I usually try to stay far away from doing lock/unlock type things with
threaded access - really testing it can get too hairy, and problems tend to
be hard to trace.
The practice we use here for EJBs is thus (it's actually not too hard to do,
and hides the fact that you're using EJBs from the front end).
Ixxx.java - interface defining business methods
xxxBean.java - implementation code: xxxBean implements SessionBean, Ixxx
xxxHome.java - standard Home interface
xxxRemote.java - remote interface, extends EJBObject, Ixxx
xxxHandler.java - wrapper class, implements Ixxx
The JavaBeans (and JSPs in some cases - no, we're not using Struts (yet))
use the xxxHandler classes for all access. The xxxHandler actually does to
the lookup, home create, portable narrow, and delegates all calls to the
EJB. The code is so straightforward it could really be generated (of
course, we don't do that). Since everything runs off of the Ixxx interface,
the compiler will catch if you change signatures in one place and not the
other. And your Remote interface is empty, since it just "joins" the
EJBObject and Ixxx interfaces.
Food for thought, there are many other ways to do this.
--jason
-----Original Message-----
From: Bryan Field-Elliot [mailto:[EMAIL PROTECTED]]
Sent: Thursday, April 05, 2001 11:33 AM
To: [EMAIL PROTECTED]
Cc: [EMAIL PROTECTED]
Subject: Re: Frames, concurrency, and EJB Stateful Session beans - a
problem.
Thanks,
That proposal would probably work, but it might be a little
over-complicated (although I am starting to suspect that every solution
is going to be yucky). I think I couldn't do your idea with just a
simple bean with a simple syncronized getter method; instead, the
wrapper bean would have to have all of the same method signatures as the
session bean, and pass through all the calls (doing syncronization first).
What I'm leaning towards right now, is finding some kind of "per-user"
syncronization, which I can "lock" at the start, and "unlock" at the
end, of every one of my Action.perform() methods. I can probably do this
with a simple class, with two static methods -- "lock" and "unlock" --
and it will take as a parameter the current user's "session" object
(Servlet session, that is), so that the locks are per-user, rather than
global.
Comments before I dive in the deep end?
Thanks,
Bryan
Abraham Kang wrote:
> Hi Bryan,
>
> Can you put the stateful session bean within a JavaBean with
synchronized
> methods so that all access to the stateful session bean is through the
> JavaBean?
>
> --Abraham
>
>> -----Original Message-----
>> From: Bryan Field-Elliot [mailto:[EMAIL PROTECTED]]
>> Sent: Thursday, April 05, 2001 8:09 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
>>
>>
>>
