The Struts2 framework provide a mechanism of controlling request data before invoking action class and after invoking action, they give service between the controller and action . Interceptors performs tasks such as Logging, Validation, File Upload, Double-submit guard etc.

 
The request processing lifecycle of Struts2 framework
User send the request on the server .
Server invoke the FilterDispatcher class.
All interceptor will be fired . Interceptors performs tasks such as Logging, Validation,File Upload,Double-submit guard etc.
Action is executed and the Result is generated by Action.
The output of Action is rendered in the view (JSP, Velocity, etc) and the result is returned to the user.
Example:-

<!DOCTYPE struts PUBLIC 
"-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
"http://struts.apache.org/dtds/struts-2.0.dtd">

<struts>
<package name="demo">
<result-types>
<result-type name="dispatcher" class="org.apache.struts2.dispatcher.ServletDispatcherResult" default="true"/>
</result-types>
<interceptors>
<interceptor name="paramSetter" class="mypack.MyInterceptor"/>
</interceptors>
<action name="login" class="mypack.LoginAction">
<interceptor-ref name="paramSetter"/>
<result name="success">/hello.jsp</result>
<result name="failure">/relogin.jsp</result>
</action>
</package>
</struts>



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