struts2 處理請求流程分析（結合源碼）3

 2.3、dispatcher.serviceAction(request, response, servletContext, mapping);方法分析

  public void serviceAction(HttpServletRequest request, HttpServletResponse response, ServletContext context,
                              ActionMapping mapping) throws ServletException {
    	//包裝了Http的四個作用域,extraContext 保存了所有的servlet 容器的作用域和struts2 包裝的容器作用域
        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 Action
        //如果之前有ValueStack 值棧存在，則用這個，否則創建一個新的，保存在extraContext 中
        ValueStack stack = (ValueStack) request.getAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY);
        if (stack != null) {
            extraContext.put(ActionContext.VALUE_STACK, ValueStackFactory.getFactory().createValueStack(stack));
        }
        String timerKey = "Handling request from Dispatcher";
        try {
            UtilTimerStack.push(timerKey);
            //獲得action 的配置信息
            String namespace = mapping.getNamespace();
            String name = mapping.getName();
            String method = mapping.getMethod();

            Configuration config = configurationManager.getConfiguration();
            //創建一個ActionProxy
            ActionProxy proxy = config.getContainer().getInstance(ActionProxyFactory.class).createActionProxy(
                    namespace, name, extraContext, true, false);
            //如果method 爲空，則設爲“excue”
            proxy.setMethod(method);
            //保存值棧供struts2 使用
            request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, proxy.getInvocation().getStack());

            // if the ActionMapping says to go straight to a result, do it!
            //如果result 不爲空的話，進行調轉
            if (mapping.getResult() != null) {
                Result result = mapping.getResult();
                //注入的是ActionInvaction
                result.execute(proxy.getInvocation());
            } else {
                proxy.execute();
            }

            // If there was a previous value stack then set it back onto the request
            if (stack != null) {
                request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, stack);
            }
        } catch (ConfigurationException e) {
            LOG.error("Could not find action or result", e);
            sendError(request, response, context, HttpServletResponse.SC_NOT_FOUND, e);
        } catch (Exception e) {
            throw new ServletException(e);
        } finally {
            UtilTimerStack.pop(timerKey);
        }
    }

 

    （1）createContextMap(request, response, mapping, context);方法

public Map<String,Object> createContextMap(HttpServletRequest request, HttpServletResponse response,
            ActionMapping mapping, ServletContext context) {

        // request map wrapping the http request objects
        Map requestMap = new RequestMap(request);

        // parameters map wrapping the http paraneters.
        Map params = null;
        if (mapping != null) {
            params = mapping.getParams();
        }
        Map requestParams = new HashMap(request.getParameterMap());
        if (params != null) {
            params.putAll(requestParams);
        } else {
            params = requestParams;
        }

        // session map wrapping the http session
        Map session = new SessionMap(request);

        // application map wrapping the ServletContext
        Map application = new ApplicationMap(context);
        //對上面的http 作用域包裝的map 進行封裝
        Map<String,Object> extraContext = createContextMap(requestMap, params, session, application, request, response, context);
       //把mapping 也放進map 裏
        extraContext.put(ServletActionContext.ACTION_MAPPING, mapping);
        return extraContext;
    }

   由此可以看出struts2 對servlet 容器的作用域都進行包裝成相應的Map ，然後放在extraContext  統一進行保存。

來看看extraContext  這個map 裏放的是全部servlet 容器作用域還有相應的struts2的包裝map，和 locale，從下面的源碼中可以看出。

 public HashMap<String,Object> createContextMap(Map requestMap,
                                    Map parameterMap,
                                    Map sessionMap,
                                    Map applicationMap,
                                    HttpServletRequest request,
                                    HttpServletResponse response,
                                    ServletContext servletContext) {
        HashMap<String,Object> extraContext = new HashMap<String,Object>();
        extraContext.put(ActionContext.PARAMETERS, new HashMap(parameterMap));
        extraContext.put(ActionContext.SESSION, sessionMap);
        extraContext.put(ActionContext.APPLICATION, applicationMap);

        Locale locale;
        if (defaultLocale != null) {
            locale = LocalizedTextUtil.localeFromString(defaultLocale, request.getLocale());
        } else {
            locale = request.getLocale();
        }

        extraContext.put(ActionContext.LOCALE, locale);
        //extraContext.put(ActionContext.DEV_MODE, Boolean.valueOf(devMode));

        extraContext.put(StrutsStatics.HTTP_REQUEST, request);
        extraContext.put(StrutsStatics.HTTP_RESPONSE, response);
        extraContext.put(StrutsStatics.SERVLET_CONTEXT, servletContext);

        // helpers to get access to request/session/application scope
        extraContext.put("request", requestMap);
        extraContext.put("session", sessionMap);
        extraContext.put("application", applicationMap);
        extraContext.put("parameters", parameterMap);

        AttributeMap attrMap = new AttributeMap(extraContext);
        extraContext.put("attr", attrMap);

        return extraContext;
    }

 

（2）ActionProxy proxy = config.getContainer().getInstance(ActionProxyFactory.class).createActionProxy(
                    namespace, name, extraContext, true, false);默認由DefaultActionProxyFactory類創建ActionProxy 。

 public ActionProxy createActionProxy(String namespace, String actionName, Map extraContext, boolean executeResult, boolean cleanupContext) throws Exception {
        //創建ActionProxy
        ActionProxy proxy = new DefaultActionProxy(namespace, actionName, extraContext, executeResult, cleanupContext);
        container.inject(proxy);
       //爲了創建ActionInvocation
        proxy.prepare();
        return proxy;
    }

 

    proxy.prepare(); 在這方法中創建ActionInvocation（默認爲DefaultActionInvocation），主要由ActionInvocation來調度Action 的實際操作

 public void prepare() throws Exception {
        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);
            }
            
            invocation = new DefaultActionInvocation(objectFactory, unknownHandler, this, extraContext, true, actionEventListener);
           //如果method 爲空，則this.method = "execute";
            resolveMethod();
        } finally {
            UtilTimerStack.pop(profileKey);
        }
    }

 

   在創建ActionInvocation 的時候有個主要的方法 init();

 protected DefaultActionInvocation(final ObjectFactory objectFactory, final UnknownHandler handler, final ActionProxy proxy, final Map extraContext, final boolean pushAction, final ActionEventListener actionEventListener) throws Exception {
    	UtilTimerStack.profile("create DefaultActionInvocation: ", 
    			new UtilTimerStack.ProfilingBlock<Object>() {
					public Object doProfiling() throws Exception {
						DefaultActionInvocation.this.proxy = proxy;
                        DefaultActionInvocation.this.objectFactory = objectFactory;
				        DefaultActionInvocation.this.extraContext = extraContext;
				        DefaultActionInvocation.this.pushAction = pushAction;
                        DefaultActionInvocation.this.unknownHandler = handler;
                        DefaultActionInvocation.this.actionEventListener = actionEventListener;
                        init();//這裏
						return null;
					}
    			});
    }

  

   init();方法，該方法創建了Action 和ActionContext

private void init() throws Exception {
      
        Map contextMap = createContextMap();
      //創建Action
        createAction(contextMap);
      
        if (pushAction) {
           //把Action 放進值棧
            stack.push(action);
        }
        //創建ActionContext
        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 interceptorList = new ArrayList(proxy.getConfig().getInterceptors());
        interceptors = interceptorList.iterator();
    }

   

    創建Action，通過objectFactory 進行創建，而這個類在struts.properties中可以重寫這個屬性 。默認爲SpringObjectFactory:struts.objectFactory=spring，在前面BeanSelectionProvider中通過配置文件爲ObjectFactory設置實現類  

protected void createAction(Map contextMap) {
        // load action
        String 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);
        }
    }


 public Object buildAction(String actionName, String namespace, ActionConfig config, Map extraContext) throws Exception {
        return buildBean(config.getClassName(), extraContext);
    }

 public Object buildBean(String className, Map extraContext) throws Exception {
        return buildBean(className, extraContext, true);
    }

 public Object buildBean(String className, Map extraContext, boolean injectInternal) throws Exception {
        Class clazz = getClassInstance(className);
        Object obj = buildBean(clazz, extraContext);
        if (injectInternal) {
            injectInternalBeans(obj);
        }
        return obj;
    }

 protected Object injectInternalBeans(Object obj) {
        if (obj != null && container != null) {
            container.inject(obj);
        }
        return obj;
    }

  

    proxy.execute();方法是struts2 中流程的重要方法。

 

    public String execute() throws Exception {
        ActionContext nestedContext = ActionContext.getContext();
        ActionContext.setContext(invocation.getInvocationContext());

        String retCode = null;

        String profileKey = "execute: ";
        try {
        	UtilTimerStack.push(profileKey);
        //這個是重點，主要的攔截器功能在這實現，執行返回跳轉的字符串
            retCode = invocation.invoke();
        } finally {
            if (cleanupContext) {
                ActionContext.setContext(nestedContext);
            }
            UtilTimerStack.pop(profileKey);
        }

        return retCode;
    }

  

   invoke 方法調用了DefaultActionInvocation的invoke()去實現Action的調用

    public String invoke() throws Exception {
	......
    	try {
	        ......

    		if (interceptors.hasNext()) {// (1)
    			final InterceptorMapping interceptor = (InterceptorMapping) interceptors.next();
    			UtilTimerStack.profile("interceptor: "+interceptor.getName(), 
    					new UtilTimerStack.ProfilingBlock<String>() {
							public String doProfiling() throws Exception {
				    			resultCode = interceptor.getInterceptor().intercept(DefaultActionInvocation.this);
				    			return null;
							}
    			});
    		} else {
    			resultCode = invokeActionOnly();
    		}

    		if (!executed) {// (2)
    			if (preResultListeners != null) {// (2)-1
    				for (Iterator iterator = preResultListeners.iterator();
    					iterator.hasNext();) {
    					PreResultListener listener = (PreResultListener) iterator.next();
    					
    					String _profileKey="preResultListener: ";
    					try {
    						UtilTimerStack.push(_profileKey);
    						listener.beforeResult(this, resultCode);
    					}
    					finally {
    						UtilTimerStack.pop(_profileKey);
    					}
    				}
    			}

    			if (proxy.getExecuteResult()) {// (2)-2
    				executeResult();
    			}

    			executed = true;
    		}

    		return resultCode;
    	}
    	finally {
    		UtilTimerStack.pop(profileKey);
    	}
    }

 

    整個方法主要由2個if從句分割，在(1)處的if從句中，主要實現了攔截器的"遞歸"調用，說它是遞歸調用，其實是一種非傳統的遞歸。傳統的遞歸應該是函數調用自身，最後達成一定條件後退出，但是這裏是將自身的引用作爲參數傳遞給intercept()，然後在intercept()內部再調用DefaultActionInvocation的invoke()，實現了遞歸調用。

利用這種方式，實現了攔截器和Action的如下的調用邏輯：

Interceptor1
Interceptor2
Interceptor3
Action
Interceptor3
Interceptor2
Interceptor1

    最後，當interceptors.hasNext()返回false時，也就是全部攔截器調用完畢之後，函數調用了invokeActionOnly();去實現Action的調用：

    public String invokeActionOnly() throws Exception {
    	return invokeAction(getAction(), proxy.getConfig());
    }

 

   invokeActionOnly()內部是使用invokeAction()去實現Action的調用的，源代碼如下：

    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);
            
            Method method;
            try {
                method = getAction().getClass().getMethod(methodName, new Class[0]);
            } catch (NoSuchMethodException e) {
                try {
                    String altMethodName = "do" + methodName.substring(0, 1).toUpperCase() + methodName.substring(1);
                    method = getAction().getClass().getMethod(altMethodName, new Class[0]);
                } catch (NoSuchMethodException e1) {
                    throw e;
                }
            }

            Object methodResult = method.invoke(action, new Object[0]);
            if (methodResult instanceof Result) {
            	this.result = (Result) methodResult;
            	return null;
            } else {
            	return (String) methodResult;
            }
        } catch (NoSuchMethodException e) {
            throw new IllegalArgumentException("The " + methodName + "() is not defined in action " + getAction().getClass() + "");
        } catch (InvocationTargetException e) {
            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);
        }
    }

 

    由這句Object methodResult = method.invoke(action, new Object[0]);可以看出，最後通過反射實現了Action的執行方法的調用。


    調用完方法之後，invoke()方法的流程來到了(2)處，由於剛剛調用完Action的那次invoke()調用此時executed爲false，所以可以進入此處的if語句。
(2)-1處調用了在PreResultListener中的定義的一些執行Result前的操作。
(2)-2處則根據配置文件中的設置執行Result。

    private void executeResult() throws Exception {
        result = createResult();// 根據配置文件構建Result

        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);
        }
    }

 

於是，最終的調用順序應該是：
Interceptor1
Interceptor2
Interceptor3
Action
PreResultListener
Result
Interceptor3
Interceptor2
Interceptor1