocalPlayer player =
playerHome.findByPrimaryKey(playerId);
sports = player.getSports();
} catch (Exception ex) {
throw new EJBException(ex.getMessage());
}
}
Iterator i = sports.iterator();
while (i.hasNext()) {
String sport = (String) i.next();
sportsList.add(sport);
}
return sportsList;
3. PlayerEJB
The getSports method is a wrapper for the ejbSelectSports method. Since
the parameter of the ejbSelectSports method is of type LocalPlayer, the
RUNNING THE ROSTERAPP EXAMPLE
getSports method passes along a reference to the entity bean instance. The
PlayerBean class implements the getSports method as follows:
public Collection getSports() throws FinderException {
}
LocalPlayer player =
(team.LocalPlayer)context.getEJBLocalObject();
return ejbSelectSports(player);
The PlayerBean class defines the ejbSelectSports method:
public abstract Collection ejbSelectSports(LocalPlayer player)
throws FinderException;
The bean’s deployment descriptor specifies the following EJB QL query for the
ejbSelectSports method:
SELECT DISTINCT t.league.sport
FROM Player p, IN (p.teams) AS t
WHERE p = ?1
Before deploying PlayerEJB, you run deploytool to generate SQL SELECT
statements for the bean’s EJB QL queries. Because PlayerEJB uses containermanaged persistence, when the ejbSelectSports method is invoked the EJB
container will execute its corresponding SQL SELECT statement.
Running the RosterApp Example
Setting Up
1. In a terminal window, start the Cloudscape database server.
cloudscape start
2. In another terminal window, start the J2EE server.
j2ee verbose
3. Run the deploytool utility.
deploytool
147
148
CONTAINER-MANAGED PERSISTENCE EXAMPLES
Deploying the Application
1. In deploytool, open the RosterApp.ear file.
a. Choose File→Open from the main menu.
b. In the Open Object dialog box, navigate to the j2eetutorial/exam
ples/ears directory.
c. Select the RosterApp.ear file.
d. Click Open Object.
2. Deploy the application.
a. In deploytool, select RosterApp from the tree view.
b. Choose Tools→Deploy from the main menu.
c. In the Introduction dialog box, select the Return Client JAR checkbox.
d. In the Client JAR File Name field, make sure that the file is called Ros
and
that its path
refers to
the
terAppClient.jar
j2eetutorial/examples/ears directory.
e. Click Next until the Review dialog box appears.
f. Click Finish.
Running the Client
1. In a terminal window, go to the j2eetutorial/examples/ears directory.
2. Set the APPCPATH environment variable to RosterAppClient.jar.
3. Type the following command:
runclient client RosterApp.ear name RosterClient textauth
4. At the login prompts, enter guest for the user name and guest123 for the
password.
deploytool Tips for Entity Beans With
Container-Managed Persistence
Chapter 2 covered the basic steps for building and packaging enterprise beans.
This section highlights the tasks in deploytool that are needed for entity beans
with container-managed persistence. The examples referenced in this section are
from A Guided Tour of the RosterApp Settings, page (128).
DEPLOYTOOL
TIPS FOR ENTITY BEANS WITH CONTAINER-MANAGED PERSIS-
Specifying the Bean’s Type
In the New Enterprise Bean wizard, specify the bean’s type and persistent management.
1. In the Edit Contents dialog box, add all of the classes required by the entity
bean and by its related beans.
2. In the General dialog box, select the Entity radio button.
3. In the General dialog box, specify the local interfaces of the entity bean.
(If the bean also has remote interfaces, specify them as well.)
4. In the Entity Settings dialog box, select the radio button for ContainerManaged Persistence (2.0). You may skip the other settings in this dialog
box and enter them later in the Entity tab.
Selecting the Persistent Fields and Abstract Schema
Name
In the Entity tab, enter the field information and the abstract schema name.
1. In the Fields To Be Persisted list, select the fields that will be saved in the
database. The names of the persistent fields are determined by the access
methods defined in the entity bean code.
2. Enter values in the Primary Key Class and Primary Key Field Name fields.
The primary key uniquely identifies the entity bean.
3. In the Abstract Schema Name field, enter a name that represents the entity
bean. This name will be referenced in the EJB QL queries.
An example is shown in the section Entity Tab (PlayerEJB), page (134).
Defining EJB QL Queries for Finder and Select
Methods
You specify these settings in the Finder/Select Methods dialog box.
1. To open the Finder/Select Methods dialog box, go to the Entity tab and
click Finder/Select Methods.
2. To display a set of finder or select methods, click one of the radio buttons
under the Show label.
3. To specify an EJB QL query, choose the name of the finder or select
method from the Method list and then enter the query in the field labeled
EJB QL Query.
150
CONTAINER-MANAGED PERSISTENCE EXAMPLES
An example is shown in the section Finder/Select Methods Dialog Box
(PlayerEJB), page (135).
Generating SQL and Specifying Table Creation
In deploytool, the various Deployment Settings dialog boxes enable you to
enter information needed by the server at runtime. These settings are specific to
the J2EE SDK implementation.
1. To open the Deployment Settings dialog box, go to the Entity tab and click
Deployment Settings.
2. With container-managed persistence, the container can automatically create or delete the database table used by the entity bean. If you’ve loaded
test data into the table, you may want to deselect the checkboxes in the
Database Table box.
3. To translate the EJB QL queries into SQL SELECT statements, click Generate Default SQL. If this button is disabled, you must first specify the
database settings.
An example is shown in the section Entity Deployment Settings Dialog Box
(PlayerEJB), page (136).
Specifying the Database JNDI Name, User Name,
and Password
You specify these settings in the Database Settings dialog box.
1. To open the Database Settings dialog box, go to the Entity tab and click
Deployment Settings. In the Deployment Settings dialog box, click Database Settings.
2. Enter a value in the Database JNDI Name field. The examples in this book
use the jdbc/Cloudscape JNDI name.
3. The Cloudscape database shipped with the J2EE SDK does not require a
user name or password. So, if your bean connects to the Cloudscape database, you may leave the User Name and Password fields blank. To connect
to other types of databases, you may need to enter values into these fields.
An example is shown in the section Database Deployment Settings Dialog Box
(PlayerEJB), page (137).
PRIMARY KEYS FOR CONTAINER-MANAGED PERSISTENCE
Defining Relationships
The Relationships tab enables you to define relationships between entity beans
that reside in the same EJB JAR file.
1. Before you create a relationship between two entity beans, you must first
create both beans with the New Enterprise Bean wizard.
2. To display the Relationships tab, select the EJB JAR in the tree view and
then select the Relationships tab.
3. To add or edit a relationship, go the Relationships tab and click the appropriate button.
4. The Add (or Edit) Relationship dialog box appears. (The Add Relationship and Edit Relationship dialog boxes are identical.)
An example is shown in the section Edit Relationship Dialog Box
(TeamJAR), page (132).
Primary Keys for Container-Managed
Persistence
If the primary key class does not belong to the J2SE or J2EE standard libraries,
then you must implement the class and package it along with the entity bean. For
example, if your entity bean requires a composite primary key (which is made up
of multiple fields), then you need to provide a customized primary key class.
The Primary Key Class
In the following example, the PurchaseOrderKey class implements a composite
key for the PurchaseOrderEJB entity bean. The key is composed of two fields,
productModel and vendorId, whose names must match two of the persistent
fields in the entity bean class.
public class PurchaseOrderKey implements java.io.Serializable {
public String productModel;
public String vendorId;
public PurchaseOrderKey() { };
public String getProductModel() {
return productModel;
151
152
CONTAINER-MANAGED PERSISTENCE EXAMPLES
}
public String getVendorId() {
}
return vendorId;
public boolean equals(Object other) {
}
if (other instanceof PurchaseOrderKey) {
return (productModel.equals(
((PurchaseOrderKey)other).productModel) &&
vendorId.equals(
((PurchaseOrderKey)other).vendorId));
}
return false;
public int hashCode() {
}
return productModel.concat(vendorId).hashCode();
}
For container-managed persistence, a primary key class must meet the following
requirements:
The access control modifier of the class is public.
All fields are declared as public.
The fields are a subset of the bean’s persistent fields.
The class has a public default constructor.
The class implements the hashCode() and equals(Object other) methods.
• The class is serializable.
•
•
•
•
•
Primary Keys in the Entity Bean Class
In the PurchaseOrderBean class, the following access methods define the persistent fields (vendorId and productModel) that make up the primary key:
PRIMARY KEYS FOR CONTAINER-MANAGED PERSISTENCE
public abstract String getVendorId();
public abstract void setVendorId(String id);
public abstract String getProductModel();
public abstract void setProductModel(String name);
The next code sample shows the ejbCreate method of the PurchaseOrderBean
class. The return type of the ejbCreate method is the primary key, but the return
value is null. Although not required, the null return value is recommended for
container-managed persistence. This approach saves overhead because the bean
does not have to instantiate the primary key class for the return value.
public PurchaseOrderKey ejbCreate (String vendorId,
String productModel, String productName)
throws CreateException {
setVendorId(vendorId);
setProductModel(productModel);
setProductName(productName);
}
return null;
Generating Primary Key Values
For some entity beans, the value of a primary key has a meaning for the business
entity. For example, in an entity bean that represents a phone call to a support
center, the primary key might include a time stamp that indicates when the call
was received. But for other beans, the key’s value is arbitrary—provided that it’s
unique. With container-managed persistence, these key values can be generated
automatically by the EJB container. To take advantage of this feature, an entity
bean must meet these requirements:
• In the deployment descriptor, the primary key class is defined as a
java.lang.Object. The primary key field is not specified.
• In the home interface, the argument of the findByPrimaryKey method
must be a java.lang.Object.
• In the entity bean class, the return type of the ejbCreate method must be
a java.lang.Object.
In these entity beans, the primary key values are in an internal field that only the
EJB container can access. You cannot associate the primary key with a persistent
field or any other instance variable. However, you can fetch the bean’s primary
153
154
CONTAINER-MANAGED PERSISTENCE EXAMPLES
key by invoking the getPrimaryKey method, and you can locate the bean by
invoking its findByPrimaryKey method.
7
A Message-Driven
Bean Example
Dale Green and Kim Haase
SINCE message-driven beans are based on the Java™ Message Service (JMS)
technology, to understand the example in this chapter you should already be
familiar with basic JMS concepts such as queues and messages. The best place
to learn about these concepts is the Java Message Service Tutorial:
http://java.sun.com/products/jms/tutorial/index.html
This chapter describes the source code of a simple message-driven bean example. Before proceeding, you should read the basic conceptual information in the
section What Is a Message-Driven Bean?, page (56).
In This Chapter
Example Application Overview 156
The J2EE™ Application Client 157
The Message-Driven Bean Class 158
The onMessage Method 158
The ejbCreate and ejbRemove Methods 159
Running the SimpleMessageEJB Example 159
Starting the J2EE™ Server 159
Creating the Queue 159
Deploying the Application 160
Running the Client 160
155
156
A MESSAGE-DRIVEN BEAN EXAMPLE
Deploytool Tips for Message-Driven Beans 161
Specifying the Bean’s Type and Transaction Management 161
Setting the Message-Driven Bean’s Characteristics 161
Deploytool Tips for JMS Clients 163
Setting the Resource References 164
Setting the Resource Environment References 164
Specifying the JNDI Names 164
Example Application Overview
This application has the following components:
• SimpleMessageClient: A J2EE™ application client that sends several
messages to a queue.
• SimpleMessageEJB: A message-driven bean that asynchronously receives
and processes the messages that are sent to the queue.
Figure 16 illustrates the structure of this application. The application client sends
messages to the queue, which was created administratively using the j2eeadmin
command. The JMS provider (in this, case the J2EE server) delivers the messages to the instances of the message-driven bean, which then processes the messages.
Figure 7–1 The SimpleMessageApp Application
The source code for this application is in the j2eetutorial/exam
ples/src/ejb/simplemessage directory. To compile the code, go to the
THE J2EE™ APPLICATION CLIENT
j2eetutorial/examples directory and type ant simplemessage. A sample
SimpleMessageApp.ear file is in the j2eetutorial/examples/ears directory.
The J2EE™ Application Client
The SimpleMessageClient sends messages to the queue that the SimpleMes
sageBean listens to. The client starts out by locating the connection factory and
queue:
queueConnectionFactory = (QueueConnectionFactory)
jndiContext.lookup
("java:comp/env/jms/MyQueueConnectionFactory");
queue = (Queue)
jndiContext.lookup("java:comp/env/jms/QueueName");
Next, the client creates the queue connection, session, and sender:
queueConnection =
queueConnectionFactory.createQueueConnection();
queueSession =
queueConnection.createQueueSession(false,
Session.AUTO_ACKNOWLEDGE);
queueSender = queueSession.createSender(queue);
Finally, the client sends several messages to the queue:
message = queueSession.createTextMessage();
for (int i = 0; i < NUM_MSGS; i++) {
message.setText("This is message " + (i + 1));
System.out.println("Sending message: " +
message.getText());
queueSender.send(message);
}
157
158
A MESSAGE-DRIVEN BEAN EXAMPLE
The Message-Driven Bean Class
The code for the SimpleMessageEJB class illustrates the requirements of a message-driven bean class:
•
•
•
•
•
•
•
It implements the MessageDrivenBean and MessageListener interfaces.
The class is defined as public.
The class cannot be defined as abstract or final.
It implements one onMessage method.
It implements one ejbCreate method and one ejbRemove method.
It contains a public constructor with no arguments.
It must not define the finalize method.
Unlike session and entity beans, message-driven beans do not have the remote or
local interfaces that define client access. Client components do not locate message-driven beans and invoke methods on them. Although message-driven beans
do not have business methods, they may contain helper methods that are invoked
internally by the onMessage method.
The onMessage Method
When the queue receives a message, the EJB™ container invokes the onMessage
method of the message-driven bean. In the SimpleMessageBean class, the
onMessage method casts the incoming message to a TextMessage and displays
the text:
public void onMessage(Message inMessage) {
TextMessage msg = null;
try {
if (inMessage instanceof TextMessage) {
msg = (TextMessage) inMessage;
System.out.println
("MESSAGE BEAN: Message received: "
+ msg.getText());
} else {
System.out.println
("Message of wrong type: "
+ inMessage.getClass().getName());
}
} catch (JMSException e) {
e.printStackTrace();
mdc.setRollbackOnly();
RUNNING THE SIMPLEMESSAGEEJB EXAMPLE
}
} catch (Throwable te) {
te.printStackTrace();
}
The ejbCreate and ejbRemove Methods
The signatures of these methods have the following requirements:
•
•
•
•
•
The access control modifier must be public.
The return type must be void .
The modifier cannot be static or final.
The throws clause must not define any application exceptions.
The method has no arguments.
In the SimpleMessageBean class, the ejbCreate and ejbRemove methods are
empty.
Running the SimpleMessageEJB Example
Starting the J2EE Server
To view the output of the message-driven bean, you must start the server in verbose mode:
j2ee verbose
Creating the Queue
1. Create the queue with the j2eeadmin command:
j2eeadmin addJmsDestination jms/MyQueue queue
2. Verify that the queue was created:
j2eeadmin listJmsDestination
Deploying the Application
1. In deploytool, open the j2eetutorial/examples/ears/SimpleMes
sageApp.ear file (File→Open).
159
160
A MESSAGE-DRIVEN BEAN EXAMPLE
2. Deploy the SimpleMessageApp application (Tools→Deploy). In the Introduction dialog box, make sure that you select the Return Client JAR
checkbox. For detailed instructions, see Deploying the J2EE™
Application, page (37).
Running the Client
1. In a terminal window, go to the j2eetutorial/examples/ears directory.
2. Set the APPCPATH environment variable to SimpleMessageAppCli
ent.jar.
3. Type the following command on a single line:
runclient client SimpleMessageApp.ear name
SimpleMessageClient textauth
4. At the login prompts, enter j2ee for the user name and j2ee for the password.
5. The client displays these lines:
Sending message: This is message 1
Sending message: This is message 2
Sending message: This is message 3
6. In the terminal window in which you’ve started the J2EE server (in verbose mode), the following lines should be displayed:
MESSAGE BEAN: Message received: This is message 1
MESSAGE BEAN: Message received: This is message 2
MESSAGE BEAN: Message received: This is message 3
deploytool Tips for Message-Driven Beans
Chapter 2 covered the basic steps for building and packaging enterprise beans.
This section describes the tasks in deploytool that are necessary for messagedriven beans. To view an example in deploytool, open the
j2eetutorial/examples/ears/SimpleMessageApp.ear file and select Sim
pleMessageEJB from the tree view.
DEPLOYTOOL
TIPS FOR MESSAGE-DRIVEN BEANS
Specifying the Bean’s Type and Transaction
Management
You specify the type when you create the bean with the New Enterprise Bean
wizard.
1. To start the wizard, select File→New→Enterprise Bean.
2. In the General dialog box of the wizard, select the Message-Driven radio
button.
3. In the Transaction Management dialog box, you may select either the
Bean-Managed or Container-Managed radio button. If you select the
Bean-Managed button, then in step 4 of the next section, you may select
the acknowledgment type.
Setting the Message-Driven Bean’s Characteristics
You may specify these settings in two places:
• The Message-Driven Bean Settings dialog box of the New Enterprise
Bean wizard
• The Message tab of the bean (see Figure 7–2)
These settings are as follows:
1. For the Destination Type, select either the Queue or Topic radio button. A
queue uses the point-to-point messaging domain and may have at most
one consumer. A topic uses the publish-subscribe messaging domain; it
may have zero, one, or many consumers.
2. In the Destination combo box, select the JNDI name of the destination that
you have created administratively. For an example, see the section Creating the Queue, page (159). The destination is either a Queue or a Topic
object; it represents the source of incoming messages and the target of outgoing messages.
3. In the Connection Factory combo box, select the appropriate object, either
a QueueConnectionFactory or a TopicConnectionFactory. These
objects produce the connections through which J2EE components access
the messaging service.
4. If you’ve specified bean-managed transactions, then you may select the
acknowledgment type—either Auto-Acknowledge or Duplicates-OK—
from the Acknowledgement combo box. The Auto-Acknowledge type
instructs the session to automatically acknowledge that the bean has consumed the message. The Duplicates-OK type instructs the session to lazily
161
162
A MESSAGE-DRIVEN BEAN EXAMPLE
acknowledge the delivery of messages; this type may result in duplicate
messages, but it reduces session overhead.
5. In the JMS Message Selector field, you may enter a statement that filters
the messages received by the bean.
Figure 7–2 Message Tab of SimpleMessageEJB
deploytool Tips for JMS Clients
For more information on JMS clients, please see the Java Message Service Tutorial:
http://java.sun.com/products/jms/tutorial/index.html
DEPLOYTOOL
TIPS FOR JMS CLIENTS
Setting the Resource References
1.
2.
3.
4.
5.
6.
7.
8.
In the tree view, select the client’s node.
Select the Resource Refs tab.
Click Add.
In the Coded Name field, enter the name that matches the parameter of the
lookup method in the client’s code. For example, if the lookup parameter
is java:comp/env/jms/MyQueueConnectionFactory, the Coded Name
should be jms/QueueConnectionFactory.
In the Type field, select the connection factory class that matches the destination type.
In the Authentication field, in most cases you will select Container. You
would select Application if your code explicitly logs on to the messaging
service.
In the Sharable field, make sure the checkbox is selected. This choice
allows the container to optimize connections.
Enter strings in the User Name and Password fields. The authentication
service of the J2EE SDK will prompt you for these fields when you run
the client.
Setting the Resource Environment References
1. Select the Resource Env. Refs tab.
2. Click Add.
3. In the Coded Name field, enter a name that matches the parameter of the
lookup call that locates the queue or topic. For example, if the lookup
parameter is java:comp/env/jms/QueueName, the Coded Name should
be jms/QueueName.
4. In the Type field, select the class that matches the destination type.
Specifying the JNDI Names
1. In the tree view, select the application’s node.
163
164
A MESSAGE-DRIVEN BEAN EXAMPLE
2. Select the JNDI Names tab and enter the appropriate names. For example,
the SimpleMessageApp discussed in this chapter uses the JNDI names
shown in Table 7–1.
Table 7–1 JNDI Names for the SimpleMessageApp Application
Component or Reference Name
JNDI Name
SimpleMessageEJB
jms/MyQueue
jms/MyQueueConnectionFactory
jms/QueueConnectionFactory
jms/QueueName
jms/MyQueue
8
Enterprise
JavaBeans™
Query Language
Dale Green
T
HE Enterprise JavaBeans™ Query Language (EJB™ QL) defines the queries
for the finder and select methods of an entity bean with container-managed persistence. A subset of SQL92, EJB QL has extensions that allow navigation over
the relationships defined in an entity bean’s abstract schema. The scope of an
EJB QL query spans the abstract schemas of related entity beans that are packaged in the same EJB JAR file.
You define EJB QL queries in the deployment descriptor of the entity bean. Typically, a tool will translate these queries into the target language of the underlying data store. Because of this translation, entity beans with container-managed
persistence are portable—their code is not tied to a specific type of data store.
This chapter relies on the material presented in earlier chapters. For conceptual
information, see the section Container-Managed Persistence, page (53). For code
examples, see Chapter 6.
In This Chapter
Terminology 166
Simplified Syntax 167
165
166
ENTERPRISE JAVABEANS™ QUERY LANGUAGE
Example Queries 167
Simple Finder Queries 167
Finder Queries That Navigate to Related Beans 169
Finder Queries with Other Conditional Expressions 170
Select Queries 172
Full Syntax 173
BNF Grammar of EJB QL 173
BNF Symbols 176
FROM Clause 176
Path Expressions 179
WHERE Clause 182
SELECT Clause 190
EJB QL Restrictions 191
Terminology
The following list defines some of the terms referred to in this chapter.
• Abstract schema: The part of an entity bean’s deployment descriptor that
defines the bean’s persistent fields and relationships.
• Abstract schema name: A logical name that is referenced in EJB QL queries. You specify an abstract schema name for each entity bean with container-managed persistence.
• Abstract schema type: All EJB QL expressions evaluate to a type. If the
expression is an abstract schema name, by default its type is the local interface of the entity bean for which the abstract schema name is defined.
• Backus-Naur Form (BNF): A notation that describes the syntax of highlevel languages. The syntax diagrams in this chapter are in BNF notation.
• navigation: The traversal of relationships in an EJB QL expression. The
navigation operator is a period.
• path expression: An expression that navigates to a related entity bean.
• persistent field: A virtual field of an entity bean with container-managed
persistence; it is stored in a database.
• relationship field: A virtual field of an entity bean with container-managed
persistence; it identifies a related entity bean.
SIMPLIFIED SYNTAX
Simplified Syntax
This section briefly describes the syntax of EJB QL so that you can quickly
move on to the section Example Queries, page (167). When you are ready to
learn about the syntax in more detail, see the section Full Syntax, page (173).
An EJB QL query has three clauses: SELECT, FROM, and WHERE. The SELECT and
FROM clauses are required, but the WHERE clause is optional. Here is the high-level
BNF syntax of an EJB QL query:
EJB QL :: = select_clause from_clause [where_clause]
The SELECT clause defines the types of the objects or values returned by the
query. A return type is either a local interface, a remote interface, or a persistent
field.
The FROM clause defines the scope of the query by declaring one or more identification variables, which may be referenced in the SELECT and WHERE clauses. An
identification variable represents one of the following elements:
• The abstract schema name of an entity bean
• A member of a collection that is the multiple side of a one-to-many relationship
The WHERE clause is a conditional expression that restricts the objects or values
retrieved by the query. Although optional, most queries have a WHERE clause.
Example Queries
The following queries are from the PlayerEJB entity bean of the RosterApp
J2EE™ application, which is documented in the Chapter 6. To see the relationships between the beans of the RosterApp, see Figure 6–1 (page 121).
Simple Finder Queries
If you are unfamiliar with EJB QL, these simple queries are a good place to start.
Example 1
SELECT OBJECT(p)
FROM Player p
167
168
ENTERPRISE JAVABEANS™ QUERY LANGUAGE
Data retrieved: All players.
Finder method: findall()
Description: The FROM clause declares an identification variable named p, omitting the optional keyword AS. If the AS keyword were included, the clause would
be written as follows:
FROM Player AS p
The Player element is the abstract schema name of the PlayerEJB entity bean.
Because the bean defines the findall method in the LocalPlayerHome interface, the objects returned by the query have the LocalPlayer type.
See also: Identification Variables, page (177)
Example 2
SELECT DISTINCT OBJECT(p)
FROM Player p
WHERE p.position = ?1
Data retrieved: The players with the position specified by the finder method’s
parameter.
Finder method: findByPosition(String position)
Description: In a SELECT clause, the OBJECT keyword must precede a standalone identification variable such as p. The DISTINCT keyword eliminates duplicate values.
The WHERE clause restricts the players retrieved by checking their position, a
persistent field of the PlayerEJB entity bean. The ?1 element denotes the input
parameter of the findByPosition method.
See also: Input Parameters, page (183),
Keywords, page (191)
DISTINCT
and
Example 3
SELECT DISTINCT OBJECT(p)
FROM Player p
WHERE p.position = ?1 AND p.name = ?2
Data retrieved: The players with the specified position and name.
OBJECT
EXAMPLE QUERIES
Finder method: findByPositionAndName(String position, String name)
Description: The position and name elements are persistent fields of the Play
erEJB entity bean. The WHERE clause compares the values of these fields with the
parameters of the findByPositionAndName method. EJB QL denotes an input
parameter with a question mark followed by an integer. The first input parameter
is ?1, the second is ?2, and so forth.
Finder Queries That Navigate to Related Beans
In EJB QL, an expression can traverse—or navigate—to related beans. These
expressions are the primary difference between EJB QL and SQL. EJB QL navigates to related beans, whereas SQL joins tables.
Example 4
SELECT DISTINCT OBJECT(p)
FROM Player p, IN (p.teams) AS t
WHERE t.city = ?1
Data retrieved: The players whose teams belong to the specified city.
Finder method: findByCity(String city)
Description: The FROM clause declares two identification variables: p and t. The
p variable represents the PlayerEJB entity bean, and the t variable represents the
related TeamEJB beans. The declaration for t references the previously declared
p variable. The IN keyword signifies that teams is a collection of related beans.
The p.teams expression navigates from a PlayerEJB bean to its related TeamEJB
beans. The period in the p.teams expression is the navigation operator.
In the WHERE clause, the period preceding the persistent variable city is a delimiter, not a navigation operator. Strictly speaking, expressions can navigate to
relationship fields (related beans), but not to persistent fields. To access a persistent field, an expression uses the period as a delimiter.
Expressions may not navigate beyond (or further qualify) relationship fields that
are collections. In the syntax of an expression, a collection-valued field is a terminal symbol. Because the teams field is a collection, the WHERE clause cannot
specify p.teams.city—an illegal expression.
See also: Path Expressions, page (179)
169
170
ENTERPRISE JAVABEANS™ QUERY LANGUAGE
Example 5
SELECT DISTINCT OBJECT(p)
FROM Player p, IN (p.teams) AS t
WHERE t.league = ?1
Data retrieved: The players that belong to the specified league.
Finder method: findByLeague(LocalLeague league)
Description: The expressions in this query navigate over two relationships. The
p.teams expression navigates the PlayerEJB-TeamEJB relationship, and the
t.league expression navigates the TeamEJBLeagueEJB relationship.
In the other examples, the input parameters are String objects, but in this example the parameter is an object whose type is a LocalLeague interface. This type
matches the league relationship field in the comparison expression of the WHERE
clause.
Example 6
SELECT DISTINCT OBJECT(p)
FROM Player p, IN (p.teams) AS t
WHERE t.league.sport = ?1
Data retrieved: The players who participate in the specified sport.
Finder method: findBySport(String sport)
Description: The sport persistent field belongs to the LeagueEJB bean. To reach
the sport field, the query must first navigate from the PlayerEJB bean to the
TeamEJB bean (p.teams) and then from the TeamEJB bean to the LeagueEJB bean
(t.league). Because the league relationship field is not a collection, it may be
followed by the sport persistent field.
Finder Queries with Other Conditional Expressions
Every WHERE clause must specify a conditional expression, of which there are
several kinds. In the previous examples, the conditional expressions are comparison expressions that test for equality. The following examples demonstrate
some of the other kinds of conditional expressions. For descriptions of all conditional expressions, see the section WHERE Clause, page (182).
EXAMPLE QUERIES
Example 7
SELECT OBJECT(p)
FROM Player p
WHERE p.teams IS EMPTY
Data retrieved: All players who do not belong to a team.
Finder method: findNotOnTeam()
Description: The teams relationship field of the PlayerEJB bean is a collection.
If a player does not belong to a team, then the teams collection is empty and the
conditional expression is TRUE.
See also: Empty Collection Comparison Expressions, page (186)
Example 8
SELECT DISTINCT OBJECT(p)
FROM Player p
WHERE p.salary BETWEEN ?1 AND ?2
Data retrieved: The players whose salaries fall within the range of the specified
salaries.
Finder method: findBySalaryRange(double low, double high)
Description: This BETWEEN expression has three arithmetic expressions: a persistent field (p.salary) and the two input parameters ( ?1 and ?2). The following
expression is equivalent to the BETWEEN expression:
p.salary >= ?1 AND p.salary <= ?2
See also: BETWEEN Expressions, page (184)
Example 9
SELECT DISTINCT OBJECT(p1)
FROM Player p1, Player p2
WHERE p1.salary > p2.salary AND p2.name = ?1
Data retrieved: All players whose salaries are higher than the salary of the player
with the specified name.
Finder method: findByHigherSalary(String name)
171
172
ENTERPRISE JAVABEANS™ QUERY LANGUAGE
Description: The FROM clause declares two identification variables (p1 and p2) of
the same type (Player). Two identification variables are needed because the
WHERE clause compares the salary of one player (p2) with that of the other players (p1).
See also: Identification Variables, page (177)
Select Queries
The queries in this section are for select methods. Unlike finder methods, a select
method may return persistent fields or other entity beans.
Example 10
SELECT DISTINCT t.league
FROM Player p, IN (p.teams) AS t
WHERE p = ?1
Data retrieved: The leagues to which the specified player belongs.
Select Method: ejbSelectLeagues(LocalPlayer player)
Description: The return type of this query is the abstract schema type of the
LeagueEJB entity bean. This abstract schema type maps to the LocalLeague
Home interface. Because the expression t.league is not a stand-alone identification variable, the OBJECT keyword is omitted.
See also: SELECT Clause, page (190)
Example 11
SELECT DISTINCT t.league.sport
FROM Player p, IN (p.teams) AS t
WHERE p = ?1
Data retrieved: The sports that the specified player participates in.
Select Method: ejbSelectSports(LocalPlayer player)
Description: This query returns a String named sport, which is a persistent
field of the LeagueEJB entity bean.
FULL SYNTAX
Full Syntax
This section discusses the EJB QL syntax, as defined in the Enterprise JavaBeans Specification. Much of the following material paraphrases or directly
quotes the Enterprise JavaBeans Specification.
BNF Grammar of EJB QL
Here is the entire BNF diagram for EJB QL:
EJB QL ::= select_clause from_clause [where_clause]
from_clause ::= FROM identification_variable_declaration
[, identification_variable_declaration]*
identification_variable_declaration ::=
collection_member_declaration |
range_variable_declaration
collection_member_declaration ::=
IN (collection_valued_path_expression) [AS] identifier
range_variable_declaration ::=
abstract_schema_name [AS] identifier
single_valued_path_expression ::=
{single_valued_navigation |
identification_variable}.cmp_field |
single_valued_navigation
single_valued_navigation ::=
identification_variable.[single_valued_cmr_field.]*
single_valued_cmr_field
collection_valued_path_expression ::=
identification_variable.[single_valued_cmr_field.]*
collection_valued_cmr_field
select_clause ::= SELECT [DISTINCT]
{single_valued_path_expression |
OBJECT(identification_variable)}
where_clause ::= WHERE conditional_expression
conditional_expression ::= conditional_term |
conditional_expression OR conditional_term
173
174
ENTERPRISE JAVABEANS™ QUERY LANGUAGE
conditional_term ::= conditional_factor |
conditional_term AND conditional_factor
conditional_factor ::= [ NOT ] conditional_test
conditional_test :: = conditional_primary
conditional_primary ::=
simple_cond_expression | (conditional_expression)
simple_cond_expression ::=
comparison_expression |
between_expression |
like_expression |
in_expression |
null_comparison_expression |
empty_collection_comparison_expression |
collection_member_expression
between_expression ::=
arithmetic_expression [NOT] BETWEEN
arithmetic_expression AND arithmetic_expression
in_expression ::=
single_valued_path_expression
[NOT] IN (string_literal [, string_literal]* )
like_expression ::=
single_valued_path_expression
[NOT] LIKE pattern_value [ESCAPE escapecharacter]
null_comparison_expression ::=
single_valued_path_expression IS [NOT] NULL
empty_collection_comparison_expression ::=
collection_valued_path_expression IS [NOT] EMPTY
collection_member_expression ::=
{single_valued_navigation | identification_variable |
input_parameter}
[NOT] MEMBER [OF] collection_valued_path_expression
comparison_expression ::=
string_value { =|<>} string_expression |
boolean_value { =|<>} boolean_expression} |
datetime_value { = | <> | > | < } datetime_expression |
entity_bean_value { = | <> } entity_bean_expression |
FULL SYNTAX
arithmetic_value comparison_operator
single_value_designator
arithmetic_value ::= single_valued_path_expression |
functions_returning_numerics
single_value_designator ::= scalar_expression
comparison_operator ::=
= | > | >= | < | <= | <>
scalar_expression ::= arithmetic_expression
arithmetic_expression ::= arithmetic_term |
arithmetic_expression { + | } arithmetic_term
arithmetic_term ::= arithmetic_factor |
arithmetic_term { * | / } arithmetic_factor
arithmetic_factor ::= { + | } arithmetic_primary
arithmetic_primary ::= single_valued_path_expression |
literal | (arithmetic_expression) |
input_parameter | functions_returning_numerics
string_value ::= single_valued_path_expression |
functions_returning_strings
string_expression ::= string_primary | input_expression
string_primary ::= single_valued_path_expression | literal |
(string_expression) | functions_returning_strings
datetime_value ::= single_valued_path_expression
datetime_expression ::= datetime_value | input_parameter
boolean_value ::= single_valued_path_expression
boolean_expression ::= single_valued_path_expression |
literal | input_parameter
entity_bean_value ::=
single_valued_navigation | identification_variable
entity_bean_expression ::= entity_bean_value | input_parameter
functions_returning_strings ::=
175
176
ENTERPRISE JAVABEANS™ QUERY LANGUAGE
CONCAT(string_expression, string_expression) |
SUBSTRING(string_expression, arithmetic_expression,
arithmetic_expression)
functions_returning_numerics::=
LENGTH(string_expression) |
LOCATE(string_expression,
string_expression[, arithmetic_expression]) |
ABS(arithmetic_expression) |
SQRT(arithmetic_expression)
BNF Symbols
Table 8–1 describes the BNF symbols used in this chapter.
Table 8–1 BNF Symbol Summary
Symbol
Description
::=
The element to the left of the symbol is defined by the constructs on the right
*
The preceding construct may occur zero or more times
{...}
The constructs within the curly braces are grouped together
[...]
The constructs within the square brackets are optional
|
An exclusive OR
BOLDFACE
A keyword (although capitalized in the BNF diagram, keywords are not case sensitive)
Whitespace
A whitespace character can be a space, horizontal tab, or
form feed
FROM Clause
The FROM clause defines the domain of the query by declaring identification variables. Here is the syntax of the FROM clause:
from_clause ::= FROM identification_variable_declaration
[, identification_variable_declaration]*
identification_variable_declaration ::=
FULL SYNTAX
collection_member_declaration |
range_variable_declaration
collection_member_declaration ::=
IN (collection_valued_path_expression) [AS] identifier
range_variable_declaration ::=
abstract_schema_name [AS] identifier
Identifiers
An identifier is a sequence of one or more characters. The first character must be
a valid first character (letter, $, _) in an identifier of the Java™ programming
language (hereafter in this chapter called simply “Java”). Each subsequent character in the sequence must be a valid non-first character (letter, digit, $, _) in a
Java identifier. (For details, see the J2SE™ API documentation of the isJav
aIdentifierStart and isJavaIdentifierPart methods of the Character
class.) The question mark (?) is a reserved character in EJB QL and cannot be
used in an identifier. Unlike a Java variable, an EJB QL identifier is not case sensitive.
An identifier cannot be the same as an EJB QL keyword:
AND
AS
BETWEEN
DISTINCT
EMPTY
FALSE
FROM
IN
IS
LIKE
MEMBER
NOT
NULL
OBJECT
OF
OR
SELECT
TRUE
UNKNOWN
WHERE
EJB QL keywords are also reserved words in SQL. In the future, the list of EJB
QL keywords may expand to include other reserved SQL words. The Enterprise
JavaBeans™ Specification recommends that you not use other reserved SQL
words for EJB QL identifiers.
Identification Variables
An identification variable is an identifier declared in the FROM clause. Although
the SELECT and WHERE clauses may reference identification variables, they cannot declare them. All identification variables must be declared in the FROM
clause.
Since an identification variable is an identifier, it has the same naming conventions and restrictions as an identifier. For example, an identification variable is
177
178
ENTERPRISE JAVABEANS™ QUERY LANGUAGE
not case sensitive and it cannot be the same as an EJB QL keyword. (See the previous section for more naming rules.) Also, within a given EJB JAR file, an
identifier name must not match the name of any entity bean or abstract schema.
The FROM clause may contain multiple declarations, separated by commas. A
declaration may reference another identification variable that has been previously declared (to the left). In the following FROM clause, the variable t references the previously declared variable p:
FROM Player p, IN (p.teams) AS t
Even if an identification variable is not used in the WHERE clause, its declaration
can affect the results of the query. For an example, compare the next two queries.
The following query returns all players, whether or not they belong to a team:
SELECT OBJECT(p)
FROM Player p
In contrast, because the next query declares the t identification variable, it
fetches all players that belong to a team:
SELECT OBJECT(p)
FROM Player p, IN (p.teams) AS t
The following query returns the same results as the preceding query, but the
WHERE clause makes it easier to read:
SELECT OBJECT(p)
FROM Player p
WHERE p.teams IS NOT EMPTY
An identification variable always designates a reference to a single value, whose
type is that of the expression used in the declaration. There are two kinds of declarations: range variable and collection member.
Range Variable Declarations
To declare an identification variable as an abstract schema type, you specify a
range variable declaration. In other words, an identification variable can range
over the abstract schema type of an entity bean. In the following example, an
identification variable named p represents the abstract schema named Player:
FROM Player p
FULL SYNTAX
A range variable declaration may include the optional AS operator:
FROM Player AS p
In most cases, to obtain objects a query navigates through the relationships with
path expressions. But for those objects that cannot be obtained by navigation,
you can use a range variable declaration to designate a starting point (or root).
If the query compares multiple values of the same abstract schema type, then the
FROM clause must declare multiple identification variables for the abstract
schema:
FROM Player p1, Player p2
For a sample of such a query, see Example 9 (page 171).
Collection Member Declarations
In a one-to-many relationship, the multiple side consists of a collection of entity
beans. An identification variable may represent a member of this collection. To
access a collection member, the path expression in the variable’s declaration
navigates through the relationships in the abstract schema. (For more information on path expressions, see the following section.) Because a path expression
may be based on another path expression, the navigation can traverse several
relationships. See Example 6 (page 170).
A collection member declaration must include the IN operator, but it may omit
the optional AS operator.
In the following example, the entity bean represented by the abstract schema
named Player has a relationship field called teams. The identification variable
named t represents a single member of the teams collection.
FROM Player p, IN (p.teams) AS t
Path Expressions
Path expressions are important constructs in the syntax of EJB QL, for several
reasons. First, they define navigation paths through the relationships in the
abstract schema. These path definitions affect both the scope and the results of a
query. Second, they may appear in any of the three main clauses of an EJB QL
query (SELECT, WHERE, FROM). Finally, although much of EJB QL is a subset of
SQL, path expressions are extensions not found in SQL.
179
180
ENTERPRISE JAVABEANS™ QUERY LANGUAGE
Syntax
There are two types of path expressions: single-valued and collection-valued.
Here is the syntax for path expressions:
single_valued_path_expression ::=
{single_valued_navigation |
identification_variable}.cmp_field |
single_valued_navigation
single_valued_navigation ::=
identification_variable.[single_valued_cmr_field.]*
single_valued_cmr_field
collection_valued_path_expression ::=
identification_variable.[single_valued_cmr_field.]*
collection_valued_cmr_field
In the preceding diagram, the cmp_field element represents a persistent field,
and the cmr_field element designates a relationship field. The term
single_valued qualifies the relationship field as the single side of a one-to-one
or one-to-many relationship; the term collection_valued designates it as the
multiple (collection) side of a relationship.
The period (.) in a path expression serves two functions. If a period precedes a
persistent field, it is a delimiter between the field and the identification variable.
If a period precedes a relationship field, it is a navigation operator.
Examples
In the following query, the WHERE clause contains a single-valued expression.
The p is an identification variable, and salary is a persistent field of Player.
SELECT DISTINCT OBJECT(p)
FROM Player p
WHERE p.salary BETWEEN ?1 AND ?2
The WHERE clause of the next example also contains a single-valued expression.
The t is an identification variable, league is a single-valued relationship field,
and sport is a persistent field of league.
SELECT DISTINCT OBJECT(p)
FROM Player p, IN (p.teams) AS t
WHERE t.league.sport = ?1
FULL SYNTAX
In the next query, the WHERE clause contains a collection-valued expression. The
p is an identification variable, and teams designates a collection-valued relationship field.
SELECT DISTINCT OBJECT(p)
FROM Player p
WHERE p.teams IS EMPTY
Expression Types
The type of an expression is the type of the object represented by the ending element, which can be one of the following:
• Persistent field
• Single-valued relationship field
• Collection-valued relationship field
For example, the type of the expression p.salary is double because the terminating persistent field (salary) is a double.
In the expression p.teams, the terminating element is a collection-valued relationship field (teams). This expression’s type is a collection of the abstract
schema type named Team. Because Team is the abstract schema name for the
TeamEJB entity bean, this type maps to the bean’s local interface, LocalTeam. For
more information on the type mapping of abstract schemas, see the section
Return Types, page (190).
Navigation
A path expression enables the query to navigate to related entity beans. The terminating elements of an expression determine whether navigation is allowed. If
an expression contains a single-valued relationship field, the navigation may
continue to an object that is related to the field. However, an expression cannot
navigate beyond a persistent field or a collection-valued relationship field. For
example, the expression p.teams.league.sport is illegal, since teams is a collection-valued relationship field. To reach the sport field, the FROM clause could
define an identification variable named t for the teams field:
FROM Player AS p, IN (p.teams) t
WHERE t.league.sport = 'soccer'
181
182
ENTERPRISE JAVABEANS™ QUERY LANGUAGE
WHERE Clause
The WHERE clause specifies a conditional expression that limits the values
returned by the query. The query returns all corresponding values in the data
store for which the conditional expression is TRUE. Although usually specified,
the WHERE clause is optional. If the WHERE clause is omitted, then the query
returns all values. The high-level syntax for the WHERE clause follows:
Where_clause ::= WHERE conditional_expression
Literals
There are three kinds of literals: string, numeric, and boolean.
String Literals
A string literal is enclosed in single quotes:
'Duke'
If a string literal contains a single quote, you indicate the quote with two single
quotes:
'Duke''s'
Like a Java String, a string literal in EJB QL uses the Unicode character encoding.
Numeric Literals
There are two types of numeric literals: exact and approximate.
An exact numeric literal is a numeric value without a decimal point, such as 65,
−233, +12. Using the Java integer syntax, exact numeric literals support numbers
in the range of a Java long.
An approximate numeric literal is a numeric value in scientific notation, such as
57., −85.7, +2.1. Using the syntax of the Java floating point literal, approximate
numeric literals support numbers in the range of a Java double.
Boolean Literals
A boolean literal is either TRUE or FALSE. These keywords are not case sensitive.
FULL SYNTAX
Input Parameters
An input parameter is designated by a question mark (?) followed by an integer.
For example, the first input parameter is ?1, the second is ?2, and so forth.
The following rules apply to input parameters:
• They can be used only in a WHERE clause.
• Their use is restricted to a single-valued path expression within a conditional expression.
• They must be numbered, starting with the integer 1.
• The number of input parameters in the WHERE clause must not exceed the
number of input parameters in the corresponding finder or select method.
• The type of an input parameter in the WHERE clause must match the type of
the corresponding argument in the finder or select method.
Conditional Expressions
A WHERE clause consists of a conditional expression, which is evaluated from left
to right within a precedence level. You may change the order of evaluation with
parentheses.
Here is the syntax of a conditional expression:
conditional_expression ::= conditional_term |
conditional_expression OR conditional_term
conditional_term ::= conditional_factor |
conditional_term AND conditional_factor
conditional_factor ::= [ NOT ] conditional_test
conditional_test :: = conditional_primary
conditional_primary ::=
simple_cond_expression | (conditional_expression)
simple_cond_expression ::=
comparison_expression |
between_expression |
like_expression |
in_expression |
null_comparison_expression |
empty_collection_comparison_expression |
collection_member_expression
183
184
ENTERPRISE JAVABEANS™ QUERY LANGUAGE
Operators and Their Precedence
Table 8–2 lists the EJB QL operators in order of decreasing precedence.
Table 8–2 EJB QL Operator Precedence
Type
Precedence Order
Navigation
. (a period)
Arithmetic
+ (unary)
* / (multiplication and division)
+ - (addition and subtraction)
Comparison
=
>
>=
<
<=
<> (not equal)
Logical
NOT
AND
OR
BETWEEN Expressions
A BETWEEN expression determines whether an arithmetic expression falls within
a range of values. The syntax of the BETWEEN expression follows:
between_expression ::=
arithmetic_expression [NOT] BETWEEN
arithmetic_expression AND arithmetic_expression
These two expressions are equivalent:
p.age BETWEEN 15 AND 19
p.age >= 15 AND p.age <= 19
The following two expressions are also equivalent:
p.age NOT BETWEEN 15 AND 19
p.age < 15 OR p.age > 19
FULL SYNTAX
If an arithmetic expression has a NULL value, then the value of the BETWEEN
expression is unknown.
IN Expressions
An IN expression determines whether or not a string belongs to a set of string literals. Here is the syntax of the IN expression:
in_expression ::=
single_valued_path_expression
[NOT] IN (string_literal [, string_literal]* )
The single-valued path expression must have a String value. If the single-valued path expression has a NULL value, then the value of the IN expression is
unknown.
In the following example, if the country is UK the expression is TRUE . If the country is Peru it is FALSE.
o.country IN ('UK', 'US', 'France')
LIKE Expressions
A LIKE expression determines whether a wildcard pattern matches a string. Here
is the syntax:
like_expression ::=
single_valued_path_expression
[NOT] LIKE pattern_value [ESCAPE escapecharacter]
The single-valued path expression must have a String value. If this value is
NULL, then the value of the LIKE expression is unknown. The pattern value is a
string literal that may contain wildcard characters. The underscore (_) wildcard
character represents any single character. The percent (%) wildcard character represents zero or more characters. The ESCAPE clause specifies an escape character
for the wildcard characters in the pattern value.
185
186
ENTERPRISE JAVABEANS™ QUERY LANGUAGE
Table 8–3 shows some sample LIKE expressions. The TRUE and FALSE columns
indicate the value of the LIKE expression for a single-valued path expression.
Table 8–3 LIKE Expression Examples
Expression
TRUE
FALSE
address.phone LIKE '12%3'
'123'
'12993'
'1234'
asentence.word LIKE 'l_se'
'lose'
'loose'
aword.underscored LIKE '\_%’ ESCAPE '\'
'_foo'
'bar'
address.phone NOT LIKE '12%3'
1234
'123'
'12993'
NULL Comparison Expressions
A NULL comparison expression tests whether a single-valued path expression has
a NULL value. Usually, this expression is used to test whether or not a single-valued relationship has been set. If a path expression contains a NULL value during
evaluation, it returns a NULL value. Here is the syntax of a NULL comparison
expression:
null_comparison_expression ::=
single_valued_path_expression IS [NOT] NULL
Empty Collection Comparison Expressions
An empty collection comparison expression tests whether a collection-valued
path expression has no elements. In other words, it tests whether or not a collection-valued relationship has been set. Here is the syntax:
empty_collection_comparison_expression ::=
collection_valued_path_expression IS [NOT] EMPTY
If the collection-valued path expression is NULL, then the empty collection comparison expression has a NULL value.
Collection Member Expressions
The collection member expression determines whether a value is a member of a
collection. The value and the collection members must have the same type. The
expression syntax follows:
FULL SYNTAX
collection_member_expression ::=
{single_valued_navigation | identification_variable |
input_parameter}
[NOT] MEMBER [OF] collection_valued_path_expression
If the collection-valued path expression is unknown, then the collection member
expression is unknown. If the collection-valued path expression designates an
empty collection, then the collection member expression is FALSE.
Functional Expressions
EJB QL includes several string and arithmetic functions, which are listed in the
following tables. In Table 8–4, the start and length arguments are of type int.
They designate positions in the String argument. In Table 8–5, the number
argument may be either an int, a float, or a double.
Table 8–4 String Expressions
Function Syntax
Return Type
CONCAT(String, String)
String
SUBSTRING(String, start, length)
String
LOCATE(String, String [, start])
int
LENGTH(String)
int
Table 8–5 Arithmetic Expressions
Function Syntax
Return Type
ABS(number)
int, float, or double
SQRT(double)
double
187
188
ENTERPRISE JAVABEANS™ QUERY LANGUAGE
NULL Values
If the target of a reference is not in the persistent store, then the target is NULL.
For conditional expressions containing NULL, EJB QL uses the semantics defined
by SQL92. Briefly, these semantics are as follows:
• If a comparison or arithmetic operation has an unknown value, it yields a
NULL value.
• If a path expression contains a NULL value during evaluation, it returns a
NULL value.
• The IS NULL test converts a NULL persistent field or a single-valued relationship field to TRUE . The IS NOT NULL test converts them to FALSE.
• Boolean operators and conditional tests use the three-valued logic defined
by the following tables. (In these tables, T stands for TRUE, F for FALSE,
and U for unknown.)
Table 8–6 AND Operator Logic
AND
T
F
U
T
T
F
U
F
F
F
F
U
U
F
U
Table 8–7 OR Operator Logic
OR
T
F
U
T
T
T
T
F
T
F
U
U
T
U
U
FULL SYNTAX
Table 8–8 NOT Operator Logic
NOT
T
F
F
T
U
U
Table 8–9 Conditional Test
Conditional Test
T
F
U
Expression IS TRUE
T
F
F
Expression IS FALSE
F
T
F
Expression is unknown
F
F
T
Equality Semantics
In EJB QL, only values of the same type can be compared. However, this rule
has one exception: Exact and approximate numeric values can be compared. In
such a comparison, the required type conversion adheres to the rules of Java
numeric promotion.
EJB QL treats compared values as if they were Java types, not as if they represented types in the underlying data store. For example, if a persistent field could
be either an integer or a NULL, then it must be designated as an Integer object,
not as an int primitive. This designation is required because a Java object can be
NULL but a primitive cannot.
Two strings are equal only if they contain the same sequence of characters. Trailing blanks are significant; for example, the strings 'abc' and 'abc ' are not
equal.
Two entity beans of the same abstract schema type are equal only if their primary
keys have the same value.
189
190
ENTERPRISE JAVABEANS™ QUERY LANGUAGE
SELECT Clause
The SELECT clause defines the types of the objects or values returned by the
query. The SELECT clause has the following syntax:
select_clause ::= SELECT [DISTINCT]
{single_valued_path_expression |
OBJECT(identification_variable)}
Return Types
The return type defined by the SELECT clause must match that of the finder or
select method for which the query is defined.
For finder method queries, the return type of the SELECT clause is the abstract
schema type of the entity bean that defines the finder method. This abstract
schema type maps to either a remote or local interface. If the bean’s remote
home interface defines the finder method, then the return type is the remote
interface (or a collection of remote interfaces). Likewise, if the local home interface defines the finder method, the return type is the local interface (or a collection). For example, the LocalPlayerHome interface of the PlayerEJB entity bean
defines the findall method:
public Collection findAll() throws FinderException;
The EJB QL query of the findall method returns a collection of LocalPlayer
interface types:
SELECT OBJECT(p)
FROM Player p
For select method queries, the return type of the SELECT clause may be one of the
following:
• The abstract schema of the entity bean that contains the select method.
• The abstract schema of a related entity bean
(By default, each of these abstract schema types maps to the local interface of the entity bean. Although uncommon, in the deployment descriptor you may override the default mapping by specifying a remote
interface.)
• A persistent field
EJB QL RESTRICTIONS
The PlayerEJB entity bean, for example, implements the ejbSelectSports
method, which returns a collection of String objects for sport. The sport is a
persistent field of the LeagueEJB entity bean. See Example 11 (page 172).
A SELECT clause cannot specify a collection-valued expression. For example, the
SELECT clause p.teams is invalid because teams is a collection. However, the
SELECT clause in the following query is valid because the t is a single element of
the teams collection:
SELECT t
FROM Player p, IN (p.teams) AS t
DISTINCT and OBJECT Keywords
The DISTINCT keyword eliminates duplicate return values. If the method of the
query returns a java.util.Collection—which allows duplicates—then you
must specify the DISTINCT keyword to eliminate duplicates. However, if the
method returns a java.util.Set, the DISTINCT keyword is redundant because a
java.util.Set may not contain duplicates.
The OBJECT keyword must precede a stand-alone identification variable, but it
must not precede a single-valued path expression. If an identification variable is
part of a single-valued path expression, it is not stand-alone.
EJB QL Restrictions
EJB QL has a few restrictions:
• Comments are not allowed.
• Date and time values are in milliseconds and use a Java long . A date or
time literal should be an integer literal. To generate a millisecond value,
you may use the java.util.Calendar class.
• Currently, container-managed persistence does not support inheritance.
For this reason, two entity beans of different types cannot be compared.
191
192
ENTERPRISE JAVABEANS™ QUERY LANGUAGE
9
Web Clients and
Components
Stephanie Bodoff
WHEN a Web client such as a browser communicates with a J2EE application, it does so through server-side objects called Web components. There are
two types of Web components: Java™ Servlets and JavaServer Pages™ (JSP™)
pages. Servlets are Java programming language classes that dynamically process
requests and construct responses. JSP pages are text-based documents that execute as servlets but allow a more natural approach to creating static content.
Although servlets and JSP pages can be used interchangeably, each has its own
strengths. Servlets are best suited to managing the control functions of an application, such as dispatching requests, and handling nontextual data. JSP pages are
more appropriate for generating text-based markup such as HTML, SVG, WML,
and XML.
This chapter describes the packaging, configuration, and deployment procedures
for Web clients. Chapters 10 and 11, cover how to develop the Web components.
Many features of JSP technology are determined by Java Servlet technology, so
you should familiarize yourself with that material even if you do not intend to
write servlets.
Most J2EE Web clients use the HTTP protocol and support for HTTP is a major
aspect of Web components. For a brief summary of HTTP protocol features, see
Appendix A.
193
194
WEB CLIENTS AND COMPONENTS
In This Chapter
Web Client Life Cycle 194
Web Application Archives 196
Creating a WAR File 197
Adding a WAR File to an EAR File 198
Adding a Web Component to a WAR File 198
Configuring Web Clients 200
Application-Level Configuration 200
WAR-Level Configuration 200
Component-Level Configuration 202
Deploying Web Clients 203
Running Web Clients 204
Updating Web Clients 204
Internationalizing Web Clients 206
Web Client Life Cycle
The server-side portion of a Web client consists of Web components, static
resource files such as images, and helper classes and libraries. The J2EE platform provides many supporting services that enhance the capabilities of Web
components and make them easier to develop. However, because it must take
these services into account, the process for creating and running a Web client is
different from that of traditional stand-alone Java classes.
Web components run within an environment called a Web container. The Web
container provides services such as request dispatching, security, concurrency,
and life-cycle management. It also gives Web components access to the J2EE
platform APIs such as naming, transactions, and e-mail.
Before it can be executed, a Web client must be packaged into a Web application
archive (WAR), which is a JAR similar to the package used for Java class libraries, and installed (or deployed) into a Web container.
Certain aspects of Web client behavior can be configured when it is deployed.
The configuration information is maintained in a text file in XML format called
a Web application deployment descriptor. When you create Web clients and
components using the J2EE SDK deploytool utility, it automatically generates
or updates the deployment descriptor based on data that you enter in deploytool
wizards and inspectors. You can also manually create a deployment descriptor
according to the schema described in the Java Servlet specification.
WEB CLIENT LIFE CYCLE
The process for creating, deploying, and executing a Web client can be summarized as follows:
1. Develop the Web component code (including possibly a deployment
descriptor).
2. Package the Web client components along with any static resources (for
example, images) and helper classes referenced by the component.
3. Deploy the application.
4. Access a URL that references the Web client.
Developing Web component code is covered in chapters 10 and 11. Steps 2
through 4 are expanded on in the following sections, illustrated with a Hello,
World-style application. This application allows a user to enter a name into an
HTML form (Figure 9–1)
Figure 9–1 Greeting Form
195
196
WEB CLIENTS AND COMPONENTS
and then displays a greeting after the name is submitted (Figure 9–2)
Figure 9–2 Response
The Hello application contains two Web components that generate the greeting
and the response. This tutorial has two versions of this application: a servlet version called Hello1App in which the components are implemented by two servlet
classes, GreetingServlet.java and ResponseServlet.java, and a JSP version called Hello2App in which the components are implemented by two JSP
pages, greeting.jsp and response.jsp. The two versions are used to illustrate
the tasks involved in packaging, deploying, and running a J2EE application that
contains Web components.
Web Application Archives
Web clients are packaged in Web application archives. In addition to Web components, a Web application archive usually contains other files, including the following:
• Server-side utility classes (database beans, shopping carts, and so on).
Often these classes conform to the JavaBeans component architecture.
• Static Web content (HTML, image, and sound files, and so on).
• Client-side classes (applets and utility classes).
Web components and static Web content files are called Web resources.
WEB APPLICATION ARCHIVES
A WAR has a specific directory structure. The top-level directory of a WAR is
the document root of the application. The document root is where JSP pages, client-side classes and archives, and static Web resources are stored.
The document root contains a subdirectory called WEBINF, which contains the
following files and directories:
• web.xml: The Web application deployment descriptor
• Tag library descriptor files (see Tag Library Descriptors (page 290))
• classes: A directory that contains server-side classes: servlets, utility
classes, and JavaBeans components
• lib: A directory that contains JAR archives of libraries (tag libraries and
any utility libraries called by server-side classes).
You can also create application-specific subdirectories (that is, package directories) in either the document root or the WEBINF/classes directory
Note: When you add classes and archives to a WAR, deploytool automatically
packages them in the WEBINF subdirectory. This is correct for Web components and
server-side utility classes, but incorrect for client-side classes such as applets and
any archives accessed by applets. To put client-side classes and archives in the correct location, you must drag them to the document root after you have added them
to the archive.
Creating a WAR File
When you add the first Web component to a J2EE application, deploytool automatically creates a new WAR file to contain the component. A later section
describes how to add a Web component.
You can also manually create a WAR in three ways:
• With the packager tool distributed with the J2EE SDK. This tool is
described in the section Packager Tool, page (440).
• With the war task of the ant portable build tool. Ant is used to build the
J2EE Tutorial examples. The example application described in the section
The Example JSP Pages, page (249) uses ant to create the WAR.
• With the JAR tool distributed with the J2SE. If you arrange your application development directory in the structure required by the WAR format,
it is straightforward to create a Web application archive file in the required
format. You simply execute the following command in the top-level directory of the application:
197
198
WEB CLIENTS AND COMPONENTS
jar cvf archiveName.war .
Note that to use any of these methods, you must also manually create a deployment descriptor in the correct format.
Adding a WAR File to an EAR File
If you manually create a WAR file or obtain a WAR file from another party, you
can add it to an existing EAR file as follows:
1. Select a J2EE application.
2. Select File→Add→Web WAR.
3. Navigate to the directory containing the WAR file, select the WAR file,
and click Add Web WAR.
See The Example JSP Pages, page (249) for an example.
You can also add a WAR file to a J2EE application using the packager tool. The
Duke’s Bank application described in Building, Packaging, Deploying, and Running the Application, page (417) uses packager.
Adding a Web Component to a WAR File
The following procedure describes how to create and add the Web component in
the Hello1App application to a WAR. Although the Web component wizard
solicits WAR and component-level configuration information when you add the
component, this chapter describes how to add the component and provide configuration information at a later time using application, WAR, and Web component inspectors:
1. Go to j2eetutorial/examples and build the example by running ant
hello1. For detailed instructions, see About the Examples, page (xxi)).
2. Create a J2EE application called Hello1App .
a. Select File→New→Application.
b. Click Browse.
c. In the file chooser, navigate to j2eetutorial/exam
ples/src/web/hello1.
d. In the File Name field, enter Hello1App.
e. Click New Application.
f. Click OK.
WEB APPLICATION ARCHIVES
3. Create the WAR file and add the GreetingServlet Web component and
all of the Hello1App application content.
a. Invoke the Web component wizard by selecting File→New→Web
Component.
b. In the combo box labelled Create New WAR File in Application select
Hello1App. Enter Hello1WAR in the field labeled WAR Display Name.
c. Click Edit to add the content files.
d. In the Edit Contents dialog box, navigate to j2eetutorial/exam
Select
GreetingServlet.class,
ples/build/web/hello1.
ResponseServlet.class, and duke.waving.gif, and click Add.
Click OK.
e. Click Next.
f. Select the Servlet radio button.
g. Click Next.
h. Select GreetingServlet from the Servlet Class combo box.
i. Click Finish.
4. Add the ResponseServlet Web component.
a. Invoke the Web component wizard by selecting File→New→Web
Component.
b. In the combo box labeled Add To Existing WAR File, select
Hello1WAR.
c. Click Next.
d. Select the Servlet radio button.
e. Click Next.
f. Select ResponseServlet from the Servlet Class combo box.
g. Click Finish.
Note: You can add JSP pages to a WAR file without creating a new Web component
for each page. You simply select the WAR file, click Edit to edit the contents of the
WAR, and add the pages. The JSP version of the Hello, World application,
described in Updating Web Clients, page (204), shows how to do this. If you choose
this method, you will not be able to specify alias paths (described in Specifying an
Alias Path, page (203)) for the pages.
199
200
WEB CLIENTS AND COMPONENTS
Configuring Web Clients
The following sections describe the Web client configuration parameters that
you will usually want to specify. Configuration parameters are specified at three
levels: application, WAR, and component. A number of security parameters can
be applied at the WAR and component levels. For information on these security
parameters, see Web-Tier Security, page (337).
Application-Level Configuration
Context Root
A context root is a name that gets mapped to the document root of a Web client.
If your client’s context root is catalog, then the request URL
http://<host>:8000/catalog/index.html
will retrieve the file index.html from the document root.
To specify the context root for Hello1App in deploytool,
1. Select Hello1App.
2. Select the Web Context tab
3. Enter hello1 in the Context Root field.
WAR-Level Configuration
The following sections give generic procedures for specifying WAR-level configuration information. For some specific examples, see The Example
Servlets, page (211).
Context Parameters
The Web components in a WAR share an object that represents their Web context
(see Accessing the Web Context (page 238)). To specify initialization parameters
that are passed to the context,
1. Select the WAR.
2. Select the Context tab.
3. Click Add.
CONFIGURING WEB CLIENTS
References to Environment Entries, Enterprise Beans,
Resource Environment Entries, or Resources
If your Web components reference environment entries, enterprise beans,
resource environment entries, or resources such as databases, you must declare
the references as follows:
1. Select the WAR.
2. Select the Environment, Enterprise Bean Refs, Resource Env. Refs or
Resource Refs tab.
3. Click Add in the pane to add a new reference.
Event Listeners
To add an event listener class (described in Handling Servlet Life-Cycle
Events, page (216)),
1.
2.
3.
4.
Select the WAR.
Select the Event Listeners tab.
Click Add.
Select the listener class from the new field in the Event Listener Classes
pane.
Error Mapping
You can specify a mapping between the status code returned in an HTTP
response or a Java programming language exception returned by any Web component and a Web resource (see Handling Errors, page (218)). To set up the mapping,
1.
2.
3.
4.
Select the WAR.
Select the File Refs tab.
Click Add in the Error Mapping pane.
Enter the HTTP status code (see HTTP Responses, page (432)) or fullyqualified class name of an exception in the Error/Exception field.
5. Enter the name of a resource to be invoked when the status code or exception is returned. The name should have a leading forward slash /.
Note: You can also define error pages for a JSP page contained in a WAR. If error
pages are defined for both the WAR and a JSP page, the JSP page’s error page takes
precedence.
201
202
WEB CLIENTS AND COMPONENTS
Filter Mapping
A Web container uses filter mapping declarations to decide which filters to apply
to a request, and in what order (see Filtering Requests and
Responses, page (228)). The container matches the request Uniform Resource
Identifier (URI) to a servlet as described in Specifying an Alias Path, page (203).
To determine which filters to apply, it matches filter mapping declarations by
servlet name or URL pattern. The order in which filters are invoked is the order
in which filter mapping declarations that match a request URI for a servlet
appear in the filter mapping list.
You specify a filter mapping in deploytool as follows:
1. Select the WAR.
2. Select the Filter Mapping tab.
3. Add a filter.
a. Click Edit Filter List.
b. Click Add.
c. Select the filter class.
d. Enter a filter name.
e. Add any filter initialization parameters.
f. Click OK.
4. Map the filter.
a. Click Add.
b. Select the filter name.
c. Select the target type. A filter can be mapped to a specific servlet or to
all servlets that match a given URL pattern.
d. Specify the target. If the target is a servlet, select the servlet from the
drop-down list. If the target is a URL pattern, enter the pattern.
Component-Level Configuration
Initialization Parameters
To specify parameters that are passed to the Web component when it is initialized,
1. Select the Web component.
2. Select the Init. Parameters tab.
3. Click Add to add a new parameter and value.
DEPLOYING WEB CLIENTS
Specifying an Alias Path
When a request is received by a Web container, it must determine which Web
component should handle the request. It does so by mapping the URL path contained in the request to a Web component. A URL path contains the context root
(described in the section Context Root, page (200)) and an alias path:
http://<host>:8000/context root/alias path
Before a servlet can be accessed, the Web container must have at least one alias
path for the component. The alias path must start with a / and end with a string
or a wildcard expression with an extension (*.jsp, for example). Since Web
containers automatically map an alias path that ends with *.jsp, you do not have
to specify an alias path for a JSP page unless you wish to refer to the page by a
name other than its file name. In the example discussed in the section Updating
Web Clients, page (204), the page greeting.jsp has an alias, /greeting, but
the page response.jsp is referenced by its file name within greeting.jsp.
You set up the mappings for the servlet version of the Hello application using the
Web component inspector as follows:
1.
2.
3.
4.
5.
6.
7.
Select the GreetingServlet Web component.
Select the Aliases tab.
Click Add to add a new mapping.
Type /greeting in the aliases list.
Select the ResponseServlet Web component.
Click Add.
Type /response in the aliases list.
Deploying Web Clients
The next step after you have created, packaged, and configured a Web client is to
deploy the EAR file that contains the client. To deploy the Hello1App application,
1.
2.
3.
4.
Select Hello1App.
Select Tools→Deploy.
Select a target server.
Click Finish.
203
204
WEB CLIENTS AND COMPONENTS
Running Web Clients
A Web client is executed when a Web browser references a URL that is mapped
to a component contained in the client. Once you have deployed the Hello1App
application, you can run the Web client by pointing a browser at
http://<host>:8000/hello1/greeting
Replace <host> with the name of the host running the J2EE server. If your
browser is running on the same host as the J2EE server, you may replace <host>
with localhost.
Updating Web Clients
During development, you will often need to make changes to Web clients. To
update a servlet you modify the source file, recompile the servlet class, update
the component in the WAR, and redeploy the application. Except for the compilation step, you update a JSP page in the same way.
To try this feature, first build, package, and deploy the JSP version of the Hello
application:
1. Go to j2eetutorial/examples/src and build the example by running
ant hello2.
2. Create a J2EE application called Hello2App .
a. Select File→New→Application.
b. In the file chooser, navigate to j2eetutorial/exam
ples/src/web/hello2.
c. In the File Name field, enter Hello2App.
d. Click New Application.
e. Click OK.
3. Create the WAR and add the greeting Web component and all of the
Hello2App application content.
a. Invoke the Web component wizard by selecting File→New→Web
Component.
b. In the combo box labeled Create New WAR File in Application select
Hello2App. Enter Hello2WAR in the field labeled WAR Display Name.
c. Click Edit to add the content files.
UPDATING WEB CLIENTS
d. In the Edit Contents dialog box, navigate to exam
ples/build/web/hello2. Select greeting.jsp, response.jsp, and
duke.waving.gif, and click Add. Click OK.
e. Click Next.
f. Select the JSP radio button.
g. Click Next.
h. Select greeting.jsp from the JSP Filename combo box.
i. Click Finish.
4.
5.
6.
7.
Add the alias /greeting for the greeting Web component.
Specify the context root hello2.
Deploy Hello2App.
Execute the application by pointing a Web browser at
http://<host>:8000/hello2/greeting. Replace <host> with the name
of the host running the J2EE server.
Now modify one of the JSP files. For example, you could replace the contents of
response.jsp with the following:
<h2>Hi, <%=username%>!</h2>
To update the file in the WAR and redeploy the application:
Edit response.jsp.
Execute ant hello2 to copy the modified file to the build directory.
Select Hello2App.
In deploytool, select Tools→Update Files.
A dialog box appears reporting the changed file.Verify that response.jsp
has been changed and dismiss the dialog box.
6. Select Tools→Deploy. Make sure the checkbox labeled Save Object
Before Deploying is checked.
1.
2.
3.
4.
5.
You can also perform steps 4 through 6 by selecting Tools→Update And Redeploy. The deploytool utility replaces the old JSP file in Hello2App.ear with
the new one and then redeploys the application.
205
206
WEB CLIENTS AND COMPONENTS
When you execute the application, the response should be changed (Figure 9–3)
Figure 9–3 New Response
Internationalizing Web Clients
Internationalization is the process of preparing an application to support various
languages. Localization is the process of adapting an internationalized application to support a specific language or locale. Although all client user interfaces
should be internationalized and localized, it is particularly important for Web clients because of the far-reaching nature of the Web. For a good overview of internationalization and localization, see
http://java.sun.com/docs/books/tutorial/i18n/index.html
In the simplest internationalized program, strings are read from a resource bundle that contains translations for the language in use. The resource bundle maps
keys used by a program to the strings displayed to the user. Thus, instead of creating strings directly in your code, you create a resource bundle that contains
translations and read the translations from that bundle using the corresponding
key. A resource bundle can be backed by a text file (properties resource bundle)
or a class (list resource bundle) containing the mappings.
In the following chapters on Web technology, the Duke’s Bookstore example is
internationalized and localized into English and Spanish. The key and value
pairs
are
contained
in
list
resource
bundles
named
mes
sages.BookMessage_*.class. To give you an idea of what the key and string
INTERNATIONALIZING WEB CLIENTS
pairs in a resource bundle look like, here are a few lines from the file mes
sages.BookMessages.java.
{"TitleCashier", "Cashier"},
{"TitleBookDescription", "Book Description"},
{"Visitor", "You are visitor number "},
{"What", "What We"re Reading"},
{"Talk", " talks about how Web components can transform the way
you develop applications for the Web. This is a must read for
any self respecting Web developer!"},
{"Start", "Start Shopping"},
To get the correct strings for a given user, a Web component retrieves the locale
(set by a browser language preference) from the request, opens the resource bundle for that locale, and then saves the bundle as a session attribute (see Associating Attributes with a Session, page (239)):
ResourceBundle messages = (ResourceBundle)session.
getAttribute("messages");
if (messages == null) {
Locale locale=request.getLocale();
messages = ResourceBundle.getBundle("WebMessages",
locale);
session.setAttribute("messages", messages);
}
A Web component retrieves the resource bundle from the session:
ResourceBundle messages =
(ResourceBundle)session.getAttribute("messages");
and looks up the string associated with the key TitleCashier as follows:
messages.getString(“TitleCashier”);
In addition to Duke’s Bookstore, both the Web client and the J2EE application
client distributed with this tutorial’s case study application, Duke’s Bank, are
internationalized; see the section Internationalization, page (415) in Chapter 18.
This has been a very brief introduction to internationalizing Web clients. For
more information on this subject, see the J2EE Blueprints:
http://java.sun.com/blueprints
207
208
WEB CLIENTS AND COMPONENTS
10
Java Servlet
Technology
Stephanie Bodoff
AS soon as the Web began to be used for delivering services, service providers
recognized the need for dynamic content. Applets, one of the earliest attempts
towards this goal, focused on using the client platform to deliver dynamic user
experiences. At the same time, developers also investigated using the server platform for this purpose. Initially, Common Gateway Interface (CGI) scripts were
the main technology used to generate dynamic content. Though widely used,
CGI scripting technology has a number of shortcomings, including platform
dependence and lack of scalability. To address these limitations, Java Servlet
technology was created as a portable way to provide dynamic, user-oriented content.
In This Chapter
What Is a Servlet? 210
The Example Servlets 211
Troubleshooting 215
Servlet Life Cycle 216
Handling Servlet Life-Cycle Events 216
Handling Errors 218
Sharing Information 218
Using Scope Objects 219
Controlling Concurrent Access to Shared Resources 220
Accessing Databases 221
209
210
JAVA SERVLET TECHNOLOGY
Initializing a Servlet 222
Writing Service Methods 223
Getting Information from Requests 223
Constructing Responses 225
Filtering Requests and Responses 228
Programming Filters 229
Programming Customized Requests and Responses 231
Specifying Filter Mappings 233
Invoking Other Web Resources 235
Including Other Resources in the Response 235
Transferring Control to Another Web Component 237
Accessing the Web Context 238
Maintaining Client State 239
Accessing a Session 239
Associating Attributes with a Session 239
Session Management 240
Session Tracking 241
Finalizing a Servlet 242
Tracking Service Requests 243
Notifying Methods to Shut Down 243
Creating Polite Long-Running Methods 244
What Is a Servlet?
A servlet is a Java programming language class used to extend the capabilities of
servers that host applications accessed via a request-response programming
model. Although servlets can respond to any type of request, they are commonly
used to extend the applications hosted by Web servers. For such applications,
Java Servlet technology defines HTTP-specific servlet classes.
The javax.servlet and javax.servlet.http packages provide interfaces and
classes for writing servlets. All servlets must implement the Servlet interface,
which defines life-cycle methods.
When implementing a generic service, you can use or extend the GenericServ
let class provided with the Java Servlet API. The HttpServlet class provides
methods, such as doGet and doPost, for handling HTTP-specific services.
This chapter focuses on writing servlets that generate responses to HTTP
requests. Some knowledge of the HTTP protocol is assumed; if you are unfamiliar with this protocol, you can get a brief introduction to HTTP in Appendix A.
THE EXAMPLE SERVLETS
The Example Servlets
This chapter uses the Duke’s Bookstore application to illustrate the tasks
involved in programming servlets. Table 10–1 lists the servlets that handle each
bookstore function. Each programming task is illustrated by one or more servlets. For example, BookDetailsServlet illustrates how to handle HTTP GET
requests, BookDetailsServlet and CatalogServlet show how to construct
responses, and CatalogServlet illustrates how to track session information.
Table 10–1 Duke’s Bookstore Example Servlets
Function
Servlet
Enter the bookstore
BookStoreServlet
Create the bookstore banner
BannerServlet
Browse the bookstore catalog
CatalogServlet
Put a book in a shopping cart
CatalogServlet,
BookDetailsServlet
Get detailed information on a specific book
BookDetailsServlet
Display the shopping cart
ShowCartServlet
Remove one or more books from the shopping cart
ShowCartServlet
Buy the books in the shopping cart
CashierServlet
Receive an acknowledgement for the purchase
ReceiptServlet
The data for the bookstore application is maintained in a database and accessed
through the helper class database.BookDB. The database package also contains
the class BookDetails, which represents a book. The shopping cart and shopping cart items are represented by the classes cart.ShoppingCart and
cart.ShoppingCartItem, respectively.
The source code for the bookstore application is located in the
j2eetutorial/examples/src/web/bookstore1 directory created when you
211
212
JAVA SERVLET TECHNOLOGY
unzip the tutorial bundle (see Downloading the Examples, page (xxii)). To build,
deploy, and run the example, follow these steps.
1. Go to j2eetutorial/examples and build the example by running ant
bookstore1 (see How to Build and Run the Examples, page (xxii)).
2. Start the j2ee server.
3. Start deploytool.
4. Start the Cloudscape database server by running cloudscape start.
5. Load the bookstore data into the database by running ant createweb
db.
6. Create a J2EE application called Bookstore1App.
a. Select File→New→Application.
b. In the file chooser, navigate to j2eetutorial/exam
ples/src/web/bookstore1.
c. In the File Name field, enter Bookstore1App.
d. Click New Application.
e. Click OK.
7. Create the WAR and add the BannerServlet Web component and all of
the Duke’s Bookstore content to the Bookstore1App application.
a. Select File→New→Web Component.
b. Click the Create New WAR File In Application radio button and select
Bookstore1App from the combo box. Enter Bookstore1WAR in the
field labeled WAR Display Name.
c. Click Edit to add the content files.
d. In the Edit Archive Contents dialog box, navigate to
j2eetutorial/examples/build/web/bookstore1. Select Ban
nerServlet.class, BookStoreServlet.class, BookDetailsServ
let.class, CatalogServlet.class, ShowCartServlet.class,
CashierServlet.class, and ReceiptServlet.class. Click Add.
Add errorpage.html and duke.books.gif. Add the cart , database,
exception, filters, listeners, messages, and util packages.
Click OK.
e. Click Next.
f. Select the Servlet radio button.
g. Click Next.
h. Select BannerServlet from the Servlet Class combo box.
213
THE EXAMPLE SERVLETS
i. Click Next twice.
j. In the Component Aliases pane, click Add and then type /banner in
the Alias field.
k. Click Finish.
8. Add each of the Web components listed in Table 10–2. For each servlet,
click the Add to Existing WAR File radio button and select
Bookstore1WAR from the combo box. Since the WAR contains all of the
servlet classes, you do not have to add any more content.
Table 10–2 Duke’s Bookstore Web Components
Web Component Name
Servlet Class
Component Alias
BookStoreServlet
BookStoreServlet
/enter
CatalogServlet
CatalogServlet
/catalog
BookDetailsServlet
BookDetailsServlet
/bookdetails
ShowCartServlet
ShowCartServlet
/showcart
CashierServlet
CashierServlet
/cashier
ReceiptServlet
ReceiptServlet
/receipt
9. Add a resource reference for the Cloudscape database.
a. Select Bookstore1WAR.
b. Select the Resource Refs tab.
c. Click Add.
d. Select javax.sql.DataSource from the Type column
e. Enter jdbc/BookDB in the Coded Name field.
f. Enter jdbc/Cloudscape in the JNDI Name field.
10.Add the listener class listeners.ContextListener (described in Handling Servlet Life-Cycle Events, page (216).
a. Select the Event Listeners tab.
b. Click Add.
c. Select the listeners.ContextListener class from the drop-down
field in the Event Listener Classes pane.
214
JAVA SERVLET TECHNOLOGY
11.Add an error page (described in Handling Errors, page (218)).
a. Select the File Refs tab.
b. In the Error Mapping panel, click Add.
c. Enter exception.BookNotFoundException in the Error/Exception
field.
d. Enter /errorpage.html in the Resource To Be Called field.
e. Repeat for exception.BooksNotFoundException and javax.serv
let.UnavailableException.
12.Add the filters filters.HitCounterFilter and filters.OrderFilter
(described in Filtering Requests and Responses, page (228)).
a. Select the Filter Mapping tab.
b. Click Edit Filter List.
c. Click Add.
d. Select filters.HitCounterFilter from the Filter Class column. The
deploytool utility will automatically enter HitCounterFilter in the
Display Name column.
e. Click Add.
f. Select filters.OrderFilter from the Filter Class column. The
deploytool utility will automatically enter OrderFilter in the Display Name column.
g. Click OK.
h. Click Add.
i. Select HitCounterFilter from the Filter Name column.
j. Select Servlet from the Target Type column.
k. Select BookStoreServlet from the Target column.
l. Repeat for OrderFilter. The target type is Servlet and the target is
ReceiptServlet.
13.Enter the context root.
a. Select Bookstore1App.
b. Select the Web Context tab.
c. Enter bookstore1.
14.Deploy the application.
a. Select Tools→Deploy.
b. Click Finish.
THE EXAMPLE SERVLETS
15.Open the bookstore URL http://<host>:8000/bookstore1/enter.
Troubleshooting
The section Common Problems and Their Solutions, page (41) (in particular,
Web Client Runtime Errors, page (45)) lists some reasons why a Web client can
fail. In addition, Duke’s Bookstore returns the following exceptions:
• BookNotFoundException: Returned if a book can’t be located in the
bookstore database. This will occur if you haven’t loaded the bookstore
database with data by running ant createwebdb or if the Cloudscape
server hasn’t been started or it has crashed.
• BooksNotFoundException: Returned if the bookstore data can’t be
retrieved. This will occur if you haven’t loaded the bookstore database
with data by running ant createwebdb or if the Cloudscape server
hasn’t been started or has crashed.
• UnavailableException: Returned if a servlet can’t retrieve the Web context attribute representing the bookstore. This will occur if you haven’t
added the listener class to the application.
Since we have specified an error page, you will see the message The applica
tion is unavailable. Please try later. If you don’t specify an error page,
the Web container generates a default page containing the message A Servlet
Exception Has Occurred and a stack trace that can help diagnose the cause of
the exception. If you use errorpage.html, you will have to look in the Web
container’s log to determine the cause of the exception. Web log files reside in
the directory
$J2EE_HOME/<logs>/<host>/web
and are named catalina.<date>.log.
The <logs> element is the directory specified by the log.directory entry in the
default.properties file. The default value is logs. The <host> element is the
name of the computer. See the Configuration Guide provided with the J2EE
SDK for more information about J2EE SDK log files.
215
216
JAVA SERVLET TECHNOLOGY
Servlet Life Cycle
The life cycle of a servlet is controlled by the container in which the servlet has
been deployed. When a request is mapped to a servlet, the container performs the
following steps.
1. If an instance of the servlet does not exist, the Web container
a. Loads the servlet class.
b. Creates an instance of the servlet class.
c. Initializes the servlet instance by calling the init method. Initialization is covered in Initializing a Servlet, page (222).
2. Invokes the service method, passing a request and response object. Service methods are discussed in the section Writing Service
Methods, page (223).
If the container needs to remove the servlet, it finalizes the servlet by calling the
servlet’s destroy method. Finalization is discussed in Finalizing a
Servlet, page (242).
Handling Servlet Life-Cycle Events
You can monitor and react to events in a servlet’s life cycle by defining listener
objects whose methods get invoked when life cycle events occur. To use these
listener objects, you must define the listener class and specify the listener class.
Defining The Listener Class
You define a listener class as an implementation of a listener interface. Table 10–
3 lists the events that can be monitored and the corresponding interface that must
be implemented. When a listener method is invoked, it is passed an event that
contains information appropriate to the event. For example, the methods in the
SERVLET LIFE CYCLE
HttpSessionListener interface are passed an HttpSessionEvent, which contains an HttpSession.
Table 10–3 Servlet Life-Cycle Events
Object
Web context (See
Accessing the Web
Context, page (238))
Session (See Maintaining Client
State, page (239))
Event
Listener Interface and Event Class
Initialization
and destruction
javax.servlet.
ServletContextListener and
ServletContextEvent
Attribute added,
removed, or
replaced
javax.servlet.
ServletContextAttributeListener and
ServletContextAttributeEvent
Creation,
invalidation,
and timeout
javax.servlet.http.
HttpSessionListener and
HttpSessionEvent
Attribute added,
removed, or
replaced
javax.servlet.http.
HttpSessionAttributeListener and
HttpSessionBindingEvent
The listeners.ContextListener class creates and removes the database
helper and counter objects used in the Duke’s Bookstore application. The methods retrieve the Web context object from ServletContextEvent and then store
(and remove) the objects as servlet context attributes.
import database.BookDB;
import javax.servlet.*;
import util.Counter;
public final class ContextListener
implements ServletContextListener {
private ServletContext context = null;
public void contextInitialized(ServletContextEvent event) {
context = event.getServletContext();
try {
BookDB bookDB = new BookDB();
context.setAttribute("bookDB", bookDB);
} catch (Exception ex) {
System.out.println(
"Couldn't create database: "
+ ex.getMessage());
217
218
JAVA SERVLET TECHNOLOGY
}
}
}
Counter counter = new Counter();
context.setAttribute("hitCounter", counter);
context.log("Created hitCounter"
+ counter.getCounter());
counter = new Counter();
context.setAttribute("orderCounter", counter);
context.log("Created orderCounter"
+ counter.getCounter());
public void contextDestroyed(ServletContextEvent event) {
context = event.getServletContext();
BookDB bookDB = context.getAttribute(
"bookDB");
bookDB.remove();
context.removeAttribute("bookDB");
context.removeAttribute("hitCounter");
context.removeAttribute("orderCounter");
}
Specifying Event Listener Classes
You specify a listener class for a WAR in the deploytool Event Listeners
inspector (see Event Listeners, page (201)).
Handling Errors
Any number of exceptions can occur when a servlet is executed. The Web container will generate a default page containing the message A Servlet Excep
tion Has Occurred when an exception occurs, but you can also specify that
the container should return a specific error page for a given exception. You specify error pages for a WAR in the deploytool File Refs inspector (see Error
Mapping, page (201)).
Sharing Information
Web components, like most objects, usually work with other objects to accomplish their tasks. There are several ways they can do this. They can use private
helper objects (for example, JavaBeans components), they can share objects that
are attributes of a public scope, they can use a database, and they can invoke
other Web resources. The Java Servlet technology mechanisms that allow a Web
SHARING INFORMATION
component to invoke other Web resources are described in the section Invoking
Other Web Resources, page (235).
Using Scope Objects
Collaborating Web components share information via objects maintained as
attributes of four scope objects. These attributes are accessed with the
[get|set]Attribute methods of the class representing the scope. Table 10–4
lists the scope objects. Figure 10–1 shows the scoped attributes maintained by the
Duke’s Bookstore application.
Table 10–4 Scope Objects
Scope
Object
Class
Accessible From
Web context
javax.servlet.
ServletContext
Web components within a Web context (see Accessing the Web Context, page (238))
session
javax.servlet.
http.HttpSession
Web components handling a request that belongs to
the session (see Maintaining Client
State, page (239))
subtype of
request
page
javax.servlet.
ServletRequest
Web components handling the request
javax.servlet.
jsp.PageContext
The JSP page that creates the object (see JavaServer
Pages™ Technology)
219
220
JAVA SERVLET TECHNOLOGY
Figure 10–1 Duke’s Bookstore Scoped Attributes
Controlling Concurrent Access to Shared Resources
In a multithreaded server, it is possible for shared resources to be accessed concurrently. Besides scope object attributes, shared resources include in-memory
data such as instance or class variables and external objects such as files, database connections, and network connections. Concurrent access can arise in several situations:
• Multiple Web components accessing objects stored in the Web context
• Multiple Web components accessing objects stored in a session
• Multiple threads within a Web component accessing instance variables. A
Web container will typically create a thread to handle each request. If you
want to ensure that a servlet instance handles only one request at a time, a
servlet can implement the SingleThreadModel interface. If a servlet
implements this interface, you are guaranteed that no two threads will execute concurrently in the servlet’s service method. A Web container can
implement this guarantee by synchronizing access to a single instance of
the servlet, or by maintaining a pool of Web component instances and dispatching each new request to a free instance. This interface does not prevent synchronization problems that result from Web components
accessing shared resources such as static class variables or external
objects.
SHARING INFORMATION
When resources can be accessed concurrently, they can be used in an inconsistent fashion. To prevent this, you must control the access using the synchronization techniques described in the Threads lesson in the Java Tutorial.
In the previous section we showed five scoped attributes shared by more than
one servlet: bookDB, cart, currency, hitCounter, and orderCounter. The
bookDB attribute is discussed in the next section. The cart, currency, and counters
can be set and read by multiple multithreaded servlets. To prevent these objects
from being used inconsistently, access is controlled by synchronized methods.
For example, here is the util.Counter class:
public class Counter {
private int counter;
public Counter() {
counter = 0;
}
public synchronized int getCounter() {
return counter;
}
public synchronized int setCounter(int c) {
counter = c;
return counter;
}
public synchronized int incCounter() {
return(++counter);
}
}
Accessing Databases
Data that is shared between Web components and is persistent between invocations of a J2EE application is usually maintained by a database. Web components use the JDBC 2.0 API to access relational databases. The data for the
bookstore application is maintained in a database and accessed through the
helper class database.BookDB. For example, ReceiptServlet invokes the
BookDB.buyBooks method to update the book inventory when a user makes a
purchase. The buyBooks method invokes buyBook for each book contained in
the shopping cart. To ensure the order is processed in its entirety, the calls to
buyBook are wrapped in a single JDBC transaction. The use of the shared database connection is synchronized via the [get|release]Connection methods.
public void buyBooks(ShoppingCart cart) throws OrderException{
Collection items = cart.getItems();
Iterator i = items.iterator();
try {
221
222
JAVA SERVLET TECHNOLOGY
}
getConnection();
con.setAutoCommit(false);
while (i.hasNext()) {
ShoppingCartItem sci = (ShoppingCartItem)i.next();
BookDetails bd = (BookDetails)sci.getItem();
String id = bd.getBookId();
int quantity = sci.getQuantity();
buyBook(id, quantity);
}
con.commit();
con.setAutoCommit(true);
releaseConnection();
} catch (Exception ex) {
try {
con.rollback();
releaseConnection();
throw new OrderException("Transaction failed: " +
ex.getMessage());
} catch (SQLException sqx) {
releaseConnection();
throw new OrderException("Rollback failed: " +
sqx.getMessage());
}
}
Initializing a Servlet
After the Web container loads and instantiates the servlet class and before it
delivers requests from clients, the Web container initializes the servlet. You can
customize this process to allow the servlet to read persistent configuration data,
initialize resources, and perform any other one-time activities by overriding the
init method of the Servlet interface. A servlet that cannot complete its initialization process should throw UnavailableException.
All the servlets that access the bookstore database (BookStoreServlet, Cata
logServlet, BookDetailsServlet, and ShowCartServlet) initialize a variable
in their init method that points to the database helper object created by the Web
context listener:
public class CatalogServlet extends HttpServlet {
private BookDB bookDB;
public void init() throws ServletException {
bookDB = (BookDB)getServletContext().
getAttribute("bookDB");
WRITING SERVICE METHODS
}
}
if (bookDB == null) throw new
UnavailableException("Couldn't get database.");
Writing Service Methods
The service provided by a servlet is implemented in the service method of a
GenericServlet, the doMethod methods (where Method can take the value Get,
Delete, Options, Post, Put, Trace) of an HttpServlet, or any other protocolspecific methods defined by a class that implements the Servlet interface. In
the rest of this chapter, the term service method will be used for any method in a
servlet class that provides a service to a client.
The general pattern for a service method is to extract information from the
request, access external resources, and then populate the response based on that
information.
For HTTP servlets, the correct procedure for populating the response is to first
fill in the response headers, then retrieve an output stream from the response, and
finally write any body content to the output stream. Response headers must
always be set before a PrintWriter or ServletOutputStream is retrieved
because the HTTP protocol expects to receive all headers before body content.
The next two sections describe how to get information from requests and generate responses.
Getting Information from Requests
A request contains data passed between a client and the servlet. All requests
implement the ServletRequest interface. This interface defines methods for
accessing the following information:
• Parameters, which are typically used to convey information between clients and servlets
• Object-valued attributes, which are typically used to pass information
between the servlet container and a servlet or between collaborating servlets
• Information about the protocol used to communicate the request and the
client and server involved in the request
• Information relevant to localization
223
224
JAVA SERVLET TECHNOLOGY
For example, in CatalogServlet the identifier of the book that a customer
wishes to purchase is included as a parameter to the request. The following code
fragment illustrates how to use the getParameter method to extract the identifier:
String bookId = request.getParameter("Add");
if (bookId != null) {
BookDetails book = bookDB.getBookDetails(bookId);
You can also retrieve an input stream from the request and manually parse the
data. To read character data, use the BufferedReader object returned by the
request’s getReader method. To read binary data, use the ServletInputStream
returned by getInputStream.
HTTP servlets are passed an HTTP request object, HttpServletRequest, which
contains the request URL, HTTP headers, query string, and so on.
An HTTP request URL contains the following parts:
http://[host]:[port][request path]?[query string]
The request path is further composed of the following elements:
• Context path: A concatenation of a forward slash (/) with the context
root of the servlet’s J2EE application.
• Servlet path: The path section that corresponds to the component alias
that activated this request. This path starts with a forward slash (/).
• Path info: The part of the request path that is not part of the context path
or the servlet path.
If the context path is /catalog, and the aliases are as listed in Table 10–5, then
Table 10–6 gives some examples of how the URL will be broken down:
Table 10–5 Aliases
Pattern
Servlet
/lawn/*
LawnServlet
/*.jsp
JSPServlet
225
WRITING SERVICE METHODS
Table 10–6 Request Path Elements
Request Path
Servlet Path
Path Info
/catalog/lawn/index.html
/lawn
/index.html
/catalog/help/feedback.jsp
/help/feedback.jsp
null
Query strings are composed of a set of parameters and values. Individual parameters are retrieved from a request with the getParameter method. There are two
ways to generate query strings:
• A query string can explicitly appear in a Web page. For example, an
HTML page generated by the CatalogServlet could contain the link
<a href="/bookstore1/catalog?Add=101">Add To Cart</a>
CatalogServlet extracts the parameter named Add as follows:
String bookId = request.getParameter("Add");
• A query string is appended to a URL when a form with a GET HTTP
method is submitted. In the Duke’s Bookstore application, CashierServ
let generates a form, then a user name input to the form is appended to
the URL that maps to ReceiptServlet, and finally ReceiptServlet
extracts the user name using the getParameter method.
Constructing Responses
A response contains data passed between a server and the client. All responses
implement the ServletResponse interface. This interface defines methods that
allow you to do the following.
• Retrieve an output stream to use to send data to the client. To send character data, use the PrintWriter returned by the response’s getWriter
method. To send binary data in a MIME body response, use the Serv
letOutputStream returned by getOutputStream. To mix binary and text
data, for example, to create a multipart response, use a ServletOutput
Stream and manage the character sections manually.
• Indicate the content type (for example, text/html), being returned by the
response. A registry of content type names is kept by the Internet Assigned
Numbers Authority (IANA) at:
226
JAVA SERVLET TECHNOLOGY
ftp://ftp.isi.edu/innotes/iana/assignments/mediatypes
• Indicate whether to buffer output. By default, any content written to the
output stream is immediately sent to the client. Buffering allows content
to be written before anything is actually sent back to the client, thus providing the servlet with more time to set appropriate status codes and headers or forward to another Web resource.
• Set localization information.
HTTP response objects, HttpServletResponse, have fields representing HTTP
headers such as
• Status codes, which are used to indicate the reason a request is not satisfied.
• Cookies, which are used to store application-specific information at the
client. Sometimes cookies are used to maintain an identifier for tracking a
user’s session (see Maintaining Client State, page (239)).
In Duke’s Bookstore, BookDetailsServlet generates an HTML page that displays information about a book that the servlet retrieves from a database. The
servlet first sets response headers: the content type of the response and the buffer
size. The servlet buffers the page content because the database access can generate an exception that would cause forwarding to an error page. By buffering the
response, the client will not see a concatenation of part of a Duke’s Bookstore
page with the error page should an error occur. The doGet method then retrieves
a PrintWriter from the response.
For filling in the response, the servlet first dispatches the request to Ban
nerServlet, which generates a common banner for all the servlets in the application. This process is discussed in the section Including Other Resources in the
Response, page (235). Then the servlet retrieves the book identifier from a
request parameter and uses the identifier to retrieve information about the book
from the bookstore database. Finally, the servlet generates HTML markup that
describes the book information and commits the response to the client by calling
the close method on the PrintWriter.
public class BookDetailsServlet extends HttpServlet {
public void doGet (HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
// set headers before accessing the Writer
response.setContentType("text/html");
response.setBufferSize(8192);
PrintWriter out = response.getWriter();
WRITING SERVICE METHODS
// then write the response
out.println("<html>" +
"<head><title>+
messages.getString("TitleBookDescription")
+</title></head>");
// Get the dispatcher; it gets the banner to the user
RequestDispatcher dispatcher =
getServletContext().
getRequestDispatcher("/banner");
if (dispatcher != null)
dispatcher.include(request, response);
}
}
//Get the identifier of the book to display
String bookId = request.getParameter("bookId");
if (bookId != null) {
// and the information about the book
try {
BookDetails bd =
bookDB.getBookDetails(bookId);
...
//Print out the information obtained
out.println("<h2>" + bd.getTitle() + "</h2>" +
...
} catch (BookNotFoundException ex) {
response.resetBuffer();
throw new ServletException(ex);
}
}
out.println("</body></html>");
out.close();
227
228
JAVA SERVLET TECHNOLOGY
BookDetailsServlet generates a page that looks like Figure 10–2.
Figure 10–2 Book Details
Filtering Requests and Responses
A filter is an object that can transform the header or content or both of a request
or response. Filters differ from Web components in that they usually do not
themselves create a response. Instead, a filter provides functionality that can be
“attached” to any kind of Web resource. As a consequence, a filter should not
have any dependencies on a Web resource for which it is acting as a filter, so that
FILTERING REQUESTS AND RESPONSES
it can be composable with more than one type of Web resource. The main tasks
that a filter can perform are as follows:
• Query the request and act accordingly
• Block the request-and-response pair from passing any further.
• Modify the request headers and data. You do this by providing a customized version of the request.
• Modify the response headers and data. You do this by providing a customized version of the response.
• Interact with external resources.
Applications of filters include authentication, logging, image conversion, data
compression, encryption, tokenizing streams, and XML transformations.
You can configure a Web resource to be filtered by a chain of zero, one, or more
filters in a specific order. This chain is specified when the Web application containing the component is deployed and is instantiated when a Web container
loads the component.
In summary, the tasks involved in using filters include
• Programming the filter
• Programming customized requests and responses
• Specifying the filter chain for each Web resource
Programming Filters
The filtering API is defined by the Filter, FilterChain, and FilterConfig
interfaces in the javax.servlet package. You define a filter by implementing
the Filter interface. The most important method in this interface is the doFil
ter method, which is passed request, response, and filter chain objects. This
method can perform the following actions:
• Examine the request headers.
• Customize the request object if it wishes to modify request headers or
data.
• Customize the response object if it wishes to modify response headers or
data
• Invoke the next entity in the filter chain. If the current filter is the last filter
in the chain that ends with the target Web component or static resource,
the next entity is the resource at the end of the chain; otherwise, it is the
next filter that was configured in the WAR. It invokes the next entity by
229
230
JAVA SERVLET TECHNOLOGY
calling the doFilter method on the chain object (passing in the request
and response it was called with, or the wrapped versions it may have created). Alternatively, it can choose to block the request by not making the
call to invoke the next entity. In the latter case, the filter is responsible for
filling out the response.
• Examine response headers after it has invoked the next filter in the chain.
• Throw an exception to indicate an error in processing.
In addition to doFilter, you must implement the init and destroy methods.
The init method is called by the container when the filter is instantiated. If you
wish to pass initialization parameters to the filter, you retrieve them from the
FilterConfig object passed to init.
The Duke’s Bookstore application uses the filters HitCounterFilter and
OrderFilter to increment and log the value of a counter when the entry and
receipt servlets are accessed.
In the doFilter method, both filters retrieve the servlet context from the filter
configuration object so that they can access the counters stored as context
attributes. After the filters have completed application-specific processing, they
invoke doFilter on the filter chain object passed into the original doFilter
method. The elided code is discussed in the next section.
public final class HitCounterFilter implements Filter {
private FilterConfig filterConfig = null;
public void init(FilterConfig filterConfig)
throws ServletException {
this.filterConfig = filterConfig;
}
public void destroy() {
this.filterConfig = null;
}
public void doFilter(ServletRequest request,
ServletResponse response, FilterChain chain)
throws IOException, ServletException {
if (filterConfig == null)
return;
StringWriter sw = new StringWriter();
PrintWriter writer = new PrintWriter(sw);
Counter counter = (Counter)filterConfig.
getServletContext().
getAttribute("hitCounter");
writer.println();
writer.println("===============");
FILTERING REQUESTS AND RESPONSES
}
}
writer.println("The number of hits is: " +
counter.incCounter());
writer.println("===============");
// Log the resulting string
writer.flush();
filterConfig.getServletContext().
log(sw.getBuffer().toString());
...
chain.doFilter(request, wrapper);
...
Programming Customized Requests and Responses
There are many ways for a filter to modify a request or response. For example, a
filter could add an attribute to the request or insert data in the response. In the
Duke’s Bookstore example, HitCounterFilter inserts the value of the counter
into the response.
A filter that modifies a response must usually capture the response before it is
returned to the client. The way to do this is to pass a stand-in stream to the
servlet that generates the response. The stand-in stream prevents the servlet from
closing the original response stream when it completes and allows the filter to
modify the servlet’s response.
To pass this stand-in stream to the servlet, the filter creates a response wrapper
that overrides the getWriter or getOutputStream method to return this stand-in
stream. The wrapper is passed to the doFilter method of the filter chain.
Wrapper methods default to calling through to the wrapped request or response
object. This approach follows the well-known Wrapper or Decorator pattern
described in Design Patterns: Elements of Reusable Object-Oriented Software
(Addison-Wesley, 1995). The following sections describe how the hit counter
filter described earlier and other types of filters use wrappers.
To override request methods, you wrap the request in an object that extends
ServletRequestWrapper or HttpServletRequestWrapper. To override
response methods, you wrap the response in an object that extends
ServletResponseWrapper or HttpServletResponseWrapper.
HitCounterFilter wraps the response in a CharResponseWrapper. The
wrapped response is passed to the next object in the filter chain, which is Book
StoreServlet. BookStoreServlet writes its response into the stream created
by CharResponseWrapper. When chain.doFilter returns, HitCounterFilter
retrieves the servlet’s response from PrintWriter and writes it to a buffer. The
231
232
JAVA SERVLET TECHNOLOGY
filter inserts the value of the counter into the buffer, resets the content length
header of the response, and finally writes the contents of the buffer to the
response stream.
PrintWriter out = response.getWriter();
CharResponseWrapper wrapper = new CharResponseWrapper(
(HttpServletResponse)response);
chain.doFilter(request, wrapper);
CharArrayWriter caw = new CharArrayWriter();
caw.write(wrapper.toString().substring(0,
wrapper.toString().indexOf("</body>")1));
caw.write("<p>\n<center><center>" +
messages.getString("Visitor") + "<font color='red'>" +
counter.getCounter() + "</font><center>");
caw.write("\n</body></html>");
response.setContentLength(caw.toString().length());
out.write(caw.toString());
out.close();
public class CharResponseWrapper extends
HttpServletResponseWrapper {
private CharArrayWriter output;
public String toString() {
return output.toString();
}
public CharResponseWrapper(HttpServletResponse response){
super(response);
output = new CharArrayWriter();
}
public PrintWriter getWriter(){
return new PrintWriter(output);
}
}
FILTERING REQUESTS AND RESPONSES
Figure 10–3 shows the entry page for Duke’s Bookstore with the hit counter.
Figure 10–3 Duke’s Bookstore Entry Page
Specifying Filter Mappings
A Web container uses filter mappings to decide how to apply filters to Web
resources. A filter mapping matches a filter to a Web component by name or to
Web resources by URL pattern. The filters are invoked in the order in which filter mappings appear in the filter mapping list of a WAR. You specify a filter
mapping list for a WAR in the deploytool Filter Mapping inspector (see Filter
Mapping, page (202)).
233
234
JAVA SERVLET TECHNOLOGY
Table 10–7 contains the filter mapping list for the Duke’s Bookstore application.
The filters are matched by servlet name and each filter chain contains only one
filter.
Table 10–7 Duke’s Bookstore Filter Mapping List
Servlet Name
Filter
BookStoreServlet
HitCounterFilter
ReceiptServlet
OrderFilter
You can map a filter to one or more Web resources, and you can map more than
one filter to a Web resource. This is illustrated in Figure 10–4, where filter F1 is
mapped to servlets S1, S2, and S3, filter F2 is mapped to servlet S2, and filter F3
is mapped to servlets S1 and S2.
Figure 10–4 Filter to Servlet Mapping
Recall that a filter chain is one of the objects passed to the doFilter method of a
filter. This chain is formed indirectly via filter mappings. The order of the filters
in the chain is the same as the order in which filter mappings appear in the Web
application deployment descriptor.
INVOKING OTHER WEB RESOURCES
When a filter is mapped to servlet S1, the Web container invokes the doFilter
method of F1. The doFilter method of each filter in S1’s filter chain is invoked
by the preceding filter in the chain via the chain.doFilter method. Since S1’s
filter chain contains filters F1 and F3, F1’s call to chain.doFilter invokes the
doFilter method of filter F3. When F3’s doFilter method completes, control
returns to F1’s doFilter method.
Invoking Other Web Resources
Web components can invoke other Web resources in two ways: indirect and
direct. A Web component indirectly invokes another Web resource when it
embeds in content returned to a client a URL that points to another Web component. In the Duke’s Bookstore application, most Web components contain
embedded URLs that point to other Web components. For example, Receipt
Servlet indirectly invokes the CatalogServlet through the embedded URL
/bookstore1/catalog.
A Web component can also directly invoke another resource while it is executing. There are two possibilities: it can include the content of another resource, or
it can forward a request to another resource.
To invoke a resource available on the server that is running a Web component,
you must first obtain a RequestDispatcher object using the getRequestDis
patcher("URL") method.
You can get a RequestDispatcher object from either a request or the Web context; however, the two methods have slightly different behavior. The method
takes the path to the requested resource as an argument. A request can take a relative path (that is, one that does not begin with a /), but the Web context requires
an absolute path. If the resource is not available, or if the server has not implemented a RequestDispatcher object for that type of resource, getRequestDis
patcher will return null. Your servlet should be prepared to deal with this
condition.
Including Other Resources in the Response
It is often useful to include another Web resource, for example, banner content or
copyright information, in the response returned from a Web component. To
include another resource, invoke the include method of a RequestDispatcher
object:
include(request, response);
235
236
JAVA SERVLET TECHNOLOGY
If the resource is static, the include method enables programmatic server-side
includes. If the resource is a Web component, the effect of the method is to send
the request to the included Web component, execute the Web component, and
then include the result of the execution in the response from the containing servlet. An included Web component has access to the request object, but it is limited
in what it can do with the response object:
• It can write to the body of the response and commit a response.
• It cannot set headers or call any method (for example, setCookie) that
affects the headers of the response.
The banner for the Duke’s Bookstore application is generated by BannerServ
let. Note that both the doGet and doPost methods are implemented because
BannerServlet can be dispatched from either method in a calling servlet.
public class BannerServlet extends HttpServlet {
public void doGet (HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
PrintWriter out = response.getWriter();
out.println("<body bgcolor=\"#ffffff\">" +
"<center>" + "<hr> <br> &nbsp;" + "<h1>" +
"<font size=\"+3\" color=\"#CC0066\">Duke's </font>" +
<img src=\"" + request.getContextPath() +
"/duke.books.gif\">" +
"<font size=\"+3\" color=\"black\">Bookstore</font>" +
"</h1>" + "</center>" + "<br> &nbsp; <hr> <br> ");
}
public void doPost (HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
}
}
PrintWriter out = response.getWriter();
out.println("<body bgcolor=\"#ffffff\">" +
"<center>" + "<hr> <br> &nbsp;" + "<h1>" +
"<font size=\"+3\" color=\"#CC0066\">Duke's </font>" +
<img src=\"" + request.getContextPath() +
"/duke.books.gif\">" +
"<font size=\"+3\" color=\"black\">Bookstore</font>" +
"</h1>" + "</center>" + "<br> &nbsp; <hr> <br> ");
INVOKING OTHER WEB RESOURCES
Each servlet in the Duke’s Bookstore application includes the result from Ban
nerServlet with the following code:
RequestDispatcher dispatcher =
getServletContext().getRequestDispatcher("/banner");
if (dispatcher != null)
dispatcher.include(request, response);
}
Transferring Control to Another Web Component
In some applications, you might want to have one Web component do preliminary processing of a request and have another component generate the response.
For example, you might want to partially process a request and then transfer to
another component depending on the nature of the request.
To transfer control to another Web component, you invoke the forward method
of a RequestDispatcher. When a request is forwarded, the request URL is set to
the path of the forwarded page. If the original URL is required for any processing, you can save it as a request attribute. The Dispatcher servlet, used by a version of the Duke’s Bookstore application described in the section A Template
Tag Library, page (308), saves the path information from the original URL,
retrieves a RequestDispatcher from the request, and then forwards to the JSP
page template.jsp.
public class Dispatcher extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response) {
request.setAttribute("selectedScreen",
request.getServletPath());
RequestDispatcher dispatcher = request.
getRequestDispatcher("/template.jsp");
if (dispatcher != null)
dispatcher.forward(request, response);
}
public void doPost(HttpServletRequest request,
...
}
The forward method should be used to give another resource responsibility for
replying to the user. If you have already accessed a ServletOutputStream or
PrintWriter object within the servlet, you cannot use this method; it throws an
IllegalStateException.
237
238
JAVA SERVLET TECHNOLOGY
Accessing the Web Context
The context in which Web components execute is an object that implements the
ServletContext interface. You retrieve the Web context with the getServlet
Context method. The Web context provides methods for accessing:
•
•
•
•
Initialization parameters
Resources associated with the Web context
Object-valued attributes
Logging capabilities
The Web context is used by the Duke’s Bookstore filters filters.HitCounter
Filter and OrderFilter, discussed in the section Filtering Requests and
Responses, page (228). The filters store a counter as a context attribute. Recall
from Controlling Concurrent Access to Shared Resources, page (220) that the
counter’s access methods are synchronized to prevent incompatible operations
by servlets that are running concurrently. A filter retrieves the counter object
with the context’s getAttribute method. The incremented value of the counter
is recorded with the context’s log method.
public final class HitCounterFilter implements Filter {
private FilterConfig filterConfig = null;
public void doFilter(ServletRequest request,
ServletResponse response, FilterChain chain)
throws IOException, ServletException {
...
StringWriter sw = new StringWriter();
PrintWriter writer = new PrintWriter(sw);
ServletContext context = filterConfig.
getServletContext();
Counter counter = (Counter)context.
getAttribute("hitCounter");
...
writer.println("The number of hits is: " +
counter.incCounter());
...
context.log(sw.getBuffer().toString());
...
}
}
MAINTAINING CLIENT STATE
Maintaining Client State
Many applications require a series of requests from a client to be associated with
one another. For example, the Duke’s Bookstore application saves the state of a
user’s shopping cart across requests. Web-based applications are responsible for
maintaining such state, called a session, because the HTTP protocol is stateless.
To support applications that need to maintain state, Java Servlet technology provides an API for managing sessions and allows several mechanisms for implementing sessions.
Accessing a Session
Sessions are represented by an HttpSession object. You access a session by
calling the getSession method of a request object. This method returns the current session associated with this request, or, if the request does not have a session, it creates one. Since getSession may modify the response header (if
cookies are the session tracking mechanism), it needs to be called before you
retrieve a PrintWriter or ServletOutputStream.
Associating Attributes with a Session
You can associate object-valued attributes with a session by name. Such
attributes are accessible by any Web component that belongs to the same Web
context and is handling a request that is part of the same session.
The Duke’s Bookstore application stores a customer’s shopping cart as a session
attribute. This allows the shopping cart to be saved between requests and also
allows cooperating servlets to access the cart. CatalogServlet adds items to the
cart; ShowCartServlet displays, deletes items from, and clears the cart; and
CashierServlet retrieves the total cost of the books in the cart.
public class CashierServlet extends HttpServlet {
public void doGet (HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
// Get the user's session and shopping cart
HttpSession session = request.getSession();
ShoppingCart cart =
(ShoppingCart)session.
239
240
JAVA SERVLET TECHNOLOGY
getAttribute("cart");
...
// Determine the total price of the user's books
double total = cart.getTotal();
Notifying Objects That Are Associated with a Session
Recall that your application can notify Web context and session listener objects
of servlet life-cycle events (see Handling Servlet Life-Cycle
Events, page (216)). You can also notify objects of certain events related to their
association with a session, such as the following:
• When the object is added to or removed from a session. To receive this
notification, your object must implement the javax.http.HttpSession
BindingListener interface.
• When the session to which the object is attached will be passivated or activated. A session will be passivated or activated when it is moved between
virtual machines or saved to and restored from persistent storage. To
receive this notification, your object must implement the
javax.http.HttpSessionActivationListener interface.
Session Management
Since there is no way for an HTTP client to signal that it no longer needs a session, each session has an associated timeout so that its resources can be
reclaimed. The timeout period can be accessed with a session’s [get|set]MaxI
nactiveInterval methods. You can also set the timeout period in deploytool:
1. Select the WAR.
2. Select the General tab.
3. Enter the timeout period in the Advanced box.
To ensure that an active session is not timed out, you should periodically access
the session via service methods because this resets the session’s time-to-live
counter.
When a particular client interaction is finished, you use the session’s invali
date method to invalidate a session on the server side and remove any session
data.
MAINTAINING CLIENT STATE
The bookstore application’s ReceiptServlet is the last servlet to access a client’s session, so it has responsibility for invalidating the session:
public class ReceiptServlet extends HttpServlet {
public void doPost(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
// Get the user's session and shopping cart
HttpSession session = request.getSession();
// Payment received invalidate the session
session.invalidate();
...
Session Tracking
A Web container can use several methods to associate a session with a user, all of
which involve passing an identifier between the client and server. The main
methods require the client to accept cookies or require the Web component to
rewrite any URL that is returned to the client.
If your application makes use of session objects, you must ensure that session
tracking is enabled by allowing the application to rewrite a URL whenever the
client turns off cookies. You do this by calling the response’s encodeURL(URL)
method on all URLs returned by a servlet. This method includes the session ID
in the URL only if cookies are disabled; otherwise, it returns the URL
unchanged.
The doGet method of ShowCartServlet encodes the three URLs at the bottom
of the shopping cart display page as follows:
out.println("<p> &nbsp; <p><strong><a href=\"" +
response.encodeURL(request.getContextPath() + "/catalog") +
"\">" + messages.getString("ContinueShopping") +
"</a> &nbsp; &nbsp; &nbsp;" +
"<a href=\"" +
response.encodeURL(request.getContextPath() + "/cashier") +
"\">" + messages.getString("Checkout") +
"</a> &nbsp; &nbsp; &nbsp;" +
"<a href=\"" +
response.encodeURL(request.getContextPath() +
"/showcart?Clear=clear") +
"\">" + messages.getString("ClearCart") +
"</a></strong>");
If cookies are turned off, the session is encoded in the Check Out URL as follows:
241
242
JAVA SERVLET TECHNOLOGY
http://localhost:8080/bookstore1/cashier;
jsessionid=c0o7fszeb1
If cookies are turned on, the URL is simply
http://localhost:8080/bookstore1/cashier
Finalizing a Servlet
When a servlet container determines that a servlet should be removed from service (for example, when a container wants to reclaim memory resources, or
when it is being shut down), it calls the destroy method of the Servlet interface. In this method, you release any resources the servlet is using and save any
persistent state. The following destroy method releases the database object created in the init method described in Initializing a Servlet, page (222):
public void destroy() {
bookDB = null;
}
All of a servlet’s service methods should be complete when a servlet is
removed. The server tries to ensure this completion by calling the destroy
method only after all service requests have returned or after a server-specific
grace period, whichever comes first.
If your servlet has potentially long-running service requests, use the techniques
described below to do the following.
• Keep track of how many threads are currently running the service
method
• Provide a clean shutdown by having the destroy method notify long-running threads of the shutdown and wait for them to complete
• Have the long-running methods poll periodically to check for shutdown
and, if necessary, stop working, clean up, and return
Tracking Service Requests
To track service requests, include in your servlet class a field that counts the
number of service methods that are running. The field should have synchronized
access methods to increment, decrement, and return its value.
FINALIZING A SERVLET
public ShutdownExample extends HttpServlet {
private int serviceCounter = 0;
...
//Access methods for serviceCounter
protected synchronized void enteringServiceMethod() {
serviceCounter++;
}
protected synchronized void leavingServiceMethod() {
serviceCounter;
}
protected synchronized int numServices() {
return serviceCounter;
}
}
The service method should increment the service counter each time the method
is entered and should decrement the counter each time the method returns. This
is one of the few times that your HttpServlet subclass should override the ser
vice method. The new method should call super.service to preserve all of the
original service method’s functionality:
protected void service(HttpServletRequest req,
HttpServletResponse resp)
throws ServletException,IOException {
enteringServiceMethod();
try {
super.service(req, resp);
} finally {
leavingServiceMethod();
}
}
Notifying Methods to Shut Down
To ensure a clean shutdown, your destroy method should not release any shared
resources until all of the service requests have completed. One part of doing this
is to check the service counter. Another part is to notify the long-running methods that it is time to shut down. For this notification, another field is required.
The field should have the usual access methods:
public ShutdownExample extends HttpServlet {
private boolean shuttingDown;
...
//Access methods for shuttingDown
protected setShuttingDown(boolean flag) {
shuttingDown = flag;
243
244
JAVA SERVLET TECHNOLOGY
}
}
protected boolean isShuttingDown() {
return shuttingDown;
}
An example of the destroy method using these fields to provide a clean shutdown follows:
public void destroy() {
/* Check to see whether there are still service methods /*
/* running, and if there are, tell them to stop. */
if (numServices() > 0) {
setShuttingDown(true);
}
}
/* Wait for the service methods to stop. */
while(numServices() > 0) {
try {
Thread.sleep(interval);
} catch (InterruptedException e) {
}
}
Creating Polite Long-Running Methods
The final step in providing a clean shutdown is to make any long-running methods behave politely. Methods that might run for a long time should check the
value of the field that notifies them of shutdowns and should interrupt their
work, if necessary.
public void doPost(...) {
...
for(i = 0; ((i < lotsOfStuffToDo) &&
!isShuttingDown()); i++) {
try {
partOfLongRunningOperation(i);
} catch (InterruptedException e) {
...
}
}
}
11
JavaServer Pages™
Technology
Stephanie Bodoff
JAVASERVER Pages™ (JSP™) technology allows you to easily create Web
content that has both static and dynamic components. JSP technology projects
all the dynamic capabilities of Java Servlet technology but provides a more natural approach to creating static content. The main features of JSP technology are:
• A language for developing JSP pages, which are text-based documents
that describe how to process a request and construct a response
• Constructs for accessing server-side objects
• Mechanisms for defining extensions to the JSP language
JSP technology also contains an API that is used by developers of Web containers, but this API is not covered in this chapter.
In This Chapter
What Is a JSP Page? 246
The Example JSP Pages 249
The Life Cycle of a JSP Page 253
Translation and Compilation 253
Execution 254
Initializing and Finalizing a JSP Page 256
Creating Static Content 257
245
246
JAVASERVER PAGES™ TECHNOLOGY
Creating Dynamic Content 257
Using Objects within JSP Pages 257
JSP Scripting Elements 260
Including Content in a JSP Page 263
Transferring Control to Another Web Component 264
Param Element 265
Including an Applet 265
Extending the JSP Language 267
What Is a JSP Page?
A JSP page is a text-based document that contains two types of text: static template data, which can be expressed in any text-based format, such as HTML,
SVG, WML, and XML; and JSP elements, which construct dynamic content. A
syntax card and reference for the JSP elements are available at:
http://java.sun.com/products/jsp/technical.html#syntax
The Web page in Figure 11–1 is a form that allows you to select a locale and displays the date in a manner appropriate to the locale.
Figure 11–1 Localized Date Form
The source code for this example is in the j2eetutorial/exam
ples/src/web/date directory created when you unzip the tutorial bundle. The
JSP page index.jsp used to create the form appears below; it is a typical mixture of static HTML markup and JSP elements. If you have developed Web
pages, you are probably familiar with the HTML document structure statements
WHAT IS A JSP PAGE?
(<head>, <body>, and so on) and the HTML statements that create a form
(<form>) and a menu (<select>). The lines in bold in the example code contain
the following types of JSP constructs:
• Directives (<%@ page ... %>) import classes in the java.util package
and the MyLocales class, and set the content type returned by the page.
• The jsp:useBean element creates an object containing a collection of
locales and initializes a variable that points to that object.
• Scriptlets (<% ... %> ) retrieve the value of the locale request parameter,
iterate over a collection of locale names, and conditionally insert HTML
text into the output.
• Expressions (<%= ... %>) insert the value of the locale name into the
response.
• The jsp:include element sends a request to another page (date.jsp) and
includes the response in the response from the calling page.
<%@ page import="java.util.*,MyLocales" %>
<%@ page contentType="text/html; charset=ISO@8859@5" %>
<html>
<head><title>Localized Dates</title></head>
<body bgcolor="white">
<jsp:useBean id="locales" scope="application"
class="MyLocales"/>
<form name="localeForm" action="index.jsp" method="post">
<b>Locale:</b>
<select name=locale>
<%
String selectedLocale = request.getParameter("locale");
Iterator i = locales.getLocaleNames().iterator();
while (i.hasNext()) {
String locale = (String)i.next();
if (selectedLocale != null &&
selectedLocale.equals(locale)) {
%>
<option selected><%=locale%></option>
<%
} else {
%>
<option><%=locale%></option>
<%
}
}
%>
</select>
<input type="submit" name="Submit" value="Get Date">
247
248
JAVASERVER PAGES™ TECHNOLOGY
</form>
<jsp:include page="date.jsp"/>
</body>
</html>
To build, deploy, and execute this JSP page:
1. Go to j2eetutorial/examples and build the example by executing ant
date (see How to Build and Run the Examples, page (xxii)).
2. Create a J2EE application called DateApp .
a. Select File→New→Application.
b. In the file chooser, navigate to j2eetutorial/exam
ples/src/web/date.
c. In the File Name field, enter DateApp.
d. Click New Application.
e. Click OK.
3. Create the WAR and add the Web components to the DateApp application.
a. Select File→New→Web Component.
b. Select DateApp from the Create New WAR File In Application combo
box.
c. Enter DateWAR in the WAR Display Name field.
d. Click Edit.
e. Navigate to j2eetutorial/examples/build/web/date. Select
index.jsp, date.jsp, MyDate.class, and MyLocales.class and
click Add, then click Finish.
f. Click Next.
g. Click JSP in the Web Component radio button, and then click Next.
h. Select index.jsp from the JSP Filename combo box. Click Finish.
4. Enter the context root.
a. Select DateApp.
b. Select the Web Context tab.
c. Enter date.
5. Deploy the application.
a. Select Tools→Deploy.
b. Click Finish.
6. Invoke the URL http://<host>:8000/date in a browser.
THE EXAMPLE JSP PAGES
You will see a combo box whose entries are locales. Select a locale and click Get
Date. You will see the date expressed in a manner appropriate for that locale.
The Example JSP Pages
To illustrate JSP technology, this chapter rewrites each servlet in the Duke’s
Bookstore application introduced in The Example Servlets, page (211) in as a
JSP page. Table 11–1 lists the functions and their corresponding JSP pages.
Table 11–1 Duke’s Bookstore Example JSP Pages
Function
JSP Pages
Enter the bookstore
bookstore.jsp
Create the bookstore banner
banner.jsp
Browse the books offered for sale
catalog.jsp
Put a book in a shopping cart
catalog.jsp and bookdetails.jsp
Get detailed information on a specific book
bookdetails.jsp
Display the shopping cart
showcart.jsp
Remove one or more books from the shopping cart
showcart.jsp
Buy the books in the shopping cart
cashier.jsp
Receive an acknowledgement for the purchase
receipt.jsp
The data for the bookstore application is still maintained in a database. However,
two changes are made to the database helper object database.BookDB:
• The database helper object is rewritten to conform to JavaBeans component design patterns as described in . This change is made so that JSP
pages can access the helper object using JSP language elements specific
to JavaBeans components.
• Instead of accessing the bookstore database directly, the helper object goes
through an enterprise bean. The advantage of using an enterprise bean is
that the helper object is no longer responsible for connecting to the data-
249
250
JAVASERVER PAGES™ TECHNOLOGY
base; this job is taken over by the enterprise bean. Furthermore, because
the EJB container maintains the pool of database connections, an enterprise bean can get a connection quicker than the helper object can. The relevant interfaces and classes for the enterprise bean are the
database.BookDBEJBHome home interface, database.BookDBEJB remote
interface, and the database.BookDBEJB implementation class, which contains all the JDBC calls to the database.
The implementation of the database helper object follows. The bean has two
instance variables: the current book and a reference to the database enterprise
bean.
public class BookDB {
private String bookId = "0";
private BookDBEJB database = null;
}
public BookDB () throws Exception {
}
public void setBookId(String bookId) {
this.bookId = bookId;
}
public void setDatabase(BookDBEJB database) {
this.database = database;
}
public BookDetails getBookDetails()
throws Exception {
try {
return (BookDetails)database.
getBookDetails(bookId);
} catch (BookNotFoundException ex) {
throw ex;
}
}
...
Finally, this version of the example contains an applet to generate a dynamic digital clock in the banner. See Including an Applet, page (265) for a description of
the JSP element that generates HTML for downloading the applet.
The source code for the application is located in the j2eetutorial/exam
ples/src/web/bookstore2 directory created when you unzip the tutorial bun-
THE EXAMPLE JSP PAGES
dle (see Downloading the Examples, page (xxii)). To build, deploy, and run the
example:
1. Go to j2eetutorial/examples and build the example by running ant
bookstore2.
2. Start the j2ee server.
3. Start deploytool.
4. Start the Cloudscape database by executing cloudscape start.
5. If you have not already created the bookstore database, run ant create
webdb.
6. Create a J2EE application called Bookstore2App.
a. Select File→New→Application.
b. In the file chooser, navigate to j2eetutorial/exam
ples/src/web/bookstore2.
c. In the File Name field, enter Bookstore2App.
d. Click New Application.
e. Click OK.
7. Add the Bookstore2WAR WAR to the Bookstore2App application.
a. Select File→Add→Web WAR.
b. In the Add Web WAR dialog box, navigate to j2eetutorial/exam
ples/build/web/bookstore2. Select bookstore2.war. Click Add
Web WAR.
8. Add the BookDBEJB enterprise bean to the application.
a. Select File→New Enterprise Bean.
b. Select Bookstore2App from the Create New JAR File In Application
combo box.
c. Type BookDBJAR in the JAR Display Name field.
d. Click Edit to add the content files.
the
e. In the Edit Archive Contents dialog box, navigate to
j2eetutorial/examples/build/web/ejb directory and add the
database and exception packages. Click Next.
f. Chose Session and Stateless for the Bean Type.
g. Select database.BookDBEJBImpl for Enterprise Bean Class.
h. In the Remote Interfaces box, select database.BookDBEJBHome for
Remote Home Interface and database.BookDBEJB for Remote Interface.
251
252
JAVASERVER PAGES™ TECHNOLOGY
i. Enter BookDBEJB for Enterprise Bean Name.
j. Click Next and then click Finish.
9. Add a resource reference for the Cloudscape database to the BookDBEJB
bean.
a. Select the BookDBEJB enterprise bean.
b. Select the Resource Refs tab.
c. Click Add.
d. Select javax.sql.DataSource from the Type column.
e. Enter jdbc/BookDB in the Coded Name field.
10.Save BookDBJAR .
a. Select BookDBJAR.
b. Select File→Save As.
c. Navigate to the directory examples/build/web/ejb.
d. Enter bookDB.jar in the File Name field.
e. Click Save EJB JAR As.
11.Add a reference to the enterprise bean BookDBEJB.
a. Select Bookstore2WAR.
b. Select the EJB Refs tab.
c. Click Add.
d. Enter ejb/BookDBEJB in the Coded Name column.
e. Select Session in the Type column.
f. Select Remote in the Interfaces column.
g. Enter database.BookDBEJBHome in the Home Interface column.
h. Enter database.BookDBEJB in the Local/Remote Interface column.
12.Specify the JNDI Names.
a. Select Bookstore2App.
b. In the Application table, locate the EJB component and enter BookD
BEJB in the JNDI Name column.
c. In the References table, locate the EJB Ref and enter BookDBEJB in the
JNDI Name column.
d. In the References table, locate the Resource component and enter
jdbc/Cloudscape in the JNDI Name column.
THE LIFE CYCLE OF A JSP PAGE
13.Enter the context root.
a. Select the Web Context tab.
b. Enter bookstore2.
14.Deploy the application.
a. Select Tools→Deploy.
b. Click Finish.
15.Open the bookstore URL http://<host>:8000/bookstore2/enter.
See Troubleshooting, page (215) for help with diagnosing common problems.
The Life Cycle of a JSP Page
A JSP page services requests as a servlet. Thus, the life cycle and many of the
capabilities of JSP pages (in particular the dynamic aspects) are determined by
Java Servlet technology and much of the discussion in this chapter refers to functions described in chapter 10.
When a request is mapped to a JSP page, it is handled by a special servlet that
first checks whether the JSP page’s servlet is older than the JSP page. If it is, it
translates the JSP page into a servlet class and compiles the class. During development, one of the advantages of JSP pages over servlets is that the build process is performed automatically.
Translation and Compilation
During the translation phase, each type of data in a JSP page is treated differently. Template data is transformed into code that will emit the data into the
stream that returns data to the client. JSP elements are treated as follows:
• Directives are used to control how the Web container translates and
executes the JSP page.
• Scripting elements are inserted into the JSP page’s servlet class. See
JSP Scripting Elements, page (260) for details.
• Elements of the form <jsp:XXX ... /> are converted into method
calls to JavaBeans components or invocations of the Java Servlet API.
253
254
JAVASERVER PAGES™ TECHNOLOGY
For a JSP page named pageName, the source for a JSP page’s servlet is kept in
the file
J2EE_HOME/repository/host/web/
context_root/_0002fpageName_jsp.java
For example, the source for the index page (named index.jsp ) for the date
localization example discussed at the beginning of the chapter would be named
J2EE_HOME/repository/host/web/date/_0002findex_jsp.java
Both the translation and compilation phases can yield errors that are only
observed when the page is requested for the first time. If an error occurs while
the page is being translated (for example, if the translator encounters a malformed JSP element), the server will return a ParseException, and the servlet
class source file will be empty or incomplete. The last incomplete line will give a
pointer to the incorrect JSP element.
If an error occurs while the JSP page is being compiled (for example, there is a
syntax error in a scriptlet), the server will return a JasperException and a message that includes the name of the JSP page’s servlet and the line where the error
occurred.
Once the page has been translated and compiled, the JSP page’s servlet for the
most part follows the servlet life cycle described in the section Servlet Life
Cycle, page (216):
1. If an instance of the JSP page’s servlet does not exist, the container:
a. Loads the JSP page’s servlet class
b. Instantiates an instance of the servlet class
c. Initializes the servlet instance by calling the jspInit method
2. Invokes the _jspService method, passing a request and response object.
If the container needs to remove the JSP page’s servlet, it calls the jspDestroy
method.
Execution
You can control various JSP page execution parameters using by page directives.
The directives that pertain to buffering output and handling errors are discussed
here. Other directives are covered in the context of specific page authoring tasks
throughout the chapter.
THE LIFE CYCLE OF A JSP PAGE
Buffering
When a JSP page is executed, output written to the response object is automatically buffered. You can set the size of the buffer with the following page directive:
<%@ page buffer="none|xxxkb" %>
A larger buffer allows more content to be written before anything is actually sent
back to the client, thus providing the JSP page with more time to set appropriate
status codes and headers or to forward to another Web resource. A smaller buffer
decreases server memory load and allows the client to start receiving data more
quickly.
Handling Errors
Any number of exceptions can arise when a JSP page is executed. To specify that
the Web container should forward control to an error page if an exception occurs,
include the following page directive at the beginning of your JSP page:
<%@ page errorPage="file_name" %>
The Duke’s Bookstore application page initdestroy.jsp contains the directive
<%@ page errorPage="errorpage.jsp"%>
The beginning of errorpage.jsp indicates that it is serving as an error page
with the following page directive:
<%@ page isErrorPage="true|false" %>
This directive makes the exception object (of type javax.servlet.jsp.JspEx
ception) available to the error page, so that you can retrieve, interpret, and possibly display information about the cause of the exception in the error page.
Note: You can also define error pages for the WAR that contains a JSP page. If error
pages are defined for both the WAR and a JSP page, the JSP page’s error page takes
precedence.
255
256
JAVASERVER PAGES™ TECHNOLOGY
Initializing and Finalizing a JSP Page
You can customize the initialization process to allow the JSP page to read persistent configuration data, initialize resources, and perform any other one-time
activities by overriding the jspInit method of the JspPage interface. You
release resources using the jspDestroy method. The methods are defined using
JSP declarations, discussed in Declarations, page (260).
The bookstore example page initdestroy.jsp defines the jspInit method to
retrieve or create an enterprise bean database.BookDBEJB that accesses the
bookstore database; initdestroy.jsp stores a reference to the bean in bookD
BEJB. The enterprise bean is created using the techniques described in .
private BookDBEJB bookDBEJB;
public void jspInit() {
bookDBEJB =
(BookDB)getServletContext().
getAttribute("bookDBEJB");
if (bookDBEJB == null) {
try {
InitialContext ic = new InitialContext();
Object objRef = ic.lookup(
"java:comp/env/ejb/BookDBEJB");
BookDBEJBHome home =
(BookDBEJBHome)PortableRemoteObject.
narrow(objRef,
database.BookDBEJBHome.class);
bookDBEJB = home.create();
getServletContext().setAttribute("bookDBEJB",
bookDBEJB);
} catch (RemoteException ex) {
System.out.println(
"Couldn’t create database bean." +
ex.getMessage());
} catch (CreateException ex) {
System.out.println(
"Couldn’t create database bean." +
ex.getMessage());
} catch (NamingException ex) {
System.out.println(
"Unable to lookup home: " +
"java:comp/env/ejb/BookDBEJB."+
ex.getMessage());
}
}
}
CREATING STATIC CONTENT
When the JSP page is removed from service, the jspDestroy method releases
the BookDBEJB variable:
public void jspDestroy() {
bookDBEJB = null;
}
Since the enterprise bean is shared between all the JSP pages, it should be initialized when the application is started, instead of in each JSP page. Java Servlet
technology provides application life cycle events and listener classes for this
purpose. As an exercise, you can move the code that manages the creation of the
enterprise bean to a context listener class. See Handling Servlet Life-Cycle
Events, page (216) for the context listener that initializes the Java Servlet version
of the bookstore application.
Creating Static Content
You create static content in a JSP page by simply writing it as if you were creating a page that consisted only of that content. Static content can be expressed in
any text-based format, such as HTML, WML, and XML. The default format is
HTML. If you want to use a format other than HTML, you include a page directive with the contentType attribute set to the format type at the beginning of
your JSP page. For example, if you want a page to contain data expressed in the
wireless markup language (WML), you need to include the following directive:
<%@ page contentType="text/vnd.wap.wml"%>
A registry of content type names is kept by the IANA at:
ftp://ftp.isi.edu/innotes/iana/assignments/mediatypes
Creating Dynamic Content
You create dynamic content by accessing Java programming language objects
from within scripting elements.
Using Objects within JSP Pages
You can access a variety of objects, including enterprise beans and JavaBeans
components, within a JSP page. JSP technology automatically makes some
257
258
JAVASERVER PAGES™ TECHNOLOGY
objects available, and you can also create and access application-specific
objects.
Implicit Objects
Implicit objects are created by the Web container and contain information related
to a particular request, page, or application. Many of the objects are defined by
the Java Servlet technology underlying JSP technology and are discussed at
length in Chapter 10. Table 11–2 summarizes the implicit objects.
Table 11–2 Implicit Objects
Variable
Class
Description
application
javax.servlet.
ServletContext
The context for the JSP page’s servlet and any Web
components contained in the same application. See
Accessing the Web Context, page (238).
config
javax.servlet.
ServletConfig
Initialization information for the JSP page’s servlet.
exception
java.lang.
Throwable
Accessible only from an error page. See Handling
Errors, page (255).
out
javax.servlet.
jsp.JspWriter
The output stream.
page
java.lang.
Object
The instance of the JSP page’s servlet processing
the current request. Not typically used by JSP page
authors.
javax.servlet.
jsp.PageContext
The context for the JSP page. Provides a single API
to manage the various scoped attributes described
in Sharing Information, page (218).
This API is used extensively when implementing
tag handlers (see Tag Handlers, page (289)).
pageContext
request
response
subtype of
javax.servlet.
ServletRequest
subtype of
javax.servlet.
ServletResponse
The request triggering the execution of the JSP
page. See Getting Information from
Requests, page (223).
The response to be returned to the client. Not typically used by JSP page authors.
CREATING DYNAMIC CONTENT
Table 11–2 Implicit Objects (Continued)
Variable
Class
Description
session
javax.servlet.
http.HttpSession
The session object for the client. See Accessing the
Web Context, page (238).
Application-Specific Objects
When possible, application behavior should be encapsulated in objects so that
page designers can focus on presentation issues. Objects can be created by developers who are proficient in the Java programming language and in accessing
databases and other services. There are four ways to create and use objects
within a JSP page:
• Instance and class variables of the JSP page’s servlet class are created in
declarations and accessed in scriptlets and expressions.
• Local variables of the JSP page’s servlet class are created and used in
scriptlets and expressions.
• Attributes of scope objects (see Using Scope Objects, page (219)) are created and used in scriptlets and expressions.
• JavaBeans components can be created and accessed using streamlined JSP
elements. These elements are discussed in the chapter 12. You can also
create a JavaBeans component in a declaration or scriptlet and invoke the
methods of a JavaBeans component in a scriptlet or expression.
Declarations, scriptlets, and expressions are described in JSP Scripting
Elements, page (260).
Shared Objects
The conditions affecting concurrent access to shared objects described in Sharing Information, page (218) apply to objects accessed from JSP pages that run as
multithreaded servlets. You can indicate how a Web container should dispatch
multiple client requests with the following page directive:
<%@ page isThreadSafe="true|false" %>
When isThreadSafe is set to true, the Web container may choose to dispatch
multiple concurrent client requests to the JSP page. This is the default setting. If
using true, you must ensure that you properly synchronize access to any shared
objects defined at the page level. This includes objects created within declara-
259
260
JAVASERVER PAGES™ TECHNOLOGY
tions, JavaBeans components with page scope, and attributes of the page scope
object.
If isThreadSafe is set to false, requests are dispatched one at a time, in the
order they were received, and access to page-level objects does not have to be
controlled. However, you still must ensure that access to attributes of the appli
cation or session scope objects and to JavaBeans components with application
or session scope is properly synchronized.
JSP Scripting Elements
JSP scripting elements are used to create and access objects, define methods, and
manage the flow of control. Since one of the goals of JSP technology is to separate static template data from the code needed to dynamically generate content,
very sparing use of JSP scripting is recommended. Much of the work that
requires the use of scripts can be eliminated by using custom tags, described in
Extending the JSP Language, page (267).
JSP technology allows a container to support any scripting language that can call
Java objects. If you wish to use a scripting language other than the default, java,
you must specify it in a page directive at the beginning of a JSP page:
<%@ page language="scripting language" %>
Since scripting elements are converted to programming language statements in
the JSP page’s servlet class, you must import any classes and packages used by a
JSP page. If the page language is java, you import a class or package with the
page directive:
<%@ page import="packagename.*, fully_qualified_classname" %>
For example, the bookstore example page showcart.jsp imports the classes
needed to implement the shopping cart with the following directive:
<%@ page import="java.util.*, cart.*" %>
Declarations
A JSP declaration is used to declare variables and methods in a page’s scripting
language. The syntax for a declaration is as follows:
<%! scripting language declaration %>
CREATING DYNAMIC CONTENT
When the scripting language is the Java programming language, variables and
methods in JSP declarations become declarations in the JSP page’s servlet class.
The bookstore example page initdestroy.jsp defines an instance variable
named bookDBEJB and the initialization and finalization methods jspInit and
jspDestroy discussed earlier in a declaration:
<%!
%>
private BookDBEJB bookDBEJB;
public void jspInit() {
...
}
public void jspDestroy() {
...
}
Scriptlets
A JSP scriptlet is used to contain any code fragment that is valid for the scripting
language used in a page. The syntax for a scriptlet is as follows:
<%
%>
scripting language statements
When the scripting language is set to java, a scriptlet is transformed into a Java
programming language statement fragment and is inserted into the service
method of the JSP page’s servlet. A programming language variable created
within a scriptlet is accessible from anywhere within the JSP page.
The JSP page showcart.jsp contains a scriptlet that retrieves an iterator from
the collection of items maintained by a shopping cart and sets up a construct to
loop through all the items in the cart. Inside the loop, the JSP page extracts properties of the book objects and formats them using HTML markup. Since the
while loop opens a block, the HTML markup is followed by a scriptlet that
closes the block.
<%
%>
Iterator i = cart.getItems().iterator();
while (i.hasNext()) {
ShoppingCartItem item =
(ShoppingCartItem)i.next();
BookDetails bd = (BookDetails)item.getItem();
261
262
JAVASERVER PAGES™ TECHNOLOGY
<%
%>
<tr>
<td align="right" bgcolor="#ffffff">
<%=item.getQuantity()%>
</td>
<td bgcolor="#ffffaa">
<strong><a href="
<%=request.getContextPath()%>/bookdetails?bookId=
<%=bd.getBookId()%>"><%=bd.getTitle()%></a></strong>
</td>
...
// End of while
}
The output appears in Figure 11–2.
Figure 11–2 Duke’s Bookstore Shopping Cart
Expressions
A JSP expression is used to insert the value of a scripting language expression,
converted into a string, into the data stream returned to the client. When the
scripting language is the Java programming language, an expression is trans-
INCLUDING CONTENT IN A JSP PAGE
formed into a statement that converts the value of the expression into a String
object and inserts it into the implicit out object.
The syntax for an expression is as follows:
<%= scripting language expression %>
Note that a semicolon is not allowed within a JSP expression, even if the same
expression has a semicolon when you use it within a scriptlet.
The following scriptlet retrieves the number of items in a shopping cart:
<%
%>
// Print a summary of the shopping cart
int num = cart.getNumberOfItems();
if (num > 0) {
Expressions are then used to insert the value of num into the output stream and
determine the appropriate string to include after the number:
<font size="+2">
<%=messages.getString("CartContents")%> <%=num%>
<%=(num==1 ? <%=messages.getString("CartItem")%> :
<%=messages.getString("CartItems"))%></font>
Including Content in a JSP Page
There are two mechanisms for including another Web resource in a JSP page: the
include directive and the jsp:include element.
The include directive is processed when the JSP page is translated into a servlet
class. The effect of the directive is to insert the text contained in another file—
either static content or another JSP page—in the including JSP page. You would
probably use the include directive to include banner content, copyright information, or any chunk of content that you might want to reuse in another page.
The syntax for the include directive is as follows:
<%@ include file="filename" %>
For example, all the bookstore application pages include the file banner.jsp
containing the banner content with the following directive:
<%@ include file="banner.jsp" %>
263
264
JAVASERVER PAGES™ TECHNOLOGY
In addition, the pages bookstore.jsp, bookdetails.jsp, catalog.jsp, and
showcart.jsp include JSP elements that create and destroy a database bean
with the following directive:
<%@ include file="initdestroy.jsp" %>
Because you must statically put an include directive in each file that reuses the
resource referenced by the directive, this approach has its limitations. For a more
flexible approach to building pages out of content chunks, see A Template Tag
Library, page (308).
The jsp:include element is processed when a JSP page is executed. The
include action allows you to include either a static or dynamic resource in a JSP
file. The results of including static and dynamic resources are quite different. If
the resource is static, its content is inserted into the calling JSP file. If the
resource is dynamic, the request is sent to the included resource, the included
page is executed, and then the result is included in the response from the calling
JSP page. The syntax for the jsp:include element is as follows:
<jsp:include page="includedPage" />
The date application introduced at the beginning of this chapter includes the
page that generates the display of the localized date with the following statement:
<jsp:include page="date.jsp"/>
Transferring Control to Another Web
Component
The mechanism for transferring control to another Web component from a JSP
page uses the functionality provided by the Java Servlet API as described in
Transferring Control to Another Web Component, page (237) in . You access
this functionality from a JSP page with the jsp:forward element:
<jsp:forward page="/main.jsp" />
Note that if any data has already been returned to a client, the jsp:forward element will fail with an IllegalStateException.
INCLUDING AN APPLET
Param Element
When an include or forward element is invoked, the original request object is
provided to the target page. If you wish to provide additional data to that page,
you can append parameters to the request object with the jsp:param element:
<jsp:include page="..." >
<jsp:param name=”param1” value="value1"/>
</jsp:include>
Including an Applet
You can include an applet or JavaBeans component in a JSP page by using the
jsp:plugin element. This element generates HTML that contains the appropriate client-browser-dependent constructs (<object> or <embed>) that will result
in the download of the Java Plug-in software (if required) and client-side component and subsequent execution of any client-side component. The syntax for the
jsp:plugin element is as follows:
<jsp:plugin
type="bean|applet"
code="objectCode"
codebase="objectCodebase"
{ align="alignment" }
{ archive="archiveList" }
{ height="height" }
{ hspace="hspace" }
{ jreversion="jreversion" }
{ name="componentName" }
{ vspace="vspace" }
{ width="width" }
{ nspluginurl="url" }
{ iepluginurl="url" } >
{ <jsp:params>
{ <jsp:param name="paramName" value="paramValue" /> }+
</jsp:params> }
{ <jsp:fallback> arbitrary_text </jsp:fallback> }
</jsp:plugin>
The jsp:plugin tag is replaced by either an <object> or <embed> tag as appropriate for the requesting client. The attributes of the jsp:plugin tag provide
configuration data for the presentation of the element as well as the version of
the plug-in required. The nspluginurl and iepluginurl attributes specify the
URL where the plug-in can be downloaded.
265
266
JAVASERVER PAGES™ TECHNOLOGY
The jsp:param elements specify parameters to the applet or JavaBeans component. The jsp:fallback element indicates the content to be used by the client
browser if the plug-in cannot be started (either because <object> or <embed> is
not supported by the client or because of some other problem).
If the plug-in can start but the applet or JavaBeans component cannot be found
or started, a plug-in-specific message will be presented to the user, most likely a
pop-up window reporting a ClassNotFoundException.
The Duke’s Bookstore page banner.jsp that creates the banner displays a
dynamic digital clock generated by DigitalClock (Figure 11–3).
Figure 11–3 Duke’s Bookstore with Applet
The jsp:plugin element used to download the applet follows:
EXTENDING THE JSP LANGUAGE
<jsp:plugin
type="applet"
code="DigitalClock.class"
codebase="/bookstore2"
jreversion="1.3"
align="center" height="25" width="300"
nspluginurl="http://java.sun.com/products/plugin/1.3.0_01
/plugininstall.html"
iepluginurl="http://java.sun.com/products/plugin/1.3.0_01
/jinstall130_01win32.cab#Version=1,3,0,1" >
<jsp:params>
<jsp:param name="language"
value="<%=request.getLocale().getLanguage()%>" />
<jsp:param name="country"
value="<%=request.getLocale().getCountry()%>" />
<jsp:param name="bgcolor" value="FFFFFF" />
<jsp:param name="fgcolor" value="CC0066" />
</jsp:params>
<jsp:fallback>
<p>Unable to start plugin.</p>
</jsp:fallback>
</jsp:plugin>
Extending the JSP Language
You can perform a wide variety of dynamic processing tasks including accessing
databases, using enterprise services such as e-mail and directories, and managing
flow control, with JavaBeans components in conjunction with scriptlets. One of
the drawbacks of scriptlets, however, is that they tend to make JSP pages more
difficult to maintain. Alternatively, JSP technology provides a mechanism,
called custom tags, that allows you to encapsulate dynamic functionality in
objects that are accessed through extensions to the JSP language. Custom tags
bring the benefits of another level of componentization to JSP pages.
For example, recall the scriptlet used to loop through and display the contents of
the Duke’s Bookstore shopping cart:
<%
%>
Iterator i = cart.getItems().iterator();
while (i.hasNext()) {
ShoppingCartItem item =
(ShoppingCartItem)i.next();
...
<tr>
267
268
JAVASERVER PAGES™ TECHNOLOGY
<%
%>
<td align="right" bgcolor="#ffffff">
<%=item.getQuantity()%>
</td>
...
}
An iterate custom tag eliminates the code logic and manages the scripting
variable item that references elements in the shopping cart:
<logic:iterate id="item"
collection="<%=cart.getItems()%>">
<tr>
<td align="right" bgcolor="#ffffff">
<%=item.getQuantity()%>
</td>
...
</logic:iterate>
Custom tags are packaged and distributed in a unit called a tag library. The syntax of custom tags is the same as that used for the JSP elements, namely,
<prefix:tag>; however, for custom tags, prefix is defined by the user of the
tag library and tag is defined by the tag developer. Chapter 13 explains how to
use and develop custom tags.
12
JavaBeans™
Components in JSP™
Pages
Stephanie Bodoff
J
AVABEANS components are Java classes that can be easily reused and composed together into applications. Any Java class that follows certain design conventions can be a JavaBeans component.
JavaServer Pages™ technology directly supports using JavaBeans components
with JSP language elements. You can easily create and initialize beans and get
and set the values of their properties. This chapter provides basic information
about JavaBeans components and the JSP language elements for accessing JavaBeans components in your JSP pages. For further information about the JavaBeans component model, see http://java.sun.com/products/javabeans.
In This Chapter
JavaBeans Component Design Conventions 270
Why Use a JavaBeans Component? 271
Creating and Using a JavaBeans Component 272
Setting JavaBeans Component Properties 273
Retrieving JavaBeans Component Properties 275
269
270
JAVABEANS™ COMPONENTS IN JSP™ PAGES
JavaBeans Component Design
Conventions
JavaBeans component design conventions govern the properties of the class, and
govern the public methods that give access to the properties.
A JavaBeans component property can be
• Read/write, read-only, or write-only
• Simple, which means it contains a single value, or indexed, which means
it represents an array of values
There is no requirement that a property be implemented by an instance variable;
the property must simply be accessible using public methods that conform to
certain conventions:
• For each readable property, the bean must have a method of the form
PropertyClass getProperty() { ... }
• For each writable property, the bean must have a method of the form set
Property(PropertyClass pc) { ... }
In addition to the property methods, a JavaBeans component must define a constructor that takes no parameters.
The Duke’s Bookstore application JSP pages enter.jsp, bookdetails.jsp,
catalog.jsp, and showcart.jsp use the database.BookDB and data
base.BookDetails JavaBeans components. BookDB provides a JavaBeans component front end to the enterprise bean BookDBEJB. Both beans are used
extensively by bean-oriented custom tags (see Tags That Define Scripting
Variables, page (298)). The JSP pages showcart.jsp and cashier.jsp use
cart.ShoppingCart to represent a user’s shopping cart.
The JSP pages catalog.jsp, showcart.jsp, and cashier.jsp use the
util.Currency JavaBeans component to format currency in a locale-sensitive
manner. The bean has two writable properties, locale and amount, and one readable property, format. The format property does not correspond to any instance
variable, but returns a function of the locale and amount properties.
public class Currency {
private Locale locale;
private double amount;
public Currency() {
locale = null;
amount = 0.0;
WHY USE A JAVABEANS COMPONENT?
}
}
public void setLocale(Locale l) {
locale = l;
}
public void setAmount(double a) {
amount = a;
}
public String getFormat() {
NumberFormat nf =
NumberFormat.getCurrencyInstance(locale);
return nf.format(amount);
}
Why Use a JavaBeans Component?
A JSP page can create and use any type of Java programming language object
within a declaration or scriptlet. The following scriptlet creates the bookstore
shopping cart and stores it as a session attribute:
<%
%>
ShoppingCart cart = (ShoppingCart)session.
getAttribute("cart");
// If the user has no cart, create a new one
if (cart == null) {
cart = new ShoppingCart();
session.setAttribute("cart", cart);
}
If the shopping cart object conforms to JavaBeans conventions, JSP pages can
use JSP elements to create and access the object. For example, the Duke’s Bookstore pages bookdetails.jsp, catalog.jsp, and showcart.jsp replace the
scriptlet with the much more concise JSP useBean element:
<jsp:useBean id="cart" class="cart.ShoppingCart"
scope="session"/>
271
272
JAVABEANS™ COMPONENTS IN JSP™ PAGES
Creating and Using a JavaBeans
Component
You declare that your JSP page will use a JavaBeans component using either one
of the following formats:
<jsp:useBean id="beanName"
class="fully_qualified_classname" scope="scope"/>
or
<jsp:useBean id="beanName"
class="fully_qualified_classname" scope="scope">
<jsp:setProperty .../>
</jsp:useBean>
The second format is used when you want to include jsp:setProperty statements, described in the next section, for initializing bean properties.
The jsp:useBean element declares that the page will use a bean that is stored
within and accessible from the specified scope, which can be application,
session, request, or page. If no such bean exists, the statement creates the
bean and stores it as an attribute of the scope object (see Using Scope
Objects, page (219)). The value of the id attribute determines the name of the
bean in the scope and the identifier used to reference the bean in other JSP elements and scriptlets.
Note: In the section JSP Scripting Elements, page (260) we mentioned that you
must import any classes and packages used by a JSP page. This rule is slightly
altered if the class is only referenced by useBean elements. In these cases, you must
only import the class if the class is in the unnamed package. For example, in What
Is a JSP Page?, page (246), the page index.jsp imports the MyLocales class. However, in the Duke’s Bookstore example, all classes are contained in packages and
thus are not explicitly imported.
The following element creates an instance of Currency if none exists, stores it as
an attribute of the session object, and makes the bean available throughout the
session by the identifier currency:
<jsp:useBean id="currency" class="util.Currency"
scope="session"/>
SETTING JAVABEANS COMPONENT PROPERTIES
Setting JavaBeans Component Properties
There are two ways to set JavaBeans component properties in a JSP page: with
the jsp:setProperty element or with a scriptlet
<% beanName.setPropName(value); %>
The syntax of the jsp:setProperty element depends on the source of the property value. Table 12–1 summarizes the various ways to set a property of a JavaBeans component using the jsp:setProperty element.
Table 12–1 Setting JavaBeans Component Properties
Value Source
Element Syntax
String constant
<jsp:setProperty name="beanName"
property="propName" value="string constant"/>
Request parameter
<jsp:setProperty name="beanName"
property="propName" param="paramName"/>
Request parameter name
matches bean property
Expression
<jsp:setProperty name="beanName"
property="propName"/>
<jsp:setProperty name="beanName"
property="*"/>
<jsp:setProperty name="beanName"
property="propName"
value="<%= expression %>"/>
1. beanName must be the same as that specified for the id attribute in a useBean element.
2. There must be a setPropName method in the JavaBeans component.
3. paramName must be a request parameter name.
A property set from a constant string or request parameter must have a type
listed in Table 12–2. Since both a constant and request parameter are strings, the
Web container automatically converts the value to the property’s type; the conversion applied is shown in the table. String values can be used to assign values
to a property that has a PropertyEditor class. When that is the case, the setAs
Text(String) method is used. A conversion failure arises if the method throws
273
274
JAVABEANS™ COMPONENTS IN JSP™ PAGES
an IllegalArgumentException. The value assigned to an indexed property
must be an array, and the rules just described apply to the elements.
Table 12–2 Valid Value Assignments
Property Type
Conversion on String Value
Bean property
Uses setAsText(stringliteral)
boolean or Boolean
As indicated in java.lang.Boolean.valueOf(String)
byte or Byte
As indicated in java.lang.Byte.valueOf(String)
char or Character
As indicated in java.lang.String.charAt(0)
double or Double
As indicated in java.lang.Double.valueOf(String)
int or Integer
As indicated in java.lang.Integer.valueOf(String)
float or Float
As indicated in java.lang.Float.valueOf(String)
long or Long
As indicated in java.lang.Long.valueOf(String)
short or Short
As indicated in java.lang.Short.valueOf(String)
Object
new String(stringliteral)
You would use a runtime expression to set the value of a property whose type is
a compound Java programming language type. Recall from the section
Expressions, page (262) that a JSP expression is used to insert the value of a
scripting language expression, converted into a String , into the stream returned
to the client. When used within a setProperty element, an expression simply
returns its value; no automatic conversion is performed. As a consequence, the
type returned from an expression must match or be castable to the type of the
property.
The Duke’s Bookstore application demonstrates how to use the setProperty
element and a scriptlet to set the current book for the database helper bean. For
example, bookstore3/bookdetails.jsp uses the form
<jsp:setProperty name="bookDB" property="bookId"/>
whereas bookstore2/bookdetails.jsp uses the form
RETRIEVING JAVABEANS COMPONENT PROPERTIES
<% bookDB.setBookId(bookId); %>
The following fragments from the page bookstore3/showcart.jsp illustrate
how to initialize a currency bean with a Locale object and amount determined
by evaluating request-time expressions. Because the first initialization is nested
in a useBean element, it is only executed when the bean is created.
<jsp:useBean id="currency" class="util.Currency"
scope="session">
<jsp:setProperty name="currency" property="locale"
value="<%= request.getLocale() %>"/>
</jsp:useBean>
<jsp:setProperty name="currency" property="amount"
value="<%=cart.getTotal()%>"/>
Retrieving JavaBeans Component
Properties
There are several ways to retrieve JavaBeans component properties. Two of the
methods (the jsp:getProperty element and an expression) convert the value of
the property into a String and insert the value into the current implicit out
object:
• <jsp:getProperty name="beanName" property="propName"/>
• <%= beanName.getPropName() %>
For both methods, beanName must be the same as that specified for the id
attribute in a useBean element, and there must be a getPropName method in the
JavaBeans component.
If you need to retrieve the value of a property without converting it and inserting
it into the out object, you must use a scriptlet:
<% Object o = beanName.getPropName(); %>
Note the differences between the expression and the scriptlet; the expression has
an = after the opening % and does not terminate with a semicolon, as does the
scriptlet.
The Duke’s Bookstore application demonstrates how to use both forms to
retrieve the formatted currency from the currency bean and insert it into the
page. For example, bookstore3/showcart.jsp uses the form
275
276
JAVABEANS™ COMPONENTS IN JSP™ PAGES
<jsp:getProperty name="currency" property="format"/>
whereas bookstore2/showcart.jsp uses the form
<%= currency.getFormat() %>
The Duke’s Bookstore application page bookstore2/showcart.jsp uses the
following scriptlet to retrieve the number of books from the shopping cart bean
and open a conditional insertion of text into the output stream:
<%
%>
// Print a summary of the shopping cart
int num = cart.getNumberOfItems();
if (num > 0) {
Although scriptlets are very useful for dynamic processing, using custom tags
(see Chapter 13) to access object properties and perform flow control is considered to be a better approach. For example, bookstore3/showcart.jsp replaces
the scriptlet with the following custom tags:
<bean:define id="num" name="cart" property="numberOfItems" />
<logic:greaterThan name="num" value="0" >
Figure 12–1 summarizes where various types of objects are stored and how those
objects can be accessed from a JSP page. Objects created by the jsp:useBean
tag are stored as attributes of the scope objects and can be accessed by
jsp:[get|set]Property tags and in scriptlets and expressions. Objects created
in declarations and scriptlets are stored as variables of the JSP page’s servlet
class and can be accessed in scriptlets and expressions.
RETRIEVING JAVABEANS COMPONENT PROPERTIES
Figure 12–1 Accessing Objects From a JSP Page
277
278
JAVABEANS™ COMPONENTS IN JSP™ PAGES
13
Custom Tags in JSP™
Pages
Stephanie Bodoff
THE standard JSP tags for invoking operations on JavaBeans™ components
and performing request dispatching simplify JSP page development and maintenance. JSP technology also provides a mechanism for encapsulating other types
of dynamic functionality in custom tags, which are extensions to the JSP language. Custom tags are usually distributed in the form of a tag library, which
defines a set of related custom tags and contains the objects that implement the
tags.
Some examples of tasks that can be performed by custom tags include operations
on implicit objects, processing forms, accessing databases and other enterprise
services such as e-mail and directories, and performing flow control. JSP tag
libraries are created by developers who are proficient at the Java programming
language and expert in accessing data and other services, and are used by Web
application designers who can focus on presentation issues rather than being
concerned with how to access enterprise services. As well as encouraging division of labor between library developers and library users, custom tags increase
productivity by encapsulating recurring tasks so that they can be reused across
more than one application.
279
280
CUSTOM TAGS IN JSP™ PAGES
Tag libraries are receiving a great deal of attention in the JSP technology community. For more information about tag libraries and for pointers to some freelyavailable libraries see
http://java.sun.com/products/jsp/taglibraries.html
In This Chapter
What is a Custom Tag? 280
The Example JSP Pages 281
Using Tags 285
Declaring Tag Libraries 285
Types of Tags 286
Defining Tags 289
Tag Handlers 289
Tag Library Descriptors 290
Simple Tags 293
Tags with Attributes 294
Tags With Bodies 296
Tags That Define Scripting Variables 298
Cooperating Tags 302
Examples 304
An Iteration Tag 304
A Template Tag Library 308
How Is a Tag Handler Invoked? 313
What is a Custom Tag?
A custom tag is a user-defined JSP language element. When a JSP page containing a custom tag is translated into a servlet, the tag is converted to operations on
an object called a tag handler. The Web container then invokes those operations
when the JSP page’s servlet is executed.
Custom tags have a rich set of features. They can
•
•
•
•
Be customized via attributes passed from the calling page.
Access all the objects available to JSP pages.
Modify the response generated by the calling page.
Communicate with each other. You can create and initialize a JavaBeans
component, create a variable that refers to that bean in one tag, and then
use the bean in another tag.
THE EXAMPLE JSP PAGES
• Be nested within one another, allowing for complex interactions within a
JSP page.
The Example JSP Pages
This chapter describes the tasks involved in using and defining tags. The chapter
illustrates the tasks with excerpts from the JSP version of the Duke’s Bookstore
application discussed in Chapter 11 rewritten to take advantage of two tag libraries: Struts and tutorial-template. The section in this chapter entitled
Examples, page (304), describes some tags in detail: the iterate tag from Struts
and the set of tags in the tutorial-template tag library.
The Struts tag library provides a framework for building internationalized Web
applications that implement the Model-View-Controller design pattern. Struts
includes a comprehensive set of utility custom tags for handling
•
•
•
•
HTML forms
Templates
JavaBeans components
Logic processing
The Duke’s Bookstore application uses tags from the Struts bean and logic
sublibraries.
The tutorial-template tag library defines a set of tags for creating an application
template. The template is a JSP page with placeholders for the parts that need to
change with each screen. Each of these placeholders is referred to as a parameter
of the template. For example, a simple template could include a title parameter
for the top of the generated screen and a body parameter to refer to a JSP page
for the custom content of the screen. The template is created with a set of nested
tags—definition, screen, and parameter—that are used to build a table of
screen definitions for Duke’s Bookstore and with an insert tag to insert parameters from the table into the screen.
281
282
CUSTOM TAGS IN JSP™ PAGES
Figure 13–1 shows the flow of a request through the following Duke’s Bookstore
Web components:
• template.jsp, which determines the structure of each screen. It uses the
insert tag to compose a screen from subcomponents.
• screendefinitions.jsp, which defines the subcomponents used by
each screen. All screens have the same banner, but different title and body
content (specified by the JSP Pages column in Table 11–1).
• Dispatcher, a servlet, which processes requests and forwards to tem
plate.jsp.
Figure 13–1 Request Flow through Duke’s Bookstore Components
The source for the Duke’s Bookstore application is located in the
j2eetutorial/examples/src/web/bookstore3 directory created when you
unzip the tutorial bundle (see Downloading the Examples, page (xxii)). To build,
deploy, and run the example:
1. Go to j2eetutorial/examples and build the application by executing
ant bookstore3 (see How to Build and Run the Examples, page (xxii)).
THE EXAMPLE JSP PAGES
2. Download and unpack Struts version 1.0 from
http://jakarta.apache.org/builds/jakartastruts/release/v1.0/
Copy strutsbean.tld, strutslogic.tld , and struts.jar from
jakartastruts1.0/lib to examples/build/web/bookstore3
Start the j2ee server.
Start deploytool.
Start the Cloudscape database by executing cloudscape start.
If you have not already created the bookstore database, run ant create
webdb.
7. Create a J2EE application called Bookstore3App.
a. Select File→New Application.
b. In the file chooser, navigate to j2eetutorial/exam
ples/src/web/bookstore3.
c. In the File Name field, enter Bookstore3App.
d. Click New Application.
e. Click OK.
3.
4.
5.
6.
8. Create the WAR and add the DispatcherServlet Web component and all
of the Duke’s Bookstore content to Bookstore3App.
a. Select File→New→Web Component.
b. Click the Create New WAR File in Application radio button and select
Bookstore3App from the combo box. Enter Bookstore3WAR in the
field labeled WAR Display Name.
c. Click Edit to add the content files. In the Edit Contents dialog box, navigate to j2eetutorial/examples/build/web/bookstore3. Select
Dispatcher.class and click Add. Add the JSP pages banner.jsp, book
store.jsp, bookdetails.jsp, catalog.jsp, showcart.jsp, cash
receipt.jsp,
initdestroy.jsp,
template.jsp,
ier.jsp,
screendefinitions.jsp,
and
errorpage.jsp.
Add
duke.books.gif, strutsbean.tld, strutslogic.tld, tutorial
template.tld, and struts.jar. Add the cart, database, messages,
taglib, and util packages. Click OK.
d. Click Next.
e. Select the Servlet radio button.
f. Click Next.
g. Select Dispatcher from the Servlet Class combo box.
283
284
CUSTOM TAGS IN JSP™ PAGES
h. Click Next twice.
i. In the Component Aliases pane, click Add and then type /enter in the
Alias field. Repeat to add the aliases /catalog, /bookdetails,
/showcart, /cashier, and /receipt.
j. Click Finish.
9. Add the BookDBEJB enterprise bean that you created in the section The
Example JSP Pages, page (249).
a. Select File→Add→EJB JAR.
b. Navigate to the directory examples/build/web/ejb.
c. Select bookDB.jar.
d. Click Add EJB JAR.
10.Add a reference to the enterprise bean BookDBEJB.
a. Select Bookstore3WAR.
b. Select the EJB Refs tab.
c. Click Add.
d. Enter ejb/BookDBEJB in the Coded Name column.
e. Enter Session in the Type column.
f. Select Remote in the Interfaces column.
g. Enter database.BookDBEJBHome in the Home Interface column.
h. Enter database.BookDBEJB in the Local/Remote Interface column.
11.Add the tag library URI to location mappings (see Declaring Tag
Libraries, page (285)):
a. Select the File Refs tab
b. Click the Add button in the JSP Tag Libraries subpane.
c. Enter the relative URI /tutorialtemplate in the Coded Reference
field.
d. Enter the absolute location /WEBINF/tutorialtemplate.tld in the
Tag Library field.
e. Repeat for /strutsbean to /WEBINF/strutsbean.tld and
/strutslogic to /WEBINF/strutslogic.tld .
12.Specify the JNDI names.
a. Select Bookstore3App.
b. In the Application table, locate the EJB component and enter BookD
BEJB in the JNDI Name column.
USING TAGS
c. In the References table, locate the EJB Ref and enter BookDBEJB in the
JNDI Name column.
d. In the References table, locate the Resource component and enter
jdbc/Cloudscape in the JNDI Name column.
13.Enter the context root.
a. Select the Web Context tab.
b. Enter bookstore3.
14.Deploy the application.
a. Select Tools→Deploy.
b. Click Finish.
15.Open the bookstore URL http://<host>:8000/bookstore3/enter.
See Troubleshooting, page (215) for help with diagnosing common problems.
Using Tags
This section describes how a page author specifies that a JSP page is using a tag
library and introduces the different types of tags.
Declaring Tag Libraries
You declare that a JSP page will use tags defined in a tag library by including a
taglib directive in the page before any custom tag is used:
<%@ taglib uri="/WEBINF/tutorialtemplate.tld" prefix="tt" %>
The uri attribute refers to a URI that uniquely identifies the tag library descriptor (TLD), described in the section Tag Library Descriptors, page (290). This
URI can be direct or indirect. The prefix attribute defines the prefix that distinguishes tags defined by a given tag library from those provided by other tag
libraries.
Tag library descriptor file names must have the extension .tld. TLD files are
stored in the WEBINF directory of the WAR or in a subdirectory of WEBINF. You
can reference a TLD directly and indirectly.
The following taglib directive directly references a TLD filename:
<%@ taglib uri="/WEBINF/tutorialtemplate.tld" prefix="tt" %>
285
286
CUSTOM TAGS IN JSP™ PAGES
This taglib directive uses a short logical name to indirectly reference the TLD:
<%@ taglib uri="/tutorialtemplate" prefix="tt" %>
A logical name must be mapped to an absolute location in the Web application
deployment descriptor. To map the logical name /tutorialtemplate to the
absolute location /WEBINF/tutorialtemplate.tld,
Select Bookstore3WAR.
Select the File Refs tab
Click the Add button in the JSP Tag Libraries subpane.
Enter the relative URI /tutorialtemplate in the Coded Reference
field.
5. Enter the absolute location /WEBINF/tutorialtemplate.tld in the
Tag Library field.
1.
2.
3.
4.
Types of Tags
JSP custom tags are written using XML syntax. They have a start tag and end
tag, and possibly a body:
<tt:tag>
body
</tt:tag>
A custom tag with no body is expressed as follows:
<tt:tag />
Simple Tags
A simple tag contains no body and no attributes:
<tt:simple />
Tags With Attributes
A custom tag can have attributes. Attributes are listed in the start tag and have
the syntax attr="value". Attribute values serve to customize the behavior of a
custom tag just as parameters are used to customize the behavior of a method.
You specify the types of a tag’s attributes in a tag library descriptor (see Tag
Library Descriptors, page (290)).
USING TAGS
You can set an attribute value from a String constant or a runtime expression.
The conversion process between the constants and runtime expressions and
attribute types follows the rules described for JavaBeans component properties
in Setting JavaBeans Component Properties, page (273).
The attributes of the Struts logic:present tag determine whether the body of
the tag is evaluated. In the following example, an attribute specifies a request
parameter named Clear:
<logic:present parameter="Clear">
The Duke’s Bookstore application page catalog.jsp uses a runtime expression
to set the value of the attribute that determines the collection of books over
which the Struts logic:iterate tag iterates:
<logic:iterate collection="<%=bookDB.getBooks()%>"
id="book" type="database.BookDetails">
Tags with Bodies
A custom tag can contain custom and core tags, scripting elements, HTML text,
and tag-dependent body content between the start and end tag.
In the following example, the Duke’s Bookstore application page showcart.jsp
uses the Struts logic:present tag to clear the shopping cart and print a message
if the request contains a parameter named Clear:
<logic:present parameter="Clear">
<% cart.clear(); %>
<font color="#ff0000" size="+2"><strong>
You just cleared your shopping cart!
</strong><br>&nbsp;<br></font>
</logic:present>
Choosing between Passing Information as Attributes or Body
As shown in the last two sections, it is possible to pass a given piece of data as an
attribute of the tag or as the tag’s body. Generally speaking, any data that is a
simple string or can be generated by evaluating a simple expression is best
passed as an attribute.
Tags That Define Scripting Variables
A custom tag can define a variable that can be used in scripts within a page. The
following example illustrates how to define and use a scripting variable that con-
287
288
CUSTOM TAGS IN JSP™ PAGES
tains an object returned from a JNDI lookup. Examples of such objects include
enterprise beans, transactions, databases, environment entries, and so on:
<tt:lookup id="tx" type="UserTransaction"
name="java:comp/UserTransaction" />
<% tx.begin(); %>
In the Duke’s Bookstore application, several pages use bean-oriented tags from
Struts to define scripting variables. For example, bookdetails.jsp uses the
bean:parameter tag to create the bookId scripting variable and set it to the
value of the bookId request parameter. The jsp:setProperty statement also
sets the bookId property of the bookDB object to the value of the bookId request
parameter. The bean:define tag retrieves the value of the bookstore database
property bookDetails and defines the result as the scripting variable book:
<bean:parameter id="bookId" name="bookId" />
<jsp:setProperty name="bookDB" property="bookId"/>
<bean:define id="book" name="bookDB" property="bookDetails"
type="database.BookDetails"/>
<h2><jsp:getProperty name="book" property="title"></h2>
Cooperating Tags
Customer tags can cooperate with each other through shared objects. In the following example, tag1 creates an object called obj1 , which is then reused by
tag2.
<tt:tag1 attr1="obj1" value1="value" />
<tt:tag2 attr1="obj1" />
In the next example, an object created by the enclosing tag of a group of nested
tags is available to all inner tags. Since the object is not named, the potential for
naming conflicts is reduced. This example illustrates how a set of cooperating
nested tags would appear in a JSP page.
<tt:outerTag>
<tt:innerTag />
</tt:outerTag>
The Duke’s Bookstore page template.jsp uses a set of cooperating tags to
define the screens of the application. These tags are described in the section A
Template Tag Library, page (308).
DEFINING TAGS
Defining Tags
To define a tag, you need to:
• Develop a tag handler and helper classes for the tag
• Declare the tag in a tag library descriptor
This section describes the properties of tag handlers and TLDs and explains how
to develop tag handlers and library descriptor elements for each type of tag introduced in the previous section.
Tag Handlers
A tag handler is an object invoked by a Web container to evaluate a custom tag
during the execution of the JSP page that references the tag. Tag handlers must
implement either the Tag or BodyTag interface. Interfaces can be used to take an
existing Java object and make it a tag handler. For newly created handlers, you
can use the TagSupport and BodyTagSupport classes as base classes. These
classes and interfaces are contained in the javax.servlet.jsp.tagext package.
Tag handler methods defined by the Tag and BodyTag interfaces are called by the
JSP page’s servlet at various points during the evaluation of the tag. When the
start tag of a custom tag is encountered, the JSP page’s servlet calls methods to
initialize the appropriate handler and then invokes the handler’s doStartTag
method. When the end tag of a custom tag is encountered, the handler’s doEnd
Tag method is invoked. Additional methods are invoked in between when a tag
handler needs to interact with the body of the tag. For further information, see
How Is a Tag Handler Invoked?, page (313). In order to provide a tag handler
implementation, you must implement the methods, summarized in Table 13–1,
that are invoked at various stages of processing the tag.
Table 13–1 Tag Handler Methods
Tag Handler Type
Methods
Simple
doStartTag, doEndTag, release
Attributes
doStartTag, doEndTag,
set/getAttribute1...N, release
Body, evaluation and no interaction
doStartTag, doEndTag, release
289
290
CUSTOM TAGS IN JSP™ PAGES
Table 13–1 Tag Handler Methods (Continued)
Tag Handler Type
Methods
Body, iterative evaluation
doStartTag, doAfterBody, doEndTag,
release
Body, interaction
doStartTag, doEndTag, release,
doInitBody, doAfterBody, release
A tag handler has access to an API that allows it to communicate with the JSP
page. The entry point to the API is the page context object (javax.serv
let.jsp.PageContext), through which a tag handler can retrieve all the other
implicit objects (request, session, and application) accessible from a JSP page.
Implicit objects can have named attributes associated with them. Such attributes
are accessed using [set|get]Attribute methods.
If the tag is nested, a tag handler also has access to the handler (called the parent)
associated with the enclosing tag.
A set of related tag handler classes (a tag library) is usually packaged and
deployed as a JAR archive.
Tag Library Descriptors
A tag library descriptor (TLD) is an XML document that describes a tag library.
A TLD contains information about a library as a whole and about each tag contained in the library. TLDs are used by a Web container to validate the tags and
by JSP page development tools.
TLD file names must have the extension .tld. TLD files are stored in the WEB
INF directory of the WAR file or in a subdirectory of WEBINF. When you add a
TLD to a WAR using deploytool, it automatically puts it into WEBINF.
A TLD must begin with an XML document prolog that specifies the version of
XML and the document type definition (DTD):
<?xml version="1.0" encoding="ISO88591" ?>
<!DOCTYPE taglib PUBLIC "//Sun Microsystems, Inc.//DTD JSP Tag
Library 1.2//EN"
"http://java.sun.com/dtd/webjsptaglibrary_1_2.dtd">
DEFINING TAGS
The J2EE SDK version 1.3 can understand version 1.1 and 1.2 DTDs. However,
this chapter documents the 1.2 version because you should use the newer version
in any tag libraries that you develop. The template library TLD, tutorialtem
plate.tld, conforms to the 1.2 version. The Struts library TLDs conform to the
1.1 version of the DTD, which has fewer elements and uses slightly different
names for some of the elements.
The root of a TLD is the taglib element. The subelements of taglib are listed
in Table 13–2:
Table 13–2 taglib Subelements
Element
Description
tlibversion
The tag library’s version
jspversion
The JSP specification version that the tag library requires
shortname
Optional name that could be used by a JSP page authoring tool to create
names with a mnemonic value
uri
A URI that uniquely identifies the tag library
displayname
Optional name intended to be displayed by tools
smallicon
Optional small icon that can be used by tools
largeicon
Optional large icon that can be used by tools
description
Optional tag-specific information
listener
See listener Element, page (291)
tag
See tag Element, page (292)
listener Element
A tag library can specify some classes that are event listeners (see Handling
Servlet Life-Cycle Events, page (216)). The listeners are listed in the TLD as
listener elements, and the Web container will instantiate the listener classes
and register them in a way analogous to listeners defined at the WAR level.
Unlike WAR-level listeners, the order in which the tag library listeners are registered is undefined. The only subelement of the listener element is the lis
291
292
CUSTOM TAGS IN JSP™ PAGES
tenerclass element, which must contain the fully qualified name of the
listener class.
tag Element
Each tag in the library is described by giving its name and the class of its tag
handler, information on the scripting variables created by the tag, and information on the tag’s attributes. Scripting variable information can be given directly
in the TLD or through a tag extra info class (see Tags That Define Scripting
Variables, page (298)). Each attribute declaration contains an indication of
whether the attribute is required, whether its value can be determined by requesttime expressions, and the type of the attribute (see Tags with
Attributes, page (294)).
A tag is specified in a TLD in a tag element. The subelements of tag are listed
in Table 13–3:
Table 13–3 tag Subelements
Element
Description
name
The unique tag name
tagclass
The fully-qualified name of the tag handler class
teiclass
Optional subclass of javax.servlet.jsp.tagext.TagExtraInfo.
See TagExtraInfo Class, page (301)
bodycontent
The body content type. See body-content Element, page (293) and bodycontent Element, page (298)
displayname
Optional name intended to be displayed by tools.
smallicon
Optional small-icon that can be used by tools.
largeicon
Optional large-icon that can be used by tools.
description
Optional tag-specific information.
variable
Optional scripting variable information. See variable Element, page (300).
attribute
Tag attribute information. See attribute Element, page (294).
DEFINING TAGS
The following sections describe the methods and TLD elements that you need to
develop for each type of tag introduced in Using Tags, page (285).
Simple Tags
Tag Handlers
The handler for a simple tag must implement the doStartTag and doEndTag
methods of the Tag interface. The doStartTag method is invoked when the start
tag is encountered. This method returns SKIP_BODY because a simple tag has no
body. The doEndTag method is invoked when the end tag is encountered. The
doEndTag method needs to return EVAL_PAGE if the rest of the page needs to be
evaluated; otherwise, it should return SKIP_PAGE.
The simple tag discussed in the first section,
<tt:simple />
would be implemented by the following tag handler:
public SimpleTag extends TagSupport {
public int doStartTag() throws JspException {
try {
pageContext.getOut().print("Hello.");
} catch (Exception ex) {
throw new JspTagException("SimpleTag: " +
ex.getMessage());
}
return SKIP_BODY;
}
public int doEndTag() {
return EVAL_PAGE;
}
}
body-content Element
Tags without bodies must declare that their body content is empty using the
bodycontent element:
<bodycontent>empty</bodycontent>
293
294
CUSTOM TAGS IN JSP™ PAGES
Tags with Attributes
Defining Attributes in a Tag Handler
For each tag attribute, you must define a property and get and set methods that
conform to the JavaBeans architecture conventions in the tag handler. For example, the tag handler for the Struts logic:present tag,
<logic:present parameter="Clear">
contains the following declaration and methods:
protected String parameter = null;
public String getParameter() {
return (this.parameter);
}
public void setParameter(String parameter) {
this.parameter = parameter;
}
Note that if your attribute is named id and your tag handler inherits from the
TagSupport class, you do not need to define the property and set and get methods because these are already defined by TagSupport.
A tag attribute whose value is a String can name an attribute of one of the
implicit objects available to tag handlers. An implicit object attribute would be
accessed by passing the tag attribute value to the [set|get]Attribute method
of the implicit object. This is a good way to pass scripting variable names to a
tag handler where they are associated with objects stored in the page context (see
Tags That Define Scripting Variables, page (298)).
attribute Element
For each tag attribute, you must specify whether the attribute is required,
whether the value can be determined by an expression, and, optionally, the type
of the attribute in an attribute element. For static values the type is always
java.lang.String. If the rtexprvalue element is true or yes, then the type
element defines the return type expected from any expression specified as the
value of the attribute.
DEFINING TAGS
<attribute>
<name>attr1</name>
<required>true|false|yes|no</required>
<rtexprvalue>true|false|yes|no</rtexprvalue>
<type>fully_qualified_type</type>
</attribute>
If a tag attribute is not required, a tag handler should provide a default value.
The tag element for the logic:present tag declares that the parameter
attribute is not required (because the tag can also test for the presence of other
entities such as bean properties) and that its value can be set by a runtime expression.
<tag>
<name>present</name>
<tagclass>org.apache.struts.taglib.
logic.PresentTag</tagclass>
<bodycontent>JSP</bodycontent>
...
<attribute>
<name>parameter</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
...
</tag>
Attribute Validation
The documentation for a tag library should describe valid values for tag
attributes. When a JSP page is translated, a Web container will enforce any constraints contained in the TLD element for each attribute.
The attributes passed to a tag can also be validated at translation time with the
isValid method of a class derived from TagExtraInfo. This class is also used
to provide information about scripting variables defined by the tag (see Tags
That Define Scripting Variables, page (298)).
The isValid method is passed the attribute information in a TagData object,
which contains attribute-value tuples for each of the tag’s attributes. Since the
validation occurs at translation time, the value of an attribute that is computed at
request time will be set to TagData.REQUEST_TIME_VALUE.
The tag <tt:twa attr1="value1"/> has the following TLD attribute element:
295
296
CUSTOM TAGS IN JSP™ PAGES
<attribute>
<name>attr1</name>
<required>true</required>
<rtexprvalue>true</a>
</attribute
This declaration indicates that the value of attr1 can be determined at runtime.
The following isValid method checks that the value of attr1 is a valid Boolean value. Note that since the value of attr1 can be computed at runtime,
isValid must check whether the tag user has chosen to provide a runtime value.
public class TwaTEI extends TagExtraInfo {
public boolean isValid(Tagdata data) {
Object o = data.getAttribute("attr1");
if (o != null && o != TagData.REQUEST_TIME_VALUE) {
if (o.toLowerCase().equals("true") ||
o.toLowerCase().equals("false") )
return true;
else
return false;
}
else
return true;
}
}
Tags With Bodies
Tag Handlers
A tag handler for a tag with a body is implemented differently depending on
whether the tag handler needs to interact with the body or not. By interact, we
mean that the tag handler reads or modifies the contents of the body.
Tag Handler Does Not Interact with the Body
If the tag handler does not need to interact with the body, the tag handler should
implement the Tag interface (or be derived from TagSupport). If the body of the
tag needs to be evaluated, the doStartTag method needs to return
EVAL_BODY_INCLUDE; otherwise, it should return SKIP_BODY.
If a tag handler needs to iteratively evaluate the body, it should implement the
IterationTag interface or be derived from TagSupport. It should return
EVAL_BODY_AGAIN from the doStartTag and doAfterBody methods if it determines that the body needs to be evaluated again.
DEFINING TAGS
Tag Handler Interacts with the Body
If the tag handler needs to interact with the body, the tag handler must implement
BodyTag (or be derived from BodyTagSupport). Such handlers typically implement the doInitBody and the doAfterBody methods. These methods interact
with body content passed to the tag handler by the JSP page’s servlet.
Body content supports several methods to read and write its contents. A tag handler can use the body content’s getString or getReader methods to extract
information from the body, and the writeOut(out) method to write the body
contents to an out stream. The writer supplied to the writeOut method is
obtained using the tag handler’s getPreviousOut method. This method is used
to ensure that a tag handler’s results are available to an enclosing tag handler.
If the body of the tag needs to be evaluated, the doStartTag method needs to
return EVAL_BODY_BUFFERED; otherwise, it should return SKIP_BODY.
doInitBody Method
The doInitBody method is called after the body content is set but before it is
evaluated. You generally use this method to perform any initialization that
depends on the body content.
doAfterBody Method
The doAfterBody method is called after the body content is evaluated. Like the
doStartTag method, doAfterBody must return an indication of whether to continue evaluating the body. Thus, if the body should be evaluated again, as would
be the case if you were implementing an iteration tag, doAfterBody should
return EVAL_BODY_BUFFERED; otherwise doAfterBody should return SKIP_BODY.
release Method
A tag handler should reset its state and release any private resources in the
release method.
The following example reads the content of the body (which contains a SQL
query) and passes it to an object that executes the query. Since the body does not
need to be reevaluated, doAfterBody returns SKIP_BODY.
public class QueryTag extends BodyTagSupport {
public int doAfterBody() throws JspTagException {
BodyContent bc = getBodyContent();
// get the bc as string
String query = bc.getString();
// clean up
bc.clearBody();
297
298
CUSTOM TAGS IN JSP™ PAGES
}
}
try {
Statement stmt = connection.createStatement();
result = stmt.executeQuery(query);
} catch (SQLException e) {
throw new JspTagException("QueryTag: " +
e.getMessage());
}
return SKIP_BODY;
body-content Element
For tags that have a body, you must specify the type of the body content using
the bodycontent element:
<bodycontent>JSP|tagdependent</bodycontent>
Body content containing custom and core tags, scripting elements, and HTML
text is categorized as JSP. This is the value declared for the Struts
logic:present tag. All other types of body content—for example, SQL statements passed to the query tag—would be labeled tagdependent.
Note that the value of the bodycontent element does not affect the interpretation of the body by the tag handler; the element is only intended to be used by an
authoring tool for rendering the body content.
Tags That Define Scripting Variables
Tag Handlers
A tag handler is responsible for creating and setting the object referred to by the
scripting variable into a context accessible from the page. It does this by using
the pageContext.setAttribute(name, value, scope) or pageCon
text.setAttribute(name, value) methods. Typically, an attribute passed to
the custom tag specifies the name of the scripting variable object; this name can
be retrieved by invoking the attribute’s get method described in Defining
Attributes in a Tag Handler, page (294).
If the value of the scripting variable is dependent on an object present in the tag
handler’s context, it can retrieve the object using the pageContext.getAt
tribute(name, scope) method.
299
DEFINING TAGS
The usual procedure is that the tag handler retrieves a scripting variable, performs some processing on the object, and then sets the scripting variable’s value
using the pageContext.setAttribute(name, object) method.
The scope that an object can have is summarized in Table 13–4. The scope constrains the accessibility and lifetime of the object.
Table 13–4 Scope of Objects
Name
Accessible From
Lifetime
page
Current page
Until the response has been sent back
to the user or the request is passed to
a new page
request
Current page and any included or
forwarded pages
Until the response has been sent back
to the user
session
Current request and any subsequent
request from the same browser
(subject to session lifetime)
The life of the user’s session
application
Current and any future request from
the same Web application
The life of the application
Providing Information about the Scripting Variable
The example described in Tags That Define Scripting Variables, page (287)
defines a scripting variable book that is used for accessing book information:
<bean:define id="book" name="bookDB" property="bookDetails"
type="database.BookDetails"/>
<font color="red" size="+2">
<%=messages.getString("CartRemoved")%>
<strong><jsp:getProperty name="book"
property="title"/></strong>
<br>&nbsp;<br>
</font>
When the JSP page containing this tag is translated, the Web container generates
code to synchronize the scripting variable with the object referenced by the vari-
300
CUSTOM TAGS IN JSP™ PAGES
able. To generate the code, the Web container requires certain information about
the scripting variable:
•
•
•
•
Variable name
Variable class
Whether the variable refers to a new or existing object
The availability of the variable
There are two ways to provide this information: by specifying the variable
TLD subelement or by defining a tag extra info class and including the tei
class element in the TLD. Using the variable element is simpler, but slightly
less flexible.
variable Element
The variable element has the following subelements:
• namegiven: The variable name as a constant
• namefromattribute: The name of an attribute whose translation-time
value will give the name of the variable
One of namegiven or namefromattribute is required. The following subelements are optional:
• variableclass: The fully qualified name of the class of the variable.
java.lang.String is the default.
• declare: Whether the variable refers to a new object. True is the default.
• scope: The scope of the scripting variable defined. NESTED is default.
Table 13–5 describes the availability of the scripting variable and the
methods in which the value of the variable must be set or reset.
Table 13–5 Scripting Variable Availability
Value
Availability
Methods
NESTED
Between the start
tag and the end tag
In doInitBody and doAfterBody for a tag handler
implementing BodyTag; otherwise, in doStartTag
AT_BEGIN
From the start tag
until the end of the
page
In doInitBody, doAfterBody, and doEndTag for a
tag handler implementing BodyTag; otherwise, in
doStartTag and doEndTag
DEFINING TAGS
Table 13–5 Scripting Variable Availability (Continued)
Value
Availability
Methods
AT_END
After the end tag
until the end of the
page
In doEndTag
The implementation of the Struts bean:define tag conforms to the JSP specification version 1.1, which requires you to define a tag extra info class. The JSP
specification version 1.2 adds the variable element. You could define the following variable element for the bean:define tag:
<tag>
<variable>
<namefromattribute>id</namefromattribute>
<variableclass>database.BookDetails</variableclass>
<declare>true</declare>
<scope>AT_BEGIN</scope>
</variable>
</tag>
TagExtraInfo Class
You define a tag extra info class by extending the class javax.serv
let.jsp.TagExtraInfo. A TagExtraInfo must implement the getVari
ableInfo method to return an array of VariableInfo objects containing the
following information:
•
•
•
•
Variable name
Variable class
Whether the variable refers to a new object
The availability of the variable
The Web container passes a parameter called data to the getVariableInfo
method that contains attribute-value tuples for each of the tag’s attributes. These
attributes can be used to provide the VariableInfo object with a scripting variable’s name and class.
The Struts tag library provides information about the scripting variable created
by the bean:define tag in the DefineTei tag extra info class. Since the name
(book) and class (database.BookDetails) of the scripting variable are passed
in as tag attributes, they can be retrieved with the data.getAttributeString
301
302
CUSTOM TAGS IN JSP™ PAGES
method and used to fill in the VariableInfo constructor. To allow the scripting
variable book to be used in the rest of the page, the scope of book is set to be
AT_BEGIN.
public class DefineTei extends TagExtraInfo {
public VariableInfo[] getVariableInfo(TagData data) {
String type = data.getAttributeString("type");
if (type == null)
type = "java.lang.Object";
return new VariableInfo[] {
new VariableInfo(data.getAttributeString("id"),
type,
true,
VariableInfo.AT_BEGIN)
};
}
}
The fully qualified name of the tag extra info class defined for a scripting variable must be declared in the TLD in the teiclass subelement of the tag element. Thus, the teiclass element for DefineTei would be as follows:
<teiclass>org.apache.struts.taglib.bean.DefineTagTei
</teiclass>
Cooperating Tags
Tags cooperate by sharing objects. JSP technology supports two styles of object
sharing. The first style requires that a shared object be named and stored in the
page context (one of the implicit objects accessible to both JSP pages and tag
handlers). To access objects created and named by another tag, a tag handler uses
the pageContext.getAttribute(name, scope) method.
In the second style of object sharing, an object created by the enclosing tag handler of a group of nested tags is available to all inner tag handlers. This form of
object sharing has the advantage that it uses a private namespace for the objects,
thus reducing the potential for naming conflicts.
To access an object created by an enclosing tag, a tag handler must first obtain its
enclosing tag with the static method TagSupport.findAncestorWith
Class(from, class) or the TagSupport.getParent method. The former
method should be used when a specific nesting of tag handlers cannot be guaranteed. Once the ancestor has been retrieved, a tag handler can access any statically
or dynamically created objects. Statically created objects are members of the
DEFINING TAGS
parent. Private objects can also be created dynamically. Such objects can be
stored in a tag handler with the setValue method and retrieved with the
getValue method.
The following example illustrates a tag handler that supports both the named and
private object approaches to sharing objects. In the example, the handler for a
query tag checks whether an attribute named connection has been set in the
doStartTag method. If the connection attribute has been set, the handler
retrieves the connection object from the page context. Otherwise, the tag handler
first retrieves the tag handler for the enclosing tag and then retrieves the connection object from that handler.
public class QueryTag extends BodyTagSupport {
private String connectionId;
public int doStartTag() throws JspException {
String cid = getConnection();
if (cid != null) {
// there is a connection id, use it
connection =(Connection)pageContext.
getAttribute(cid);
} else {
ConnectionTag ancestorTag =
(ConnectionTag)findAncestorWithClass(this,
ConnectionTag.class);
if (ancestorTag == null) {
throw new JspTagException("A query without
a connection attribute must be nested
within a connection tag.");
}
connection = ancestorTag.getConnection();
}
}
}
The query tag implemented by this tag handler could be used in either of the following ways:
<tt:connection id="con01" ....> ... </tt:connection>
<tt:query id="balances" connection="con01">
SELECT account, balance FROM acct_table
where customer_number = <%= request.getCustno()%>
</tt:query>
<tt:connection ...>
<x:query id="balances">
303
304
CUSTOM TAGS IN JSP™ PAGES
SELECT account, balance FROM acct_table
where customer_number = <%= request.getCustno()%>
</x:query>
</tt:connection>
The TLD for the tag handler must indicate that the connection attribute is
optional with the following declaration:
<tag>
...
<attribute>
<name>connection</name>
<required>false</required>
</attribute>
</tag>
Examples
The custom tags described in this section demonstrate solutions to two recurring
problems in developing JSP applications: minimizing the amount of Java programming in JSP pages and ensuring a common look and feel across applications. In doing so, they illustrate many of the styles of tags discussed in the first
part of the chapter.
An Iteration Tag
Constructing page content that is dependent on dynamically generated data often
requires the use of flow control scripting statements. By moving the flow control
logic to tag handlers, flow control tags reduce the amount of scripting needed in
JSP pages.
The Struts logic:iterate tag retrieves objects from a collection stored in a JavaBeans component and assigns them to a scripting variable. The body of the tag
retrieves information from the scripting variable. While elements remain in the
collection, the iterate tag causes the body to be reevaluated.
JSP Page
Two Duke’s Bookstore application pages, catalog.jsp and showcart.jsp, use
the logic:iterate tag to iterate over collections of objects. An excerpt from
catalog.jsp is shown below. The JSP page initializes the iterate tag with a
collection (named by the property attribute) of the bookDB bean. The iterate
tag sets the book scripting variable on each iteration over the collection. The
EXAMPLES
bookId property of the book variable is exposed as another scripting variable.
Properties of both variables are used to dynamically generate a table containing
links to other pages and book catalog information.
<logic:iterate name="bookDB" property="books"
id="book" type="database.BookDetails">
<bean:define id="bookId" name="book" property="bookId"
type="java.lang.String"/>
<tr>
<td bgcolor="#ffffaa">
<a href="<%=request.getContextPath()%>
/bookdetails?bookId=<%=bookId%>">
<strong><jsp:getProperty name="book"
property="title"/>&nbsp;</strong></a></td>
<td bgcolor="#ffffaa" rowspan=2>
<jsp:setProperty name="currency" property="amount"
value="<%=book.getPrice()%>"/>
<jsp:getProperty name="currency" property="format"/>
&nbsp;</td>
<td bgcolor="#ffffaa" rowspan=2>
<a href="<%=request.getContextPath()%>
/catalog?Add=<%=bookId%>">
&nbsp;<%=messages.getString("CartAdd")%>
&nbsp;</a></td></tr>
<tr>
<td bgcolor="#ffffff">
&nbsp;&nbsp;<%=messages.getString("By")%> <em>
<jsp:getProperty name="book"
property="firstName"/>&nbsp;
<jsp:getProperty name="book"
property="surname"/></em></td></tr>
</logic:iterate>
Tag Handler
The implementation of the Struts logic:iterate tag conforms to the capabilities of the JSP version 1.1 specification, which requires you to extend the
BodyTagSupport class. The JSP version 1.2 specification adds features
(described in the section Tag Handler Does Not Interact with the
Body, page (296)) that simplify programming tags that iteratively evaluate their
body. The following discussion is based on an implementation that uses these
features.
305
306
CUSTOM TAGS IN JSP™ PAGES
The logic:iterate tag supports initializing the collection in several ways: from
a collection provided as a tag attribute or from a collection that is a bean or a
property of a bean. Our example uses the latter method. Most of the code in
doStartTag is concerned with constructing an iterator over the collection object.
The method first checks if the handler’s collection property is set and, if not,
proceeds to check the bean and property attributes. If the bean and property
attributes are both set, doStartTag calls a utility method that uses JavaBeans
introspection methods to retrieve the collection. Once the collection object is
determined, the method constructs the iterator.
If the iterator contains more elements, doStartTag sets the value of the scripting
variable to the next element and then indicates that the body should be evaluated;
otherwise, it ends the iteration by returning SKIP_BODY.
After the body has been evaluated, the doAfterBody method retrieves the body
content and writes it to the out stream. The body content object is then cleared in
preparation for another body evaluation. If the iterator contains more elements,
doAfterBody again sets the value of the scripting variable to the next element
and returns EVAL_BODY_AGAIN to indicate that the body should be evaluated
again. This causes the reexecution of doAfterBody. When there are no remaining elements, doAfterBody terminates the process by returning SKIP_BODY.
public class IterateTag extends TagSupport {
protected Iterator iterator = null;
protected Object collection = null;
protected String id = null;
protected String name = null;
protected String property = null;
protected String type = null;
public int doStartTag() throws JspException {
Object collection = this.collection;
if (collection == null) {
try {
Object bean = pageContext.findAttribute(name);
if (bean == null) {
... throw an exception
}
if (property == null)
collection = bean;
else
collection =
PropertyUtils.
getProperty(bean, property);
if (collection == null) {
... throw an exception
}
EXAMPLES
} catch
... catch exceptions thrown
by PropertyUtils.getProperty
}
}
}
}
// Construct an iterator for this collection
if (collection instanceof Collection)
iterator = ((Collection) collection).iterator();
else if (collection instanceof Iterator)
iterator = (Iterator) collection;
...
}
// Store the first value and evaluate,
// or skip the body if none
if (iterator.hasNext()) {
Object element = iterator.next();
pageContext.setAttribute(id, element);
return (EVAL_BODY_AGAIN);
} else
return (SKIP_BODY);
public int doAfterBody() throws JspException {
if (bodyContent != null) {
try {
JspWriter out = getPreviousOut();
out.print(bodyContent.getString());
bodyContent.clearBody();
} catch (IOException e) {
...
}
}
if (iterator.hasNext()) {
Object element = iterator.next();
pageContext.setAttribute(id, element);
return (EVAL_BODY_AGAIN);
} else
return (SKIP_BODY);
}
}
Tag Extra Info Class
Information about the scripting variable is provided in the IterateTei tag extra
info class. The name and class of the scripting variable are passed in as tag
attributes and used to fill in the VariableInfo constructor.
307
308
CUSTOM TAGS IN JSP™ PAGES
public class IterateTei extends TagExtraInfo {
public VariableInfo[] getVariableInfo(TagData data) {
String type = data.getAttributeString("type");
if (type == null)
type = "java.lang.Object";
}
return new VariableInfo[] {
new VariableInfo(data.getAttributeString("id"),
type,
true,
VariableInfo.AT_BEGIN)
};
}
A Template Tag Library
A template provides a way to separate the common elements that are part of each
screen from the elements that change with each screen of an application. Putting
all the common elements together into one file makes it easier to maintain and
enforce a consistent look and feel in all the screens. It also makes development
of individual screens easier because the designer can focus on portions of a
screen that are specific to that screen while the template takes care of the common portions.
The template is a JSP page with placeholders for the parts that need to change
with each screen. Each of these placeholders is referred to as a parameter of the
template. For example, a simple template could include a title parameter for the
top of the generated screen and a body parameter to refer to a JSP page for the
custom content of the screen.
The template uses a set of nested tags—definition, screen, and parameter—
to define a table of screen definition for an application screen and uses an
insert tag to insert parameters from a screen definition into the application
screen.
JSP Page
The template for the Duke’s Bookstore example, template.jsp, is shown
below. This page includes a JSP page that creates the screen definition and then
uses the insert tag to insert parameters from the definition into the application
screen.
EXAMPLES
<%@ taglib uri="/tutorialtemplate.tld" prefix="tt" %>
<%@ page errorPage="errorpage.jsp" %>
<%@ include file="screendefinitions.jsp" %><html>
<head>
<title>
<tt:insert definition="bookstore"
parameter="title"/>
</title>
</head>
<tt:insert definition="bookstore"
parameter="banner"/>
<tt:insert definition="bookstore"
parameter="body"/>
</body>
</html>
screendefinitions.jsp creates a screen definition based on a request attribute
selectedScreen:
<tt:definition name="bookstore"
screen="<%= (String)request.
getAttribute(\"selectedScreen\") %>">
<tt:screen id="/enter">
<tt:parameter name="title"
value="Duke's Bookstore" direct="true"/>
<tt:parameter name="banner"
value="/banner.jsp" direct="false"/>
<tt:parameter name="body"
value="/bookstore.jsp" direct="false"/>
</tt:screen>
<tt:screen id="/catalog">
<tt:parameter name="title"
value="<%=messages.getString("TitleBookCatalog")%>"
direct="true"/>
...
</tt:definition>
The template is instantiated by the Dispatcher servlet. Dispatcher first gets the
requested screen and stores it as an attribute of the request. This is necessary
because when the request is forwarded to template.jsp, the request URL
doesn’t contain the original request (for example, /bookstore3/catalog) but
instead reflects the path (/bookstore3/template.jsp) of the forwarded page.
Finally, the servlet dispatches the request to template.jsp:
309
310
CUSTOM TAGS IN JSP™ PAGES
public class Dispatcher extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response) {
request.setAttribute("selectedScreen",
request.getServletPath());
RequestDispatcher dispatcher =
request.getRequestDispatcher("/template.jsp");
if (dispatcher != null)
dispatcher.forward(request, response);
}
public void doPost(HttpServletRequest request,
HttpServletResponse response) {
request.setAttribute("selectedScreen",
request.getServletPath());
RequestDispatcher dispatcher =
request.getRequestDispatcher("/template.jsp");
if (dispatcher != null)
dispatcher.forward(request, response);
}
}
Tag Handlers
The template tag library contains four tag handlers—DefinitionTag,
ScreenTag, ParameterTag, and InsertTag—that demonstrate the use of cooperating tags. DefinitionTag, ScreenTag, and ParameterTag comprise a set of
nested tag handlers that share public and private objects. DefinitionTag creates
a public named object called definition that is used by InsertTag.
In doStartTag, DefinitionTag creates a public object named screens that
contains a hash table of screen definitions. A screen definition consists of a
screen identifier and a set of parameters associated with the screen.
public int doStartTag() {
HashMap screens = null;
screens = (HashMap) pageContext.getAttribute("screens",
pageContext.APPLICATION_SCOPE);
if (screens == null)
pageContext.setAttribute("screens", new HashMap(),
pageContext.APPLICATION_SCOPE);
return EVAL_BODY_INCLUDE;
}
311
EXAMPLES
The table of screen definitions is filled in by ScreenTag and ParameterTag from
text provided as attributes to these tags. Table 13–6 shows the contents of the
screen definitions hash table for the Duke’s Bookstore application.
Table 13–6 Screen Definitions
Screen Id
Title
Banner
Body
/enter
Duke's Bookstore
/banner.jsp
/bookstore.jsp
/catalog
Book Catalog
/banner.jsp
/catalog.jsp
/bookdetails
Book Description
/banner.jsp
/bookdetails.jsp
/showcart
Your Shopping Cart
/banner.jsp
/showcart.jsp
/cashier
Cashier
/banner.jsp
/cashier.jsp
/receipt
Receipt
/banner.jsp
/receipt.jsp
In doEndTag, DefinitionTag creates a public object of class Definition,
selects a screen definition from the screens object based on the URL passed in
the request, and uses it to initialize the Definition object.
public int doEndTag()throws JspTagException {
try {
Definition definition = new Definition();
Hashtable screens = null;
ArrayList params = null;
TagSupport screen = null;
screens = (HashMap)
pageContext.getAttribute("screens",
pageContext.APPLICATION_SCOPE);
if (screens != null)
params = (ArrayList) screens.get(screenId);
else
...
if (params == null)
...
Iterator ir = null;
if (params != null)
ir = params.iterator();
while ((ir != null) && ir.hasNext())
definition.setParam((Parameter) ir.next());
// put the definition in the page context
312
CUSTOM TAGS IN JSP™ PAGES
}
pageContext.setAttribute(
definitionName, definition);
} catch (Exception ex) {
ex.printStackTrace();
}
return EVAL_PAGE;
If the URL passed in the request is /enter, the Definition contains the items
from the first row of Table 13–6:
Table 1
Title
Banner
Body
Duke’s Bookstore
/banner.jsp
/bookstore.jsp
The definition for the URL /enter is shown in Table 13–7. The definition specifies that the value of the Title parameter, Duke’s Bookstore, should be inserted
directly into the output stream, but the values of Banner and Body should be
dynamically included.
Table 13–7 Screen Definition for the URL /enter
Parameter
Name
Parameter Value
isDirect
title
Duke's Bookstore
true
banner
/banner.jsp
false
body
/bookstore.jsp
false
InsertTag uses Definition to insert parameters of the screen definition into
the response. In the doStartTag method, it retrieves the definition object from
the page context.
HOW IS A TAG HANDLER INVOKED?
public int doStartTag() {
// get the definition from the page context
definition = (Definition) pageContext.
getAttribute(definitionName);
// get the parameter
if (parameterName != null && definition != null)
parameter = (Parameter)definition.
getParam(parameterName);
if (parameter != null)
directInclude = parameter.isDirect();
return SKIP_BODY;
}
The doEndTag method inserts the parameter value. If the parameter is direct, it is
directly inserted into the response; otherwise, the request is sent to the parameter
and the response is dynamically included into the overall response.
public int doEndTag()throws JspTagException {
try {
if (directInclude && parameter != null)
pageContext.getOut().print(parameter.getValue());
else {
if ((parameter != null) &&
(parameter.getValue() != null))
pageContext.include(parameter.getValue());
}
} catch (Exception ex) {
throw new JspTagException(ex.getMessage());
}
return EVAL_PAGE;
}
How Is a Tag Handler Invoked?
The Tag interface defines the basic protocol between a tag handler and a JSP
page’s servlet. It defines the life cycle and the methods to be invoked when the
start and end tags are encountered.
The JSP page’s servlet invokes the setPageContext, setParent, and attribute
setting methods before calling doStartTag. The JSP page’s servlet also guarantees that release will be invoked on the tag handler before the end of the page.
Here is a typical tag handler method invocation sequence:
313
314
CUSTOM TAGS IN JSP™ PAGES
ATag t = new ATag();
t.setPageContext(...);
t.setParent(...);
t.setAttribute1(value1);
t.setAttribute2(value2);
t.doStartTag();
t.doEndTag();
t.release();
The BodyTag interface extends Tag by defining additional methods that let a tag
handler access its body. The interface provides three new methods:
setBodyContent: Creates body content and adds to the tag handler
doInitBody: Called before evaluation of the tag body
doAfterBody: Called after evaluation of the tag body
A typical invocation sequence is as follows:
t.doStartTag();
out = pageContext.pushBody();
t.setBodyContent(out);
// perform any initialization needed after body content is set
t.doInitBody();
t.doAfterBody();
// while doAfterBody returns EVAL_BODY_BUFFERED we
// iterate body evaluation
...
t.doAfterBody();
t.doEndTag();
t.pageContext.popBody();
t.release();
14
Transactions
Dale Green
A typical enterprise application accesses and stores information in one or more
databases. Because this information is critical for business operations, it must be
accurate, current, and reliable. Data integrity would be lost if multiple programs
were allowed to simultaneously update the same information. It would also be
lost if a system that failed while processing a business transaction were to leave
the affected data only partially updated. By preventing both of these scenarios,
software transactions ensure data integrity. Transactions control the concurrent
access of data by multiple programs. In the event of a system failure, transactions make sure that after recovery the data will be in a consistent state.
In This Chapter
What Is a Transaction? 316
Container-Managed Transactions 316
Transaction Attributes 317
Rolling Back a Container-Managed Transaction 321
Synchronizing a Session Bean’s Instance Variables 322
Methods Not Allowed in Container-Managed Transactions 323
Bean-Managed Transactions 323
JDBC Transactions 324
JTA Transactions 325
Returning without Committing 326
Methods Not Allowed in Bean-Managed Transactions 327
Summary of Transaction Options for Enterprise Beans 327
Transaction Timeouts 328
Isolation Levels 329
Updating Multiple Databases 329
315
316
TRANSACTIONS
Transactions in Web Components 331
What Is a Transaction?
To emulate a business transaction, a program may need to perform several steps.
A financial program, for example, might transfer funds from a checking account
to a savings account with the steps listed in the following pseudocode.
begin transaction
debit checking account
credit savings account
update history log
commit transaction
Either all three of these steps must complete, or none of them at all. Otherwise,
data integrity is lost. Because the steps within a transaction are a unified whole, a
transaction is often defined as an indivisible unit of work.
A transaction can end in two ways: with a commit or a rollback. When a transaction commits, the data modifications made by its statements are saved. If a statement within a transaction fails, the transaction rolls back, undoing the effects of
all statements in the transaction. In the pseudocode, for example, if a disk drive
crashed during the credit step, the transaction would roll back and undo the
data modifications made by the debit statement. Although the transaction
failed, data integrity would be intact because the accounts still balance.
In the preceding pseudocode, the begin and commit statements mark the boundaries of the transaction. When designing an enterprise bean, you determine how
the boundaries are set by specifying either container-managed or bean-managed
transactions.
Container-Managed Transactions
In an enterprise bean with container-managed transactions, the EJB™ container
sets the boundaries of the transactions. You can use container-managed transactions with any type of enterprise bean: session, entity, or message-driven. Container-managed transactions simplify development because the enterprise bean
code does not explicitly mark the transaction’s boundaries. The code does not
include statements that begin and end the transaction.
CONTAINER-MANAGED TRANSACTIONS
Typically, the container begins a transaction immediately before an enterprise
bean method starts. It commits the transaction just before the method exits. Each
method can be associated with a single transaction. Nested or multiple transactions are not allowed within a method.
Container-managed transactions do not require all methods to be associated with
transactions. When deploying a bean, you specify which of the bean’s methods
are associated with transactions by setting the transaction attributes.
Transaction Attributes
A transaction attribute controls the scope of a transaction. Figure 14–1 illustrates
why controlling the scope is important. In the diagram, methodA begins a transaction and then invokes methodB of Bean2. When methodB executes, does it
run within the scope of the transaction started by method-A or does it execute
with a new transaction? The answer depends on the transaction attribute of
methodB.
Figure 14–1 Transaction Scope
A transaction attribute may have one of the following values:
•
•
•
•
•
•
Required
RequiresNew
Mandatory
NotSupported
Supports
Never
317
318
TRANSACTIONS
Required
If the client is running within a transaction and invokes the enterprise bean’s
method, the method executes within the client’s transaction. If the client is not
associated with a transaction, the container starts a new transaction before running the method.
The Required attribute will work for most transactions. Therefore, you may
want to use it as a default, at least in the early phases of development. Because
transaction attributes are declarative, you can easily change them at a later time.
RequiresNew
If the client is running within a transaction and invokes the enterprise bean’s
method, the container takes the following steps:
1.
2.
3.
4.
Suspends the client’s transaction
Starts a new transaction
Delegates the call to the method
Resumes the client’s transaction after the method completes
If the client is not associated with a transaction, the container starts a new transaction before running the method.
You should use the RequiresNew attribute when you want to ensure that the
method always runs within a new transaction.
Mandatory
If the client is running within a transaction and invokes the enterprise bean’s
method, the method executes within the client’s transaction. If the client is not
associated with a transaction, the container throws the TransactionRequire
dException.
Use the Mandatory attribute if the enterprise bean’s method must use the transaction of the client.
NotSupported
If the client is running within a transaction and invokes the enterprise bean’s
method, the container suspends the client’s transaction before invoking the
method. After the method has completed, the container resumes the client’s
transaction.
If the client is not associated with a transaction, the container does not start a
new transaction before running the method.
CONTAINER-MANAGED TRANSACTIONS
Use the NotSupported attribute for methods that don’t need transactions.
Because transactions involve overhead, this attribute may improve performance.
Supports
If the client is running within a transaction and invokes the enterprise bean’s
method, the method executes within the client’s transaction. If the client is not
associated with a transaction, the container does not start a new transaction
before running the method.
Because the transactional behavior of the method may vary, you should use the
Supports attribute with caution.
Never
If the client is running within a transaction and invokes the enterprise bean’s
method, the container throws a RemoteException. If the client is not associated
with a transaction, the container does not start a new transaction before running
the method.
Summary of Transaction Attributes
Table 14–1 summarizes the effects of the transaction attributes. Both the T1 and
T2 transactions are controlled by the container. A T1 transaction is associated
with the client that calls a method in the enterprise bean. In most cases, the client
is another enterprise bean. A T2 transaction is started by the container just before
the method executes.
In the last column of Table 14–1, the word “None” means that the business
method does not execute within a transaction controlled by the container. However, the database calls in such a business method might be controlled by the
transaction manager of the DBMS.
Table 14–1 Transaction Attributes and Scope
Transaction
Attribute
Client’s
Transaction
Business Method’s
Transaction
Required
None
T2
T1
T1
319
320
TRANSACTIONS
Table 14–1 Transaction Attributes and Scope (Continued)
Transaction
Attribute
Client’s
Transaction
Business Method’s
Transaction
RequiresNew
None
T2
T1
T2
None
error
T1
T1
None
None
T1
None
None
None
T1
T1
None
None
T1
Error
Mandatory
NotSupported
Supports
Never
Setting Transaction Attributes
Because transaction attributes are stored in the deployment descriptor, they can
be changed during several phases of J2EE™ application development: enterprise
bean creation, application assembly, and deployment. However, as an enterprise
bean developer, it is your responsibility to specify the attributes when creating
the bean. The attributes should be modified only by an application developer
who is assembling components into larger applications. Do not expect the person
who is deploying the J2EE application to specify the transaction attributes.
You can specify the transaction attributes for the entire enterprise bean or for
individual methods. If you’ve specified one attribute for a method and another
for the bean, the attribute for the method takes precedence. When specifying
attributes for individual methods, the requirements differ with the type of bean.
Session beans need the attributes defined for business methods, but do not allow
them for the create methods. Entity beans require transaction attributes for the
business, create, remove, and finder methods. Message-driven beans require
transaction attributes (either Required or NotSupported) for the onMessage
method.
CONTAINER-MANAGED TRANSACTIONS
Rolling Back a Container-Managed Transaction
There are two ways to roll back a container-managed transaction. First, if a system exception is thrown, the container will automatically roll back the transaction. Second, by invoking the setRollbackOnly method of the EJBContext
interface, the bean method instructs the container to roll back the transaction. If
the bean throws an application exception, the rollback is not automatic, but may
be initiated by a call to setRollbackOnly. For a description of system and application exceptions, see Handling Exceptions, page (116).
The source code for the following example is in the j2eetutorial/exam
ples/src/ejb/bank directory. To compile the code, go to the
j2eetutorial/examples directory and type ant bank. To create the database
tables, type ant createbanktable. A sample BankApp.ear file is in the
j2eetutorial/examples/ears directory.
The transferToSaving method of the BankEJB example illustrates the set
RollbackOnly method. If a negative checking balance occurs, transferToSav
ing invokes setRollBackOnly and throws an application exception
(InsufficientBalanceException). The updateChecking and updateSaving
methods update database tables. If the updates fail, these methods throw a
SQLException and the transferToSaving method throws an EJBException.
Because the EJBException is a system exception, it causes the container to automatically roll back the transaction. Here is the code for the transferToSaving
method:
public void transferToSaving(double amount) throws
InsufficientBalanceException {
checkingBalance = amount;
savingBalance += amount;
}
try {
updateChecking(checkingBalance);
if (checkingBalance < 0.00) {
context.setRollbackOnly();
throw new InsufficientBalanceException();
}
updateSaving(savingBalance);
} catch (SQLException ex) {
throw new EJBException
("Transaction failed due to SQLException: "
+ ex.getMessage());
}
321
322
TRANSACTIONS
When the container rolls back a transaction, it always undoes the changes to data
made by SQL calls within the transaction. However, only in entity beans will the
container undo changes made to instance variables. (It does so by automatically
invoking the entity bean’s ejbLoad method, which loads the instance variables
from the database.) When a rollback occurs, a session bean must explicitly reset
any instance variables changed within the transaction. The easiest way to reset a
session bean’s instance variables is by implementing the SessionSynchroniza
tion interface.
Synchronizing a Session Bean’s Instance Variables
The SessionSynchronization interface, which is optional, allows you to synchronize the instance variables with their corresponding values in the database.
The container invokes the SessionSynchronization methods—afterBegin,
beforeCompletion, and afterCompletion—at each of the main stages of a
transaction.
The afterBegin method informs the instance that a new transaction has begun.
The container invokes afterBegin immediately before it invokes the business
method. The afterBegin method is a good place to load the instance variables
from the database. The BankBean class, for example, loads the checkingBal
ance and savingBalance variables in the afterBegin method:
public void afterBegin() {
}
System.out.println("afterBegin()");
try {
checkingBalance = selectChecking();
savingBalance = selectSaving();
} catch (SQLException ex) {
throw new EJBException("afterBegin Exception: " +
ex.getMessage());
}
The container invokes the beforeCompletion method after the business method
has finished, but just before the transaction commits. The beforeCompletion
method is the last opportunity for the session bean to roll back the transaction
(by calling setRollbackOnly). If it hasn’t already updated the database with the
values of the instance variables, the session bean may do so in the beforeCom
pletion method.
The afterCompletion method indicates that the transaction has completed. It
has a single boolean parameter, whose value is true if the transaction was com-
BEAN-MANAGED TRANSACTIONS
mitted and false if it was rolled back. If a rollback occurred, the session bean
can refresh its instance variables from the database in the afterCompletion
method:
public void afterCompletion(boolean committed) {
}
System.out.println("afterCompletion: " + committed);
if (committed == false) {
try {
checkingBalance = selectChecking();
savingBalance = selectSaving();
} catch (SQLException ex) {
throw new EJBException("afterCompletion SQLException:
" + ex.getMessage());
}
}
Methods Not Allowed in Container-Managed
Transactions
You should not invoke any method that might interfere with the transaction
boundaries set by the container. The list of prohibited methods follows:
• The commit, setAutoCommit, and rollback methods of java.sql.Con
nection
• The getUserTransaction method of javax.ejb.EJBContext
• Any method of javax.transaction.UserTransaction
You may, however, use these methods to set boundaries in bean-managed transactions.
Bean-Managed Transactions
In a bean-managed transaction, the code in the session or message-driven bean
explicitly marks the boundaries of the transaction. An entity bean cannot have
bean-managed transactions; it must use container-managed transactions instead.
Although beans with container-managed transactions require less coding, they
have one limitation: When a method is executing, it can be associated with either
a single transaction or no transaction at all. If this limitation will make coding
your bean difficult, you should consider using bean-managed transactions.
323
324
TRANSACTIONS
The following pseudocode illustrates the kind of fine-grained control you can
obtain with bean-managed transactions. By checking various conditions, the
pseudocode decides whether to start or stop different transactions within the
business method.
begin transaction
...
update tablea
...
if (conditionx)
commit transaction
else if (conditiony)
update tableb
commit transaction
else
rollback transaction
begin transaction
update tablec
commit transaction
When coding a bean-managed transaction for session or message-driven beans,
you must decide whether to use JDBC or JTA transactions. The sections that follow discuss both types of transactions.
JDBC Transactions
A JDBC transaction is controlled by the transaction manager of the DBMS. You
may want to use JDBC transactions when wrapping legacy code inside a session
bean. To code a JDBC transaction, you invoke the commit and rollback methods of the java.sql.Connection interface. The beginning of a transaction is
implicit. A transaction begins with the first SQL statement that follows the most
recent commit , rollback, or connect statement. (This rule is generally true, but
may vary with DBMS vendor.)
Source Code
The source code for the following example is in the j2eetutorial/exam
ples/src/ejb/warehouse directory. To compile the code, go to the
j2eetutorial/examples directory and type ant bank. To create the database
tables, type ant createwarehousetable. A sample WarehouseApp.ear file is
in the j2eetutorial/examples/ears directory.
The following code is from the WarehouseEJB example, a session bean that uses
the Connection interface’s methods to delimit bean-managed transactions. The
BEAN-MANAGED TRANSACTIONS
ship method starts by invoking setAutoCommit on the Connection object
named con. This invocation tells the DBMS not to automatically commit every
SQL statement. Next, the ship method calls routines that update the order_item
and inventory database tables. If the updates succeed, the transaction is committed. If an exception is thrown, however, the transaction is rolled back.
public void ship (String productId, String orderId, int
quantity) {
}
try {
con.setAutoCommit(false);
updateOrderItem(productId, orderId);
updateInventory(productId, quantity);
con.commit();
} catch (Exception ex) {
try {
con.rollback();
throw new EJBException("Transaction failed: " +
ex.getMessage());
} catch (SQLException sqx) {
throw new EJBException("Rollback failed: " +
sqx.getMessage());
}
}
JTA Transactions
JTA is the abbreviation for the Java™ Transaction API. This API allows you to
demarcate transactions in a manner that is independent of the transaction manager implementation. The J2EE SDK implements the transaction manager with
the Java Transaction Service (JTS). But your code doesn’t call the JTS methods
directly. Instead, it invokes the JTA methods, which then call the lower-level JTS
routines.
A JTA transaction is controlled by the J2EE transaction manager. You may want
to use a JTA transaction because it can span updates to multiple databases from
different vendors. A particular DBMS’s transaction manager may not work with
heterogeneous databases. However, the J2EE transaction manager does have one
limitation—it does not support nested transactions. In other words, it cannot start
a transaction for an instance until the previous transaction has ended.
The source code for the following example is in the j2eetutorial/exam
ples/src/ejb/teller directory. To compile the code, go to the
j2eetutorial/examples directory and type ant teller. To create the database
325
326
TRANSACTIONS
tables, type ant createbankteller. A sample TellerApp.ear file is in the
j2eetutorial/examples/ears directory.
To demarcate a JTA transaction, you invoke the begin, commit, and rollback
methods of the javax.transaction.UserTransaction interface. The following code, taken from the TellerBean class, demonstrates the UserTransaction
methods. The begin and commit invocations delimit the updates to the database.
If the updates fail, the code invokes the rollback method and throws an EJBEx
ception.
public void withdrawCash(double amount) {
UserTransaction ut = context.getUserTransaction();
}
try {
ut.begin();
updateChecking(amount);
machineBalance = amount;
insertMachine(machineBalance);
ut.commit();
} catch (Exception ex) {
try {
ut.rollback();
} catch (SystemException syex) {
throw new EJBException
("Rollback failed: " + syex.getMessage());
}
throw new EJBException
("Transaction failed: " + ex.getMessage());
}
Returning without Committing
In a stateless session bean with bean-managed transactions, a business method
must commit or roll back a transaction before returning. However, a stateful session bean does not have this restriction.
In a stateful session bean with a JTA transaction, the association between the
bean instance and the transaction is retained across multiple client calls. Even if
each business method called by the client opens and closes the database connection, the association is retained until the instance completes the transaction.
In a stateful session bean with a JDBC transaction, the JDBC connection retains
the association between the bean instance and the transaction across multiple
calls. If the connection is closed, the association is not retained.
SUMMARY OF TRANSACTION OPTIONS FOR ENTERPRISE BEANS327
Methods Not Allowed in Bean-Managed
Transactions
Do not invoke the getRollbackOnly and setRollbackOnly methods of the
EJBContext interface in bean-managed transactions. These methods should be
used only in container-managed transactions. For bean-managed transactions,
invoke the getStatus and rollback methods of the UserTransaction interface.
Summary of Transaction Options for
Enterprise Beans
If you’re unsure about how to set up transactions in an enterprise bean, here’s a
tip: In the bean’s deployment descriptor, specify container-managed transactions. Then, set the Required transaction attribute for the entire bean. This
approach will work most of the time.
Table 14–2 lists the types of transactions that are allowed for the different types
of enterprise beans. An entity bean must use container-managed transactions.
With container-managed transactions, you specify the transaction attributes in
the deployment descriptor and you roll back a transaction with the setRoll
backOnly method of the EJBContext interface.
A session bean may have either container-managed or bean-managed transactions. There are two types of bean-managed transactions: JDBC and JTA transactions. You delimit JDBC transactions with the commit and rollback methods
of the Connection interface. To demarcate JTA transactions, you invoke the
begin, commit, and rollback methods of the UserTransaction interface.
In a session bean with bean-managed transactions, it is possible to mix JDBC
and JTA transactions. This practice is not recommended, however, because it
could make your code difficult to debug and maintain.
328
TRANSACTIONS
Like a session bean, a message-driven bean may have either container-managed
or bean-managed transactions.
Table 14–2 Allowed Transaction Types for Enterprise Beans
Bean-Managed
Bean Type
Container-Managed
JTA
JDBC
Entity
Y
N
N
Session
Y
Y
Y
Message-driven
Y
Y
Y
Transaction Timeouts
For container-managed transactions, you control the transaction timeout interval
by setting the value of the transaction.timeout property in the
default.properties file, which is in the config directory of your J2EE SDK
installation. For example, you would set the timeout value to 5 seconds as follows:
transaction.timeout=5
With this setting, if the transaction has not completed within 5 seconds, the EJB
container rolls it back.
When the J2EE SDK is first installed, the timeout value is set to 0:
transaction.timeout=0
If the value is 0, the transaction will not time out.
Only enterprise beans with container-managed transactions are affected by the
transaction.timeout property. For enterprise beans with bean-managed JTA
transactions, you invoke the setTransactionTimeout method of the User
Transaction interface.
ISOLATION LEVELS
Isolation Levels
Transactions not only ensure the full completion (or rollback) of the statements
that they enclose but also isolate the data modified by the statements. The isolation level describes the degree to which the data being updated is visible to other
transactions.
Suppose that a transaction in one program updates a customer’s phone number,
but before the transaction commits another program reads the same phone number. Will the second program read the updated and uncommitted phone number
or will it read the old one? The answer depends on the isolation level of the
transaction. If the transaction allows other programs to read uncommitted data,
performance may improve because the other programs don’t have to wait until
the transaction ends. But there’s a trade-off—if the transaction rolls back,
another program might read the wrong data.
You cannot modify the isolation level of entity beans with container-managed
persistence. These beans use the default isolation level of the DBMS, which is
usually READ_COMMITTED.
For entity beans with bean-managed persistence and for all session beans, you
can set the isolation level programmatically with the API provided by the underlying DBMS. A DBMS, for example, might allow you to permit uncommitted
reads by invoking the setTransactionIsolation method:
Connection con;
...
con.setTransactionIsolation(TRANSACTION_READ_UNCOMMITTED);
Do not change the isolation level in the middle of a transaction. Usually, such a
change causes the DBMS software to issue an implicit commit. Because the isolation levels offered by DBMS vendors may vary, you should check the DBMS
documentation for more information. Isolation levels are not standardized for the
J2EE platform.
Updating Multiple Databases
The J2EE transaction manager controls all enterprise bean transactions except
for bean-managed JDBC transactions. The J2EE transaction manager allows an
enterprise bean to update multiple databases within a transaction. The figures
that follow show two scenarios for updating multiple databases in a single transaction.
329
330
TRANSACTIONS
In Figure 14–2, the client invokes a business method in BeanA. The business
method begins a transaction, updates Database X, updates Database Y, and
invokes a business method in BeanB. The second business method updates
Database Z and returns control to the business method in BeanA, which commits the transaction. All three database updates occur in the same transaction.
Figure 14–2 Updating Multiple Databases
In Figure 14–3, the client calls a business method in BeanA, which begins a
transaction and updates Database X. Then, BeanA invokes a method in BeanB,
which resides in a remote J2EE server. The method in BeanB updates Database
Y. The transaction managers of the J2EE servers ensure that both databases are
updated in the same transaction.
TRANSACTIONS IN WEB COMPONENTS
Figure 14–3 Updating Multiple Databases across J2EE Servers
Transactions in Web Components
You may demarcate a transaction in a Web component with either the
java.sql.Connection or javax.transaction.UserTransaction interface.
These are the same interfaces that a session bean with bean-managed transactions may use. Transactions demarcated with the Connection interface are discussed in the section JDBC Transactions, page (324) and those with the
UserTransaction interface are discussed in the section JTA
Transactions, page (325). For an example of a Web component using transactions, see Accessing Databases, page (221).
331
332
TRANSACTIONS
15
Security
Eric Jendrock
T
he J2EE application programming model insulates developers from mechanism-specific implementation details of application security. J2EE provides this
insulation in a way that enhances the portability of applications, allowing them
to be deployed in diverse security environments.
Some of the material in this chapter assumes that you have an understanding of
basic security concepts. To learn more about these concepts, we highly recommend that you explore the Security trail in the Java Tutorial (see
http://java.sun.com/docs/books/tutorial/security1.2/index.html)
before you begin this chapter.
In This Chapter
Overview 334
Security Roles 335
Declaring and Linking Role References 335
Mapping Roles to J2EE Users and Groups 337
Web-Tier Security 337
Protecting Web Resources 337
Controlling Access to Web Resources 338
Authenticating Users of Web Resources 338
Using Programmatic Security in the Web Tier 340
Unprotected Web Resources 340
EJB-Tier Security 341
Declaring Method Permissions 341
Using Programmatic Security in the EJB Tier 341
Unprotected EJB-Tier Resources 342
333
334
SECURITY
Application Client-Tier Security 342
Specifying the Application Client’s Callback Handler 343
EIS-Tier Security 343
Configuring Sign-On 344
Container-Managed Sign-On 344
Component-Managed Sign-On 344
Configuring Resource Adapter Security 345
Propagating Security Identity 346
Configuring a Component’s Propagated Security Identity 347
Configuring Client Authentication 347
J2EE Users, Realms, and Groups 348
Managing J2EE Users and Groups 349
Setting Up a Server Certificate 350
Overview
The J2EE platform defines declarative contracts between those who develop and
assemble application components and those who configure applications in operational environments. In the context of application security, application providers are required to declare the security requirements of their applications in such
a way that these requirements can be satisfied during application configuration.
The declarative security mechanisms used in an application are expressed in a
declarative syntax in a document called a deployment descriptor. An application
deployer then employs container-specific tools to map the application requirements that are in a deployment descriptor to security mechanisms that are implemented by J2EE containers. The J2EE SDK provides this functionality with
deploytool.
Programmatic security refers to security decisions that are made by securityaware applications. Programmatic security is useful when declarative security
alone is not sufficient to express the security model of an application. For example, an application might make authorization decisions based on the time of day,
the parameters of a call, or the internal state of an enterprise bean or Web component. Another application might restrict access based on user information stored
in a database.
J2EE applications are made up of components that can be deployed into different
containers. These components are used to build a multitier enterprise application. The goal of the J2EE security architecture is to achieve end-to-end security
by securing each tier.
SECURITY ROLES
The tiers can contain both protected and unprotected resources. Often, you need
to protect resources to ensure that only authorized users have access. Authorization provides controlled access to protected resources. Authorization is based on
identification and authentication. Identification is a process that enables recognition of an entity by a system, and authentication is a process that verifies the
identity of a user, device, or other entity in a computer system, usually as a prerequisite to allowing access to resources in a system.
Authorization is not required to access unprotected resources. Because authorization is built upon authentication, authentication is also not needed to access
unprotected resources. Accessing a resource without authentication is referred to
as unauthenticated or anonymous access.
Security Roles
When you design an enterprise bean or Web component, you should always
think about the kinds of users who will access the component. For example, an
Account enterprise bean might be accessed by customers, bank tellers, and
branch managers. Each of these user categories is called a security role, an
abstract logical grouping of users that is defined by the person who assembles
the application. When an application is deployed, the deployer will map the roles
to security identities in the operational environment.
A J2EE group also represents a category of users, but it has a different scope
from a role. A J2EE group is designated for the entire J2EE server, whereas a
role covers only a specific application in a J2EE server.
To create a role for a J2EE application, you declare it for the EJB JAR file or for
the WAR file that is contained in the application. For example, you could use the
following procedure to create a role in deploytool.
1. Select the enterprise bean’s EJB JAR file or the Web component’s WAR
file.
2. In the Roles tabbed pane, click Add.
3. In the table, enter values for the Name and Description fields.
Declaring and Linking Role References
A security role reference allows an enterprise bean or Web component to reference an existing security role. A security role is an application-specific logical
grouping of users, classified by common traits such as customer profile or job
title. When an application is deployed, roles are mapped to security identities,
335
336
SECURITY
such as principals (identities assigned to users as a result of authentication) or
groups, in the operational environment. Based on this, a user with a certain security role has associated access rights to a J2EE application. The link is the actual
name of the security role that is being referenced.
During application assembly, the assembler creates security roles for the application and associates these roles with available security mechanisms. The assembler then resolves the security role references in individual servlets and JSPs by
linking them to roles defined for the application.
The security role reference defines a mapping between the name of a role that is
called from a Web component using isUserInRole(String name) (see Using
Programmatic Security in the Web Tier, page (340)) or from an enterprise bean
using isCallerInRole(String name) (see Using Programmatic Security in the
EJB Tier, page (341)) and the name of a security role that has been defined for
the application. For example, to map the security role reference cust to the security role with role name bankCustomer, you would do the following:
1. Select the Web component or enterprise bean.
2. Select the Security tab.
3. If the cust entry does not appear in the Role Names Referenced In Code
pane, click the Add button.
4. Enter the name of the security role reference cust in the Coded Name column.
5. From the drop-down menu in the Role Name column, select the security
role name bankCustomer that maps to the coded name.
If the security role name to which you want to map the security role reference is not listed in the Role Name column, click Edit Roles and add the
role (see Security Roles, page (335)).
6. Click on the folded paper icon to add a description for the cust role reference.
7. In the Description dialog box, enter a description.
8. Click OK to accept the description, or Cancel to cancel it.
In this example, isUserInRole("bankCustomer") and isUserInRole("cust")
will both return true for the methods indicated in the Method Permissions pane.
Because a coded name is linked to a role name, you can change the role name at
a later time without having to change the coded name. For example, if you were
to change the role name from bankCustomer to something else, you wouldn’t
WEB-TIER SECURITY
need to change the cust name in the code. However, you would need to relink
the cust coded name to the new role name.
Mapping Roles to J2EE Users and Groups
When you are developing a J2EE application, you should know the roles of your
users, but you probably won’t know exactly who the users will be. That’s taken
care of in the J2EE security architecture, because after your component has been
deployed, the administrator of the J2EE server will map the roles to the J2EE
users (or groups) of the default realm. In the Account bean example, the administrator might assign the user Sally to the Manager role, and the users Bob, Ted,
and Clara to the Teller role.
An administrator can map roles to J2EE users and groups by using the following
procedure in deploytool:
1.
2.
3.
4.
Select the J2EE application.
In the Security tab, select the appropriate role from the Role Name list.
Click Add.
In the Users dialog box, select the users and groups that should belong to
the role. (See Managing J2EE Users and Groups, page (349) for information about creating users and groups with deploytool.)
Web-Tier Security
The following sections address protecting resources and authenticating users in
the Web tier.
Protecting Web Resources
You can protect Web resources by specifying a security constraint. A security
constraint determines who is authorized to access a Web resource collection,
which is a list of URL patterns and HTTP methods that describe a set of
resources to be protected. Security constraints can be defined using deploytool,
as described in Controlling Access to Web Resources, page (338).
If you try to access a protected Web resource as an unauthenticated user, the Web
container will try to authenticate you. The container will only accept the request
after you have proven your identity to the container and have been granted permission to access the resource.
337
338
SECURITY
Controlling Access to Web Resources
Use the following procedure in deploytool to specify a security constraint to
control access to a Web resource.
1.
2.
3.
4.
Select the WAR containing the Web resource.
Select the Security tab.
Click the Add button in the Security Constraints section of the screen.
Click the Edit button adjacent to the Web Resource Collection field to add
a Web resource collection to the security constraint. The Web resource
collection describes a URL pattern and HTTP method pair that refer to the
resources that need to be protected.
5. Click the Edit button adjacent to the Authorized Roles field to add one or
more roles to the security constraint. You are specifying the set of roles
that are allowed to access the Web resource collection.
Authenticating Users of Web Resources
When you try to access a protected Web resource, the Web container activates
the authentication mechanism that has been configured for that resource. You
can configure the following authentication mechanisms for a Web resource:
• HTTP basic authentication
• Form-based authentication
• Client-certificate authentication
Basic Authentication
If you specify HTTP basic authentication, the Web server will authenticate a
user by using the user name and password obtained from the Web client.
Form-Based Authentication
If you specify form-based authentication, you can customize the login screen
and error pages that are presented to the end user by an HTTP browser.
Neither form-based authentication nor HTTP basic authentication is particularly
secure. In form-based authentication, the content of the user dialog box is sent as
plain text, and the target server is not authenticated. Basic authentication sends
user names and passwords over the Internet as text that is uuencoded, but not
encrypted. This form of authentication, which uses Base64 encoding, can expose
your user names and passwords unless all connections are over SSL. If someone
WEB-TIER SECURITY
can intercept the transmission, the username and password information can easily be decoded.
Client-Certificate Authentication
Client-certificate authentication is a more secure method of authentication than
either basic or form-based authentication. It uses HTTP over SSL (HTTPS), in
which the server and, optionally, the client authenticate each other with Public
Key Certificates. Secure Sockets Layer (SSL) provides data encryption, server
authentication, message integrity, and optional client authentication for a TCP/IP
connection. You can think of a public key certificate as the digital equivalent of a
passport. It is issued by a trusted organization, which is called a certificate
authority (CA), and provides identification for the bearer. If you specify clientcertificate authentication, the Web server will authenticate the client using an
X.509 certificate, a public key certificate that conforms to a standard that is
defined by X.509 Public Key Infrastructure (PKI).
Configuring Web Resources’ Authentication Mechanism
To configure the authentication mechanism that the Web resources in a WAR
will use:
1. Select the WAR containing the Web resource.
2. Select the Security tab.
3. Choose one of the following authentication mechanisms from the User
Authentication Method pull-down menu:
• None
• Basic
• Client-Certificate
• Form Based
a. If you choose form-based authentication, you must select Settings and
fill in the Realm Name, Login Page, and Error Page fields in the Settings dialog. The error page is displayed when the user cannot be
logged in.
b. If you choose basic authentication, you must select Settings and enter
Default in the Realm name field in the settings dialog box.
339
340
SECURITY
Using SSL to Enhance the Confidentiality of HTTP Basic and
Form-Based Authentication
Passwords are not protected for confidentiality with HTTP basic or form-based
authentication. To overcome this limitation, you can run these authentication
protocols over an SSL-protected session and ensure that all message content is
protected for confidentiality.
To configure HTTP basic or form-based authentication over SSL:
1. Select the Web component. The Web Component inspector will be displayed.
2. From the Security tab, make sure that Basic or Form Based has been
selected in the User Authentication Method pull-down menu.
3. Click on the Add button in the Security Constraint section.
4. Click on the security constraint that was added.
5. Select CONFIDENTIAL in the Network Security Requirement pull-down
menu.
Using Programmatic Security in the Web Tier
Programmatic security is used by security-aware applications when declarative
security alone is not sufficient to express the security model of the application.
Programmatic security consists of the following methods of the HttpServle
tRequest interface:
• getRemoteUser
• isUserInRole
• getUserPrincipal
You can use the getRemoteUser method to determine the user name with which
the client authenticated. The isUserInRole method is used to determine if a user
is in a specific security role. The getUserPrincipal method returns a
java.security.Principal object.
These APIs allow servlets to make business logic decisions based on the logical
role of the remote user. They also allow the servlet to determine the principal
name of the current user.
Unprotected Web Resources
Many applications feature unprotected Web content, which any caller can access
without authentication. In the Web tier, unrestricted access is provided simply by
not configuring an authentication mechanism.
EJB-TIER SECURITY
EJB-Tier Security
The following sections describe declarative and programmatic security mechanisms that can be used to protect resources in the EJB tier. The protected
resources include methods of enterprise beans that are called from the application clients, Web components, or other enterprise beans.
You can protect EJB-tier resources by doing the following:
• Declaring method permissions
• Mapping roles to J2EE users and groups
Declaring Method Permissions
After you’ve defined the roles, you can define the method permissions of an
enterprise bean. Method permissions indicate which roles are allowed to invoke
which methods.
Use the following procedure in deploytool to specify method permissions by
mapping roles to methods.
1. Select the enterprise bean.
2. Select the Security tab.
3. In the Method Permissions table, select Sel Roles in the Availability column.
4. Then select a role’s checkbox if that role should be allowed to invoke a
method.
Using Programmatic Security in the EJB Tier
Programmatic security in the EJB tier consists of the getCallerPrincipal and
the isCallerInRole methods. You can use the getCallerPrincipal method to
determine the caller of the enterprise bean, and the isCallerInRole method to
determine the caller’s role.
The getCallerPrincipal method of the EJBContext interface returns the
java.security.Principal object that identifies the caller of the enterprise
bean. (In this case, a principal is the same as a user.) In the following example,
341
342
SECURITY
the getUser method of an enterprise bean returns the name of the J2EE user that
invoked it:
public String getUser() {
return context.getCallerPrincipal().getName();
}
You can determine whether an enterprise bean’s caller belongs to a particular
role by invoking the isCallerInRole method:
boolean result = context.isCallerInRole("Customer");
Unprotected EJB-Tier Resources
By default, the J2EE SDK assigns the ANYONE role to a method. The guest user,
which is anonymous and unauthenticated, belongs to the ANYONE role. Therefore,
if you do not map the roles, any user may invoke the methods of an enterprise
bean.
Application Client-Tier Security
Authentication requirements for J2EE application clients are the same as the
requirements for other J2EE components. Access to protected resources in either
the EJB tier or the Web tier requires user authentication, whereas access to
unprotected resources does not.
An application client can use the Java Authentication and Authorization Service
(JAAS) for authentication. JAAS implements a Java version of the standard
Pluggable Authentication Module (PAM) framework, which permits applications to remain independent from underlying authentication technologies. You
can plug new or updated authentication technologies under an application without making any modifications to the application itself. Applications enable the
authentication process by instantiating a LoginContext object, which, in turn,
references a configuration to determine the authentication technologies or login
modules that will be used to perform the authentication.
A typical login module could prompt for and verify a user name and password.
Other modules could read and verify a voice or fingerprint sample.
In some cases, a login module needs to communicate with the user to obtain
authentication information. Login modules use a javax.security.auth.call
back.CallbackHandler for this purpose. Applications implement the Call
EIS-TIER SECURITY
backHandler interface and pass it to the login context, which forwards it directly
to the underlying login modules. A login module uses the callback handler both
to gather input (such as a password or smart card PIN number) from users or to
supply information (such as status information) to users. By allowing the application to specify the callback handler, an underlying login module can remain
independent of the different ways applications interact with users.
For example, the implementation of a callback handler for a GUI application
might display a window to solicit user input. Or, the implementation of a callback handler for a command line tool might simply prompt the user for input
directly from the command line.
The login module passes an array of appropriate callbacks to the callback handler’s handle method (for example, a NameCallback for the user name and a
PasswordCallback for the password), and the callback handler performs the
requested user interaction and sets appropriate values in the callbacks. For example, to process a NameCallback, the CallbackHandler may prompt for a name,
retrieve the value from the user, and call the setName method of the NameCall
back to store the name.
Specifying the Application Client’s Callback
Handler
Use the following procedure in deploytool to specify a callback handler for an
application client.
1. Select the application client JAR.
2. Select the General tab.
3. From the CallbackHandler Class menu, select the CallbackHandler class
that will be used as an interface to gather user authentication data.
EIS-Tier Security
In the EIS tier, an application component requests a connection to an EIS
resource. As part of this connection, the EIS may require a sign-on to the
resource. The application component provider has two choices for the design of
the EIS sign-on:
• With the container-managed sign-on approach, the application component
lets the container take the responsibility of configuring and managing the
343
344
SECURITY
EIS sign-on. The container determines the user name and password for
establishing a connection to an EIS instance.
• With the component-managed sign-on approach, the application component code manages EIS sign-on by including code that performs the signon process to an EIS.
The component provider can use deploytool to choose the type of sign-on.
Configuring Sign-On
Use the following procedure in deploytool to configure the type of sign-on.
1.
2.
3.
4.
Select the component.
Select the Resource Refs tab.
Click Add.
In the Authentication combo box, select either Container for containermanaged sign-on or Application for component-managed sign-on.
Container-Managed Sign-On
With container-managed sign-on, an application component does not have to
pass any security information for signing on to the resource to the getConnec
tion() method. The security information is supplied by the container, as shown
in the following example.
// Business method in an application component
Context initctx = new InitialContext();
// perform JNDI lookup to obtain a connection factory
javax.resource.cci.ConnectionFactory cxf =
(javax.resource.cci.ConnectionFactory)initctx.lookup(
“java:comp/env/eis/MainframeCxFactory”);
// Invoke factory to obtain a connection. The security
// information is not passed in the getConnection method
javax.resource.cci.Connection cx = cxf.getConnection();
...
Component-Managed Sign-On
With component-managed sign-on, an application component is responsible for
passing the security information that is needed for signing on to the resource to
EIS-TIER SECURITY
the getConnection() method. Security information could be a user name and
password, for example, as shown in the following example.
// Method in an application component
Context initctx = new InitialContext();
// perform JNDI lookup to obtain a connection factory
javax.resource.cci.ConnectionFactory cxf =
(javax.resource.cci.ConnectionFactory)initctx.lookup(
“java:comp/env/eis/MainframeCxFactory”);
// Invoke factory to obtain a connection
com.myeis.ConnectionSpecImpl properties = //..
// get a new ConnectionSpec
properties.setUserName(“...”);
properties.setPassword(“...”);
javax.resource.cci.Connection cx =
cxf.getConnection(properties);
...
Configuring Resource Adapter Security
In addition to configuring the sign-on, you must also configure the resource
adapter security. To add security to a resource adapter, complete the following
steps:
1. Select the resource adapter RAR (Resource Adapter Archive).
2. Select the Security tab. In the Authentication Mechanisms pane, select the
authentication mechanisms that this resource adapter supports:
• Password: A user and password is required to connect to an EIS.
• Kerberos Version 5.0: The resource adapter supports the Kerberos
authentication mechanism. See RFC-1510, The Kerberos Network
Authentication Service (V5), for details. This specification can be
found at http://www.ietf.org/rfc/rfc1510.txt.
You can select no mechanism, one mechanism, or multiple mechanisms.
If you do not select a mechanism, no security authentication will be supported.
3. Select Reauthentication Supported if the resource adapter supports performing reauthentication on an existing physical connection. Reauthentication will be performed when an application server calls the
345
346
SECURITY
getConnection() method with a security context that is different from
the one that was used to establish the connection.
4. In the Security Permissions pane, click the Add button to add a security
permission that your resource adapter needs to access system resources in
your operational environment. Specify only permissions that are not
included in the default set, which are listed in Table 2 of Section 11.2 in
the J2EE™ Connector Architecture Specification 1.0.
5. For each security permission, click the rightmost column labeled with a
folded paper icon to enter a description for the permission.
To delete a security permission, select the permission in the table and click
Delete.
Propagating Security Identity
When you deploy an enterprise bean or Web component, you can specify the
security identity that will be propagated (illustrated in Figure 15–1) to enterprise
beans invoked from within that component.
Figure 15–1 Security Identity Propagation
You can choose one of the following propagation styles:
• The caller identity of the intermediate component is propagated to the target enterprise bean. This technique is used when the target container trusts
the intermediate container.
PROPAGATING SECURITY IDENTITY
• A specific identity is propagated to the target enterprise bean. This technique is used when the target container expects access via a specific identity.
Configuring a Component’s Propagated Security
Identity
You use deploytool to select the type of security identity that is propagated
from an enterprise bean or Web component.
To configure an enterprise bean or Web component to propagate the caller identity with which the component is running:
1. Select the component.
2. Select the Security tab.
3. In the Security Identity pane, select the Use Caller ID radio button.
To configure a component to propagate a security identity other than that with
which the component is running:
1.
2.
3.
4.
5.
Select the component.
Select the Security tab.
In the Security Identity pane, select the Run As Specified Role option.
Use the drop-down menu to select the role with which to run.
After you select the role, you can select a user from that role. To do this,
select Deployment Settings.
6. From Run As Specified User, select the user name that the client will use
to invoke the enterprise bean’s methods.
7. Click OK.
Configuring Client Authentication
If an application component in an application client container accesses a protected method on a bean, use client authentication.
In deploytool, use the following procedure to configure client authentication:
1. Select the target enterprise bean.
2. Select the Security tab.
3. Select Deployment Settings to display the Security Deployment Settings
dialog box.
347
348
SECURITY
4. Select the SSL Required checkbox to enable SSL.
5. In the Client Authentication pane, select Certificate as the method by
which the server expects the client to authenticate itself to the server.
6. Click OK.
Trust Between Containers
When an enterprise bean is designed so that either the original caller identity or a
designated identity is used to call a target bean, the target bean will receive the
propagated identity only; it will not receive any authentication data.
There is no way for the target container to authenticate the propagated security
identity. However, since the security identity is used in authorization checks (for
example, method permissions or with the isCallerInRole() method), it is
vitally important that the security identity be authentic. Since there is no authentication data available to authenticate the propagated identity, the target must
trust that the calling container has propagated an authenticated security identity.
By default, the J2EE SDK server is configured to trust identities that are propagated from different containers. Therefore, there are no special steps that you
need to take to set up a trust relationship.
J2EE Users, Realms, and Groups
A J2EE user is similar to an operating system user. Typically, both types of users
represent people. However, these two types of users are not the same. The J2EE
authentication service has no knowledge of the user name and password you provide when you log on to the operating system. The J2EE authentication service
is not connected to the security mechanism of the operating system. The two
security services manage users that belong to different realms.
A realm is a collection of users that are controlled by the same authentication
policy. The J2EE authentication service governs users in two realms: certificate
and default.
Certificates are used with the HTTPS protocol to authenticate Web browser clients. To verify the identity of a user in the certificate realm, the authentication
service verifies an X.509 certificate. For step-by-step instructions, see Setting
Up a Server Certificate, page (350). The common name field of the X.509 certificate is used as the principal name.
J2EE USERS, REALMS, AND GROUPS
In most cases, the J2EE authentication service verifies user identity by checking
the default realm. This realm is used for the authentication of all clients except
for Web browser clients that use the HTTPS protocol and certificates.
A J2EE user of the default realm can belong to a J2EE group. (A user in the certificate realm cannot.) A J2EE group is a category of users classified by common
traits, such as job title or customer profile. For example, most customers of an ecommerce application might belong to the CUSTOMER group, but the big spenders
would belong to the PREFERRED group. Categorizing users into groups makes it
easier to control the access of large numbers of users. The section EJB-Tier
Security, page (341) explains how to control user access to enterprise beans.
Managing J2EE Users and Groups
This section shows how to use deploytool to do the following:
•
•
•
•
•
Display all users in the default realm
Add a user to the default realm
Add a user to the certificate realm
Remove a user
Add a group to the default realm (you cannot add a group to the certificate
realm)
• Remove a group from the default realm
Use the following procedure to display all users in the default or certificate
realm.
1. Select the server to which you want to add users or groups, or both.
2. Select Tools→Server Configuration to display the Configuration Installation screen.
3. Under J2EE Server in the tree view, select Users.
4. Select the realm (Default or Certificate).
Use the following procedure to add a user to the default realm.
1. Click Add User.
2. Enter a user name and a password in the appropriate fields.
3. In the Group Membership pane, select the group (from Available groups)
to which the user you are adding will belong. To select multiple groups,
repeat this step.
4. Click Add to move your selection(s) to Groups.
349
350
SECURITY
5. Click OK when done.
Use the following procedure to add a new group to the default realm.
1.
2.
3.
4.
Click Edit Groups.
From the Groups window, click Add.
Select the line you just added and enter the name of the group to add.
Click OK when done.
Use the following procedure to remove a group from the default realm.
1.
2.
3.
4.
5.
Click Edit Groups.
From the Groups window, select the group to remove.
Click Delete.
Click Yes when prompted.
Click OK when done.
Use the following procedure to add a new user to the certificate realm.
1.
2.
3.
4.
5.
Select the Certificate realm.
Click Add User.
Select the directory where the certificate is located.
Select the certificate file name.
Click OK when done.
Setting Up a Server Certificate
Certificates are used with the HTTPS protocol to authenticate Web clients. The
HTTPS service of the J2EE server will not run unless a server certificate has
been installed. Use the following procedure to set up a J2EE server certificate.
1. Generate a key pair and a self-signed certificate.
The keytool utility enables you to create the certificate. The keytool
utility that ships with the J2EE SDK has the same syntax as the one that
ships with the J2SE software. However, the J2EE SDK version programmatically adds a Java Cryptographic Extension provider that has implementations of RSA algorithms. This provider enables you to import RSAsigned certificates.
SETTING UP A SERVER CERTIFICATE
To generate the certificate, run the keytool utility as follows, substituting
<certificate.alias> with the alias of your certificate and <keystore.
filename> with the name of your keystore file:
keytool genkey keyalg RSA alias <certificate.alias>
keystore <keystore.filename>
2. The keytool utility prompts you for the following information:
a. Keystore password: Enter a password. (You may want to use
“changeit” to be consistent with the default password of the J2EE
SDK keystore.)
b. First and last name: Enter the fully qualified name of your server. This
fully-qualified name includes the host name and the domain name.
c. Organizational unit: Enter the appropriate value.
d. Organization: Enter the appropriate value.
e. City or locality: Enter the appropriate value.
f. State or province: Enter the unabbreviated name.
g. Two-letter country code: For the USA, the two-letter country code is
US.
h. Key password for alias: Do not enter a password. Press the Return key.
3. Import the certificate.
If your certificate will be signed by a CA other than Verisign, you must
import the CA certificate. Otherwise, you may skip this step. (Even if
your certificate will be signed by Verisign Test CA, you must import it.)
To import the certificate, perform these tasks:
a. Request the CA certificate from your CA. Store the certificate in a file.
b. To install the CA certificate in the Java 2 Platform, Standard Edition,
run the keytool utility as follows. (You must have the required permissions to modify the $JAVA_HOME/jre/lib/security/cacerts file.)
keytool import trustcacerts alias <ca.cert.alias>
file <ca.cert.filename>
4. If you want to have your certificate digitally signed by a CA, do the following:
a. Generate a Certificate Signing Request (CSR).
351
352
SECURITY
keytool certreq sigalg MD5withRSA alias <cert.alias>
file <csr.filename>
b. Send the contents of the <csr.filename> for signing. If you are using
Verisign CA, go to http://digitalid.verisign.com/. Verisign will
send the signed certificate via e-mail. Store this certificate in a file.
c. Import the signed certificate that you received in email into the server:
keytool import alias <cert.alias> file
<signed.cert.file>
16
Resource
Connections
Dale Green
BOTH enterprise beans and Web components can access a wide variety of
resources, including databases, mail sessions, Java™ Message Service objects,
and URLs. The J2EE™ platform provides mechanisms that allow you to access
all of these resources in a similar manner. This chapter describes how to get connections to several types of resources. Although the code samples in this chapter
are from enterprise beans, they will also work in Web components.
In This Chapter
JNDI Names and Resource References 353
deploytool Tips for Resource References 354
Database Connections for Enterprise Beans 356
Coded Connections 357
Connection Pooling 359
Mail Session Connections 359
Running the ConfirmerEJB Example 361
URL Connections 362
Running the HTMLReaderEJB Example 363
JNDI Names and Resource References
First, let’s define some terms.
353
354
RESOURCE CONNECTIONS
JNDI is the acronym for the Java Naming and Directory Interface API. J2EE
components locate objects by invoking the JNDI lookup method.
A JNDI name is a people-friendly name for an object. These names are bound to
their objects by the naming and directory service that is provided by the J2EE
server. Because J2EE components access this service through the JNDI API, we
usually refer to an object’s people-friendly name as its JNDI name. The JNDI
name of the Cloudscape database is jdbc/Cloudscape. When it starts up, the
J2EE server reads information from a configuration file and automatically adds
JNDI database names such as jdbc/Cloudscape to the name space.
A connection factory is an object that produces connection objects that enable a
J2EE component to access a resource. The connection factory for a database is a
javax.sql.DataSource object, which creates a java.sql.Connection object.
A resource reference is an element in a deployment descriptor that identifies the
component’s coded name for the resource. More specifically, the coded name
references a connection factory for the resource. In the example in the following
section, the resource reference name is jdbc/SavingsAccountDB .
The JNDI name of a resource and the name of the resource reference are not the
same. This approach to naming requires that you map the two names before
deployment, but it also decouples components from resources. Because of this
decoupling, if at a later time the component needs to access a different resource,
you don’t have to change the name in the code. This flexibility also makes it easier for you to assemble J2EE applications from preexisting components.
deploytool Tips for Resource References
The instructions that follow refer to the entity bean described in the section The
SavingsAccountEJB Example, page (84). The SavingsAccountEJB code is in
the j2eetutorial/examples/src/ejb/savingsaccount directory. A sample
SavingsAccountApp.ear file is in the j2eetutorial/examples/ears directory.
Specifying a Resource Reference
1.
2.
3.
4.
In deploytool, select SavingsAccountEJB from the tree.
Select the Resource Refs tab.
Click Add.
In the Coded Name field, enter jdbc/SavingsAccountDB.
The SavingsAccountBean code refers to the database as follows:
private String dbName = "java:comp/env/jdbc/SavingsAccountDB";
JNDI NAMES AND RESOURCE REFERENCES
The java:comp/env prefix is the name of the JNDI context for the component. The jdbc/SavingsAccountDB string is the JNDI name for the
resource reference. The JNDI names for JDBC DataSource objects are
stored in the java:comp/env/jdbc subcontext.
5. In the Type combo box, select javax.sql.DataSource. A DataSource
object is a factory for database connections.
6. In the Authentication combo box, select Container.
7. If you want other enterprise beans to share the connections acquired from
the DataSource, select the Sharable checkbox.
If the preceding steps are followed, the Resource Refs tab will appear as shown
in Figure 16–1.
Figure 16–1 Resource Refs Tabbed Pane of SavingsAccountEJB
Mapping a Resource Reference to a JNDI Name
1. Select the J2EE application from the tree.
355
356
RESOURCE CONNECTIONS
2. Select the JNDI Names tab.
3. In the References table, select the row containing the resource reference.
For the SavingsAccountEJB example, the resource reference is
jdbc/SavingsAccountDB, the name you entered in the Coded Name field
of the Resource Refs tab.
4. In the row you just selected, enter the JNDI name. For the SavingsAc
countEJB example, you would enter jdbc/Cloudscape in the JNDI Name
field.
The JNDI Names tab for SavingsAccountApp is shown in Figure 16–2.
Figure 16–2 JNDI Names Tab of SavingsAccountApp
Database Connections for Enterprise Beans
The persistence type of an enterprise bean determines whether or not you code
the connection routine. You must code the connection for enterprise beans that
access a database and do not have container-managed persistence. Such beans
DATABASE CONNECTIONS FOR ENTERPRISE BEANS
include entity beans with bean-managed persistence and session beans. For
entity beans with container-managed persistence, deploytool generates the connection routines for you.
Coded Connections
How to Connect
The code examples in this section are from the SavingsAccountBean class,
which connects to the database via the following steps.
1. Specify the database name.
private String dbName = "java:comp/env/jdbc/SavingsAccountDB";
2. Obtain the DataSource associated with the logical name.
InitialContext ic = new InitialContext();
DataSource ds = (DataSource) ic.lookup(dbName);
3. Get the Connection from the DataSource.
Connection con =
ds.getConnection();
When to Connect
When coding an enterprise bean, you must decide how long it will retain the
connection. Generally you have two choices: either hold the connection for the
lifetime of the bean, or hold it only during each database call. Your choice determines the method (or methods) in which your bean connects to a database.
Long-Term Connections
You can design an enterprise bean that holds a database connection for its entire
lifetime. Because the bean connects and disconnects just once, its code is slightly
easier to write. But there’s a trade-off—other components cannot acquire the
connection. Session and entity beans issue the lifelong connections in different
methods.
Session Beans
The EJB™ container invokes the ejbCreate method at the beginning of a session bean’s life cycle and invokes the ejbRemove method at the end. To retain a
connection for the lifetime of a session bean, you connect to the database in ejb
Create and disconnect in ejbRemove. If the session bean is stateful, you must
357
358
RESOURCE CONNECTIONS
also connect in ejbActivate and disconnect in ejbPassivate. A stateful session bean requires these additional calls because the EJB container may passivate the bean during its lifetime. During passivation, a stateful session bean is
saved in secondary storage, but a database connection cannot be saved in this
manner. Because a stateless session bean cannot be passivated, it does not
require the additional calls in ejbActivate and ejbPassivate. For more information on activation and passivation, see The Life Cycle of a Stateful Session
Bean, page (64). For an example of a stateful session bean with a long-term connection, see the TellerBean.java code in the j2eetutorial/exam
ples/ejb/teller directory.
Entity Beans with Container-Managed Persistence
After instantiating an entity bean and moving it to the pooled stage, the EJB container invokes the setEntityContext method. Conversely, the EJB container
invokes the unsetEntityContext method when the entity bean leaves the
pooled stage and becomes eligible for garbage collection. To retain a database
connection for its entire life span, an entity bean connects in the setEntityCon
text method and disconnects in the unsetEntityContext method. To see a diagram of the life cycle, see Figure 3–5. For an example of an entity bean with a
long-term connection, see the SavingsAccountBean.java code in the
j2eetutorial/examples/ejb/savingsaccount directory.
Short-term Connections
Briefly held connections allow many components to share the same connection.
Because the EJB container manages a pool of database connections, enterprise
beans can quickly obtain and release the connections. For example, a business
method might connect to a database, insert a row, and then disconnect.
In a session bean, a business method that connects to a database should be transactional. The transaction will help maintain data integrity.
deploytool Tips for Specifying Database Users and Passwords
The instructions in this section do not apply to entity beans with container-managed persistence. For those entity beans, see the instructions in Specifying the
Database JNDI Name, User Name, and Password, page (150).
To connect to the Cloudscape database bundled with this release, you do not
specify a database user name and password; authentication is performed by a
separate service. For more information about authentication, see Chapter 15.
However, some types of databases do require a user name and password during
connection. For these databases, if the getConnection call has no parameters,
MAIL SESSION CONNECTIONS
you must specify the database user name and password with deploytool. To
specify these values, perform these steps:
1. Select the enterprise bean in the tree view.
2. Select the Resource Refs tab.
3. Select the appropriate row in the table labeled, Resource Factories Referenced in Code, and enter the database user name and password in the fields
at the bottom.
If you wish to obtain the database user name and password programmatically,
you do not need to specify them with deploytool. In this case, you include the
database user name and password in the arguments of the getConnection
method:
con = dataSource.getConnection(dbUser, dbPassword);
Connection Pooling
The EJB container maintains the pool of database connections. This pool is
transparent to the enterprise beans. When an enterprise bean requests a connection, the container fetches one from the pool and assigns it to the bean. Because
the time-consuming connection has already been made, the bean quickly gets a
connection. The bean may release the connection after each database call, since
it can rapidly get another connection. Because such a bean holds the connection
for a short time, the same connection can be shared sequentially by many beans.
Mail Session Connections
If you’ve ever ordered a product from a Web site, you’ve probably received an email confirming your order. The ConfirmerBean class demonstrates how to send
e-mail from an enterprise bean.
The source code for this example is in the j2eetutorial/exam
ples/src/ejb/confirmer directory. To compile the code, go to the
j2eetutorial/examples directory and type ant confirmer. A sample Con
firmerApp.ear file is in the j2eetutorial/examples/ears directory.
In the sendNotice method of the ConfirmerBean class, the lookup method
returns a Session object, which represents a mail session. Like a database connection, a mail session is a resource. As with any resource, you must link the
coded name (TheMailSession) with a JNDI name. Using the Session object as
an argument, the sendNotice method creates an empty Message object. After
359
360
RESOURCE CONNECTIONS
calling several set methods on the Message object, sendNotice invokes the
send method of the Transport class to send the message on its way. The source
code for the sendNotice method follows.
public void sendNotice(String recipient) {
try {
Context initial = new InitialContext();
Session session =
(Session) initial.lookup(
"java:comp/env/TheMailSession");
Message msg = new MimeMessage(session);
msg.setFrom();
msg.setRecipients(Message.RecipientType.TO,
InternetAddress.parse(recipient, false));
msg.setSubject("Test Message from ConfirmerBean");
DateFormat dateFormatter =
DateFormat.getDateTimeInstance(
DateFormat.LONG, DateFormat.SHORT);
Date timeStamp = new Date();
String messageText = "Thank you for your order." + '\n' +
"We received your order on " +
dateFormatter.format(timeStamp) + ".";
msg.setText(messageText);
msg.setHeader("XMailer", mailer);
msg.setSentDate(timeStamp);
Transport.send(msg);
}
} catch(Exception e) {
throw new EJBException(e.getMessage());
}
MAIL SESSION CONNECTIONS
Running the ConfirmerEJB Example
Deploying the Application
1. In deploytool, open the j2eetutorial/examples/ears/Confirmer
App.ear file (File→Open).
2. In the Resource Refs tab of the bean, specify the resource reference for the
mail session with the values shown in Table 16–1.
Table 16–1 Resource Refs for the ConfirmerEJB Example
Field Name
Value
Coded Name
TheMailSession
Type
javax.mail.Session
Authentication
Application
From
(your email address)
Host
(mail server host)
User Name
(your UNIX or Windows user name)
3. Deploy the SavingsAccountApp application (Tools→Deploy). In the
Introduction dialog box, make sure that you select the Return Client JAR
checkbox.
Running the Client
1. In a terminal window, go to the j2eetutorial/examples/ears directory.
2. Set the APPCPATH environment variable to ConfirmerAppClient.jar.
3. Type the following command on a single line, replacing <recipient>
with the e-mail address of the person who will receive the message.
runclient client ConfirmerApp.ear name ConfirmerClient
textauth <recipient>
4. At the login prompts, enter guest for the user name and guest123 for the
password.
361
362
RESOURCE CONNECTIONS
Troubleshooting
If the application cannot connect to the mail server it will generate this exception:
javax.mail.MessagingException: Could not connect to SMTP host
To fix this problem, make sure that the mail server is running and that you’ve
entered the correct name for the mail server host in the Resource Refs tab of the
deploytool.
URL Connections
A Uniform Resource Locator (URL) specifies the location of a resource on the
Web. The HTMLReaderBean class shows how to connect to a URL from within an
enterprise bean.
The source code for this example is in the j2eetutorial/exam
ples/src/ejb/htmlreader directory. To compile the code, go to the
j2eetutorial/examples directory and type ant htmlreader. A sample HTML
ReaderApp.ear file is in the j2eetutorial/examples/ears directory.
The getContents method of the HTMLReaderBean class returns a String that
contains the contents of an HTML file. This method looks up the java.net.URL
object associated with a coded name (url/MyURL), opens a connection to it, and
then reads its contents from an InputStream. Before deploying the application,
you must map the coded name (url/MyURL) to a JNDI name (a URL string).
Here is the source code for the getContents method.
public StringBuffer getContents() throws HTTPResponseException
{
Context context;
URL url;
StringBuffer buffer;
String line;
int responseCode;
HttpURLConnection connection;
InputStream input;
DataInputStream dataInput;
try {
context = new InitialContext();
url = (URL)context.lookup("java:comp/env/url/MyURL");
URL CONNECTIONS
connection = (HttpURLConnection)url.openConnection();
responseCode = connection.getResponseCode();
} catch (Exception ex) {
throw new EJBException(ex.getMessage());
}
if (responseCode != HttpURLConnection.HTTP_OK) {
throw new HTTPResponseException("HTTP response code: " +
String.valueOf(responseCode));
}
try {
buffer = new StringBuffer();
input = connection.getInputStream();
dataInput = new DataInputStream(input);
while ((line = dataInput.readLine()) != null) {
buffer.append(line);
buffer.append('\n’);
}
} catch (Exception ex) {
throw new EJBException(ex.getMessage());
}
}
return buffer;
Running the HTMLReaderEJB Example
Deploying the Application
1. In deploytool, open the j2eetutorial/examples/ears/HTMLReader
App.ear file (File→Open).
2. Deploy the HTMLReaderApp application (Tools→Deploy). In the Introduction dialog box, make sure that you select the Return Client JAR checkbox.
Running the Client
1. In a terminal window, go to the j2eetutorial/examples/ears directory.
2. Set the APPCPATH environment variable to HTMLReaderAppClient.jar.
3. Type the following command on a single line:
runclient client HTMLReaderApp.ear name
HTMLReaderClient textauth
363
364
RESOURCE CONNECTIONS
4. At the login prompts, enter guest for the user name and guest123 for the
password.
5. The client displays the contents of the index.html file that resides in the
public_html directory of your J2EE SDK installation.
17
J2EE™ Connector
Architecture
Dale Green and Beth Stearns
THE other chapters in this book are intended for business application developers, but this chapter is for advanced users such as system integrators and tools
developers. The examples in this chapter demonstrate the J2EE™ Connector
architecture by accessing relational databases. However, this technology is not a
substitute for the JDBC™ API. Business application developers should continue
to use the JDBC API to access relational databases.
The J2EE Connector architecture enables J2EE components such as enterprise
beans to interact with enterprise information systems (EISs). EIS software
includes various types of systems: enterprise resource planning (ERP), mainframe transaction processing, and non-relational databases, among others. The
J2EE Connector architecture simplifies the integration of diverse EISs. Each EIS
requires just one implementation of the J2EE Connector architecture. Because an
implementation adheres to the J2EE Connector Specification, it is portable
across all compliant J2EE servers.
In This Chapter
About Resource Adapters 366
Resource Adapter Contracts 366
Administering Resource Adapters 368
365
366
J2EE™ CONNECTOR ARCHITECTURE
The Black Box Resource Adapters 369
Transaction Levels 369
Properties 370
Configuring JDBC™ Drivers 371
Resource Adapter Tutorial 372
Setting Up 372
Deploying the Resource Adapter 372
Testing the Resource Adapter 373
Common Client Interface 375
Overview of the CCI 375
Programming with the CCI 377
Writing a CCI Client 386
CCI Tutorial 386
About Resource Adapters
A resource adapter is a J2EE component that implements the J2EE Connector
architecture for a specific EIS. It is through the resource adapter that a J2EE
application communicates with an EIS (see Figure 17–1).
Stored in a Resource Adapter Archive (RAR) file, a resource adapter may be
deployed on any J2EE server, much like the EAR file of a J2EE application. A
RAR file may be contained in an EAR file or it may exist as a separate file.
A resource adapter is analogous to a JDBC driver. Both provide a standard API
through which an application can access a resource that is outside the J2EE
server. For a resource adapter, the outside resource is an EIS; for a JDBC driver,
it is a DBMS. Resource adapters and JDBC drivers are rarely created by application developers. In most cases, both types of software are built by vendors who
sell products such as tools, servers, or integration software.
Resource Adapter Contracts
Figure 17–1 shows the two types of contracts implemented by a resource
adapter. The application contract defines the API through which a J2EE component such as an enterprise bean accesses the EIS. This API is the only view that
the component has of the EIS. The resource adapter itself and its system contracts are transparent to the J2EE component.
The system contracts link the resource adapter to important services—connection, transaction, and security—that are managed by the J2EE server.
ABOUT RESOURCE ADAPTERS
The connection management contract supports connection pooling, a technique
that enhances application performance and scalability. Connection pooling is
transparent to the application, which simply obtains a connection to the EIS.
Because of the transaction management contract, a call to the EIS may be
enclosed in an XA transaction. XA transactions are global—they may contain
calls to multiple EISs, databases, and enterprise bean business methods.
Although often appropriate, XA transactions are not mandatory. Instead, an
application may use local transactions, which are managed by the individual
EIS, or it may use no transactions at all.
To protect the information in an EIS, the security management contract provides
these mechanisms: authentication, authorization, and secure communication
between the J2EE server and the EIS.
Figure 17–1 Accessing an EIS Through a Resource Adapter
367
368
J2EE™ CONNECTOR ARCHITECTURE
Administering Resource Adapters
Installing a resource adapter is a two-step process:
1. Deploy the RAR file containing the resource adapter onto a server.
The following command, for example, deploys a sample black box
resource adapter onto the local host. (For Windows, in the following commands omit the backslash character, change $J2EE_HOME to %J2EE_HOME%,
and enter the entire command on a single line.)
deploytool deployConnector \
$J2EE_HOME/lib/connector/cciblackboxtx.rar \
localhost
2. Add a connection factory for the resource adapter.
Suppose that you wanted to add a connection factory for the resource
adapter in the cciblackboxtx.rar file. The JNDI name of the connection factory will be eis/MyCciBlackBoxTx. To override the default value
of the property named ConnnectionURL, you specify the URL of a database. (A property is a name-value pair used to configure a connection factory.) To add the connection factory, you might enter the following
j2eeadmin command:
j2eeadmin addConnectorFactory \
eis/MyCciBlackBoxTx \
cciblackboxtx.rar \
props \
ConnectionURL=jdbc:oracle:thin:@myhost:1521:ACCTDB
For the full syntax of the deploytool and j2eeadmin commands, see
Appendix B. These commands also list and remove resource adapters and connection factories.
To list the resource adapters that have been deployed, use the following command:
deploytool listConnectors localhost
To list the connection factories that have been added, use the following command:
j2eeadmin listConnectorFactory
To uninstall the resource adapter deployed in step 1, use the following command:
THE BLACK BOX RESOURCE ADAPTERS
deploytool undeployConnector cciblackboxtx.rar localhost
To remove the connection factory added in step 2, use the following command:
j2eeadmin removeConnectorFactory eis/MyCciBlackBoxTx
The Black Box Resource Adapters
The J2EE SDK includes several black box resource adapters for performing endto-end and compatibility testing. The underlying EIS of these adapters is a relational DBMS. The client API is the JDBC 2.0 API and the javax.sql.Data
Source interface. Underneath, the black box adapters use JDBC drivers to
communicate with relational databases. For more information, see Configuring
JDBC™ Drivers, page (371).
Note: Although the black box adapters use JDBC, resource adapters are not meant
to replace JDBC for accessing relational databases. The black box adapters are for
testing purposes only. Because they use JDBC, they can be plugged into existing
tests that also use JDBC.
Transaction Levels
The black box resource adapters reside in the $J2EE_HOME/lib/connector
(UNIX) or %J2EE_HOME%\lib\connector (Windows) subdirectory. Table 17–1
lists the black box RAR files and the different transaction levels that they support.
Table 17–1 Black Box Transaction Levels
File
Transaction Level
blackboxnotx.rar
NO_TRANSACTION
blackboxtx.rar
LOCAL_TRANSACTION
blackboxxa.rar
XA_TRANSACTION
cciblackboxtx.rar
LOCAL_TRANSACTION
cciblackboxxa.rar
XA_TRANSACTION
369
370
J2EE™ CONNECTOR ARCHITECTURE
For the XA_TRANSACTION level, the underlying JDBC driver must support the XA
requirements as defined by the JDBC 2.0 API.
Properties
A resource adapter may contain properties, that is, name-value pairs containing
information specific to the resource adapter and its underlying EIS. These properties are defined in the deployment descriptor of each black box RAR file.
Because the EIS of a black box adapter is a relational database, the properties
contain information required for connecting to a database. Table 17–2 lists the
properties of the black box adapter files. Table 17–3 shows the default values for
the black box properties.
Table 17–2 Black Box Properties
File
Property Name
Description
blackboxnotx.rar
ConnectionURL
URL of database
blackboxtx.rar
ConnectionURL
URL of database
blackboxxa.rar
XADataSourceName
JNDI name of XADataSource
cciblackboxtx.rar
ConnectionURL
URL of database
cciblackboxxa.rar
XADataSourceName
JNDI name of XADataSource
Table 17–3 Default Values for Black Box Properties
Property Name
Description
ConnectionURL
jdbc:cloudscape:rmi:CloudscapeDB;create=true
XADataSourceName
jdbc/XACloudscape_xa
To override a default property value, you set the value when adding a connection
factory with the j2eeadmin command. See the section Administering Resource
Adapters, page (368).
THE BLACK BOX RESOURCE ADAPTERS
Configuring JDBC™ Drivers
If you are running the black box adapters against a Cloudscape database, you
may skip this section. If you are using a database other than Cloudscape, you
should perform the steps that follow.
The Non-XA Black Box Adapters
1. Set the JDBC driver class. Use the j2eeadmin tool with the addJdb
cDriver option and specify the driver class name. The syntax for this
option is as follows:
j2eeadmin addJdbcDriver <class name>
2. Edit the bin/userconfig.sh (UNIX) or bin\userconfig.bat (Windows) file, setting the J2EE_CLASSPATH variable to the location of the
JDBC driver classes.
3. Restart the J2EE server.
The XA Black Box Adapters
1. Set the XADatasource property. With the j2eeadmin tool and the addJd
bcXADatasource option, specify the JNDI name and class name for the
XADatasource property. Optionally, you may specify the XA user name
and password and you may override the default property value. The syntax
follows:
j2eeadmin addJdbcXADatasource <jndi.name> <class.name>
[<xa.user.name> <xa.password>]
[props (<name>=<value>)+]
The preceding command results in two data sources. One is a DataSource
object with the specified JNDI name from which the J2EE application
gets a Connection instance. The other is an XADatasource object whose
JNDI name is the <jndi.name> parameter appended with two underscores and xa (<jndi.name>__xa). Behind the scenes, the DataSource
uses the XADataSource to create connections.
2. Restart the J2EE server.
371
372
J2EE™ CONNECTOR ARCHITECTURE
Resource Adapter Tutorial
This tutorial shows how to deploy the black box resource adapter stored in the
blackboxtx.rar file. To test the resource adapter, you will modify the exam
ples/src/ejb/savingsaccount/SavingsAccountBean.java file so that it
accesses the Cloudscape database through the resource adapter. The SavingsAc
countBean.java file is also used in another example; see Running the SavingsAccountEJB Example, page (97)
Setting Up
1. Start the J2EE server.
j2ee verbose
2. Follow the instructions in the section, Setting Up the Database, page (97).
Deploying the Resource Adapter
1. Deploy a black box resource adapter that is packaged in the blackbox
tx.rar file.
UNIX
deploytool deployConnector \
$J2EE_HOME/lib/connector/blackboxtx.rar localhost
Windows (Enter the following and all subsequent Windows commands on
a single line.)
deploytool deployConnector
%J2EE_HOME%\lib\connector\blackboxtx.rar localhost
2. Add a connection factory for the resource adapter. The JNDI name for the
connection factory is eis/MyBlackBoxTx.
UNIX
j2eeadmin addConnectorFactory \
eis/MyBlackBoxTx blackboxtx.rar
Windows
RESOURCE ADAPTER TUTORIAL
j2eeadmin addConnectorFactory
eis/MyBlackBoxTx blackboxtx.rar
3. Verify that the resource adapter has been deployed.
deploytool listConnectors localhost
The deploytool utility displays these lines:
Installed connector(s):
Connector Name: blackboxtx.rar
Installed connection factories:
Connection Factory JNDI Name: eis/MyBlackBoxTx
Testing the Resource Adapter
1. If you are new to the J2EE SDK, you should first read the instructions in
Chapter 2.
2. Locate the SavingsAccountBean.java source code, which resides in the
j2eetutorial/examples/src/ejb/savingsaccount directory.
3. Edit the SavingsAccountBean.java source code, changing the value
assigned to the dbName variable as follows:
private String dbName = "java:comp/env/MyEIS";
4. Compile the source code in the savingsaccount directory.
a. Go to j2eetutorial/examples.
b. Type ant savingsaccount.
5. Replace the new SavingsAccountBean.class file in the existing Sav
ingsAccountApp.ear file.
a. In the GUI deploytool, open the j2eetutorial/exam
ples/ears/SavingsAccountApp.ear file.
b. On the General tab of the SavingsAccountJAR, click Edit.
c. In the Available Files field, locate the j2eetutorial/exam
ples/build/ejb/SavingsAccountBean.class file.
d. Drag and drop the SavingsAccountBean.class file from the Available Files field to the Contents field.
e. Click OK.
373
374
J2EE™ CONNECTOR ARCHITECTURE
6. Change the resource factory reference.
a. Select the Resource Refs tab of SavingsAccountEJB.
b. Select the item whose Coded Name entry is jdbc/SavingsAccountDB.
c. Click Delete.
d. Click Add.
e. Enter the values specified in Table 17–4.
Table 17–4 Resource References Values
Field
Value
Coded Name
MyEIS
Type
javax.sql.DataSource
Authentication
Container
JNDI Name
eis/MyBlackBoxTx
The eis/MyBlackBoxTx JNDI name matches the name of the connection
factory that you added in step 2 of Deploying the Resource
Adapter, page (372). The MyEIS value of the Coded Name field corresponds to this line in the SavingsAccountBean.java source code:
private String dbName = "java:comp/env/MyEIS";
Although it is included in the source code, the java:comp/env/ subcontext is implicit in the Coded Name field of the Resource Refs tab.
7. Save the SavingsAccountApp application (File→Save).
8. Deploy the SavingsAccountApp application.
a. Select Tools→Deploy.
b. In the Introduction dialog box, select Return Client Jar.
COMMON CLIENT INTERFACE
c. In the JNDI Names dialog box, verify that the JNDI names in Table 17–
5 have been specified.
Table 17–5 JNDI Names
Component or Reference Name
JNDI Name
SavingsAccountEJB
MySavingsAccount
MyEIS
eis/MyBlackBoxTx
ejb/SimpleSavingsAccount
MySavingsAccount
9. To run the application, follow the directions in the section Running the
Client, page (98).
Common Client Interface
This section describes how components use the Connector architecture Common
Client Interface (CCI) API and a resource adapter to access data from an EIS.
Overview of the CCI
Defined by the J2EE Connector Architecture specification, the CCI defines a set
of interfaces and classes whose methods allow a client to perform typical data
access operations. Our example CoffeeEJB session bean includes methods that
375
376
J2EE™ CONNECTOR ARCHITECTURE
illustrate how to use the CCI, in particular, the following CCI interfaces and
classes:
• ConnectionFactory: Provides an application component with a Connec
tion instance to an EIS.
• Connection: Represents the connection to the underlying EIS.
• ConnectionSpec: Provides a means for an application component to pass
connection-request-specific properties to the ConnectionFactory when
making a connection request.
• Interaction: Provides a means for an application component to execute
EIS functions, such as database stored procedures.
• InteractionSpec: Holds properties pertaining to an application component’s interaction with an EIS.
• Record: The superclass for the different kinds of record instances. Record
instances may be MappedRecord, IndexedRecord, or ResultSet
instances, which all inherit from the Record interface.
• RecordFactory: Provides an application component with a Record
instance.
• IndexedRecord: Represents an ordered collection of Record instances
based on the java.util.List interface.
A client or application component that uses the CCI to interact with an underlying EIS does so in a prescribed manner. The component must establish a connection to the EIS’s resource manager, and it does so using the ConnectionFactory.
The Connection object represents the actual connection to the EIS and is used
for subsequent interactions with the EIS.
The component performs its interactions with the EIS, such as accessing data
from a specific table, using an Interaction object. The application component
defines the Interaction object using an InteractionSpec object. When the
application component reads data from the EIS (such as from database tables) or
writes to those tables, it does so using a particular type of Record instance, either
a MappedRecord, IndexedRecord, or ResultSet instance. Just as the Connec
tionFactory creates Connection instances, a RecordFactory creates Record
instances.
Our example shows how a session bean uses a resource adapter to add and read
records in a relational database. The example shows how to invoke stored procedures, which are business logic functions stored in a database and specific to an
enterprise’s operation. Stored procedures consist of SQL code to perform operations related to the business needs of an organization. They are kept in the data-
COMMON CLIENT INTERFACE
base and can be invoked when needed, just as you might invoke a Java™
method. In addition to showing how to use the CCI to invoke stored procedures,
we’ll also explain how to pass parameters to stored procedures and how to map
the parameter data types from SQL to those of the Java programming language.
Programming with the CCI
The code for the following example is in the examples/src/connector/cci
directory.
To illustrate how to use a CCI resource adapter, we’ve written a session bean and
a client of that bean. These pieces of code illustrate how clients invoke the different CCI methods that resource adapters built on CCI might make available. Our
example uses the two sample CCI-specific resource adapters:
cciblackbox_tx.rar and cciblackbox_xa.rar.
The Coffee session bean is much like any other session bean. It has a home
interface (CoffeeHome), a remote interface (Coffee), and an implementation
class (CoffeeEJB). To keep things simple, we’ve called the client CoffeeCli
ent.
Let’s start with the session bean interfaces and classes. The home interface, Cof
feeHome, is like any other session bean home interface. It extends EJBHome and
defines a create method to return a reference to the Coffee remote interface.
The Coffee remote interface defines the bean’s two methods that may be called
by a client.
public void insertCoffee(String name, int quantity)
throws RemoteException;
public int getCoffeeCount() throws RemoteException;
Now let’s examine the CoffeeEJB session bean implementation class to see how
it uses the CCI. To begin with, notice that CoffeeEJB imports the
javax.resource CCI
interfaces and classes, along with the
javax.resource.ResourceException and the sample cciblackbox classes.
import javax.resource.cci.*;
import javax.resource.ResourceException;
import com.sun.connector.cciblackbox.*;
Obtaining a Database Connection
Prior to obtaining a database connection, the session bean does some set up work
in its setSessionContext method. (See the following code example.) Specifi-
377
378
J2EE™ CONNECTOR ARCHITECTURE
cally, the setSessionContext method sets the user and password values, and
instantiates a ConnectionFactory. These values and objects remain available to
the other session bean methods. (In this and subsequent code examples, the numbers in the left margin correspond to the explanation that follows the code.)
1
2
3
public void setSessionContext(SessionContext sc) {
try {
this.sc = sc;
Context ic = new InitialContext();
user = (String) ic.lookup("java:comp/env/user");
password = (String) ic.lookup
("java:comp/env/password");
cf = (ConnectionFactory) ic.lookup
("java:comp/env/CCIEIS");
} catch (NamingException ex) {
ex.printStackTrace();
}
}
1. Establish a JNDI InitialContext.
2. Use the JNDI InitialContext.lookup method to find the user and password values.
3. Use the lookup method to locate the ConnectionFactory for the CCI
black box resource adapter and obtain a reference to it.
CoffeeEJB uses its private method getCCIConnection to establish a connection
to the underlying resource manager or database. A client of the Coffee session
bean cannot invoke this method directly. Rather, the session bean uses this
method internally to establish a connection to the database. The following code
uses the CCI to establish a database connection.
1
2
private Connection getCCIConnection() {
Connection con = null;
try {
ConnectionSpec spec =
new CciConnectionSpec(user, password);
con = cf.getConnection(spec);
} catch (ResourceException ex) {
COMMON CLIENT INTERFACE
}
ex.printStackTrace();
}
return con;
1. Instantiate a new CciConnectionSpec object with the user and password
values obtained by the setSessionContext method. The CciConnec
tionSpec class is the implementation of the ConnectionSpec interface.
2. Call the ConnectionFactory.getConnection method to obtain a connection to the database. (The reference to the ConnectionFactory was
obtained in the setSessionContext method.) Use the CciConnection
Spec object to pass the required properties to the ConnectionFactory.
The getConnection method returns a Connection object.
The CoffeeEJB bean also includes a private method, closeCCIConnection , to
close a connection. The method invokes the Connection object’s close method
from within a try/catch block. Like the getCCIConnection method, this is a
private method intended to be called from within the session bean.
private void closeCCIConnection(Connection con) {
try {
con.close();
} catch (ResourceException ex) {
ex.printStackTrace();
}
}
Database Stored Procedures
The sample CCI black box adapters call database stored procedures. It is important to understand stored procedures before delving into how to read or write
data using the sample CCI black box adapters. The methods of these sample CCI
adapters do not actually read data from a database or update database data.
Instead, these sample CCI adapters enable you to invoke database stored procedures, and it is the stored procedures that actually read or write to the database.
A stored procedure is a business logic method or function that is stored in a database and is specific for the enterprise’s business. Typically, stored procedures
consist of SQL code, though in certain cases (such as with Cloudscape) they may
consist of code written in the Java™ programming language. Stored procedures
perform operations related to the business needs of an organization. They are
kept in the database, and applications can invoke them when needed.
379
380
J2EE™ CONNECTOR ARCHITECTURE
Stored procedures are typically SQL statements. Our example calls two stored
procedures: COUNTCOFFEE and INSERTCOFFEE. The COUNTCOFFEE procedure
merely counts the number of coffee records in the Coffee table, as follows:
SELECT COUNT(*) FROM COFFEE
The INSERTCOFFFEE procedure adds a record with two values, passed to the procedure as parameters, to the same Coffee table, as follows:
INSERT INTO COFFEE VALUES (?,?)
Mapping to Stored Procedure Parameters
When you invoke a stored procedure from your application component, you may
have to pass argument values to the procedure. For example, when you invoke
the INSERTCOFFEE procedure, you pass it two values for the Coffee record elements. Likewise, you must be prepared to receive values that a stored procedure
returns.
The stored procedure, in turn, passes its set of parameters to the database management system (DBMS) to carry out its operation and may receive values back
from the DBMS. Database stored procedures specify, for each of their parameters, the SQL type of the parameter value and the mode of the parameter. Mode
can be input (IN), output (OUT), or both input and output (INOUT). An input
parameter only passes data in to the DBMS, and an output parameter only
receives data back from the DBMS. An INOUT parameter accepts both input and
output data.
When you use the CCI execute method to invoke a database stored procedure
you also create an instance of an InputRecord, provided that you’re passing a
parameter to the stored procedure and that the stored procedure you’re executing
returns data (possibly an OutputRecord instance). The InputRecord and Out
putRecord are instances of the supported Record types: IndexedRecord,
MappedRecord, or ResultSet. In our example, we instantiate an InputRecord
and an OutputRecord that are both IndexedRecord instances.
Note: The CCI black box adapters only support IndexedRecord types.
The InputRecord maps the IN and INOUT parameters for the stored procedure,
and the OutputRecord maps the OUT and INOUT parameters. Each element of an
input or output record corresponds to a stored procedure parameter. That is, there
is an entry in the InputRecord for each IN and INOUT parameter declared in the
COMMON CLIENT INTERFACE
stored procedure. Not only does the InputRecord have the same number of elements as the procedure’s input parameters, but they also are declared in the same
order as in the procedure’s parameter list. The same holds true for the Outpu
tRecord, though its list of elements matches only the OUT and INOUT parameters.
For example, suppose you have a stored procedure X that declares three parameters. The first parameter is an IN parameter, the second is an OUT parameter, and
the third is an INOUT parameter. Figure 17–2 shows how the elements of an
InputRecord and an OutputRecord map to this stored procedure.
Figure 17–2 Mapping Stored Procedure Parameters to CCI Record Elements
When you use the CCI black box adapter, you designate the parameter type and
mode in the same way, though the underlying Oracle or Cloudscape DBMS
declares the mode differently. Oracle designates the parameter’s mode in the
stored procedure declaration, along with the parameter’s type declaration. For
example, an Oracle INSERTCOFFEE procedure declares its two IN parameters as
follows:
procedure INSERTCOFFEE (name IN VARCHAR2, qty IN INTEGER)
An Oracle COUNTCOFFEE procedure declares its parameter N as an OUT parameter:
procedure COUNTCOFFEE (N OUT INTEGER)
Cloudscape, which declares a stored procedure as a method signature in the
Java™ programming language, indicates an IN parameter using a single value,
and an INOUT parameter using an array. The method’s return value is the OUT
parameter. For example, Cloudscape declares the IN parameters (name and qty)
381
382
J2EE™ CONNECTOR ARCHITECTURE
for insertCoffee and the OUT parameter (the method’s return value) for count
Coffee as follows:
public static void insertCoffee(String name, int qty)
public int countCoffee()
If qty were an INOUT parameter, then Cloudscape would declares it as
public static void insertCoffee(String name, int[] qty)
Oracle would declare it as
procedure INSERTCOFFEE (name IN VARCHAR2, qty INOUT INTEGER)
You must also map the SQL type of each value to its corresponding Java type.
Thus, if the SQL type is an integer, then the InputRecord or OutputRecord element must be defined as an Integer object. If the SQL type is a VARCHAR, then
the Java type must be a String object. Thus, when you add the element to the
Record, you declare it to be an object of the proper type. For example, add an
integer and a string element to an InputRecord as follows:
iRec.add (new Integer (intval));
iRec.add (new String ("Mocha Java"));
Note: The JDBC Specification defines the type mapping of SQL and the Java programming language.
Reading Database Records
The getCoffeeCount method of CoffeeEJB illustrates how to use the CCI to
read records from a database table. This method does not directly read the database records itself; instead, it invokes a procedure stored in the database called
COUNTCOFFEE. It is the stored procedure that actually reads the records in the
database table.
The CCI provides interfaces for three types of records: IndexedRecord, Mappe
dRecord, and ResultSet. These three record types inherit from the base interface, Record. They differ only in how they map the record elements within the
record. Our example uses IndexedRecord, which is the only record type currently supported. IndexedRecord holds its record elements in an ordered,
indexed collection based on java.util.List. As a result, we use an Iterator
object to access the individual elements in the list.
COMMON CLIENT INTERFACE
Let’s begin by looking at how the getCoffeeCount method uses the CCI to
invoke a database stored procedure. Again, note that the numbers in the margin
to the left of the code correspond to the explanation after the code example.
1
2
3
4
5
6
7
8
9
10
public int getCoffeeCount() {
int count = 1;
try {
Connection con = getCCIConnection();
Interaction ix = con.createInteraction();
CciInteractionSpec iSpec =
new CciInteractionSpec();
iSpec.setSchema(user);
iSpec.setCatalog(null);
iSpec.setFunctionName("COUNTCOFFEE");
RecordFactory rf = cf.getRecordFactory();
IndexedRecord iRec =
rf.createIndexedRecord("InputRecord");
Record oRec = ix.execute(iSpec, iRec);
Iterator iterator =
((IndexedRecord)oRec).iterator();
while(iterator.hasNext()) {
Object obj = iterator.next();
if(obj instanceof Integer) {
count = ((Integer)obj).intValue();
}
else if(obj instanceof BigDecimal) {
count = ((BigDecimal)obj).intValue();
}
}
closeCCIConnection(con);
}catch(ResourceException ex) {
ex.printStackTrace();
}
return count;
}
1. Obtain a connection to the database.
2. Create a new Interaction instance. The getCoffeeCount method creates a new Interaction instance because it is this object that enables the
session bean to execute EIS functions such as invoking stored procedures.
3. Instantiate a CciInteractionSpec object. The session bean must pass
certain properties to the Interaction object, such as schema name, catalog name, and the name of the stored procedure. It does this by instantiating a CciInteractionSpec object. The CciInteractionSpec is the
implementation class for the InteractionSpec interface, and it holds
383
384
J2EE™ CONNECTOR ARCHITECTURE
properties required by the Interaction object to interact with an EIS
instance. (Note that our example uses a Cloudscape database, which does
not require a catalog name.)
4. Set values for the CciInteractionSpec instance’s fields. The session
bean uses the CciInteractionSpec methods setSchema, setCatalog,
and setFunctionName to set the required values into the instance’s fields.
Our example passes COUNTCOFFEE to setFunctionName because this is the
name of the stored procedure it intends to invoke.
5. The getCoffeeCount method uses the ConnectionFactory to obtain a
reference to a RecordFactory so that it can create an IndexedRecord
instance. We obtain an IndexedRecord (or a MappedRecord or a Result
Set) using a RecordFactory.
6. Invoke the createIndexedRecord method of RecordFactory. This
method creates a new IndexedRecord using the name InputRecord,
which is passed to it as an argument.
7. The getCoffeeCount method has completed the required set-up work and
can invoke the stored procedure COUNTCOFFEE. It does this using the
Interaction instance’s execute method. Notice that it passes two
objects to the execute method: the InteractionSpec object, whose properties reference the COUNTCOFFEE stored procedure, and the Indexe
dRecord object, which the method expects to be an input Record. The
execute method returns an output Record object.
8. The getCoffeeCount method uses an Iterator to retrieve the individual
elements from the returned IndexedRecord. It casts the output Record
object to an IndexedRecord. IndexedRecord contains an iterator method
that it inherits from java.util.List.
9. Retrieve each element in the returned record object using the itera
tor.hasNext method. Each extracted element is an Object, and the bean
evaluates whether it is an integer or decimal value and processes it accordingly.
10. Close the connection to the database.
Inserting Database Records
The CoffeeEJB session bean implements the insertCoffee method to add new
records into the Coffee database table. This method invokes the INSERTCOFFEE
stored procedure, which inserts a record with the values (name and qty) passed
to it as arguments.
COMMON CLIENT INTERFACE
The insertCoffee method shown here illustrates how to use the CCI to invoke
a stored procedure that expects to be passed argument values. This example
shows the code for the insertCoffee method and is followed by an explanation.
1
2
3
4
5
6
7
8
9
public void insertCoffee(String name, int qty) {
try {
Connection con = getCCIConnection();
Interaction ix = con.createInteraction();
CciInteractionSpec iSpec =
new CciInteractionSpec();
iSpec.setFunctionName("INSERTCOFFEE");
iSpec.setSchema(user);
iSpec.setCatalog(null);
RecordFactory rf = cf.getRecordFactory();
IndexedRecord iRec =
rf.createIndexedRecord("InputRecord");
boolean flag = iRec.add(name);
flag = iRec.add(new Integer(qty));
ix.execute(iSpec, iRec);
closeCCIConnection(con);
}catch(ResourceException ex) {
ex.printStackTrace();
}
}
1. Establish a connection to the database.
2. Create a new Interaction instance for the connection so that the bean
can execute the database’s stored procedures.
3. Instantiate a CciInteractionSpec object so that the bean can pass the
necessary properties—schema name, catalog name, and stored procedure
name—to the Interaction object. The CciInteractionSpec class
implements the InteractionSpec interface and holds properties that the
Interaction object requires to communicate with the database instance.
4. Set the required values into the new CciInteractionSpec instance’s
fields, using the instance’s setSchema, setCatalog, and setFunction
Name methods. Our example passes INSERTCOFFEE to setFunctionName,
and user to setSchema.
5. Obtain a reference to a RecordFactory using the ConnectionFactory
object’s getRecordFactory method.
6. Invoke the RecordFactory object’s createIndexedRecord method to
create a new IndexedRecord with the name InputRecord.
7. Use the IndexedRecord add method to set the values for the two elements
in the new record. Call the add method once for each element. Our exam-
385
386
J2EE™ CONNECTOR ARCHITECTURE
ple sets the first record element to the name value and the second element
to the qty value. Notice that qty is set to an Integer object when passed
to the add method. The CoffeeEJB session bean is now ready to add the
new record to the database.
8. Call the Interaction instance’s execute method to invoke the stored
procedure INSERTCOFFEE. Just as we did when invoking the COUNTCOFFEE
procedure, we pass two objects to the execute method: the Interaction
Spec object with the correctly set properties for the INSERTCOFFEE stored
procedure, and the IndexedRecord object representing an input Record.
The execute method is not expected to return anything in this case.
9. Close the connection to the database.
Writing a CCI Client
A client application that relies on a CCI resource adapter is very much like any
other J2EE client that uses enterprise bean methods. Our CoffeeClient application uses the methods of the CoffeeEJB session bean to access the Coffee table
in the underlying database. CoffeeClient invokes the Coffee.getCoffeeCount
method to read the Coffee table records and invokes the Coffee.insertCoffee
method to add records to the table.
CCI Tutorial
This tutorial shows how to deploy and test the sample CCI black box adapter
with the code described in the preceding sections. This code has been packaged
into a J2EE application EAR file named CoffeeApp.ear, which is located in the
j2eetutorial/examples/ears directory. The source code is in
j2eetutorial/examples/src/connector/cci. To compile the source code, go
to the j2eetutorial/examples directory and type ant cci.
Deploying the Resource Adapter
1. Use the deploytool utility to deploy the CCI black box resource adapter.
Specify the name of the resource adapter’s RAR file (cciblackbox
tx.rar), plus the name of the server (localhost).
UNIX
deploytool deployConnector \
$J2EE_HOME/lib/connector/cciblackboxtx.rar localhost
COMMON CLIENT INTERFACE
Windows (Note that this command and all subsequent Windows commands must be entered on a single line.)
deploytool deployConnector
%J2EE_HOME%\lib\connector\cciblackboxtx.rar localhost
2. Next, add a connection factory for the deployed CCI adapter. The connection factory supplies a data source connection for the adapter. Use
j2eeadmin to create the connection factory, specifying the adapter’s JNDI
name plus the server name. Here, we add a connection factory for our CCI
adapter whose JNDI name is eis/CciBlackBoxTx on the server local
host.
UNIX
j2eeadmin addConnectorFactory \
eis/CciBlackBoxTx cciblackboxtx.rar
Windows
j2eeadmin addConnectorFactory
eis/CciBlackBoxTx cciblackboxtx.rar
3. Verify that the resource adapter has been deployed.
deploytool listConnectors localhost
The deploytool utility displays these lines:
Installed connector(s):
Connector Name: cciblackboxtx.rar
Installed connection factories:
Connection Factory JNDI name: eis/CciBlackBoxTx
Setting Up the Database
For Cloudscape, use the following procedure.
1. Create the stored procedure.
a. To compile the stored procedure, go to the j2eetutorial/examples
directory and type ant procs. This command will put the
Procs.class file in the j2eetutorial/examples/build/connec
tor/procs directory.
b. Locate the bin/userconfig.sh (UNIX) or bin\userconfig.bat
(Windows) file in your J2EE SDK installation. Edit the file so that the
387
388
J2EE™ CONNECTOR ARCHITECTURE
J2EE_CLASSPATH variable points to the directory that contains the
Procs.class file.
c. Restart the Cloudscape server.
d. Go to the j2eetutorial/examples directory and type ant create
procsalias. This command creates aliases for the methods in
Procs.class. Cloudscape uses method aliases to simulate stored procedures.
2. To create the Coffee table, go to the j2eetutorial/examples directory and
type ant createcoffeetable.
For Oracle, use the following procedure.
1. Start the database server.
2. Run the j2eetutorial/examples/sql/oracle.sql script, which creates
both the stored procedures and the Coffee table.
Browsing the CoffeeApp Application
1. In the GUI deploytool, open the j2eetutorial/examples/ears/Cof
feeApp.ear file.
2. Select the Resource Refs tab of the CoffeeBean component and note the
following (Figure 17–3).
• The Coded Name of CCIEIS corresponds to the following line in the
CoffeeEJB.java source code:
cf = (ConnectionFactory) ic.lookup("java:comp/env/CCIEIS");
COMMON CLIENT INTERFACE
Figure 17–3 Resource Refs Tab of the CoffeeApp Application
• The JNDI Name of eis/CciBlackBoxTx matches the name of the connection factory you added in step 2 of Deploying the Resource
Adapter, page (386).
• The User Name and Password fields contain dummy values (XXX),
since this EAR file was tested with a Cloudscape database. For other
types of databases, you may be required to insert actual values in these
fields. For these databases, you should also insert actual values in the
Env. Entries tab of CoffeeBean.
3. Select the JNDI Names tab of CoffeeApp (Figure 17–4). Note that the
CCIEIS value in the Reference Name field has been mapped to the
eis/CciBlackBoxTx value in the JNDI Name field.
389
390
J2EE™ CONNECTOR ARCHITECTURE
Figure 17–4 JNDI Tab of the CoffeeApp Application
Deploying and Running the CoffeeApp Application
1. Deploy the application.
a. In the GUI deploytool, select Tools→Deploy.
b. In the Introduction dialog box, select Return Client Jar.
2. In a terminal window, go to the j2eetutorial/examples/ears directory.
3. Set the APPCPATH environment variable to the name of the stub client JAR
file: CoffeeAppClient.jar.
4. Run the client.
runclient client CoffeeApp.ear name CoffeeClient
textauth
5. At the login prompts, enter guest as the user name and guest123 as the
password.
18
The Duke’s Bank
Application
Stephanie Bodoff, Dale Green, Eric Jendrock,
and Monica Pawlan
THIS chapter describes the Duke’s Bank application, an online banking application. Duke’s Bank has two clients: a J2EE application client used by administrators to manage customers and accounts, and a Web client used by customers to
access account histories and perform transactions. The clients access the customer, account, and transaction information maintained in a database through
enterprise beans. The Duke’s Bank application demonstrates how all the component technologies—enterprise beans, J2EE application clients, and Web components—presented in this tutorial are put together to provide a simple but
functional application.
Figure 18–1 gives a high-level view of how the components interact. This chapter looks at each of the component types in detail and concludes with a discussion of how to build, deploy, and run the application.
391
392
THE DUKE’S BANK APPLICATION
Figure 18–1 Duke’s Bank Application
ENTERPRISE BEANS
In This Chapter
Enterprise Beans 393
Session Beans 394
CustomerControllerEJB 396
TxControllerEJB 396
Entity Beans 397
Helper Classes 397
Database Tables 398
Protecting the Enterprise Beans 400
Application Client 400
The Classes and Their Relationships 402
BankAdmin Class 403
EventHandle Class 404
DataModel Class 406
Web Client 409
Design Strategies 410
Web Client Life Cycle 411
Protecting the Web Resources 415
Internationalization 415
Building, Packaging, Deploying, and Running the Application 417
Adding Groups and Users to the Realm 417
Starting the J2EE Server, deploytool, and Database 418
Compiling the Enterprise Beans 419
Packaging the Enterprise Beans 419
Compiling the Web Client 420
Packaging the Web Client 420
Compiling the J2EE Application Client 420
Packaging the J2EE Application Client 421
Packaging the Enterprise Archive File 421
Opening the Enterprise Archive File 421
Reviewing JNDI Names 423
Mapping the Security Roles to Groups 425
Deploying the Duke’s Bank Application 426
Creating the Bank Database 426
Running the J2EE Application Client 427
Running the Web Client 428
Enterprise Beans
Figure 18–2 takes a closer look at the access paths between the clients, enterprise
beans, and database tables. As you can see, the end-user clients (Web and J2EE
application clients) access only the session beans. Within the enterprise bean tier,
393
394
THE DUKE’S BANK APPLICATION
the session beans are clients of the entity beans. On the back end of the application, the entity beans access the database tables that store the entity states.
Figure 18–2 Enterprise Beans in the Duke’s Bank Application
The
source
code
for
these
enterprise
beans
j2eetutorial/bank/src/com/sun/ebank/ejb subdirectory.
is
in
the
Session Beans
The Duke’s Bank application has three session beans: AccountControllerEJB,
CustomerControllerEJB, and TxControllerEJB. (Tx stands for a business
transaction, such as transferring funds.) These session beans provide a client’s
view of the application’s business logic. Hidden from the clients are the serverside routines that implement the business logic, access databases, manage relationships, and perform error checking.
AccountControllerEJB
The business methods of the AccountControllerEJB session bean perform
tasks that fall into the following categories: creating and removing entity beans,
ENTERPRISE BEANS
managing the account-customer relationship, and getting the account information.
The following methods create and remove entity beans:
• createAccount
• removeAccount
These methods of the AccountControllerEJB session bean call the create and
remove methods of the AccountEJB entity bean. The createAccount and
removeAccount methods throw application exceptions to indicate invalid
method arguments. The createAccount method throws an IllegalAccount
TypeException if the type argument is neither Checking, Savings, Credit , nor
Money Market. The createAccount method also verifies that the specified customer exists by invoking the findByPrimaryKey method of the CustomerEJB
entity bean. If the result of this verification is false, the createAccount method
throws a CustomerNotFoundException.
The following methods manage the account-customer relationship:
• addCustomerToAccount
• removeCustomerFromAccount
The AccountEJB and CustomerEJB entity beans have a many-to-many relationship. A bank account may be jointly held by more than one customer, and a customer may have multiple accounts. Because the entity beans use bean-managed
persistence, there are several ways to manage this relationship. For more information,
see
Mapping
Table
Relationships
for
Bean-Managed
Persistence, page (99).
In the Duke’s Bank application, the addCustomerToAccount and removeCus
tomerFromAccount methods of the AccountControllerEJB session bean manage the account-customer relationship. The addCustomerToAccount method, for
example, starts by verifying that the customer exists. To create the relationship,
addCustomerToAccount
method
inserts
a
row
into
the
the
customer_account_xref database table. In this cross-reference table, each row
contains the customerId and accountId of the related entities. To remove a
relationship, the removeCustomerFromAccount method deletes a row from the
customer_account_xref table. If a client calls the removeAccount method,
then all rows for the specified accountId are removed from the
customer_account_xref table.
The following methods get the account information:
• getAccountsOfCustomer
• getDetails
395
396
THE DUKE’S BANK APPLICATION
The AccountControllerEJB session bean has two get methods. The getAc
countsOfCustomer method returns all of the accounts of a given customer by
invoking the findByCustomer method of the AccountEJB entity bean. Instead of
implementing a get method for every instance variable, the AccountControl
lerEJB has a getDetails method that returns an object (AccountDetails) that
encapsulates the entire state of an AccountEJB bean. Because it can invoke a single method to retrieve the entire state, the client avoids the overhead associated
with multiple remote calls.
CustomerControllerEJB
Because it is the AccountControllerEJB bean that manages the customeraccount relationship, CustomerControllerEJB is the simpler of these two session beans. A client creates a CustomerEJB entity bean by invoking the create
Customer method of the CustomerControllerEJB session bean. To remove a
customer, the client calls the removeCustomer method, which not only invokes
the remove method of CustomerEJB, but also deletes from the
customer_account_xref table all rows that identify the customer.
The CustomerControllerEJB session bean has two methods that return multiple
customers: getCustomersOfAccount and getCustomersOfLastName. These
methods call the corresponding finder methods—findbyAccountId and find
ByLastName—of CustomerEJB.
TxControllerEJB
The TxControllerEJB session bean handles bank transactions. In addition to its
get methods, getTxsOfAccount and getDetails, the TxControllerEJB bean
has several methods that change the balances of the bank accounts:
•
•
•
•
•
withdraw
deposit
makeCharge
makePayment
transferFunds
These methods access an AccountEJB entity bean to verify the account type and
to set the new balance. The withdraw and deposit methods are for non-credit
accounts, whereas the makeCharge and makePayment methods are for credit
accounts. If the type method argument does not match the account, these methods throw an IllegalAccountTypeException. If a withdrawal were to result in
a negative balance, then the withdraw method throws an InsufficientFund
ENTERPRISE BEANS
sException. If a credit charge attempts to exceed the account’s credit line, the
makeCharge method throws an InsufficientCreditException.
The transferFunds method also checks the account type and new balance; if
necessary, it throws the same exceptions as the withdraw and makeCharge methods. The transferFunds method subtracts from the balance of one AccountEJB
instance and adds the same amount to another instance. Because both of these
steps must complete, the transferFunds method has a Required transaction
attribute. If either step fails, the entire operation is rolled back and the balances
remain unchanged.
Entity Beans
For each business entity represented in our simple bank, the Duke’s Bank application has a matching entity bean:
• AccountEJB
• CustomerEJB
• TxEJB
The purpose of these beans is to provide an object view of these database tables:
account, customer, and tx. For each column in a table, the corresponding entity
bean has an instance variable. Because they use bean-managed persistence, the
entity beans contain the SQL statements that access the tables. For example, the
create method of the CustomerEJB entity bean calls the SQL INSERT command.
Unlike the session beans, the entity beans do not validate method parameters
(except for the primary key parameter of ejbCreate). During the design phase,
we decided that the session beans would check the parameters and throw the
application exceptions, such as CustomerNotInAccountException and Illega
lAccountTypeException. Consequently, if some other application were to
include these entity beans, its session beans would also have to validate the
method parameters.
Helper Classes
The EJB JAR files include several helper classes that are used by the enterprise
beans.
The
source
code
for
these
classes
is
in
the
397
398
THE DUKE’S BANK APPLICATION
j2eetutorial/bank/src/com/sun/ebank/util
briefly describes the helper classes.
subdirectory.
Table
18–1
Table 18–1 Helper Classes for the Application’s Enterprise Beans
Class Name
Description
AccountDetails
Encapsulates the state of an AccountEJB instance. Returned by the
getDetails methods of AccountControllerEJB and
AccountEJB.
CodedNames
Defines the strings that are the logical names in the calls of the lookup
method. (For example: java:comp/env/ejb/account). The EJB
Getter class references these strings.
CustomerDetails
Encapsulates the state of a CustomerEJB instance. Returned by the
getDetails methods of CustomerControllerEJB and Customer
EJB.
DBHelper
Provides methods that generate the next primary keys (for example,
getNextAccountId).
Debug
Has simple methods for printing a debugging message from an enterprise bean. These messages appear on the stdout of the J2EE server if
it’s run with the verbose option.
DomainUtil
Contains validation methods: getAccountTypes, checkAccount
Type, and isCreditAccount.
EJBGetter
Has methods that locate (by invoking lookup) and return home interfaces (for example, getAccountControllerHome).
TxDetails
Encapsulates the state of a TxEJB instance. Returned by the getDe
tails methods of TxControllerEJB and TxEJB.
Database Tables
A database table of the Duke’s Bank application may be categorized by its purpose: representing business entities and holding the next primary key.
Tables Representing Business Entities
Figure 18–3 shows relationships between the database tables. The customer and
account tables have a many-to-many relationship: A customer may have several
bank accounts, and each account may be owned by more than one customer. This
ENTERPRISE BEANS
many-to-many relationship is implemented by the cross reference table named
customer_account_xref. The account and tx tables have a one-to-many relationship: A bank account may have many transactions, but each transaction
refers to a single account.
Figure 18–3 makes use of several abbreviations. PK stands for primary key, the
value that uniquely identifies a row in a table. FK is an abbreviation for foreign
key, which is the primary key of the related table. Tx is short for transaction,
such as a deposit or withdrawal.
Figure 18–3 Database Tables in the Duke’s Bank Application
Tables That Hold the Next Primary Key
These tables have the following names:
• next_account_id
• next_customer_id
• next_tx_id
Each of these tables has a single column named id. The value of id is the next
primary key that is passed to the create method of an entity bean. For example,
before it creates a new AccountEJB entity bean, the AccountControllerEJB
session bean must obtain a unique key by invoking the getNextAccountId
method of the DBHelper class. The getNextAccountId method reads the id
399
400
THE DUKE’S BANK APPLICATION
from the next_account_id table, increments the id value in the table, and then
returns the id.
Protecting the Enterprise Beans
In the J2EE platform, you can protect an enterprise bean by specifying the security roles that can access its methods (see EJB-Tier Security, page (341)). In the
Duke’s Bank application, two roles are defined—BankCustomer and BankAd
min—because two categories of operations are defined by the enterprise beans.
A user in the BankAdmin role is allowed to perform administrative functions: creating or removing an account, adding a customer to or removing a customer
from an account, setting a credit line, and setting an initial balance. A user in the
BankCustomer role is allowed to deposit, withdraw, transfer funds, make charges
and payments, and list the account’s transactions. Notice that there is no overlap
in functions that users in either role can perform.
Access to these functions was restricted to the appropriate role by setting method
permissions on selected methods of the CustomerControllerEJB, AccountCon
trollerEJB, and TxControllerEJB enterprise beans. For example, by allowing
only users in the BankAdmin role to access the createAccount method in the
AccountControllerEJB enterprise bean, you have denied users in the BankCus
tomer role or any other role permission to create bank accounts. To see the
method permissions that have been set, in deploytool locate the CustomerCon
trollerEJB, AccountControllerEJB, and TxControllerEJB enterprise beans
in the tree view. For each bean, select the Security tab and examine the method
permissions.
Application Client
Sometimes, enterprise applications use a stand-alone client application for handling tasks such as system or application administration. For example, the
Duke’s Bank application uses a J2EE application client to manually administer
customers and accounts. This capability is useful in the event the site becomes
inaccessible for any reason or a customer prefers to communicate things such as
changes to account information by phone.
A J2EE application client is a standalone program launched from the command
line or desktop; it accesses enterprise beans running on the J2EE application
server.
APPLICATION CLIENT
The application client shown in Figure 18–4 handles basic customer and account
administration for the banking application through a Swing user interface. The
bank administrator can perform any of the following functions by making menu
selections.
Figure 18–4 Application Client
Customer Administration
•
•
•
•
View customer information
Add a new customer to the database
Update customer information
Find customer ID
Account Administration
•
•
•
•
Create a new account
Add a new customer to an existing account
View account information
Remove an account from the database
Error and informational messages appear in the left pane under Application
Message Watch:, and data is entered and displayed in the right pane.
401
402
THE DUKE’S BANK APPLICATION
The Classes and Their Relationships
The J2EE application client is divided into three classes: BankAdmin , EventHan
dle, and DataModel; the relationships among the classes are depicted in Figure
18–5.
Figure 18–5 Relationships among Classes
BankAdmin builds the initial user interface, creates the EventHandle object, and
provides methods for the EventHandle and DataModel objects to call to update
the user interface.
EventHandle listens for button clicks by the user, takes action based on which
button the user clicks, creates the DataModel object, calls methods in the Data
Model object to write data to and read data from the underlying database, and
calls methods in the BankAdmin object to update the user interface when actions
complete.
APPLICATION CLIENT
DataModel retrieves data from the user interface, performs data checks, writes
valid data to and reads stored data from the underlying database, and calls methods in the BankAdmin object to update the user interface based on the success of
the database read or write operation.
BankAdmin Class
The BankAdmin class, which creates the user interface, is the class with the main
method, and provides protected methods for the other BankAdmin application
classes to call.
main Method
The main method creates instances of the BankAdmin and EventHandle classes.
Arguments passed to the main method are used to initialize a locale, which is
passed to the BankAdmin constructor.
public static void main(String args[]) {
String language, country;
if(args.length == 1) {
language = new String(args[0]);
currentLocale = new Locale(language, "");
} else if(args.length == 2) {
language = new String(args[0]);
country = new String(args[1]);
currentLocale = new Locale(language, country);
} else
currentLocale = Locale.getDefault();
frame = new BankAdmin(currentLocale);
frame.setTitle(messages.getString("CustAndAccountAdmin"));
WindowListener l = new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
};
frame.addWindowListener(l);
frame.pack();
frame.setVisible(true);
ehandle = new EventHandle(frame, messages);
System.exit(0);
}
}
403
404
THE DUKE’S BANK APPLICATION
Constructor
The BankAdmin constructor creates the initial user interface, which consists of a
menu bar and two panels. The menu bar contains the customer and account
menus, the left panel contains a message area, and the right panel is a data display or update area.
Class Methods
The BankAdmin class provides methods that other objects call when they need to
update the user interface. These methods are as follows:
• clearMessages: Clears the application messages that appear in the left
panel
• resetPanelTwo: Resets the right panel when the user selects OK to signal
the end of a data view or update operation
• createPanelTwoActLabels: Creates labels for account fields when
account information is either viewed or updated
• createActFields: Creates account fields when account information is
either viewed or updated
• createPanelTwoCustLabels: Creates labels for customer fields when
customer information is either viewed or updated
• createCustFields: Creates customer fields when account information is
either viewed or updated
• addCustToActFields: Creates labels and fields for when an add customer
to account operation is invoked
• makeRadioButtons: Makes radio buttons for selecting the account type
when a new account is created
• getDescription: Makes the radio button labels that describe each available account type
EventHandle Class
The EventHandle class implements the ActionListener interface, which provides a method interface for handling action events. Like all other interfaces in
the Java programming language, ActionListener defines a set of methods, but
does not implement their behavior. Instead, you provide the implementations
because they take application-specific actions.
APPLICATION CLIENT
Constructor
The constructor receives an instance of the ResourceBundle and BankAdmin
classes and assigns them to its private instance variable so that the EventHandle
object has access to the application client’s localized text and can update the user
interface as needed. Lastly, the constructor calls the hookupEvents method to
create the inner classes to listen for and handle action events.
public EventHandle(BankAdmin frame, ResourceBundle messages) {
this.frame = frame;
this.messages = messages;
this.dataModel = new DataModel(frame, messages);
//Hook up action events
hookupEvents();
}
actionPerformed Method
The ActionListener interface has only one method, the actionPerformed
method. This method handles action events generated by the BankAdmin user
interface when users create a new account. Specifically, it sets the account
description when a bank administrator selects an account type radio button and
sets the current balance to the beginning balance for new accounts when a bank
administrator presses the Return key in the Beginning Balance field.
hookupEvents Method
The EventHandle class uses inner classes to handle menu and button press
events. An inner class is a class nested or defined inside another class. Using
inner classes in this way modularizes the code, making it easier to read and
maintain. EventHandle inner classes manage the following application client
operations:
•
•
•
•
•
•
•
•
•
View customer information
Create new customer
Update customer information
Find customer ID by last name
View account information
Create new account
Add customer to account
Remove account
Clear data on Cancel button press
405
406
THE DUKE’S BANK APPLICATION
• Process data on OK button press
DataModel Class
The DataModel class provides methods for reading data from the database, writing data to the database, retrieving data from the user interface, and checking
that data before it is written to the database.
Constructor
The constructor receives an instance of the BankAdmin class and assigns it to its
private instance variable so that the DataModel object can display error messages in the user interface when its checkActData, checkCustData, or write
Data method detects errors. It also receives an instance of the ResourceBundle
class and assigns it to its private instance variable so that the DataModel object
has access to the application client’s localized text.
Because the DataModel class interacts with the database, the constructor also has
the code to establish connections with the remote interfaces for the Customer
Controller and AccountController enterprise beans, and to use their remote
interfaces to create an instance of the CustomerController and AccountCon
troller enterprise beans.
//Constructor
public DataModel(BankAdmin frame, ResourceBundle messages) {
this.frame = frame;
this.messages = messages;
//Look up and create CustomerController bean
try {
CustomerControllerHome customerControllerHome =
EJBGetter.
getCustomerControllerHome();
customer = customerControllerHome.create();
} catch (Exception NamingException) {
NamingException.printStackTrace();
}
//Look up and create AccountController bean
try {
AccountControllerHome accountControllerHome =
EJBGetter.getAccountControllerHome();
account = accountControllerHome.create();
} catch (Exception NamingException) {
NamingException.printStackTrace();
}
}
APPLICATION CLIENT
Methods
The getData method retrieves data from the user interface text fields and uses
the String.trim method to remove extra control characters such as spaces and
returns. Its one parameter is a JTextfield so that any instance of the JText
field class can be passed in for processing.
private String getData(JTextField component) {
String text, trimmed;
if(component.getText().length() > 0) {
text = component.getText();
trimmed = text.trim();
return trimmed;
} else {
text = null;
return text;
}
}
The checkCustData method stores customer data retrieved by the getData
method, but first checks the data to be sure all required fields have data, the middle initial is no longer than one character, and the state is no longer than two
characters. If everything checks out, the writeData method is called. If there are
errors, they are printed to the user interface in the BankAdmin object. The check
ActData method uses a similar model to check and store account data.
The createCustInf and createActInf methods are called by the EventHandle
class to refresh the Panel 2 display in the event of a view, update, or add action
event.
Create Customer Information
• For a view or update event, the createCustInf method gets the customer
information for the specified customer from the database and passes it to
the createCustFields method in the BankAdmin class. A Boolean variable is used to determine whether the createCustFields method should
create read-only fields for a view event or writable fields for an update
event.
• For create event, the createCustInf method calls the createCustFields
method in the BankAdmin class with null data and a Boolean variable to
create empty editable fields for the user to enter customer data.
Create Account Information
• For a view or update event, the createActInf method gets the account
information for the specified account from the database and passes it to the
407
408
THE DUKE’S BANK APPLICATION
createActFields method in the BankAdmin class. A Boolean variable is
used to determine whether the createActFields method should create
read-only fields for a view event or writable fields for an update event.
• For a create event, the createActInf method calls the createActFields
method in the BankAdmin class with null data and a Boolean variable to
create empty editable fields for the user to enter customer data.
• Adding a customer to an account or removing an account events operate
directly on the database without creating any user interface components.
WEB CLIENT
Web Client
In the Duke’s Bank application, the Web client is used by customers to access
account information and perform operations on accounts. For example, Figure
18–6 shows an account history screen.
Figure 18–6 Account History
409
410
THE DUKE’S BANK APPLICATION
Table 18–2 lists the functions the client supports, the URLs used to access the
functions, and the components that implement the functions.
Table 18–2 Web Client
JavaBeans
Component
Function
URL Aliases
JSP Pages
Home page
/main
main.jsp
Log on or off the
application
/logon
/logonError
/logoff
logon.jsp
logonError.jsp
logoff.jsp
List account
/accountList
accountList.jsp
List the history of
an account
/accountHist
accountHist.jsp
AccountHistory
Bean
Transfer funds
between accounts
/transferFunds
/transferAck
transferFunds.jsp
transferAck.jsp
TransferBean
Withdraw and
deposit funds
/atm
/atmAck
atm.jsp
atmAck.jsp
ATMBean
Error handling
/error
error.jsp
Design Strategies
The main job of the JSP pages in the Duke’s Bank application is presentation. A
strategy for developing maintainable JSP pages is to minimize the amount of
scripting embedded in the pages. In order to achieve this, most dynamic processing tasks are delegated to enterprise beans, custom tags, and JavaBeans components.
In the Duke’s Bank application, the JSP pages use enterprise beans to handle
interactions with the database. In addition, the JSP pages rely heavily on JavaBeans components for interactions with the enterprise beans. In the Duke’s
Bookstore application, presented in chapters 10 to 13, the BookDB JavaBeans
component acted as a front end to a database or as a facade to the interface provided by an enterprise bean. In the Duke’s Bank application, TransferBean
plays the same role. However, the other JavaBeans components have much
richer functionality. ATMBean invokes enterprise bean methods and sets acknowl-
WEB CLIENT
edgement strings according to customer input, and AccountHistoryBean massages the data returned from the enterprise beans in order to present the view of
the data required by the customer.
The Web client uses a template mechanism implemented by custom tags (discussed in A Template Tag Library, page (308)) to maintain a common look
across all the JSP pages. The template mechanism consists of three components:
• template.jsp determines the structure of each screen. It uses the insert
tag to compose a screen from subcomponents.
• screendefinitions.jsp defines the subcomponents used by each
screen. All screens have the same banner, but different title and body content (specified by the JSP Pages column in Table 18–2).
• Dispatcher, a servlet, processes requests and forwards to template.jsp.
Finally, the Web client uses three logic tags—iterate, equal, and notEqual—
from the Struts tag library discussed in the section The Example JSP
Pages, page (281) to perform flow control.
Web Client Life Cycle
Initializing the Client Components
Responsibility for managing the enterprise beans used by the Web client rests
with the BeanManager class. It creates customer, account, and transaction controller enterprise beans and provides methods for retrieving the beans.
When instantiated, BeanManager retrieves the home interface for each bean from
the helper class EJBGetter and creates an instance by calling the create method
of the home interface. Because this is an application-level function, BeanMan
ager itself is created and stored as a context attribute by a ContextListener
(see Handling Servlet Life-Cycle Events, page (216)) when the client is first initialized.
public class BeanManager {
private CustomerController custctl;
private AccountController acctctl;
private TxController txctl;
public BeanManager() {
if (custctl == null) {
try {
CustomerControllerHome home =
EJBGetter.getCustomerControllerHome();
custctl = home.create();
411
412
THE DUKE’S BANK APPLICATION
} catch (RemoteException ex) {
System.out.println("...”);
} catch (CreateException ex) {
System.out.println();
} catch (NamingException ex) {
System.out.println();
}
}
}
public CustomerController getCustomerController() {
return custctl;
}
...
public final class ContextListener
implements ServletContextListener {
private ServletContext context = null;
...
public void contextInitialized(ServletContextEvent event) {
this.context = event.getServletContext();
context.setAttribute("beanManager",
new BeanManager());
context.log("contextInitialized()");
}
...
}
Request Processing
All requests for the URLs listed in Table 18–2 are mapped to the dispatcher
Web component, which is implemented by the Dispatcher servlet:
public class Dispatcher extends HttpServlet {
public void doPost(HttpServletRequest request,
HttpServletResponse response) {
...
String selectedScreen = request.getServletPath();
request.setAttribute("selectedScreen", selectedScreen);
BeanManager beanManager = getServletContext().getAttribute(
"beanManager");
...
if (selectedScreen.equals("/accountHist")) {
...
} else if (selectedScreen.equals("/transferAck")) {
String fromAccountId =
request.getParameter("fromAccountId");
String toAccountId =
WEB CLIENT
}
}
request.getParameter("toAccountId");
if ( (fromAccountId == null) || (toAccountId == null)) {
request.setAttribute("selectedScreen", "/error");
request.setAttribute("errorMessage",
messages.getString("AccountError"));
} else {
TransferBean transferBean = new TransferBean();
request.setAttribute("transferBean",
transferBean);
transferBean.setMessages(messages);
transferBean.setFromAccountId(fromAccountId);
transferBean.setToAccountId(toAccountId);
transferBean.setBeanManager(beanManager);
try {
transferBean.setTransferAmount(new
BigDecimal(request.
getParameter("transferAmount")));
String errorMessage = transferBean.populate();
if (errorMessage != null) {
request.setAttribute("selectedScreen",
"/error");
request.setAttribute("errorMessage",
errorMessage);
}
} catch (NumberFormatException e) {
request.setAttribute("selectedScreen",
"/error");
request.setAttribute("errorMessage",
messages.getString("AmountError"));
}
}
...
try {
request.getRequestDispatcher("/template.jsp").
forward(request, response);
} catch(Exception e) {
}
When a request is delivered, Dispatcher does the following:
1. Retrieves and saves the incoming request URL in the request attribute
selectedScreen. This is done because the URL will be modified when
the request is later forwarded to the application’s template page.
2. Creates a JavaBeans component and stores the bean as a request attribute.
413
414
THE DUKE’S BANK APPLICATION
3. Parses and validates the request parameters. If a parameter is invalid, Dis
patcher may reset the request alias to an error page. Otherwise, it initializes the JavaBeans component.
4. Calls the populate method of the JavaBeans component. This method
retrieves data from the enterprise beans and processes the data according
to options specified by the customer.
5. Forwards the request to template.jsp.
As mentioned earlier, template.jsp generates the response by including the
responses from subcomponents. If the request is a GET, the body subcomponent
usually retrieves data from the enterprise bean directly; otherwise it retrieves
data from the JavaBeans component initialized by Dispatcher.
Figure 18–7 summarizes the interaction between these components.
Figure 18–7 Web Component Interaction
INTERNATIONALIZATION
Protecting the Web Resources
In the J2EE platform, a Web resource is protected from anonymous access by
specifying which security roles can access the resource (see Controlling Access
to Web Resources, page (338)). This is known as a security constraint. The Web
container guarantees that only certain users acting in roles specified in the security constraint can access the resource. In order for the Web container to enforce
the security constraint, the application must specify a means for users to identify
themselves (described in Authenticating Users of Web Resources, page (338))
and the Web container must support mapping a role to a user.
In the Duke’s Bank Web client, all of the URLs listed in Table 18–2 are restricted
to the security role BankCustomer. The application requires users to identify
themselves via the form-based login mechanism. When a customer tries to
access a Web client URL, and has not been authenticated, the Web container displays the form-based login URL /logon, which is mapped to the JSP page
logon.jsp. This page contains a form that requires a customer to enter an identifier and password. The Web container retrieves this information, maps it to a
security role, and verifies that the role matches that specified in the security constraint. Note that in order for the Web container to check the validity of the
authentication information and perform the mapping, you must perform these
two steps when you deploy the application:
1. Add the customer’s group, ID, and password to the default realm of the
container (see J2EE Users, Realms, and Groups, page (348)).
2. Map the BankCustomer role to the customer or customer’s group (see
J2EE Users, Realms, and Groups, page (348)).
Once the customer has been authenticated, the identifier provided by the customer is used as a key to identify the customer’s accounts. The identifier is
retrieved from the request as follows:
<% ArrayList accounts =
beanManager.getAccountController().getAccountsOfCustomer(
request.getUserPrincipal().getName()); %>
Internationalization
The J2EE application client and Web client distributed with the Duke’s Bank
application are internationalized. All strings that appear in the user interfaces are
retrieved from resource bundles. The administration client uses resource bundles
named AdminMessages_*.properties. The Web client uses resource bundles
415
416
THE DUKE’S BANK APPLICATION
named WebMessages_*.properties. Both clients are distributed with English
and Spanish resource bundles.
The application client retrieves locale information from the command line. For
example, to use the Spanish resource bundle, invoke the application like this:
runclient client BankApp.ear name BankAdmin es
The administration client class BankAdmin creates a ResourceBundle with a
locale created from the command-line arguments:
//Constructor
public BankAdmin(Locale currentLocale) {
//Internationalization setup
messages = ResourceBundle.getBundle("AdminMessages",
currentLocale);
The Web client Dispatcher component retrieves the locale (set by a browser
language preference) from the request, opens the resource bundle, and then saves
the bundle as a session attribute:
ResourceBundle messages = (ResourceBundle)session.
getAttribute("messages");
if (messages == null) {
Locale locale=request.getLocale();
messages = ResourceBundle.getBundle("WebMessages",
locale);
session.setAttribute("messages", messages);
}
In the Web client, each JSP page first retrieves the resource bundle from the session:
<% ResourceBundle messages =
(ResourceBundle)session.getAttribute("messages"); %>
and then looks up any string that it needs in the bundle. For example, here is how
accountHist.jsp generates the headings for the transactions table:
<td><b><%=messages.getString("TxDate")%></b></td>
<td><b><%=messages.getString("TxDescription")%></b></td>
<td><b><%=messages.getString("TxAmount")%></b></td>
<td><b><%=messages.getString("TxRunningBalance")%></b></td>
BUILDING, PACKAGING, DEPLOYING, AND RUNNING THE APPLICATION417
Building, Packaging, Deploying, and
Running the Application
To build the Duke’s Bank application, you must have downloaded and unzipped
the tutorial bundle as described in Downloading the Examples, page (xxii).
When you install the bundle, the Duke’s Bank application files are placed in the
following directory structure of the j2eetutorial directory:
/bank
/dd deployment descriptors
accountejb.xml
appclient.xml
customerejb.xml
runtimeac.xml
runtimeapp.xml
txejb.xml
web.xml
/src
/com component classes
/sun/ebank/appclient
/sun/ebank/ejb
/sun/ebank/web
/web JSP pages, images
/sql database scripts
createtable.sql
insert.sql
To simplify building, packaging, and deploying the Duke’s Bank application, the
tutorial bundle includes deployment descriptors, source code, and a build.xml
file that contains the automated ant tasks. If you haven’t run ant yet, please see
How to Build and Run the Examples, page (xxii).
After you compile the source code, the resulting class files will reside in the
j2eetutorial/bank/build subdirectory. When you package the components
and the application, the resulting archive files are placed in the
j2eetutorial/bank/jar subdirectory.
Adding Groups and Users to the Realm
To run the J2EE application and Web clients, you must add groups and users to
the default security realm. To create the Customer and Admin groups, add the
418
THE DUKE’S BANK APPLICATION
user 200 to the Customer group, and add the user admin to the Admin group in
deploytool:
1. Select Tools→Server Configuration
2. In the tree, select the Users node.
3. Make sure that Default is selected in the Realm combo box.
4. Click Add User.
5. Click Edit Groups.
6. Click Add.
7. Enter Customer.
8. Click Add.
9. Enter Admin.
10.Click OK.
11.Enter 200 for User Name: and j2ee for Password:
12.Select the Customer group from the Available Groups list.
13.Click Add.
14.Click Apply.
15.Enter admin for User Name and j2ee for Password.
16.Select the Admin Group from the Available Groups list.
17.Click Add.
18.Click OK.
You can perform the same tasks with the realmtool command-line utility:
1.
2.
3.
4.
realmtool
realmtool
realmtool
realmtool
addGroup Customer
add 200 j2ee Customer
addGroup Admin
add admin j2ee Admin
Starting the J2EE Server, deploytool, and Database
J2EE Server
Start the J2EE server:
j2ee verbose
BUILDING, PACKAGING, DEPLOYING, AND RUNNING THE APPLICATION419
Deploytool
After the J2EE server reports startup complete, run deploytool:
1. If the deploytool utility is not running, launch it from the command line:
deploytool
2. If deploytool is already running, reconnect to the J2EE server:
a. Select File→Add Server
b. In the Add Server dialog box, enter localhost in the Server Name
field.
c. Click OK.
Cloudscape
Start the Cloudscape database server:
cloudscape start
Compiling the Enterprise Beans
In a different window, go to the j2eetutorial/bank subdirectory of the tutorial
distribution and type this command:
ant compileejb
Packaging the Enterprise Beans
To package the enterprise beans, type the following:
ant packageejb
The preceding command packages the class files and the deployment descriptors
into the following EJB JAR files, which reside in the j2eetutorial/bank/jar
subdirectory.
accountejb.jar
customerejb.jar
txejb.jar
When packaging a component in this chapter, ant may report that it cannot find
a file (such as accountejb.jar) to delete. You may ignore these messages.
420
THE DUKE’S BANK APPLICATION
Compiling the Web Client
To compile the Web client, go to the j2eetutorial/bank directory of the tutorial distribution and execute the following:
ant compileweb
Packaging the Web Client
The Web client uses the Struts tag library discussed in The Example JSP
Pages, page (281). Before you can package the Web client, you must download
and install Struts version 1.0 from
http://jakarta.apache.org/builds/jakartastruts/release/v1.0/
Copy strutslogic.tld and struts.jar from jakartastruts1.0/lib to
j2eetutorial/bank/jar. Then change to the j2eetutorial/bank directory
and type the following:
ant packageweb
This command packages the servlet class, JSP pages, JavaBeans component
classes, tag libraries, and the Web application deployment descriptor into web
client.war and puts this file in j2eetutorial/bank/jar.
Compiling the J2EE Application Client
To compile the application client, go to the j2eetutorial/bank subdirectory
and run this command:
ant compileac
BUILDING, PACKAGING, DEPLOYING, AND RUNNING THE APPLICATION421
Packaging the J2EE Application Client
1. Go to the j2eetutorial/bank directory and run this command:
ant packageac
This command creates the appclient.jar
j2eetutorial/bank/jar directory.
file
in
the
2. From the same directory, type the following:
ant setruntimeac
This
command
adds
a
runtime
deployment
descriptor
(j2eetutorial/bank/dd/runtimeac.xml) to appclient.jar.
Packaging the Enterprise Archive File
1. To create the Duke’s Bank enterprise archive file, go to the
j2eetutorial/bank directory and run this command:
ant assembleapp
This command creates the DukesBankApp.ear
j2eetutorial/bank/jar directory.
file
in
the
2. From the same directory, type the following:
ant setruntimeapp
This
command
adds
a
runtime
deployment
descriptor
(j2eetutorial/bank/dd/runtimeapp.xml) to DukesBankApp.ear.
Opening the Enterprise Archive File
In deploytool, open the EAR as follows:
1.
2.
3.
4.
Select File →Open.
Go to the j2eetutorial/bank/jar subdirectory.
Select DukesBankApp.ear.
Click Open Object.
422
THE DUKE’S BANK APPLICATION
You should see the screen shown in Figure 18–8 in deploytool:
Figure 18–8 Duke’s Bank Application Archives and Components
BUILDING, PACKAGING, DEPLOYING, AND RUNNING THE APPLICATION423
Reviewing JNDI Names
With DukesBankApp selected, click the JNDI Names tab. The JNDI Name column is shown in Figure 18–9. The order may be a little different on your own
display.
Figure 18–9 JNDI Names
424
THE DUKE’S BANK APPLICATION
A JNDI name is the name the J2EE server uses to look up enterprise beans and
resources. When you look up an enterprise bean, you supply statements similar
to those shown in the following code. The actual lookup takes place in the third
line of code, in which the getCustomerControllerHome method of
com.sun.ebank.utilEJBGetter is called. EJBGetter is a utility class that
retrieves a coded JNDI name from com.sun.ebank.util.CodedNames. In this
example, the application client is looking up the coded name for the Customer
Controller remote interface:
try {
customerControllerHome =
EJBGetter.getCustomerControllerHome();
customer = customerControllerHome.create();
} catch (Exception NamingException) {
NamingException.printStackTrace();
}
public static CustomerHome getCustomerHome() throws
NamingException {
InitialContext initial = new InitialContext();
Object objref = initial.lookup(
CodedNames.CUSTOMER_EJBHOME);
BankAdmin (the display name for the main class of the application client) references ejb/customerController, which is the coded name defined in Coded
Names for the CustomerController remote interface.
The JNDI name is stored in the J2EE application deployment descriptor, and the
J2EE server uses it to look up the CustomerControllerEJB bean. In Figure 18–
9 you see that CustomerControllerEJB is mapped to the same JNDI name as is
ejb/customerController. It does not matter what the JNDI name is, as long as
it is the same name for the remote interface lookup as you use for its corresponding bean. So, looking at the table, you can say that the application client
(BankAdmin) looks up the CustomerController remote interface, which uses
the JNDI name of MyCustomerController, and the J2EE server uses the MyCus
tomerController JNDI name to find the corresponding CustomerControl
lerEJB object.
The other rows in the table have the mappings for the other enterprise beans. All
of these beans are stored in the JAR files you added to the J2EE application during assembly. Their implementations have coded names for looking up either
other enterprise beans or the database driver.
BUILDING, PACKAGING, DEPLOYING, AND RUNNING THE APPLICATION425
The JNDI name for the database driver is jdbc/Cloudscape. This name is the
default coded name supplied in a configuration file of your J2EE SDK installation. For more information, see the Configuration Guide of the J2EE SDK.
Mapping the Security Roles to Groups
To map the BankAdmin role to the Admin group and the BankCustomer role to the
Customer group:
In deploytool, select DukesBankApp.
In the Security tab, select the BankAdmin role from the Role Name list.
Click Add.
In the User Groups dialog box, select the Admin group in the Group Name
list.
5. Click OK.
6. In the Security tab, select the BankCustomer role from the Role Name list.
7. Click Add.
8. In the User Groups dialog box, select the Customer group in the Group
Name list.
9. Click OK.
10.From the main menu, select File→Save.
1.
2.
3.
4.
Figure 18–10 shows the BankCustomer role selected and the Customer group to
which it is mapped.
426
THE DUKE’S BANK APPLICATION
Figure 18–10 BankCustomer Role Mapped to Customer Group
Deploying the Duke’s Bank Application
To deploy the application:
1. Select the DukesBankApp application.
2. Select Tools→Deploy.
3. Select the checkbox labeled Return Client Jar. By default, the directory for
the returned JAR file is the same as where the EAR file is stored. The
default name of the client JAR file is the application name with Cli
ent.jar appended, in this case, DukesBankAppClient.jar.
4. Click Finish.
Creating the Bank Database
You have to create and enter data into the appropriate tables so that the enterprise
beans have something to read from and write to the database. To create and pop-
BUILDING, PACKAGING, DEPLOYING, AND RUNNING THE APPLICATION427
ulate the database tables, in a terminal window go to the j2eetutorial/bank
directory and type the following commands:
1. ant dbcreatetable
2. ant dbinsert
Running the J2EE Application Client
To run the J2EE application client:
1. In a terminal window, go to j2eetutorial/bank/jar.
2. Set the APPCPATH environment variable to DukesBankAppClient.jar.
3. To run the English version of the client, execute the following command:
runclient client DukesBankApp.ear name BankAdmin
4. To run the Spanish version, include the es language code:
runclient client DukesBankApp.ear name BankAdmin es
The DukesBankApp.ear parameter is the name of the J2EE application
EAR file, and the BankAdmin parameter is the display name of the application client.
5. At the login prompts, type in admin for the user name and j2ee for the
password. The next thing you should see is the application shown in Figure 18–11.
428
THE DUKE’S BANK APPLICATION
Figure 18–11 BankAdmin J2EE Application Client
Running the Web Client
To run the Web client:
1. Open the bank URL, http://<host>:8000/bank/main, in a Web
browser. If your J2EE server is running on the same host as your Web
browser, replace <host> with localhost. To see the Spanish version of
the application, set your browser language preference to any Spanish dialect.
2. The application will display the login page. Enter 200 for the customer ID
and j2ee for the password. Click Submit.
3. Select an application function: Account List, Transfer Funds, ATM, or
Logoff. Once you have a list of accounts, you can get an account history
by selecting an account link.
Note: The first time you select a new page, particularly a complicated page like an
account history, it takes some time to display because the J2EE server must translate
the page into a servlet class and compile and load the class.
BUILDING, PACKAGING, DEPLOYING, AND RUNNING THE APPLICATION429
If you select Account List, you will see the screen shown in Figure 18–12.
Figure 18–12 Account List
430
THE DUKE’S BANK APPLICATION
A
HTTP Overview
Stephanie Bodoff
MOST J2EE Web clients use the HTTP protocol to communicate with a J2EE
server. HTTP defines the requests that a client can send to a server and the
responses that the server can send in reply. Each request contains a URL, which
is a string that identifies a Web component or a static object such as an HTML
page or image file.
The J2EE server converts an HTTP request to an HTTP request object and delivers it to the Web component identified by the request URL. The Web component
fills in an HTTP response object, which the server converts to an HTTP response
and sends to the client.
This appendix provides some introductory material on the HTTP protocol. For
further information on this protocol, see the Internet RFCs 1945 (HTTP/1.0) and
2616 (HTTP/1.1), which can be downloaded from
http://www.rfceditor.org/rfc.html
In This Appendix
HTTP Requests 432
HTTP Responses 432
431
432
HTTP OVERVIEW
HTTP Requests
An HTTP request consists of a request method, a request URL, header fields,
and a body. HTTP 1.1 defines the following request methods:
•
•
•
•
•
•
•
GET: Retrieves the resource identified by the request URL
HEAD: Returns the headers identified by the request URL
POST: Sends data of unlimited length to the Web server
PUT: Stores a resource under the request URL
DELETE: Removes the resource identified by the request URL
OPTIONS: Returns the HTTP methods the server supports
TRACE: Returns the header fields sent with the TRACE request
HTTP 1.0 includes only the GET, HEAD, and POST methods. Although J2EE servers are only required to support HTTP 1.0, in practice many servers, including
the J2EE SDK, support HTTP 1.1.
HTTP Responses
An HTTP response contains a result code, header fields, and a body. The HTTP
protocol expects the result code and all header fields to be returned before any
body content.
Some commonly used status codes include the following:
• 404: Indicates that the requested resource is not available
• 401: Indicates that the request requires HTTP authentication
• 500: Indicates an error inside the HTTP server which prevented it from
fulfilling the request
• 503: Indicates that the HTTP server is temporarily overloaded, and unable
to handle the request
B
™
J2EE SDK Tools
THE J2EE™ SDK includes a number of tools, which are described in this
appendix.
In This Appendix
J2EE Administration Tool 434
Cleanup Tool 435
Cloudscape Server 435
Starting Cloudscape 436
Stopping Cloudscape 436
Running the Interactive SQL Tool 436
Cloudscape Server Configuration 437
Deployment Tool 438
J2EE Server 439
Key Tool 439
Packager Tool 440
EJB JAR File 440
Web Application WAR File 441
Application Client JAR File 441
J2EE Application EAR File 442
Specifying the Runtime Deployment Descriptor 442
Resource Adapter RAR File 443
Realm Tool 444
Examples 444
runclient Script 445
Syntax 445
Example 446
Accessing a Remote Server 446
Preventing the User Name and Password Prompts 447
Verifier Tool 447
Command-Line Verifier 447
Stand-Alone GUI Verifier 448
433
J2EE™ SDK TOOLS
434
J2EE Administration Tool
The j2eeadmin tool is a command-line script that enables you to add and
remove these resources: JDBC™ drivers and data sources, JMS destinations and
connection factories, and resource adapter connection factories.
Table B–1 j2eeadmin Tool Options
Option
addConnectorFactory
<jndiname>
[<appname>:]
<rarfilename>
[<xausername>
<xapassword>]
[props
(<name>=<value>)+]
Description
Adds a connection factory with the specified <jndi
name>. The connection factory is contained in the RAR
file specified by <rarfilename>. The <rarfile
name> must be the base name of the file; it cannot
include any prefix ending in / (UNIX) or \ (Windows). If
the RAR file is contained in an EAR file, then the name
of the J2EE application name must be specified by
<appname>, followed by a colon. Optionally, a user
name and password for the factory may be specified.
Also optional is the props flag, followed by one or
more name-value pairs that specify properties for this
factory. To prevent the shell from interpreting characters
in the values, enclose the values in single or double
quotes.
addJdbcDriver
<classname>
Adds the JDBC driver specified by its fully qualified
<classname>. You must also update the
J2EE_CLASSPATH environment variable in the file
bin\userconfig.bat. Then you must restart the J2EE
server.
addJdbcDatasource
<jndiname> <url>
Adds the JDBC DataSource with the specified <jndi
name> and <url>.
addJdbcXADatasource
<jndiname>
<classname>
[<xausername>
<xapassword>]
[props
<name>=<value>)+]
Adds the JDBC XADataSource with the specified
<jndiname> and fully-qualified <classname>.
Optionally, a user name and password for the Data
Source may be specified. Also optional is the props
flag, followed by one or more name-value pairs that
specify properties for this DataSource.
addJmsDestination
<jndiname>
(queue|topic)
Adds a JMS destination with the specified <jndi
name> and declares the destination as either a queue or
topic.
CLEANUP TOOL
Table B–1 j2eeadmin Tool Options (Continued)
Option
Description
addJmsFactory
<jndiname>
(queue|topic)
[props
(<name>=<value>)+]
Adds a JMS connection factory with the specified
<jndiname> and destination type, either queue or
topic. Optionally, one or more properties may be specified with name-value pairs.
list<resourcetype>
Lists resources of the specified <resourcetype>,
either ConnectorFactory, JdbcDriver, JdbcData
source, JdbcXADatasource, JmsDestination, or
JmsFactory. There is no space between list and
<resourcetype>.
remove<resourcetype>
<jndiname>
Removes the resource of the specified <resource
type> and <jndiname>. (See the description of list for the allowed <resourcetype> elements.)
removeAll<resourcetype>
Removes all resources of the specified <resource
type>. (See the description of list for the allowed
<resourcetype> elements.)
Cleanup Tool
The cleanup tool is a command-line script that removes all deployed applications from your J2EE server. It will not delete the component files (JAR, WAR,
EAR).
Note: Use this utility with care!
Cloudscape Server
The examples in this manual have been tested with the Cloudscape DBMS,
which is included in the J2EE SDK.
435
J2EE™ SDK TOOLS
436
Starting Cloudscape
Before your enterprise beans can access a Cloudscape database, you must run the
Cloudscape server from the command line:
cloudscape start
You should see output similar to the following:
Mon Aug 09 11:50:30 PDT 1999: [RmiJdbc]
COM.cloudscape.core.JDBCDriver registered in DriverManager
Mon Aug 09 11:50:30 PDT 1999: [RmiJdbc] Binding . . ..
Mon Aug 09 11:50:30 PDT 1999: [RmiJdbc] No installation of
RMI Security Manager...
Mon Aug 09 11:50:31 PDT 1999: [RmiJdbc] RmiJdbcServer
bound in rmi registry
Stopping Cloudscape
To stop the server type the following command:
cloudscape stop
You should see output similar to the following:
Attempting to shutdown RmiJdbc server
RmiJdbc Server RmiAddr is: //buzz/RmiJdbcServer
WARNING: Shutdown was successful!
Note: If you stop the server with Control-c, files will not be closed properly. When
the server is started the next time, it must perform recovery by rolling back noncommitted transactions and possibly applying the forward log.
Running the Interactive SQL Tool
The Cloudscape product includes a text-based, interactive tool called ij. (This
tool is not supported by Sun Microsystems, Inc.) You can run the ij tool by typing this command:
cloudscape isql
CLOUDSCAPE SERVER
Within the tool, each command you type must end in a semicolon. The commands in the next example display all rows from the orders table, execute a
SQL script named myscript.sql, and end the tool session:
ij> select * from orders;
ij> run 'myscript.sql';
ij> exit;
The following example runs a SQL script from the command line:
cloudscape isql < myscript.sql
This command lists the names of all user tables in the database:
ij> select tablename from sys.systables
where tabletype = 'T';
The next example displays the column names of the orders table:
ij> select columnname from sys.syscolumns
where referenceid =
(select tableid from sys.systables
where tablename = 'orders');
Before you deploy an entity bean with container-managed persistence, you use
deploytool to generate the bean’s SQL statements. Because the table names in
these SQL statements are case sensitive, you must enclose them in double
quotes:
ij> select * from "TeamBeanTable";
For more information on the ij tool, please refer to the online documentation on
the Cloudscape Web site:
http://www.cloudscape.com
Cloudscape Server Configuration
The default database used by the Cloudscape server is named CloudscapeDB.
This database will reside in the cloudscape directory of your J2EE SDK installation. The CloudscapeDB database will be created automatically the first time it
is accessed. The driver for the Cloudscape server is already configured in the
config/default.properties file. No further changes by you are necessary.
437
J2EE™ SDK TOOLS
438
Deployment Tool
The deploytool utility has two versions: GUI and command line. The GUI version enables you to package components and to deploy applications. If you run
the deploytool script with no options, the GUI version is launched.
The GUI version includes online help information that is context sensitive. To
access a help topic for a particular dialog box or tab, press F1.
The command-line version of the tool enables you to deploy and undeploy applications. To package components from the command line, use the packager tool.
Table B–2 deploytool Options
Option
Description
deploy
<ear-filename>
<servername>
[<clientstubjar>]
Deploys the J2EE application contained in the EAR
file specified by <earfilename> onto the J2EE
server running on the machine specified by
<servername>. Optionally, a JAR file for a standalone Java application client may be created by specifying <clientstubjar>.
deployConnector
<rarfilename>
<servername>
Deploys the resource adapter contained in the RAR
file specified by <rarfilename> onto the J2EE
server running on the machine specified by
<servername>.
generateSQL
<earfilename>
<servername>
[noOverWrite]
Generates SQL statements for all entity beans with
container-managed persistence. These beans are in
the EAR file specified by <earfilename> that has
been deployed on the J2EE server running on the
machine specified by <servername>. If the
noOverWrite option is specified, then existing SQL
statements are not overwritten.
listApps
<servername>
Lists the J2EE applications that are deployed on the
J2EE server running on the machine specified by
<servername>.
listConnectors
<servername>
Lists the resource adapters that are deployed on the
J2EE server running on the machine specified by
<servername>.
J2EE SERVER
Table B–2 deploytool Options (Continued)
Option
Description
undeployConnector
<rarfilename>
<servername>
Undeploys the resource adapter contained in the file
specified by <rarfilename> from the J2EE server
running on the machine specified by <server
name>.
uninstall
<appname>
<servername>
Undeploys the J2EE application whose name is
<appname> from the J2EE server running on the
machine specified by <servername>.
help
Displays options.
ui
Runs the GUI version (default).
J2EE Server
To launch the J2EE server, run the j2ee script from the command-line prompt.
Table B–3 j2ee Options
Option
Description
verbose
Redirects all logging output to the current shell.
version
Displays the version number.
stop
Stops the J2EE server.
To run the HTTPS service of the J2EE server, you must install a server certificate. For instructions, see Chapter 15.
Key Tool
The keytool utility creates public and private keys and generates X.509 selfsigned certificates. The J2EE SDK version of the keytool utility has the same
options as the version distributed with the J2SE SDK. For more information, see
Chapter 15 and the J2EE SDK Configuration Guide.
439
J2EE™ SDK TOOLS
440
Packager Tool
The packager tool is a command-line script that enables you to package J2EE
components. This tool is for advanced users who do not want to use deploytool
to package J2EE components. With packager, you can create the following
component packages:
•
•
•
•
•
EJB JAR file
Web application WAR file
Application client JAR file
J2EE application EAR file
Resource adapter RAR file
The packager tool also enables you to set the runtime deployment information
of an application EAR file.
Note: To make them easier to read, the examples that follow contain line breaks
within the commands. When typing these commands, do not include the line breaks.
EJB JAR File
Syntax
packager ejbJar <root.directory> <file.list>
<ejb.dd> <ejb.jar>
Example
The following command packages the three Hello classes and the hello
jar.xml deployment descriptor into the HelloEJB.jar file:
packager ejbJar /home/duke/classes/
HelloHome.class:HelloEJB.class:HelloRemote.class
hellojar.xml HelloEJB.jar
PACKAGER TOOL
Web Application WAR File
Syntax
packager webArchive
[classpath <root.directory> [classFiles <file.list>]]
<content.root> [contentFiles <file.list>] <web.dd> <web.war>
Example
The following command packages helper classes and JSP™ pages into the
bookstore2.war file:
packager webArchive classpath .
classFiles
cart\ShoppingCart.class:cart\ShoppingCartItem.class:
database\BookDB.class:util\Currency.class
.
contentFiles
banner.jsp:bookdetails.jsp:bookstore.jsp:cashier.jsp:
catalog.jsp:DigitalClock.class:duke.books.gif:
errorpage.jsp:initdestroy.jsp:receipt.jsp:showcart.jsp
web.xml bookstore2.war
Application Client JAR File
Syntax
packager applicationClient <root.directory> <file.list>
<main.class> <appclient.dd> <appclient.jar>
Example
The following command creates the appClient.jar file:
packager applicationClient classes
hola:hello/HelloUtil.class
package.Main client.xml appClient.jar
441
J2EE™ SDK TOOLS
442
J2EE Application EAR File
Syntax
packager enterpriseArchive <file.only.list>
[alternativeDescriptorEntries <file.only.list>]
[libraryJars <file.list>] <app.name> <app.ear>
Example
In the following command, the optional alternativeDescriptorEntries flag
allows you to specify the external descriptor entry name of each component as
you wish it to appear in the EAR file:
packager enterpriseArchive
myWeb.war:myEJB.jar:appClient.ear
alternativeDescriptorEntries
myWeb/web.xml:myEjb/myEjb.xml:client/client.xml
myAppName myApp.ear
Specifying the Runtime Deployment Descriptor
The preceding example specified the enterpriseArchive flag to create a portable J2EE application EAR file. This file is portable because you can import it
into any J2EE environment that conforms to the J2EE Specification. Although
you can import the file into the deploytool, you cannot deploy it on the J2EE
server until it contains a runtime deployment descriptor. This deployment
descriptor is an XML file that contains information such as the JNDI names of
the application’s enterprise beans.
Syntax
packager setRuntime <app.ear>|<appclient.jar> <runtime.xml>
[o <output.file>]
Example
In the following command, the setRuntime flag instructs packager to insert
the runtime deployment descriptor (sunj2eeri.xml) into the myApp.ear file:
packager setRuntime MyApp.ear sunj2eeri.xml
The following command copies MyApp.ear to OtherApp.ear, inserts the deployment descriptor into the OtherApp.ear file, and leaves MyApp.ear unchanged:
PACKAGER TOOL
packager setRuntime MyApp.ear sunj2eeri.xml o OtherApp.ear
To obtain an example of the runtime deployment descriptor, extract it from an
EAR file that you’ve already deployed:
jar xvf SomeApp.ear
The DTD of the runtime deployment descriptor is in the lib/dtds/sunj2ee
ridtd file of your J2EE SDK installation.
Note: The runtime deployment descriptor (sunj2eeri<version>.xml) is not
required by the J2EE Specification. This descriptor is unique to the J2EE SDK and
may change in future releases.
Resource Adapter RAR File
Syntax
packager connector <root.directory> <file.list>
ra.xml myConnector.rar
Example
In this example, the jar command packages the files under the com directory
into myfiles.jar. The packager command creates a RAR file named theCon
nector.rar that contains myfiles.jar and the myra.xml deployment descriptor:
jar cvf myadapter.jar com
packager connector . myadapter.jar myra.xml theConnector.rar
443
J2EE™ SDK TOOLS
444
Realm Tool
The realmtool utility is a command-line script that enables you to add and
remove J2EE users and to import certificate files.
Table B–4 realmtool Options
Option
Description
show
Lists the realm names.
list <realm-name>
Lists the users in the specified realm. This release
has two realms: default and certificate.
listGroups
Lists the groups in the default realm.
userGroups <username>
Lists the groups in the default realm to which the
specified user belongs.
add <username password
group[,group]>
Adds the specified user to the default realm.
addGroup <group>
Adds a group to the default realm.
import <certificatefile>
Adds a user to the certificate realm by importing a file containing an X.509 certificate.
remove <realmname user
name>
Removes a user from the specified realm.
removeGroup <group>
Removes a group.
Examples
To display all users in the default realm, type this command:
realmtool list default
To add a user to the default realm you specify the add flag. The following command will add a user named robin who is protected by the password red, and
will include robin in the bird and wing groups:
realmtool add robin red bird,wing
RUNCLIENT
SCRIPT
To add a user to the certificate realm, you import a file containing the X.509 certificate that identifies the user:
realmtool import certificatefile
To remove a user, you specify the remove flag. For example, to remove a user
named sparrow from the default realm, you would type the following command:
realmtool remove default sparrow
To add a group to the default realm you specify the addGroup flag. The following command adds the wing group:
realmtool addGroup wing
(You cannot add a group to the certificate realm.)
To remove a group from the default realm, you specify the removeGroup flag:
realmtool removeGroup wing
runclient Script
To run a J2EE application client, you execute the runclient script from a command-line prompt.
Syntax
runclient client <appjar> [name <name>]
[textauth] [app.args]
Table B–5 runclient Options
Option
Description
client <appjar>
The J2EE application EAR file
name <name>
The display name of the J2EE application client
component
445
J2EE™ SDK TOOLS
446
Table B–5 runclient Options (Continued)
Option
Description
textauth
Causes the client container to prompt for the user
name and password are from the command line, not
from a pop-up window
<appargs>
Any arguments required by the J2EE application
Example
Before executing the runclient command, you must set the APPCPATH environment variable to the name of the client JAR stub file that is generated during
deployment. The following example shows how to set APPCPATH on a Windows
machine. The runclient command that follows launches a client named Fabu
lousClient. The J2EE application of this client resides in the FabulousApp.ear
file.
set APPCPATH=FabulousAppClient.jar
runclient client FabulousApp.ear name FabulousClient
Accessing a Remote Server
If the J2EE application client will reside on a different machine than the J2EE
server, before executing runclient you must do the following:
1. Install the J2EE SDK on the remote client’s machine. The SDK must be
on the client’s machine so that you can run its runclient script. You do
not need to start the J2EE server on the client’s machine.
2. Copy the EAR file to the remote client’s machine.
3. Copy the client JAR stub file to the remote client’s machine.
4. Set the APPCPATH environment variable to the name of the client JAR stub
file.
5. Set the VMARGS environment variable to the following value:
Dorg.omg.CORBA.ORBInitialHost=<remote.host>
For example, if the remote host were named murphy, you would set the
VMARGS variable on a Windows machine as follows:
set VMARGS=Dorg.omg.CORBA.ORBInitialHost=murphy
VERIFIER TOOL
Preventing the User Name and Password Prompts
During iterative development, you may find it convenient to prevent the client
container from prompting for the user name and password. To prevent these
prompts, set the VMARGS environment variable to the following value:
Dj2eelogin.name=guest Dj2eelogin.password=guest123
Verifier Tool
The verifier tool validates J2EE archive files (EAR, WAR, JAR).
You can run verifier three ways:
• From within the deploytool GUI
• As a command-line utility
• As a stand-alone GUI utility
To run verifier from within the deploytool GUI, choose Verifier from the
Tools menu. The following sections explain how to run the verifier the other two
ways.
Command-Line Verifier
The command-line verifier tool has the following syntax:
verifier [options] <filename>
The filename argument is the name of a J2EE component file.
Table B–6 verifier Options
Syntax
Description
v
Displays a verbose version of output.
o <outputfile>
Writes the results to the specified <outputfile>, overriding the
default Results.txt file.
u
Runs the stand-alone GUI version.
447
J2EE™ SDK TOOLS
448
Table B–6 verifier Options
Syntax
Description
<reportlevel>
Determines whether warnings or failures are reported. The
<reportlevel> may be either a, w, or f:
a (all results)
w (warnings only)
f (failures only)
By default, only warnings and failures are reported.
Stand-Alone GUI Verifier
To run the stand-alone GUI verifier tool, follow these steps:
1. From the command-line prompt, type:
verifier u
2. To select a file for verification, click Add.
3. Select the radio button to indicate the report level:
• All Results
• Failures Only
• Failures and Warnings Only
4. Click OK.
5. The verifier tool lists the details in the lower portion of the screen.
C
Examples
Table C–1 lists the examples in the tutorial and specifies the chapter or section in
which each is discussed.
Table C–1 Examples
Chapter or Section
Directory
(examples/src)
Features
Container-Managed
Transactions, page (316)
ejb/bank
Rolling back a container-managed transaction, synchronizing a session bean’s instance
variables with the database
values
The CartEJB
Example, page (70)
ejb/cart
A stateful session bean
Accessing Environment
Entries, page (78)
ejb/checker
A session bean with environment entries
Container-Managed Persistence
Examples, page (119),
Example Queries, page (167)
ejb/cmproster
An application with containermanaged entity beans and
relationships
Mail Session
Connections, page (359)
ejb/confirmer
Sending e-mail from an enterprise bean
449
450
EXAMPLES
Table C–1 Examples (Continued)
Chapter or Section
Directory
(examples/src)
Features
ejb/converter
Step-by-step instructions for
building a simple application
with a session bean, JSP page,
and J2EE application client
Many-to-Many
Relationships, page (110)
ejb/enroller
Mapping a many-to-many
relationship between database
tables to a pair of entity beans
with bean-managed persistence
URL Connections, page (362)
ejb/htmlreader
Connecting to a URL from an
enterprise bean
ejb/order
Mapping a one-to-many relationship between database
tables to a helper class and an
entity bean with bean-managed persistence
An Entity Bean for the Child
Table, page (107)
ejb/salesrep
Mapping a one-to-many relationship between database
tables to a pair of entity beans
with bean-managed persistence
The SavingsAccountEJB
Example, page (84),
Database Connections for Enterprise Beans, page (356)
ejb/savingsaccount
An entity bean with beanmanaged persistence
A Message-Driven Bean
Example, page (155)
ejb/simplemessage
A simple message-driven bean
that listens to a JMS queue
ejb/storagebin
Mapping a one-to-one relationship between database
tables to a pair of entity beans
with bean-managed persistence
Getting Started, page (21)
A Helper Class for the Child
Table, page (103)
One-to-One
Relationships, page (99)
451
Table C–1 Examples (Continued)
Chapter or Section
Directory
(examples/src)
Features
Bean-managed transactions
with the javax.transac
JTA Transactions, page (325)
ejb/teller
tion.UserTransaction
interface
JDBC Transactions, page (324)
ejb/warehouse
Bean-managed transactions
with the java.sql.Connec
tion interface
Java Servlet
Technology, page (209)
web/bookstore1
Servlet-based Web application
JavaServer Pages™
Technology, page (245)
web/bookstore2
JSP™ based Web application,
w/ 1 enterprise bean
Custom Tags in JSP™
Pages, page (279)
web/bookstore3
JSP based Web application,
with JSP custom tags and one
enterprise bean
JavaServer Pages™
Technology, page (245)
web/date
Simple JSP pages
Web Clients and
Components, page (193)
web/hello1
Simple servlet
Web Clients and
Components, page (193)
web/hello2
Simple JSP pages
connector/cci
Connecting to a resource
adapter through the Common
Client Interface (CCI) API of
the J2EE Connector architecture
bank
Full-featured J2EE application
including J2EE application
client, entity and session
beans, servlet, JSP pages, and
JSP custom tags.
Programming with the
CCI, page (377)
The Duke’s Bank
Application, page (391)
452
EXAMPLES
Glossary
abstract schema
The part of an entity bean’s deployment descriptor that defines the bean’s
persistent fields and relationships.
abstract schema name
A logical name that is referenced in Enterprise JavaBeans™ (EJB QL) queries.
access control
The methods by which interactions with resources are limited to collections
of users or programs for the purpose of enforcing integrity, confidentiality,
or availability constraints.
ACID
The acronym for the four properties guaranteed by transactions: atomicity,
consistency, isolation, and durability.
activation
The process of transferring an enterprise bean from secondary storage to
memory. (See passivation.)
applet
A component that typically executes in a Web browser, but can execute in a
variety of other applications or devices that support the applet programming
model.
applet container
A container that includes support for the applet programming model.
Application Component Provider
A vendor that provides the Java classes that implement components’ methods, JSP page definitions, and any required deployment descriptors.
453
454
GLOSSARY
Application Assembler
A person that combines components and modules into deployable application units.
application client
A first-tier client component that executes in its own Java virtual machine.
Application clients have access to some (JNDI, JDBC, RMI-IIOP, JMS)
J2EE platform APIs.
application client container
A container that supports application client components.
application client module
A software unit that consists of one or more classes and an application client
deployment descriptor.
authentication
The process by which an entity proves to another entity that it is acting on
behalf of a specific identity. The J2EE platform requires three types of
authentication: basic, form-based, and mutual, and supports digest authentication.
authorization
The process by which access to a method or resource is determined. Authorization in the J2EE platform depends upon the determination of whether the
principal associated with a request through authentication is in a given security role. A security role is a logical grouping of users defined by an Application Component Provider or Assembler. A Deployer maps security roles to
security identities. Security identities may be principals or groups in the
operational environment.
authorization constraint
An authorization rule that determines who is permitted to access a Web
resource collection.
basic authentication
An authentication mechanism in which a Web server authenticates an entity
with a user name and password obtained using the Web client’s built-in
authentication mechanism.
bean-managed persistence
Data transfer between an entity bean’s variables and a resource manager
managed by the entity bean.
bean-managed transaction
A transaction whose boundaries are defined by an enterprise bean.
GLOSSARY
business logic
The code that implements the functionality of an application. In the Enterprise JavaBeans model, this logic is implemented by the methods of an
enterprise bean.
business method
A method of an enterprise bean that implements the business logic or rules
of an application.
callback methods
Component methods called by the container to notify the component of
important events in its life cycle.
caller
Same as caller principal.
caller principal
The principal that identifies the invoker of the enterprise bean method.
cascade delete
A deletion that triggers another deletion. A cascade delete may be specified
for an entity bean with container-managed persistence.
client certificate authentication
An authentication mechanism in which a client uses a X.509 certificate to
establish its identity.
commit
The point in a transaction when all updates to any resources involved in the
transaction are made permanent.
component
An application-level software unit supported by a container. Components
are configurable at deployment time. The J2EE platform defines four types
of components: enterprise beans, Web components, applets, and application
clients.
component contract
The contract between a component and its container. The contract includes:
life cycle management of the component, a context interface that the
instance uses to obtain various information and services from its container,
and a list of services that every container must provide for its components.
connection
See resource manager connection.
connection factory
See resource manager connection factory.
455
456
GLOSSARY
connector
A standard extension mechanism for containers to provide connectivity to
enterprise information systems. A connector is specific to an enterprise
information system and consists of a resource adapter and application development tools for enterprise information system connectivity. The resource
adapter is plugged in to a container through its support for system-level contracts defined in the connector architecture.
Connector architecture
An architecture for integration of J2EE products with enterprise information
systems. There are two parts to this architecture: a resource adapter provided
by an enterprise information system vendor and the J2EE product that allows
this resource adapter to plug in. This architecture defines a set of contracts
that a resource adapter has to support to plug in to a J2EE product, for example, transactions, security, and resource management.
container
An entity that provides life cycle management, security, deployment, and
runtime services to components. Each type of container (EJB, Web, JSP,
servlet, applet, and application client) also provides component-specific services.
container-managed persistence
Data transfer between an entity bean’s variables and a resource manager
managed by the entity bean’s container.
container-managed transaction
A transaction whose boundaries are defined by an EJB container. An entity
bean must use container-managed transactions.
context attribute
An object bound into the context associated with a servlet.
context root
A name that gets mapped to the document root of a Web client.
conversational state
The field values of a session bean plus the transitive closure of the objects
reachable from the bean’s fields. The transitive closure of a bean is defined
in terms of the serialization protocol for the Java programming language,
that is, the fields that would be stored by serializing the bean instance.
CORBA
Common Object Request Broker Architecture. A language independent, distributed object model specified by the Object Management Group.
GLOSSARY
create method
A method defined in the home interface and invoked by a client to create an
enterprise bean.
credentials
The information describing the security attributes of a principal.
CSS
Cascading Style Sheet. A stylesheet used with HTML and XML documents
to add a style to all elements marked with a particular tag, for the direction of
browsers or other presentation mechanisms.
CTS
Compatibility Test Suite. A suite of compatibility tests for verifying that a
J2EE product complies with the J2EE platform specification.
delegation
An act whereby one principal authorizes another principal to use its identity
or privileges with some restrictions.
Deployer
A person who installs modules and J2EE applications into an operational
environment.
deployment
The process whereby software is installed into an operational environment.
deployment descriptor
An XML file provided with each module and application that describes how
they should be deployed. The deployment descriptor directs a deployment
tool to deploy a module or application with specific container options and
describes specific configuration requirements that a Deployer must resolve.
destination
A JMS administered object that encapsulates the identity of a JMS queue or
topic. See point-to-point messaging system, publish/subscribe messaging
system.
digest authentication
An authentication mechanism in which a Web client authenticates to a Web
server by sending the server a message digest along its HTTP request message. The digest is computed by employing a one-way hash algorithm to a
concatenation of the HTTP request message and the client’s password. The
digest is typically much smaller than the HTTP request, and doesn’t contain
the password.
457
458
GLOSSARY
distributed application
An application made up of distinct components running in separate runtime
environments, usually on different platforms connected via a network. Typical distributed applications are two-tier (client-server), three-tier (clientmiddleware-server), and multitier (client-multiple middleware-multiple
servers).
document root
The top-level directory of a WAR. The document root is where JSP pages,
client-side classes and archives, and static Web resources are stored.
DOM
Document Object Model. A tree of objects with interfaces for traversing the
tree and writing an XML version of it, as defined by the W3C specification.
DTD
Document Type Definition. A description of the structure and properties of a
class of XML files.
durable subscription
In a JMS publish/subscribe messaging system, a subscription that continues
to exist whether or not there is a current active subscriber object. If there is
no active subscriber, JMS retains the subscription’s messages until they are
received by the subscription or until they expire.
EAR file
A JAR archive that contains a J2EE application.
EJB™
See Enterprise JavaBeans™.
EJB container
A container that implements the EJB component contract of the J2EE architecture. This contract specifies a runtime environment for enterprise beans
that includes security, concurrency, life cycle management, transaction,
deployment, naming, and other services. An EJB container is provided by an
EJB or J2EE server.
EJB Container Provider
A vendor that supplies an EJB container.
EJB context
An object that allows an enterprise bean to invoke services provided by the
container and to obtain the information about the caller of a client-invoked
method.
GLOSSARY
EJB home object
An object that provides the life cycle operations (create, remove, find) for an
enterprise bean. The class for the EJB home object is generated by the container’s deployment tools. The EJB home object implements the enterprise
bean’s home interface. The client references an EJB home object to perform
life cycle operations on an EJB object. The client uses JNDI to locate an EJB
home object.
EJB JAR file
A JAR archive that contains an EJB module.
EJB module
A software unit that consists of one or more enterprise beans and an EJB
deployment descriptor.
EJB object
An object whose class implements the enterprise bean’s remote interface. A
client never references an enterprise bean instance directly; a client always
references an EJB object. The class of an EJB object is generated by a container’s deployment tools.
EJB server
Software provides services to an EJB container. For example, an EJB container typically relies on a transaction manager that is part of the EJB server
to perform the two-phase commit across all the participating resource managers. The J2EE architecture assumes that an EJB container is hosted by an
EJB server from the same vendor, so does not specify the contract between
these two entities. An EJB server may host one or more EJB containers.
EJB Server Provider
A vendor that supplies an EJB server.
enterprise bean
A component that implements a business task or business entity and resides
in an EJB container; either an entity bean, session bean, or message-driven
bean.
enterprise information system
The applications that comprise an enterprise’s existing system for handling
company-wide information. These applications provide an information
infrastructure for an enterprise. An enterprise information system offers a
well defined set of services to its clients. These services are exposed to clients as local and/or remote interfaces. Examples of enterprise information
systems include: enterprise resource planning systems, mainframe transaction processing systems, and legacy database systems.
459
460
GLOSSARY
enterprise information system resource
An entity that provides enterprise information system-specific functionality
to its clients. Examples are: a record or set of records in a database system, a
business object in an enterprise resource planning system, and a transaction
program in a transaction processing system.
Enterprise Bean Provider
An application programmer who produces enterprise bean classes, remote
and home interfaces, and deployment descriptor files, and packages them in
an EJB JAR file.
Enterprise JavaBeans™ (EJB™)
A component architecture for the development and deployment of objectoriented, distributed, enterprise-level applications. Applications written
using the Enterprise JavaBeans architecture are scalable, transactional, and
secure.
Enterprise JavaBeans Query Language (EJB QL)
Defines the queries for the finder and select methods of an entity bean with
container-managed persistence. A subset of SQL92, EJB QL has extensions
that allow navigation over the relationships defined in an entity bean’s
abstract schema.
entity bean
An enterprise bean that represents persistent data maintained in a database.
An entity bean can manage its own persistence or it can delegate this function to its container. An entity bean is identified by a primary key. If the container in which an entity bean is hosted crashes, the entity bean, its primary
key, and any remote references survive the crash.
filter
An object that can transform the header and/or content of a request or
response. Filters differ from Web components in that they usually do not
themselves create responses but rather they modify or adapt the requests for
a resource, and modify or adapt responses from a resource. A filter should
not have any dependencies on a Web resource for which it is acting as a filter
so that it can be composable with more than one type of Web resource.
finder method
A method defined in the home interface and invoked by a client to locate an
entity bean.
form-based authentication
An authentication mechanism in which a Web container provides an application-specific form for logging in.
GLOSSARY
group
A collection of principals within a given security policy domain.
handle
An object that identifies an enterprise bean. A client may serialize the handle, and then later deserialize it to obtain a reference to the enterprise bean.
home interface
One of two interfaces for an enterprise bean. The home interface defines
zero or more methods for managing an enterprise bean. The home interface
of a session bean defines create and remove methods, while the home interface of an entity bean defines create, finder, and remove methods.
home handle
An object that can be used to obtain a reference of the home interface. A
home handle can be serialized and written to stable storage and deserialized
to obtain the reference.
HTML
Hypertext Markup Language. A markup language for hypertext documents
on the Internet. HTML enables the embedding of images, sounds, video
streams, form fields, references to other objects with URLs and basic text
formatting.
HTTP
Hypertext Transfer Protocol. The Internet protocol used to fetch hypertext
objects from remote hosts. HTTP messages consist of requests from client to
server and responses from server to client.
HTTPS
HTTP layered over the SSL protocol.
impersonation
An act whereby one entity assumes the identity and privileges of another
entity without restrictions and without any indication visible to the recipients
of the impersonator’s calls that delegation has taken place. Impersonation is
a case of simple delegation.
IDL
Interface Definition Language. A language used to define interfaces to
remote CORBA objects. The interfaces are independent of operating systems and programming languages.
IIOP
Internet Inter-ORB Protocol. A protocol used for communication between
CORBA object request brokers.
461
462
GLOSSARY
initialization parameter
A parameter that initializes the context associated with a servlet.
ISV
Independent Software Vendor.
J2EE™
See Java 2 Platform, Enterprise Edition.
J2ME™
See Java 2 Platform, Micro Edition.
J2SE™
See Java 2 Platform, Standard Edition.
J2EE application
Any deployable unit of J2EE functionality. This can be a single module or a
group of modules packaged into an .ear file with a J2EE application deployment descriptor. J2EE applications are typically engineered to be distributed
across multiple computing tiers.
J2EE product
An implementation that conforms to the J2EE platform specification.
J2EE Product Provider
A vendor that supplies a J2EE product.
J2EE server
The runtime portion of a J2EE product. A J2EE server provides EJB and/or
Web containers.
JAR Java ARchive
A platform-independent file format that permits many files to be aggregated
into one file.
Java™ 2 Platform, Enterprise Edition (J2EE)
An environment for developing and deploying enterprise applications. The
J2EE platform consists of a set of services, application programming interfaces (APIs), and protocols that provide the functionality for developing
multitiered, Web-based applications.
Java™ 2 Platform, Micro Edition (J2SE)
A highly optimized Java runtime environment targeting a wide range of consumer products, including pagers, cellular phones, screenphones, digital settop boxes and car navigation systems.
Java™ 2 Platform, Standard Edition (J2SE)
The core Java technology platform.
GLOSSARY
Java™ 2 SDK, Enterprise Edition (J2EE SDK)
Sun’s implementation of the J2EE platform. This implementation provides
an operational definition of the J2EE platform.
Java™ Message Service (JMS)
An API for using enterprise messaging systems such as IBM MQ Series,
TIBCO Rendezvous, and so on.
Java Naming and Directory Interface™ (JNDI)
An API that provides naming and directory functionality.
Java™ Transaction API (JTA)
An API that allows applications and J2EE servers to access transactions.
Java™ Transaction Service (JTS)
Specifies the implementation of a transaction manager which supports JTA
and implements the Java mapping of the OMG Object Transaction Service
(OTS) 1.1 specification at the level below the API.
JavaBeans™ component
A Java class that can be manipulated in a visual builder tool and composed
into applications. A JavaBeans component must adhere to certain property
and event interface conventions.
Java IDL
A technology that provides CORBA interoperability and connectivity capabilities for the J2EE platform. These capabilities enable J2EE applications to
invoke operations on remote network services using the OMG IDL and IIOP.
JavaMail™
An API for sending and receiving email.
JavaServer Pages™ (JSP™)
An extensible Web technology that uses template data, custom elements,
scripting languages, and server-side Java objects to return dynamic content
to a client. Typically the template data is HTML or XML elements, and in
many cases the client is a Web browser.
JDBC™
An API for database-independent connectivity between the J2EE platform
and a wide range of data sources.
JMS
See Java Message Service.
JMS administered object
A preconfigured JMS object (a resource manager connection factory or a
destination) created by an administrator for the use of JMS clients and
placed in a JNDI namespace.
463
464
GLOSSARY
JMS application
One or more JMS clients that exchange messages.
JMS client
A Java language program that sends and/or receives messages.
JMS provider
A messaging system that implements the Java Message Service as well as
other administrative and control functionality needed in a full-featured messaging product.
JMS session
A single-threaded context for sending and receiving JMS messages. A JMS
session can be non-transacted, locally transacted, or participating in a distributed transaction.
JNDI
See Java Naming and Directory Interface.
JSP
See JavaServer Pages.
JSP action
A JSP element that can act on implicit objects and other server-side objects
or can define new scripting variables. Actions follow the XML syntax for
elements with a start tag, a body and an end tag; if the body is empty it can
also use the empty tag syntax. The tag must use a prefix.
JSP action, custom
An action described in a portable manner by a tag library descriptor and a
collection of Java classes and imported into a JSP page by a taglib directive. A custom action is invoked when a JSP page uses a custom tag.
JSP action, standard
An action that is defined in the JSP specification and is always available to a
JSP file without being imported.
JSP application
A stand-alone Web application, written using the JavaServer Pages technology, that can contain JSP pages, servlets, HTML files, images, applets, and
JavaBeans components.
JSP container
A container that provides the same services as a servlet container and an
engine that interprets and processes JSP pages into a servlet.
GLOSSARY
JSP container, distributed
A JSP container that can run a Web application that is tagged as distributable
and is spread across multiple Java virtual machines that might be running on
different hosts.
JSP declaration
A JSP scripting element that declares methods, variables, or both in a JSP
file.
JSP directive
A JSP element that gives an instruction to the JSP container and is interpreted at translation time.
JSP element
A portion of a JSP page that is recognized by a JSP translator. An element
can be a directive, an action, or a scripting element.
JSP expression
A scripting element that contains a valid scripting language expression that
is evaluated, converted to a String, and placed into the implicit out object.
JSP file
A file that contains a JSP page. In the Servlet 2.2 specification, a JSP file
must have a .jsp extension.
JSP page
A text-based document using fixed template data and JSP elements that
describes how to process a request to create a response.
JSP scripting element
A JSP declaration, scriptlet, or expression, whose tag syntax is defined by
the JSP specification, and whose content is written according to the scripting
language used in the JSP page. The JSP specification describes the syntax
and semantics for the case where the language page attribute is "java".
JSP scriptlet
A JSP scripting element containing any code fragment that is valid in the
scripting language used in the JSP page. The JSP specification describes
what is a valid scriptlet for the case where the language page attribute is
"java".
JSP tag
A piece of text between a left angle bracket and a right angle bracket that is
used in a JSP file as part of a JSP element. The tag is distinguishable as
markup, as opposed to data, because it is surrounded by angle brackets.
465
466
GLOSSARY
JSP tag library
A collection of custom tags identifying custom actions described via a tag
library descriptor and Java classes.
JTA
See Java Transaction API.
JTS
See Java Transaction Service.
life cycle
The framework events of a component’s existence. Each type of component
has defining events which mark its transition into states where it has varying
availability for use. For example, a servlet is created and has its init method
called by its container prior to invocation of its service method by clients or
other servlets who require its functionality. After the call of its init method
it has the data and readiness for its intended use. The servlet’s destroy
method is called by its container prior to the ending of its existence so that
processing associated with winding up may be done, and resources may be
released. The init and destroy methods in this example are callback methods. Similar considerations apply to all J2EE component types: enterprise
beans, Web components (servlets or JSP pages), applets, and application clients.
message
In the Java Message Service, an asynchronous request, report, or event that
is created, sent, and consumed by an enterprise application, not by a human.
It contains vital information needed to coordinate enterprise applications, in
the form of precisely formatted data that describes specific business actions.
MessageConsumer
An object created by a JMS session that is used for receiving messages sent
to a destination.
MessageProducer
An object created by a JMS session that is used for sending messages to a
destination.
message-driven bean
An enterprise bean that is an asynchronous message consumer. A messagedriven bean has no state for a specific client, but its instance variables may
contain state across the handling of client messages, including an open database connection and an object reference to an EJB object. A client accesses a
message-driven bean by sending messages to the destination for which the
message-driven bean is a message listener.
GLOSSARY
method permission
An authorization rule that determines who is permitted to execute one or
more enterprise bean methods.
module
A software unit that consists of one or more J2EE components of the same
container type and one deployment descriptor of that type. There are three
types of modules: EJB, Web, and application client. Modules can be
deployed as stand-alone units or assembled into an application.
mutual authentication
An authentication mechanism employed by two parties for the purpose of
proving each other’s identity to one another.
naming context
A set of associations between unique, atomic, people-friendly identifiers and
objects.
naming environment
A mechanism that allows a component to be customized without the need to
access or change the component’s source code. A container implements the
component’s naming environment, and provides it to the component as a
JNDI naming context. Each component names and accesses its environment
entries using the java:comp/env JNDI context. The environment entries are
declaratively specified in the component’s deployment descriptor.
non-JMS client
A messaging client program that uses a message system’s native client API
instead of the Java Message Service.
ORB
Object Request Broker. A library than enables CORBA objects to locate and
communicate with one another.
OS principal
A principal native to the operating system on which the J2EE platform is
executing.
OTS
Object Transaction Service. A definition of the interfaces that permit
CORBA objects to participate in transactions.
passivation
The process of transferring an enterprise bean from memory to secondary
storage. (See activation.)
467
468
GLOSSARY
persistence
The protocol for transferring the state of an entity bean between its instance
variables and an underlying database.
persistent field
A virtual field of an entity bean with container-managed persistence, it is
stored in a database.
POA
Portable Object Adapter. A CORBA standard for building server-side applications that are portable across heterogeneous ORBs.
point-to-point message system
A messaging system built around the concept of message queues. Each message is addressed to a specific queue; clients extract messages from the
queue(s) established to hold their messages.
principal
The identity assigned to an user as a result of authentication.
privilege
A security attribute that does not have the property of uniqueness and that
may be shared by many principals.
primary key
An object that uniquely identifies an entity bean within a home.
publish/subscribe message system
A messaging system in which clients address messages to a specific node in
a content hierarchy. Publishers and subscribers are generally anonymous and
may dynamically publish or subscribe to the content hierarchy. The system
takes care of distributing the messages arriving from a node’s multiple publishers to its multiple subscribers.
queue
See point-to-point messaging system.
RAR
A JAR archive that contains a resource adapter.
realm
See security policy domain. Also, a string, passed as part of an HTTP request
during basic authentication, that defines a protection space. The protected
resources on a server can be partitioned into a set of protection spaces, each
with its own authentication scheme and/or authorization database.
re-entrant entity bean
An entity bean that can handle multiple simultaneous, interleaved, or nested
invocations which will not interfere with each other.
GLOSSARY
Reference Implementation
See Java 2 SDK, Enterprise Edition.
relationship field
A virtual field of an entity bean with container-managed persistence, it identifies a related entity bean.
remote interface
One of two interfaces for an enterprise bean. The remote interface defines
the business methods callable by a client.
remove method
Method defined in the home interface and invoked by a client to destroy an
enterprise bean.
resource adapter
A system-level software driver that is used by an EJB container or an application client to connect to an enterprise information system. A resource
adapter is typically specific to an enterprise information system. It is available as a library and is used within the address space of the server or client
using it. A resource adapter plugs in to a container. The application components deployed on the container then use the client API (exposed by adapter)
or tool generated high-level abstractions to access the underlying enterprise
information system. The resource adapter and EJB container collaborate to
provide the underlying mechanisms—transactions, security, and connection
pooling—for connectivity to the enterprise information system.
resource manager
Provides access to a set of shared resources. A resource manager participates
in transactions that are externally controlled and coordinated by a transaction
manager. A resource manager is typically in different address space or on a
different machine from the clients that access it. Note: An enterprise information system is referred to as resource manager when it is mentioned in the
context of resource and transaction management.
resource manager connection
An object that represents a session with a resource manager.
resource manager connection factory
An object used for creating a resource manager connection.
RMI
Remote Method Invocation. A technology that allows an object running in
one Java virtual machine to invoke methods on an object running in a different Java virtual machine.
469
470
GLOSSARY
RMI-IIOP
A version of RMI implemented to use the CORBA IIOP protocol. RMI over
IIOP provides interoperability with CORBA objects implemented in any
language if all the remote interfaces are originally defined as RMI interfaces.
role (development)
The function performed by a party in the development and deployment
phases of an application developed using J2EE technology. The roles are:
Application Component Provider, Application Assembler, Deployer, J2EE
Product Provider, EJB Container Provider, EJB Server Provider, Web Container Provider, Web Server Provider, Tool Provider, and System Administrator.
role (security)
An abstract logical grouping of users that is defined by the Application
Assembler. When an application is deployed, the roles are mapped to security identities, such as principals or groups, in the operational environment.
role mapping
The process of associating the groups and/or principals recognized by the
container to security roles specified in the deployment descriptor. Security
roles have to be mapped by the Deployer before the component is installed
in the server.
rollback
The point in a transaction when all updates to any resources involved in the
transaction are reversed.
SAX
Simple API for XML. An event-driven, serial-access mechanism for accessing XML documents.
security attributes
A set of properties associated with a principal. Security attributes can be
associated with a principal by an authentication protocol and/or by a J2EE
Product Provider.
security constraint
A declarative way to annotate the intended protection of Web content. A
security constraint consists of a Web resource collection, an authorization
constraint, and a user data constraint.
security context
An object that encapsulates the shared state information regarding security
between two entities.
GLOSSARY
security permission
A mechanism, defined by J2SE, used by the J2EE platform to express the
programming restrictions imposed on Application Component Providers.
security permission set
The minimum set of security permissions that a J2EE Product Provider must
provide for the execution of each component type.
security policy domain
A scope over which security policies are defined and enforced by a security
administrator. A security policy domain has a collection of users (or principals), uses a well defined authentication protocol(s) for authenticating users
(or principals), and may have groups to simplify setting of security policies.
security role
See role (security).
security technology domain
A scope over which the same security mechanism is used to enforce a security policy. Multiple security policy domains can exist within a single technology domain.
security view
The set of security roles defined by the Application Assembler.
server principal
The OS principal that the server is executing as.
servlet
A Java program that extends the functionality of a Web server, generating
dynamic content and interacting with Web clients using a request-response
paradigm.
servlet container
A container that provides the network services over which requests and
responses are sent, decodes requests, and formats responses. All servlet containers must support HTTP as a protocol for requests and responses, but may
also support additional request-response protocols such as HTTPS.
servlet container, distributed
A servlet container that can run a Web application that is tagged as distributable and that executes across multiple Java virtual machines running on the
same host or on different hosts.
servlet context
An object that contains a servlet’s view of the Web application within which
the servlet is running. Using the context, a servlet can log events, obtain
471
472
GLOSSARY
URL references to resources, and set and store attributes that other servlets
in the context can use.
servlet mapping
Defines an association between a URL pattern and a servlet. The mapping is
used to map requests to servlets.
session
An object used by a servlet to track a user’s interaction with a Web application across multiple HTTP requests.
session bean
An enterprise bean that is created by a client and that usually exists only for
the duration of a single client-server session. A session bean performs operations, such as calculations or accessing a database, for the client. While a
session bean may be transactional, it is not recoverable should a system
crash occur. Session bean objects can be either stateless or they can maintain
conversational state across methods and transactions. If a session bean maintains state, then the EJB container manages this state if the object must be
removed from memory. However, the session bean object itself must manage its own persistent data.
SSL
Secure Socket Layer. A security protocol that provides privacy over the
Internet. The protocol allows client-server applications to communicate in a
way that cannot be eavesdropped or tampered with. Servers are always
authenticated and clients are optionally authenticated.
SQL
Structured Query Language. The standardized relational database language
for defining database objects and manipulating data.
SQL/J
A set of standards that includes specifications for embedding SQL statements in methods in the Java programming language and specifications for
calling Java static methods as SQL stored procedures and user-defined functions. An SQL checker can detects errors in static SQL statements at program development time, rather than at execution time as with a JDBC driver.
stateful session bean
A session bean with a conversational state.
stateless session bean
A session bean with no conversational state. All instances of a stateless session bean are identical.
GLOSSARY
System Administrator
The person responsible for configuring and administering the enterprise’s
computers, networks, and software systems.
topic
See publish-subscribe messaging system.
transaction
An atomic unit of work that modifies data. A transaction encloses one or
more program statements, all of which either complete or roll back. Transactions enable multiple users to access the same data concurrently.
transaction attribute
A value specified in an enterprise bean’s deployment descriptor that is used
by the EJB container to control the transaction scope when the enterprise
bean’s methods are invoked. A transaction attribute can have the following
values: Required, RequiresNew, Supports, NotSupported, Mandatory,
Never.
transaction isolation level
The degree to which the intermediate state of the data being modified by a
transaction is visible to other concurrent transactions and data being modified by other transactions is visible to it.
transaction manager
Provides the services and management functions required to support transaction demarcation, transactional resource management, synchronization, and
transaction context propagation.
Tool Provider
An organization or software vendor that provides tools used for the development, packaging, and deployment of J2EE applications.
URI
Uniform Resource Identifier. A compact string of characters for identifying
an abstract or physical resource. A URI is either a URL or a URN. URLs and
URNs are concrete entities that actually exist; A URI is an abstract superclass.
URL
Uniform Resource Locator. A standard for writing a textual reference to an
arbitrary piece of data in the World Wide Web. A URL looks like proto
col://host/localinfo where protocol specifies a protocol for fetching
the object (such as HTTP or FTP), host specifies the Internet name of the
targeted host, and localinfo is a string (often a file name) passed to the protocol handler on the remote host.
473
474
GLOSSARY
URL path
The URL passed by a HTTP request to invoke a servlet. The URL consists
of the Context Path + Servlet Path + Path Info, where
• Context Path is the path prefix associated with a servlet context that this
servlet is a part of. If this context is the default context rooted at the base
of the Web server’s URL namespace, the path prefix will be an empty
string. Otherwise, the path prefix starts with a / character but does not end
with a / character.
• Servlet Path is the path section that directly corresponds to the mapping
which activated this request. This path starts with a / character.
• Path Info is the part of the request path that is not part of the Context Path
or the Servlet Path.
URN
Uniform Resource Name. A unique identifier that identifies an entity, but
doesn’t tell where it is located. A system can use a URN to look up an entity
locally before trying to find it on the Web. It also allows the Web location to
change, while still allowing the entity to be found.
user data constraint
Indicates how data between a client and a Web container should be protected. The protection can be the prevention of tampering with the data or
prevention of eavesdropping on the data.
WAR file
A JAR archive that contains a Web module.
Web application
An application written for the Internet, including those built with Java technologies such as JavaServer Pages and servlets, as well as those built with
non-Java technologies such as CGI and Perl.
Web application, distributable
A Web application that uses J2EE technology written so that it can be
deployed in a Web container distributed across multiple Java virtual
machines running on the same host or different hosts. The deployment
descriptor for such an application uses the distributable element.
Web component
A component that provides services in response to requests; either a servlet
or a JSP page.
Web container
A container that implements the Web component contract of the J2EE architecture. This contract specifies a runtime environment for Web components
GLOSSARY
that includes security, concurrency, life cycle management, transaction,
deployment, and other services. A Web container provides the same services
as a JSP container and a federated view of the J2EE platform APIs. A Web
container is provided by a Web or J2EE server.
Web container, distributed
A Web container that can run a Web application that is tagged as distributable and that executes across multiple Java virtual machines running on the
same host or on different hosts.
Web Container Provider
A vendor that supplies a Web container.
Web module
A unit that consists of one or more Web components, other resources, and a
Web deployment descriptor.
Web resource
A static or dynamic object contained in a Web application archive that can
be referenced by a URL.
Web resource collection
A list of URL patterns and HTTP methods that describe a set of resources to
be protected.
Web server
Software that provides services to access the Internet, an intranet, or an
extranet. A Web server hosts Web sites, provides support for HTTP and
other protocols, and executes server-side programs (such as CGI scripts or
servlets) that perform certain functions. In the J2EE architecture, a Web
server provides services to a Web container. For example, a Web container
typically relies on a Web server to provide HTTP message handling. The
J2EE architecture assumes that a Web container is hosted by a Web server
from the same vendor, so does not specify the contract between these two
entities. A Web server may host one or more Web containers.
Web Server Provider
A vendor that supplies a Web server.
XML
Extensible Markup Language. A markup language that allows you to define
the tags (markup) needed to identify the content, data, and text, in XML documents. It differs from HTML the markup language most often used to
present information on the internet. HTML has fixed tags that deal mainly
with style or presentation. An XML document must undergo a transformation into a language with style tags under the control of a stylesheet before it
can be presented by a browser or other presentation mechanism. Two types
475
476
GLOSSARY
of style sheets used with XML are CSS and XSL. Typically, XML is transformed into HTML for presentation. Although tags may be defined as
needed in the generation of an XML document, a Document Type Definition
(DTD) may be used to define the elements allowed in a particular type of
document. A document may be compared with the rules in the DTD to determine its validity and to locate particular elements in the document. J2EE
deployment descriptors are expressed in XML with DTDs defining allowed
elements. Programs for processing XML documents use SAX or DOM APIs.
J2EE deployment descriptors are expressed in XML.
XSL
Extensible Stylesheet Language. An XML transformation language used for
transforming XML documents into documents with flow object tags for presentation purposes. The transformation aspect of XSL has been abstracted
into XSLT with the XSL name now used to designate the presentation flow
language. XSL is a direct descendent of the DSSSL style language for
SGML (Standard Generalized Markup Language), the language from which
XML was subsetted. It was designed to have all the capabilities of CSS, the
stylesheet often used with HTML. XSL flow objects can be presented by
specialized browsers, and themselves transformed into PDF documents.
XSLT
XSL Transformation. An XML file that controls the transformation of an
XML document into another XML document or HTML. The target document often will have presentation related tags dictating how it will be rendered by a browser or other presentation mechanism. XSLT was formerly
part of XSL, which also included a tag language of style flow objects.
Biographies
Web Components
Stephanie Bodoff is a staff writer at Sun Microsystems. She has been
involved with object-oriented enterprise software since graduating from
Columbia University with an M.S. in electrical engineering. For several
years she worked as a software engineer on distributed computing and telecommunications systems and object-oriented software development methods. Since her conversion to technical writing, Stephanie has documented
object-oriented databases, application servers, and enterprise application
development methods. She is a co-author of Designing Enterprise Applications with the Java™ 2 Platform, Enterprise Edition and Object-Oriented
Software Development: The Fusion Method.
Enterprise JavaBeans
Dale Green is a staff writer with Sun Microsystems, where he documents
the J2EE™ platform. In previous positions he programmed business applications, designed databases, taught technical classes, and documented
RDBMS products. He wrote the internationalization and reflection trails for
the Java Tutorial Continued. In his current position he writes about Enterprise JavaBeans™ technology and the J2EE SDK.
Message-Driven Beans
Kim Haase is a staff writer with Sun Microsystems, where she documents
the J2EE platform. In previous positions she has documented compilers,
debuggers, and floating-point programming. She currently writes about the
Java™ Message Service and J2EE SDK tools.
477
478
Security
Eric Jendrock is a staff writer with Sun Microsystems, where he documents
the J2EE platform. Previously, he documented middleware products and
standards. Currently, he writes about the J2EE Compatibility Test Suite and
J2EE security.
Overview
Monica Pawlan is a staff writer for the Java Developer Connection (JDC),
and was a contributing author for the Java Tutorial. She is the author of
Essentials of the Java Programming Language: A Hands-On Guide and coauthor of Advanced Programming for the Java 2 Platform. She has a background in 2D and 3D graphics, security, and database products, and loves to
study and write about emerging technologies. When not writing, she spends
her spare time gardening, studying classical piano, and dreaming of far away
places—some of which she occasionally visits.
J2EE Connector Technology
Beth Stearns is the president of Computer Ease Publishing, a computer consulting firm she founded in 1982. Her client list includes Sun Microsystems
Inc., Silicon Graphics Inc., Oracle Corporation, and Xerox Corporation,
among others. Her Understanding EDT, a guide to Digital Equipment Corporation’s text editor, has sold throughout the world. She received her B.S.
degree from Cornell University and a master’s degree from Adelphi University. Beth wrote the JNI trail for the Java Tutorial. She is a co-author of
Applying Enterprise JavaBeans: Component-Based Development for the
J2EE Platform.
Index
A
abstract schemas 53
defined 166
deployment descriptors 53
deploytool 135
EJB QL 165
hidden from clients 58
names 166
naming conventions 63
types 166
access methods
examples 133, 139
local interfaces 128
persistent fields 54, 123
primary keys 152
relationship fields 55, 124
See deploytool
audience of this tutorial xxi
authentication 335, 358, 367
J2EE application clients
configuring 347
Web resources 338
authentication 338
client-certificate 339
configuring 339
Duke’s Bank 415
form-based 338
HTTP basic 338
setting up client-certificate
350
SSL protection 340
authorization 335, 367
ant
downloading xxiii
examples 26
running xxiii
See also ANT_HOME
version xxiii
ANT_HOME xxiii, 23
Apache Software Foundation xxiii
Jakarta project xxiii
APPCPATH 37
applet containers 10
applets 4, 6
Application Deployment Tool
B
bean-managed persistence
database connections 357
defined 52
examples 84, 104, 112
isolation levels 329
relationships 53
bean-managed transactions
See transactions, bean-managed
BufferedReader 224
479
480
INDEX
business logic 48, 92
business methods 30, 32, 58
client calls 73
database connections 358
examples 91, 125
exceptions 74
local interfaces 128
message-driven beans 158
requirements 74
transactions 319–320, 322,
326, 330
business objects 51, 83
C
cascade delete 134
CCI
See J2EE Connector technology, CCI
cleanup 435
when to use 46
Cloudscape database
container-managed
persistence 137
interactive SQL tool 436
JNDI name 354
method aliases 388
resource adapters 371–372
starting 97, 436
stopping 97, 436
commit 323–324, 326–327
commits
See transactions, commits
Common Client Interface
See J2EE Connector technology, CCI
concurrent access 315
Connection 323–325, 327, 331,
354, 357, 371, 376
connection factories
databases 355
defined 354
queues 157
resource adapters 368
See also DataSource
ConnectionFactory 376
connectors
See J2EE Connector technology
container-managed persistence 53
database connections 357–358
EJB QL 53, 165
examples 119
isolation levels 329
relationships 53
container-managed relationships
bidirectional 55
defined 53
deploytool 131
direction 59, 120, 133
EJB QL 56
examples 120
local access 59
many-to-many 55
many-to-one 55
multiplicity 55, 120, 133
one-to-many 55, 167
one-to-one 55, 180
unidirectional 55
container-managed transactions
See transactions, containermanaged
containers 8
See also
applet containers
EJB containers
481
INDEX
J2EE application clients,
containers
Web containers
services 9
Context 29
context roots 200
specifying 37, 200
create 320
bean-managed persistence 85
compared to ejbCreate 75
container-managed
persistence
137
examples 29, 72, 105
life cycles 64–65
requirements 75, 95, 127
custom tags 267
attributes 286
validation 295
bodies 287
cooperating 288
defining 289
examples 304, 308
scripting variables
defining 287
providing
information
about 300–302
Struts tag library 281
tag handlers 289
defining scripting variables 298
methods 289
simple tag 293
with attributes 294
with bodies 296
tag library descriptors
See tag library descriptors
tutorial-template tag library
281
D
data integrity 315–316, 358
databases
bean-managed persistence 83,
94
business methods 91
clients 4, 48, 58
Cloudscape
See Cloudscape database
connection factories 355
connections 57, 65, 74, 116,
326, 356
creating tables 84, 97, 136
data recovery 315
deleting rows 87
Duke’s Bank tables 398
EIS tier 3
entity beans and tables 51
exceptions 116
foreign keys 54, 100
inserting rows 85
isolation levels 329
J2EE SDK 15
JNDI names 137, 354
message-driven beans 57
multiple 325, 329
persistent fields 54
portable beans 53
primary keys 100, 113
read-only data 51
referential constraints 100
relationships for bean-managed persistence 99
resource references 354
See also persistence
482
INDEX
stored procedures 376, 379
synchronizing with entity
beans 88
table relationships
many-to-many 110
one-to-many 103
one-to-one 99
transactions
See transactions
DataSource 354–355, 357, 371
deployer role 14
deployment descriptors 11
abstract schema 53
container-managed
persistence 123
creating 62
EJB QL 165
enterprise bean 62
viewing 27
enterprise beans 63
J2EE application client
viewing 31
primary key class 113
transaction attributes 320
Web application 194
viewing 34
deploytool
bean-managed persistence 99
container-managed
persistence 128, 148
database users and passwords
358
message-driven beans 160
online help 23
options 438
redeploy operation 39
resource adapters 368
resource references 354
starting 23
wizards 19
Design Patterns, Elements of Reusable Object-Oriented Software
231
destroy 242
development roles 11
doAfterBody 297
doEndTag 293
doFilter 229–230, 234–235
doGet 223
doInitBody 297
doPost 223
doStartTag 293
downloading
J2EE SDK xxii
J2SE xxiii
tutorial xxii
Duke’s Bank 391
building 417
database tables 398
deploying 426
enterprise beans 393–400
J2EE application client 400–
408
running 427
JNDI names 423–424
packaging 417
Web client 409–416
component interaction 414
running 428
E
EAR files 11
adding WAR file 198
EJB JAR files 62
examples xxii
INDEX
EIS 8, 365, 370, 375–376
EJB components
See enterprise beans
EJB containers 10
bean-managed persistence 85
connection pools 359
container-managed
persistence 52
container-managed transactions 316
EJB QL 53
generating primary keys 153
instance contexts 80
instantiating enterprise beans
64, 72
onMessage 158
persistence 119
persistent fields 123
relationships 53, 119
services 47–48
EJB JAR files
container-managed relationships 60
contents 11
EJB QL 165, 178
examples 26
portability 62
EJB QL 165
abstract schemas 166, 178, 190
arithmetic functions 187
boolean logic 188
case sensitivity 177
cmp_field 180
cmr_field 180
collection member declarations 179
collections 179, 186
comments 191
compared to SQL 165, 169,
177
conditional expressions 182–
183
delimiters 180
deployment descriptors 53
deploytool 135, 149
domain of query 165, 176, 178
examples 167
finder methods 53, 145
identification variables 167,
176–177
input parameters 183
multiple declarations 178
navigation 166, 169, 179, 181
navigation operator 169, 180
null values 186, 188
operators 184
parameters 168
path expressions 166, 179
range variables 178
relationship direction 56
scope 165
select methods 124
string functions 187
syntax diagram 173
translated into SQL 145
types 181, 189–190
ejbActivate 64, 66–67, 358
EJBContext 321, 323, 327
ejbCreate
bean-managed persistence 85
compared to create 75
container-managed
persistence 126
database connections 357
examples 72, 85, 105, 126, 138
life cycles 64–65, 68
483
484
INDEX
message-driven beans 159
primary keys 67, 114, 153
requirements 73
ejbFindByPrimaryKey 89, 115
EJBHome 75
ejbLoad 88, 108, 111, 126, 322
EJBObject 76
ejbPassivate 64, 66–67, 358
ejbPostCreate 66, 87, 126
ejbRemove
bean-managed persistence 87,
112
container-managed
persistence 126
database connections 357
examples 87
life cycles 64, 66, 68
message-driven beans 159
ejbStore 88, 126
enterprise beans 7, 24–25, 47
accessing 58
business methods
See business methods 25
compiling 26
contents 62
database connections 356
defined 48
deployment 62
development role 13
distribution 60
Duke’s Bank 393–400
protecting 400
entity beans
See entity beans
environment entries 78
home interfaces
See home interfaces
interfaces 58, 62
life cycles 58, 63
local access 59
local home interfaces
See local home interfaces
local interfaces
See local interfaces
lookups 29
mapping references to JNDI
names 36
message-driven beans
See message-driven beans
method permissions
See method permissions
packaging 26
performance 60–62
persistence
See persistence
propagating security identity
346
protecting 341
references 29, 32, 35
remote access 58
remote interfaces
See remote interfaces
sending e-mail 359
session beans
See session beans
state 55
transactions 327
types 8, 49
unprotected 342
URL connections 362
Enterprise Information Systems
See EIS
Enterprise JavaBeans Query Language
See EJB QL
EnterpriseBean 72
INDEX
entity beans 51
bean-managed persistence
See bean-managed persistence
collections 179
container-managed
persistence
See
container-managed
persistence 53
container-managed
versus
bean-managed 122
database connections 358
Duke’s Bank 397
equality 80
finder methods 59
garbage collection 67
isolation levels 329
persistent state 56
primary keys
See primary keys
transactions 320, 322–323,
327
EntityBean 85
EntityContext 80, 87
environment entries 78
environment variables xxiii, 23
examples
classpath 26
downloading xxii
location xxii, 22
troubleshooting 41, 215
exceptions
business methods 74
create 76, 95
ejbCreate 73, 86
ejbFindByPrimaryKey 91
ejbRemove 88
enterprise beans 116
javax.ejb 117
mail server exceptions 362
mapping to Web resources 201
rolling back transactions 116,
321, 325–326
SQL 321
transactions 318–319
Web components 201
F
Filter 229
filter chains 229, 234
filters 228
defining 229
mapping to Web components
233
mapping to Web resources
233–235
overriding request methods
231
overriding response methods
231
response wrapper 231
findByPrimaryKey 109, 139, 141
finder methods
bean-managed persistence 89
compared to select methods
124
container-managed
persistence 122
deploytool 135
EJB QL 167
examples 89, 101, 145, 190
home interfaces 95
local home interfaces 127
returning collections 106
transactions 320
485
486
INDEX
forward 237
G
garbage collection 67–68
GenericServlet 210
getCallerPrincipal 341
getEJBObject 87
getObject 80
getParameter 224
getPrimaryKey 87, 115
getRemoteUser 340
getRequestDispatcher 235
getServletContext 238
getSession 239
getters
See access methods
getUserPrincipal 340
H
helper classes 62, 76, 103
Duke’s Bank 397
home interfaces 75, 94
defined 58
examples 25, 75, 94
home methods 93
locating 28, 33
home methods 92, 96
HTTP protocol 431
HTTP requests 224, 432
methods 432
query strings 225
See also requests
URLs 224
HTTP responses 226, 432
See also responses
status codes 201, 432
mapping to Web resources
201
HttpServlet 210
HttpServletRequest 224
HttpServletResponse 226
HttpSession 239
I
identification 335
include 235, 263
init 222
installation 23
internationalization
J2EE application clients
Duke’s Bank 415
Web clients
Duke’s Bank 415
invalidate 240
isCallerInRole 341
isIdentical 80
isolation levels 329
isThreadSafe 259
isUserInRole 340
isValid 295
J
j2ee
options 439
See also J2EE server
J2EE application clients 5, 28
containers 10
Duke’s Bank 400–408
classes 402
running 427
examples 30, 157, 403
JAR files 11, 28
INDEX
packaging 31
See also runclient
J2EE applications 3
assembler role 13
components 11
deploying 37
design guidelines xxv
iterative development 39
See also Duke’s Bank 391
tiers 2
J2EE BluePrints xxv
J2EE clients 4
application clients 5
See also J2EE application
clients
Web clients 4
See also Web clients
Web clients versus J2EE application clients 5
J2EE components
defined 3
more information xxiv
types 3
J2EE Connector technology 365
architecture version 18
CCI 375
more information xxv
resource adapters
See resource adapters
J2EE group 335, 349
J2EE platform 1–2
J2EE SDK 14
databases 15
downloading xxii, 14
installing 23
tools 19
J2EE security architecture 334
J2EE server 10
restarting 46
starting and stopping 23
J2EE specifications xxi
J2EE Technology in Practice 18
J2EE_HOME xxiii, 23
j2eeadmin 159, 368, 371, 434
J2SE
downloading xxiii
required version xxiii
JAAS 18
JAF 17
JAR files
j2ee.jar 26
See also
EJB JAR files
J2EE application clients,
JAR files
Java API for XML Processing
See JAXP
Java Authentication and Authorization Service
See JAAS
Java Message Service
See JMS
Java Message Service Tutorial 56
Java Naming and Directory Interface
See JNDI
Java Servlet technology 16
See also servlets
Java Transaction API
See JTA
Java Tutorial xxi
JAVA_HOME xxiii, 23
JavaBeans Activation Framework
See JAF
JavaBeans components 5
benefits of using 271
487
488
INDEX
creating in JSP pages 272
design conventions 270
Duke’s Bank 410
in WAR files 196
methods 270
properties 270
retrieving in JSP pages 275
setting in JSP pages 273
using in JSP pages 272
JavaMail API 17
more information xxv
JavaServer Pages (JSP) technology 16
See also JSP pages
javax.resource 377
javax.servlet 210
javax.servlet.http 210
javax.servlet.jsp.tagext 289
JAXP 17
more information xxv
tutorial xxiv
JDBC API 15
more information xxv
transactions
See transactions, JDBC
versus J2EE Connector technology 365
JMS 16
examples 155
message listeners 56
message-driven beans
See message-driven beans
more information xxv
tutorial xxiv, 8, 155
JNDI 16, 29
deploytool 36, 129, 150, 355
JMS destination 161
lookup 29, 354, 357, 359, 378
mail sessions 359
more information xxv
names 353
Duke’s Bank 423–424
naming context 29
resource adapters 368, 371
resource references 353
tutorial xxiv
URL connections 362
JSP declarations 260
JSP expressions 262
JSP pages 246
compilation 253
errors 254
compiling 34
creating and using objects 259
creating dynamic content 257
creating static content 257
custom tags
See custom tags
declarations
See JSP declarations
Duke’s Bank 410
eliminating scripting 267
error page 255
examples 32, 196, 248–249,
281
execution 254
expressions
See JSP expressions
finalization 256
forwarding to an error page
255
forwarding to other Web components 264
implicit objects 258
importing classes and packages 260
489
INDEX
importing tag libraries 285
including applets or JavaBeans
components 265
including other Web resources
263
initialization 256
JavaBeans components
creating 272
retrieving properties 275
setting properties 273
from constants 273
from request parameters 273
from runtime expressions 274
using 272
life cycle 253
scripting elements
See JSP scripting elements
scriptlets
See JSP scriptlets
setting buffer size 255
shared objects 259
specifying scripting language
260
translation 253
enforcing constraints for
custom tag attributes 295
errors 254
URLs for running 38
JSP scripting elements 260
JSP scriptlets 261
drawbacks 267
JSP tag libraries 268
jsp:fallback 266
jsp:forward 264
jsp:getProperty 275
jsp:include 264
jsp:param 265–266
jsp:plugin 265
jsp:setProperty 273
jspDestroy 256
jspInit 256
JTA 17
See also
transactions, JTA
JTS API 325
K
keytool
439
L
listener classes 216
defining 216
Duke’s Bank 411
examples 217
specifying 218
listener interfaces 216
local home interfaces 126
defined 59
examples 137
local interfaces 128
defined 59
examples 127–128, 139
requirements 97
lookup
See JNDI, lookup
M
mail sessions 359
message-driven beans 56
accessing 57
490
INDEX
defined 56
garbage collection 68
onMessage method 57
requirements 158
transactions 316, 320, 323–
324, 328
messages 155
method permissions
Duke’s Bank 400
specifying 341
O
onMessage
158
P
packager 440
application client JAR files
441
EAR files 442
EJB JAR files 440
RAR files 443
setting runtime deployment
descriptor 442
WAR files 441
PATH xxiii, 23
persistence
bean-managed
See bean-managed persistence
container-managed
See
container-managed
persistence
entity beans 51
session beans 50
types 52
persistent fields 54
deploytool 135
EJB QL 166, 180
examples 124
physical schemas 53
prerequisites xxii
primary keys
automatically generating 153
bean-managed persistence 113
composite 113, 151
container-managed
persistence 151
defined 52
examples 113, 151
methods for setting 67
returned by create 85
See also ejbFindByPrimaryKey
printing the tutorial xxv
PrintWriter 225
Q
queues 156, 158
R
RAR files 366, 370
realms 348
certificate 348
default 348
Duke’s Bank
adding groups and users 417
managing users and groups
349
realmtool 444
reference implementation
See J2EE SDK
relationship fields
INDEX
defined 54
deploytool
133
direction 55
EJB QL 166, 180
examples 124
modifying by local clients 143
relationships
bean-managed persistence 53
container-managed
See container-managed relationships
multiplicities 55
release 297
remote interfaces
defined 58
example 24
examples 76, 96
requirements 76
remove
bean-managed persistence 87
life cycles 64, 66
transactions 320
RequestDispatcher 235
requests 223
appending parameters 265
customizing 231
getting information from 223
retrieving a locale 207
See also HTTP requests
required software xxii
resource adapters 366
archive files
See RAR files
black box testing 369
CCI 375
deploying 368
examples 372, 377
properties 370
security 345
resource bundles 206
resource connections 353
resource references 353, 374
responses 225
buffering output 226
customizing 231
See also HTTP responses
setting headers 223
roles
development
See development roles
security
See security roles
rollback 316, 323–324, 326–327
rollbacks
See transactions, rollbacks
runclient
examples 38
options 445
S
security
application client tier 342
callback handlers 343
login modules 342
specifying a callback handler 343
authentication
See authentication
declarative 334
EIS tier 343
component-managed signon 344
configuring sign-on 344
container-managed signon 344
491
492
INDEX
sign-on 343
EJB tier
method permissions
See method permissions
programmatic 341
login example 38
programmatic 334
resource adapter 345
Web tier 337
programmatic 340
security constraints
specifying 338
security identity 346
caller identity 346
configuring propagation 347
propagating to enterprise
beans 346
specific identity 347
security role references 335
mapping to security roles 336
security roles 335
creating 335
Duke’s Bank 400
mapping to groups 425
mapping to J2EE users and
groups 337
select methods 124, 135, 147
EJB QL 172, 190
Servlet 210
ServletContext 238
ServletInputStream 224
ServletOutputStream 225
ServletRequest 223
ServletResponse 225
servlets 210
binary data
reading 224
writing 225
character data
reading 224
writing 225
Duke’s Bank 412
examples 196
finalization 242
initialization 222
failure 222
life cycle 216
life cycle events
handling 216
service methods 223
notifying 243
programming long running
244
tracking service requests 242
session beans 49
activation 64
clients 49
compared to entity beans 52
database connections 357–358
databases 322
Duke’s Bank 394–397
equality 80
examples 25, 69, 79
isolation levels 329
passivation 64
requirements 70
stateful 50–51
stateless 50–51, 57
transactions 320, 322, 324,
326–327, 331
SessionBean 72
SessionContext 80
sessions 239
associating attributes 239
associating with user 241
493
INDEX
via cookies 241
via URL rewriting 241
invalidating 240
notifying objects associated
with 240
setEntityContext 65, 106, 108, 358
setMessageDrivenContext 68
setSessionContext 64, 81, 377
setters
See access methods
SingleThreadModel 220
SQL xxii, 15, 53, 84–85, 87–88,
94, 136, 145, 150, 169, 177, 322,
324–325, 380
SQL92 165, 188
T
tag handlers
life cycle 313
tag library descriptors 290
attribute 294
bodycontent 293, 298
filenames 285
listener 291
mapping name to location 286
tag 292
taglib 291
variable 300
TagExtraInfo 295
taglib 285
timeouts 328
transactions 315, 324
attributes 317
bean-managed 316, 323, 327–
328, 331
boundaries 52, 316, 323
business methods
See
business methods,
transactions
commits 316, 322, 324–327,
329–330
container-managed 316, 323,
327–328
database connections 358
defined 316
entity beans
See entity beans, transactions
examples 321–323, 325–326,
329
exceptions
See exceptions, transactions
JDBC 324, 327, 329
JTA 324–325, 327–328
levels for resource adapters
369
managers 319, 324–325, 329–
330
message-driven beans 57
See message-driven beans,
transactions
nested 317, 325
resource adapters 367
rollbacks 316, 321–322, 324,
326–327, 329
scope 317
session beans
See session beans, transactions
shared data 52
tips 327
Web components 221, 331
XA 367, 371
troubleshooting 41, 362
494
INDEX
U
UnavailableException 222
unsetEntityContext 66, 358
URL 353, 362
UserTransaction 323, 326–328,
331
utility classes 62, 84
V
verifier
options 447
running 45
W
WAR files 194
adding component files 198
adding to EAR files 198
adding Web component files
34
contents 11
creating 197
directory structure 197
JavaBeans components in 196
specifying error pages 218
Web application archives
See WAR files
Web clients 4, 193
configuring 194, 200
deploying 203
Duke’s Bank 409–416
custom tags 411
initialization 411
JavaBeans
components
410
JSP template 411
request processing 412
running 428
examples 32
internationalizing 206
J2EE Blueprints 207
maintaining state across requests 239
packaging 196
running 204
updating 204
Web components 6, 193
accessing databases from 221
adding to WAR files 198
applets 6
concurrent access to shared resources 220
connecting to resources 353
development role 13
enterprise bean references 35
forwarding to other Web components 237
including other Web resources
235
invoking other Web resources
235
JSP pages
See JSP pages 193
mapping filters to 233
packaging 34
runtime environment 194
scope objects 219
servlets
See servlets
sharing information 218
transactions 221, 331
types 6, 193
utility classes 6
Web context 238
Web containers 10, 194
loading and initializing serv-
INDEX
lets 216
Web resources 196
Duke’s Bank
protecting 415
mapping filters to 233–235
protecting 337
unprotected 340
work flows 51
X
XML 17
495
Download PDF
Similar pages