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()
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); }
}
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;
} 
