Struts 2 creating own interceptor

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

Summary steps :

  1. Create a class implements com.opensymphony.xwork2.interceptor.Interceptor.
  2. Implement the intercept(ActionInvocation invocation) method.
  3. Configure the interceptor in the struts.xml.
  4. 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: true
15 Julai 2010 11:37:42 AM com.opensymphony.xwork2.util.logging.commons.CommonsLogger info
INFO: Overriding property struts.configuration.xml.reload - old value: false new value: true

CustomInterceptor init() is called...

15 Julai 2010 11:37:42 AM org.apache.coyote.http11.Http11Protocol start
INFO: Starting Coyote HTTP/1.1 on http-8080
15 Julai 2010 11:37:42 AM org.apache.jk.common.ChannelSocket init
INFO: JK: ajp13 listening on /0.0.0.0:8009
15 Julai 2010 11:37:42 AM org.apache.jk.server.JkMain start
INFO: Jk running ID=0 time=0/20  config=null
15 Julai 2010 11:37:42 AM org.apache.catalina.startup.Catalina start
INFO: 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: true
15 Julai 2010 11:37:42 AM com.opensymphony.xwork2.util.logging.commons.CommonsLogger info
INFO: Overriding property struts.configuration.xml.reload - old value: false new value: true

CustomInterceptor init() is called...

15 Julai 2010 11:37:42 AM org.apache.coyote.http11.Http11Protocol start
INFO: Starting Coyote HTTP/1.1 on http-8080
15 Julai 2010 11:37:42 AM org.apache.jk.common.ChannelSocket init
INFO: JK: ajp13 listening on /0.0.0.0:8009
15 Julai 2010 11:37:42 AM org.apache.jk.server.JkMain start
INFO: Jk running ID=0 time=0/20  config=null
15 Julai 2010 11:37:42 AM org.apache.catalina.startup.Catalina start
INFO: Server startup in 994 ms

CustomInterceptor, before invocation.invoke()...
HelloAction execute() is called
CustomInterceptor, after invocation.invoke()...

Reference

  1. Struts 2 interceptor documentation
  2. Struts 2 building your own interceptor

About the Author

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mkyong
Founder of Mkyong.com, love Java and open source stuff. Follow him on Twitter, or befriend him on Facebook or Google Plus. If you like my tutorials, consider make a donation to these charities.

Comments

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Binh Thanh Nguyen
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Binh Thanh Nguyen

Thanks, nice post

Anand kumar
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Anand kumar

Thank you for the inputs, I have one doubt. How can I add a message in interceptor.
My test case is to add an error message in the user session is invalid.

Thomas Lionel
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Thomas Lionel
Instead of defining the interceptor for all the actions, you can overwrite the default interceptor with your own stack. ^[a-zA-Z0-9_]+$ 40 info /WEB-INF/Hello.jsp DEFAULT /WEB-INF/CatchAll.jsp
tho
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tho

I do not understand why the message “HelloAction execute() is called” occurs before message
“CustomInterceptor, after invocation.invoke()…”
Could you explain about my concern ?

Meow
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Meow

As you know, interceptors is used to pre and post request processing.
In pre processing “CustomInterceptor, before invocation.invoke()…” will print. While calling of String result = invocation.invoke(); the execution will go to action class and “HelloAction execute() is called” will be printed. now “CustomInterceptor, after invocation.invoke()…” is post processing of request which execute after action class.

tho
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tho

I do not understand why the message “HelloAction execute() is called” occurs before message
“CustomInterceptor, after invocation.invoke()…”
Could you explain for my concern ?

saran
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saran
Please clarify my doubt? iam new to struts2 i have an custom interceptor for checking session valid or not. i am returning “login” if session is invalid. now my aim is to display login page if the if interceptor returns “login” . but i dont know how to handle returned string “loing” here is my code. Map session = ActionContext.getContext().getSession(); if(session.get("user") != null ){ return invocation.invoke(); else return "login"; <interceptor name="sessionCheck" class="com.edu.interceptor.SessionCheckInterceptor"></interceptor> my action class is as follows: @ParentPackage("myParentPackage") @InterceptorRef(value = "sessionCheck") public class CreateCustomer extends ActionSupport{ @Action(value = "/createCustomerAction" ,results = { @Result(name = "success" , type = "json"),… Read more »
Javier
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Javier

Excellent post.
I make an interceptor to manage my Hibernate transactions.
In this applications, I work with annotations. It’s my first time. And I want to link my action with my created interceptor. I know that I have the annotations: InterceptorRef or InterceptorRefs to link my action. But, is there some annotation to declare my interceptor without use the struts.xml file?
Thanks.

Sundar Sathya Narayanan
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Sundar Sathya Narayanan

hi javier where u able to identify solution for using custom interceptor in annotation ? if yes , can u pls post the code snippet

abhishek
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abhishek
exception while working with interceptor: type Exception report message descriptionThe server encountered an internal error () that prevented it from fulfilling this request. exception org.apache.jasper.JasperException: The Struts dispatcher cannot be found. This is usually caused by using Struts tags without the associated filter. Struts tags are only usable when the request has passed through its servlet filter, which initializes the Struts dispatcher needed for this tag. – [unknown location] root cause The Struts dispatcher cannot be found. This is usually caused by using Struts tags without the associated filter. Struts tags are only usable when the request has passed through… Read more »
Jeremy Lee
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Jeremy Lee

oh, i get it !
Maybe the jar is broken

2012-6-21 9:05:40 org.apache.catalina.loader.WebappClassLoader modified
??: Additional JARs have been added : ‘struts2-dojo-plugin-2.1.8.jar’

Jeremy Lee
Guest
Jeremy Lee
There is something wrong when i run the program on Tomcat 6, something wrong happened,that is “CustomInterceptor init() is called…” is printed out every 2 seconds, when I don’t even make any request to the application. Why? ============================== 2012-6-21 9:05:17 org.apache.tomcat.util.digester.SetPropertiesRule begin ??: [SetPropertiesRule]{Server/Service/Engine/Host/Context} Setting property ‘source’ to ‘org.eclipse.jst.j2ee.server:Struts2ExampleInterceptor’ did not find a matching property. 2012-6-21 9:05:17 org.apache.catalina.core.AprLifecycleListener init ??: The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: C:\Java\jdk1.5.0_06\bin;.;C:\WINDOWS\system32;C:\WINDOWS;C:\Program Files\Windows Resource Kits\Tools\;D:\oracle\ora92\bin;D:\app\liguocai\product\11.1.0\db_1\bin;D:\oracle\ora92\bin;C:\Java\jdk1.5.0_06\bin;C:\Program Files\Oracle\jre\1.3.1\bin;C:\Program Files\Oracle\jre\1.1.8\bin;C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem;C:\Program Files\Intel\WiFi\bin\;C:\Program Files\Common Files\Intel\WirelessCommon\;C:\Program Files\NTRU Cryptosystems\NTRU TCG Software Stack\bin\;E:\DevEnviroment\TortoiseSVN\bin;E:\DevEnviroment\apache-ant-1.8.2\bin;C:\WINDOWS\system32\WindowsPowerShell\v1.0;C:\Program Files\Android\android-sdk\tools;E:\PROGRA~1\IBM\SQLLIB\BIN;E:\PROGRA~1\IBM\SQLLIB\FUNCTION;E:\PROGRA~1\IBM\SQLLIB\SAMPLES\REPL;F:\Program Files\Microsoft Visual Studio\Common\Tools\WinNT;F:\Program Files\Microsoft Visual… Read more »
Sundar Sathya Narayanan
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Sundar Sathya Narayanan

hi All,

am creating custom Interceptor and trying to use it in annotation InterceptorRef , i dont have any struts.xml defined , following error is thrown when i start application

Caused by: Unable to find interceptor class referenced by ref-name customInterceptor – [unknown location]

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