Sounds like a good idea, but wouldn't the invokation from
the helper class to the session bean cause a re-entrancy
problem? Unless it's a stateless bean and the event is handled
by another instance from the pool. If it's a stateful bean,
how would this work?
Regards,
Frank
-----Original Message-----
From: A mailing list for Enterprise JavaBeans development
[mailto:[EMAIL PROTECTED]]On Behalf Of Rickard Öberg
Sent: Friday, January 21, 2000 4:25 AM
To: [EMAIL PROTECTED]
Subject: Re: JMS and EJB:using a Helper class
Hey
Proneel Guptan wrote:
> To get around this restriction, we developed a helper class which
> implements the MessageListener interface.
Which is a good idea.
> The session bean does the
> following:
> synchronize(helperObject)
> {
> helperObject.start(); // To switch on listening for messages in
> the JMS session in helperObject
> helperObject.wait(); // handle InterruptedException
> helperObject.stop(); // To switch off listening for messages in
> the JMS session in helperObject
> // process the message, which is stored in the helperObject
> }
>
> The helperObject meanwhile, in its onMessage() method:
> synchronize(this)
> {
> // process message received as input to onMessage()
> notifyAll();
> }
>
> Note that we ensure that the message listening is switched on only
> when the session bean is actually waiting for a response.
Whoa.. now you're in trouble. The "wait" is not allowed (thread
modification operations are a no-no), and your transaction is likely to
time out. In essense you're using JMS in a synchronous way. Not a good
idea.
I would do something like this instead:
* In the session bean you should indeed register a helper class with
JMS, and the helper class should hold a reference to the session bean
(get it in the session bean by doing ctx.getEJBObject()).
* On onMessage your helper class should call the session bean, and
preferably not the same method as did the register above. You can
provide the message on the call
* Your session bean may now process the message
i.e. in SessionBean:
public void listen()
{
Helper h = new Helper(ctx.getEJBObject());
<register h with JMS somehow>
}
public void doStuff(Message m)
{
// Process the JMS message
}
and in Helper:
..
MySession theBean;
public Helper(MySession ms)
{
theBean = ms;
}
public void onMessage(Message m)
{
theBean.doStuff(m);
}
-----------
I'm a newbie on JMS myself, but something like that should work well.
And it only uses short transactions, whereas your solution involves one
long transaction (=bad).
HopeThisWorks(tm) :-)
/Rickard
--
Rickard Öberg
@home: +46 13 177937
Email: [EMAIL PROTECTED]
http://www.dreambean.com
Question reality
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