Hello World Using Struts 2

When you click on a hyperlink or submit an HTML form in a Struts 2 web application, the input is not sent to another server page, but to a Java class that you provide. These classes are called

Action

s. After the

Action

fires, a

Result

selects a resource to render the response. The resource is generally a server page, but it can also be a PDF file, an Excel spreadsheet, or a Java applet window.

Suppose you want to create a simple “Hello World” example that displays a welcome message. After setting up an empty basic Struts 2 web application , to create a “Hello World” example, you need to do four things:

Create a class to store the welcome message (the model)

Create a server page to present the message (the view)

Create an Action class to control the interaction between the user, the model, and the view (the controller)

Create a mapping (

struts.xml

) to couple the Action class and view

By creating these components, we are separating the work flow into three well-known concerns: the View, the Model, and the Controller. Separating concerns makes it easier to manage applications as they become more complex.

Let’s look at an example model class, Action, server page, and mapping. If you like, fire up your Java IDE, and enter the code as we go.

The Code

Let’s modify either the basic_struts project to add a model class to store our message, a view that displays our message, an Action class to act as the controller, and a configuration that ties everything together.

Step 1 - Create The Model Class

MessageStore.java

If you’re using the Basic_Struts2_Ant project to start with create the

MessageStore

class in the

src

folder and if you’re using the Basic_Struts2_Mvn class create the

MessageStore

class in

src/main/java

. Be sure to note the package statement below.

MessageStore.java

package org.apache.struts.helloworld.model;

public class MessageStore {

private String message;

public MessageStore() {

setMessage("Hello Struts User");
}

public String getMessage() {

return message;
}

public void setMessage(String message) {

this.message = message;
}

}

In the model class above note the use of public set and get methods to allow access to the private

message

String attribute. The Struts 2 framework requires that objects you want to expose to the view (

HelloWorld.jsp

) follow the JavaBean-style conventions.

Step 2 - Create The Action Class

HelloWorldAction.java

We need an Action class to act as the Controller. The Action class responds to a user action (in this example that action will be clicking an HTML hyperlink and sending a specific URL to the Servlet container). One or more of the Action class’s methods are executed and a

String

result is returned. Based on the value of the result, a specific view page (in this example that view page is

HelloWorld.jsp

) is rendered.

HelloWorldAction.java
package org.apache.struts.helloworld.action;

import org.apache.struts.helloworld.model.MessageStore;
import com.opensymphony.xwork2.ActionSupport;

public class HelloWorldAction extends ActionSupport {

private static final long serialVersionUID = 1L;

private MessageStore messageStore;

public String execute() throws Exception {

messageStore = new MessageStore() ;
return SUCCESS;
}

public MessageStore getMessageStore() {
return messageStore;
}

public void setMessageStore(MessageStore messageStore) {
this.messageStore = messageStore;
}

}

The Struts 2 framework will create an object of the

HelloWorldAction

class and call the

execute

method in response to a user’s action (clicking on a hyperlink that sends a specific URL to the Servlet container).

In this example, the

execute

method creates an object of class

MessageStore

and then returns the

String

constant

SUCCESS

.

Note also the public getter and setter methods for the private

MessageStore

object. Since we want to make the

MessageStore

object available to the view page,

HelloWorld.jsp

we need to follow the JavaBean-style of providing get and set methods.

Step 3 - Create The View HelloWorld.jsp

We need a server page to present the message that is stored in the model class

MessageStore

. Create the below JSP in the

WebContent

folder (if using Ant) or in

src/main/webapp

(if using Maven).

HelloWorld.jsp

<%@ 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>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Hello World!</title>
</head>

<body>
<h2><s:property value="messageStore.message" /></h2>
</body>
</html>

The

taglib

directive tells the Servlet container that this page will be using the Struts 2 tags and that these tags will be preceded by an

s

.

The

<s:property>

tag displays the value returned by calling the method

getMessageStore

of the

HelloWorldAction

controller class. That method returns a

MessageStore

object. By adding the

.message

onto the

messageStore

part of the value attribute we are telling the Struts 2 framework to call the

getMessage

method of that

MessageStore

object. The

getMessage

method of class

MessageStore

returns a

String

. It is that

String

that will be displayed by the

<s:property>

tag.

Step 4 - Add The Struts Configuration In struts.xml

We need a mapping to tie the URL, the

HelloWorldAction

class (controller), and

the

HelloWorld.jsp

(the view) together. The mapping tells the Struts 2 framework which class will respond to the user’s action (the URL), which method of that class will be executed, and what view to render based on the

String

result that method returns.

Edit the

struts.xml

file (in the Mvn project that file is in the

src/main/resources

folder) to add the action mapping. Place the

action

node (

action name="hello"

) between the opening and closing

package

node, just after the action mapping with the

name="index"

. Your complete

struts.xml

should look like:

struts.xml

<?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="basicstruts2" extends="struts-default">
<action name="index">
<result>/index.jsp</result>
</action>

<action name="hello" class="org.apache.struts.helloworld.action.HelloWorldAction" method="execute">
<result name="success">/HelloWorld.jsp</result>
</action>
</package>
</struts>

Step 5 - Create The URL Action

In

index.jsp

(see

WebContent

folder for Ant project and

src/main/webapp

for Mvn project) let’s add an Action URL the user can click on to tell the Struts 2 framework to run the

execute

method of the

HelloWorldAction

class and render the

HelloWorld.jsp

view.

First add the

taglib

directive at the top of the jsp

<%@ taglib prefix="s" uri="/struts-tags" %>

. Next add this

p

tag

<p><a href="<s:url action='hello'/>">Hello World</a></p>

after the

h1

tag. Your new

index.jsp

should look like:

index.jsp

<%@ 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>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Basic Struts 2 Application - Welcome</title>
</head>
<body>
<h1>Welcome To Struts 2!</h1>
<p><a href="<s:url action='hello'/>">Hello World</a></p>
</body>
</html>

The Struts

url

tag creates the URL with an action of

hello

. The

hello

action was mapped to the

HelloWorldAction

class and its

execute

method. When the user clicks on the above URL it will cause the Struts 2 framework to run the

execute

method of the

HelloWorldAction

class. After that method returns the

String

success, the view page

HelloWorld.jsp

will be rendered.

Step 6 - Build the WAR File and Run The Application

Execute

mvn clean package

to create the war file.

Copy the war file to your Servlet container. After your Servlet container successfully deploys the war file go to this URL http://localhost:8080/helloworld/index.action where you should see the following:



Click on the Hello World link and you should get the

HelloWorld.jsp

page:

How the Code Works

Your browser sends to the web server a request for the URL

http://localhost:8080/Hello_World_Struts2_Ant/hello.action

.

The container receives from the web server a request for the resource

hello.action

. According to the settings loaded from the

web.xml

, the container finds that all requests are being routed to

org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter

, including the

*.action

requests. The

StrutsPrepareAndExecuteFilter

is the entry point into the framework.

The framework looks for an action mapping named “

hello

“, and it finds that this mapping corresponds to the class “

HelloWorldAction

“. The framework instantiates the Action and calls the Action’s

execute

method.

The

execute

method creates the

MessageStore

object and returns

SUCCESS

. The framework checks the action mapping to see what page to load if

SUCCESS

is returned. The framework tells the container to render as the response to the request, the resource

HelloWorld.jsp

.

As the page

HelloWorld.jsp

is being processed, the

<s:property value="messageStore.message" />

tag calls the getter

getMessageStore

of the

HelloWorld

Action and then calls the

getMessage

of the

MessageStore

object returned by

getMessageStore

, and the tag merges into the response the value of the

message

attribute.

A pure HTML response is sent back to the browser.

What to Remember

The framework uses Actions to process HTML forms and other requests. The Action class returns a result-name such as

SUCCESS

,

ERROR

, or

INPUT

. Based on the mappings loaded from the

struts.xml

, a given result-name may select a page (as in this example), another action, or some other web resource (image, PDF).

When a server page is rendered, most often it will include dynamic data provided by the Action. To make it easy to display dynamic data, the framework provides a set of tags that can be used along with HTML markup to create a server page.