At the very least, I would appreciate feedback from the JMS EG on where the mapping falls down so we can enhance the CDI API as needed.
On 26 Sep 2011, at 19:43, Pete Muir wrote:
> Interesting, I wasn't aware of this discussion/conclusion, and would be interested to read more about it.
>
> I suppose my next favorite approach is to offer MDBs outside of the EJB container, than invent an entirely new API for it. Have you guys considered that?
>
> On 26 Sep 2011, at 18:34, reza_rahman_at_lycos.com wrote:
>
>> Pete,
>>
>> We actually discussed this in the JMS 2 EG in relative detail. I know it's very tempting to think about CDI events and JMS messages as being synonymous (the similarities are obvious). The problem is that the current set of JMS features do not map very well to CDI events. It isn't as obvious when you look at asynchronous message receipt in particular (as we are here). The feature loss is more obvious when for example we start discussing sending JMS messages. Now, if the features/flexibility lost were corner cases anyway, it would not be a big deal. The issue is that the JMS features potentially lost are frequently used in the real world today.
>>
>> I think it's best to keep the CDI Event/JMS bridge as a non-standard portable extension (a la Seam JMS) and think about CDI events and JMS messages as orthogonal concerns from a Java EE standpoint (just as it is today). The other way of doing this would be to try to enhance CDI events to match the JMS model more. I don't think that would be a sensible thing to do for the simple reason that these really are very different concerns.
>>
>> Hope this makes sense - I can understand that this is probably not the response you want to really hear...
>>
>> Cheers,
>> Reza
>>
>>
>> Sep 26, 2011 12:59:10 PM, jsr345-experts_at_ejb-spec.java.net wrote:
>> Reza,
>>
>> Would you like to see this instead of, as well as, or not as much as, a bridge from JMS to CDI events?
>>
>> On 26 Sep 2011, at 01:12, Reza Rahman wrote:
>>
>>> Marina,
>>>
>>> Sorry it took so long to respond to this. It's been a crazy couple of weeks :-(.
>>>
>>> As I mentioned previously, the basic idea is to separate asynchronous message processing from the current MDB component model. So, in a newer model, any Java EE managed bean (including perhaps a Servlet) could receive a JMS asynchronous message like this:
>>>
>>> public class SomeBean {
>>> ...
>>> @Listens
>>> @JmsDestination("jms/SomeQueue")
>>> @JmsConnectionFactory("jms/ConnectionFactory")
>>> @JmsSessionMode(AUTO_ACKNOWLEDGE)
>>> @JmsMessageSelector("foo=bar")
>>> public void someMethod(Message message) {
>>> ...
>>> }
>>> ...
>>> }
>>>
>>> Because this would be loosely modeled after CDI/DI, the message receiver method parameters could be quite powerful. So we could do things like this:
>>>
>>> @Listens
>>> public void someMethod(MyMessage message) {
>>>
>>> @Listens
>>> public void someMethod(String message) {
>>>
>>> @Listens
>>> public void someMethod(byte[] message) {
>>>
>>> @Listens
>>> public void someMethod(Map message) {
>>>
>>> @Listens
>>> public void someMethod(MyMessage message,
>>> @JmsCorrelationId String correlationId,
>>> @JmsReplyTo Destination destination,
>>> @JmsProperty("myProperty") int someProperty) {
>>>
>>> @Listens
>>> public void someMethod(Message message, @Inject SomeOtherBean otherBean) {
>>>
>>> Because such listener methods need to be transactional, it's difficult to go too far with this without decoupling declarative transactions from the EJB component model. It's also the case that things like concurrency must be figured out for this model (perhaps by decoupling @Lock from EJB or defining @PoolScoped, @TransactionScoped or @MaxConcurrency). Besides enabling messaging for non-EJB components, this enhancement would also enable us to treat JMS with first-class citizen semantics and move away from the over-generalized JCA based semantics that we have today. We could also similarly support a JCA based model like this:
>>>
>>> public class SomeBean {
>>> @Listens
>>> @ActivationConfigProperty(propertyName="mailServer", propertyValue="mailHost"),
>>> @ActivationConfigProperty(propertyName="mailFolder", propertyValue="INBOX"),
>>> @ActivationConfigProperty(propertyName="storeProtocol", propertyValue="imap"),
>>> @ActivationConfigProperty(propertyName="userName", propertyValue=""),
>>> @ActivationConfigProperty(propertyName="password", propertyValue="secret")
>>> public void someMethod(Message message) {
>>> ...
>>> }
>>> }
>>>
>>> Now, I think this is going to take quite a bit of work to standardize, so I am not sure it is right for EJB 3.2. Also, I think we should go down this path after the current JMS 2 discussion of a higher-level dependency injection based API is resolved. For example, we may be able to re-use some of the annotations being developed as part of that API. Also, any new JMS related annotations could be defined in javax.jms rather than javax.ejb. Similarly, I wonder if the JCA listener related annotations really belong in javax.resource?
>>>
>>> Note, I don't think any of this need be bound directly to CDI or CDI events per se, although I can see us using some JSR 330 annotations and underlying implementations using the CDI portable extension SPI (in a relatively container specific manner).
>>>
>>> Hope it helps. Let me know if I need to explain anything in greater detail. I have kept this brief and high-level on purpose.
>>>
>>> Cheers,
>>> Reza
>>>
>>>
>>> On 9/12/2011 6:21 PM, Marina Vatkina wrote:
>>>> Reza,
>>>>
>>>> There is a plan (stay tuned) to make CMTs available outside EJBs. But how does it affect MDBs in the EJB container?
>>>>
>>>> thanks,
>>>> -marina
>>>>
>>>> Reza Rahman wrote:
>>>>> Marina,
>>>>>
>>>>> I think it's hard to have this discussion without starting to talk about decoupling transactions (and other services) from the EJB component model. Did you still want to have this discussion now?
>>>>>
>>>>> Cheers,
>>>>> Reza
>>>>>
>>>>>
>>>>> On 9/9/2011 9:11 PM, Marina Vatkina wrote:
>>>>>> Experts,
>>>>>>
>>>>>> Does any of you have a wish-list for the MDB improvements in the EJB spec? This should be a purely EJB related changes, as the JMS 2.0 EG is looking carefully at the overall JMS revamp.
>>>>>>
>>>>>> thanks,
>>>>>> -marina
>>>>>>
>>>>>>
>>>>>>
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>>>>>>
>>>>>
>>>>
>>>>
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>>>>
>>>
>>
>