OReilly enterprise javabeans 3 0 5th edition may 2006 ISBN 059600978x

As described in this book, the resulting Java Persistence APIreplaces container-managed persistence with a lighter-weight,Plain Old Java Object POJO persistence layer.. Chapter 2, Archit

By Bill Burke, Richard Monson-Haefel

Publisher: O'Reilly Pub Date: May 16, 2006 Print ISBN-10: 0-596-00978-X Pages: 760

Table of Contents | Index

By Bill Burke, Richard Monson-Haefel

Publisher: O'Reilly Pub Date: May 16, 2006 Print ISBN-10: 0-596-00978-X Pages: 760

by Bill Burke and Richard Monson-Haefel

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ISBN: 0-596-00978-X

[M]

Enterprise JavaBeans™ is the core component technology of theJava Enterprise Edition platform It is an enterprise

infrastructure designed to provide developers with the

automatic management of many of the services essential toenterprise applications The EJB containerthe immediate

environment of enterprise bean components and the provider ofmanaged services to themis at the center of this architecture

However, to use this managed environment in earlier versions

of EJB, developers had to write to APIs that focused more onthe EJB container's requirements than on the business logic ofenterprise applications Consequently, EJB development wasunnecessarily complex For example:

Implementation of various EJB interfaces led to a lot of

boilerplate code for methods that were required by the

interface, but not needed by the application

An XML deployment descriptor was required to integrate theapplication with its environment and with container

services Access to the components' environment was

clumsy and nonintuitive

The design of container-managed persistence made domainobject modeling unnecessarily complex and heavyweight.While container-managed persistence was originally

conceived as an ease-of-use facility, in practice, it was

awkward and limiting

The purpose of the EJB 3.0 release was to refocus EJB on

simplifying the developer's tasksand to fix all of these problems,and more

of complexity in the earlier EJB releases This involved

examining criticisms of EJB; understanding which EJB designpatterns were really antipatterns; identifying APIs that wereclumsy to use, were nonintuitive to newcomers to the

technology, or could be dispensed with entirely; and recognizingother aspects of the technology that were obstacles to ease ofuse

The preliminary list of what needed to be fixed together with aproposal for how the task could be approached formed the basis

of JSR 220, the Java Community Process specification requestwith which I launched EJB 3.0 Starting with the initial list of theAPIs that needed improvement, the EJB 3.0 Expert Group

undertook the process of brainstorming on better, simpler

constructs Bill Burke, the chief architect of the JBoss

application server and author of this book, was one of the keyparticipants in this effort

The Expert Group's work has resulted in a major simplificationand improvement All of the key EJB APIs are easier to use, andthe configuration-by-exception approach of EJB 3.0 allows

developers to rely on expected default behaviors The XML

deployment descriptor has become unnecessary, except for

addressing more advanced cases

The Java language metadata facility, newly added to Java SE,aided us in making these simplifications EJB 3.0 uses metadataannotations to express within Java code the dependencies ofEJB components upon container services, and thus to avoid theneed to provide a deployment descriptor Further, EJB 3.0

provides default values for metadata so that in general, thismetadata can be sparse

By using metadata annotations to designate environment

dependencies and life cycle callbacks, EJB 3.0 has also beenable to eliminate the requirement for the bean class to

implement to the EnterpriseBean interfaces A bean class can

We were able to eliminate the earlier EJBHome factory patterns

as well by requiring smarter interpositioning on the part of thecontainer (transparently to the application) in creating

references to components and their instances at the time oflookup or injection Session beans can now be programmed asordinary Java classes with ordinary business interfaces, ratherthan as heavyweight components

These and other changes have greatly simplified the developerview Further, they leave the underlying EJB architecture

fundamentally unchanged, providing a migration path to EJB3.0

The simplification of container-managed persistence provided agreater challenge We began the effort here with the same

steps as the simplification of session beans and message-drivenbeans: elimination of unneeded interfaces, use of annotationsfor configuration information, and so on It soon became clear,however, that EJB persistence needed a more radical

transformation Further, the success of lighter-weight

object/relational mapping technologies such as Hibernate gaveclear guidance to the direction that this transformation shouldtake

As described in this book, the resulting Java Persistence APIreplaces container-managed persistence with a lighter-weight,Plain Old Java Object (POJO) persistence layer This layer

provides extensive support for domain object modeling,

including inheritance and polymorphism; numerous

enhancements to the EJB QL query language to provide richquery capabilities; and a specification for portable

object/relational mapping through use of annotations or an XMLdescriptor Persistent entities are now instances of ordinary (butmanaged) Java classes As such, they can be created with new

and passed to other application tiers as ordinary Java objects

environments

Bill Burke's contributions to EJB 3.0 and the Java PersistenceAPI have been numerous and far reaching As chief architect forthe JBoss application server, he brought to the EJB 3.0 ExpertGroup key insights on container innovations, extensive

experience with the Hibernate object/relational persistence

technology, and a broad perspective on the needs of developersand their use of the EJB technology in real-world applications

In this new edition of Enterprise JavaBeans, based on the

earlier work by Richard Monson-Haefel, Bill Burke shares theseinsights together with his in-depth perspective on how thesenew, simplified EJB 3.0 APIs transform the enterprise Java

Author's Note

In the spring of 2000, I left my CORBA development job at Ionaand went to a small startup that was building an e-marketingportal Coming from a CORBA background to an Enterprise

JavaBeans™ project was a bit alien to me I remember thinking,

"Why does the server side need a component model?" I quicklylearned that declarative transaction, security, and persistencemetadata played a crucial role in developing business

applications

Like many startups at that time, we ran into funding problems

at the end of 2000 We were about to go into beta with our firstcustomers when our problems were compounded when our

application server vendor revoked our demo license and

demanded payment We had to find a free solution fast, andthat was when I stumbled into the open source application

server, JBoss

It didn't take very long to convert to JBoss, but I found thatJBoss 2.0 was a bit raw in some areas I had an extensive

background in writing middleware under the tutelage of SteveVinoski at Iona, so it wasn't too difficult to jump into the

codebase I immediately began fixing bugs here and there,

submitting patches to the JBoss mail list After a few months ofcontributing, I received a strange email:

what do you do in real life

The email was from JBoss's founder, Marc Fleury Let me tellyou, JBoss was the first open source project I had ever

message from Morpheus in the movie The Matrix I responded

to Marc's email, saying I worked for a struggling startup andthat I had written middleware at my previous job at Iona I got

a one-sentence response from Marc:

do you want to take the red pill

I was hooked I replied yes, and my journey down the rabbithole began I became a CVS committer and first worked on

entity bean synchronization Later that year, I helped SachaLabourey on JBoss's first clustering implementation The rest ishistory

Back in 2002, Richard Monson-Haefel, the original author of theEJB book series, contacted Marc about contributing a JBoss

workbook Marc wasn't interested, so he introduced Richard toSacha Labourey and me, and we wrote the workbook that

O'Reilly published with its book, Enterprise JavaBeans, Fourth

Edition When Richard retired from writing last year, I guess mywork was good enough that O'Reilly offered me the opportunity

to update the series to the latest EJB 3.0 specification

Who Should Read This Book

This book explains and demonstrates the fundamentals of theEJB 3.0 and Java Persistence programming models AlthoughEJB makes application development much simpler, it is still acomplex technology that requires a great deal of time and study

to master This book provides a straightforward, no-nonsenseexplanation of the underlying technology, Java™ classes andinterfaces, the component model, and the runtime behavior ofEJB It does not include material on previous versions of the

Although this book focuses on the fundamentals, it's not a

"dummies" book EJB is an extremely complex and ambitiousenterprise technology While using EJB may be fairly simple, theamount of work required to understand and master EJB is

significant Before reading this book, you should be fluent in theJava language and have some practical experience developingbusiness solutions Experience with distributed object systems

explains what EJB is, how it works, and when to use it The

JBoss workbook provides step-by-step instructions for installing,configuring, and running the examples from the manuscript onthe JBoss 4.0 Application Server

Part I: The EJB 3.0 Standard

Part 1 was adapted from Richard Monson-Haefel's fourth edition

of this book by yours truly, Bill Burke Linda DeMichiel, the EJB3.0 specification lead, wrote the foreword to this book Jason T.Greene adapted Chapters 18 and 19 Here is a summary of thecontent of the technical manuscript chapters:

This chapter defines component transaction monitors andexplains how they form the underlying technology of theEJB component model

Chapter 2, Architectural Overview

This chapter defines the architecture of the EJB componentmodel and examines the differences between the threebasic types of enterprise beans: entity beans, session

Chapter 5, Persistence: EntityManager

This chapter explains how entity beans interact with thenew entity manager service

This chapter defines the basic relational database mappingprovided by the Java Persistence specification

Chapter 7, Entity Relationships

This chapter picks up where Chapter 6 left off, expandingyour understanding of persistence and complex bean-to-bean relationships

Chapter 8, Entity Inheritance

This chapter discusses entity bean inheritance and how anobject hierarchy can be mapped to a relational database

events

Chapter 11, Session Beans

This chapter shows how to develop stateless and statefulsession beans.

Chapter 18, EJB 3.0: Web Services Standards

This chapter explains the XML, SOAP, WSLD, and UDDI webservices standards

Chapter 19, EJB 3.0 and Web Services

This chapter discusses how the JAX-RPC API supports webservices in EJB

Chapter 20, Java EE

This chapter provides an overview of Java EE 5 and explainshow EJB 3.0 fits into this new platform

Chapter 21, EJB Design in the Real World

This chapter provides some basic design strategies that cansimplify your EJB development efforts and make your EJBsystem more efficient

Part II: The JBoss Workbook

The JBoss workbook shows how to execute examples from

those chapters in the book that include at least one significantexample You'll want to read the introduction to the workbook

to set up JBoss and configure it for the examples After that,

you're reading For example, if you are reading Chapter 6 onmapping persistent objects, use the "Exercises for Chapter 6"chapter of the workbook to develop and run the examples onJBoss

Software and Versions

This book covers EJB 3.0 and Java Persistence 1.0 It uses Javalanguage features from the Java SE 5 platform, including JDBC.Because the focus of this book is on developing vendor-

independent EJB components and solutions, I have stayed awayfrom proprietary extensions and vendor-dependent idioms Youcan use any EJB-compliant server with this book, but you

should be familiar with your server's specific installation,

deployment, and runtime-management procedures to work withthe examples A workbook for the JBoss Application Server isincluded at the end of this book to help you get started

to the TravelAgent EJB when we want to talk about the

enterprise bean in general and the Customer entity when wewant to talk about entity beans If we put the name in a

constant-width font, we are referring explicitly to the bean'sinterface or class; thus, TRavelAgentRemote is the remote interface

Using Code Examples

This book is here to help you get your job done In general, youmay use the code in this book in your programs and

documentation You do not need to contact us for permissionunless you're reproducing a significant portion of the code Forexample, writing a program that uses several chunks of codefrom this book does not require permission Selling or

distributing a CD-ROM of examples from O'Reilly books doesrequire permission Answering a question by citing this bookand quoting example code does not require permission

Incorporating a significant amount of example code from thisbook into your product's documentation does require

permission

We appreciate, but do not require, attribution An attributionusually includes the title, author, publisher, and ISBN For

example: "Enterprise JavaBeans 3.0, Fifth Edition, by Bill Burke

and Richard Monson-Haefel Copyright 2006 O'Reilly Media,Inc., 0-596-00978-X."

If you feel your use of code examples falls outside fair use orthe permission given above, feel free to contact us at

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Acknowledgments

Many individuals share the credit for this book's developmentand delivery Michael Loukides, the editor, and his team werepivotal to the success of every edition of this book Without histeam's experience, craft, and guidance, this book would nothave been possible I want to thank Jason T Greene for takingover the web services chapters I had no desire to learn JAX-WSbeyond the @WebService annotation Without the earlier work ofRichard Monson-Haefel, this book would not have been possible

It amazes me how the structure of this book could last five

editions, and it is a testament to Richard's writing capabilities Ialso want to thank Richard for passing the baton to me on thisseries It has been a great opportunity for me and for JBoss Inc

Many expert technical reviewers helped ensure that the

material was technically accurate and true to the spirit of EJBand Java Persistence Of special note are Emmanuel Bernard,who sits with Gavin King and me on the EJB 3.0 Expert Group

as JBoss's representatives, as well as John Mazzitelli, who wasthe only reviewer to read every single chapter Richard Monson-Haefel was also instrumental in providing feedback Other

Thanks also to Linda DeMichiel, the EJB 3.0 specification lead

I want to thank my mother for staying up late at night to edit

my English papers in high school decades ago I haven't

forgotten, Mom! Finally, I want to thank my wife, Monica, forputting up with this grumpy old troll Her love and support areall I need in life

Chapter 1: Introduction

Chapter 2: Architectural Overview

Chapter 3: Resource Management and Primary ServicesChapter 4: Developing Your First Beans

Chapter 21: EJB Design in the Real World

This book is about Enterprise JavaBeans 3.0, the latest version

of the Enterprise JavaBeans specification, and its counterpart,the new Java Persistence specification Just as the Java platformhas revolutionized the way we think about software

development, the Enterprise JavaBeans (EJB) and Java

Persistence specifications have revolutionized the way we thinkabout developing mission-critical enterprise software They

combine server-side components with distributed object

technologies, asynchronous messaging, web services, and

persistence to greatly simplify the task of application

development It automatically takes into account many of therequirements of business systems, including security, resourcepooling, concurrency, and transactional integrity

This book shows you how to use Enterprise JavaBeans and JavaPersistence to develop scalable, portable business systems Butbefore we can start talking about EJB itself, we'll need a briefintroduction to the technologies addressed by EJB and Java

Persistence, such as component models, distributed objects,asynchronous messaging, and web services In Chapter 2, we'lllearn about the overall architecture that EJB and Persistenceprovide In Chapters 3 and 4, we'll look at how these APIs areintegrated together in a Java enterprise environment The rest

independence Since it was first released, Java has been

marketed as "write once, run anywhere." While the hype hasgotten a little heavy-handed at times, code written with Sun'sJava programming language is remarkably platform-

a particular database implementation; just change JDBC

drivers, and you change databases.[*] It's the same with EJBand Java Persistence Ideally, an EJB component (an enterprisebean) or a Java Persistence object (an entity bean) can run inany application server that implements these specifications.[ ]

This means that you can develop and deploy your EJB businesssystem in one server, such as BEA's WebLogic, and later move it

to a different EJB server, such as Pramati, Sybase's EAServer, orIBM's WebSphere, or to an open source project such as JBoss,Apache Geronimo, or JOnAS Implementation independencemeans that your business components do not depend on thebrand of server, which gives you many more options before,during, and after development and deployment

[*] In some cases, differences in a database vendor's support for SQL may require customization of SQL

statements used in development.

[ ] Provided that the bean components and EJB servers comply with the specification, and no proprietary

functionality is used in development.

Object-oriented languages such as Java, C++, C#, Python, andRuby are used to write software that is flexible, extensible, andreusablethe three axioms of object-oriented development Inbusiness systems, object-oriented languages are used to

improve development of GUIs, to simplify access to data, and toencapsulate the business logic The encapsulation of businesslogic into business objects is a fairly recent focus in the

information-technology industry Business is fluid, which meansthat a business's products, processes, and objectives evolveover time If the software that models the business can be

encapsulated into business objects, it becomes flexible,

extensible, and reusable, and therefore evolves as the businessevolves

A server-side component model may define an architecture for

developing distributed business objects that combines the

accessibility of distributed object systems with the fluidity ofobjectified business logic Server-side component models areused on middle-tier application servers, which manage the

components at runtime and make them available to remote

clients They provide a baseline of functionality that makes iteasy to develop distributed business objects and assemble theminto business solutions

Server-side components can also be used to model other

aspects of a business system, such as presentation and routing

A Java servlet, for example, is a server-side component thatgenerates HTML and XML data for the presentation layer of aweb application (Struts and JSF components are also examples

of this type of server-side component) EJB message-drivenbeans, discussed later in this book, are server-side componentsthat can be used to consume and process asynchronous

messages

component model Server-side component models often supportattribute-based programming, which allows the runtime

behavior of the component to be modified when it is deployed,without having to change the programming code in the

component Depending on the component model, the serveradministrator can declare a server-side component's

transactional, security, and even persistence behavior by settingthese attributes to specific values

As an organization's services, products, and operating

procedures evolve, server-side components can be

reassembled, modified, and extended so that the business

system reflects those changes Imagine a business system as acollection of server-side components that model concepts such

as customers, products, reservations, and warehouses Eachcomponent is like a Lego™ block that can be combined withother components to build a business solution Products can bestored in the warehouse or delivered to a customer; a customercan make a reservation or purchase a product You can

assemble components, take them apart, use them in differentcombinations, and change their definitions A business systembased on server-side components is fluid because it is

objectified, and it is accessible because the components can bedistributed

1.1.1 Enterprise JavaBeans Defined

Sun Microsystems' definition of the Enterprise JavaBeans

architecture is as follows:

The Enterprise JavaBeans architecture is a component

This means the EJB specification offers a standard model forbuilding server-side components that represent business

processes (purchasing, inventory, and so on) Once you havebuilt a set of components that fit the requirements of your

business, you can combine them to create business

applications On top of that, as "distributed" components, theydon't all have to reside on the same server Components canreside wherever it's most convenient: a TravelAgent componentcan "live" near the reservation database, or a Purchase

business-process component can live near the user interface.You can do whatever's necessary to minimize latency, share theprocessing load, or maximize reliability

Persistence is a higher-level abstraction above JDBC The

persistence layer maps objects to database storage so that theycan be queried, loaded, updated, or removed without having to

go through a verbose API such as JDBC In older versions ofEJB, persistence was part of the EJB platform Starting with EJB3.0, persistence has been spun off to its own specification,

called the Java Persistence API

The Java Persistence API defines a way to map regular, plain old

Java objects (sometimes referred to as POJOs) to a database.These plain Java objects are called entity beans Entity beansare like any other Java class, except that they have been

mapped, using Java Persistence metadata, to a database

Therefore, they may be inserted and loaded from a databasewithout the developer writing any JDBC connection code or

reading from result sets The Java Persistence API also defines aquery language that has features that parallel those in SQL, but

is tailored to work with Java objects rather than a raw relationalschema

In the EJB 2.1 specification, entity beans were very

"heavyweight" and dependent on the application server and theentire Java EE runtime environment In Java Persistence, entitybeans are regular Java objects that are managed by a

persistence service Unlike their EJB 2.1 counterparts, entities

in Java Persistence are not required to implement any specialspec-defined interfaces or classes Another weakness of the

older specification was that it left individual vendors to decidehow an object should be mapped to a particular database

representation This made EJB 2.1 entity beans mostly

nonportable between vendors The new Java Persistence

specification defines a complete object to relational mapping(ORM) so that entity beans can be ported easily from vendor tovendor Furthermore, because entity beans are now plain Java

application server and can even be used to transfer data

between a client and a server This makes designs simpler andmore compact

In addition to supporting RMI-based distributed business

objects, Enterprise JavaBeans supports asynchronous

messaging An asynchronous messaging system allows two ormore applications to exchange information in the form of

messages A message, in this case, is a self-contained package

of business data and network routing headers The businessdata contained in a message can be anythingdepending on thebusiness scenarioand usually contains information about somebusiness transaction In enterprise systems, messages inform

an application of some event or occurrence in another system

Asynchronous messages may be transmitted from one

application to another on a network using message-orientedmiddleware (MOM) MOM products ensure that messages areproperly distributed among applications In addition, MOM

usually provides fault-tolerance, load-balancing, scalability, andtransactional support for enterprises that need to reliably

message In this way, the applications that receive messagesand those that send messages are decoupled Senders and

receivers are not bound to each other in any way and may sendand receive messages as they see fit

so that it supports both RMI and asynchronous messaging EJB3.0 supports asynchronous messaging through the Java

(JMS) possible

JMS is a vendor-agnostic Java API that can be used with manydifferent MOM vendors JMS is very similar to JDBC in that anapplication developer can reuse the same API to access manydifferent systems If a vendor provides a compliant service

provider for JMS, the JMS API can be used to send messages toand receive messages from that vendor For example, you canuse the same JMS API to send messages with Progress's

driven bean types to support all kinds of protocols, includingSMTP for email, SNMP for device control, peer-to-peer protocols(e.g., BEEP and Jabber), and many other open and proprietarymessaging systems In addition, the message-driven bean hasbecome an elegant option for serving connections to legacytransaction processing systems like CICS, IMS, openUTM, andothers

The expansion of message-driven beans in EJB 2.1 to otherprotocols was made possible by the new Java EE ConnectorArchitecture (JCA 1.5), which defines a portable programmingmodel for interfacing with enterprise information systems Theuse of JCA in Java EE is analogous to the use of USB in

computer hardware A computer that supports USB can

interface with just about any USB-compliant device Similarly,

an EJB 3.0 container that supports JCA 1.5 can interface withany JCA 1.5-compliant resource For example, if Vendor XYZcreates a new message-driven bean component for its