Action的执行机制

ActionProxyFactory:
  create ActionProxy factory,create ActionInvocation,create    ActionProxy
ActionProxy:
serves as client code's handle to execute an action,it holds an ActionInvocation which reprents the current   satate of the execution of the action.ActionProxy is created by a ActionProxyFactory in a dispatcher.ActionProxy sets up the execute context for the ActionInvocation and then calls invoke() on the ActionInvocation.
ActionInvocation: reprents the current state of the execution of the action,it holds the action instance ,the interceptors to be applied,the map of results,and an ActionContext.
ActionContext： which includes the request parameters,the application map ,the session map,the Local, and the ServletRequest and ServletResponse.

执行过程如下：
     （1）在web.xml中指定的ServletDispacter或者FilterDispatcher，负责调用ActionProxyFactory完成ActionProxy的创建，
ActionProxy proxy = ActionProxyFactory.getFactory().createActionProxy(namespace, actionName, context);
     （2）ActionProxy 为ActionInvocation设定执行环境上下文，并调用ActionInvocation的invoke()方法
     （3）关键在于ActionInvocation的invoke()方法，

public String invoke() throws Exception {
        if (executed) {
            throw new IllegalStateException("Action has already executed");
        }
        if (interceptors.hasNext()) {  // notice here is if ,not  while 
            InterceptorMapping interceptor = (InterceptorMapping) interceptors.next();
                  /** 调用拦截器的方法，将ActionInvocation作为参数
                    *  在intercept(this);中回调invoke() 方法，是一种递归的方式
                    */
                resultCode = interceptor.getInterceptor().intercept(this);
        } else {
            resultCode = invokeActionOnly();//当没有了拦截器没有调用时就invokeAction！然后返回！因为是递归调用的！然后按反顺序返回进行剩下的没完成部分...
        }

        // 做结果返回前的处理
        // this is needed because the result will be executed, then control will return to the Interceptor, which will
        // return above and flow through again
        if (!executed) {
            if (preResultListeners != null) {
                for (Iterator iterator = preResultListeners.iterator();
                     iterator.hasNext();) {
                    PreResultListener listener = (PreResultListener) iterator.next();
                    listener.beforeResult(this, resultCode);
                }
            }
            // now execute the result, if we're supposed to
            if (proxy.getExecuteResult()) {
               //执行结果的返回
                executeResult();
            }
            executed = true;
        }
        return resultCode;
    }