SpringMVC流程及原始碼分析

前言

? 學了一遍SpringMVC以后，想著做一個總結，復習一下，復習寫下面的總結的時候才發現，其實自己學的并不徹底、牢固、也沒有學全，視頻跟書本是要結合起來一起，每一位老師的視頻可能提到的東西都不一致，也導致也不是很全面，書本上會講的筆記系統、全面，同時我自己也是一個初學者，下面總結的可能并不完善、正確，希望看到的大神給我指出，在此非常感謝，

• SpringMVC流程及原始碼分析
• 一 、Spring核心模塊
  • 1、核心模塊
  • 2、Spring版本命名規則（補充）
• 二、SpringMVC流程及原理
  • 1、執行流程
    • 1.1、執行流程
    • 1.2、執行流程說明：
      • 1.2.1、第02、03說明
      • 1.2.2、第04說明
      • 1.2.2、SpringMVC組件說明
      • 1.2.3、SpringMVC詳細流程圖
• 二、原始碼分析
  • 1、初始化
    • 1.1、ApplicationContext
  • 2、前端控制器（中央處理器）DistepcherServlet
    • 2.1、查找處理器映射器HandlerMapping
    • 2.2、根據處理器映射器HandlerMapping回傳結果呼叫處理器配接器HandlerAdapter
    • 2.3、檢查攔截器Interceptor
    • 2.3、處理器配接器HandlerAdapter執行Handler（Controller）回傳ModelAndView
    • 2.4、視圖決議器ViewResolver
    • 2.5、視圖View
      • 2.5.1、視圖物件的作用
      • 2.5.2、View介面圖
      • 2.5.3、View的實作類圖
      • 2.5.4、View的UML圖
      • 2.5.5、常用的View視圖類
    • 2.6、其他重要的點
      • 2.6.1、DispatcherServlet.properties
• 三、參考參考資料
  • 1、參考資料
  • 2、參考資料

一 、Spring核心模塊

1、核心模塊

? Spring Web MVC （下文簡稱為 SpringMVC ）是 Spring 提供 Web 應用的框架設計，屬于表現層的框架，SpringMVC是Spring框架的一部分，
Spring框架包括大致六大模塊，核心容器（Core Container）、AOP和設備支持、資料訪問及集成、Web、報文發送、Test

圖片來源于Spring官網5.0.0.M5：

? https://docs.spring.io/spring-framework/docs/5.0.0.M5/spring-framework-reference/html/overview.html#overview-modules

對于Spring5模塊圖，有2點疑問：
1、不清楚為什么在Spring官網上5.0版本以后，Release版（穩定版）的都未找到模塊圖，但是在M（里程碑版）版找到 了，如果有人在5.0以后的Release版（穩定版）找到，麻煩給我留個言，謝謝，
2、在其他博文中看到Spring5模塊結構圖是這樣的：

挺奇怪這個圖是哪里來的？（路過的大神請指點）

對于問題2，我在Spring5.2.13.RELEASE GA中，找到了如下所示資訊：

拷貝以上資訊：

Spring Framework Documentation

Version 5.2.13.RELEASE

What’s New, Upgrade Notes, Supported Versions, and other topics, independent of release cadence, are maintained externally on the project’s Github Wiki.

按照以上資訊的Web Servlet、Web Reactive已經是分屬于不同的模塊了，

• Web Servlet：Spring MVC, WebSocket, SockJS, STOMP Messaging.
• Web Reactive：Spring WebFlux, WebClient, WebSocket.

Spring官方檔案：https://spring.io/projects/spring-framework#learn/

2、Spring版本命名規則（補充）

上面提到了Spring又不同的版本，在此記錄一下各個版本的意義，

二、SpringMVC流程及原理

1、執行流程

SpringMVC執行流程圖
圖片來源：三、參考參考資料

1.1、執行流程

• 01、用戶發送出請求到前端控制器(中央處理器)DispatcherServlet進行處理，

• 02、前端控制器DispatcherServlet收到請求后，呼叫處理器映射器HandlerMapping，

• 03、處理器映射器HandlerMapping（處理器映射器）根據request請求的URL等資訊查找能夠進行處理的Handler，以及相關攔截器interceptor，并構造HandlerExecutionChain執行鏈，然后將構造好的HandlerExecutionChain執行鏈物件回傳給前端控制器DispatcherServlet，

• 04、前端控制器DispatcherServlet根據處理器映射器HandlerMapping的

• 05、處理器配接器HandlerAdapter經過適配呼叫具體的處理器（Handler/Controller），即業務中自己寫的Controller，

• 06、Controller處理完后回傳ModelAndView（springmvc的封裝物件，將model和view封裝在一起）給處理器配接器HandlerAdapter;

• 07、處理器配接器HandlerAdapter將Controller執行結果ModelAndView回傳給前端控制器DispatcherServlet，

• 08、前端控制器DispatcherServlet呼叫視圖決議器ViewReslover處理ModelAndView，

• 09、視圖決議器ViewReslover決議后根據邏輯視圖名決議成物理視圖名即具體的頁面地址，生成并回傳具體物件View（springmvc封裝物件，是一個介面），

• 10、前端控制器DispatcherServlet根據物件View進行視圖渲染,填充Model，

• 11、前端控制器DispatcherServlet向用戶回傳回應

1.2、執行流程說明：

1.2.1、第02、03說明

(1) 處理器映射器:springmvc框架中的一種物件，框架把實作了HandlerMapping介面的類都叫做映射器(多個);

(2) 處理器映射器作用:根據請求，從springmvc容器物件中獲取處理器物件(MyController controller = ctx.getBean("some")

(3) 框架把找到的處理器物件放到一個叫做處理器執行鏈(HandlerExecutionChain)的類保存

(4) HandlerExecutionchain:類中保存著
?a：處理器物件(MyController);
?b：專案中的所有的攔截器List

(5) 方法呼叫:HandlerExecutionChain mappedHandler - getHandler (processedRequest);

1.2.2、第04說明

(1) HandlerExecutionChain執行鏈找到對應的處理器映射器HandlerAdapter，
(2) 處理器配接器：springmvc框架中的物件，需要實作HandlerAdapter介面，
(3) 處理器配接器作用：執行處理器方法(呼叫MyController.doSome()得到回傳值ModelAndView )
(4) 前端控制器中呼叫配接器:HandlerAdapter ha =getHandlerAdapter (mappedHandler.getHandler());
(5) 執行處理器方法:mv= ha.handle (processedRequest, response, mappedHandler.getHandler());

第08說明：
(1) 視圖決議器：springmvc中的物件，需要實作ViewResoler介面(可以有多個)
(2) 視圖決議器作用：組成視圖完整路徑，使用前綴，后綴，并創建View物件，
(3) view是一個介面，表示視圖的，在框架中jsp,htm1不是string表示，而是使用view和他的實作類表示視圖，

InternalResourceview：視圖類，表示jsp檔案，視圖決議器會創建InternalResourceView類物件， 這個物件的里面，有一個屬性url-/WEB-INF/view/show.jsp

1.2.2、SpringMVC組件說明

• (1). 前端控制器（DispatcherServlet）：接收請求，回應結果，相當于電腦的CPU，
• (2). 處理器映射器（HandlerMapping）：根據URL去查找處理器．
• (3). 處理器（Handler）：（需要程式員去寫代碼處理邏輯的）．
• (4). 處理器配接器（HandlerAdapter）：會把處理器包裝成配接器，這樣就可以支持多種型別的處理器，類比筆記本的配接器（配接器模式的應用）．
• (5). 視圖決議器（ViewResovler）：進行視圖決議，多回傳的字串，進行處理，可以決議成對應的頁面．

1.2.3、SpringMVC詳細流程圖

綜上所述，總結下SpringMVC的詳細流程圖：

圖片來源：三、參考參考資料

二、原始碼分析

以下原始碼來源jar包：spring-webmvc-5.25.RELEASE.jar

1、初始化

1.1、ApplicationContext

? ApplicationContext初始化入口類：ApplicationObjectSupport的setApplicationContext方法，setApplicationContext方法中核心部分就是初始化容器initApplicationContext(context)，子類AbstractDetectingUrlHandlerMapping實作了該方法，
類圖：

UML圖：

? RequestMappingHandlerMapping ,用于注解@Controller,@RequestMapping來定義controller.
初始化時,3個類的大致分工如下:

• AbstractHandlerMethodMapping定義整個演算法流程;
• RequestMappingInfoHandlerMapping提供匹配條件RequestMappingInfo的決議處理;
• RequestMappingHandlerMapping根據@RequestMapping注解生成 RequestMappingInfo,同時提供isHandler實作

2、前端控制器（中央處理器）DistepcherServlet

? 從上面的流程圖可以看到前端控制器（中央處理器）DistepcherServlet是SpringMVC核心，查看DistepcherServlet類的繼承情況，
UML圖：
從繼承關系看出:
? DistepcherServlet ---> FrameworkServlet ---> HttpServletBean---> HttpServlet
? 那就說明DistepcherServlet 類也是一個Servlet類，那最終核心的方法就是service()方法，即Servlet的核心方法，
? 那就找service()方法，在DistepcherServlet中沒有servic()方法，在父類FrameworkServlet有service()方法，原始碼如下：
來源：

org.springframework.web.servlet.FrameworkServlet.service(HttpServletRequest request, HttpServletResponse response)

/**
	 * Override the parent class implementation in order to intercept PATCH requests.
	 */
	@Override
	protected void service(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		HttpMethod httpMethod = HttpMethod.resolve(request.getMethod());
		if (httpMethod == HttpMethod.PATCH || httpMethod == null) {
			processRequest(request, response);
		}
		else {
			super.service(request, response);
		}
	}

可以看到：
FrameworkServlet.service(HttpServletRequest request, HttpServletResponse response)拿到request請求，判斷當前請求是否是PATCH請求，不是的就呼叫父類的servic()方法，掉用父類中的service方法就是去呼叫該類中doPost(),doGet()方法，根據不同的請求方式然后走doPost()或者doGet()，呼叫中以doGet()為例，
FrameworkServlet類的doGet()原始碼：

/**
	 * Delegate GET requests to processRequest/doService.
	 * <p>Will also be invoked by HttpServlet's default implementation of {@code doHead},
	 * with a {@code NoBodyResponse} that just captures the content length.
	 * @see #doService
	 * @see #doHead
	 */
	@Override
	protected final void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		processRequest(request, response);
	}

? doGet()又呼叫FrameworkServlet類中的processRequest(request, response);

/**
	 * Process this request, publishing an event regardless of the outcome.
	 * <p>The actual event handling is performed by the abstract
	 * {@link #doService} template method.
	 */
	protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		long startTime = System.currentTimeMillis();
		Throwable failureCause = null;

		LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
		LocaleContext localeContext = buildLocaleContext(request);

		RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();
		ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);

		WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
		asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());

		initContextHolders(request, localeContext, requestAttributes);

		try {
			doService(request, response);
		}
		catch (ServletException | IOException ex) {
			failureCause = ex;
			throw ex;
		}
		catch (Throwable ex) {
			failureCause = ex;
			throw new NestedServletException("Request processing failed", ex);
		}

		finally {
			resetContextHolders(request, previousLocaleContext, previousAttributes);
			if (requestAttributes != null) {
				requestAttributes.requestCompleted();
			}
			logResult(request, response, failureCause, asyncManager);
			publishRequestHandledEvent(request, response, startTime, failureCause);
		}
	}

? processRequest(request, response)方法中最關鍵的又呼叫了doService(request, response)；查看FrameworkServlet類中的doService(request, response)，或者是除錯跟蹤可知，doService(request, response)由子類DispatcherServlet實作，

原始碼來源：

org.springframework.web.servlet.FrameworkServlet.doService(HttpServletRequest request, HttpServletResponse response)

/**
	 * Subclasses must implement this method to do the work of request handling,
	 * receiving a centralized callback for GET, POST, PUT and DELETE.
	 * <p>The contract is essentially the same as that for the commonly overridden
	 * {@code doGet} or {@code doPost} methods of HttpServlet.
	 * <p>This class intercepts calls to ensure that exception handling and
	 * event publication takes place.
	 * @param request current HTTP request
	 * @param response current HTTP response
	 * @throws Exception in case of any kind of processing failure
	 * @see javax.servlet.http.HttpServlet#doGet
	 * @see javax.servlet.http.HttpServlet#doPost
	 */
	protected abstract void doService(HttpServletRequest request, HttpServletResponse response)
			throws Exception;

? 查看DispatcherServlet中的doService(HttpServletRequest request, HttpServletResponse response)方法

/**
	 * Exposes the DispatcherServlet-specific request attributes and delegates to {@link #doDispatch}
	 * for the actual dispatching.
	 */
	@Override
	protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
		logRequest(request);

		// Keep a snapshot of the request attributes in case of an include,
		// to be able to restore the original attributes after the include.
		Map<String, Object> attributesSnapshot = null;
		if (WebUtils.isIncludeRequest(request)) {
			attributesSnapshot = new HashMap<>();
			Enumeration<?> attrNames = request.getAttributeNames();
			while (attrNames.hasMoreElements()) {
				String attrName = (String) attrNames.nextElement();
				if (this.cleanupAfterInclude || attrName.startsWith(DEFAULT_STRATEGIES_PREFIX)) {
					attributesSnapshot.put(attrName, request.getAttribute(attrName));
				}
			}
		}

		// Make framework objects available to handlers and view objects.
		request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
		request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
		request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
		request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource());

		if (this.flashMapManager != null) {
			FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
			if (inputFlashMap != null) {
				request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
			}
			request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
			request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);
		}

		try {
			doDispatch(request, response);
		}
		finally {
			if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
				// Restore the original attribute snapshot, in case of an include.
				if (attributesSnapshot != null) {
					restoreAttributesAfterInclude(request, attributesSnapshot);
				}
			}
		}
	}

? DispatcherServlet的doService()方法中最終呼叫doDispatch(request, response)，查看原始碼如下：
org.springframework.web.servlet.DispatcherServlet.doDispatch()

/**
	 * Process the actual dispatching to the handler.
	 * <p>The handler will be obtained by applying the servlet's HandlerMappings in order.
	 * The HandlerAdapter will be obtained by querying the servlet's installed HandlerAdapters
	 * to find the first that supports the handler class.
	 * <p>All HTTP methods are handled by this method. It's up to HandlerAdapters or handlers
	 * themselves to decide which methods are acceptable.
	 * @param request current HTTP request
	 * @param response current HTTP response
	 * @throws Exception in case of any kind of processing failure
	 */
	protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
		HttpServletRequest processedRequest = request;
		HandlerExecutionChain mappedHandler = null;
		boolean multipartRequestParsed = false;

		WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

		try {
			ModelAndView mv = null;
			Exception dispatchException = null;

			try {
				// 檔案上傳相關，判斷是不是二進制請求
				processedRequest = checkMultipart(request);
				multipartRequestParsed = (processedRequest != request);
				// 取得處理當前請求的controller,這里也稱為hanlder處理器,第一個步驟的意義就在這里體現了.這里并不是直接回傳controller,而是回傳的HandlerExecutionChain請求處理器鏈物件,該物件封裝了handler和攔截器interceptors.
				// Determine handler for the current request.
				mappedHandler = getHandler(processedRequest);
				// 如果handler為空,則回傳404
				if (mappedHandler == null) {
					noHandlerFound(processedRequest, response);
					return;
				}
				//3. 獲取處理request的處理器配接器HandlerAdapter
				// Determine handler adapter for the current request.
				HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

				// Process last-modified header, if supported by the handler.
				String method = request.getMethod();
				boolean isGet = "GET".equals(method);
				if (isGet || "HEAD".equals(method)) {
					long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
					if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
						return;
					}
				}
				//處理器配接器執行之前，檢查攔截器的方法
				if (!mappedHandler.applyPreHandle(processedRequest, response)) {
					return;
				}
				//處理器配接器根據找到，執行handler，回傳ModelAndView
				// Actually invoke the handler.
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

				if (asyncManager.isConcurrentHandlingStarted()) {
					return;
				}

				applyDefaultViewName(processedRequest, mv);
				mappedHandler.applyPostHandle(processedRequest, response, mv);
			}
			catch (Exception ex) {
				dispatchException = ex;
			}
			catch (Throwable err) {
				// As of 4.3, we're processing Errors thrown from handler methods as well,
				// making them available for @ExceptionHandler methods and other scenarios.
				dispatchException = new NestedServletException("Handler dispatch failed", err);
			}
			processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
		}
		catch (Exception ex) {
			triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
		}
		catch (Throwable err) {
			triggerAfterCompletion(processedRequest, response, mappedHandler,
					new NestedServletException("Handler processing failed", err));
		}
		finally {
			if (asyncManager.isConcurrentHandlingStarted()) {
				// Instead of postHandle and afterCompletion
				if (mappedHandler != null) {
					mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
				}
			}
			else {
				// Clean up any resources used by a multipart request.
				if (multipartRequestParsed) {
					cleanupMultipart(processedRequest);
				}
			}
		}
	}

? 可以看出doDispatch()就是SpringMVC的核心代碼了，分析doDispatch()：

2.1、查找處理器映射器HandlerMapping

? 首先看下處理器映射器HandlerMapping類圖：

doDispatch()關鍵代碼：

HandlerExecutionChain mappedHandler = null;

mappedHandler = getHandler(processedRequest);

? mappedHandler是一個執行鏈HandlerExecutionChain 物件，這里封裝了handler和攔截器interceptors，getHandler(processedRequest)方法就是從處理器映射器HandlerMapping中找到url和controller的對應關系，并回傳給前端控制器DispatchServlet，
查看getHandler(processedRequest);原始碼：

/**
	 * Return the HandlerExecutionChain for this request.
	 * <p>Tries all handler mappings in order.
	 * @param request current HTTP request
	 * @return the HandlerExecutionChain, or {@code null} if no handler could be found
	 */
	@Nullable
	protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
		if (this.handlerMappings != null) {
			for (HandlerMapping mapping : this.handlerMappings) {
				HandlerExecutionChain handler = mapping.getHandler(request);
				if (handler != null) {
					return handler;
				}
			}
		}
		return null;
	}

除錯代碼如下：

從代碼除錯中可以看到handlerMapping中有三個物件：

this.handlerMappings = {ArrayList@4662}  size = 3
 0 = {BeanNameUrlHandlerMapping@4791} 
 1 = {RequestMappingHandlerMapping@4792} 
 2 = {RouterFunctionMapping@4793} 

• BeanNameUrlHandlerMapping：初始化時會將urlpath做映射存盤（xml）；

• RequestMappingHandlerMapping：初始化時會將Controller中配置@RequestMapping注解的方法做映射存盤（注解）；

• RouterFunctionMapping：
  （這個物件不是太理解）
  這也就是為什么要去HandlerMapping找一個Handler了，因為處理器映射器HandlerMapping有不同的實作：

• 1、xml方式

• 2、注解方式

接著看getHandler(HttpServletRequest request)方法，先遍歷HandlerMappers，查找控制器找到之后就回傳執行鏈HandlerExecutionChain型別的Handler，

可以看到回傳的Handler中，拿到的就是我們自己編碼的Controller類，以及攔截器（演示專案中未撰寫，所以除錯匯總回傳的Handler最后是0 interceptors）
HandlerExecutionChain with [com.bjpowernode.controller.MyController#doSome()] and 0 interceptors

將正在除錯的idea打開自己撰寫的Controller來對照，發現一致：

2.2、根據處理器映射器HandlerMapping回傳結果呼叫處理器配接器HandlerAdapter

doDispatch()里面的關鍵代碼：

HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

原始碼如下：

/**
	 * Return the HandlerAdapter for this handler object.
	 * @param handler the handler object to find an adapter for
	 * @throws ServletException if no HandlerAdapter can be found for the handler. This is a fatal error.
	 */
	protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
		if (this.handlerAdapters != null) {
			for (HandlerAdapter adapter : this.handlerAdapters) {
				if (adapter.supports(handler)) {
					return adapter;
				}
			}
		}
		throw new ServletException("No adapter for handler [" + handler +
				"]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
	}

為什么還要獲取處理器配接器HandlerAdapter：與獲取處理器映射器HandlerMapping一樣，Spring提供了不通的處理器配接器，
除錯如下：

查看DEBUG除錯模式中getHandlerAdapter（）方法在中的：
handler、adapter、this.handlerAdapters

以下是拷貝的結果：
handler

handler = {HandlerMethod@4792} "com.bjpowernode.controller.MyController#doSome()"
 logger = {LogAdapter$JavaUtilLog@4858} 
 bean = {MyController@4859} 
 beanFactory = {DefaultListableBeanFactory@4847} "org.springframework.beans.factory.support.DefaultListableBeanFactory@56b5a4c3: defining beans [myController,org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.context.event.internalEventListenerProcessor,org.springframework.context.event.internalEventListenerFactory,org.springframework.web.servlet.view.InternalResourceViewResolver#0]; root of factory hierarchy"
 beanType = {Class@3782} "class com.bjpowernode.controller.MyController"
 method = {Method@4860} "public org.springframework.web.servlet.ModelAndView com.bjpowernode.controller.MyController.doSome()"
 bridgedMethod = {Method@4860} "public org.springframework.web.servlet.ModelAndView com.bjpowernode.controller.MyController.doSome()"
 parameters = {MethodParameter[0]@4861} 
 responseStatus = null
 responseStatusReason = null
 resolvedFromHandlerMethod = {HandlerMethod@4863} "com.bjpowernode.controller.MyController#doSome()"
 interfaceParameterAnnotations = null
 description = "com.bjpowernode.controller.MyController#doSome()"

adapter

adapter = {RequestMappingHandlerAdapter@4827} 
 customArgumentResolvers = null
 argumentResolvers = {HandlerMethodArgumentResolverComposite@4833} 
 initBinderArgumentResolvers = {HandlerMethodArgumentResolverComposite@4834} 
 customReturnValueHandlers = null
 returnValueHandlers = {HandlerMethodReturnValueHandlerComposite@4835} 
 modelAndViewResolvers = null
 contentNegotiationManager = {ContentNegotiationManager@4836} 
 messageConverters = {ArrayList@4837}  size = 4
 requestResponseBodyAdvice = {ArrayList@4838}  size = 0
 webBindingInitializer = null
 taskExecutor = {SimpleAsyncTaskExecutor@4839} 
 asyncRequestTimeout = null
 callableInterceptors = {CallableProcessingInterceptor[0]@4840} 
 deferredResultInterceptors = {DeferredResultProcessingInterceptor[0]@4842} 
 reactiveAdapterRegistry = {ReactiveAdapterRegistry@4844} 
 ignoreDefaultModelOnRedirect = false
 cacheSecondsForSessionAttributeHandlers = 0
 synchronizeOnSession = false
 sessionAttributeStore = {DefaultSessionAttributeStore@4845} 
 parameterNameDiscoverer = {DefaultParameterNameDiscoverer@4846} 
 beanFactory = {DefaultListableBeanFactory@4847} "org.springframework.beans.factory.support.DefaultListableBeanFactory@56b5a4c3: defining beans [myController,org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.context.event.internalEventListenerProcessor,org.springframework.context.event.internalEventListenerFactory,org.springframework.web.servlet.view.InternalResourceViewResolver#0]; root of factory hierarchy"
 sessionAttributesHandlerCache = {ConcurrentHashMap@4848}  size = 0
 initBinderCache = {ConcurrentHashMap@4849}  size = 0
 initBinderAdviceCache = {LinkedHashMap@4850}  size = 0
 modelAttributeCache = {ConcurrentHashMap@4851}  size = 0
 modelAttributeAdviceCache = {LinkedHashMap@4852}  size = 0
 order = 2147483647
 supportedMethods = null
 allowHeader = "GET,HEAD,POST,PUT,PATCH,DELETE,OPTIONS"
 requireSession = false
 cacheControl = null
 cacheSeconds = -1
 varyByRequestHeaders = null
 useExpiresHeader = false
 useCacheControlHeader = true
 useCacheControlNoStore = true
 alwaysMustRevalidate = false
 servletContext = {ApplicationContextFacade@4754} 
 logger = {LogAdapter$JavaUtilLog@4854} 
 applicationContext = {XmlWebApplicationContext@4665} "WebApplicationContext for namespace 'myweb-servlet', started on Tue Mar 02 23:25:35 CST 2021"
 messageSourceAccessor = {MessageSourceAccessor@4855} 

this.handlerAdapters

this.handlerAdapters = {ArrayList@4658}  size = 4
 0 = {HttpRequestHandlerAdapter@4810} 
 1 = {SimpleControllerHandlerAdapter@4820} //XML方式
 2 = {RequestMappingHandlerAdapter@4827} //注解方式
 3 = {HandlerFunctionAdapter@4832} 

可以看到找到4個處理器配接器，通過DEBUG模式可以看到，此次取到的處理器配接器HandlerAdapter是：RequestMappingHandlerAdapter

ha = {RequestMappingHandlerAdapter@4827} 

2.3、檢查攔截器Interceptor

doDispatch()中的關鍵代碼：

if (!mappedHandler.applyPreHandle(processedRequest, response)) {
					return;
				}
org.springframework.web.servlet.HandlerExecutionChain#applyPreHandle

applyPreHandle(processedRequest, response)原始碼：

/**
	 * Apply preHandle methods of registered interceptors.
	 * @return {@code true} if the execution chain should proceed with the
	 * next interceptor or the handler itself. Else, DispatcherServlet assumes
	 * that this interceptor has already dealt with the response itself.
	 */
	boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
		HandlerInterceptor[] interceptors = getInterceptors();
		if (!ObjectUtils.isEmpty(interceptors)) {
			for (int i = 0; i < interceptors.length; i++) {
				HandlerInterceptor interceptor = interceptors[i];
				if (!interceptor.preHandle(request, response, this.handler)) {
					triggerAfterCompletion(request, response, null);
					return false;
				}
				this.interceptorIndex = i;
			}
		}
		return true;
	}

2.3、處理器配接器HandlerAdapter執行Handler（Controller）回傳ModelAndView

doDispatch()中的關鍵代碼：

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

DEBUG模式除錯，是跳到了：
org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter#handle
原始碼如下：

/**
	 * This implementation expects the handler to be an {@link HandlerMethod}.
	 */
	@Override
	@Nullable
	public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
			throws Exception {

		return handleInternal(request, response, (HandlerMethod) handler);
	}

再往下看handleInternal(request, response, (HandlerMethod) handler)方法，
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter#handleInternal

@Override
	protected ModelAndView handleInternal(HttpServletRequest request,
			HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

		ModelAndView mav;
		checkRequest(request);

		// 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) {
					mav = invokeHandlerMethod(request, response, handlerMethod);
				}
			}
			else {
				// No HttpSession available -> no mutex necessary
				mav = invokeHandlerMethod(request, response, handlerMethod);
			}
		}
		else {
			// No synchronization on session demanded at all...
			mav = invokeHandlerMethod(request, response, handlerMethod);
		}

		if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
			if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
				applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
			}
			else {
				prepareResponse(response);
			}
		}

		return mav;
	}

注意，handleInternal(request, response, (HandlerMethod) handler)方法的回傳值是ModelAndView ，這里就完成了處理器配接器HandlerAdapter執行Handler（Controller）并將結果ModelAndView回傳給前端控制器DistepchServlet

2.4、視圖決議器ViewResolver

??接上2.3：前端控制器DistepchServlet接收到處理器配接器HandlerAdapter回傳的ModelAndView以后，這里分2種情況：

• (1)、如果ModelAndView里面是邏輯視圖
  前端控制器DistepchServlet呼叫視圖決議器ViewResolver通過邏輯視圖查找真正的視圖物件View，并回傳給前端控制器DistepchServlet，
• (2)、如果ModelAndView里面是非邏輯視圖：
  如：MappingJackson2JsonView（把當前資料轉為為JSON資料，并不需要對視圖邏輯名稱進行轉換）

總結一下：
視圖決議器ViewResolver介面主要作用是決議前端控制器DispatcherServlet傳遞的邏輯視圖名，并將決議結果的真正的視圖物件View傳回給前端控制器DispatcherServlet

ViewResolverd的實作類：

ViewResolver的UML:

2.5、視圖View

2.5.1、視圖物件的作用

• (1)、將控制器回傳的資料處理渲染，最侄訓傳客戶端展示給用戶，主要就是完成轉發或者是重定向的操作.，
• (2)、為了實作視圖模型和具體實作技術的解耦（指的是Spring在org.springframework.web.servlet包中定義的抽象View介面），詳見2.5.2View介面圖，
• (3)、視圖物件View由視圖決議器負責實體化，由于視圖是無狀態（每一次請求都會創建一個新的view物件）的，所以不會有執行緒安全的問題.

2.5.2、View介面圖

2.5.3、View的實作類圖

2.5.4、View的UML圖

.png)

2.5.5、常用的View視圖類

2.6、其他重要的點

2.6.1、DispatcherServlet.properties

DispatcherServlet.properties檔案是在SpringMVC架包中：

DispatcherServlet.properties內容：

# Default implementation classes for DispatcherServlet's strategy interfaces.
# Used as fallback when no matching beans are found in the DispatcherServlet context.
# Not meant to be customized by application developers.

org.springframework.web.servlet.LocaleResolver=
	org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver

org.springframework.web.servlet.ThemeResolver=
	org.springframework.web.servlet.theme.FixedThemeResolver

org.springframework.web.servlet.HandlerMapping=
	org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\
	org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping,\
	org.springframework.web.servlet.function.support.RouterFunctionMapping

org.springframework.web.servlet.HandlerAdapter=
	org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\
	org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\
	org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter,\
	org.springframework.web.servlet.function.support.HandlerFunctionAdapter


org.springframework.web.servlet.HandlerExceptionResolver=
	org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver,\
	org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,\
	org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver

org.springframework.web.servlet.RequestToViewNameTranslator=
	org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator

org.springframework.web.servlet.ViewResolver=
	org.springframework.web.servlet.view.InternalResourceViewResolver

org.springframework.web.servlet.FlashMapManager=
	org.springframework.web.servlet.support.SessionFlashMapManager

SpringMVC為什么能加載不同處理器映射器HandlerMapping、處理器配接器handlerAdapter，就是因為框架配置了這個DispatcherServlet.properties檔案，

三、參考參考資料

1、參考資料

• SpringMVC流程圖參考地址：https://www.iqiyi.com/w_19s2gmyazh.html

• SpringMVC流程圖參考地址2：https://blog.csdn.net/win7system/article/details/90674757

• View視圖作用參考地址：https://blog.csdn.net/qq_43193797/article/details/84928603

• Spring官方檔案：https://spring.io/projects/spring-framework#learn/

  在寫此文的時候可能還有少部分是參考了其他資料，但是整理的時候我已經找不到原文出處了，如果原文作者看到，請及時聯系我，我在文章中加上參考出處，謝謝！

2、參考資料

• 參考：w3cschool-Spring MVC 4.2.4.RELEASE 中文檔案：

  https://www.w3cschool.cn/spring_mvc_documentation_linesh_translation/

• 參考：https://www.cnblogs.com/leftthen/category/790002.html

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轉載宣告:

? 寫博客不易，請尊重原作者！！

? 歡迎大家閱讀、轉載，如果是整文轉載請在文章開頭或者結尾處 注明 原文地址、作者，如果是大段參考請 備注 參考鏈接，

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