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：

 

    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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