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<h3 class="post-title entry-title"><a
href="http://blog.athico.com/2011/01/drools-content-based-routing-with-camel.html">http://blog.athico.com/2011/01/drools-content-based-routing-with-camel.html</a><br>
</h3>
<h3 class="post-title entry-title"><a
href="http://blog.athico.com/2011/01/drools-content-based-routing-with-camel.html">Drools
Content Based Routing with Camel (John Ellis)</a>
</h3>
John Ellis has done a nice writeup of his work on improving Drools
to work with Camel for CBR. You'll need to use the latest version of
Drools from trunk, which can be found in the maven repository that's
5.2.0-SNAPSHOT, <a
href="https://repository.jboss.org/nexus/content/groups/public/org/drools/">https://repository.jboss.org/nexus/content/groups/public/org/drools/</a>.<br>
<br>
For bonus points I'd love to see a further Drools and Camel tutorial
around OSGi's EventAdmin, <a href="http://">http://camel.apache.org/eventadmin.html</a>.<br>
<br>
One of Camel's greatest strengths is the explicit support for <a
href="http://www.eaipatterns.com/toc.html">Enterprise Integration
Patterns</a>. Drools itself is particularly well suited to work
alongside Camel to implement two commonly used integration patterns:
the Content Based Router and the Dynamic Router. Both patterns
leverage the ability of a Drools Endpoint to rapidly evaluate
properties of a message, while the Dynamic Router can also integrate
the Drools Policy as a dynamic rule based on feedback from a control
channel.
<p style="margin-bottom: 0cm;">The Camel routes required for message
routing do not differ much from the previous Drools Endpoint
example. You may even be able to omit the Drools Policy if you
wish to inspect only the headers of messages being routed instead
of interrogating the body of each message. For example, a DRL
could be defined that takes action on inbound messages such as:<br>
<br>
</p>
<pre class="brush:drl">import org.apache.camel.Message;
rule "WriteOperations"
when
$message : Message(headers["OPERATION"] == "WRITE");
then
$message.setHeader("routingSlip", "activemq:queue:op.write");
end
rule "ReadOperations"
when
$message : Message(headers["OPERATION"] == "READ");
then
$message.setHeader("routingSlip", "activemq:queue:op.read");
end</pre>
<br>
Example 1: DRL for Routing Based on Message Headers<br>
<br>
Here the custom header “OPERATION” is evaluated to see if it is set
to the value “WRITE” or “READ.” Depending on the value of this
header, a routing slip is defined for the message. The Routing Slip
is another Enterprise Integration Pattern supported by Camel that
may contain one or more URIs. The message is then sequentially sent
to each URI defined.<br>
<br>
The Camel routing itself is simply defined as:<br>
<br>
<pre class="brush:drl"><route>
<from uri="activemq:queue:router"/>
<to uri="drools:brokerNode/cbrKSession?action=insertMessage"/>
<routingSlip uriDelimiter="#">
<header>routingSlip</header>
</routingSlip>
</route></pre>
<br>
Example 2: Camel Routes for Content Based Routing<br>
<br>
Here we explicitly inform Camel that routing slips are defined as
values within the “routingSlip” header and each URI is delimited by
a # character. The headers set within the DRL are then interpreted
as each message exits the Drools endpoint.<br>
<br>
Content based routing with a Drools Endpoint offers several
advantages over Camel's default implementation. The DRL format
itself allows routing to be specified more succinctly than Sprint
DSLs or Camel RouteBuilders. Conditional operations are also
evaluated more efficiently within Drools and are thread-safe,
allowing a high volume of messages to be routed concurrently.
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