Mark Hapner wrote:
> EJB/JMS can be used to solve this problem; however, it should be noted
that the
> main benefit of integrating JMS with EJB is to enable notification driven
> application integration, i.e. 'business events'.
> This problem can be handled using JMS in the following way (see the JMS
spec for
> full details):
> The schedule lookup uses JMS to create and send a request/reply style
message to
> a stateless session, message listener DB Query EJB (which the container
would
> activate on message receipt, and to which it would deliver the message
using the
> JMS MessageListener onMessage(Message) method). Meanwhile the schedule
lookup
> would continue on to load its data and then do a synchronous receive on
the
> message's ReplyTo destination (normally a destination that is unique for
this
> message, in JMS speak, a temporary destination). When the DB Query EJB
has
> finished the query it responds with the result in a reply message.
This example relates to inter-bean communications. Can you comment on
whether JMS is also the approved means of passing event notification to
non-bean clients? I am surprised that the EJB spec does not prescribe here
(I have not read 1.1 yet). I have seen statements to the effect that
enterprise beans (unlike non-enterprise beans) do not generally send or
receive events; but that is manifestly not true: you only need think of
online trading etc.
Certainly, attempting to implement the standard Java event model on EJBs
does not work too well. Some EJB server providers (e.g. Weblogic) provide
their own event services, but presumably not portably. If not JMS, then
what?
Thanks
Steve Chamberlain
Schneider Electric
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