Cedric Beust wrote:
>
> > From: A mailing list for Enterprise JavaBeans development
> > [mailto:[EMAIL PROTECTED]]On Behalf Of Ian McCallion
>
> > 2. An EJB is either an MDB or it isn't; it's either driven by messages
> > or by RMI. It would be really useful for an MDB, SFSB, or even an
> > Entity Bean to be able to fire off a JMS message and be woken up
> > when the reply arrived.
>
> Aren't these two sentences contradictory?
No.
> It looks like you want your SFSB
> to behave synchronously (it sleeps until it gets a reply), so why publishing
> the message on a JMS Destination instead of making an RMI call?
Messaging systems such as IBM MQSeries support a request/reply paradigm. The
advantage of using messaging over synchronous calls comes when the timescale
involved in the request/reply increases. With messaging (because messages can
be hardened) the reply could reliably come back and be processed correctly a
week later, even after the server had been shut down and restarted. But this is
something that is quite impractical using synchronous mechanisms such as RMI.
One of the reasons why message brokers and workflow products are different
beasts from application servers is that one deals with asynchronous messaging
(with request/reply handled badly) and the other deals with synchronous calls
(with asynchronous messaging handled badly).
By supporting what I proposed, a workflow script could be interpreted by an EJB,
allowing application servers to take an even broader role in enterprise
applications.
========================================
Ian McCallion
Alexis Systems Limited
Romsey, UK
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