Preface

THIS book, now in its second edition, provides in-depth coverage of the Enterprise JavaBeans™ (EJB) 2.1 architecture, explaining how to develop and deploy enterprise applications by using the latest EJB component architecture. This second edition covers the new 2.0 and 2.1 features of the EJB architecture, including message-driven beans and asynchronous communication, enhanced container-managed persistence, support for Web services, and the EJB™ Query Language (EJB QL).

This book is part of the successful Java BluePrints program created by Sun Microsystems with the introduction of the Java™ 2 Platform, Enterprise Edition (J2EE™ platform). The Java BluePrints program has been used by thousands of application architects, developers, and students to attain a better understanding of the programming model inherent in the J2EE platform.

This book and the Java BluePrints program do not provide information on how to use individual Java technologies to write applications that's the role of the companion Java Tutorial program. Instead, Java BluePrints focuses on guidelines for application architecture.

Readers of this book should be familiar with the Java™ programming language, should have a basic knowledge of the J2EE platform, and should have had some exposure to enterprise beans and the EJB architecture. Although we briefly cover the basics of the EJB architecture, this book is not meant to be a tutorial for those just getting started with enterprise beans. Instead, the book provides in-depth coverage of the EJB 2.0 and 2.1 architectures for information technology (IT) personnel implementing applications in-house and for independent software vendors (ISVs) developing generic applications for sale to enterprises.

The EJB architecture defines a component model for enterprise applications, focusing on the following:

• How to design an application as a set of components

• How the components interact with each other

• How the components interact with their EJB container

The EJB architecture defines these interactions as contracts, which enable applications to use components from different sources. Because EJB components must adhere to these contracts, an application can consist of software components from multiple vendors.

The EJB specification defines the architecture contracts mainly from the point of view of the container vendor. In contrast, this book presents the EJB architecture from the point of view of the application developer that is, the person who develops EJB applications.

A detailed description of the development of two enterprise applications forms the backbone of the book. Although the example applications are relatively simple, they illustrate many of the typical problems encountered in enterprise application development. We use these examples to show how the EJB architecture helps developers solve these problems.

The first example is a benefits enrollment application developed in-house by an IT department. This application works well for explaining how a session bean works and for illustrating how developers use session beans.

The second example turns the benefits application from the first example into an application developed by an ISV. An ISV's design goals differ from those of an in-house IT department. The ISV must design the application so that it can be easily deployed in many different customers' operational environments. Because each customer has a unique operational environment, the ISV must address a number of challenges. In addition, an ISV typically needs to design the application so that it can be extended by a customer or integrator. We illustrate how the entity bean architecture helps ISVs to overcome these challenges.

The EJB 2.1 architecture makes it possible to implement applications as Web services. This updated edition of the book includes a chapter that describes how to incorporate and use enterprise beans in a Web service.

These annotated examples illustrate many of the techniques for applying the EJB architecture to specific problems in enterprise application development. In addition, we describe the individual features of the EJB architecture and discuss when and how they should be used in applications.

Although the typical application developer does not need to know how the EJB container works, we illustrate some of the inner workings of the EJB container. We do this mainly to give the reader an appreciation of how much work the container performs on behalf of the application.