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| <a href="index.html" title="back to Getting started"><< back to Getting started</a> |
| |
| <h1 class="no_toc" id="introducing-interceptors">Introducing Interceptors</h1> |
| |
| <ul id="markdown-toc"> |
| <li><a href="#introduction" id="markdown-toc-introduction">Introduction</a></li> |
| <li><a href="#introducing-interceptors-1" id="markdown-toc-introducing-interceptors-1">Introducing Interceptors</a></li> |
| <li><a href="#run-the-example" id="markdown-toc-run-the-example">Run The Example</a></li> |
| <li><a href="#create-your-own-interceptor" id="markdown-toc-create-your-own-interceptor">Create Your Own Interceptor</a></li> |
| <li><a href="#summary" id="markdown-toc-summary">Summary</a></li> |
| </ul> |
| |
| <p>The example code for this tutorial, <strong>interceptors</strong>, is available at <a href="https://github.com/apache/struts-examples">struts-examples</a></p> |
| |
| <h2 id="introduction">Introduction</h2> |
| |
| <p>So far our tutorials have not delved into the inner workings of the Struts 2 framework. But in this tutorial we’ll |
| introduce a key set of classes the Struts 2 framework relies upon to do most of the work whenever an Action is executed. |
| In this tutorial’s example project there is a register link that is mapped in the Struts XML configuration file (<code class="highlighter-rouge">struts.xml</code>) |
| to the execute method of class Register. Before that execute method is called much work is done behind the scenes |
| by the Struts 2 framework. For example:</p> |
| |
| <ol> |
| <li>Handling any exceptions generated</li> |
| <li>Converting the String request parameters to the Register class’s instance fields where the name values match</li> |
| <li>Calling the validate method and/or the external XML validation</li> |
| </ol> |
| |
| <p>After the execute method is completed more work must be done</p> |
| |
| <ol> |
| <li>Handling any exceptions generated</li> |
| <li>Converting the <code class="highlighter-rouge">Register</code> class’s instance fields to String values for display in the view page</li> |
| <li>Forwarding to the correct view page depending on the result String returned by the execute method</li> |
| </ol> |
| |
| <p>The above list of tasks are not complete - several other tasks are done before and after the execution of the Action.</p> |
| |
| <p>The benefit of using Struts 2 is all this work happens automatically. You can focus on the logic of the controller |
| (the Struts 2 ActionSupport class), the Service layer, the data access layer, your domain models, etc.</p> |
| |
| <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> |
| |
| <h2 id="introducing-interceptors-1">Introducing Interceptors</h2> |
| |
| <p>The tasks that are done by the Struts 2 framework before and after an Action is executed are done by Struts 2 interceptors. |
| Interceptors are standard Java classes included in the Struts 2 core jar which are executed in a specific order.</p> |
| |
| <p>In our example application there is a package node in struts.xml. The package node has an attribute of extends with |
| a value of “struts-default.” The value “struts-default” identifies to the framework the specific stack of interceptors |
| that will be executed before and after the Actions in that package.</p> |
| |
| <p>If you want to learn more about the inner workings of interceptors, what interceptors belong to the struts default stack, |
| and what are all the interceptors included with Struts 2, visit <a href="../core-developers/interceptors.html">Understanding Interceptors</a> .</p> |
| |
| <p>Sometime the Struts 2 default stack of interceptors are not exactly what you need for a particular action. You may want |
| to use interceptors that are not part of the Struts 2 default stack. For an individual Action or for the entire |
| package of Actions, you can specify a different stack of interceptors that the Action or package should use. Below is |
| how you would specify that the register Action should use both the <a href="../core-developers/logging-interceptor.html">logger</a> |
| and <a href="../core-developers/timer-interceptor.html">timer</a> interceptors in addition to the interceptors provided by the default stack.</p> |
| |
| <p><strong>Specify Specific Interceptors For An Action</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">"register"</span> <span class="na">class=</span><span class="s">"org.apache.struts.register.action.Register"</span> <span class="na">method=</span><span class="s">"execute"</span><span class="nt">></span> |
| <span class="nt"><interceptor-ref</span> <span class="na">name=</span><span class="s">"timer"</span> <span class="nt">/></span> |
| <span class="nt"><interceptor-ref</span> <span class="na">name=</span><span class="s">"logger"</span> <span class="nt">/></span> |
| <span class="nt"><interceptor-ref</span> <span class="na">name=</span><span class="s">"defaultStack"</span><span class="nt">></span> |
| <span class="nt"><param</span> <span class="na">name=</span><span class="s">"exception.logEnabled"</span><span class="nt">></span>true<span class="nt"></param></span> |
| <span class="nt"><param</span> <span class="na">name=</span><span class="s">"exception.logLevel"</span><span class="nt">></span>ERROR<span class="nt"></param></span> |
| <span class="nt"></interceptor-ref></span> |
| <span class="nt"><result</span> <span class="na">name=</span><span class="s">"success"</span><span class="nt">></span>thankyou.jsp<span class="nt"></result></span> |
| <span class="nt"><result</span> <span class="na">name=</span><span class="s">"input"</span><span class="nt">></span>register.jsp<span class="nt"></result></span> |
| <span class="nt"></action></span> |
| </code></pre></div></div> |
| |
| <p>The logger interceptor logs the start and end of the execution of an Action. The timer interceptor logs the amount |
| of time (in milliseconds) for execution of the Action. These two interceptors used together can provide developers |
| useful feedback.</p> |
| |
| <p>In the code example above note the three interceptor-ref nodes. Each one has a value for the name attribute. For the register |
| Action we are instructing the framework to use the <code class="highlighter-rouge">timer</code>, <code class="highlighter-rouge">logger</code>, and <code class="highlighter-rouge">defaultStack</code> interceptors. The <code class="highlighter-rouge">defaultStack</code> |
| are all the interceptors normally executed for an Action.</p> |
| |
| <p>How did I know to use the value of timer for the name attribute and even that there is a timer interceptor? |
| On the <a href="../core-developers/interceptors.html">Interceptors</a> web page in the Struts 2 documentation are a list of interceptors |
| that come with the Struts 2 framework and what the name value is for each interceptor.</p> |
| |
| <p>How did I know that the timer interceptor isn’t part of the defaultStack of interceptors already? Again on the Interceptors |
| documentation web page is a list of which interceptors belong to the <code class="highlighter-rouge">defaultStack</code>.</p> |
| |
| <p>Note the param nodes. These nodes are used to provide a value to the setLogEnabled and setLogLevel methods |
| of the <a href="../core-developers/exception-interceptor.html">Exception Interceptor</a>. Providing the values of true and ERROR |
| will cause the Struts 2 framework to log any exceptions not caught by the application’s code and to log those exceptions |
| at the ERROR level.</p> |
| |
| <h2 id="run-the-example">Run The Example</h2> |
| |
| <p>In the example application follow the README instructions to build, deploy, and run the application. View the output |
| sent to the JVM console to see the log messages generated by the logger and timer interceptors. You should see log messages |
| similar to the following:</p> |
| |
| <div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>INFO: Starting execution stack for action //register |
| Nov 20, 2010 9:55:48 AM com.opensymphony.xwork2.util.logging.jdk.JdkLogger info |
| INFO: Finishing execution stack for action //register |
| Nov 20, 2010 9:55:48 AM com.opensymphony.xwork2.util.logging.jdk.JdkLogger info |
| INFO: Executed action /register!execute took 177 ms. |
| </code></pre></div></div> |
| |
| <p>If you wanted to have the logger and timer interceptors executed for all Actions in a package you would use |
| the following in <code class="highlighter-rouge">struts.xml</code>:</p> |
| |
| <p><strong>Specify Specific Interceptors For A Package</strong></p> |
| |
| <div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><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">></span> |
| <span class="nt"><interceptors></span> |
| <span class="nt"><interceptor-stack</span> <span class="na">name=</span><span class="s">"appDefault"</span><span class="nt">></span> |
| <span class="nt"><interceptor-ref</span> <span class="na">name=</span><span class="s">"timer"</span> <span class="nt">/></span> |
| <span class="nt"><interceptor-ref</span> <span class="na">name=</span><span class="s">"logger"</span> <span class="nt">/></span> |
| <span class="nt"><interceptor-ref</span> <span class="na">name=</span><span class="s">"defaultStack"</span> <span class="nt">/></span> |
| <span class="nt"></interceptor-stack></span> |
| <span class="nt"></interceptors></span> |
| |
| <span class="nt"><default-interceptor-ref</span> <span class="na">name=</span><span class="s">"appDefault"</span> <span class="nt">/></span> |
| |
| <span class="c"><!-- rest of package omitted --></span> |
| |
| <span class="nt"></package></span> |
| </code></pre></div></div> |
| |
| <p>In the code above we use the interceptors node to define a new stack of interceptors that includes the <code class="highlighter-rouge">timer</code>, <code class="highlighter-rouge">logger</code>, |
| and <code class="highlighter-rouge">defaultStack</code> interceptors. We give this new interceptor stack a name of appDefault. Then we use the <code class="highlighter-rouge">default-interceptor-ref</code> |
| node to specify that for all Actions defined inside this package node the <code class="highlighter-rouge">appDefault</code> stack of interceptors are to be used. |
| Thus the <code class="highlighter-rouge">timer</code> and <code class="highlighter-rouge">logger</code> interceptor will be executed for each Action in this package.</p> |
| |
| <p>Note that in both examples we are still executing all the other interceptors by including the defaultStack as one |
| of the <code class="highlighter-rouge">interceptor-ref</code> nodes. When you specify what interceptors you want to use for an Action or a package then only |
| those interceptors are executed. So if in the example we had left out the <code class="highlighter-rouge">interceptor-ref</code> for <code class="highlighter-rouge">defaultStack</code> only |
| the <code class="highlighter-rouge">logger</code> and <code class="highlighter-rouge">timer</code> interceptors would have executed.</p> |
| |
| <h2 id="create-your-own-interceptor">Create Your Own Interceptor</h2> |
| |
| <p>In addition to specifying your own stack of interceptors, you can also write your own new interceptor and add it to |
| the stack that is executed. The Struts <a href="../core-developers/writing-interceptors.html">Writing Interceptors</a> guide explains |
| how to do this. For example, you could create your own interceptor to handle authentication and authorization.</p> |
| |
| <h2 id="summary">Summary</h2> |
| |
| <p>Interceptors provide the Struts 2 framework with both power and flexibility. Developers may add additional interceptors |
| (either ones provided by Struts 2 or ones they create) to the stack of interceptors executed when an Action class is called.</p> |
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