Applying Enterprise JavaBeans: Component-Based Development for the J2EE Platform, 2nd Edition

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 takes the benefits application from the first example, which was developed in-house, and turns it into an application developed by an ISV. An ISV has different design goals from that 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 to the two application examples, 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.

Other Sources of Information

You should refer to other publications related to the Java 2 platform, Enterprise Edition application architecture (J2EE™). The following books are of particular interest to those developing other application components besides enterprise beans:

Note about the Example Applications

It is important to note that the example applications described in the book are written without the use of an interactive development environment (IDE). Normally, enterprise developers use a commercial IDE when developing EJB applications. An IDE generates much of the JDBC and other database access code—code that is often tedious to write by hand. However, we wanted our examples to illustrate how the EJB architecture works and, had we used an IDE, the code generated by the IDE would obscure the discussion of the EJB architecture. Therefore, we chose to write all the code manually. Keep this in mind and realize that developing with the EJB architecture is easier than some of our code samples may indicate because in practice a lot of the code is generated automatically by the IDE.

Because our goal is to illustrate the use of the EJB architecture, we wanted to keep the code relatively simple. As a result, we don’t always show what some developers would consider to be the best coding practices for enterprise applications. By including code to show such practices, we would have obscured the EJB discussion. For the sake of simplicity of the code examples, we sometimes do not handle properly all exceptions thrown by the code.

Contents of the Book

The book begins by describing the advantages of the EJB architecture. Chapter 1, Advantages of the Enterprise JavaBeans™ Architecture, discusses the different enterprise application architectures and how they have evolved, especially with the growth of the Web. It describes the current state-of-the-art EJB, J2EE, and Web Services architectures, and how they are well suited to meet today’s enterprise computing needs.

Chapter 2, Enterprise JavaBeans Architecture Overview, provides a concise overview of the EJB architecture. For someone not so familiar with the EJB architecture, this chapter is a good starting point because it defines the EJB terminology and the structure of enterprise beans. It defines and describes EJB applications, and such basic concepts as business entities and business processes. It provides an overview of the different enterprise bean types, the parts that comprise an enterprise bean, and how to use enterprise beans to model business logic of enterprise applications.

The development of an EJB application can be thought of in terms of the tasks that need to be performed. To that end, Chapter 3, Enterprise JavaBeans Roles, delineates the roles and tasks involved during the application development process.

Once the stage has been set and the introductory material explained, the book focuses on session beans, entity beans, and message-driven beans. Two chapters focus on session beans and two chapters focus on entity beans. Chapter 4, Working with Session Beans, focuses on typical programming styles for applications using session beans. This chapter is of interest to bean developers implementing session beans and to application programmers developing session bean clients. For bean developers, the chapter describes how best to implement the methods of a session bean. For application programmers developing session bean clients, it shows how to use the session bean home, remote, and local interfaces properly. An extensive benefits enrollment application example illustrates the key points about session beans.

Chapter 5, Session Bean in Its Container, describes the support and services that an EJB container provides for a session bean. Containers typically provide services to session beans when they are deployed and customized for a particular operational environment, and at runtime, when a client application invokes the session bean. Although the container services are hidden from the bean developer and the client programmer, these services go a long way in simplifying bean and application development. This chapter describes much of what goes on behind the scenes.

After completing the discussion of session beans, Chapter 6, Enterprise Application Integration Using Message-Driven Beans and Connectors, presents message-driven beans. A message-driven bean is a new type of enterprise bean introduced in the latest EJB architecture. It enables asynchronous message-oriented communication with enterprise beans. This chapter presents the basic concepts of the Java Message Service (JMS) and then describes how to develop message-driven beans. The benefits enrollment application from the session bean chapter is extended to show how to integrate it with a payroll application in a loosely coupled manner using message-driven beans.

The book then shifts its focus to entity beans. Entity beans differ significantly from session beans. Chapter 7, Understanding Entity Beans, combines a presentation of the basic concepts regarding programming with entity beans, from both the client and bean developer points of view, along with a discussion of the services that the container provides to entity beans. This chapter is analogous to Chapter 5 for session beans. The chapter also provides a detailed description of strategies for managing entity object state: bean-managed and container-managed persistence, including the EJB QL query language. Chapter 8, Entity Bean Application Example, takes the benefits enrollment application example used for session beans and shows how to write the same application using entity beans. The example illustrates many of the techniques for working with entity beans and using container-managed persistence. It also illustrates how entity beans can be used by ISVs to make their application reusable across many customers’ operational environments.

Web services technologies have become prominent in the last few years as a means to integrate applications across enterprises using interoperable, standards-based protocols and service description formats. Chapter 9, Using Enterprise JavaBeans in Web Services, introduces Web services technologies. It describes how to use the EJB architecture to build and access Web services using new Java standard APIs that are currently being developed. Virtually all applications using enterprise beans rely on transactions. Chapter 10, Understanding Transactions, describes the EJB architecture approach to transaction demarcation. It covers the essential aspects of transactions necessary for application developers.

Security is another area of critical importance to enterprise applications. The EJB architecture provides declarative support for security management. Chapter 11, Managing Security, describes the EJB security environment, particularly from the point of view of the application developer.

Last, the book includes an appendix that contains the API reference, a second appendix that contains code samples of supporting classes, and a glossary of terms. The reference section contains all the interfaces defined by the EJB architecture as well as the methods within each interface.

Acknowledgments

We would like to thank the following individuals who, on short notice, took the time to review the early draft of the book and who provided us with invaluable feedback: Mark Hapner, Bill Shannon, Rahul Sharma, Rick Cattell, George Copeland (IBM), Susan Cheung (Oracle), Liane Acker (Encore Development), Jim Frentress (nPassage, Inc.), Moshe Sambol (GTE), and John Stearns.

Likewise, we want to thank the following individuals for reviewing the final draft of the book and for providing feedback: Liane Acker (Encore Development), Ken Nordby (IBM), Jorgen Thelin (Orbware), Marc Fleury (Telkel), Jim Healy, and Jim Frentress (nPassage, Inc.).

We especially want to thank Walter Jenny and Rahul Sharma. Walter’s programming brought the entity bean example application to life at the JavaOne show this past June. Rahul not only reviewed both drafts of the book, he also developed the PayrollBean to use the Connector specification to access a mainframe application.

We also want to acknowledge the following people who helped us accomplish all the tasks necessary to publish this book: Jeff Jackson, for enthusiastically encouraging us to do this book; Lisa Friendly and Jim Inscore, for assisting us with publication details; and Mike Hendrickson and Ross Venables, among others at Addison-Wesley, who had the flexibility to adapt their schedules to ours.

Index

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