SpringMVC源碼分析（二）之請求如何轉寄到對應的Controller

    

        在前一篇對DispatcherServlet的分析中，初略的過了下請求是如何處理的，本文將重點分析，HandlerMapping與HandlerAdapter是如何工作的

       

         在web容器啟動的過程中，會初初始化一系列SpringMVC所需的類，這裡我們看看AbstractHandlerMethodMapping類的initHandlerMethods方法

         

          如果bean中有相應註解  檢測HandlerMethod

    

          具體看看 selectMethods方法的實現

而其中的inspect方法  調用了 getMappingForMethod方法  具體實現 由其子類 RequestMappingHandlerMapping實現

protected RequestMappingInfo getMappingForMethod(Method method, Class<?> handlerType) {RequestMappingInfo info = createRequestMappingInfo(method);if (info != null) {RequestMappingInfo typeInfo = createRequestMappingInfo(handlerType);if (typeInfo != null) {info = typeInfo.combine(info);}}return info;}

此方法返回的是一個RequestMappingInfo類執行個體，可見我們之前methods Map中的T 類型就為RequestMappingInfo

此類是一個封裝了各種請求映射條件並實現了RequestCondition介面的類。有各種RequestCondition實作類別屬性，patternsCondition，methodsCondition，paramsCondition，headersCondition，consumesCondition以及producesCondition，這個請
求條件看屬性名稱也瞭解，分別代表http請求的路徑模式、方法、參數、頭部等資訊。

繼續看getMappingForMethod方法，createRequestMappingInfo的具體實現如下：

private RequestMappingInfo createRequestMappingInfo(AnnotatedElement element) {RequestMapping requestMapping = AnnotatedElementUtils.findMergedAnnotation(element, RequestMapping.class);RequestCondition<?> condition = (element instanceof Class<?> ?getCustomTypeCondition((Class<?>) element) : getCustomMethodCondition((Method) element));return (requestMapping != null ? createRequestMappingInfo(requestMapping, condition) : null);}

首先找到方法的@RequestMapping註解，然後擷取RequestCondition ,如果有註解，則調用具體建立方法，否則返回null

protected RequestMappingInfo createRequestMappingInfo(RequestMapping requestMapping, RequestCondition<?> customCondition) {return RequestMappingInfo.paths(resolveEmbeddedValuesInPatterns(requestMapping.path())).methods(requestMapping.method()).params(requestMapping.params()).headers(requestMapping.headers()).consumes(requestMapping.consumes()).produces(requestMapping.produces()).mappingName(requestMapping.name()).customCondition(customCondition).options(this.config).build();}

除了pathCondithion 其他都是直接使用 requestMapping註解中的condition

回頭再看registerHandlerMethod方法

到此 就註冊完URL相關操作

回頭再看 doDispatch方法中 getHandler的調用 最終會調用getHandlerInternal方法，具體實現：

protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);if (logger.isDebugEnabled()) {logger.debug("Looking up handler method for path " + lookupPath);}this.mappingRegistry.acquireReadLock();try {HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);if (logger.isDebugEnabled()) {if (handlerMethod != null) {logger.debug("Returning handler method [" + handlerMethod + "]");}else {logger.debug("Did not find handler method for [" + lookupPath + "]");}}return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);}finally {this.mappingRegistry.releaseReadLock();}}

關鍵代碼是通過調用 lookupHandlerMethod擷取 handlerMethod

以上都是基於Controller方法的映射 RequestMappingHandlerMapping，關於靜態資源的映射 這裡就不作詳細說明了，對應的handlerMpping 為SimpleUrlHandlerMapping

HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);

通過handler 和 request構建 HandlerExecutionChain

protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?(HandlerExecutionChain) handler : new HandlerExecutionChain(handler));String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);for (HandlerInterceptor interceptor : this.adaptedInterceptors) {if (interceptor instanceof MappedInterceptor) {MappedInterceptor mappedInterceptor = (MappedInterceptor) interceptor;if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) {chain.addInterceptor(mappedInterceptor.getInterceptor());}}else {chain.addInterceptor(interceptor);}}return chain;}

HandlerAdapter的擷取以及是如何工作的

       同樣在doDispatch中 我們通過handler來擷取handlerAdapter

HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {   for (HandlerAdapter ha : this.handlerAdapters) {      if (logger.isTraceEnabled()) {         logger.trace("Testing handler adapter [" + ha + "]");      }      if (ha.supports(handler)) {         return ha;      }   }   throw new ServletException("No adapter for handler [" + handler +         "]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");}

這裡使用的handlerAdapters是在private void initHandlerAdapters(ApplicationContext context)方法中得到初始化的，大致思想就是將所有實現了HandlerAdapter介面的類的執行個體都找出來放到這個list中
我們以RequestMappingHandlerAdapter 執行個體來分析 對應的supports方法為 父類 AbstractHandlerMethodAdapter 方法：

public final boolean supports(Object handler) {return (handler instanceof HandlerMethod && supportsInternal((HandlerMethod) handler));}

 在RequestMappingHandlerAdapter實現 supportsInternal：

protected boolean supportsInternal(HandlerMethod handlerMethod) {return true;}

可以發現RequestMappingHandlerAdapter 是對所有handlerMethod 進行適配調用

回到doDispatch

mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

handler的調用  核心方法handleInternal的實現為：

protected ModelAndView handleInternal(HttpServletRequest request,HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {checkRequest(request);if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);}else {prepareResponse(response);}// Execute invokeHandlerMethod in synchronized block if required.if (this.synchronizeOnSession) {HttpSession session = request.getSession(false);if (session != null) {Object mutex = WebUtils.getSessionMutex(session);synchronized (mutex) {return invokeHandlerMethod(request, response, handlerMethod);}}}return invokeHandlerMethod(request, response, handlerMethod);}

內容很多，我們只需要重點關心invokeHandlerMethod

protected ModelAndView invokeHandlerMethod(HttpServletRequest request,HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {ServletWebRequest webRequest = new ServletWebRequest(request, response);WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);invocableMethod.setDataBinderFactory(binderFactory);invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);ModelAndViewContainer mavContainer = new ModelAndViewContainer();mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));modelFactory.initModel(webRequest, mavContainer, invocableMethod);mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);asyncWebRequest.setTimeout(this.asyncRequestTimeout);WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);asyncManager.setTaskExecutor(this.taskExecutor);asyncManager.setAsyncWebRequest(asyncWebRequest);asyncManager.registerCallableInterceptors(this.callableInterceptors);asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);if (asyncManager.hasConcurrentResult()) {Object result = asyncManager.getConcurrentResult();mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];asyncManager.clearConcurrentResult();if (logger.isDebugEnabled()) {logger.debug("Found concurrent result value [" + result + "]");}invocableMethod = invocableMethod.wrapConcurrentResult(result);}invocableMethod.invokeAndHandle(webRequest, mavContainer);if (asyncManager.isConcurrentHandlingStarted()) {return null;}return getModelAndView(mavContainer, modelFactory, webRequest);}

在此方法中，會根據 handlerMethod 建立ServletInvocableHandlerMethod 對象，設定方法執行過程中相應的 resovler

然後調用 invokeAndHandle：

public void invokeAndHandle(ServletWebRequest webRequest,ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception {                   //執行請求 並返回結果Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);setResponseStatus(webRequest);if (returnValue == null) {if (isRequestNotModified(webRequest) || hasResponseStatus() || mavContainer.isRequestHandled()) {mavContainer.setRequestHandled(true);return;}}else if (StringUtils.hasText(this.responseReason)) {mavContainer.setRequestHandled(true);return;}mavContainer.setRequestHandled(false);try {this.returnValueHandlers.handleReturnValue(returnValue, getReturnValueType(returnValue), mavContainer, webRequest);}catch (Exception ex) {if (logger.isTraceEnabled()) {logger.trace(getReturnValueHandlingErrorMessage("Error handling return value", returnValue), ex);}throw ex;}}

可以看到 第一行調用 invokeForRequest執行請求

public Object invokeForRequest(NativeWebRequest request, ModelAndViewContainer mavContainer,Object... providedArgs) throws Exception {Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);if (logger.isTraceEnabled()) {logger.trace("Invoking '" + ClassUtils.getQualifiedMethodName(getMethod(), getBeanType()) +"' with arguments " + Arrays.toString(args));}Object returnValue = doInvoke(args);if (logger.isTraceEnabled()) {logger.trace("Method [" + ClassUtils.getQualifiedMethodName(getMethod(), getBeanType()) +"] returned [" + returnValue + "]");}return returnValue;}

繼續跟doInvoke方法，對於上面的請求參數解析下一篇部落格會分析，本文只分析方法的調用

其中的getBridgedMethod為：

protected Method getBridgedMethod() {return this.bridgedMethod;}

而我們的bridgedMethod是什麼呢，不知道大家有沒有留意到，在前面我提到過的 ServletInvocableHandlerMethod 執行個體的建立

ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);

而createInvocableHandlerMethod 就是好調用ServletInvocableHandlerMethod  HandlerMethod參數 建構函式，最終會調用HandlerMethod建構函式：

protected HandlerMethod(HandlerMethod handlerMethod) {Assert.notNull(handlerMethod, "HandlerMethod is required");this.bean = handlerMethod.bean;this.beanFactory = handlerMethod.beanFactory;this.beanType = handlerMethod.beanType;this.method = handlerMethod.method;this.bridgedMethod = handlerMethod.bridgedMethod;this.parameters = handlerMethod.parameters;this.responseStatus = handlerMethod.responseStatus;this.responseStatusReason = handlerMethod.responseStatusReason;this.resolvedFromHandlerMethod = handlerMethod.resolvedFromHandlerMethod;}

其中就有對 bridgedMethod 的賦值，這下就應該清楚了  adapter是如何來調用我們Controller的方法啦

本節重點分析了 RequestMappingHandlerMapping 與 RequestMappingHandlerAdapter的工作原理以及過程