SpringMVC源码分析

//org.springframework.web.servlet.DispatcherServlet
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
		HttpServletRequest processedRequest = request;
		//执行器链，包含了handler和一些拦截器
		HandlerExecutionChain mappedHandler = null;
		boolean multipartRequestParsed = false;
		//异步管理器
		WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

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

			try {
				//1. 检查是否是文件上传的请求
				processedRequest = checkMultipart(request);
				multipartRequestParsed = (processedRequest != request);

				// Determine handler for the current request.
				/*
					2. 取得处理当前请求的Controller，这里也称为Handler，即处理器。这里并不是直接返回controller，
					而是返回HandlerExecutionChain  请求处理链对象 该对象封装了Handler和Inteceptor
				 */
				mappedHandler = getHandler(processedRequest);
				if (mappedHandler == null) {
					// 如果handler为空， 则返回404
					noHandlerFound(processedRequest, response);
					return;
				}

				// Determine handler adapter for the current request.
				// 3. 获取处理请求的处理器适配器 HandlerAdapter
				HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

				// Process last-modified header, if supported by the handler.
				// 处理last-modeified 请求头
				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;
					}
				}
				//===============拦截器的第一个拦截时机
				if (!mappedHandler.applyPreHandle(processedRequest, response)) {
					return;
				}

				// Actually invoke the handler.
				// 4 实际处理器处理请求，返回结果视图对象
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

				if (asyncManager.isConcurrentHandlingStarted()) {
					return;
				}
				//结果视图对象的处理
				applyDefaultViewName(processedRequest, mv);

				//==============拦截器的第二个拦截时机
				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);
			}
			//跳转视图页面，渲染视图
			processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
		}
		catch (Exception ex) {
			//最终会调用HandlerInterceptor的afterCompletion方法
			//========拦截器的第三个拦截时机————视图页面渲染完成之后拦截
			triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
		}
		catch (Throwable err) {
			//最终会调用HandlerInterceptor的afterCompletion方法
			//========拦截器的第三个拦截时机————视图页面渲染完成之后拦截
			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);
				}
			}
		}
	}

	@Nullable
	protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
        //handlerMappings是一个 ArrayList ———— List<HandlerMapping> handlerMappings
        //而HandlerMapping 则存储了url和handler的映射关系
		if (this.handlerMappings != null) {
            /**
			 * 遍历 handlerMappings ：
			 * 	1. BeanNameUrlHandlerMapping ，早期的一种使用方式
			 * 	2. RequestMappingHandlerMapping，我们的请求所使用的
			 */
			for (HandlerMapping mapping : this.handlerMappings) {
				HandlerExecutionChain handler = mapping.getHandler(request);
				if (handler != null) {
					return handler;
				}
			}
		}
		return null;
	}

	protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
        //List<HandlerAdapter> handlerAdapters
		if (this.handlerAdapters != null) {
            /*
				遍历 handlerAdapters：
				遍历各个HandlerAdapter，看哪个Adapter⽀持处理当前Handler：
				handlerAdapters是一个List<HandlerAdapter>，HandlerAdapter是一个接口，里面有几个实现类:
				1. HttpRequestHandlerAdapter ——实现接口的方式
				2. SimpleControllerHandlerAdapter ——实现Controller接口的方式
				3. RequestMappingHandlerAdapter ——是不是HandlerMethod（RequestMappingHandlerMapping封装的）的实例
			 */
			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");
	}

//org.springframework.web.servlet.DispatcherServlet	
	
//多部件解析器，文件上传之类的
@Nullable
private MultipartResolver multipartResolver;

//区域化 国际化解析器
@Nullable
private LocaleResolver localeResolver;

//主题解析器
@Nullable
private ThemeResolver themeResolver;

//处理器映射器组件
@Nullable
private List<HandlerMapping> handlerMappings;

//处理器适配器组件
@Nullable
private List<HandlerAdapter> handlerAdapters;

//异常解析器
@Nullable
private List<HandlerExceptionResolver> handlerExceptionResolvers;

//默认视图名转换器组件
@Nullable
private RequestToViewNameTranslator viewNameTranslator;

//flash属性管理组件
@Nullable
private FlashMapManager flashMapManager;

//视图解析器
@Nullable
private List<ViewResolver> viewResolvers;

//org.springframework.web.servlet.DispatcherServlet

//主要完成组件的初始化
@Override
protected void onRefresh(ApplicationContext context) {
	//初始化策略
	initStrategies(context);
}

protected void initStrategies(ApplicationContext context) {
   // 多文件上传的组件
   initMultipartResolver(context);
   // 初始化本地语语言环境
   initLocaleResolver(context);
   // 初始化模板处理器
   initThemeResolver(context);
   // 初始化HandlerMapping
   initHandlerMappings(context);
   // 初始化参数适配器
   initHandlerAdapters(context);
   // 初始化异常拦截器
   initHandlerExceptionResolvers(context);
   // 初始化视图预处理器
   initRequestToViewNameTranslator(context);
   // 初始化视图转换器
   initViewResolvers(context);
   // 初始化FlashMap 管理器
   initFlashMapManager(context);
}

//org.springframework.web.servlet.DispatcherServlet#doDispatch

// 4 实际处理器处理请求，返回结果视图对象
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

//跳转视图页面，渲染视图
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);