Mastering Enterprise Javabeans

669 Pages·2002·2.176 MB·English

by  Ed Roman, Scott W Ambler, Tyler Jewell

Mastering Enterprise
JavaBeans™
Second Edition
Ed Roman
Scott Ambler
Tyler Jewell
Wiley Computer Publishing
John Wiley & Sons, Inc.
NEW YORK • CHICHESTER • WEINHEIM • BRISBANE • SINGAPORE • TORONTO
Publisher: Robert Ipsen
Editor: Robert M. Elliott
Developmental Editor: Emilie Herman
Managing Editor: John Atkins
Associate New Media Editor: Brian Snapp
Text Design & Composition: MacAllister Publishing Services, LLC
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Copyright © 2002 by The Middleware Company. All rights reserved.
Published by John Wiley & Sons, Inc.
Published simultaneously in Canada.
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Library of Congress Cataloging-in-Publication Data:
ISBN: 0-471-41711-4
Printed in the United States of America.
10 9 8 7 6 5 4 3 2 1
To my wonderful wife, Younhi.
—Ed Roman

CO NTE NTS
Acknowledgments xix
Preface xxi
Introduction xxv
About the Author xxxi
Part One Overview 1
Chapter 1 Overview 3
The Motivation for EJB 4
Divide and Conquer to the Extreme 5
Component Architectures 12
Introducing Enterprise JavaBeans 13
Why Java? 14
EJB as a Business Solution 14
The EJB Ecosystem 16
The Bean Provider 17
The Application Assembler 17
The EJB Deployer 18
The System Administrator 19
The Container and Server Provider 19
The Tool Vendors 20
Summary of Roles 20
The Java 2 Platform, Enterprise Edition (J2EE) 22
The J2EE Technologies 23
Summary 26
Chapter 2 EJB Fundamentals 29
Enterprise Beans 29
Types of Beans 30
Distributed Objects: The Foundation for EJB 32
Distributed Objects and Middleware 34
Explicit Middleware 34
Implicit Middleware 35
What Constitutes an Enterprise Bean? 37
The Enterprise Bean Class 37
vii
viii CONTENTS
The EJB Object 38
The Home Object 44
The Local Interfaces 46
Deployment Descriptors 50
Vendor-Specific Files 51
Ejb-Jar File 51
Summary of Terms 52
Summary 54
Chapter 3 Writing Your First Bean 55
How to Develop an EJB Component 55
The Remote Interface 57
The Local Interface 58
The Home Interface 58
The Local Home Interface 59
The Bean Class 62
The Deployment Descriptor 66
The Vendor-Specific Files 67
The Ejb-jar File 67
Deploying the Bean 68
The Optional EJB Client JAR file 68
Understanding How to Call Beans 69
Looking up a Home Object 70
Running the System 74
The Server-Side Output 75
The Client-Side Output 75
Implementing Component Interfaces 75
A Solution 76
Summary 77
Part Two The Triad of Beans 79
Chapter 4 Introduction to Session Beans 81
Session Bean Lifetime 81
Session Bean Subtypes 82
Stateful Session Beans 82
Stateless Session Beans 83
Special Characteristics of Stateful Session Beans 84
Achieving the Effect of Pooling with Stateful Beans 85
The Rules Governing Conversational State 86
Activation and Passivation Callbacks 87
CONTENTS ix
Method Implementation Summary 89
A Simple Stateful Session Bean 89
Life Cycle Diagrams for Session Beans 100
Summary 103
Chapter 5 Introduction to Entity Beans 105
Persistence Concepts 105
Java Object Serialization 106
Object-Relational Mapping 106
Object Databases 109
What Is an Entity Bean? 109
About the Files that Make up an Entity Bean 112
Features of Entity Beans 112
Entity Beans Survive Failures 112
Entity Bean Instances Are a View into a Database 113
Several Entity Bean Instances May Represent the Same
Underlying Data 114
Entity Bean Instances Can Be Pooled 116
There Are Two Ways to Persist Entity Beans 118
Creation and Removal of Entity Beans 119
Entity Beans Can Be Found 121
You Can Modify Entity Bean Data without Using EJB 123
Entity Contexts 124
getEJBLocalObject() / getEJBObject() 124
getPrimaryKey() 125
Summary 126
Chapter 6 Writing Bean-Managed Persistent Entity Beans 127
Entity Bean Coding Basics 127
Finding Existing Entity Beans: ejbFind() 129
Bean-Managed Persistence Example:ABank Account 136
Account.java 137
AccountLocal.java 138
AccountHome.java 138
AccountLocalHome.java 138
AccountPK.java 139
AccountBean.java 143
AccountException.java 156
Client.java 156
The Deployment Descriptor 156
The Container-Specific Deployment Descriptor 161
Setting up the Database 161
Running the Client Program 161
Server-Side Output 162
Client-Side Output 163
x CONTENTS
Putting It All Together: Walking through a BMP Entity
Bean’s Life Cycle 163
Summary 166
Chapter 7 Writing Container-Managed Persistent Entity Beans 167
Features of CMP Entity Beans 167
CMP Entity Beans Are Subclassed 167
CMP Entity Beans Have No Declared Fields 168
CMP Get/Set Methods Are Defined in the Subclass 170
CMP Entity Beans Have an Abstract Persistence Schema 172
CMP Entity Beans Have a Query Language 173
CMP Entity Beans Can Have ejbSelect() Methods 175
Implementation Guidelines for Container-Managed
Persistence 176
Container-Managed Persistence Example:AProduct Line 180
Product.java 181
ProductLocal.java 182
ProductHome.java 182
ProductLocalHome.java 184
ProductPK.java 184
ProductBean.java 187
The Deployment Descriptor 191
The Container-Specific Deployment Descriptor 195
Client.java 196
Running the Client Program 196
The Life Cycle of a CMP Entity Bean 200
Summary 200
Chapter 8 Introduction to Message-Driven Beans 201
Motivation to Use Message-Driven Beans 201
The Java Message Service (JMS) 203
Messaging Domains 204
The JMS API 206
Integrating JMS with EJB 211
What Is a Message-Driven Bean? 212
Developing Message-Driven Beans 214
The Semantics 214
A Simple Example 215
Advanced Concepts 223
Message-Driven Bean Gotchas 225
Message Ordering 225
Missed ejbRemove() Calls 226
Poison Messages 228
CONTENTS xi
How to Return Results Back to Message Producers 230
The Future: Asynchronous Method Invocations 235
Summary 236
Chapter 9 Adding Functionality to Your Beans 237
Calling Beans from Other Beans 237
Default JNDI Lookups 238
Understanding EJB References 239
Resource Factories 241
Environment Properties 244
Understanding EJB Security 245
Security Step 1: Authentication 246
Security Step 2: Authorization 257
Security Propagation 266
Understanding Handles 268
Home Handles 269
Summary 270
Part Three Advanced Enterprise JavaBeans Concepts 271
Chapter 10 Transactions 275
Motivation for Transactions 276
Atomic Operations 276
Network or Machine Failure 277
Multiple Users Sharing Data 278
Benefits of Transactions 279
The ACID Properties 280
Transactional Models 282
Flat Transactions 282
Nested Transactions 284
Other Transactional Models 286
Enlisting in Transactions with Enterprise JavaBeans 286
Underlying Transaction System Abstraction 287
Declarative, Programmatic, and Client-Initiated Transactions 287
Choosing a Transaction Style 290
Container-Managed Transactions 292
EJB Transaction Attribute Values 294
Programmatic Transactions in EJB 300
CORBA’s Object Transaction Service (OTS) 300
The Java Transaction Service (JTS) 301
The Java Transaction API (JTA) 301
Declarative versus Programmatic Transactions Example 304
xii CONTENTS
Transactions from Client Code 306
Transactional Isolation 307
The Need for Concurrency Control 308
Isolation and EJB 309
The Dirty Read Problem 311
The Unrepeatable Read Problem 312
The Phantom Problem 313
Transaction Isolation Summary 314
Isolation and EJB 315
Pessimistic and Optimistic Concurrency Control 316
Distributed Transactions 316
Durability and the Two-Phase Commit Protocol 317
The Transactional Communications Protocol and Transaction
Contexts 318
Designing Transactional Conversations in EJB 320
Summary 323
Chapter 11 BMP and CMP Relationships 325
The CMP and BMP Difference 326
Cardinality 326
1:1 Relationships 328
1:N Relationships 332
M:N Relationships 336
Directionality 344
Implementing Directionality with BMP 344
Implementing Directionality with CMP 345
Directionality May Not Map to Database Schemas 347
Bidirectional or Unidirectional? 349
Lazy Loading 349
Aggregation vs. Composition and Cascading Deletes 350
Relationships and EJB-QL 352
Recursive Relationships 353
Circular Relationships 354
Referential Integrity 355
Relationships, Referential Integrity, and Client Code 357
Summary 360
Chapter 12 Persistence Best Practices 361
When to Use Entity Beans 362
Control 362
Parameter Passing Analogy 362
Procedural Versus Object-Oriented 363
Caching 363