http://blog.athico.com/2011/01/drools-content-based-routing-with-camel.html
Drools Content Based Routing with Camel (John Ellis)
<
http://blog.athico.com/2011/01/drools-content-based-routing-with-camel.ht...
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,
https://repository.jboss.org/nexus/content/groups/public/org/drools/.
For bonus points I'd love to see a further Drools and Camel tutorial
around OSGi's EventAdmin,
http://camel.apache.org/eventadmin.html <http://>.
One of Camel's greatest strengths is the explicit support for Enterprise
Integration Patterns <
http://www.eaipatterns.com/toc.html>. 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.
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:
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
Example 1: DRL for Routing Based on Message Headers
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.
The Camel routing itself is simply defined as:
<route>
<from uri="activemq:queue:router"/>
<to uri="drools:brokerNode/cbrKSession?action=insertMessage"/>
<routingSlip uriDelimiter="#">
<header>routingSlip</header>
</routingSlip>
</route>
Example 2: Camel Routes for Content Based Routing
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.
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.