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<h1 class="no_toc" id="hello-world-using-struts-2">Hello World Using Struts 2</h1>
<ul id="markdown-toc">
<li><a href="#description" id="markdown-toc-description">Description</a></li>
<li><a href="#the-code" id="markdown-toc-the-code">The Code</a> <ul>
<li><a href="#step-1---create-the-model-class-messagestorejava" id="markdown-toc-step-1---create-the-model-class-messagestorejava">Step 1 - Create The Model Class MessageStore.java</a></li>
<li><a href="#step-2---create-the-action-class-helloworldactionjava" id="markdown-toc-step-2---create-the-action-class-helloworldactionjava">Step 2 - Create The Action Class HelloWorldAction.java</a></li>
<li><a href="#step-3---create-the-view-helloworldjsp" id="markdown-toc-step-3---create-the-view-helloworldjsp">Step 3 - Create The View HelloWorld.jsp</a></li>
<li><a href="#step-4---add-the-struts-configuration-in-strutsxml" id="markdown-toc-step-4---add-the-struts-configuration-in-strutsxml">Step 4 - Add The Struts Configuration In struts.xml</a></li>
<li><a href="#step-5---create-the-url-action" id="markdown-toc-step-5---create-the-url-action">Step 5 - Create The URL Action</a></li>
<li><a href="#step-6---build-the-war-file-and-run-the-application" id="markdown-toc-step-6---build-the-war-file-and-run-the-application">Step 6 - Build the WAR File and Run The Application</a></li>
</ul>
</li>
<li><a href="#how-the-code-works" id="markdown-toc-how-the-code-works">How the Code Works</a></li>
<li><a href="#what-to-remember" id="markdown-toc-what-to-remember">What to Remember</a></li>
</ul>
<h2 id="description">Description</h2>
<p>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 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.</p>
<p>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 (see <a href="how-to-create-a-struts2-web-application.html">How To Create A Struts 2 Web Application</a>),
to create a “Hello World” example, you need to do four things:</p>
<ol>
<li>Create a class to store the welcome message (the model)</li>
<li>Create a server page to present the message (the view)</li>
<li>Create an Action class to control the interaction between the user, the model, and the view (the controller)</li>
<li>Create a mapping (<code class="highlighter-rouge">struts.xml</code>) to couple the Action class and view</li>
</ol>
<p>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.</p>
<p>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.</p>
<blockquote>
<p>This tutorial assumes you’ve completed the <a href="how-to-create-a-struts2-web-application.html">How To Create A Struts 2 Web Application</a>
tutorial and have a working basic Struts project. The example code for this tutorial, helloworld, is available for checkout
from the Struts 2 GitHub repository at <a href="https://github.com/apache/struts-examples">struts-examples</a>. The example projects
use Maven to manage the artifact dependencies and to build the .war files.</p>
</blockquote>
<h2 id="the-code">The Code</h2>
<p>Let’s modify the basic-struts project to add the following:</p>
<ul>
<li>a model class to store our message</li>
<li>a view that displays our message</li>
<li>an Action class to act as the controller</li>
<li>a configuration that ties everything together</li>
</ul>
<blockquote>
<p>The <a href="http://struts.apache.org/mail.html">Struts 2 user mailing list</a> is an excellent place to get help. If you are
having a problem getting this application to work search the Struts 2 mailing list. If you don’t find an answer
to your problem, post a question on the mailing list.</p>
</blockquote>
<h3 id="step-1---create-the-model-class-messagestorejava">Step 1 - Create The Model Class MessageStore.java</h3>
<p>Create the <code class="highlighter-rouge">MessageStore</code> class in <code class="highlighter-rouge">src/main/java</code>. Be sure to note the package statement below.</p>
<blockquote>
<p>Note that in the code shown below the JavaDoc comments are omitted. In the download example, JavaDoc comments are included.</p>
</blockquote>
<p><strong>MessageStore.java</strong></p>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kn">package</span> <span class="n">org</span><span class="o">.</span><span class="na">apache</span><span class="o">.</span><span class="na">struts</span><span class="o">.</span><span class="na">helloworld</span><span class="o">.</span><span class="na">model</span><span class="o">;</span>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">MessageStore</span> <span class="o">{</span>
<span class="kd">private</span> <span class="n">String</span> <span class="n">message</span><span class="o">;</span>
<span class="kd">public</span> <span class="nf">MessageStore</span><span class="o">()</span> <span class="o">{</span>
<span class="n">message</span> <span class="o">=</span> <span class="s">"Hello Struts User"</span><span class="o">;</span>
<span class="o">}</span>
<span class="kd">public</span> <span class="n">String</span> <span class="nf">getMessage</span><span class="o">()</span> <span class="o">{</span>
<span class="k">return</span> <span class="n">message</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
</code></pre></div></div>
<p>Note the use of the public getter method to allow access to the private message String attribute. The Struts 2 framework
requires that objects you want to expose to the view (<code class="highlighter-rouge">HelloWorld.jsp</code>) follow the <a href="http://en.wikipedia.org/wiki/JavaBean#JavaBean_conventions">JavaBean-style conventions</a>.</p>
<h3 id="step-2---create-the-action-class-helloworldactionjava">Step 2 - Create The Action Class HelloWorldAction.java</h3>
<p>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 <code class="highlighter-rouge">HelloWorld.jsp</code>) is rendered.</p>
<p>Note the package and import statements below.</p>
<p><strong>HelloWorldAction.java</strong></p>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kn">package</span> <span class="n">org</span><span class="o">.</span><span class="na">apache</span><span class="o">.</span><span class="na">struts</span><span class="o">.</span><span class="na">helloworld</span><span class="o">.</span><span class="na">action</span><span class="o">;</span>
<span class="kn">import</span> <span class="nn">org.apache.struts.helloworld.model.MessageStore</span><span class="o">;</span>
<span class="kn">import</span> <span class="nn">com.opensymphony.xwork2.ActionSupport</span><span class="o">;</span>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">HelloWorldAction</span> <span class="kd">extends</span> <span class="n">ActionSupport</span> <span class="o">{</span>
<span class="kd">private</span> <span class="n">MessageStore</span> <span class="n">messageStore</span><span class="o">;</span>
<span class="kd">public</span> <span class="n">String</span> <span class="nf">execute</span><span class="o">()</span> <span class="o">{</span>
<span class="n">messageStore</span> <span class="o">=</span> <span class="k">new</span> <span class="n">MessageStore</span><span class="o">()</span> <span class="o">;</span>
<span class="k">return</span> <span class="n">SUCCESS</span><span class="o">;</span>
<span class="o">}</span>
<span class="kd">public</span> <span class="n">MessageStore</span> <span class="nf">getMessageStore</span><span class="o">()</span> <span class="o">{</span>
<span class="k">return</span> <span class="n">messageStore</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
</code></pre></div></div>
<p>The Struts 2 framework will create an object of the <code class="highlighter-rouge">HelloWorldAction</code> 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).</p>
<p>In this example, the execute method creates an object of class <code class="highlighter-rouge">MessageStore</code> and then returns the String constant <code class="highlighter-rouge">SUCCESS</code>.</p>
<p>Note also the public getter method for the private <code class="highlighter-rouge">MessageStore</code> object. Since we want to make the <code class="highlighter-rouge">MessageStore</code> object
available to the view page, <code class="highlighter-rouge">HelloWorld.jsp</code>, we need to follow the <a href="http://en.wikipedia.org/wiki/JavaBean#JavaBean_conventions">JavaBean-style</a>
of providing getter and setter methods where needed.</p>
<h3 id="step-3---create-the-view-helloworldjsp">Step 3 - Create The View HelloWorld.jsp</h3>
<p>We need a server page to present the message that is stored in the model class <code class="highlighter-rouge">MessageStore</code>. Create the below JSP in
the <code class="highlighter-rouge">src/main/webapp</code> folder.</p>
<p><strong>HelloWorld.jsp</strong></p>
<pre><code class="language-jsp">&lt;!DOCTYPE html&gt;
&lt;%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8" %&gt;
&lt;%@ taglib prefix="s" uri="/struts-tags" %&gt;
&lt;html&gt;
&lt;head&gt;
&lt;meta http-equiv="Content-Type" content="text/html; charset=UTF-8"&gt;
&lt;title&gt;Hello World!&lt;/title&gt;
&lt;/head&gt;
&lt;body&gt;
&lt;h2&gt;&lt;s:property value="messageStore.message" /&gt;&lt;/h2&gt;
&lt;/body&gt;
&lt;/html&gt;
</code></pre>
<p>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 <code class="highlighter-rouge">s</code>.</p>
<p>The <code class="highlighter-rouge">&lt;s:property&gt;</code> tag displays the value returned by calling the method <code class="highlighter-rouge">getMessageStore</code> of the <code class="highlighter-rouge">HelloWorldAction</code> 
controller class. That method returns a <code class="highlighter-rouge">MessageStore</code> object. By adding the <code class="highlighter-rouge">.message</code> onto the messageStore part of
the value attribute we are telling the Struts 2 framework to call the <code class="highlighter-rouge">getMessage</code> method of that <code class="highlighter-rouge">MessageStore</code> object.
The <code class="highlighter-rouge">getMessage</code> method of class <code class="highlighter-rouge">MessageStore</code> returns a String. It is that String that will be displayed by the <code class="highlighter-rouge">&lt;s:property&gt;</code> tag.</p>
<p>We’ll learn more about tags in the next tutorial. See the <em>Struts Tags</em> for more information about tags.</p>
<h3 id="step-4---add-the-struts-configuration-in-strutsxml">Step 4 - Add The Struts Configuration In struts.xml</h3>
<p>We need a mapping to tie the URL, the <code class="highlighter-rouge">HelloWorldAction</code> class (controller), and the <code class="highlighter-rouge">HelloWorld.jsp</code> (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.</p>
<p>Edit the <code class="highlighter-rouge">struts.xml</code> file (in the Mvn project that file is in the <code class="highlighter-rouge">src/main/resources</code> folder) to add the action mapping.
Place the action node (action <code class="highlighter-rouge">name="hello"</code>) between the opening and closing package node, just after the action mapping
with the <code class="highlighter-rouge">name="index"</code>. Your complete <code class="highlighter-rouge">struts.xml</code> should look like:</p>
<p><strong>struts.xml</strong></p>
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="cp">&lt;?xml version="1.0" encoding="UTF-8"?&gt;</span>
<span class="cp">&lt;!DOCTYPE struts PUBLIC
"-//Apache Software Foundation//DTD Struts Configuration 2.5//EN"
"http://struts.apache.org/dtds/struts-2.5.dtd"&gt;</span>
<span class="nt">&lt;struts&gt;</span>
<span class="nt">&lt;constant</span> <span class="na">name=</span><span class="s">"struts.devMode"</span> <span class="na">value=</span><span class="s">"true"</span> <span class="nt">/&gt;</span>
<span class="nt">&lt;package</span> <span class="na">name=</span><span class="s">"basicstruts2"</span> <span class="na">extends=</span><span class="s">"struts-default"</span><span class="nt">&gt;</span>
<span class="nt">&lt;action</span> <span class="na">name=</span><span class="s">"index"</span><span class="nt">&gt;</span>
<span class="nt">&lt;result&gt;</span>/index.jsp<span class="nt">&lt;/result&gt;</span>
<span class="nt">&lt;/action&gt;</span>
<span class="nt">&lt;action</span> <span class="na">name=</span><span class="s">"hello"</span> <span class="na">class=</span><span class="s">"org.apache.struts.helloworld.action.HelloWorldAction"</span> <span class="na">method=</span><span class="s">"execute"</span><span class="nt">&gt;</span>
<span class="nt">&lt;result</span> <span class="na">name=</span><span class="s">"success"</span><span class="nt">&gt;</span>/HelloWorld.jsp<span class="nt">&lt;/result&gt;</span>
<span class="nt">&lt;/action&gt;</span>
<span class="nt">&lt;/package&gt;</span>
<span class="nt">&lt;/struts&gt;</span>
</code></pre></div></div>
<h3 id="step-5---create-the-url-action">Step 5 - Create The URL Action</h3>
<p>Let’s add an Action URL inside <code class="highlighter-rouge">index.jsp</code> (see <code class="highlighter-rouge">src/main/webapp</code> folder) so the user can click on a link to tell the Struts 2
framework to run the execute method of the <code class="highlighter-rouge">HelloWorldAction</code> class and render the <code class="highlighter-rouge">HelloWorld.jsp</code> view.</p>
<p>First add the taglib directive at the top of the jsp <code class="highlighter-rouge">&lt;%@ taglib prefix="s" uri="/struts-tags" %&gt;</code>. Next add this <code class="highlighter-rouge">p</code> tag
<code class="highlighter-rouge">&lt;p&gt;&lt;a href="&lt;s:url action='hello'/&gt;"&gt;Hello World&lt;/a&gt;&lt;/p&gt;</code> after the h1 tag. Your new index.jsp should look like:</p>
<p><strong>index.jsp</strong></p>
<pre><code class="language-jsp">&lt;!DOCTYPE html&gt;
&lt;%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8" %&gt;
&lt;%@ taglib prefix="s" uri="/struts-tags" %&gt;
&lt;html&gt;
&lt;head&gt;
&lt;meta http-equiv="Content-Type" content="text/html; charset=UTF-8"&gt;
&lt;title&gt;Basic Struts 2 Application - Welcome&lt;/title&gt;
&lt;/head&gt;
&lt;body&gt;
&lt;h1&gt;Welcome To Struts 2!&lt;/h1&gt;
&lt;p&gt;&lt;a href="&lt;s:url action='hello'/&gt;"&gt;Hello World&lt;/a&gt;&lt;/p&gt;
&lt;/body&gt;
&lt;/html&gt;
</code></pre>
<p>The Struts url tag creates the URL with an action of hello. The hello action was mapped to the <code class="highlighter-rouge">HelloWorldAction</code> class
and its <code class="highlighter-rouge">execute</code> method. When the user clicks on the above URL it will cause the Struts 2 framework to run the execute
method of the <code class="highlighter-rouge">HelloWorldAction</code> class. After that method returns the String <code class="highlighter-rouge">success</code> (constant <code class="highlighter-rouge">SUCCESS</code>), the view
page <code class="highlighter-rouge">HelloWorld.jsp</code> will be rendered.</p>
<h3 id="step-6---build-the-war-file-and-run-the-application">Step 6 - Build the WAR File and Run The Application</h3>
<p>Execute <code class="highlighter-rouge">mvn jetty:run</code> to run the application.</p>
<p>Go to this URL <a href="http://localhost:8080/helloworld/index.action">http://localhost:8080/helloworld/index.action</a> where you
should see the following:</p>
<p><img src="attachments/helloworld_index_action.png" alt="helloworld_index_action.png" /></p>
<p>Click on the Hello World link and you should get the HelloWorld.jsp page:</p>
<p><img src="attachments/helloworld_hello_action.png" alt="helloworld_hello_action.png" /></p>
<h2 id="how-the-code-works">How the Code Works</h2>
<p>Your browser sends to the web server a request for the URL <a href="http://localhost:8080/helloworld/hello.action">http://localhost:8080/helloworld/hello.action</a>.</p>
<ol>
<li>The container receives from the web server a request for the resource <code class="highlighter-rouge">hello.action</code>. According to the settings loaded
from the <a href="../core-developers/web-xml.html">web.xml</a>, the container finds that all requests are being routed to
<code class="highlighter-rouge">org.apache.struts2.dispatcher.filter.StrutsPrepareAndExecuteFilter</code>, including the <code class="highlighter-rouge">*.action</code> requests.
The <code class="highlighter-rouge">StrutsPrepareAndExecuteFilter</code> is the entry point into the framework.</li>
<li>The framework looks for an action mapping named “hello”, and it finds that this mapping corresponds to the class
<code class="highlighter-rouge">HelloWorldAction</code>. The framework instantiates the Action and calls the Action’s <code class="highlighter-rouge">execute</code> method.</li>
<li>The <code class="highlighter-rouge">execute</code> method creates the MessageStore object and returns <code class="highlighter-rouge">SUCCESS</code> (=<code class="highlighter-rouge">"success"</code>). The framework checks
the action mapping to see what page to load if <code class="highlighter-rouge">SUCCESS</code> is returned. The framework tells the container to render
as the response to the request, the resource <code class="highlighter-rouge">HelloWorld.jsp</code>.</li>
<li>As the page <code class="highlighter-rouge">HelloWorld.jsp</code> is being processed, the <code class="highlighter-rouge">&lt;s:property value="messageStore.message" /&gt;</code> tag calls the getter
<code class="highlighter-rouge">getMessageStore</code> of the <code class="highlighter-rouge">HelloWorld</code> Action and then calls the <code class="highlighter-rouge">getMessage</code> of the MessageStore object returned
by <code class="highlighter-rouge">getMessageStore</code>. The tag merges the value of the message attribute into the response.</li>
<li>A pure HTML response is sent back to the browser.</li>
</ol>
<h2 id="what-to-remember">What to Remember</h2>
<p>The framework uses Actions to process HTML forms and other requests. The <code class="highlighter-rouge">Action</code> class returns a result-name such
as <code class="highlighter-rouge">SUCCESS</code>, <code class="highlighter-rouge">ERROR</code> or <code class="highlighter-rouge">INPUT</code>. Based on the mappings loaded from the <code class="highlighter-rouge">struts.xml</code>, a given result-name may select
a page (as in this example), another action, or some other web resource (image, PDF).</p>
<p>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.</p>
<table>
<tbody>
<tr>
<td>Return to <a href="how-to-create-a-struts2-web-application.html">How to create a Struts 2 web application</a></td>
<td>or</td>
<td>onward to <a href="using-tags.html">Using Struts 2 Tags</a></td>
</tr>
</tbody>
</table>
</section>
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