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.

Java代码  

1. public ActionProxy createActionProxy(String namespace, String actionName, String methodName, Map<String, Object> extraContext, boolean executeResult, boolean cleanupContext) {  
2.       
3.     ActionInvocation inv = new DefaultActionInvocation(extraContext, true);  
4.     container.inject(inv);  
5.     return createActionProxy(inv, namespace, actionName, methodName, executeResult, cleanupContext);  
6. }  

 下面先看DefaultActionInvocation的init方法

Java代码  

1. public void init(ActionProxy proxy) {  
2.     this.proxy = proxy;  
3.     Map<String, Object> contextMap = createContextMap();  
4.   
5.     // Setting this so that other classes, like object factories, can use the ActionProxy and other  
6.     // contextual information to operate  
7.     ActionContext actionContext = ActionContext.getContext();  
8.   
9.     if (actionContext != null) {  
10.         actionContext.setActionInvocation(this);  
11.     }  
12.     //创建Action,struts2中每一个Request都会创建一个新的Action  
13.     createAction(contextMap);  
14.   
15.     if (pushAction) {  
16.         stack.push(action);  
17.         contextMap.put("action", action);  
18.     }  
19.   
20.     invocationContext = new ActionContext(contextMap);  
21.     invocationContext.setName(proxy.getActionName());  
22.   
23.     // get a new List so we don‘t get problems with the iterator if someone changes the list  
24.     List<InterceptorMapping> interceptorList = new ArrayList<InterceptorMapping>(proxy.getConfig().getInterceptors());  
25.     interceptors = interceptorList.iterator();  
26. }  
27.       
28. protected void createAction(Map<String, Object> contextMap) {  
29.     // load action  
30.     String timerKey = "actionCreate: " + proxy.getActionName();  
31.     try {  
32.         UtilTimerStack.push(timerKey);  
33.         //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  
34.         //在前面BeanSelectionProvider中通过配置文件为ObjectFactory设置实现类  
35.         //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  
36.         action = objectFactory.buildAction(proxy.getActionName(), proxy.getNamespace(), proxy.getConfig(), contextMap);  
37.     } catch (InstantiationException e) {  
38.         throw new XWorkException("Unable to intantiate Action!", e, proxy.getConfig());  
39.     } catch (IllegalAccessException e) {  
40.         throw new XWorkException("Illegal access to constructor, is it public?", e, proxy.getConfig());  
41.     } catch (Exception e) {  
42.        ...  
43.     } finally {  
44.         UtilTimerStack.pop(timerKey);  
45.     }  
46.   
47.     if (actionEventListener != null) {  
48.         action = actionEventListener.prepare(action, stack);  
49.     }  
50. }  
51. //SpringObjectFactory  
52. public Object buildBean(String beanName, Map<String, Object> extraContext, boolean injectInternal) throws Exception {  
53.     Object o = null;  
54.     try {  
55.         //SpringObjectFactory会通过web.xml中的context-param:contextConfigLocation自动注入ClassPathXmlApplicationContext  
56.         o = appContext.getBean(beanName);  
57.     } catch (NoSuchBeanDefinitionException e) {  
58.         Class beanClazz = getClassInstance(beanName);  
59.         o = buildBean(beanClazz, extraContext);  
60.     }  
61.     if (injectInternal) {  
62.         injectInternalBeans(o);  
63.     }  
64.     return o;  
65. }  

Java代码  

1. //接下来看看DefaultActionInvocation 的invoke方法  
2. public String invoke() throws Exception {  
3.     String profileKey = "invoke: ";  
4.     try {  
5.         UtilTimerStack.push(profileKey);  
6.      
7.         if (executed) {  
8.             throw new IllegalStateException("Action has already executed");  
9.         }  
10.         //递归执行interceptor  
11.         if (interceptors.hasNext()) {  
12.             //interceptors是InterceptorMapping实际上是像一个像FilterChain一样的Interceptor链  
13.             //通过调用Invocation.invoke()实现递归牡循环  
14.             final InterceptorMapping interceptor = (InterceptorMapping) interceptors.next();  
15.             String interceptorMsg = "interceptor: " + interceptor.getName();  
16.             UtilTimerStack.push(interceptorMsg);  
17.             try {    
18.                  //在每个Interceptor的方法中都会return invocation.invoke()         
19.                  resultCode = interceptor.getInterceptor().intercept(DefaultActionInvocation.this);  
20.                 }  
21.             finally {  
22.                 UtilTimerStack.pop(interceptorMsg);  
23.             }  
24.         } else {    
25.             //当所有interceptor都执行完,最后执行Action,invokeActionOnly会调用invokeAction()方法  
26.             resultCode = invokeActionOnly();  
27.         }  
28.   
29.         // this is needed because the result will be executed, then control will return to the Interceptor, which will  
30.         // return above and flow through again    
31.         //在Result返回之前调用preResultListeners   
32.         //通过executed控制,只执行一次   
33.         if (!executed) {  
34.             if (preResultListeners != null) {   
35.                 for (Object preResultListener : preResultListeners) {   
36.                     PreResultListener listener = (PreResultListener) preResultListener;  
37.                                                                   
38.                     String _profileKey = "preResultListener: ";   
39.                     try {                                         
40.                         UtilTimerStack.push(_profileKey);                               
41.                         listener.beforeResult(this, resultCode);  
42.                     }                                             
43.                     finally {                                     
44.                         UtilTimerStack.pop(_profileKey);          
45.                     }                                             
46.                 }                                                 
47.             }                                                     
48.                                                                   
49.             // now execute the result, if we‘re supposed to       
50.             //执行Result                                          
51.             if (proxy.getExecuteResult()) {                       
52.                 executeResult();                                  
53.             }                                                     
54.                                                                   
55.             executed = true;                                      
56.         }                                                         
57.                                                                   
58.         return resultCode;                                        
59.     }                                                             
60.     finally {                                                     
61.         UtilTimerStack.pop(profileKey);                           
62.     }                                                             
63. }   
64.   
65. //invokeAction  
66. protected String invokeAction(Object action,ActionConfig actionConfig)throws Exception{  
67.     String methodName = proxy.getMethod();  
68.   
69.     String timerKey = "invokeAction: " + proxy.getActionName();  
70.     try {  
71.         UtilTimerStack.push(timerKey);  
72.   
73.         boolean methodCalled = false;  
74.         Object methodResult = null;  
75.         Method method = null;  
76.         try {  
77.             //java反射机制得到要执行的方法  
78.             method = getAction().getClass().getMethod(methodName, new Class[0]);  
79.         } catch (NoSuchMethodException e) {  
80.             // hmm -- OK, try doXxx instead  
81.             //如果没有对应的方法，则使用do+Xxxx来再次获得方法     
82.             try {  
83.                 String altMethodName = "do" + methodName.substring(0, 1).toUpperCase() + methodName.substring(1);  
84.                 method = getAction().getClass().getMethod(altMethodName, new Class[0]);  
85.             } catch (NoSuchMethodException e1) {  
86.                 // well, give the unknown handler a shot  
87.                 if (unknownHandlerManager.hasUnknownHandlers()) {  
88.                     try {  
89.                         methodResult = unknownHandlerManager.handleUnknownMethod(action, methodName);  
90.                         methodCalled = true;  
91.                     } catch (NoSuchMethodException e2) {  
92.                         // throw the original one  
93.                         throw e;  
94.                     }  
95.                 } else {  
96.                     throw e;  
97.                 }  
98.             }  
99.         }  
100.         //执行Method  
101.         if (!methodCalled) {  
102.             methodResult = method.invoke(action, new Object[0]);  
103.         }  
104.         //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  
105.         if (methodResult instanceof Result) {  
106.             this.explicitResult = (Result) methodResult;  
107.   
108.             // Wire the result automatically  
109.             container.inject(explicitResult);  
110.             return null;  
111.         } else {  
112.             return (String) methodResult;  
113.         }  
114.     } catch (NoSuchMethodException e) {  
115.         throw new IllegalArgumentException("The " + methodName + "() is not defined in action " + getAction().getClass() + "");  
116.     } catch (InvocationTargetException e) {  
117.         // We try to return the source exception.  
118.         Throwable t = e.getTargetException();  
119.   
120.         if (actionEventListener != null) {  
121.             String result = actionEventListener.handleException(t, getStack());  
122.             if (result != null) {  
123.                 return result;  
124.             }  
125.         }  
126.         if (t instanceof Exception) {  
127.             throw (Exception) t;  
128.         } else {  
129.             throw e;  
130.         }  
131.     } finally {  
132.         UtilTimerStack.pop(timerKey);  
133.     }  
134. }  

 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。

Java代码  

1. private void executeResult() throws Exception {  
2.     //根据ResultConfig创建Result   
3.     result = createResult();  
4.   
5.     String timerKey = "executeResult: " + getResultCode();  
6.     try {  
7.         UtilTimerStack.push(timerKey);  
8.         if (result != null) {  
9.         //开始执行Result,  
10.         //可以参考Result的实现，如用了比较多的ServletDispatcherResult,ServletActionRedirectResult,ServletRedirectResult   
11.             result.execute(this);  
12.         } else if (resultCode != null && !Action.NONE.equals(resultCode)) {  
13.             throw new ConfigurationException("No result defined for action " + getAction().getClass().getName()  
14.                     + " and result " + getResultCode(), proxy.getConfig());  
15.         } else {  
16.             if (LOG.isDebugEnabled()) {  
17.                 LOG.debug("No result returned for action " + getAction().getClass().getName() + " at " + proxy.getConfig().getLocation());  
18.             }  
19.         }  
20.     } finally {  
21.         UtilTimerStack.pop(timerKey);  
22.     }  
23. }            
24.   
25. public Result createResult() throws Exception {  
26.     //如果Action中直接返回的Result类型,在invokeAction()保存在explicitResult  
27.     if (explicitResult != null) {                             
28.         Result ret = explicitResult;                          
29.         explicitResult = null;                                
30.                                                               
31.         return ret;                                           
32.     }  
33.     //返回的是String则从config中得到当前Action的Results列表  
34.     ActionConfig config = proxy.getConfig();                  
35.     Map<String, ResultConfig> results = config.getResults();  
36.                                                               
37.     ResultConfig resultConfig = null;                         
38.                                                               
39.     synchronized (config) {                                   
40.         try {   
41.             //通过返回的String来匹配resultConfig    
42.             resultConfig = results.get(resultCode);           
43.         } catch (NullPointerException e) {                    
44.             // swallow                                        
45.         }                                                     
46.         if (resultConfig == null) {                           
47.             // If no result is found for the given resultCode, try to get a wildcard ‘*‘ match.  
48.             //如果找不到对应name的ResultConfig，则使用name为*的Result    
49.             //说明可以用*通配所有的Result                                
50.             resultConfig = results.get("*");  
51.         }                                     
52.     }                                         
53.                                               
54.     if (resultConfig != null) {               
55.         try {  
56.             //创建Result   
57.             return objectFactory.buildResult(resultConfig, invocationContext.getContextMap());  
58.         } catch (Exception e) {  
59.             LOG.error("There was an exception while instantiating the result of type " + resultConfig.getClassName(), e);  
60.             throw new XWorkException(e, resultConfig);  
61.         }   
62.     } else if (resultCode != null && !Action.NONE.equals(resultCode) && unknownHandlerManager.hasUnknownHandlers()) {  
63.         return unknownHandlerManager.handleUnknownResult(invocationContext, proxy.getActionName(), proxy.getConfig(), resultCode);  
64.     }             
65.     return null;  
66. }     
67.   
68. public Result buildResult(ResultConfig resultConfig, Map<String, Object> extraContext) throws Exception {  
69.     String resultClassName = resultConfig.getClassName();  
70.     Result result = null;                                  
71.                                                            
72.     if (resultClassName != null) {  
73.         //buildBean中会用反射机制Class.newInstance来创建bean   
74.         result = (Result) buildBean(resultClassName, extraContext);  
75.         Map<String, String> params = resultConfig.getParams();       
76.         if (params != null) {                                        
77.             for (Map.Entry<String, String> paramEntry : params.entrySet()) {  
78.                 try {  
79.                      //reflectionProvider参见OgnlReflectionProvider；  
80.               //resultConfig.getParams()就是result配置文件里所配置的参数<param></param>   
81.                      //setProperties方法最终调用的是Ognl类的setValue方法     
82.               //这句其实就是把param名值设置到根对象result上  
83.                     reflectionProvider.setProperty(paramEntry.getKey(), paramEntry.getValue(), result, extraContext, true);  
84.                 } catch (ReflectionException ex) {   
85.                     if (LOG.isErrorEnabled())        
86.                         LOG.error("Unable to set parameter [#0] in result of type [#1]", ex,  
87.                                 paramEntry.getKey(), resultConfig.getClassName());  
88.                     if (result instanceof ReflectionExceptionHandler) {             
89.                         ((ReflectionExceptionHandler) result).handle(ex);           
90.                     }  
91.                 }      
92.             }          
93.         }              
94.     }                  
95.                        
96.     return result;     
97. }   

Structs ActionProxy深度阅读