Struts 2 creating own interceptor

In this tutorial, it shows how to create an own interceptor in Struts 2.

Summary steps :

• Create a class implements com.opensymphony.xwork2.interceptor.Interceptor.
• Implement the intercept(ActionInvocation invocation) method.
• Configure the interceptor in the struts.xml.
• Link it to action.

Struts 2 interceptors

Struts 2 comes with many ready interceptors, make sure you check the list of the available Struts 2 interceptors before you create your own interceptor.
A complete example to create an own interceptor :

1. Action

A simple action to forward the user request and print a message.

HelloAction.java

package com.mkyong.common.action;import com.opensymphony.xwork2.ActionSupport;public class HelloAction extends ActionSupport{    public String execute() throws Exception {        System.out.println("HelloAction execute() is called");        return SUCCESS;    }}

2. Interceptor

A full interceptor example.

PrintMsgInterceptor.java

package com.mkyong.common.interceptor;import com.opensymphony.xwork2.ActionInvocation;import com.opensymphony.xwork2.interceptor.Interceptor;public class PrintMsgInterceptor implements Interceptor{        //called during interceptor destruction    public void destroy() {        System.out.println("CustomInterceptor destroy() is called...");    }    //called during interceptor initialization    public void init() {        System.out.println("CustomInterceptor init() is called...");    }    //put interceptor code here    public String intercept(ActionInvocation invocation) throws Exception {        System.out.println("CustomInterceptor, before invocation.invoke()...");        String result = invocation.invoke();        System.out.println("CustomInterceptor, after invocation.invoke()...");        return result;    }}

Explanation

The interceptor class must implements the com.opensymphony.xwork2.interceptor.Interceptor interface. During interceptor initialization, init() is called; interceptor destruction, destroy() is called. In last, put all interceptor code that does the work inside the intercept(ActionInvocation invocation) method.

invocation.invoke()

In the interceptor intercept() method, you must called the invocation.invoke() and return it’s result. This is the method responsible for calling the next interceptor or the action. The action will failed to continue without calling the invocation.invoke() method.

destroy() is not reliable

It’s not recommend to put any code inside the destroy(), because this method is not reliable. When your application server is force shutdown or be killed by command, the destroy() will not be called.

3. struts.xml

Configure the interceptor in the struts.xml file.

<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE struts PUBLIC"-//Apache Software Foundation//DTD Struts Configuration 2.0//EN""http://struts.apache.org/dtds/struts-2.0.dtd"><struts>  <package name="default" namespace="/" extends="struts-default">    <interceptors>      <interceptor name="printMsgInterceptor"     class="com.mkyong.common.interceptor.PrintMsgInterceptor"></interceptor>         <interceptor-stack name="newStack">            <interceptor-ref name="printMsgInterceptor"/>        <interceptor-ref name="defaultStack" />          </interceptor-stack>    </interceptors>    <action name="helloAction"     class="com.mkyong.common.action.HelloAction" >    <interceptor-ref name="newStack"/>    <result name="success">pages/hello.jsp</result>     </action>   </package></struts>

4. Demo

During the server initialization, the interceptor init() method is called.

INFO: Overriding property struts.i18n.reload - old value: false new value: true15 Julai 2010 11:37:42 AM com.opensymphony.xwork2.util.logging.commons.CommonsLogger infoINFO: Overriding property struts.configuration.xml.reload - old value: false new value: trueCustomInterceptor init() is called...15 Julai 2010 11:37:42 AM org.apache.coyote.http11.Http11Protocol startINFO: Starting Coyote HTTP/1.1 on http-808015 Julai 2010 11:37:42 AM org.apache.jk.common.ChannelSocket initINFO: JK: ajp13 listening on /0.0.0.0:800915 Julai 2010 11:37:42 AM org.apache.jk.server.JkMain startINFO: Jk running ID=0 time=0/20  config=null15 Julai 2010 11:37:42 AM org.apache.catalina.startup.Catalina startINFO: Server startup in 994 ms

While you access the action via URL : http://localhost:8080/Struts2Example/helloAction.action

INFO: Overriding property struts.i18n.reload - old value: false new value: true15 Julai 2010 11:37:42 AM com.opensymphony.xwork2.util.logging.commons.CommonsLogger infoINFO: Overriding property struts.configuration.xml.reload - old value: false new value: trueCustomInterceptor init() is called...15 Julai 2010 11:37:42 AM org.apache.coyote.http11.Http11Protocol startINFO: Starting Coyote HTTP/1.1 on http-808015 Julai 2010 11:37:42 AM org.apache.jk.common.ChannelSocket initINFO: JK: ajp13 listening on /0.0.0.0:800915 Julai 2010 11:37:42 AM org.apache.jk.server.JkMain startINFO: Jk running ID=0 time=0/20  config=null15 Julai 2010 11:37:42 AM org.apache.catalina.startup.Catalina startINFO: Server startup in 994 msCustomInterceptor, before invocation.invoke()...HelloAction execute() is calledCustomInterceptor, after invocation.invoke()...