简析SpringMVC源码

先从容器初始化开始看。
直接看干货代码，就不一个一个挨着看了，我觉得也没必要，看主要的就行了，看多了也记不住。
看FrameworkServlet->initServletBean方法

	@Override
	protected final void initServletBean() throws ServletException {
		getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");
		if (this.logger.isInfoEnabled()) {
			this.logger.info("FrameworkServlet '" + getServletName() + "': initialization started");
		}
		long startTime = System.currentTimeMillis();

		try {
		//看这个方法 初始化web上下文
			this.webApplicationContext = initWebApplicationContext();
			initFrameworkServlet();
		}
		
		if (this.logger.isInfoEnabled()) {
			long elapsedTime = System.currentTimeMillis() - startTime;
			this.logger.info("FrameworkServlet '" + getServletName() + "': initialization completed in " +
					elapsedTime + " ms");
		}
	}

protected WebApplicationContext initWebApplicationContext() {
//得到父容器，也相当于SpringIOC容器
		WebApplicationContext rootContext =
				WebApplicationContextUtils.getWebApplicationContext(getServletContext());
		WebApplicationContext wac = null;

		if (this.webApplicationContext != null) {
			// A context instance was injected at construction time -> use it
			wac = this.webApplicationContext;
			if (wac instanceof ConfigurableWebApplicationContext) {
				ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
				if (!cwac.isActive()) {
					if (cwac.getParent() == null) {
						//设置为当前容器的父容器
						cwac.setParent(rootContext);
					}
				
					configureAndRefreshWebApplicationContext(cwac);
				}
			}
		}
		if (wac == null) {
			wac = findWebApplicationContext();
		}
		if (wac == null) {
			wac = createWebApplicationContext(rootContext);
		}

		if (!this.refreshEventReceived) {
			//下面看这个方法
			onRefresh(wac);
		}

		if (this.publishContext) {
			String attrName = getServletContextAttributeName();
			getServletContext().setAttribute(attrName, wac);
		}

		return wac;
	}

	

上面的onRefresh方法，最终调用的是DispatcherServlet ->initStrategies方法

protected void initStrategies(ApplicationContext context) {
		initMultipartResolver(context);
		initLocaleResolver(context);
		initThemeResolver(context);
		initHandlerMappings(context);
		initHandlerAdapters(context);
		initHandlerExceptionResolvers(context);
		initRequestToViewNameTranslator(context);
		initViewResolvers(context);
		initFlashMapManager(context);
	}

说明容器启动的时候，初始化了很多的bean，比如我们看initHandlerMapping的源码

private void initHandlerMappings(ApplicationContext context) {
		this.handlerMappings = null;

		if (this.detectAllHandlerMappings) {
			// Find all HandlerMappings in the ApplicationContext, including ancestor contexts.
			Map<String, HandlerMapping> matchingBeans =
					BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
			if (!matchingBeans.isEmpty()) {
				this.handlerMappings = new ArrayList<HandlerMapping>(matchingBeans.values());
				// We keep HandlerMappings in sorted order.
				AnnotationAwareOrderComparator.sort(this.handlerMappings);
			}
		}
		else {
			try {
			//从上下文中取出HandlerMapping这个bean,设置到DispatcherServlet属性中
				HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class);
				this.handlerMappings = Collections.singletonList(hm);
			}
			catch (NoSuchBeanDefinitionException ex) {
				// Ignore, we'll add a default HandlerMapping later.
			}
		}

		// Ensure we have at least one HandlerMapping, by registering
		// a default HandlerMapping if no other mappings are found.
		if (this.handlerMappings == null) {
			this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
			if (logger.isDebugEnabled()) {
				logger.debug("No HandlerMappings found in servlet '" + getServletName() + "': using default");
			}
		}
	}

下面我们看看RequestMappingHandlerMapping ->afterPropertiesSet方法

@Override
	public void afterPropertiesSet() {
		this.config = new RequestMappingInfo.BuilderConfiguration();
		this.config.setPathHelper(getUrlPathHelper());
		this.config.setPathMatcher(getPathMatcher());
		this.config.setSuffixPatternMatch(this.useSuffixPatternMatch);
		this.config.setTrailingSlashMatch(this.useTrailingSlashMatch);
		this.config.setRegisteredSuffixPatternMatch(this.useRegisteredSuffixPatternMatch);
		this.config.setContentNegotiationManager(getContentNegotiationManager());

		super.afterPropertiesSet();
	}

为bean设置了很多属性（实现了InitializingBean接口，在bean初始时，会调用afterPropertiesSet方法）

下面我们看具体有请求来时，SpringMVC怎么处理的
看DispatcherServlet的doDispatch方法

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 {
			//检查媒体类型
				processedRequest = checkMultipart(request);
				multipartRequestParsed = (processedRequest != request);

				// Determine handler for the current request.
				//通过请求获取HandlerExecutionChain
				mappedHandler = getHandler(processedRequest);
				if (mappedHandler == null || mappedHandler.getHandler() == null) {
					noHandlerFound(processedRequest, response);
					return;
				}

				// Determine handler adapter for the current request.
				//通过handler获取到HandlerAdapter 
				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 (logger.isDebugEnabled()) {
						logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
					}
					if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
						return;
					}
				}
			//如果有实现HandlerInterceptor接口，会执行preHandler方法
			//返回false，就直接return了
				if (!mappedHandler.applyPreHandle(processedRequest, response)) {
					return;
				}

				// Actually invoke the handler.
				//执行具体的handler方法，也就是具体的Controller里的方法
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

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

				applyDefaultViewName(processedRequest, mv);
				//直接HandlerInterceptor postHadler方法
				mappedHandler.applyPostHandle(processedRequest, response, mv);
			}
			catch (Exception ex) {
				dispatchException = ex;
			}
			//处理返回，里面 会调用HandlerInterceptor -》afterCompletion方法
			processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
		}
		catch (Exception ex) {
			triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
		}
		catch (Error err) {
			triggerAfterCompletionWithError(processedRequest, response, mappedHandler, 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);
				}
			}
		}
	}

通过请求URL是怎么知道具体的处理器的？
在启动时，会解析注解保存：
1.匹配被@Controller和@RequestMapping注解的类
2.找到Handler类中的方法Method，也就是Controller类中的方法
3.建立集合Map<Method,RequestMappingInfo>映射（Method:方法，RequestMappingInfo：@RequestMapping）
4.便利Map，建立新的映射关系：URL和RequestMappingInfo关系；RequestMappingInfo和HandlerMethod对象映射。

有请求来是：
1.从请求中解析出URL
2.根据URL从URL和RequestMappingInfo关系map中找到RequestMappingInfo（会有多个RequestMappingInfo，比如@GetMapping(“user”),@PutMapping(“user”)url是一样的，但是对应两个RequestMapping）
3.根据多个RequestMappingInfo和Request匹配(匹配Request请求方法)，得到合适的RequestMappingInfo
4.根据RequestMappingInfo去RequestMappingInfo和HandlerMethod对象映射中得到HandlerMethod，这个对象就对应一个唯一的Controller中的方法，也就是我们的Handler
5.后面就是通过Handler得到HandlerAdater，由HandlerAdater调用Handler方法，将结果返回给DispatcherServlet。

描述的不是很清晰，后面细化一下。