How To implement a periodically polled queue.

[anupamsen <an...@yahoo.com>]

Hi,

I have the following requirement -

1) If a message is received on the save entity route and the authentication
server is not available, then queue up the request in the
*periodicallyPolledInputQueue*.
2) The *periodicallyPolledInputQueue* thus may have n number of messages.
3) Every 30 minutes fetch all the messages in the
*periodicallyPolledInputQueue* and queue them back up to the *saveEntity*
queue using a producer template in the processor
*periodicallyPolledInputHandler* 


<route id="saveEntityRoute"
errorHandlerRef="PeriodicallyPolledInputQueue-ErrorHandler" trace="true">
  <from uri="jms:queue:JMS-Server/saveEntity?concurrentConsumers=10" />
  <camel:transacted ref="PROPAGATION_REQUIRED"/>
  <process ref="authenticator" />
  <camel:choice>
    <camel:when>
      
      <camel:simple>${header.SESSION_ID} == null and
${header.SERVER_AVAILABLE_TOKEN} == 'NO'</camel:simple>
      <to
uri="jms:queue:JMS-Server/periodicallyPolledInputQueue?disableReplyTo=true"
/>
    </camel:when>
    <camel:when>
      
      
      <camel:simple>${header.SESSION_ID} == null and
${header.SERVER_AVAILABLE_TOKEN} != 'NO'</camel:simple>
      <camel:stop></camel:stop>
    </camel:when>
    <camel:otherwise>
      <to uri="xslt:xsl/Transform.xsl" />
      <convertBodyTo type="java.lang.String"/>
      <delay><constant>300</constant></delay>
      <to uri="bean:entityData?method=saveEntity(${body},
${header.SESSION_ID}, ${header.ACK_ID})"/>
      <to uri="jms:queue:JMS-Server/saveEntityAck?disableReplyTo=true" />
    </camel:otherwise>
  </camel:choice>
</route>


<route id="periodicallyPolledInputQueueHandlerRoute">
  <from
uri="quartz://periodicallyPolledInputQueueHandler?cron=0+0/30+*+*+*+?"/>
  <camel:transacted ref="PROPAGATION_REQUIRED"/>
  <pollEnrich
uri="jms:queue:JMS-Server/periodicallyPolledInputQueue?disableReplyTo=true"/>
  <process ref="periodicallyPolledInputHandler" />
</route>

The goal is to  setup a fail-safe system that would ensure that the
integration layer is available even if the authentication system is down and
we can reprocess the messages.

The questions now -
1) Is this approach correct.
2) I tested this works but strangely just picks a single message only from
the input queue "periodicallyPolledInputQueue" even if tehre are n messages
lying. Is this teh behaviour of quarts+pollenrich on JMS?

Thanks.



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Re: How To implement a periodically polled queue.

[anupamsen <an...@yahoo.com>]

Thanks Claus, for the reply.

I thought so, but then for the time-being my problem is solved and maybe in
future we can see some new component in Camel for this as I believe JMS
(with peristent store) is a reasonable fallback for retrying in case any of
the services being unreachable/down.

Cheers,
Anupam



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Re: How To implement a periodically polled queue.

[Claus Ibsen <cl...@gmail.com>]

On Tue, Sep 25, 2012 at 9:36 PM, anupamsen <an...@yahoo.com> wrote:
> For the time being, I am using a consumer template to fetch n number of
> messages in the *periodicallyPolledInputHandler* processor triggered from
> the quartz and pushing it to the originating queue using a producer
> template.
>

Yeah this is a doable approach.

> Is there a better way of doing this?
>

Not really as the control structure in the DSL would not support this easily.

eg its kinda like a while loop while there is more messages to poll.

while(more) {
   message = poll message
   do stuff
}

The loop DSL does not support a "while" structure.

And pollEnrich is single message only.
We had looked into making pollEnrich support multiple message (batch
like) but that causes other problems.



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-- 
Claus Ibsen
-----------------
Red Hat, Inc.
FuseSource is now part of Red Hat
Email: cibsen@redhat.com
Web: http://fusesource.com
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Blog: http://davsclaus.com
Author of Camel in Action: http://www.manning.com/ibsen

Re: How To implement a periodically polled queue.

[anupamsen <an...@yahoo.com>]

For the time being, I am using a consumer template to fetch n number of
messages in the *periodicallyPolledInputHandler* processor triggered from
the quartz and pushing it to the originating queue using a producer
template. 

Is there a better way of doing this?



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