Dinesh on Java: Struts 2 Actions

Actions are the core of the Struts2 framework, as they are for any MVC (Model View Controller) framework. Each URL is mapped to a specific action, which provides the processing logic necessary to service the request from the user.

But the action also serves in two other important capacities. First, the action plays an important role in the transfer of data from the request through to the view, whether its a JSP or other type of result. Second, the action must assist the framework in determining which result should render the view that will be returned in the response to the request.

Create Action:
The only requirement for actions in Struts2 is that there must be one no-argument method that returns either a String or Result object and must be a POJO. If the no-argument method is not specified, the default behavior is to use the execute() method.

Optionally you can extend the ActionSupport class which implements six interfaces including Action interface. The Action interface is as follows:

public interface Action {
   public static final String SUCCESS = "success";
   public static final String NONE = "none";
   public static final String ERROR = "error";
   public static final String INPUT = "input";
   public static final String LOGIN = "login";
   public String execute() throws Exception;
}

Let us take a look at the action method in the Hello World example:

package com.dineshonjava.struts2.action;

/**
 * @author Dinesh Rajput
 *
 */
public class HelloWorldAction {
 private static final long serialVersionUID = 4956157388836635122L;
 private String name;

    public String execute() throws Exception {
       return "success";
    }  

    public String getName() {
       return name;
    }

    public void setName(String name) {
       this.name = name;
    }
}

To illustrate the point that the action method controls the view, let us make the following change to the execute method and extend the class ActionSupport as follows:

package com.dineshonjava.struts2.action;

import com.opensymphony.xwork2.ActionSupport;

/**
 * @author Dinesh Rajput
 *
 */
public class HelloWorldAction extends ActionSupport {
 private static final long serialVersionUID = 4956157388836635122L;
 private String name;

   public String execute() throws Exception {
            if ("SECRET".equals(name))
            {
                return SUCCESS;
            }else{
               return ERROR;  
            }
          }

    public String getName() {
       return name;
    }

    public void setName(String name) {
       this.name = name;
    }
}

In this example, we have some logic in the execute method to look at the name attribute. If the attribute equals to the string "SECRET", we return SUCCESS as the result otherwise we return ERROR as the result. Because we have extended ActionSupport, so we can use String constants SUCCESS and ERROR. Now, let us modify our struts.xml file as follows:

<?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>
   <constant name="struts.devMode" value="true" />
   <package name="helloworld" extends="struts-default">
      <action name="hello" class="com.dineshonjava.struts2.action.HelloWorldAction" method="execute">
         <result name="success">/success.jsp</result>
          <result name="error">/error.jsp</result>
      </action>
   </package>
 </struts>

Create a View-
Let us create the below jsp file success.jsp in the WebRoot folder in your eclipse project. To do this, right click on the WebRoot folder in the project explorer and select New >JSP File. This file will be called in case return result is SUCCESS which is a String constant "success" as defined in Action interface

<%@ page contentType="text/html; charset=UTF-8" %>
<%@ taglib prefix="s" uri="/struts-tags" %>
<html>
<head>
<title>Hello World</title>
</head>
<body>
   Hello World, <s:property value="name"/>
</body>
</html>

Following is the file which will be invoked by the framework in case action result is ERROR which is equal to String constant "error". Following is the content of error.jsp

<%@ page contentType="text/html; charset=UTF-8" %>
<%@ taglib prefix="s" uri="/struts-tags" %>
<html>
<head>
<title>Access Denied</title>
</head>
<body>
   You are not authorized to view this page.
</body>
</html>

We also need to create index.jsp in the WebRoot folder. This file will serve as the initial action URL where the user can click to tell the Struts 2 framework to call the execute method of the HelloWorldAction class and render the success.jsp view.

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
   pageEncoding="ISO-8859-1"%>
<%@ taglib prefix="s" uri="/struts-tags"%>
   <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" 
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>Hello World</title>
</head>
<body>
   <h1>Hello World From Struts2</h1>
   <form action="hello">
      <label for="name">Please enter your name</label><br/>
      <input type="text" name="name"/>
      <input type="submit" value="Say Hello"/>
   </form>
</body>
</html>

That's it, there is no change required web.xml file, so let us use same web.xml which we had created in Examples chapter. Now we are ready to run our Hello World application using Struts 2 framework.

Execute the Application-
Right click on the project name and click Export > WAR File to create a War file. Then deploy this WAR in the Tomcat's webapps directory. Finally, start Tomcat server and try to access
URL http://localhost:8080/doj/. This will give you following screen:

Let us enter a word as "SECRET" and you should see the following page:

Now enter any word other than "dinesh" and you should see the following page:

Download Source Code
Struts2Action.zip

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