Wizard API updated!
Tim Boudreau has released a new version of the Swing Wizard library (version 0.997) that fixes the WizardException bug reported in JavaWorld's recent Open Source Java Project profile. The article's examples have been reworked to test out the new, improved WizardException. Thanks, Tim, for this helpful fix!
Open Source Java Projects: The Wizard API

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The state of Java middleware, Part 2: Enterprise JavaBeans

Learn how Enterprise JavaBeans fits into your enterprise -- and which tools support EJB

By Anil Hemrajani, JavaWorld.com, 04/01/99

Last month JavaWorld published the first article in this two-part series, covering the state of Java middleware. The first article provided an overview of the many features offered and promised by Java middleware; this article focuses specifically on one of those features: Enterprise JavaBeans (EJB).

By now you've probably heard about EJB, read articles about it, and possibly even written a few enterprise beans yourself. However, if you're like many people out there, you might not understand the big picture -- despite the fact that working with EJB is supposed to be extremely simple. Here's a list of questions many developers new to EJB struggle with:

  • What are all the features of EJB?
  • What tools are available today that support EJB?
  • When should I use session beans versus entity beans?
  • When to use a stateful session bean versus a statelessone?
  • What are the dos and don'ts of EJB development?
  • How does EJB relate to JDBC 2.0 (Java Database Connectivity) and the transaction management APIs?
  • How does EJB's security work?
  • How do complex joins in an existing relational database work with entity bean mapping?


This article addresses these and other common concerns about EJB. It includes examples of how some vendors provide EJB support. Moreover, this article addresses the following key issues:

  • Whydo we need EJB?
  • Whowill support EJB?
  • Whatexactly is EJB?
  • Howdo you develop, deploy, and manage EJB?
  • Howdo you integrate EJB with existing systems?
  • Wheredoes EJB go from here?

In short, this article describes the current state of EJB and the Java middleware (tools) that support it. Rather than focus on in-depth coding examples, I devote attention to the more challenging aspects of working with EJB: the design issues and tools selection. To learn more about nitty-gritty programming with EJB, see the JavaWorld articles in the Resources section below. Furthermore, EJB programming (developing enterprise beans), in my opinion, is the easy part (as Sun intended it to be); design issues and tools selection are the more challenging aspects of working with EJB.

Note that throughout this article I use the terms Java middleware, application servers, and EJB servers somewhat interchangeably. Marketeers, authors of the EJB (or CORBA/DCOM) specification, and niche developers may see many distinctions among these terms, but for the purpose of this article they all mean the same thing.

Note also that this article is jam-packed with information on EJB. While it may seem overwhelming, don't be discouraged: EJB developers typically don't have to deal with all the issues discussed here. In fact, the EJB specifications define several roles and responsibilities that can be handled by either one person or several people, depending on the size of your project. Nevertheless, an understanding of the big picture is essential. And remember, developing enterprise beans is actually extremely simple.

Why do we need EJB?

Ever since the Web began to make the Internet popular and useful for almost everyone (not just the government and students), new Net technologies (Internet, intranet and extranet) have emerged from all directions and organizations. It is now close to impossible to keep up with these technologies at the speed they're being introduced.

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Resources
  • Visit Sun's EJB home page for articles, specifications, press releases, and links related to EJB http://java.sun.com/products/ejb/
  • SunWorldarticle on EJB, designed to help readers determine if this technology is right for their companies. See the IT Architectcolumn "Expanding your server-side toolkit with EJB" http://www.sunworld.com/swol-04-1999/swol-04-itarchitect.html?jw
  • The Divya.com Web site provides a complete list of currently available Java application servers and related vendor white papers http://divya.com/links.html
  • Download the free EJB Guide from Nova Labs http://www.nova-labs.com/EJBGuide/EJBGuide.htm
  • For CORBA-specific information, visit The Object Management Group's Web site http://www.omg.org/.
  • Previous EJB features in JavaWorld
  • "Write a session EJB" by Michael Shoffner (Java Step by Step, July 1998) http://www.javaworld.com/javaworld/jw-07-1998/jw-07-step.html
  • "Enterprise JavaBeansComing soon to a server near you" by Bryan Morgan (Distributed Objects, June 1998) http://www.javaworld.com/javaworld/jw-06-1998/jw-06-distributed.html
  • EJB features on the Java Developer Connection
  • "Enterprise JavaBeansWorking with Entity and Session Beans" http://developer.java.sun.com/developer/technicalArticles/EBeans/SampApp/
  • "An Introduction to Enterprise JavaBeans Technology" http://developer.java.sun.com/developer/technicalArticles/EBeans/