ONJava.com    
 Published on ONJava.com (http://www.onjava.com/)
 See this if you're having trouble printing code examples


EJB 2

Stateful Session EJBs: Beasts of Burden

10/02/2001

That's right. You heard it here first. I'm calling Stateful Session EJBs (SFSBs) the J2EE beasts of burden. I don't care for them. I despise them. I really hate them.

I don't dislike what they offer to developers. Rather, I dislike their conniving, misleading, and subtle nature that permits developers to make some of the worst architecture decisions I've seen. SFSBs have a very limited use in development and should rarely be seen. But somehow, these infiltrating creatures have wormed their way into designs where they do not belong. This article discusses the true purpose of SFSBs, where they belong in a J2EE design, and the situations where they should not be used. Heed this advice and perhaps we can harness the beast to create more robust architectures instead of creating more burdens by using SFSBs incorrectly.

The intent of Stateful Session EJBs

An Stateful Session EJB is a server-side object designed to hold data on behalf of a particular client. SFSBs should be used to store session-oriented data. Session-oriented data is used to track a multi-request sequence, ordering, or any associated data that is part of a sequence. SFSBs, however, have a limited lifespan and are not intended to survive server crashes. SFSBs are the only type of EJB that can receive callback notifications about the lifecycle of transactions that the bean participates in.

When SFSBs should not be used

When SFSBs should be used in non-web systems

For systems that do not have a servlet/JSP front-end, SFSBs should be used to track session-oriented state similar to the way a web-based system would use an HttpSession object. This was the primary intent of SFSBs when they were created.

When SFSBs should be used in web systems

Systems that have JSP/servlet front-ends should use HttpSession objects to store session-oriented state on behalf of a client. Applications that manage an HttpSession object and an SFSB for a single client wind up duplicating effort that does not need to be duplicated. There are two reasons to use an SFSB in conjunction with an HttpSession object:

Conclusion

SFSBs have their place in J2EE systems; it's just very small. If your designs use SFSBs for session-oriented data and avoid using SFSBs as distributed data caches, your systems will be more reliable. If you have a requirement you think SFSBs can satisfy and that requirement is not listed in this article, you should give some hard thought to another solution.

Tyler Jewell , Director, Technical Evangelism, BEA Systems Tyler oversees BEA's technology evangelism efforts that are focused on driving early adoption of strategic BEA technologies into the ISV and developer community.


Read more EJB 2 columns.

Return to ONJava.com.

Copyright © 2009 O'Reilly Media, Inc.