[jbossseam-issues] [JBoss JIRA] Commented: (JBSEAM-4235) Improve asynchronous JMS support

[Dan Allen (JIRA)]

    [ https://jira.jboss.org/jira/browse/JBSEAM-4235?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12471790#action_12471790 ] 

Dan Allen commented on JBSEAM-4235:
-----------------------------------

I have a prototype available in Seam 2.1 and 2.2 branches (SVN). This is a tough problem because the invocation of an MDB is fundamentally different from a session bean or any other component. Instead of the application getting a reference and invoking the instance, it's the container that does this work. Thus, there is little opportunity for Seam to get its hands in there and enhance it. Simply adding @Asynchronous to the onMessage() method won't do anything at all.

I have come up with two approaches that will work.

#1. An EJB interceptor - ContextualMessageHandlerRequestInterceptor

Apply this interceptor to your MDB as follows:

@Interceptor(ContextualMessageHandlerRequestInterceptor.class)
public class MyListener implements MessageListener { ... }

Now you can use Component.getInstance() from within onMessage() to look up request-scoped, application-scoped, or business-process scoped components. To use a business-scoped component, you must pass either taskId or processId as a Long property in the payload of the message object.

#2. A contextual callback

Alternatively, you can use the technique that the interceptor uses to execute code within the boundaries of a Seam life cycle. There is some convenience baked in. You can provide as a type parameter the type you want to pass to Component.getInstance() to retrieve your delegate component.

try
{
    new ContextualMessageHandlerRequest<MyMessageProcessor>(message) {
        @Override
        public void process() throws Exception {
            getDelegate().process(getTextMessage().getText());
        }
    }.run();
} catch (Exception e) {
    // log me or something
}

Internally, this will call:

((MyMessageProcessor) Component.getInstance(MyMessageProcessor.class)).process((TextMessage) message).getText());

Let me know what you think about these solutions.

> Improve asynchronous JMS support
> --------------------------------
>
>                 Key: JBSEAM-4235
>                 URL: https://jira.jboss.org/jira/browse/JBSEAM-4235
>             Project: Seam
>          Issue Type: Feature Request
>          Components: Async
>    Affects Versions: The future
>         Environment: JBOSS 5.0 with Seam 2.1
>            Reporter: Leo van den berg
>             Fix For: The future
>
>
> At the moment Seam doesn't fully support the use of asynchronous messaging within the server environment. A proposed solution is to add the same type of support to "JMS-enabled" beans as is available for the timers (EJB and Quartz). It should be possible to simply add the @Asynchronous annotation to the onMessage method and have the Seam components available in the same way.
> At the moment this is only possible with some tricks (as suggested in mentioned Seam forum thread by Dan Allen), but it would be a good extension to JMS to have it as standard functionality available.
> Additionally examles could be added to the documentation and examples-directory of the download to show how to use asynchronous JMS-messaging in a Seam-application.
>  

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