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From "James Strachan" <james.strac...@gmail.com>
Subject Re: Posting to a virtual topic's physical queue
Date Wed, 23 May 2007 17:05:20 GMT
On 5/23/07, sbuberl <sbuberl@gmail.com> wrote:
>
>
>
> James.Strachan wrote:
> >
> > On 5/23/07, sbuberl <sbuberl@gmail.com> wrote:
> >>
> >> Hi.
> >>
> >> My server posts live highway traffic accidents and events to topics, but
> >> most messages are only updates on existing event data. So I set up my
> >> server
> >> to monitor when a client logs in/out and sends them all live events in
> >> one
> >> message. I can't use durable subscriptions on topics because that would
> >> send
> >> them lots of old data as well when my subscribers only want the live
> >> data.
> >>
> >> I successfull intergrated activeMQ with JBoss and I have beans monitoring
> >> when a client logs in/out and when they create a consumer on the event
> >> topic
> >> with my database.  All updates get sent to the following virtual topic:
> >> <virtualTopic name="ATIS" prefix="Consumers.*." />
> >>
> >> The problem is: how can I retrieve the queue to send to with JBoss?
> >
> > Given your requirements, you probably don't want to use a queue per
> > client as you only want live messages being sent. Virtual topics &
> > queues work like durable topic subscribers.
> >
> > I'd recommend just using a Topic with non-persistent delivery of the
> > messages
> >
> > --
> > James
> > -------
> > http://macstrac.blogspot.com/
> >
> >
>
> Thanks for the advice on switching off virtual topics.  I was fine with one
> topic before, but I switched to virtual topics and queues because I still
> need to have each client have its own queue/topic in order to send a logging
> in client a "refresh" message (as stated before, a single message of all
> live events in one message).

There's a cooler solution. You can send individual initial messages to
consumers via topics using the subscription recovery policy and a
custom initial message query...
http://activemq.apache.org/subscription-recovery-policy.html

basically as a topic subscription starts you have the option to send
one or more intiial messages. You just use this

http://activemq.apache.org/maven/activemq-core/apidocs/org/apache/activemq/broker/region/policy/QueryBasedSubscriptionRecoveryPolicy.html

and then provide your own implementation of

http://activemq.apache.org/maven/activemq-core/apidocs/org/apache/activemq/broker/region/policy/MessageQuery.html

which can just create the initial refresh message(s).

i.e. you could support some kinda 'last image caching' type thing
where the consumer receives the last stable state first before any
future updates


> So if I switch to regular topics, I'm still
> stuck in the same boat of binding each client topic to JBoss JNDI?

There's only 1 topic for all clients; so 1 JNDI entry (if you use JNDI
- personally I try and avoid it at all costs & use Spring or Java code
instead :)


-- 
James
-------
http://macstrac.blogspot.com/

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