struts2默认拦截器之prepare
在struts2的struts-default.xml中定义了一个name为prepare拦截器，实现类是com.opensymphony.xwork2.interceptor.PrepareInterceptor，它的作用是为实现了com.opensymphony.xwork2.Preparable接口的action调用相关方法。该拦截器有两个参数：alwaysInvokePrepare，firstCallPrepareDo，两者的类型都是boolean,默认值分别是true，false。
该拦截器的核心代码如下：
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public String doIntercept(ActionInvocation invocation) throws Exception { Object action = invocation.getAction(); if (action instanceof Preparable) { try { String[] prefixes; if (firstCallPrepareDo) { prefixes = new String[] {ALT_PREPARE_PREFIX, PREPARE_PREFIX}; } else { prefixes = new String[] {PREPARE_PREFIX, ALT_PREPARE_PREFIX}; } PrefixMethodInvocationUtil.invokePrefixMethod(invocation, prefixes); } catch (InvocationTargetException e) { /* * The invoked method threw an exception and reflection wrapped it * in an InvocationTargetException. * If possible re-throw the original exception so that normal * exception handling will take place. */ Throwable cause = e.getCause(); if (cause instanceof Exception) { throw (Exception) cause; } else if(cause instanceof Error) { throw (Error) cause; } else { /* * The cause is not an Exception or Error (must be Throwable) so * just re-throw the wrapped exception. */ throw e; } } if (alwaysInvokePrepare) { ((Preparable) action).prepare(); } } return invocation.invoke(); }该代码的逻辑非常简单，如果action实现了com.opensymphony.xwork2.Preparable接口，则在调用setXXX和execute()方法之前调用系列方法。如果firstCallPrepareDo为true，则调用prepareDoXXX方法，否则调用prepareXXX方法(XXX为action对应的方法)。接下来查看alwaysInvokePrepare状态，如果其值为true则调用com.opensymphony.xwork2.Preparable接口的prepare方法。最后将action转交给下一个拦截器。
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