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Apache Struts 2 Documentation
Hello World
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Added by victorsosa, last edited by Ted Husted on Feb 12, 2007 (view change)

When you submit a HTML form to the framework, the input is not sent to another server page, but to a Java class that you provide. These classes are called Actions. 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 "tutorial" web application (see Ready, Set, Go!), to create a "Hello World" example, you need to do three things:

1. Create a server page to present the messages
2. Create an Action class to create the message
3. Create a mapping to couple the action and page

   | By creating these components, we are separating the workflow 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 Action, server page, and mapping. If you like, fire up your IDE, and enter the code as we go.

## The Code

First, we need a server page to present the message.

HelloWorld.jsp

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

    <html>
        <head>
            <title>Hello World!</title>
        </head>
        <body>
            <h2><s:property value="message" /></h2>
        </body>
    </html>

Second, we need an Action class to create the message.

HelloWorld.java

    package tutorial;
    import com.opensymphony.xwork2.ActionSupport;
    public class HelloWorld extends ActionSupport {

        public static final String MESSAGE = "Struts is up and running ...";

        public String execute() throws Exception {
            setMessage(MESSAGE);
            return SUCCESS;
        }

        private String message;

        public void setMessage(String message){
            this.message = message;
        }

        public String getMessage() {
            return message;
        }
    }

Third, we need a mapping to tie it all together.

Edit the `struts.xml` file to add the `HelloWorld` mapping.

struts.xml

    <!DOCTYPE struts PUBLIC
        "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
        "http://struts.apache.org/dtds/struts-2.0.dtd">
    <struts>
        <package name="tutorial" extends="struts-default">
            <action name="HelloWorld" class="tutorial.HelloWorld">
                <result>/HelloWorld.jsp</result>
            </action>
            <!-- Add your actions here -->
        </package>
    </struts>

Go ahead and try it now! Deploy the application and open http://localhost:8080/tutorial/HelloWorld.action and see what happens! You should see a page with the title "Hello World!" and the message "Struts is up and running!".

| Don't forget Compile your Action to `WEB-INF/classes` and restart your container if necessary. If you are using maven, you can just run:
    > mvn jetty:run

## How the Code Works

Your browser sends to the web server a request for the URL http://localhost:8080/tutorial/HelloWorld.action.

1. The container receives the request for `HelloWorld.action` from the web server. According to the settings loaded from the web.xml, the container finds that all requests are being routed to `org.apache.struts2.dispatcher.FilterDispatcher`, including the `*.action` requests. The FilterDispatcher is the entry point into the framework.
2. The framework looks for an action mapping named "HelloWorld". It finds that this mapping corresponds to the class "HelloWorld," instantiates the Action, and calls the Action's `execute` method.
3. The `execute` method sets the message 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 `HelloWorld.jsp` as the response to the request.
4. As the page `HelloWorld.jsp` is being processed, the `<s:property value="message" />` tag calls the getter `getMessage` of the `HelloWorld` Action, and merges the value of the message into the response.
5. A pure HMTL response is sent back to the browser.

For detailed information on Struts 2 architecture see Big Picture.

## Testing Actions

Testing an Action is easy. Here's a test for our Hello World Action.

HelloWorldTest.java

    package tutorial;
    import junit.framework.TestCase;
    import com.opensymphony.xwork2.Action;
    import com.opensymphony.xwork2.ActionSupport;

    public class HelloWorldTest extends TestCase {
      public void testHelloWorld() throws Exception {

        HelloWorld hello_world = new HelloWorld();
        String result = hello_world.execute();

        assertTrue("Expected a success result!",
          ActionSupport.SUCCESS.equals(result));

        assertTrue("Expected the default message!",
          HelloWorld.MESSAGE.equals(hello_world.getMessage()));

        }
    }

## 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 be used along with HTML markup to create a server page.

Next | Onward to Using Tags
Prev | Return to Ready, Set, Go!