On 07/05/2013 14:38, Nigel Deakin wrote:
> On 07/05/2013 14:27, Nigel Deakin wrote:
>> https://java.net/jira/browse/JMS_SPEC-121
>> Injection of JMSContext objects not possible in a WebSocket @OnMessage or @OnClose callback method
>>
>> If you inject a {{JMSContext}} into a websocket {{ServerEndpoint}} you can use it in the {{_at_OnOpen}} callback, but if
>> you attempt to use it from the {{_at_OnMessage}} or {_at_OnClose}} callbacks you get an exception from the CDI container
>> because there is no valid request scope or transaction scope. From a user perspective it would seem reasonable to expect
>> to be able to use an injected {{JMSContext}} in these places.
>
> JMS 2.0 defines an injected JMSContext to have transaction scope if there is a current transaction, and request scope
> otherwise. However neither scope is available in a websocket @OnMessage or @OnClose callback.
>
> This seems to be an inconsistency in the CDI specification. Although there is no valid HTTP request during the
> @OnMessage and @OnClose callbacks, CDI already widens the definition of @RequestScoped to cover cases which have no
> relationship with HTTP. For example CDI 1.0 states that a MDB's onMessage method is executed within a request scope,
> even though there is no HTTP request involved. Now that WebSockets are part of Java EE 7 (JSR 356), it seems a bit
> arbitrary for a MDB callback to have a valid request scope, but for a WebSocket callback to not be.
>
> I asked the CDI expert group to consider whether a future version of CDI should extend the definition of @RequestScoped
> to include a WebSocket @OnMessage callback. This is https://issues.jboss.org/browse/CDI-370
This issue has now been picked up by the Java EE expert group. Joint spec lead Bill Shannon is considering whether it
should be resolved as "an errata to the existing spec(s), or whether it's a missing requirement that would require a new
revision of the spec(s)" (By "spec" he's referring to CDI and/or WebSockets, not JMS).
Here's his email to the Java EE experts:
https://java.net/projects/javaee-spec/lists/jsr342-experts/archive/2013-05/message/0
Bill's suggestion is that a WebSocket @OnMessage callback should have a valid request scope, where the lifecycle of the
request lasts for the duration of the WebSocket endpoint. However he's asking for comments.
My reaction is each WebSocket @OnMessage callback should constitute a separate request, just like a MDB message callback
currently does. Defining that multiple @OnMessage callbacks occur in the same request doesn't seem right to me - this
sounds closer to the definition of session scope than the definition of request scope.
Discussions are continuing - I'll keep this group updated on progress. If you have a view please make it here (and I'll
pass it on) or directly to the Java EE EG via the Java EE user alias.
Nigel