Design Review

[Paul Lowry <pl...@newbay.com>]

Hi all,

I have written a route to do the following:
- expose a restful service
- invoke a http server
- catch errors;
  put the associated messages on an error queue
- catch connection exceptions and unknown business errors;
  put the associated request messages on a retry queue
- every 24 hours, poll the retry queue;
  invoke the http server again
  increment a retry counter
  and when a retry limit is reached...
  move the associated messages on the error queue

Can someone please review my route (below), and tell me if I have missed
any useful solutions, or if this is the optimal approach?

Also, is there any handy way to implement an exponential backoff in my
http client?

Thanks,
Paul


<camelContext xmlns="http://camel.apache.org/schema/spring"
id="SPGClient">

  <endpoint id="frontend"
uri="restlet:http://localhost:8080/myclient/{param}"/>
  <endpoint id="httpServer" uri="http://localhost:8080/myserver"/>
  <endpoint id="workQueue" uri="direct:INTERNAL_QUEUE"/>
  <endpoint id="errorQueue"
uri="activemq:ERROR_QUEUE?exchangePattern=InOnly"/>
  <endpoint id="retryQueue"
uri="activemq:RETRY_QUEUE?exchangePattern=InOnly"/>
  <endpoint id="retryTimer" uri="quartz://myTimer/0/0/12/*/*/$"/>

  <route id="frontendRoute">
    <from ref="frontend"/>
    <!-- inject param into message body -->
    <process ref="paramProcessor"/>
    <!-- prepare to invoke http server -->
    <setHeader headerName="CamelHttpMethod">
      <constant>POST</constant>
    </setHeader>
    <setHeader headerName="Content-Type">
      <constant>text/xml</constant>
    </setHeader>
    <removeHeader headerName="CamelHttpUri"/>
    <to ref="workQueue"/>
  </route>

  <route id="backendRoute">
    <from ref="workQueue"/>
    <doTry>
      <!-- invoke the http server -->
      <to ref="httpServer"/>
      <doCatch>
        <!-- if the server is not running -->
        <exception>java.net.ConnectException</exception>
        <!-- put the message on the retry queue -->
        <to ref="retryQueue"/>
      </doCatch>
    </doTry>
    <!-- process the http server's response -->
    <choice>
      <when>
        <xpath>in:header('result') = 'SUCCESS'</xpath>
        <setHeader headerName="Exchange.HTTP_RESPONSE_CODE">
          <constant>200</constant>
        </setHeader>
      </when>
      <when>
        <xpath>in:header('result') = 'ERROR'</xpath>
        <to ref="errorQueue"/>
      </when>
      <otherwise>
        <to ref="retryQueue"/>
      </otherwise>
    </choice>
  </route>

  <route id="retryRoute">
    <!-- every day at noon -->
    <from ref="retryTimer"/>
    <!-- read from the retry queue -->
    <pollEnrich ref="retryQueue"/>
    <!-- check a retry counter -->
    <choice>
      <when>
        <xpath>in:header('retries') > 3</xpath>
        <to ref="errorQueue"/>
      <stop/>
      </when>
      <otherwise>
        <!-- invoke "backendRoute" again -->
        <setExchangePattern pattern="InOnly"/>
        <to ref="workQueue"/>
      </otherwise>
    </choice>
    <!-- increment the retry counter -->
    <process ref="incrementRetryCounterProcessor"/>
  </route>

</camelContext>

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