[cdi-dev] JMS 2.1: Proposal to allow any CDI managed bean in a Java EE application to listen for JMS messages

[Romain Manni-Bucau]

So if I get it right the issue is for now in CDI you don't really know if
the backing instance - if exists - is created or not (ie toString() is not
enough). I think on this point CDI can be enhanced to have a
isInstantiated() method in its SPI and potentially a forceInstantiation()
one to solve it - would also allow to fix the @Startup issue.

Now for JMS having an event based SPI would be a good addition allowing
some programmatic registration - naming is to completely to rework but the
idea would be:


public void startJms(@Observes final JmsAfterStart jmsStart) {
    jmsStart.registerListener(message -> System.out.println(message))
                 .registerListener(new MyTypedMessageListener()); // or
even an injected instance
}

// JmsBeforeShutdown would be needed as well with a unregister for symmetry
but auto deregistration is possible as well

with MyTypedMessageListener:

public class MyTypedMessageListener {
      public void onMessage(MyTypedMessageICreatedInMyApp msg() {}
}

For this last case a really elegant solution would be to just reuse
@Observes to fire the message from the jms "container" listener and
propagate it to the "user" listener. This would then allow to decouple the
application listener from JMS.

For client side having a custom qualifier supporting placeholding - a bit
like jbatch for system properties - would be nice and would allow to skip
JNDI which means enabling SE usage as well.


Romain Manni-Bucau
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2015-08-25 15:51 GMT+02:00 Nigel Deakin <nigel.deakin at oracle.com>:

> On 24/08/2015 21:24, John D. Ament wrote:
> >
> > Hi Nigel!
> >
> > Glad to hear from you.  Was wondering, is there a way to manually
> register listeners?
>
> The current proposal is is for the bean to start listening just as soon as
> it is created (by CDI), and for it to stop
> listening just before it is destroyed (by CDI).
>
> As you suggesting that CDI would create the listener, but the application
> would call some method to tell it to start
> listening? or did you have something else in mind?
>
>  > It would be great if this could
> > be leveraged in a CDI SE environment as well as EE environment.
>
> I see that work is underway for CDI 2.0 to define how CDI might work in a
> Java SE environment. I don't see why a similar
> portable extension could not be created for use in Java SE. Since there
> would be no need to support Java EE behaviour
> such as transactions this could be built directly on top of the JMS
> provider's Java SE client. No need to use a resource
> adapter. However since the @JMSListener and @JMSConnectionFactory
> annotations use JNDI there would be a need to be a way
> to specify which JNDI InitialContext to use. I'm not proposing any of this
> at the moment, but it might perhaps be
> something that we (the JMS expert group) could consider later on as a
> optional part of JMS 2.1.
>
> There's also the Java EE application client to consider.
>
> Nigel
>
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