下面开始讲一下主菜ActionProxy了.在这之前最好先去了解一下动态Proxy的基本知识.
ActionProxy是Action的一个代理类，也就是说Action的调用是通过ActionProxy实现的，其实就是调用了ActionProxy.execute()方法，而该方法又调用了ActionInvocation.invoke()方法。归根到底，最后调用的是DefaultActionInvocation.invokeAction()方法。
DefaultActionInvocation()->init()->createAction()。 
最后通过调用ActionProxy.exute()-->ActionInvocation.invoke()-->Intercepter.intercept()-->ActionInvocation.invokeActionOnly()-->invokeAction()

这里的步骤是先由ActionProxyFactory创建ActionInvocation和ActionProxy.

public ActionProxy createActionProxy(String namespace, String actionName, String methodName, Map<String, Object> extraContext, boolean executeResult, boolean cleanupContext) {     ActionInvocation inv = new DefaultActionInvocation(extraContext, true);     container.inject(inv);     return createActionProxy(inv, namespace, actionName, methodName, executeResult, cleanupContext);     
} 

下面先看DefaultActionInvocation的init方法

public void init(ActionProxy proxy) {     this.proxy = proxy;     Map<String, Object> contextMap = createContextMap();     // Setting this so that other classes, like object factories, can use the ActionProxy and other     // contextual information to operate     ActionContext actionContext = ActionContext.getContext();     if (actionContext != null) {     actionContext.setActionInvocation(this);     }     //创建Action,struts2中每一个Request都会创建一个新的Action     createAction(contextMap);     if (pushAction) {     stack.push(action);     contextMap.put("action", action);     }     invocationContext = new ActionContext(contextMap);     invocationContext.setName(proxy.getActionName());     // get a new List so we don't get problems with the iterator if someone changes the list     List<InterceptorMapping> interceptorList = new ArrayList<InterceptorMapping>(proxy.getConfig().getInterceptors());     interceptors = interceptorList.iterator();     
}     protected void createAction(Map<String, Object> contextMap) {     // load action     String timerKey = "actionCreate: " + proxy.getActionName();     try {     UtilTimerStack.push(timerKey);     //默认为SpringObjectFactory:struts.objectFactory=spring.这里非常巧妙,在struts.properties中可以重写这个属性     //在前面BeanSelectionProvider中通过配置文件为ObjectFactory设置实现类     //这里以Spring为例,这里会调到SpringObjectFactory的buildBean方法,可以通过ApplicationContext的getBean()方法得到Spring的Bean     action = objectFactory.buildAction(proxy.getActionName(), proxy.getNamespace(), proxy.getConfig(), contextMap);     } catch (InstantiationException e) {     throw new XWorkException("Unable to intantiate Action!", e, proxy.getConfig());     } catch (IllegalAccessException e) {     throw new XWorkException("Illegal access to constructor, is it public?", e, proxy.getConfig());     } catch (Exception e) {     ...     } finally {     UtilTimerStack.pop(timerKey);     }     if (actionEventListener != null) {     action = actionEventListener.prepare(action, stack);     }     
}     
//SpringObjectFactory     
public Object buildBean(String beanName, Map<String, Object> extraContext, boolean injectInternal) throws Exception {     Object o = null;     try {     //SpringObjectFactory会通过web.xml中的context-param:contextConfigLocation自动注入ClassPathXmlApplicationContext     o = appContext.getBean(beanName);     } catch (NoSuchBeanDefinitionException e) {     Class beanClazz = getClassInstance(beanName);     o = buildBean(beanClazz, extraContext);     }     if (injectInternal) {     injectInternalBeans(o);     }     return o;     
}    

//接下来看看DefaultActionInvocation 的invoke方法     
public String invoke() throws Exception {     String profileKey = "invoke: ";     try {     UtilTimerStack.push(profileKey);     if (executed) {     throw new IllegalStateException("Action has already executed");     }     //递归执行interceptor     if (interceptors.hasNext()) {     //interceptors是InterceptorMapping实际上是像一个像FilterChain一样的Interceptor链     //通过调用Invocation.invoke()实现递归牡循环     final InterceptorMapping interceptor = (InterceptorMapping) interceptors.next();     String interceptorMsg = "interceptor: " + interceptor.getName();     UtilTimerStack.push(interceptorMsg);     try {       //在每个Interceptor的方法中都会return invocation.invoke()            resultCode = interceptor.getInterceptor().intercept(DefaultActionInvocation.this);     }     finally {     UtilTimerStack.pop(interceptorMsg);     }     } else {       //当所有interceptor都执行完,最后执行Action,invokeActionOnly会调用invokeAction()方法     resultCode = invokeActionOnly();     }     // this is needed because the result will be executed, then control will return to the Interceptor, which will     // return above and flow through again       //在Result返回之前调用preResultListeners      //通过executed控制,只执行一次      if (!executed) {     if (preResultListeners != null) {      for (Object preResultListener : preResultListeners) {      PreResultListener listener = (PreResultListener) preResultListener;     String _profileKey = "preResultListener: ";      try {                                            UtilTimerStack.push(_profileKey);                                  listener.beforeResult(this, resultCode);     }                                                finally {                                        UtilTimerStack.pop(_profileKey);             }                                                }                                                    }                                                        // now execute the result, if we're supposed to          //执行Result                                             if (proxy.getExecuteResult()) {                          executeResult();                                     }                                                        executed = true;                                         }                                                            return resultCode;                                           }                                                                finally {                                                        UtilTimerStack.pop(profileKey);                              }                                                                
}      //invokeAction     
protected String invokeAction(Object action,ActionConfig actionConfig)throws Exception{     String methodName = proxy.getMethod();     String timerKey = "invokeAction: " + proxy.getActionName();     try {     UtilTimerStack.push(timerKey);     boolean methodCalled = false;     Object methodResult = null;     Method method = null;     try {     //java反射机制得到要执行的方法     method = getAction().getClass().getMethod(methodName, new Class[0]);     } catch (NoSuchMethodException e) {     // hmm -- OK, try doXxx instead     //如果没有对应的方法，则使用do+Xxxx来再次获得方法        try {     String altMethodName = "do" + methodName.substring(0, 1).toUpperCase() + methodName.substring(1);     method = getAction().getClass().getMethod(altMethodName, new Class[0]);     } catch (NoSuchMethodException e1) {     // well, give the unknown handler a shot     if (unknownHandlerManager.hasUnknownHandlers()) {     try {     methodResult = unknownHandlerManager.handleUnknownMethod(action, methodName);     methodCalled = true;     } catch (NoSuchMethodException e2) {     // throw the original one     throw e;     }     } else {     throw e;     }     }     }     //执行Method     if (!methodCalled) {     methodResult = method.invoke(action, new Object[0]);     }     //从这里可以看出可以Action的方法可以返回String去匹配Result,也可以直接返回Result类     if (methodResult instanceof Result) {     this.explicitResult = (Result) methodResult;     // Wire the result automatically     container.inject(explicitResult);     return null;     } else {     return (String) methodResult;     }     } catch (NoSuchMethodException e) {     throw new IllegalArgumentException("The " + methodName + "() is not defined in action " + getAction().getClass() + "");     } catch (InvocationTargetException e) {     // We try to return the source exception.     Throwable t = e.getTargetException();     if (actionEventListener != null) {     String result = actionEventListener.handleException(t, getStack());     if (result != null) {     return result;     }     }     if (t instanceof Exception) {     throw (Exception) t;     } else {     throw e;     }     } finally {     UtilTimerStack.pop(timerKey);     }     
}    

action执行完了，还要根据ResultConfig返回到view，也就是在invoke方法中调用executeResult方法。

private void executeResult() throws Exception {     //根据ResultConfig创建Result      result = createResult();     String timerKey = "executeResult: " + getResultCode();     try {     UtilTimerStack.push(timerKey);     if (result != null) {     //开始执行Result,     //可以参考Result的实现，如用了比较多的ServletDispatcherResult,ServletActionRedirectResult,ServletRedirectResult      result.execute(this);     } else if (resultCode != null && !Action.NONE.equals(resultCode)) {     throw new ConfigurationException("No result defined for action " + getAction().getClass().getName()     + " and result " + getResultCode(), proxy.getConfig());     } else {     if (LOG.isDebugEnabled()) {     LOG.debug("No result returned for action " + getAction().getClass().getName() + " at " + proxy.getConfig().getLocation());     }     }     } finally {     UtilTimerStack.pop(timerKey);     }     
}               public Result createResult() throws Exception {     //如果Action中直接返回的Result类型,在invokeAction()保存在explicitResult     if (explicitResult != null) {                                Result ret = explicitResult;                             explicitResult = null;                                   return ret;                                              }     //返回的是String则从config中得到当前Action的Results列表     ActionConfig config = proxy.getConfig();                     Map<String, ResultConfig> results = config.getResults();     ResultConfig resultConfig = null;                            synchronized (config) {                                      try {      //通过返回的String来匹配resultConfig       resultConfig = results.get(resultCode);              } catch (NullPointerException e) {                       // swallow                                           }                                                        if (resultConfig == null) {                              // If no result is found for the given resultCode, try to get a wildcard '*' match.     //如果找不到对应name的ResultConfig，则使用name为*的Result       //说明可以用*通配所有的Result                                   resultConfig = results.get("*");     }                                        }                                            if (resultConfig != null) {                  try {     //创建Result      return objectFactory.buildResult(resultConfig, invocationContext.getContextMap());     } catch (Exception e) {     LOG.error("There was an exception while instantiating the result of type " + resultConfig.getClassName(), e);     throw new XWorkException(e, resultConfig);     }      } else if (resultCode != null && !Action.NONE.equals(resultCode) && unknownHandlerManager.hasUnknownHandlers()) {     return unknownHandlerManager.handleUnknownResult(invocationContext, proxy.getActionName(), proxy.getConfig(), resultCode);     }                return null;     
}        public Result buildResult(ResultConfig resultConfig, Map<String, Object> extraContext) throws Exception {     String resultClassName = resultConfig.getClassName();     Result result = null;                                     if (resultClassName != null) {     //buildBean中会用反射机制Class.newInstance来创建bean      result = (Result) buildBean(resultClassName, extraContext);     Map<String, String> params = resultConfig.getParams();          if (params != null) {                                           for (Map.Entry<String, String> paramEntry : params.entrySet()) {     try {     //reflectionProvider参见OgnlReflectionProvider；     //resultConfig.getParams()就是result配置文件里所配置的参数<param></param>      //setProperties方法最终调用的是Ognl类的setValue方法        //这句其实就是把param名值设置到根对象result上     reflectionProvider.setProperty(paramEntry.getKey(), paramEntry.getValue(), result, extraContext, true);     } catch (ReflectionException ex) {      if (LOG.isErrorEnabled())           LOG.error("Unable to set parameter [#0] in result of type [#1]", ex,     paramEntry.getKey(), resultConfig.getClassName());     if (result instanceof ReflectionExceptionHandler) {                ((ReflectionExceptionHandler) result).handle(ex);              }     }         }             }                 }                     return result;        
}   

最后看一张在网上看到的一个调用流程图作为参考：