head first ejb.pdf

Head First EJB ™

by Kathy Sierra and Bert Bates

Printed in the United States of America.

Published by O’Reilly Media, Inc., 1005 Gravenstein Highway North, Sebastopol, CA 95472.

O’Reilly books may be purchased for educational, business, or sales promotional use. Online editions are

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Editor: Mike Loukides

Cover Designer: Edie Freedman

Interior Decorators: Kathy Sierra and Bert Bates

Anthropomorphizer: Bert Bates

Bean Wrangler:

Kathy Sierra

Printing History:

October 2003: First Edition.

The O’Reilly logo is a registered trademark of O’Reilly Media, Inc. Java and all Java-based trademarks and logos

are trademarks or registered trademarks of Sun Microsystems, Inc., in the United States and other countries.

O’Reilly Media, Inc. is independent of Sun Microsystems.

Many of the designations used by manufacturers and sellers to distinguish their products are claimed as

trademarks.

Where those designations appear in this book, and O’Reilly was aware of a trademark claim, the designations

have been printed in caps or initial caps.

While every precaution has been taken in the preparation of this book, the publisher and the authors assume no

responsibility for errors or omissions, or for damages resulting from the use of the information contained herein.

In other words, if you use anything in Head First EJB™ to, say, run a nuclear power plant or air trafic control

system, you’re on your own.

And although some people have been able to pass the exam simply by placing this book under their pillow each

night for three consecutive weeks, we generally don’t recommend it. Most people ind it helpful to actually read

the book or at least look at the pictures.

ISBN-10: 0-596-00571-7

ISBN-13: 978-0-596-00571-9

[M]

[8/07]

Table of Contents (summary)

Intro

xix

1 Welcome to EJB: an introduction

2 EJB Architecture: architectural overview

3 Exposing Yourself: the client view

111

4 Being a Session Bean: session bean lifecycle

173

5 Entities are Persistent: entity bean intro

259

6 Being an Entity Bean: bean/entity synchronization

295

7 When Beans Relate: entity bean relationships

373

8 Getting the Message: message-driven beans

437

9 The Atomic Age: EJB transactions

469

10 When Beans Go Bad: exceptions in EJB

525

11 Protect Your Secrets: security in EJB

569

12 The Joy of Deployment: a bean’s environment

599

A Appendix A: Final Mock Exam

637

Table of Contents (the real thing)

Your brain on EJB. Here you are trying to learn something, while here your brain

is doing you a favor by making sure the learning doesn’t stick . Your brain’s thinking, “Better

leave room for more important things, like which wild animals to avoid and whether naked

snowboarding is a bad idea.” So how do you trick your brain into thinking that your life

depends on knowing EJB?

Who is this book for?

xviii

We know what your brain is thinking

xix

Metacognition

xxi

Bend your brain into submission

xxiii

What you need for this book

xxiv

Passing the certiication exam

xxvi

Technical reviewers

xxviii

Acknowledgements

xxix

i Intro

1 Welcome to EJB

Enterprise JavaBeans are easy. Well, at least when you compare EJB

to what you’d have to do to write your own scalable, transactional, secure, persistent,

concurrent enterprise component server. In this chapter, we’ll develop, deploy, and run an

EJB application, and then dive into the details. Before we’re done, we’ll look at the use,

benei ts, and characteristics of EJB, and we’ll look (briel y) at how EJB containers work.

Exam objectives

Server

What is EJB all about?

No more vendor lock-in!

How does it all work?

Behind the scenes...

EJB Container

Beans come in three l avors

The Advice Guy bean

Five things you do to build a bean

EJB Roles and Responsibilities

Tutorial

Coffee Cram

2 EJB Architecture

EJB is about infrastructure. Your components are the building blocks. With

EJB, you can build big applications. The kind of applications that could run everything

from the Victoria’s Secret back-end to document-handling systems at CERN. But an

architecture with this much l exibility, power, and scalability isn’t simple. It all begins with a

distributed programming model...

Exam objectives

<<interface>>

EnterpriseBean

no methods

Making a Remote method call

<<interface>>

Remote

(J2SE API)

(J2EE API)

What about arguments and return values?

no methods

The client calls business methods through the Remote interface

(J2EE API)

<<interface>>

EJBObject

// several methods

(J2EE API)

<<interface>>

SessionBean

// several methods

EJB uses RMI

The Remote object is not the bean, it’s the bean’s bodyguard

YOU write this

interface

(the remote

component

interface)

<<interface>>

BookCart

addBook()

removeBook()

showBooksInCart()

doCheckout()

YOU write this

class

(the bean class)

BookCartBean

addBook()

removeBook()

showBooksInCart()

doCheckout()

// other methods

Architectural overview: Session beans

Architectural overview: Entity beans

Architectural overview: Creating a Stateful Session bean

100

Architectural overview: Creating a Stateless Session bean

101

Architectural overview: Message-driven beans

106

Organize your beans

108

3 Exposing Yourself

You can’t keep your bean private. Clients need to see what you’ve got.

(Except for message-driven beans, which don’t have a client view). The Advice Bean

exposes the getAdvice() method in its Component interface—the place where you declare

business methods. But that’s not all the client sees. Remember, the Advice interface

extends EJBObject, an interface with methods of its own . Methods the client can see.

Methods the client can call . And it works the same way with the Home interface.

Stateless

beans

Exam objectives

112

What the client really wants

113

What’s JNDI?

116

PortableRemoteObject.narrow() (exotic casting)

121

Writing the Remote home interface for a session bean

125

bean

Thankfully, we’ve got handles (online shopping takes time)

139

bean

Which methods make sense for the local client interfaces?

148

Why so many remove methods?

151

For stateless session beans from

the same home, isIdentical() always

returns true, even for different beans.

Comparing Remote vs. Local interfaces

154

Arguments to Remote vs. local methods

163

Coffee Cram

168

4 Being a Session Bean

Session beans are created and removed. If you’re lucky, you’re a

state less bean. Because the life of a state ful bean is tied to the whims of a heartless

client. Stateful beans are created at the client’s insistence, and live and die only to serve

that one client. But ahhhh, the life of a stateless bean is fabulous! Pools, those little

umbrella drinks, and no boredom since you get to meet so many different clients.

Exam objectives

174

For me? This is

such a special moment!

Once in a lifetime...

Container callbacks, for the special moments in a bean’s life

181

Bean Creation

188

Bean things you can do within business methods

199

Passivation: a stateful bean’s chance at scalability

200

Bean Removal

208

Writing a Session Bean: your job as Bean Provider

230

SessionContext: you need it more than it needs you

240

Coffee Cram

244

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