Something I didnt think before but if you can register a method reference
then CDI event system starts to be useless:
xxx.register(myCdiBean::listenOn);
can be something to investigate API wise maybe
Romain Manni-Bucau
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2015-08-26 11:43 GMT+02:00 Nigel Deakin <nigel.deakin(a)oracle.com>:
> On 25.08.2015 16:05, Romain Manni-Bucau wrote:
>>
>> 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.
On 25/08/2015 15:26, Jozef Hartinger wrote:
> Agreed. I think we should leverage the existing CDI event/observer
> functionality instead of introducing a completely new
> delivery mechanism.
>
Can you please say a bit more about what you have in mind?
Romain suggests using events to invoke the "user" listener from the "JMS
container listener".
That's a useful distinction. Just to clarify the terminology:
"user" listener = listener bean provided by the application
"JMS container listener" = JMS consumer provided by the application server
or resource adapter
There needs to be one consumer for every listener bean since the two need
to have the same lifecycle, and also so we can implement JMS queue sematics
which require that a message from a queue is delivered to one and only one
listener.
The transaction needs to be started by the consumer before invoking the
listener and ended after the listener returns. This allows the
acknowledgement of the message (which is performed by the consumer) to take
place in the same transaction as is used by the listener's method.
Currently I'm proposing that the "consumer" invokes the
"listener" by a
simple method call. I suppose instead of simply invoking the method it
could fire a synchronous event, which only the associated listener instance
would receive, but I'm not sure what the benefit of this would be. Since
JMS semantics are very different from CDI event semantics I think there's a
danger that this will be confusing, since the user might think they were
getting CDI event semantics, but they were actually getting JMS semantics.
Since this is a bit of a FAQ, it might be useful to explore the
differences between the two semantics, but currently they seem profoundly
different to me. That's why my proposals are built on the CDI bean
lifecycle model but not the CDI event observer model.
Nigel