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| <h1 id="writing-interceptors">Writing Interceptors</h1> |
| |
| <p>See the <a href="interceptors">Interceptors</a> page for an overview of how interceptors work.</p> |
| |
| <h2 id="interceptor-interface">Interceptor interface</h2> |
| |
| <p>Interceptors must implement the <code class="language-plaintext highlighter-rouge">com.opensymphony.xwork2.interceptor.Interceptor</code> interface.</p> |
| |
| <p><strong>Interceptor.java</strong></p> |
| |
| <div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">interface</span> <span class="nc">Interceptor</span> <span class="kd">extends</span> <span class="nc">Serializable</span> <span class="o">{</span> |
| |
| <span class="kt">void</span> <span class="nf">destroy</span><span class="o">();</span> |
| |
| <span class="kt">void</span> <span class="nf">init</span><span class="o">();</span> |
| |
| <span class="nc">String</span> <span class="nf">intercept</span><span class="o">(</span><span class="nc">ActionInvocation</span> <span class="n">invocation</span><span class="o">)</span> <span class="kd">throws</span> <span class="nc">Exception</span><span class="o">;</span> |
| <span class="o">}</span> |
| </code></pre></div></div> |
| |
| <p>The <code class="language-plaintext highlighter-rouge">init</code> method is called the after interceptor is instantiated and before calling <code class="language-plaintext highlighter-rouge">intercept</code>. This is the place |
| to allocate any resources used by the interceptor.</p> |
| |
| <p>The <code class="language-plaintext highlighter-rouge">intercept</code> method is where the interceptor code is written. Just like an action method, <code class="language-plaintext highlighter-rouge">intercept</code> returns |
| a result used by Struts to forward the request to another web resource. Calling <code class="language-plaintext highlighter-rouge">invoke</code> on the parameter of type |
| <code class="language-plaintext highlighter-rouge">ActionInvocation</code> will execute the action (if this is the last interceptor on the stack) or another interceptor.</p> |
| |
| <blockquote> |
| <p>Keep in mind that <code class="language-plaintext highlighter-rouge">invoke</code> will return <strong>after</strong> the result has been called (eg. after you JSP has been rendered), |
| making it perfect for things like open-session-in-view patterns. If you want to do something before the result gets |
| called, you should implement a <code class="language-plaintext highlighter-rouge">PreResultListener</code>.</p> |
| </blockquote> |
| |
| <p>Overwrite <code class="language-plaintext highlighter-rouge">destroy</code> to release resources on application shutdown.</p> |
| |
| <h2 id="thread-safety">Thread Safety</h2> |
| |
| <p><strong>Interceptors must be thread-safe!</strong></p> |
| |
| <blockquote> |
| <p>A Struts 2 Action instance is created for every request and do not need to be thread-safe. Conversely, Interceptors |
| are shared between requests and must be <a href="http://en.wikipedia.org/wiki/Thread-safety">thread-safe</a>.</p> |
| </blockquote> |
| |
| <h2 id="abstractinterceptor">AbstractInterceptor</h2> |
| |
| <p>The AbstractInterceptor class provides an empty implementation of <code class="language-plaintext highlighter-rouge">init</code> and <code class="language-plaintext highlighter-rouge">destroy</code>, and can be used if these |
| methods are not going to be implemented.</p> |
| |
| <h2 id="mapping">Mapping</h2> |
| |
| <p>Interceptors are declared using the <code class="language-plaintext highlighter-rouge"><interceptor/></code> element, nested inside the <code class="language-plaintext highlighter-rouge"><interceptors/></code> element. |
| Example from <code class="language-plaintext highlighter-rouge">struts-default.xml</code>:</p> |
| |
| <div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><struts></span> |
| ... |
| |
| <span class="nt"><package</span> <span class="na">name=</span><span class="s">"struts-default"</span><span class="nt">></span> |
| <span class="nt"><interceptors></span> |
| <span class="nt"><interceptor</span> <span class="na">name=</span><span class="s">"alias"</span> <span class="na">class=</span><span class="s">"com.opensymphony.xwork2.interceptor.AliasInterceptor"</span><span class="nt">/></span> |
| <span class="nt"><interceptor</span> <span class="na">name=</span><span class="s">"autowiring"</span> <span class="na">class=</span><span class="s">"com.opensymphony.xwork2.spring.interceptor.ActionAutowiringInterceptor"</span><span class="nt">/></span> |
| ... |
| <span class="nt"></interceptors></span> |
| <span class="nt"></package></span> |
| |
| ... |
| <span class="nt"></struts></span> |
| </code></pre></div></div> |
| |
| <h3 id="example">Example</h3> |
| |
| <p>Assuming there is an action of type “MyAction”, with a setDate(Date) method, this simple interceptor will set the date |
| of the action to the current date:</p> |
| |
| <p><strong>Interceptor Example</strong></p> |
| |
| <div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kn">import</span> <span class="nn">com.opensymphony.xwork2.ActionInvocation</span><span class="o">;</span> |
| <span class="kn">import</span> <span class="nn">com.opensymphony.xwork2.interceptor.AbstractInterceptor</span><span class="o">;</span> |
| |
| <span class="kd">public</span> <span class="kd">class</span> <span class="nc">SimpleInterceptor</span> <span class="kd">extends</span> <span class="nc">AbstractInterceptor</span> <span class="o">{</span> |
| |
| <span class="kd">public</span> <span class="nc">String</span> <span class="nf">intercept</span><span class="o">(</span><span class="nc">ActionInvocation</span> <span class="n">invocation</span><span class="o">)</span> <span class="kd">throws</span> <span class="nc">Exception</span> <span class="o">{</span> |
| <span class="nc">MyAction</span> <span class="n">action</span> <span class="o">=</span> <span class="o">(</span><span class="nc">MyAction</span><span class="o">)</span><span class="n">invocation</span><span class="o">.</span><span class="na">getAction</span><span class="o">();</span> |
| <span class="n">action</span><span class="o">.</span><span class="na">setDate</span><span class="o">(</span><span class="k">new</span> <span class="nc">Date</span><span class="o">());</span> |
| <span class="k">return</span> <span class="n">invocation</span><span class="o">.</span><span class="na">invoke</span><span class="o">();</span> |
| <span class="o">}</span> |
| <span class="o">}</span> |
| </code></pre></div></div> |
| |
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