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| <h1 id="exception-configuration">Exception Configuration</h1> |
| |
| <p>Exception mappings is a powerful feature for dealing with an Action class that throws an Exception. The core idea is |
| that an Exception thrown during the Action method can be automatically caught and mapped to a predefined Result. This |
| declarative strategy is especially useful for frameworks, like Hibernate and Acegi, that throw RuntimeExceptions.</p> |
| |
| <p>As with many other parts of the framework, an Interceptor is needed to activate the exception mapping functionality. |
| Below is a snippet from <code class="highlighter-rouge">struts-default.xml</code> which has the exception mapping already activated.</p> |
| |
| <p><strong>snippet of struts-default.xml</strong></p> |
| |
| <div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code>... |
| <span class="nt"><interceptors></span> |
| ... |
| <span class="nt"><interceptor</span> <span class="na">name=</span><span class="s">"exception"</span> <span class="na">class=</span><span class="s">"com.opensymphony.xwork.interceptor.ExceptionMappingInterceptor"</span><span class="nt">/></span> |
| ... |
| <span class="nt"></interceptors></span> |
| |
| <span class="nt"><interceptor-stack</span> <span class="na">name=</span><span class="s">"defaultStack"</span><span class="nt">></span> |
| <span class="nt"><interceptor-ref</span> <span class="na">name=</span><span class="s">"exception"</span><span class="nt">/></span> |
| <span class="nt"><interceptor-ref</span> <span class="na">name=</span><span class="s">"alias"</span><span class="nt">/></span> |
| <span class="nt"><interceptor-ref</span> <span class="na">name=</span><span class="s">"servlet-config"</span><span class="nt">/></span> |
| <span class="nt"><interceptor-ref</span> <span class="na">name=</span><span class="s">"prepare"</span><span class="nt">/></span> |
| <span class="nt"><interceptor-ref</span> <span class="na">name=</span><span class="s">"i18n"</span><span class="nt">/></span> |
| <span class="nt"><interceptor-ref</span> <span class="na">name=</span><span class="s">"chain"</span><span class="nt">/></span> |
| <span class="nt"><interceptor-ref</span> <span class="na">name=</span><span class="s">"debugging"</span><span class="nt">/></span> |
| <span class="nt"><interceptor-ref</span> <span class="na">name=</span><span class="s">"profiling"</span><span class="nt">/></span> |
| <span class="nt"><interceptor-ref</span> <span class="na">name=</span><span class="s">"scoped-model-driven"</span><span class="nt">/></span> |
| <span class="nt"><interceptor-ref</span> <span class="na">name=</span><span class="s">"model-driven"</span><span class="nt">/></span> |
| <span class="nt"><interceptor-ref</span> <span class="na">name=</span><span class="s">"fileUpload"</span><span class="nt">/></span> |
| <span class="nt"><interceptor-ref</span> <span class="na">name=</span><span class="s">"checkbox"</span><span class="nt">/></span> |
| <span class="nt"><interceptor-ref</span> <span class="na">name=</span><span class="s">"static-params"</span><span class="nt">/></span> |
| <span class="nt"><interceptor-ref</span> <span class="na">name=</span><span class="s">"params"</span><span class="nt">/></span> |
| <span class="nt"><interceptor-ref</span> <span class="na">name=</span><span class="s">"conversionError"</span><span class="nt">/></span> |
| <span class="nt"><interceptor-ref</span> <span class="na">name=</span><span class="s">"validation"</span><span class="nt">></span> |
| <span class="nt"><param</span> <span class="na">name=</span><span class="s">"excludeMethods"</span><span class="nt">></span>input,back,cancel,browse<span class="nt"></param></span> |
| <span class="nt"></interceptor-ref></span> |
| <span class="nt"><interceptor-ref</span> <span class="na">name=</span><span class="s">"workflow"</span><span class="nt">></span> |
| <span class="nt"><param</span> <span class="na">name=</span><span class="s">"excludeMethods"</span><span class="nt">></span>input,back,cancel,browse<span class="nt"></param></span> |
| <span class="nt"></interceptor-ref></span> |
| <span class="nt"></interceptor-stack></span> |
| ... |
| </code></pre></div></div> |
| |
| <p>To use exception mapping, we simply need to map Exceptions to specific Results. The framework provides two ways |
| to declare an exception mapping <code class="highlighter-rouge"><exception-mapping/></code> - globally or for a specific action mapping. The exception |
| mapping element takes two attributes, <code class="highlighter-rouge">exception</code> and <code class="highlighter-rouge">result</code>.</p> |
| |
| <p>When declaring an exception mapping, the Interceptor will find the closest class inheritance match between the Exception |
| thrown and the Exception declared. The Interceptor will examine all declared mappings applicable to the action mapping, |
| first local and then global mappings. If a match is found, the Result is processed, just as if it had been returned |
| by the Action.</p> |
| |
| <blockquote> |
| <p>This process follows the same rules as a Result returned from an Action. It first looks for the Result in the local |
| action mapping, and if not found, it looks for a global Result.</p> |
| </blockquote> |
| |
| <p>Below is an example of global and local exception mappings.</p> |
| |
| <p><strong>snippet from struts.xml</strong></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">"default"</span><span class="nt">></span> |
| ... |
| <span class="nt"><global-results></span> |
| <span class="nt"><result</span> <span class="na">name=</span><span class="s">"login"</span> <span class="na">type=</span><span class="s">"redirect"</span><span class="nt">></span>/Login.action<span class="nt"></result></span> |
| <span class="nt"><result</span> <span class="na">name=</span><span class="s">"Exception"</span><span class="nt">></span>/Exception.jsp<span class="nt"></result></span> |
| <span class="nt"></global-results></span> |
| |
| <span class="nt"><global-exception-mappings></span> |
| <span class="nt"><exception-mapping</span> <span class="na">exception=</span><span class="s">"java.sql.SQLException"</span> <span class="na">result=</span><span class="s">"SQLException"</span><span class="nt">/></span> |
| <span class="nt"><exception-mapping</span> <span class="na">exception=</span><span class="s">"java.lang.Exception"</span> <span class="na">result=</span><span class="s">"Exception"</span><span class="nt">/></span> |
| <span class="nt"></global-exception-mappings></span> |
| ... |
| <span class="nt"><action</span> <span class="na">name=</span><span class="s">"DataAccess"</span> <span class="na">class=</span><span class="s">"com.company.DataAccess"</span><span class="nt">></span> |
| <span class="nt"><exception-mapping</span> <span class="na">exception=</span><span class="s">"com.company.SecurityException"</span> <span class="na">result=</span><span class="s">"login"</span><span class="nt">/></span> |
| <span class="nt"><result</span> <span class="na">name=</span><span class="s">"SQLException"</span> <span class="na">type=</span><span class="s">"chain"</span><span class="nt">></span>SQLExceptionAction<span class="nt"></result></span> |
| <span class="nt"><result></span>/DataAccess.jsp<span class="nt"></result></span> |
| <span class="nt"></action></span> |
| ... |
| <span class="nt"></package></span> |
| <span class="nt"></xwork></span> |
| </code></pre></div></div> |
| |
| <p>In the example above, here is what happens based upon each Exception:</p> |
| |
| <ul> |
| <li>A <code class="highlighter-rouge">java.sql.SQLException</code> will chain to the <code class="highlighter-rouge">SQLExceptionAction</code> (action mapping not shown)</li> |
| <li>A <code class="highlighter-rouge">com.company.SecurityException</code> will redirect to <code class="highlighter-rouge">Login.action</code></li> |
| <li>Any other exception that extends <code class="highlighter-rouge">java.lang.Exception</code> will return the <code class="highlighter-rouge">/Exception.jsp</code> page</li> |
| </ul> |
| |
| <h2 id="exception-values-on-the-valuestack">Exception Values on the ValueStack</h2> |
| |
| <p>By default, the <code class="highlighter-rouge">ExceptionMappingInterceptor</code> adds the following values to the Value Stack:</p> |
| |
| <table> |
| <thead> |
| <tr> |
| <th>exception</th> |
| <th>The exception object itself</th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr> |
| <td>exceptionStack</td> |
| <td>The value from the stack trace</td> |
| </tr> |
| </tbody> |
| </table> |
| |
| <p><strong>Sample JSP using Error and Exception Values</strong></p> |
| |
| <pre><code class="language-jsp"><h2>An unexpected error has occurred</h2> |
| <p> |
| Please report this error to your system administrator |
| or appropriate technical support personnel. |
| Thank you for your cooperation. |
| </p> |
| <hr/> |
| <h3>Error Message</h3> |
| <s:actionerror/> |
| <p> |
| <s:property value="%{exception.message}"/> |
| </p> |
| <hr/> |
| <h3>Technical Details</h3> |
| <p> |
| <s:property value="%{exceptionStack}"/> |
| </p> |
| </code></pre> |
| |
| <h2 id="exception-in-constructors">Exception in constructors</h2> |
| |
| <p>Global exception mappings are designed to be used with exceptions thrown by action methods (like <code class="highlighter-rouge">execute</code>). exceptions |
| thrown from constructors will <strong>not</strong> be handled by global exception mappings.</p> |
| |
| </section> |
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