上一节分析了FilterDispatcher中的doFilter（）方法中的前半部分，主要是分析了通过actionMapper.getMapping获取ActionMapping对象，解析请求路径，寻找出namespace,name等信息。
这章详细讲解doFilter（）后面的重点dispatcher.serviceAction（）。
这里主要的工作是根据ActionMapping对象，创建一个新的action对象，action对象是通过java反射机制差创建的，这里也就是说明了为什么struts2是单实例。然后再创建action方法实例，并且执行该方法。
整个流程如图：
1、 继续分析doFilter（），正式执行action
dispatcher.serviceAction(request, response, servletContext, mapping);public void serviceAction(HttpServletRequest request, HttpServletResponse response, ServletContext context,ActionMapping mapping) throws ServletException {//创建mvc运行的数据环境Map<String, Object> extraContext = createContextMap(request, response, mapping, context);// If there was a previous value stack, then create a new copy and pass it in to be used by the new ActionValueStack stack = (ValueStack) request.getAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY);boolean nullStack = stack == null; //没有找到已存在的valueStack，则从ActionContext中获取当前线程的valuesif (nullStack) {ActionContext ctx = ActionContext.getContext();if (ctx != null) {stack = ctx.getValueStack();}}if (stack != null) {extraContext.put(ActionContext.VALUE_STACK, valueStackFactory.createValueStack(stack));}String timerKey = "Handling request from Dispatcher";try {UtilTimerStack.push(timerKey);String namespace = mapping.getNamespace();String name = mapping.getName();String method = mapping.getMethod();Configuration config = configurationManager.getConfiguration(); //创建一个ActionProxy，这里已经完全进入xwork的世界了ActionProxy proxy = config.getContainer().getInstance(ActionProxyFactory.class).createActionProxy(namespace, name, method, extraContext, true, false);request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, proxy.getInvocation().getStack());// if the ActionMapping says to go straight to a result, do it!if (mapping.getResult() != null) {Result result = mapping.getResult();result.execute(proxy.getInvocation());} else { //执行ActionProxy，真正运行xwork中的mvc实现proxy.execute();}// If there was a previous value stack then set it back onto the requestif (!nullStack) {request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, stack);}} catch (ConfigurationException e) {// WW-2874 Only log error if in devModeif(devMode) {String reqStr = request.getRequestURI();if (request.getQueryString() != null) {reqStr = reqStr + "?" + request.getQueryString();}LOG.error("Could not find action or result\n" + reqStr, e);}else {if (LOG.isWarnEnabled()) {LOG.warn("Could not find action or result", e);}}sendError(request, response, context, HttpServletResponse.SC_NOT_FOUND, e);} catch (Exception e) {sendError(request, response, context, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, e);} finally {UtilTimerStack.pop(timerKey);}}注释：（1） //createContextMap方法主要把Application、Session、Request的key value值拷贝到Map中
（2） config.getContainer().getInstance(ActionProxyFactory.class)创建一个Action的代理对象，ActionProxyFactory是创建ActionProxy的工厂
参考实现类:DefaultActionProxy和DefaultActionProxyFactory
（3）createActionProxy()方法创建一个action 的代理对象
2、createActionProxy（）创建一个新的action对象，源码：
public ActionProxy createActionProxy(String namespace, String actionName, Map<String, Object> extraContext, boolean executeResult, boolean cleanupContext) {return createActionProxy(namespace, actionName, null, extraContext, executeResult, cleanupContext);}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);}(2)创建了DefaultActionInvocation对象，并且把上面封装的参数map传进去
在这首先有必要详细讲解一下DefaultActionInvocation这个类，这个类主要的作用操作ActionProxy，然后再回来：
3、DefaultActionInvocation中init（）方法：
public void init(ActionProxy proxy) {this.proxy = proxy; //创建上下文环境，这里的contextMap与ActionContext的上下文环境一致Map<String, Object> contextMap = createContextMap();// Setting this so that other classes, like object factories, can use the ActionProxy and other// contextual information to operate //将ActionInvocation对象设置到actionContext中，这样做得好处可以利用actionContext的数据共享特性，将ActionInvocation在整个执行周期共享。ActionContext actionContext = ActionContext.getContext();if (actionContext != null) {actionContext.setActionInvocation(this);}createAction(contextMap);//这里是重点，创建action对象 //将action对象置于valueStack中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 listList<InterceptorMapping> interceptorList = new ArrayList<InterceptorMapping>(proxy.getConfig().getInterceptors());interceptors = interceptorList.iterator();//拦截器}注释：（1）创建上下文环境
（2）ActionInvocation对象的共享
（3）创建action对象，createAction(contextMap)创建Action,struts2中每一个Request都会创建一个新的Action
（4）将action对象置入valueStack
（5）创建ActionInvocation的上下文环境
（6）将拦截器堆栈置于初始调度状态，并且把proxy中的拦截器，传值给全局变量interceptors（Iterator<InterceptorMapping>）
3.1 看看createAction()方法
protected void createAction(Map<String, Object> contextMap) {// load actionString timerKey = "actionCreate: " + proxy.getActionName();try {UtilTimerStack.push(timerKey);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) {String gripe = "";if (proxy == null) {gripe = "Whoa! No ActionProxy instance found in current ActionInvocation. This is bad ... very bad";} else if (proxy.getConfig() == null) {gripe = "Sheesh. Where'd that ActionProxy get to? I can't find it in the current ActionInvocation!?";} else if (proxy.getConfig().getClassName() == null) {gripe = "No Action defined for '" + proxy.getActionName() + "' in namespace '" + proxy.getNamespace() + "'";} else {gripe = "Unable to instantiate Action, " + proxy.getConfig().getClassName() + ", defined for '" + proxy.getActionName() + "' in namespace '" + proxy.getNamespace() + "'";}gripe += (((" -- " + e.getMessage()) != null) ? e.getMessage() : " [no message in exception]");throw new XWorkException(gripe, e, proxy.getConfig());} finally {UtilTimerStack.pop(timerKey);}if (actionEventListener != null) {action = actionEventListener.prepare(action, stack);}}3.2buildAction（）方法：
public Object buildAction(String actionName, String namespace, ActionConfig config, Map<String, Object> extraContext) throws Exception {return buildBean(config.getClassName(), extraContext);}public Object buildBean(String className, Map<String, Object> extraContext) throws Exception {return buildBean(className, extraContext, true);}public Object buildBean(String className, Map<String, Object> extraContext, boolean injectInternal) throws Exception {Class clazz = getClassInstance(className);Object obj = buildBean(clazz, extraContext);if (injectInternal) {injectInternalBeans(obj);}return obj;}4、DefaultActionInvocation中的invoke（）方法：
/*** @throws ConfigurationException If no result can be found with the returned code*/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()) { //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 {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 toif (proxy.getExecuteResult()) { //执行Result executeResult();}executed = true;}return resultCode;}finally {UtilTimerStack.pop(profileKey);}}注释：（1）执行每一个拦截器
（2）执行action方法，并且返回结果类型
（3）执行每一个PreResultListener对象的beforeResult（）方法
（4）执行结果
这个流程就是典型的struts流程图中的中间的那一部分。
4.1 invokeActionOnly()方法：
public String invokeActionOnly() throws Exception {return invokeAction(getAction(), proxy.getConfig());}protected String invokeAction(Object action, ActionConfig actionConfig) throws Exception {String methodName = proxy.getMethod();if (LOG.isDebugEnabled()) {LOG.debug("Executing action method = " + actionConfig.getMethodName());}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 insteadtry { //如果没有对应的方法，则使用do+Xxxx来再次获得方法 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 shotif (unknownHandlerManager.hasUnknownHandlers()) {try {methodResult = unknownHandlerManager.handleUnknownMethod(action, methodName);methodCalled = true;} catch (NoSuchMethodException e2) {// throw the original onethrow e;}} else {throw e;}}}if (!methodCalled) {//执行Method methodResult = method.invoke(action, new Object[0]);}if (methodResult instanceof Result) {this.explicitResult = (Result) methodResult;// Wire the result automaticallycontainer.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);}}（2）执行该方法
4.2action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 {result = createResult();String timerKey = "executeResult: " + getResultCode();try {UtilTimerStack.push(timerKey);if (result != null) {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);}}
（2）执行该结果
4.2.1 createResult()
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;}ActionConfig config = proxy.getConfig();Map<String, ResultConfig> results = config.getResults();ResultConfig resultConfig = null;synchronized (config) {try { //返回的是String则从config中得到当前Action的Results列表 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;}
（2）如果explicitResult为null，就通过resultCode在返回列表中查找相应的返回配置、
（3）通过objectFactory.buildResult创建result对象
5、返回到步骤2createActionProxy（）中，创建完成DefaultActionInvocation对象，继续调用createActionProxy(inv, namespace, actionName, methodName, executeResult, cleanupContext)
public ActionProxy createActionProxy(ActionInvocation inv, String namespace, String actionName, String methodName, boolean executeResult, boolean cleanupContext) {DefaultActionProxy proxy = new DefaultActionProxy(inv, namespace, actionName, methodName, executeResult, cleanupContext);container.inject(proxy);proxy.prepare();return proxy;}（2）执行proxy.prepare()
6、DefaultActionProxy的构造函数：
protected DefaultActionProxy(ActionInvocation inv, String namespace, String actionName, String methodName, boolean executeResult, boolean cleanupContext) {this.invocation = inv;this.cleanupContext = cleanupContext;if (LOG.isDebugEnabled()) {LOG.debug("Creating an DefaultActionProxy for namespace " + namespace + " and action name " + actionName);}this.actionName = actionName;this.namespace = namespace;this.executeResult = executeResult;this.method = methodName;}
protected void prepare() {String profileKey = "create DefaultActionProxy: ";try {UtilTimerStack.push(profileKey);config = configuration.getRuntimeConfiguration().getActionConfig(namespace, actionName);if (config == null && unknownHandler != null) {config = unknownHandler.handleUnknownAction(namespace, actionName);}if (config == null) {String message;if ((namespace != null) && (namespace.trim().length() > 0)) {message = LocalizedTextUtil.findDefaultText(XWorkMessages.MISSING_PACKAGE_ACTION_EXCEPTION, Locale.getDefault(), new String[]{namespace, actionName});} else {message = LocalizedTextUtil.findDefaultText(XWorkMessages.MISSING_ACTION_EXCEPTION, Locale.getDefault(), new String[]{actionName});}throw new ConfigurationException(message);}resolveMethod();if (!config.isAllowedMethod(method)) {throw new ConfigurationException("Invalid method: "+method+" for action "+actionName);}invocation.init(this);} finally {UtilTimerStack.pop(profileKey);}}（2） resolveMethod()解析方法名称
（3） invocation.init(this)
8、resolveMethod()
private void resolveMethod() {// if the method is set to null, use the one from the configuration// if the one from the configuration is also null, use "execute"if (!TextUtils.stringSet(this.method)) {this.method = config.getMethodName();if (!TextUtils.stringSet(this.method)) {this.method = "execute";}}} 8、到这里就创建好ActionProxy对象，返回到步骤1serviceAction方法中，分析ActionProxy proxy = config.getContainer().getInstance(ActionProxyFactory.class).createActionProxy(
namespace, name, method, extraContext, true, false)。
创建完成ActionProxy对象，就会执行 proxy.execute()
public String execute() throws Exception {ActionContext nestedContext = ActionContext.getContext();ActionContext.setContext(invocation.getInvocationContext());String retCode = null;String profileKey = "execute: ";try {UtilTimerStack.push(profileKey);retCode = invocation.invoke();} finally {if (cleanupContext) {ActionContext.setContext(nestedContext);}UtilTimerStack.pop(profileKey);}return retCode;}注释：这里调用invocation.invoke()。