Applying Enterprise Javabeans: Component-Based Development for the J2ee Platform

• Authors: Vlada Matena;Mark Hapner
• Venue: Applying Enterprise Javabeans: Component-Based Development for the J2ee Platform
• Year: 2000

From the Book:This book provides an in-depth coverage of the Enterprise JavaBeans™ architecture. It describes how to distribute enterprise applications using the EJB component architecture. Readers of this book should be familiar with the Java™ programming language and 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 an in-depth coverage of the EJB architecture for 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. It describes: 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, and they 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 1.1 specification defines the architecture contracts mainly from the point of view of the container vendor. In contrast, this book tries to present 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. While theexample 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 such 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 such that the application can be extended by a customer or integrator. We illustrate how the entity bean architecture helps ISVs to overcome these challenges. These two 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 try to 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 J2EE. The following books are of particular interest to those developing other application components besides enterprise beans: Java™ 2 Platform, Enterprise Edition Specification, Version 1.2, Copyright 1999, Sun Microsystems, Inc. Available at http://java.sun.com/j2ee/docs.html. Java™ 2 Platform, Enterprise Edition Connector Specification, Copyright 2000, Sun Microsystems, Inc. Java™ 2 Platform, Enterprise Edition, Platform and Component Specification, Shannon, Hapner, Matena, Davidson, Pelegri-Llopart, Cable, Enterprise Team, Copyright 2000, Sun Microsystems, Inc. Enterprise JavaBeans™ 1.1 Specification, Final Release, Copyright 1999, 2000, Sun Microsystems, Inc. Enterprise JavaBeans™ 2.0 Specification, Public Draft, Copyright 2000, Sun Microsystems, Inc. Developing Enterprise Applications with the Java™ 2 Platform, Enterprise Edition, Version 1.0., Kassem, Enterprise Team, Copyright 2000, Sun Microsystems, Inc. RMI over IIOP 1.0.1 Specification, at http://java.sun.com/products/rmi-iiop. Note About the Example Applications It is important to note that the example application in Chapter 4, Working with Session Beans, and the entity bean application in Chapter 7, Entity Bean Application Example, 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 manually write all the code. Keep this in mind and realize that developing with the EJB architecture is easier than some of our code samples might indicate since in practice a lot of the code would be generated automatically by the IDE. Because our goal is to illustrate using 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 and J2EE 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 in the application development process. Once the stage has been set and the introductory material explained, the book focuses on session beans and entity 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 properly use the session bean home and remote interfaces. 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 to simplifying bean and application development. This chapter describes much of what goes on behind the scenes. After completing its discussion of session beans, the book shifts its focus to entity beans. Entity beans differ significantly from session beans. Chapter 6, 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. Chapter 7, Entity Bean Application Example, takes the Benefits example application 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. It also illustrates how entity beans can be used by ISVs to make their application reusable across many customers' operational environments. Virtually all applications using enterprise beans rely on transactions. Chapter 8, 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 9, Managing Security, describes the EJB security environment, particularly from the point of view of the application developer. Last, the book includes an appendix containing 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.