How the Message Router EIP can be implemented using WSO2 ESB

Introduction to Message Router.

Message router reads the content of the message, and based on the content of the message it directs to the incoming message to the correct recipient. Message router is useful handling scenarios like when the specific logical function is distributed among several physical systems and we need to deliver the message to the correct service.

The following diagram describes behavior of message router.

Message router by practical example

Now lets have a look on how message router works by a practical scenario.

Assume that we have deployed "Echo" service in WSO2 Application server. Here we need to deliver the incoming message (string or integer) to the different locations. What you need to do is first create a proxy service in WSO2 ESB by giving the end points of the services and WSDL of the echo service deployed in Application server.

Create a proxy service as follows in WSO2 ESB

<?xml version="1.0" encoding="UTF-8"?>
<proxy xmlns="http://ws.apache.org/ns/synapse"
       name="test1"
       transports="https,http"
       statistics="disable"
       trace="disable"
       startOnLoad="true">
   <target>
      <inSequence>
         <log level="full"/>
         <switch source="local-name(/*/*/*)">
            <case regex="echoString">
               <log level="custom">
                  <property name="return" value="String"/>
               </log>
               <send>
                  <endpoint>
                     <address uri="http://localhost:9763/services/echo"/>
                  </endpoint>
               </send>
            </case>
            <case regex="echoInt">
               <log level="custom">
                  <property name="return" value="Int"/>
               </log>
               <send>
                  <endpoint>
                     <address uri="http://localhost:9764/services/echo"/>
                  </endpoint>
               </send>
            </case>
            <default>
               <log level="custom">
                  <property name="return" value="default case"/>
                  <property name="return" expression="local-name(/*/*/*)"/>
               </log>
            </default>
         </switch>
      </inSequence>
      <outSequence>
         <send/>
      </outSequence>
      <faultSequence>
         <log level="full">
            <property name="MESSAGE" value="Executing default 'fault' sequence"/>
            <property name="ERROR_CODE" expression="get-property('ERROR_CODE')"/>
            <property name="ERROR_MESSAGE" expression="get-property('ERROR_MESSAGE')"/>
         </log>
         <drop/>
      </faultSequence>
   </target>
   <publishWSDL uri="http://localhost:9763/services/echo?wsdl"/>
   <description/>
</proxy>

What happens in this proxy service is switch mediator observes the message and filters out the content based on the given xpath  expression. If the filtered content is matched with the case,(string/integer) the message will be routed to the specific endpoint. if the matching condition is not fount the message will be directed to the default case.

Once you invoke the above proxy you will receive a responses as follows.

case 1 - string

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:echo="http://echo.services.core.carbon.wso2.org">
<soapenv:Body>
      <echo:echoString>
         <!--Optional:-->
         <in>chathurika</in>
      </echo:echoString>
   </soapenv:Body>
</soapenv:Envelope>

[2014-04-06 00:01:46,824]  INFO - LogMediator return = String

case 2 - integer

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:echo="http://echo.services.core.carbon.wso2.org">
<soapenv:Body>
      <echo:echoInt>
         <!--Optional:-->
         <in>123</in>
      </echo:echoInt>
   </soapenv:Body>
</soapenv:Envelope>

[2014-04-06 00:05:28,934]  INFO - LogMediator return = Int

Case - default

<soapenv:Envelope xmlns:soapenv="http://www.w3.org/2003/05/soap-envelope"><soapenv:Body><p:echoStringArrays xmlns:p="http://echo.services.core.carbon.wso2.org">
<!--0 or more occurrences--><a>aaa</a>
<!--0 or more occurrences--><b>bbbb</b>
<!--0 to 1 occurrence--><c>vvvvv</c>
</p:echoStringArrays></soapenv:Body>
</soapenv:Envelope>

[2014-04-06 00:33:55,953]  INFO - LogMediator return = default case, return = echoStringArrays