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| <h1 id="action-chaining">Action Chaining</h1> |
| |
| <p>The framework provides the ability to chain multiple actions into a defined sequence or workflow. This feature works |
| by applying a <a href="chain-result.html">Chain Result</a> to a given Action, and intercepting its target Action’s invocation |
| with a <a href="chaining-interceptor.html">Chaining Interceptor</a>.</p> |
| |
| <blockquote> |
| <p>As a rule, Action Chaining is not recommended. First explore other options, such as the <code class="highlighter-rouge">Redirect After Post</code> technique.</p> |
| </blockquote> |
| |
| <h2 id="chain-result">Chain Result</h2> |
| |
| <p>The <a href="chain-result.html">Chain Result</a> is a result type that invokes an Action with its own Interceptor Stack and Result. |
| This Interceptor allows an Action to forward requests to a target Action, while propagating the state of the source Action. |
| Below is an example of how to define this sequence.</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">"public"</span> <span class="na">extends=</span><span class="s">"struts-default"</span><span class="nt">></span> |
| <span class="c"><!-- Chain creatAccount to login, using the default parameter --></span> |
| <span class="nt"><action</span> <span class="na">name=</span><span class="s">"createAccount"</span> <span class="na">class=</span><span class="s">"..."</span><span class="nt">></span> |
| <span class="nt"><result</span> <span class="na">type=</span><span class="s">"chain"</span><span class="nt">></span>login<span class="nt"></result></span> |
| <span class="nt"></action></span> |
| |
| <span class="nt"><action</span> <span class="na">name=</span><span class="s">"login"</span> <span class="na">class=</span><span class="s">"..."</span><span class="nt">></span> |
| <span class="c"><!-- Chain to another namespace --></span> |
| <span class="nt"><result</span> <span class="na">type=</span><span class="s">"chain"</span><span class="nt">></span> |
| <span class="nt"><param</span> <span class="na">name=</span><span class="s">"actionName"</span><span class="nt">></span>dashboard<span class="nt"></param></span> |
| <span class="nt"><param</span> <span class="na">name=</span><span class="s">"namespace"</span><span class="nt">></span>/secure<span class="nt"></param></span> |
| <span class="nt"></result></span> |
| <span class="nt"></action></span> |
| <span class="nt"></package></span> |
| |
| <span class="nt"><package</span> <span class="na">name=</span><span class="s">"secure"</span> <span class="na">extends=</span><span class="s">"struts-default"</span> <span class="na">namespace=</span><span class="s">"/secure"</span><span class="nt">></span> |
| <span class="nt"><action</span> <span class="na">name=</span><span class="s">"dashboard"</span> <span class="na">class=</span><span class="s">"..."</span><span class="nt">></span> |
| <span class="nt"><result></span>dashboard.jsp<span class="nt"></result></span> |
| <span class="nt"></action></span> |
| <span class="nt"></package></span> |
| </code></pre></div></div> |
| |
| <p>Another action mapping in the same namespace (or the default “” namespace) can be executed after this action mapping |
| (see <a href="configuration-files.html">Configuration Files</a>). An optional “namespace” parameter may also be added to specify |
| an action in a different namespace.</p> |
| |
| <h2 id="chaining-interceptor">Chaining Interceptor</h2> |
| |
| <p>If you need to copy the properties from your previous Actions in the chain to the current action, you should apply |
| the <a href="chaining-interceptor.html">Chaining Interceptor</a>. The Interceptor will copy the original parameters from the request, |
| and the ValueStack is passed in to the target Action. The source Action is remembered by the ValueStack, allowing |
| the target Action to access the properties of the preceding Action(s) using the ValueStack, and also makes these |
| properties available to the final result of the chain, such as the JSP or Velocity page.</p> |
| |
| <p>One common use of Action chaining is to provide lookup lists (like for a dropdown list of states). Since these Actions |
| get put on the ValueStack, their properties will be available in the view. This functionality can also be done using |
| the ActionTag to execute an Action from the display page. You may also use |
| the <a href="redirect-action-result.html">Redirect Action Result</a> to accomplish this.</p> |
| |
| <h2 id="use-with-care">Use with care</h2> |
| |
| <p>Experience shows that chaining should be used with care. If chaining is overused, an application can turn into |
| “spaghetti code”. Actions should be treated as a <a href="http://martinfowler.com/eaaCatalog/transactionScript.html">Transaction Script</a>, |
| rather than as methods in a <a href="http://msdn2.microsoft.com/en\-us/library/aa291571(VS.71).aspx">Business Facade</a>. Be sure |
| to ask yourself why you need to chain from one Action to another. Is a navigational issue, or could the logic in Action2 |
| be pushed back to a support class or business facade so that Action1 can call it too?</p> |
| |
| <p>Ideally, Action classes should be as short as possible. All the core logic should be pushed back to a support class |
| or a business facade, so that Actions only call methods. Actions are best used as adapters, rather than as a class |
| where coding logic is defined.</p> |
| |
| </section> |
| </article> |
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