Depending on the complexity of your integration requirements Groovy scripts could be provided inline as CDATA in XML configuration or as a reference to a file containing Groovy script. To enable Groovy support Spring Integration defines GroovyScriptExecutingMessageProcessor which will create a groovy Binding object identifying Message Payload as payload variable and Message Headers as headers variable. All that is left for you to do is write script that uses these variables. Below are couple of sample configurations:

Filter

<filter input-channel="referencedScriptInput">
   <groovy:script location="some/path/to/groovy/file/GroovyFilterTests.groovy"/>
</filter>

<filter input-channel="inlineScriptInput">
     <groovy:script><![CDATA[
     return payload == 'good'
   ]]></groovy:script>
</filter>

You see that script could be included inline or via location attribute using the groovy namespace sport. 

Other supported elements are router, service-activator, transformer, splitter

Another interesting aspect of using Groovy support is framework's ability to update (reload) scripts  without restarting the Application Context. To accomplish this all you need is specify refresh-check-delay attribute on script element. The reason for this attribute is to make reloading of the script more efficient. 

<groovy:script location="..." refresh-check-delay="5000"/>

In the above example for the next 5 seconds after you update the script you'll still be using the old script and after 5 seconds the context will be updated with the new script. This is a good example where  'near real time' is acceptable.

<groovy:script location="..." refresh-check-delay="0"/>

In the above example the context will be updated with the new script every time the script is modified. Basically this is the example of the 'real-time' and might not be the most efficient way.

<groovy:script location="..." refresh-check-delay="-1"/>

Any negative number value means the script will never be refreshed after initial initialization of application context. DEFAULT BEHAVIOR