Can anybody explain with generic example what callout mediator does? and how to configure source and target ? How callout mediator is different from send mediator?
You can find a good explanation in the WSO2 Documentation of the Callout Mediator.
Here is a simple example we often use to send the whole content and store the response inside a property:
<callout serviceURL="http://wsf.cdyne.com/WeatherWS/Weather.asmx" action="http://ws.cdyne.com/WeatherWS/GetWeatherInformation">
<source type="envelope"/>
<target key="response"/>
</callout>
<!-- print the response property -->
<log level="custom">
<property name="response" expression="get-property('response')"/>
</log>