Checking the non-existent of a property using WSO2 ESB 4.6

You can't simply do a string regex matching, if you are to check the non-existence of a property. What you could do is to leverage the boolean Xpath function [1], within a filter mediator.

Please see the following sample proxy configuration:

<proxy xmlns="http://ws.apache.org/ns/synapse" name="TEST" transports="https,http" statistics="disable" trace="disable" startOnLoad="true">
   <target>
      <inSequence>
         <filter source="boolean(get-property('accept'))" regex="false">
            <then>
               <log level="custom">
                  <property name="*********" value="NULL Property Value"/>
               </log>
            </then>
            <else>
               <log level="custom">
                  <property name="*********" value="NOT NULL Property Value"/>
               </log>
            </else>
         </filter>
         <send/>
      </inSequence>
      <outSequence>
         <log/>
         <send/>
      </outSequence>
   </target>
   <description></description>
</proxy>
                             

Hope this will save some amount of time of quite a bit of you :-)

[1] http://www.w3.org/TR/xpath/#function-boolean