Brian,
Disclaimer: I'm new to EJB and still trying to understand when to use
stateful/stateless session beans.
Given that, I found your situation interesting. First I'll try to help you
if I can. There is an article in the February 2001 WebSphere Advisor by Tony
Higham, on page 10, titled "The Reality of EJB". It should be available on
their web site. He talks about problems like yours and recommends an
approach where you use stateless beans but an alternative state-handling
mechanism such as HttpSession to hold the user's data. Will that sort of
thing work for you? It sounds more light-weight than stashing the whole
session bean and/or accessor JavaBean with synchronized methods into the
session. There are also some good patterns for using session beans in the
IBM Redbook "Design and Implement Servlets, JSPs, and EJBs for IBM WebSphere
Application Server", which is available for download on the IBM Redbooks
site. You might find some ideas there.
Now that I've tried to help, if you could, explain your aversion to
stateless and why they won't work for you in this situation, so that I can
learn more.
Thanks, your questions and contributions here are very useful to me.
Bill Hines
Sun Certified Java Programmer
Hershey Foods Corp
-----Original Message-----
From: Bryan Field-Elliot [mailto:[EMAIL PROTECTED]]
Sent: Thursday, April 05, 2001 11:09 AM
To: [EMAIL PROTECTED]
Subject: Frames, concurrency, and EJB Stateful Session beans - a
problem.
I'm having a design problem with my system, which is not really Struts
specific, but since there are a lot of EJB users here, I thought I'd
throw it on this list for comments --
My business logic is all implemented in a Stateful EJB Session bean. All
Struts users get one instance of the session bean, whose reference is
stored in the Servlet's Session scope.
All of my Struts actions are simple; they take data from the user
(usually in ActionForms), pass them to some method in the EJB Session
bean, and store the results in beans for the JSP page to render.
However, my design calls for a few places where there is a frameset, and
in another place, where two browser windows open up showing two
different views. The problem here, is that EJB requires that a Stateful
Session bean have only one thread of execution within it (e.g. no
concurrency). So, when two different Struts actions (or custom tags) try
to invoke a method on the same EJB Session bean reference at the same
time, one of them will fail with an exception thrown by the EJB
container (in my case, jBoss).
Can anyone recommend an easy, general-purpose solution to this problem?
(Please don't say, "switch to stateless session beans"). I suppose I
need to syncronize access to the EJB bean from the client (and, in this
case, the client is Struts), but I'm not sure how to do this quickly and
elegantly.
Comments would be appreciated,
Bryan
