OGNL: Object Graph navigation language. Top level object for this is a context map-ActionContext which consist of application,session,valuestack,request, parameters,attributes etc.
It supports two task: data transfer and type_conversion. For type conversion we can create our own converter classes.
Refer any Action Property:
<s:property value="name"/>
Refer any Session attributes:
<s:property value="#session.name"/>
Refer any Request Object:
<s:property value="#request.name"/>