[javaee-spec users] [jsr342-experts] Re: proposed MDB improvements

From: David Blevins <>
Date: Fri, 8 Mar 2013 19:27:35 -0800

I fully support this proposal and want to thank Bill and crew for working to get this in so late. I've created a few implementations for the RI of the basic idea using feedback from Bill and Marina and this version of the proposal is definitely the best by far.

The getEndpointClass() method is a significant improvement over the beanClass property. The conditional activation of the new functionality based on a "no methods" message listener interface is what I would call a harmless and effective choice that 1) doesn't adversely affect existing RAs, 2) doesn't eliminate more robust syntax in the future, and 3) doesn't create any mess or API that would need to be deprecated when better syntax is created.

I'd best describe it as a razor sharp change made with a scalpel that could have huge potential upside. Given the amount we'll learn over the next 2-3 years about how people find new uses for our old code, this balance is just right.

A definite win for EE 7 that opens the door for considerable fun in EE 8.


On Mar 8, 2013, at 11:18 AM, Markus Eisele <> wrote:

> Hi Bill,
> thanks for listening to David's proposal. I support it and I
> understand the limitations given for the EE 7 scope.
> The proposed re-scoping sounds ok to me, but I am interested to read
> David's thought on it, too.
> Thanks,
> - Markus
> On 8 March 2013 20:11, Bill Shannon <> wrote:
>> Expert group members,
>> I need your feedback by Wednesday, March 13.
>> David Blevins has proposed some changes to the Message Driven Bean support:
>> This Jira entry tracks this proposal:
>> As you can see from the number of votes, this proposal has received quite a
>> bit of support, so we've been looking into what it would take to implement
>> it for Java EE 7.
>> Given how late we are in the release, we need to carefully manage the
>> risk associated with such a change, and limit the scope accordingly.
>> At this point we have proposed spec changes and a prototype implementation
>> that we're comfortable with. I'd like to describe the spec changes and
>> get your feedback as to whether this is a reasonable and safe addition
>> to Java EE 7. It will be helpful to read David's background proposal
>> above.
>> The first change is a minor addition to the Connectors spec:
>> - Add a method to MessageEndpointFactory:
>> /**
>> * Return the Class object corresponding to the message
>> * endpoint class. The resource adapter may use this to
>> * introspect the message endpoint class to discover
>> * annotations, interfaces implemented, etc. and modify
>> * the behavior of the resource adapter accordingly.
>> */
>> public Class<?> getEndpointClass();
>> This ability for the resource adapter to introspect the MDB class
>> seems useful independent of any other change, and it's a simple,
>> localized change to the Connector spec.
>> This would require updating the in-progress Connector spec Maintenance
>> Review.
>> The second change is a change to the EJB spec to require that the
>> MessageEndpointFactory.createEndpoint class behave differently in
>> certain situations. To support the use cases in David's proposal,
>> the resource adapter needs access to a proxy that implements all of
>> the public methods of the MDB class, not just the methods of the
>> message listener interface.
>> The simple approach would be to require that the proxy returned by
>> the createEndpoint method always include all the public methods, as
>> well as implementing the message listener interface. That change is
>> too risky for this release.
>> In the expected use cases, the resource adapter will use reflection
>> to invoke the methods of the MDB, based on annotations on those methods.
>> The message listener interface is unnecessary in these use cases.
>> Ultimately, we would like to remove the need for a message listener
>> interface, and provide another mechanism for associating an MDB class
>> with a resource adapter (e.g., based on annotations). That too is too
>> risky for this release.
>> As a compromise, our proposal for now is this:
>> - If the message listener interface has no methods, the EJB container
>> must provide a proxy returned from the createEndpoint method that
>> implements all the public methods of the MDB class, as well as the
>> message listener interface. (Perhaps that should be all the public
>> *business* methods, so that Object methods need not be exposed?)
>> This preserves the existing algorithm for associating a resource
>> adapter with an MDB, and redefines a currently useless case to be useful.
>> We can enhance this in a future release to provide more flexible binding
>> between an MDB and a resource adapter.
>> If you think these changes are reasonable and it's appropriate to add
>> them to Java EE 7 at this late date, please speak up. As usual we'll
>> interpret silence as consent, but we'd greatly prefer to have vocal
>> support.
>> And of course if you see any problems at all with this proposal, I'm
>> confident that you'll speak up immediately.
>> Lacking serious issues or objections by Wednesday, March 13, we'll
>> proceed with this proposal.
>> Thanks.