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| <h1 class="no_toc" id="spring-and-struts-2">Spring and Struts 2</h1> |
| |
| <ul id="markdown-toc"> |
| <li><a href="#introduction" id="markdown-toc-introduction">Introduction</a></li> |
| <li><a href="#struts-2-spring-plugin" id="markdown-toc-struts-2-spring-plugin">Struts 2 Spring Plugin</a></li> |
| <li><a href="#spring-configuration-file" id="markdown-toc-spring-configuration-file">Spring Configuration File</a></li> |
| <li><a href="#alternative---have-spring-manage-creation-of-actionsupport-class" id="markdown-toc-alternative---have-spring-manage-creation-of-actionsupport-class">Alternative - Have Spring Manage Creation Of ActionSupport Class</a></li> |
| <li><a href="#summary" id="markdown-toc-summary">Summary</a></li> |
| </ul> |
| |
| <p>The example code for this tutorial, <strong>spring-struts</strong>, is available for checkout at <a href="https://github.com/apache/struts-examples">struts-examples</a></p> |
| |
| <h2 id="introduction">Introduction</h2> |
| |
| <p>In the execute method of many Struts 2 ActionSupport classes are statements that create objects and then have those |
| objects execute methods that perform needed tasks. Whenever one class creates an object of another class that introduces |
| a dependency between the two classes. The Spring framework makes it easier for the application developer to manage these |
| dependencies and helps make the application more flexible and maintainable. This tutorial will show you how to use Struts 2 |
| and Spring together to manage the dependencies between your ActionSupport classes and other classes in your application.</p> |
| |
| <blockquote> |
| <p>This tutorial assumes you understand how to use the Spring framework to manage dependencies between classes. You can |
| learn more about Spring by reading the documentation at <a href="https://spring.io/docs">https://spring.io/docs</a></p> |
| </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 the tutorial example applications 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> |
| |
| <p>If you examine the example application for the <a href="themes.html">Struts 2 Themes</a> tutorial you’ll see this code in the |
| <code class="highlighter-rouge">EditAction</code> class</p> |
| |
| <p><strong>EditAction Class Hard-Coded Dependency</strong></p> |
| |
| <div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">private</span> <span class="n">EditService</span> <span class="n">editService</span> <span class="o">=</span> <span class="k">new</span> <span class="n">EditServiceInMemory</span><span class="o">();</span> |
| </code></pre></div></div> |
| |
| <p>The above statement hard-codes a dependency between the <code class="highlighter-rouge">EditAction</code> class and the <code class="highlighter-rouge">EditServiceInMemory</code> class. This is |
| poor design for two reasons.</p> |
| |
| <ol> |
| <li>If I need to replace the <code class="highlighter-rouge">EditServiceInMemory</code> with another class that implements the <code class="highlighter-rouge">EditService</code> interface I’ll |
| have to hunt down and replace all statements where I hard-coded the dependency.</li> |
| <li>I cannot test <code class="highlighter-rouge">EditAction</code> without using the <code class="highlighter-rouge">EditServiceInMemory</code> class. I cannot isolate <code class="highlighter-rouge">EditAction</code> by using |
| a stub implementation of <code class="highlighter-rouge">EditService</code> when writing my test case because the use of <code class="highlighter-rouge">EditServiceInMemory</code> is hard-coded.</li> |
| </ol> |
| |
| <p>Spring provides a mechanism to manage dependencies by injecting them at run time. Struts 2 ActionSupport classes—like |
| any other Java class—can be injected with a dependent object by the Spring framework. So instead of having the above code, |
| I would have this statement in <code class="highlighter-rouge">EditAction</code>.</p> |
| |
| <p><strong>EditAction Class No Hard-Coded Dependency</strong></p> |
| |
| <div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">private</span> <span class="n">EditService</span> <span class="n">editService</span><span class="o">;</span> |
| </code></pre></div></div> |
| |
| <p>At run time the Spring framework will provide an object of a class that implements the EditService interface.</p> |
| |
| <h2 id="struts-2-spring-plugin">Struts 2 Spring Plugin</h2> |
| |
| <p>Struts 2 provides a plugin that enables Spring to inject into the ActionSupport classes any dependent objects you’ve |
| specified in the Spring configuration file. Consult <a href="../plugins/spring/">Spring Plugin documentation</a> for more information |
| about how the plugin works.</p> |
| |
| <p>For a Maven application you’ll need to add a dependency to the struts2-spring-plugin jar (see the Maven example application |
| for this tutorial). The plugin’s pom.xml includes transitive dependencies to the Spring jar files.</p> |
| |
| <blockquote> |
| <p>The current version (<code class="highlighter-rouge">2.5.10.1</code>) of the Struts 2 Spring plugin has transitive dependencies to the Spring <code class="highlighter-rouge">4.1.6.RELEASE</code> version. |
| If you want to use the latest version of Spring, then you should exclude the transitive dependencies in your pom.xml |
| for the Struts 2 Spring plugin and then declare dependency nodes to the current version of the Spring jar files. |
| If you are using Ant and explicitly including the jar files in your application, then just include the latest version |
| of the Spring jar files.</p> |
| </blockquote> |
| |
| <p>In your <code class="highlighter-rouge">ActionSupport</code> class you must have a set method for the dependent object that follows standard Java bean naming |
| conventions. If you examine the <code class="highlighter-rouge">EditAction</code> class for this tutorial’s application you’ll see this set method.</p> |
| |
| <div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="kt">void</span> <span class="nf">setEditService</span><span class="o">(</span><span class="n">EditService</span> <span class="n">editService</span><span class="o">)</span> <span class="o">{</span> |
| <span class="k">this</span><span class="o">.</span><span class="na">editService</span> <span class="o">=</span> <span class="n">editService</span><span class="o">;</span> |
| <span class="o">}</span> |
| </code></pre></div></div> |
| |
| <p>Spring will use that set method to provide an object of type <code class="highlighter-rouge">EditService</code> to the <code class="highlighter-rouge">EditAction</code> class at run time.</p> |
| |
| <p>To make our application “Spring aware” we need to add this line to web.xml.</p> |
| |
| <p><strong>Spring Listener In web.xml</strong></p> |
| |
| <div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><listener></span> |
| <span class="nt"><listener-class></span>org.springframework.web.context.ContextLoaderListener<span class="nt"></listener-class></span> |
| <span class="nt"></listener></span> |
| </code></pre></div></div> |
| |
| <p>The above code will activate the Spring framework when the application is started up by the Servlet container. By default |
| Spring will look for a configuration file name applicationContext.xml in WEB-INF (consult the Spring documentation for |
| how you can change where Spring looks and what the configuration file name is).</p> |
| |
| <h2 id="spring-configuration-file">Spring Configuration File</h2> |
| |
| <p>In the Spring configuration file we create a bean node for those objects we want Spring to create an instance of and inject |
| into our ActionSupport class. In the example application is this <code class="highlighter-rouge">applicationContext.xml</code>.</p> |
| |
| <p><strong>Spring Configuration File</strong></p> |
| |
| <div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="cp"><?xml version="1.0" encoding="UTF-8"?></span> |
| <span class="nt"><beans</span> <span class="na">xmlns=</span><span class="s">"http://www.springframework.org/schema/beans"</span> |
| <span class="na">xmlns:xsi=</span><span class="s">"http://www.w3.org/2001/XMLSchema-instance"</span> |
| <span class="na">xsi:schemaLocation=</span><span class="s">" |
| http://www.springframework.org/schema/beans |
| http://www.springframework.org/schema/beans/spring-beans.xsd"</span><span class="nt">></span> |
| |
| <span class="nt"><bean</span> <span class="na">id=</span><span class="s">"editService"</span> <span class="na">class=</span><span class="s">"org.apache.struts.edit.service.EditServiceInMemory"</span> <span class="nt">/></span> |
| |
| <span class="nt"></beans></span> |
| </code></pre></div></div> |
| |
| <p>Note the id value above. By default the Spring plugin works with Spring to autowire the dependencies of the ActionClass |
| by <code class="highlighter-rouge">name</code>. Spring will create an object of class EditServiceMemory and provide that object to any ActionSupport class |
| that has a setEditService method with an argument of type EditService. Consult the <a href="../plugins/spring/">Spring Plugin</a> |
| documentation for how to change the default autowire method.</p> |
| |
| <p>The editService bean created by Spring will have a scope of singleton since that is the default scope. Consult section |
| 3.5 of the <a href="https://spring.io/docs">Spring documentation</a> for how to configure the bean definition to use a different |
| scope (e.g. request or session).</p> |
| |
| <h2 id="alternative---have-spring-manage-creation-of-actionsupport-class">Alternative - Have Spring Manage Creation Of ActionSupport Class</h2> |
| |
| <p>Using the above methodology, the Struts 2 framework will still manage the creation of the <code class="highlighter-rouge">ActionSupport</code> class. If you |
| prefer you can configure the application so that Spring will create the ActionSupport class also. To support this technique |
| you need to add a bean node to the Spring configuration file for the ActionSupport class.</p> |
| |
| <p><strong>Spring Configuration For ActionSupport Class Managed By Spring</strong></p> |
| |
| <div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="cp"><?xml version="1.0" encoding="UTF-8"?></span> |
| <span class="nt"><beans</span> <span class="na">xmlns=</span><span class="s">"http://www.springframework.org/schema/beans"</span> |
| <span class="na">xmlns:xsi=</span><span class="s">"http://www.w3.org/2001/XMLSchema-instance"</span> |
| <span class="na">xsi:schemaLocation=</span><span class="s">" |
| http://www.springframework.org/schema/beans |
| http://www.springframework.org/schema/beans/spring-beans.xsd"</span><span class="nt">></span> |
| |
| <span class="nt"><bean</span> <span class="na">id=</span><span class="s">"editService"</span> <span class="na">class=</span><span class="s">"org.apache.struts.edit.service.EditServiceInMemory"</span> <span class="nt">/></span> |
| |
| <span class="nt"><bean</span> <span class="na">id=</span><span class="s">"editAction"</span> <span class="na">class=</span><span class="s">"org.apache.struts.edit.action.EditAction"</span> <span class="na">scope=</span><span class="s">"prototype"</span><span class="nt">></span> |
| <span class="nt"><property</span> <span class="na">name=</span><span class="s">"editService"</span> <span class="na">ref=</span><span class="s">"editService"</span> <span class="nt">/></span> |
| <span class="nt"></bean></span> |
| |
| <span class="nt"></beans></span> |
| </code></pre></div></div> |
| |
| <p>Note in the above that there is an <code class="highlighter-rouge">editAction</code> bean and its <code class="highlighter-rouge">editService</code> property is set to the <code class="highlighter-rouge">editService</code> bean. |
| Since we are having Spring manage the <code class="highlighter-rouge">EditAction</code> class we must specify any properties of <code class="highlighter-rouge">EditAction</code> that we want Spring |
| to inject. Please remember that actions must be created on each request, they cannot be <code class="highlighter-rouge">singletons</code>- this is the default |
| <code class="highlighter-rouge">scope</code> that’s why it must be changed to <code class="highlighter-rouge">prototype</code>.</p> |
| |
| <p>In the <code class="highlighter-rouge">struts.xml</code> configuration file you must specify the Spring id value for the class attribute of the action node. |
| This tells Struts to get a bean with that id value from Spring for the Action class.</p> |
| |
| <p><strong>Struts Configuration For Spring Managed ActionSupport Class</strong></p> |
| |
| <div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><action</span> <span class="na">name=</span><span class="s">"edit"</span> <span class="na">class=</span><span class="s">"editAction"</span> <span class="na">method=</span><span class="s">"input"</span><span class="nt">></span> |
| <span class="nt"><result</span> <span class="na">name=</span><span class="s">"input"</span><span class="nt">></span>/edit.jsp<span class="nt"></result></span> |
| <span class="nt"></action></span> |
| </code></pre></div></div> |
| |
| <h2 id="summary">Summary</h2> |
| |
| <p>In this tutorial we reviewed how to use the Struts 2 Spring plugin to integrate Spring and Struts. By using the Struts 2 |
| Spring plugin you can have Spring manage the dependencies of your ActionSupport classes. Of course you can also take |
| advantage of the many other benefits (AOP, Spring JDBC) that the Spring framework provides.</p> |
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