瀑布式DEBUG Spring MVC源码

阅读本文章大概需要8分钟左右。相信会让你对Spring MVC的理解更加深刻，更上一层楼。

SpringMVC图解

粒度很粗的图解

粒度比较粗的图解

粒度一般的图解

FrameworkServlet

FrameworkServlet是Spring MVC框架中的基本Servlet，集成提供了Spring应用的上下文。通过读取我们在web.xml中配置的ContextConfigLocation、ContextLoaderListener、ContextClass属性注入上下文。子类必须重写doService()方法去处理请求。

假如我们要请求http://localhost:8081/order/detail?orderId=1,由于我们的请求方式是GET，会进入到doGet()方法。实际上这个方法会把请求委托给processRequest()和doService()处理。

/**
	 * 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);
	}

在processRequest()方法中，会处理这个请求，并且不管结果如何，都会发布一个请求事件。实际上处理请求是子类DispatcherServlet的doService()方法完成的。

/**
	 * 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 ex) {
			failureCause = ex;
			throw ex;
		}
		catch (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();
			}

			if (logger.isDebugEnabled()) {
				if (failureCause != null) {
					this.logger.debug("Could not complete request", failureCause);
				}
				else {
					if (asyncManager.isConcurrentHandlingStarted()) {
						logger.debug("Leaving response open for concurrent processing");
					}
					else {
						this.logger.debug("Successfully completed request");
					}
				}
			}

			publishRequestHandledEvent(request, response, startTime, failureCause);
		}
	}

DispatcherServlet

DispatcherServlet就是一个前端控制器，集中提供请求处理机制。将url映射到指定的Controller处理，Controller处理完毕后将ModelAndView返回给DispatcherServlet，DispatcherServlet通过viewResovler进行视图解析，然后将model填充到view，响应给用户。

doService()方法会将判断该请求是不是包含请求。如果是包含请求，会将request对象的参数进行快照，以便在包含后恢复这些属性。这些属性分别是

javax.servlet.include.request_uri
javax.servlet.include.context_path
javax.servlet.include.servlet_path
javax.servlet.include.path_info
javax.servlet.include.query_string

接着将Spring MVC框架的全局对象注入到request对象中，让handler和view对象可用。接着调用doDispatch()方法

protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
		if (logger.isDebugEnabled()) {
			String resumed = WebAsyncUtils.getAsyncManager(request).hasConcurrentResult() ? " resumed" : "";
			logger.debug("DispatcherServlet with name '" + getServletName() + "'" + resumed +
					" processing " + request.getMethod() + " request for [" + getRequestUri(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<String, Object>();
			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());

		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);
				}
			}
		}
	}

doDispatch()这个方法很核心，把请求调度给真正的handler去处理。

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 {
				processedRequest = checkMultipart(request);
				multipartRequestParsed = (processedRequest != request);

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

				// 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 (logger.isDebugEnabled()) {
						logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
					}
					if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
						return;
					}
				}

				if (!mappedHandler.applyPreHandle(processedRequest, response)) {
					return;
				}

				// 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);
				}
			}
		}
	}

checkMultipart(request)判断这个请求是否是Multipart，比如文件上传就是Multipart请求。如果是Multipart请求就交给multipartResolver处理，如果不是Multipart返回当前的请求。

protected HttpServletRequest checkMultipart(HttpServletRequest request) throws MultipartException {
		if (this.multipartResolver != null && this.multipartResolver.isMultipart(request)) {
			if (WebUtils.getNativeRequest(request, MultipartHttpServletRequest.class) != null) {
				logger.debug("Request is already a MultipartHttpServletRequest - if not in a forward, " +
						"this typically results from an additional MultipartFilter in web.xml");
			}
			else if (hasMultipartException(request) ) {
				logger.debug("Multipart resolution failed for current request before - " +
						"skipping re-resolution for undisturbed error rendering");
			}
			else {
				try {
					return this.multipartResolver.resolveMultipart(request);
				}
				catch (MultipartException ex) {
					if (request.getAttribute(WebUtils.ERROR_EXCEPTION_ATTRIBUTE) != null) {
						logger.debug("Multipart resolution failed for error dispatch", ex);
						// Keep processing error dispatch with regular request handle below
					}
					else {
						throw ex;
					}
				}
			}
		}
		// If not returned before: return original request.
		return request;
	}

multipartRequestParsed = (processedRequest != request)判断处理后的请求是否和处理前的请求一致。如果不一致，multipartRequestParsed标志为true，代表这个请求已经被multipartResolver处理过了。

// Determine handler for the current request.
				mappedHandler = getHandler(processedRequest);

在getHandler(processedRequest)里面通过遍历所有的handlerMapping，调用handlerMapping对象中的getHandler(request)方法获得HandlerExecutionChain对象。实际上这里的handlerMapping对象是RequestMappingHandlerMapping对象。

protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
		for (HandlerMapping hm : this.handlerMappings) {
			if (logger.isTraceEnabled()) {
				logger.trace(
						"Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'");
			}
			HandlerExecutionChain handler = hm.getHandler(request);
			if (handler != null) {
				return handler;
			}
		}
		return null;
	}

进入到AbstractHandlerMapping中的getHandler(request)，一看究竟。handler是通过getHandlerInternal(request)获得的。

/**
	 * Look up a handler for the given request, falling back to the default
	 * handler if no specific one is found.
	 * @param request current HTTP request
	 * @return the corresponding handler instance, or the default handler
	 * @see #getHandlerInternal
	 */
	@Override
	public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
		Object handler = getHandlerInternal(request);
		if (handler == null) {
			handler = getDefaultHandler();
		}
		if (handler == null) {
			return null;
		}
		// Bean name or resolved handler?
		if (handler instanceof String) {
			String handlerName = (String) handler;
			handler = getApplicationContext().getBean(handlerName);
		}

		HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
		if (CorsUtils.isCorsRequest(request)) {
			CorsConfiguration globalConfig = this.globalCorsConfigSource.getCorsConfiguration(request);
			CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
			CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);
			executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
		}
		return executionChain;
	}

进入到AbstractHandlerMethodMapping中的getHandlerInternal(request)方法，先从request对象获取当前要查询的lookupPath。

@Override
	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();
		}
	}

这里的mappingRegistry说白了就是一个映射关系注册中心，里面维护了所有mapping到处理程序handlerMethod的映射关系，以便查找和提供并发访问。所以每次通过访问显式获得锁，访问结束后要显式释放锁。

/**
	 * A registry that maintains all mappings to handler methods, exposing methods
	 * to perform lookups and providing concurrent access.
	 *
	 * <p>Package-private for testing purposes.
	 */
	class MappingRegistry {

		private final Map<T, MappingRegistration<T>> registry = new HashMap<T, MappingRegistration<T>>();

		private final Map<T, HandlerMethod> mappingLookup = new LinkedHashMap<T, HandlerMethod>();

		private final MultiValueMap<String, T> urlLookup = new LinkedMultiValueMap<String, T>();

		private final Map<String, List<HandlerMethod>> nameLookup =
				new ConcurrentHashMap<String, List<HandlerMethod>>();

		private final Map<HandlerMethod, CorsConfiguration> corsLookup =
				new ConcurrentHashMap<HandlerMethod, CorsConfiguration>();

		private final ReentrantReadWriteLock readWriteLock = new ReentrantReadWriteLock();

		/**
		 * Return all mappings and handler methods. Not thread-safe.
		 * @see #acquireReadLock()
		 */
		public Map<T, HandlerMethod> getMappings() {
			return this.mappingLookup;
		}

		/**
		 * Return matches for the given URL path. Not thread-safe.
		 * @see #acquireReadLock()
		 */
		public List<T> getMappingsByUrl(String urlPath) {
			return this.urlLookup.get(urlPath);
		}

		/**
		 * Return handler methods by mapping name. Thread-safe for concurrent use.
		 */
		public List<HandlerMethod> getHandlerMethodsByMappingName(String mappingName) {
			return this.nameLookup.get(mappingName);
		}

		/**
		 * Return CORS configuration. Thread-safe for concurrent use.
		 */
		public CorsConfiguration getCorsConfiguration(HandlerMethod handlerMethod) {
			HandlerMethod original = handlerMethod.getResolvedFromHandlerMethod();
			return this.corsLookup.get(original != null ? original : handlerMethod);
		}

		/**
		 * Acquire the read lock when using getMappings and getMappingsByUrl.
		 */
		public void acquireReadLock() {
			this.readWriteLock.readLock().lock();
		}

		/**
		 * Release the read lock after using getMappings and getMappingsByUrl.
		 */
		public void releaseReadLock() {
			this.readWriteLock.readLock().unlock();
		}

		public void register(T mapping, Object handler, Method method) {
			this.readWriteLock.writeLock().lock();
			try {
				HandlerMethod handlerMethod = createHandlerMethod(handler, method);
				assertUniqueMethodMapping(handlerMethod, mapping);

				if (logger.isInfoEnabled()) {
					logger.info("Mapped /"" + mapping + "/" onto " + handlerMethod);
				}
				this.mappingLookup.put(mapping, handlerMethod);

				List<String> directUrls = getDirectUrls(mapping);
				for (String url : directUrls) {
					this.urlLookup.add(url, mapping);
				}

				String name = null;
				if (getNamingStrategy() != null) {
					name = getNamingStrategy().getName(handlerMethod, mapping);
					addMappingName(name, handlerMethod);
				}

				CorsConfiguration corsConfig = initCorsConfiguration(handler, method, mapping);
				if (corsConfig != null) {
					this.corsLookup.put(handlerMethod, corsConfig);
				}

				this.registry.put(mapping, new MappingRegistration<T>(mapping, handlerMethod, directUrls, name));
			}
			finally {
				this.readWriteLock.writeLock().unlock();
			}
		}

		private void assertUniqueMethodMapping(HandlerMethod newHandlerMethod, T mapping) {
			HandlerMethod handlerMethod = this.mappingLookup.get(mapping);
			if (handlerMethod != null && !handlerMethod.equals(newHandlerMethod)) {
				throw new IllegalStateException(
						"Ambiguous mapping. Cannot map '" +	newHandlerMethod.getBean() + "' method /n" +
						newHandlerMethod + "/nto " + mapping + ": There is already '" +
						handlerMethod.getBean() + "' bean method/n" + handlerMethod + " mapped.");
			}
		}

		private List<String> getDirectUrls(T mapping) {
			List<String> urls = new ArrayList<String>(1);
			for (String path : getMappingPathPatterns(mapping)) {
				if (!getPathMatcher().isPattern(path)) {
					urls.add(path);
				}
			}
			return urls;
		}

		private void addMappingName(String name, HandlerMethod handlerMethod) {
			List<HandlerMethod> oldList = this.nameLookup.get(name);
			if (oldList == null) {
				oldList = Collections.<HandlerMethod>emptyList();
			}

			for (HandlerMethod current : oldList) {
				if (handlerMethod.equals(current)) {
					return;
				}
			}

			if (logger.isTraceEnabled()) {
				logger.trace("Mapping name '" + name + "'");
			}

			List<HandlerMethod> newList = new ArrayList<HandlerMethod>(oldList.size() + 1);
			newList.addAll(oldList);
			newList.add(handlerMethod);
			this.nameLookup.put(name, newList);

			if (newList.size() > 1) {
				if (logger.isTraceEnabled()) {
					logger.trace("Mapping name clash for handlerMethods " + newList +
							". Consider assigning explicit names.");
				}
			}
		}

		public void unregister(T mapping) {
			this.readWriteLock.writeLock().lock();
			try {
				MappingRegistration<T> definition = this.registry.remove(mapping);
				if (definition == null) {
					return;
				}

				this.mappingLookup.remove(definition.getMapping());

				for (String url : definition.getDirectUrls()) {
					List<T> list = this.urlLookup.get(url);
					if (list != null) {
						list.remove(definition.getMapping());
						if (list.isEmpty()) {
							this.urlLookup.remove(url);
						}
					}
				}

				removeMappingName(definition);

				this.corsLookup.remove(definition.getHandlerMethod());
			}
			finally {
				this.readWriteLock.writeLock().unlock();
			}
		}

		private void removeMappingName(MappingRegistration<T> definition) {
			String name = definition.getMappingName();
			if (name == null) {
				return;
			}
			HandlerMethod handlerMethod = definition.getHandlerMethod();
			List<HandlerMethod> oldList = this.nameLookup.get(name);
			if (oldList == null) {
				return;
			}
			if (oldList.size() <= 1) {
				this.nameLookup.remove(name);
				return;
			}
			List<HandlerMethod> newList = new ArrayList<HandlerMethod>(oldList.size() - 1);
			for (HandlerMethod current : oldList) {
				if (!current.equals(handlerMethod)) {
					newList.add(current);
				}
			}
			this.nameLookup.put(name, newList);
		}
	}

我们继续回到AbstractHandlerMethodMapping中的getHandlerInternal(request)方法中，通过调用this.mappingRegistry.acquireReadLock()方法申请获得mapping注册中心中的读锁。

this.mappingRegistry.acquireReadLock();

HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);

接着调用lookupHandlerMethod(lookupPath, request)，通过url匹配的方式获得合适的hanlderMethod。

/**
	 * Look up the best-matching handler method for the current request.
	 * If multiple matches are found, the best match is selected.
	 * @param lookupPath mapping lookup path within the current servlet mapping
	 * @param request the current request
	 * @return the best-matching handler method, or {@code null} if no match
	 * @see #handleMatch(Object, String, HttpServletRequest)
	 * @see #handleNoMatch(Set, String, HttpServletRequest)
	 */
	protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
		List<Match> matches = new ArrayList<Match>();
                //通过lookupPath，在this.urlLookup.get(urlPath)获取List<RequestMappingInfo>集合
		List<T> directPathMatches = this.mappingRegistry.getMappingsByUrl(lookupPath);
		if (directPathMatches != null) {
			addMatchingMappings(directPathMatches, matches, request);
		}
		if (matches.isEmpty()) {
			// No choice but to go through all mappings...
			addMatchingMappings(this.mappingRegistry.getMappings().keySet(), matches, request);
		}

		if (!matches.isEmpty()) {
			Comparator<Match> comparator = new MatchComparator(getMappingComparator(request));
			Collections.sort(matches, comparator);
			if (logger.isTraceEnabled()) {
				logger.trace("Found " + matches.size() + " matching mapping(s) for [" +
						lookupPath + "] : " + matches);
			}
			Match bestMatch = matches.get(0);
			if (matches.size() > 1) {
				if (CorsUtils.isPreFlightRequest(request)) {
					return PREFLIGHT_AMBIGUOUS_MATCH;
				}
				Match secondBestMatch = matches.get(1);
				if (comparator.compare(bestMatch, secondBestMatch) == 0) {
					Method m1 = bestMatch.handlerMethod.getMethod();
					Method m2 = secondBestMatch.handlerMethod.getMethod();
					throw new IllegalStateException("Ambiguous handler methods mapped for HTTP path '" +
							request.getRequestURL() + "': {" + m1 + ", " + m2 + "}");
				}
			}
			handleMatch(bestMatch.mapping, lookupPath, request);
			return bestMatch.handlerMethod;
		}
		else {
			return handleNoMatch(this.mappingRegistry.getMappings().keySet(), lookupPath, request);
		}
	}

我们可以关注List directPathMatches = this.mappingRegistry.getMappingsByUrl(lookupPath);这个方法实际上是从mappingRegistry中的urlLookup获得List集合. urlLookup的结构是Map<K, List>， K是url, List对应着RequestMappingInfo，实际上每一个RequestMapping最后都会被封装成RequestMappingInfo.

我们可以看到directPathMatches不为空，会调用addMatchingMappings(directPathMatches, matches, request)，我们仔细关注T match = getMatchingMapping(mapping, request)这一行代码。

private void addMatchingMappings(Collection<T> mappings, List<Match> matches, HttpServletRequest request) {
		for (T mapping : mappings) {
			T match = getMatchingMapping(mapping, request);
			if (match != null) {
				matches.add(new Match(match, this.mappingRegistry.getMappings().get(mapping)));
			}
		}
	}

当前请求的url和RequestMappingInfo中的PatternsRequestCondition对象中的url集合中是否匹配，如果匹配成功，返回一个新的RequestMappingInfo。

/**
	 * Checks if all conditions in this request mapping info match the provided request and returns
	 * a potentially new request mapping info with conditions tailored to the current request.
	 * <p>For example the returned instance may contain the subset of URL patterns that match to
	 * the current request, sorted with best matching patterns on top.
	 * @return a new instance in case all conditions match; or {@code null} otherwise
	 */
	@Override
	public RequestMappingInfo getMatchingCondition(HttpServletRequest request) {
		RequestMethodsRequestCondition methods = this.methodsCondition.getMatchingCondition(request);
		ParamsRequestCondition params = this.paramsCondition.getMatchingCondition(request);
		HeadersRequestCondition headers = this.headersCondition.getMatchingCondition(request);
		ConsumesRequestCondition consumes = this.consumesCondition.getMatchingCondition(request);
		ProducesRequestCondition produces = this.producesCondition.getMatchingCondition(request);

		if (methods == null || params == null || headers == null || consumes == null || produces == null) {
			return null;
		}

		PatternsRequestCondition patterns = this.patternsCondition.getMatchingCondition(request);
		if (patterns == null) {
			return null;
		}

		RequestConditionHolder custom = this.customConditionHolder.getMatchingCondition(request);
		if (custom == null) {
			return null;
		}

		return new RequestMappingInfo(this.name, patterns,
				methods, params, headers, consumes, produces, custom.getCondition());
	}

接着关注matches.add(new Match(match, this.mappingRegistry.getMappings().get(mapping)));这一行代码，Match是AbstractHandlerMethodMapping的内部类，this.mappingRegistry.getMappings()是获取映射注册中心的mappingLookup对象，其结构为Map<RequestMappingInfo, HandlerMethod>。

/**
	 * A thin wrapper around a matched HandlerMethod and its mapping, for the purpose of
	 * comparing the best match with a comparator in the context of the current request.
	 */
	private class Match {

		private final T mapping;

		private final HandlerMethod handlerMethod;

		public Match(T mapping, HandlerMethod handlerMethod) {
			this.mapping = mapping;
			this.handlerMethod = handlerMethod;
		}

		@Override
		public String toString() {
			return this.mapping.toString();
		}
	}

回到AbstractHandlerMethodMapping中的lookupHandlerMethod(String lookupPath, HttpServletRequest request)方法，如果matches为空，则遍历mappingRegistry中的mappingLookup集合，并且填充到matches。最后通过排序比较，获得matches集合中的第一个Match对象，此对象也是最匹配的，返回Match对象中的handlerMethod。

if (matches.isEmpty()) {
			// No choice but to go through all mappings...
			addMatchingMappings(this.mappingRegistry.getMappings().keySet(), matches, request);
		}

回到AbstractHandlerMethodMapping中的getHandlerInternal(HttpServletRequest request)方法，如果获得的handlerMethod不为空，调用createWithResolvedBean()方法。其中的逻辑是如果当前handlerMethod中的bean只是bean的名称而不是真正的bean实例时，那么通过名称获得bean的实例。并且返回一个新的HandlerMethod。这里的bean是handlerMethd所属于的类。比如UserController中有一个login()方法，bean就是UserController，login就是HandlerMethod。最后释放mappingRegistry的读锁。

return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);

/**
	 * If the provided instance contains a bean name rather than an object instance,
	 * the bean name is resolved before a {@link HandlerMethod} is created and returned.
	 */
	public HandlerMethod createWithResolvedBean() {
		Object handler = this.bean;
		if (this.bean instanceof String) {
			String beanName = (String) this.bean;
			handler = this.beanFactory.getBean(beanName);
		}
		return new HandlerMethod(this, handler);
	}

回到AbstractHandlerMapping中的getHandler(HttpServletRequest request)方法，接着调用 getHandlerExecutionChain(handler, request)，遍历所有的handlerInterceptor，把handler和handlerInterceptor(拦截器)封装成handlerExecutionChain(处理程序链)。还有一点就是MappedInterceptor里面有includePatterns和excludePatterns属性。通过这2个属性，设置需要被拦截的url和不需要被拦截的url。

/**
	 * Build a {@link HandlerExecutionChain} for the given handler, including
	 * applicable interceptors.
	 * <p>The default implementation builds a standard {@link HandlerExecutionChain}
	 * with the given handler, the handler mapping's common interceptors, and any
	 * {@link MappedInterceptor}s matching to the current request URL. Interceptors
	 * are added in the order they were registered. Subclasses may override this
	 * in order to extend/rearrange the list of interceptors.
	 * <p><b>NOTE:</b> The passed-in handler object may be a raw handler or a
	 * pre-built {@link HandlerExecutionChain}. This method should handle those
	 * two cases explicitly, either building a new {@link HandlerExecutionChain}
	 * or extending the existing chain.
	 * <p>For simply adding an interceptor in a custom subclass, consider calling
	 * {@code super.getHandlerExecutionChain(handler, request)} and invoking
	 * {@link HandlerExecutionChain#addInterceptor} on the returned chain object.
	 * @param handler the resolved handler instance (never {@code null})
	 * @param request current HTTP request
	 * @return the HandlerExecutionChain (never {@code null})
	 * @see #getAdaptedInterceptors()
	 */
	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;
	}

返回到AbstractHandlerMapping中的getHandler(request)中，我们已经获取到executionChain对象，可以返回该对象。

HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);

返回到DispatcherServlet中的getHandler(HttpServletRequest request)返回当前request请求中的executionChain对象

HandlerExecutionChain handler = hm.getHandler(request);

我们继续回到DispatchServlet中的doDispatcher()方法，如果当前handlerExecutionChain(处理程序执行链)等于空或者handlerExecutionChain中的handlerMethod为空的话，就会抛出著名的NoHandlerFoundException异常

if (mappedHandler == null || mappedHandler.getHandler() == null) {
					noHandlerFound(processedRequest, response);
					return;
				}

如果你不信，可以点开noHandlerFound(processedRequest, response);

/**
	 * No handler found -> set appropriate HTTP response status.
	 * @param request current HTTP request
	 * @param response current HTTP response
	 * @throws Exception if preparing the response failed
	 */
	protected void noHandlerFound(HttpServletRequest request, HttpServletResponse response) throws Exception {
		if (pageNotFoundLogger.isWarnEnabled()) {
			pageNotFoundLogger.warn("No mapping found for HTTP request with URI [" + getRequestUri(request) +
					"] in DispatcherServlet with name '" + getServletName() + "'");
		}
		if (this.throwExceptionIfNoHandlerFound) {
			throw new NoHandlerFoundException(request.getMethod(), getRequestUri(request),
					new ServletServerHttpRequest(request).getHeaders());
		}
		else {
			response.sendError(HttpServletResponse.SC_NOT_FOUND);
		}
	}

接着看，我要从当前请求获取能够支持当前handlerMethod的适配器。

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

点开代码看看，看看细节。主要是循环当前所有的handlerAdapters，通过supports()判断是否支持当前handlerMethod，这种循环比对思想在Spring MVC源码随处可见。

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");
	}

进入到AbstractHandlerMethodAdapter中的supports()方法，通过判断当前handler对象是否是HandlerMethod类的实例和是否支持当前handlerMethod。

/**
	 * This implementation expects the handler to be an {@link HandlerMethod}.
	 * @param handler the handler instance to check
	 * @return whether or not this adapter can adapt the given handler
	 */
	@Override
	public final boolean supports(Object handler) {
		return (handler instanceof HandlerMethod && supportsInternal((HandlerMethod) handler));
	}

点开，进入到RequestMappingHandlerAdapter中的supportsInternal(),恍然大悟。这个方法总是返回true，因为任何方法的参数和返回值都以某种方式处理

/**
	 * Always return {@code true} since any method argument and return value
	 * type will be processed in some way. A method argument not recognized
	 * by any HandlerMethodArgumentResolver is interpreted as a request parameter
	 * if it is a simple type, or as a model attribute otherwise. A return value
	 * not recognized by any HandlerMethodReturnValueHandler will be interpreted
	 * as a model attribute.
	 */
	@Override
	protected boolean supportsInternal(HandlerMethod handlerMethod) {
		return true;
	}

判断request的请求方式，如果是GET或者是HEAD，用户当前请求上一次请求的时间戳，通过checkNotModified()判断是否修改过。如果没有修改过，返回状态码304。

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handlerExecutionChain中的拦截器preHandle返回false，就不会调用postHandle()，直接清理资源，然后返回。

if (!mappedHandler.applyPreHandle(processedRequest, response)) {
					return;
				}

进入HandlerExecutionChain中的applyPreHandle(processedRequest, response)方法。遍历HandlerExecutionChain中的所有拦截器,如果拦截器中的preHandle(request, response, this.handler)返回false，那么直接调用triggerAfterCompletion(request, response, null)进行资源清理，返回false。通过记录interceptorIndex来标志当前执行的拦截器。

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;

triggerAfterCompletion()方法，也是大同小异。遍历所有拦截器，调用拦截器中清理资源的方法afterCompletion()。

void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, Exception ex)
			throws Exception {

		HandlerInterceptor[] interceptors = getInterceptors();
		if (!ObjectUtils.isEmpty(interceptors)) {
			for (int i = this.interceptorIndex; i >= 0; i--) {
				HandlerInterceptor interceptor = interceptors[i];
				try {
					interceptor.afterCompletion(request, response, this.handler, ex);
				}
				catch (Throwable ex2) {
					logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
				}
			}
		}
	}

小高潮来了，handlerAdapter（处理程序适配器)开始调用handlerMethod(处理程序)的功能方法。

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

进入到AbstractHandlerMethodAdapter中的handle()方法

@Override
	public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
			throws Exception {

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

进入RequestMappingHandlerAdapter中的handleInternal()方法，我们可以仔细看看这个方法做了什么。

@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) {
                        //获取session，如果为空直接返回null
			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;
	}

通过调用WebContentGenerator中的checkRequest()方法，判断支持的请求方式是否包含当前请求的方式，如果supportedMethods不为空且不支持当前请求方式，会抛出著名的HttpRequestMetohdNotSupportedException。如果需要session且从当前请求获得不到session，同样抛出HttpSessionRequiredException异常。

/**
	 * Check the given request for supported methods and a required session, if any.
	 * @param request current HTTP request
	 * @throws ServletException if the request cannot be handled because a check failed
	 * @since 4.2
	 */
	protected final void checkRequest(HttpServletRequest request) throws ServletException {
		// Check whether we should support the request method.
		String method = request.getMethod();
		if (this.supportedMethods != null && !this.supportedMethods.contains(method)) {
			throw new HttpRequestMethodNotSupportedException(method, this.supportedMethods);
		}

		// Check whether a session is required.
		if (this.requireSession && request.getSession(false) == null) {
			throw new HttpSessionRequiredException("Pre-existing session required but none found");
		}
	}

通过synchronizeOnSession标识符，判断调用invokeHandlerMethod是否需要同步机制。 然后调用invokeHandlerMethod()

mav = invokeHandlerMethod(request, response, handlerMethod);

进入到RequestMappingHandlerAdapter中的invokeHandlerMethod()中，首先RequestMappingHandlerAdapter支持{@link #setCustomArgumentResolvers}和{@link #setCustomReturnValueHandlers}配置自定义参数和自定义返回值，也支持来配置{@link #setArgumentResolvers}和{@link #setReturnValueHandlers}所有参数和返回值。

HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

		ServletWebRequest webRequest = new ServletWebRequest(request, response);
		try {
			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);
		}
		finally {
			webRequest.requestCompleted();
		}
	}

创建WebDataBinderFactory实例，用于创建WebDataBinder对象，用于web参数绑定。

WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);

比如我们现在有一个需求，从前台传来的日期字符串，我们要全部解析成Date类型的。一般有3种方式解决：PropertyEditor、Formatter、Converter去解决。最常见的做法实现WebBindingInitializer接口，通过WebDataBinder注册属性编辑器。

/**
 * WebBindingInitializer
 */
public class WebBindingInitializer implements org.springframework.web.bind.support.WebBindingInitializer {

    /* (non-Javadoc)
     * @see org.springframework.web.bind.support.WebBindingInitializer#initBinder(org.springframework.web.bind.WebDataBinder, org.springframework.web.context.request.WebRequest)
     */
    @Override
    public void initBinder(WebDataBinder binder, WebRequest request) {
        binder.registerCustomEditor(String.class, new DatePropertyEditor());
    }

}

回到正轨，看一下是怎么创建WebDataBinderFactory实例。

private WebDataBinderFactory getDataBinderFactory(HandlerMethod handlerMethod) throws Exception {
		Class<?> handlerType = handlerMethod.getBeanType();
		Set<Method> methods = this.initBinderCache.get(handlerType);
		if (methods == null) {
			methods = MethodIntrospector.selectMethods(handlerType, INIT_BINDER_METHODS);
			this.initBinderCache.put(handlerType, methods);
		}
		List<InvocableHandlerMethod> initBinderMethods = new ArrayList<InvocableHandlerMethod>();
		// Global methods first
		for (Entry<ControllerAdviceBean, Set<Method>> entry : this.initBinderAdviceCache.entrySet()) {
			if (entry.getKey().isApplicableToBeanType(handlerType)) {
				Object bean = entry.getKey().resolveBean();
				for (Method method : entry.getValue()) {
					initBinderMethods.add(createInitBinderMethod(bean, method));
				}
			}
		}
		for (Method method : methods) {
			Object bean = handlerMethod.getBean();
			initBinderMethods.add(createInitBinderMethod(bean, method));
		}
		return createDataBinderFactory(initBinderMethods);
	}

获得handlerMethod所在类的类型。通过所在类的类型获得从initBinderCache缓存中获得当前类所有的方法。这些方法应该是被@InitBinder注解的方法。

private final Map<Class<?>, Set<Method>> initBinderCache = new ConcurrentHashMap<Class<?>, Set<Method>>(64);

如果methods等于空，那么我们去获得当前类下被@InitBinder注解的方法，并放入到initBinderCache缓存中。

if (methods == null) {
			methods = MethodIntrospector.selectMethods(handlerType, INIT_BINDER_METHODS);
			this.initBinderCache.put(handlerType, methods);
		}

优先遍历被@ControllerAdvice注解全局类中的方法，再遍历被@Controller注解的类的方法。通过createInitBinderMethod(bean, method)方法创建InvocableHandlerMethod对象(用于参数准备，准备当中会用到WebDataBinderFactory创建WebDataBinder实例进行参数转换解析绑定，方法调用)，并且放入到initBinderMethods集合中。

// Global methods first
		for (Entry<ControllerAdviceBean, Set<Method>> entry : this.initBinderAdviceCache.entrySet()) {
			if (entry.getKey().isApplicableToBeanType(handlerType)) {
				Object bean = entry.getKey().resolveBean();
				for (Method method : entry.getValue()) {
					initBinderMethods.add(createInitBinderMethod(bean, method));
				}
			}
		}
		for (Method method : methods) {
			Object bean = handlerMethod.getBean();
			initBinderMethods.add(createInitBinderMethod(bean, method));
		}

创建InvocableHandlerMethod对象，注入initBinderArgumentResolvers属性、parameterNameDiscoverer(属性名字发现器)、DefaultDataBinderFactory实例。我们发现要创建一个DefaultDataBinderFactory必须要传入webBindingInitializer。

private InvocableHandlerMethod createInitBinderMethod(Object bean, Method method) {
		InvocableHandlerMethod binderMethod = new InvocableHandlerMethod(bean, method);
		binderMethod.setHandlerMethodArgumentResolvers(this.initBinderArgumentResolvers);
		binderMethod.setDataBinderFactory(new DefaultDataBinderFactory(this.webBindingInitializer));
		binderMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);
		return binderMethod;
	}

最后调用createDataBinderFactory(initBinderMethods)方法创建ServletRequestDataBinderFactory实例，同样也要传入webBindingInitializer。ServletRequestDataBinderFactory是InitBinderDataBinderFactory的子类。

createDataBinderFactory(initBinderMethods);

	protected InitBinderDataBinderFactory createDataBinderFactory(List<InvocableHandlerMethod> binderMethods)
			throws Exception {

		return new ServletRequestDataBinderFactory(binderMethods, getWebBindingInitializer());
	}

接着创建出ModelFactory实例，我们首先要搞清楚ModelFactory是干啥的。ModelFactory作用是在控制器方法调用前初始化Model模型，调用后对Model模型进行更新。在初始化时，通过调用被@ModelAttribute注解的方法，Model模型会在会话中被临时存储的属性填充。

ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);

我们再来看是如何创建ModelFactory实例的，其实和创建WebDataBinderFactory的逻辑差不多。首先获取sessionAttributesHandler对象,同样这个对象是从sessionAttributesHandlerCache缓存获得到的。key是handlerMethod所在类的类型。如果sessionAttributesHandler没有从缓存中获取到，那么锁住缓存，再从缓存中取一遍。如果sessionAttributesHandler还为空的话，那么自己通过new SessionAttributesHandler(handlerType, sessionAttributeStore)创建一个默认的sessionAttributesHandler对象，并放入到缓存中。这种思想是享元设计模式。

/**
	 * Return the {@link SessionAttributesHandler} instance for the given handler type
	 * (never {@code null}).
	 */
	private SessionAttributesHandler getSessionAttributesHandler(HandlerMethod handlerMethod) {
		Class<?> handlerType = handlerMethod.getBeanType();
		SessionAttributesHandler sessionAttrHandler = this.sessionAttributesHandlerCache.get(handlerType);
		if (sessionAttrHandler == null) {
			synchronized (this.sessionAttributesHandlerCache) {
				sessionAttrHandler = this.sessionAttributesHandlerCache.get(handlerType);
				if (sessionAttrHandler == null) {
					sessionAttrHandler = new SessionAttributesHandler(handlerType, sessionAttributeStore);
					this.sessionAttributesHandlerCache.put(handlerType, sessionAttrHandler);
				}
			}
		}
		return sessionAttrHandler;
	}

创建SessionAttributesHandler过程

/**
	 * Create a new instance for a controller type. Session attribute names and
	 * types are extracted from the {@code @SessionAttributes} annotation, if
	 * present, on the given type.
	 * @param handlerType the controller type
	 * @param sessionAttributeStore used for session access
	 */
	public SessionAttributesHandler(Class<?> handlerType, SessionAttributeStore sessionAttributeStore) {
		Assert.notNull(sessionAttributeStore, "SessionAttributeStore may not be null");
		this.sessionAttributeStore = sessionAttributeStore;

		SessionAttributes annotation =
				AnnotatedElementUtils.findMergedAnnotation(handlerType, SessionAttributes.class);
		if (annotation != null) {
			this.attributeNames.addAll(Arrays.asList(annotation.names()));
			this.attributeTypes.addAll(Arrays.asList(annotation.types()));
		}
		this.knownAttributeNames.addAll(this.attributeNames);
	}

接着通过modelAttributeCache中获取handlerMethod所在类中所有被@ModelAttribute注解且没有被@RequestMapping注解的方法。如果没有从缓存中查找到，那么通过 MethodIntrospector.selectMethods(handlerType, MODEL_ATTRIBUTE_METHODS)查找，并加入到modelAttributeCache缓存中。

private ModelFactory getModelFactory(HandlerMethod handlerMethod, WebDataBinderFactory binderFactory) {
		SessionAttributesHandler sessionAttrHandler = getSessionAttributesHandler(handlerMethod);
		Class<?> handlerType = handlerMethod.getBeanType();
		Set<Method> methods = this.modelAttributeCache.get(handlerType);
		if (methods == null) {
			methods = MethodIntrospector.selectMethods(handlerType, MODEL_ATTRIBUTE_METHODS);
			this.modelAttributeCache.put(handlerType, methods);
		}
		List<InvocableHandlerMethod> attrMethods = new ArrayList<InvocableHandlerMethod>();
		// Global methods first
		for (Entry<ControllerAdviceBean, Set<Method>> entry : this.modelAttributeAdviceCache.entrySet()) {
			if (entry.getKey().isApplicableToBeanType(handlerType)) {
				Object bean = entry.getKey().resolveBean();
				for (Method method : entry.getValue()) {
					attrMethods.add(createModelAttributeMethod(binderFactory, bean, method));
				}
			}
		}
		for (Method method : methods) {
			Object bean = handlerMethod.getBean();
			attrMethods.add(createModelAttributeMethod(binderFactory, bean, method));
		}
		return new ModelFactory(attrMethods, binderFactory, sessionAttrHandler);
	}

接着老操作，通过createModelAttributeMethod(binderFactory, bean, method)方法创建InvocableHandlerMethod对象，并放入到attrMethods集合中。

private InvocableHandlerMethod createModelAttributeMethod(WebDataBinderFactory factory, Object bean, Method method) {
		InvocableHandlerMethod attrMethod = new InvocableHandlerMethod(bean, method);
		attrMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
		attrMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);
		attrMethod.setDataBinderFactory(factory);
		return attrMethod;
	}

终于到了new ModelFactory()这一步。通过handlerMethods集合、WebDataBinderFactory实例，SessionAttributesHandler实例创建出ModelFactory实例。

public ModelFactory(List<InvocableHandlerMethod> handlerMethods,
			WebDataBinderFactory binderFactory, SessionAttributesHandler attributeHandler) {

		if (handlerMethods != null) {
			for (InvocableHandlerMethod handlerMethod : handlerMethods) {
				this.modelMethods.add(new ModelMethod(handlerMethod));
			}
		}
		this.dataBinderFactory = binderFactory;
		this.sessionAttributesHandler = attributeHandler;
	}

既然binderFactory、modelFactory都被我们造出来了，那肯定要干正紧事情了。对handlerMethod进行下一步包装，填充argumentResolvers(HandlerMethodArgumentResolverComposite)、returnValueHandlers(HandlerMethodReturnValueHandlerComposite)、binderFactory、parameterNameDiscoverer属性包装成ServletInvocableHandlerMethod。ServletInvocableHandlerMethod的作用对处理程序的返回值进行处理和ResponseStatus处理。

ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
			invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
			invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
			invocableMethod.setDataBinderFactory(binderFactory);
			invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);

实例化ModelAndViewContainer容器，把request里面的属性名为"org.springframework.web.servlet.DispatcherServlet.INPUT_FLASH_MAP"的重定向参数注入到容器中的model模型中。FlashMap的作用是在redirect中传递参数。重定向是会生成新的request，那么传递参数就不能直接用request进行传递。

ModelAndViewContainer mavContainer = new ModelAndViewContainer();
			mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
			modelFactory.initModel(webRequest, mavContainer, invocableMethod);
			mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);

我们关注到initModel(webRequest, mavCOntainer, invocableMethod)这一行，它到底干了什么事情。首先从request中获取检索@SessionAttribute中名称的属性，以Map<String, Object>的结构存储起来，并且放入到ModelAndViewContainer容器的model中。

public void initModel(NativeWebRequest request, ModelAndViewContainer container,
			HandlerMethod handlerMethod) throws Exception {

		Map<String, ?> sessionAttributes = this.sessionAttributesHandler.retrieveAttributes(request);
		container.mergeAttributes(sessionAttributes);
		invokeModelAttributeMethods(request, container);

		for (String name : findSessionAttributeArguments(handlerMethod)) {
			if (!container.containsAttribute(name)) {
				Object value = this.sessionAttributesHandler.retrieveAttribute(request, name);
				if (value == null) {
					throw new HttpSessionRequiredException("Expected session attribute '" + name + "'", name);
				}
				container.addAttribute(name, value);
			}
		}
	}

接着调用invokeModelAttributeMethods(request, container)方法，将被@ModelAttribute注解的handlerMethod中的模型填充到ModelAndViewContainer容器中的model。只有当容器中不包含当前@ModelAtrribute中的属性时才添加该属性至容器。同时还要判断当前@ModelAttribute中的属性能不能添加到容器中，如果不能，那么放到容器中的bindingDisabledAttributes进行标记。然后提前调用被@ModelAttribute注解的handlerMethod，只有handlerMethod的返回值类型是void，才能将进行数据绑定(也就是绑定到容器中的model里)。如果handlerMethod的返回类不是void，那太好了可以进行数据绑定。数据绑定的规则是如果@ModelAttribute注解设置value和name属性了，优先选择value和name属性作为model中的key，如果没有设置value和name属性，选择被@ModelAttribute注解的handlerMethod的返回类型名称(首字母小写)作为model中的key。

private void invokeModelAttributeMethods(NativeWebRequest request, ModelAndViewContainer container)
			throws Exception {

		while (!this.modelMethods.isEmpty()) {
			InvocableHandlerMethod modelMethod = getNextModelMethod(container).getHandlerMethod();
			ModelAttribute ann = modelMethod.getMethodAnnotation(ModelAttribute.class);
			if (container.containsAttribute(ann.name())) {
				if (!ann.binding()) {
					container.setBindingDisabled(ann.name());
				}
				continue;
			}

			Object returnValue = modelMethod.invokeForRequest(request, container);
			if (!modelMethod.isVoid()){
				String returnValueName = getNameForReturnValue(returnValue, modelMethod.getReturnType());
				if (!ann.binding()) {
					container.setBindingDisabled(returnValueName);
				}
				if (!container.containsAttribute(returnValueName)) {
					container.addAttribute(returnValueName, returnValue);
				}
			}
		}
	}

说的通俗点，如果被@ModelAttribute注解的handlerMethod返回类型是Collection或者是数组类型，那么填充到model中的key就是方法返回类型名称(首字母小写)再拼接上List。看下面例子，key就是stringList

@ModelAttribute
    public List<String> baseTest1() {
        List<String> list = new ArrayList<>();
        list.add("1");
        return list;
    }

    @ModelAttribute
    public String[] baseTest2() {
        String[] strings = new String[1];
        strings[0] = "1";
        return strings;
    }

如果返回类型是String或者是Map，那么key就是string、map

@ModelAttribute
    public String baseTest() {
        return "1";
    }

    @ModelAttribute
    public Map<String, String> baseTest3() {
        Map<String, String> map = new HashMap<>();
        map.put("username", "password");
        return map;
    }

为什么会是这样呢，可以看到ModelFactory中的getNameForReturnType()，首先判断@ModelAttribute注解value属性是不是为空。如果不为空，取value属性的值。如果为空，进行Conventions.getVariableNameForReturnType(method, resolvedType, returnValue)操作。

public static String getNameForReturnValue(Object returnValue, MethodParameter returnType) {
		ModelAttribute ann = returnType.getMethodAnnotation(ModelAttribute.class);
		if (ann != null && StringUtils.hasText(ann.value())) {
			return ann.value();
		}
		else {
			Method method = returnType.getMethod();
			Class<?> containingClass = returnType.getContainingClass();
			Class<?> resolvedType = GenericTypeResolver.resolveReturnType(method, containingClass);
			return Conventions.getVariableNameForReturnType(method, resolvedType, returnValue);
		}
	}

看到getVariableNameForReturnType()，心中的疑惑应该解开了把。如果返回类型是Object类型，我们会通过返回值来得出它实际返回类型，再通过实际返回类型推出所在类的简称，再进行格式化返回其短名称(也就是首字母小写，也可以说小驼峰)。如果返回类型是Array类型或者是Collection类型，就在其返回基础上再拼接"List"字符串。

public static String getVariableNameForReturnType(Method method, Class<?> resolvedType, Object value) {
		Assert.notNull(method, "Method must not be null");

		if (Object.class == resolvedType) {
			if (value == null) {
				throw new IllegalArgumentException("Cannot generate variable name for an Object return type with null value");
			}
			return getVariableName(value);
		}

		Class<?> valueClass;
		boolean pluralize = false;

		if (resolvedType.isArray()) {
			valueClass = resolvedType.getComponentType();
			pluralize = true;
		}
		else if (Collection.class.isAssignableFrom(resolvedType)) {
			valueClass = ResolvableType.forMethodReturnType(method).asCollection().resolveGeneric();
			if (valueClass == null) {
				if (!(value instanceof Collection)) {
					throw new IllegalArgumentException(
							"Cannot generate variable name for non-typed Collection return type and a non-Collection value");
				}
				Collection<?> collection = (Collection<?>) value;
				if (collection.isEmpty()) {
					throw new IllegalArgumentException(
							"Cannot generate variable name for non-typed Collection return type and an empty Collection value");
				}
				Object valueToCheck = peekAhead(collection);
				valueClass = getClassForValue(valueToCheck);
			}
			pluralize = true;
		}
		else {
			valueClass = resolvedType;
		}

		String name = ClassUtils.getShortNameAsProperty(valueClass);
		return (pluralize ? pluralize(name) : name);
	}

    private static final String PLURAL_SUFFIX = "List";

	private static String pluralize(String name) {
		return name + PLURAL_SUFFIX;
	}

回到ModelFactory中的initModel()上，把目光集中到下面这行代码上。

for (String name : findSessionAttributeArguments(handlerMethod)) {
			if (!container.containsAttribute(name)) {
				Object value = this.sessionAttributesHandler.retrieveAttribute(request, name);
				if (value == null) {
					throw new HttpSessionRequiredException("Expected session attribute '" + name + "'", name);
				}
				container.addAttribute(name, value);
			}
		}

遍历HandlerMethod的参数，判断参数是否被@ModelAttribute注解，如果有，继续判断这个参数和参数类型是否和当前handlerMethod所在类中的@SessionAttributes注解中的参数和类型是否保持一致。

/**
	 * Find {@code @ModelAttribute} arguments also listed as {@code @SessionAttributes}.
	 */
	private List<String> findSessionAttributeArguments(HandlerMethod handlerMethod) {
		List<String> result = new ArrayList<String>();
		for (MethodParameter parameter : handlerMethod.getMethodParameters()) {
			if (parameter.hasParameterAnnotation(ModelAttribute.class)) {
				String name = getNameForParameter(parameter);
				Class<?> paramType = parameter.getParameterType();
				if (this.sessionAttributesHandler.isHandlerSessionAttribute(name, paramType)) {
					result.add(name);
				}
			}
		}
		return result;
	}

/**
	 * Whether the attribute name or type match the names and types specified
	 * via {@code @SessionAttributes} on the underlying controller.
	 * <p>Attributes successfully resolved through this method are "remembered"
	 * and subsequently used in {@link #retrieveAttributes(WebRequest)} and
	 * {@link #cleanupAttributes(WebRequest)}.
	 * @param attributeName the attribute name to check
	 * @param attributeType the type for the attribute
	 */
	public boolean isHandlerSessionAttribute(String attributeName, Class<?> attributeType) {
		Assert.notNull(attributeName, "Attribute name must not be null");
		if (this.attributeNames.contains(attributeName) || this.attributeTypes.contains(attributeType)) {
			this.knownAttributeNames.add(attributeName);
			return true;
		}
		else {
			return false;
		}
	}

通过findSessionAttributeArguments(handlerMethod)方法，我们得到了合适的参数名称集合。遍历这个集合，我们要判断ModelAndViewContainer容器中是否存在相同名称的参数。如果不存在，我们从sessionAttributeStore根据名称中获得这个参数的值，最后将参数绑定到容器中。

for (String name : findSessionAttributeArguments(handlerMethod)) {
            if (!container.containsAttribute(name)) {
                Object value = this.sessionAttributesHandler.retrieveAttribute(request, name);
                if (value == null) {
                    throw new HttpSessionRequiredException("Expected session attribute '" + name + "'", name);
                }
                container.addAttribute(name, value);
            }
        }

设置ModelAndViewContainer容器使用defaultModel(默认模型)，而不是redirectModel(重定向模型)。

mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);

   //ModelAndViewContainer类中的方法
	public ModelMap getModel() {
		if (useDefaultModel()) {
			return this.defaultModel;
		}
		else {
			if (this.redirectModel == null) {
				this.redirectModel = new ModelMap();
			}
			return this.redirectModel;
		}
	}

	private boolean useDefaultModel() {
		return (!this.redirectModelScenario || (this.redirectModel == null && !this.ignoreDefaultModelOnRedirect));
	}

处理一些异步请求。

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);
			}

接着invocableMethod去调用invokeAndHandle这个方法。invokeAndHandle是ServletInvocableHandlerMethod中的方法。

invocableMethod.invokeAndHandle(webRequest, mavContainer);
			if (asyncManager.isConcurrentHandlingStarted()) {
				return null;
			}

			return getModelAndView(mavContainer, modelFactory, webRequest);

ServletInvocableMethod中的invokeAndHandle()其实是间接调用handlerMethod，然后处理handlerMethod的返回值。

/**
	 * Invoke the method and handle the return value through one of the
	 * configured {@link HandlerMethodReturnValueHandler}s.
	 * @param webRequest the current request
	 * @param mavContainer the ModelAndViewContainer for this request
	 * @param providedArgs "given" arguments matched by type (not resolved)
	 */
	public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {

		Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
		setResponseStatus(webRequest);

		if (returnValue == null) {
			if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) {
				mavContainer.setRequestHandled(true);
				return;
			}
		}
		else if (StringUtils.hasText(getResponseStatusReason())) {
			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;
		}
	}

我们可以看到invokeForRequest(webRequest, mavContainer, providedArgs)这个方法会返回handlerMethod的返回值。这个方法在给定请求的上下文中解析handlerMethod的方法参数后，然后去调用handlerMethod。参数的解析是通过 {@link HandlerMethodArgumentResolver}完成的。

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;
	}

InvocableHandlerMethod中的getMethodArgumentValues()这个方法是获取handlerMethod的参数。首先获取handlerMethod中的所有参数数组，数组类型是MethodParameter。遍历参数数组，给每一个参数初始化parameterNameDisconverer(参数名称发现器)。

private Object[] getMethodArgumentValues(NativeWebRequest request, ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {

		MethodParameter[] parameters = getMethodParameters();
		Object[] args = new Object[parameters.length];
		for (int i = 0; i < parameters.length; i++) {
			MethodParameter parameter = parameters[i];
			parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);
			args[i] = resolveProvidedArgument(parameter, providedArgs);
			if (args[i] != null) {
				continue;
			}
			if (this.argumentResolvers.supportsParameter(parameter)) {
				try {
					args[i] = this.argumentResolvers.resolveArgument(
							parameter, mavContainer, request, this.dataBinderFactory);
					continue;
				}
				catch (Exception ex) {
					if (logger.isDebugEnabled()) {
						logger.debug(getArgumentResolutionErrorMessage("Failed to resolve", i), ex);
					}
					throw ex;
				}
			}
			if (args[i] == null) {
				throw new IllegalStateException("Could not resolve method parameter at index " +
						parameter.getParameterIndex() + " in " + parameter.getMethod().toGenericString() +
						": " + getArgumentResolutionErrorMessage("No suitable resolver for", i));
			}
		}
		return args;
	}

看到resolveProvidedArgument(parameter, providedArgs)这行代码，里面会对提供的providedArgs参数进行类型判断，判断它是否和MethodParameter类型匹配。如果类型匹配，返回提供的参数。如果不匹配，返回null。

args[i] = resolveProvidedArgument(parameter, providedArgs);
	/**
	 * Attempt to resolve a method parameter from the list of provided argument values.
	 */
	private Object resolveProvidedArgument(MethodParameter parameter, Object... providedArgs) {
		if (providedArgs == null) {
			return null;
		}
		for (Object providedArg : providedArgs) {
			if (parameter.getParameterType().isInstance(providedArg)) {
				return providedArg;
			}
		}
		return null;
	}

接着看，如果提供的参数值不为空，那么跳出当前循环，继续下一次循环。

args[i] = resolveProvidedArgument(parameter, providedArgs);
            if (args[i] != null) {
                continue;
            }

我们通过supportParameter()方法判断argumentResolvers(这是HandlerMethodArgumentResovlerComposite对象，参数解析器处理链)是否支持parameter这种类型的参数解析。

if (this.argumentResolvers.supportsParameter(parameter)) {
                try {
                    args[i] = this.argumentResolvers.resolveArgument(
                            parameter, mavContainer, request, this.dataBinderFactory);
                    continue;
                }
                catch (Exception ex) {
                    if (logger.isDebugEnabled()) {
                        logger.debug(getArgumentResolutionErrorMessage("Failed to resolve", i), ex);
                    }
                    throw ex;
                }
            }

HandlerMethodArgumentResovlerComposite中的supportsParamter()方法，通过parameter参数类型去获得合适的HandlerMethodArgumentResolver(参数解析器)。如果没有合适的参数解析器，那么就说明HandlerMethodArgumentResolverComposite中没有合适的参数解析器能解析这种类型的参数。

/**
	 * Whether the given {@linkplain MethodParameter method parameter} is supported by any registered
	 * {@link HandlerMethodArgumentResolver}.
	 */
	@Override
	public boolean supportsParameter(MethodParameter parameter) {
		return (getArgumentResolver(parameter) != null);
	}

首先通过parameter参数类型从argumentResolverCache缓存中获得合适的参数解析器。 如果没有找到，那么遍历HandlerMethodArgumentResolverComposite中所有的参数器，直到找到能够解析该parameter类型的参数解析器为止，且放入到argumentResolverCache缓存中，缓存的初始容量是256。

/**
	 * Find a registered {@link HandlerMethodArgumentResolver} that supports the given method parameter.
	 */
	private HandlerMethodArgumentResolver getArgumentResolver(MethodParameter parameter) {
		HandlerMethodArgumentResolver result = this.argumentResolverCache.get(parameter);
		if (result == null) {
			for (HandlerMethodArgumentResolver methodArgumentResolver : this.argumentResolvers) {
				if (logger.isTraceEnabled()) {
					logger.trace("Testing if argument resolver [" + methodArgumentResolver + "] supports [" +
							parameter.getGenericParameterType() + "]");
				}
				if (methodArgumentResolver.supportsParameter(parameter)) {
					result = methodArgumentResolver;
					this.argumentResolverCache.put(parameter, result);
					break;
				}
			}
		}
		return result;
	}

如果最后的参数还为空的话，那么很遗憾抛IllegalStateException异常,没有合适的参数解析器能够解析这个参数。

if (args[i] == null) {
				throw new IllegalStateException("Could not resolve method parameter at index " +
						parameter.getParameterIndex() + " in " + parameter.getMethod().toGenericString() +
						": " + getArgumentResolutionErrorMessage("No suitable resolver for", i));
			}

到了最为关键的一步，开始解析参数。

try {
					args[i] = this.argumentResolvers.resolveArgument(
							parameter, mavContainer, request, this.dataBinderFactory);
					continue;
				}
				catch (Exception ex) {
					if (logger.isDebugEnabled()) {
						logger.debug(getArgumentResolutionErrorMessage("Failed to resolve", i), ex);
					}
					throw ex;
				}

进入到HandlerMethodArgumentResolverComposite中的resolveArgument()放到，老样子从缓存中获得合适的参数解析器。并且由这个参数解析器来解析这个参数。

/**
	 * Iterate over registered {@link HandlerMethodArgumentResolver}s and invoke the one that supports it.
	 * @throws IllegalStateException if no suitable {@link HandlerMethodArgumentResolver} is found.
	 */
	@Override
	public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
			NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {

		HandlerMethodArgumentResolver resolver = getArgumentResolver(parameter);
		if (resolver == null) {
			throw new IllegalArgumentException("Unknown parameter type [" + parameter.getParameterType().getName() + "]");
		}
		return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory);
	}

HandlerMethod所需的方法参数都已经解析完毕，那么就可以开始调用HandlerMethod了。回到InvocableHandlerMethod中的invokeForRequest()方法。

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;
	}

调用doInvoke(args)方法，我们可以看到通过ReflectionUtils.makeAccessible(getBridgedMethod())让handlerMethod方法具有访问性，必要要显式的设置它具有访问性。然后准备好handlerMethod所在类的实例和方法参数，反射调用handlerMethod。

/**
	 * Invoke the handler method with the given argument values.
	 */
	protected Object doInvoke(Object... args) throws Exception {
		ReflectionUtils.makeAccessible(getBridgedMethod());
		try {
			return getBridgedMethod().invoke(getBean(), args);
		}
		catch (IllegalArgumentException ex) {
			assertTargetBean(getBridgedMethod(), getBean(), args);
			String text = (ex.getMessage() != null ? ex.getMessage() : "Illegal argument");
			throw new IllegalStateException(getInvocationErrorMessage(text, args), ex);
		}
		catch (InvocationTargetException ex) {
			// Unwrap for HandlerExceptionResolvers ...
			Throwable targetException = ex.getTargetException();
			if (targetException instanceof RuntimeException) {
				throw (RuntimeException) targetException;
			}
			else if (targetException instanceof Error) {
				throw (Error) targetException;
			}
			else if (targetException instanceof Exception) {
				throw (Exception) targetException;
			}
			else {
				String text = getInvocationErrorMessage("Failed to invoke handler method", args);
				throw new IllegalStateException(text, targetException);
			}
		}
	}

handlerMethod调用完毕后，可以要对返回值进行处理的操作。这时候可以关注ServletInvocableHandlerMethod中的invokeAndHandle()方法。首先是设置ResponseStatus的状态，如果有用到{@link ResponseStatus}注解来设置响应状态。mavContainer.setRequestHandled(false)只是初始化时默认采用view的解决方案，设置为true表示response直接处理，不需要view的解决方案。

public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {

		Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
		setResponseStatus(webRequest);

		if (returnValue == null) {
			if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) {
				mavContainer.setRequestHandled(true);
				return;
			}
		}
		else if (StringUtils.hasText(getResponseStatusReason())) {
			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;
		}
	}

实际上handlerMethod的返回值处理是通过HandlerMethodReturnValueHandlerComposite的handleReturnValue()方法，还是老样子，遍历所有的返回值处理器，通过supportsReturnType()判断是否支持该返回值的类型。如果类型支持的话，那么就让合适的HandlerMethodReturnValueHandler去处理handlerMethod的返回值。这里的returnType其实是ReturnValueMethodParameter类型的。(有兴趣，可以看HandlerMethod这个类)

// 调用HandlerMethodReturnValueHandlerComposite的handleReturnValue()方法
   this.returnValueHandlers.handleReturnValue(
					returnValue, getReturnValueType(returnValue), mavContainer, webRequest);

	/**
	 * Iterate over registered {@link HandlerMethodReturnValueHandler}s and invoke the one that supports it.
	 * @throws IllegalStateException if no suitable {@link HandlerMethodReturnValueHandler} is found.
	 */
	@Override
	public void handleReturnValue(Object returnValue, MethodParameter returnType,
			ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {

		HandlerMethodReturnValueHandler handler = selectHandler(returnValue, returnType);
		if (handler == null) {
			throw new IllegalArgumentException("Unknown return value type: " + returnType.getParameterType().getName());
		}
		handler.handleReturnValue(returnValue, returnType, mavContainer, webRequest);
	}

	private HandlerMethodReturnValueHandler selectHandler(Object value, MethodParameter returnType) {
		boolean isAsyncValue = isAsyncReturnValue(value, returnType);
		for (HandlerMethodReturnValueHandler handler : this.returnValueHandlers) {
			if (isAsyncValue && !(handler instanceof AsyncHandlerMethodReturnValueHandler)) {
				continue;
			}
			if (handler.supportsReturnType(returnType)) {
				return handler;
			}
		}
		return null;
	}

回到RequestMappingHandlerAdapter中的invokeHandlerMethod()方法中

protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
			HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

                        ...
			invocableMethod.invokeAndHandle(webRequest, mavContainer);
			if (asyncManager.isConcurrentHandlingStarted()) {
				return null;
			}

			return getModelAndView(mavContainer, modelFactory, webRequest);
		}
		finally {
			webRequest.requestCompleted();
		}
	}

首先调用modelFactory.updateModel(webRequest, mavContainer)将被@SessionAtrributes注解的模型属性上升到会话级别。如果mavContainer采用的是response直接处理策略，说明没有采用view的解决方案，直接返回null即可。将ModelAndViewContainer中的model、视图的名称、HttpStatus填充到ModelAndView中。如果mavContainer没有指定逻辑视图(或者说 view不是String类型的)的话，那么就设置视图对象。如果model是RedirectAttributes的实例，那么说明是model是重定向所需要的属性，我们把model填充到FlashMap即可。

private ModelAndView getModelAndView(ModelAndViewContainer mavContainer,
			ModelFactory modelFactory, NativeWebRequest webRequest) throws Exception {

		modelFactory.updateModel(webRequest, mavContainer);
		if (mavContainer.isRequestHandled()) {
			return null;
		}
		ModelMap model = mavContainer.getModel();
		ModelAndView mav = new ModelAndView(mavContainer.getViewName(), model, mavContainer.getStatus());
		if (!mavContainer.isViewReference()) {
			mav.setView((View) mavContainer.getView());
		}
		if (model instanceof RedirectAttributes) {
			Map<String, ?> flashAttributes = ((RedirectAttributes) model).getFlashAttributes();
			HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class);
			RequestContextUtils.getOutputFlashMap(request).putAll(flashAttributes);
		}
		return mav;
	}

这里的updateModel()首先获得defaultModel，然后判断当前会话是否处理完毕。如果处理完毕，进行资源清理操作。如果没有处理完毕，把当前request中的model对象保存在SessionAttributesHandler中的sessionAttributeStore中，方便下次请求。如果container采用的是view策略并且使用的是默认model模型，那么就调用updateBindingResult(request, defaultModel)方法，为需要它的属性添加到BindingResult属性到defaultModel中。

/**
	 * Promote model attributes listed as {@code @SessionAttributes} to the session.
	 * Add {@link BindingResult} attributes where necessary.
	 * @param request the current request
	 * @param container contains the model to update
	 * @throws Exception if creating BindingResult attributes fails
	 */
	public void updateModel(NativeWebRequest request, ModelAndViewContainer container) throws Exception {
		ModelMap defaultModel = container.getDefaultModel();
		if (container.getSessionStatus().isComplete()){
			this.sessionAttributesHandler.cleanupAttributes(request);
		}
		else {
			this.sessionAttributesHandler.storeAttributes(request, defaultModel);
		}
		if (!container.isRequestHandled() && container.getModel() == defaultModel) {
			updateBindingResult(request, defaultModel);
		}
	}

回到RequestMappingHandlerAdapter中的hanlderInternal()方法中，如果response的响应条没有设置Cache-control属性的话，如果handlerMethod对应的SessionAttributesHandler中维护了被@SessionAtrribute注解的model，那么设置Cache-control为no store模式。否则设置Cache-control为-1。

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

		ModelAndView mav;
		checkRequest(request);

         ...
			// No synchronization on session demanded at all...
			mav = invokeHandlerMethod(request, response, handlerMethod);

		if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
			if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
             // 调用的是WebContentGeneratorl类中的方法
				applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
			}
			else {
				prepareResponse(response);
			}
		}

		return mav;
	}

回到DispatcherServlet中的doDispatch()方法，我们通过适配器调用HandlerExecutionChain中的handler返回ModelAndView，如果ModelAndView中没有视图引用，那么申请设置默认的视图名称。然后调用HandlerExecutionChain中所有的拦截器中的postHandle()方法，对handlerMethod返回的结果进行加强处理。

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
                ...

				// 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);
				}
			}
		}
	}

接着调用processDispatchResult()方法，开始对处理程序调用返回的结构进行处理。要么是ModelAndView，要么解析成ModelAndView的异常。如果异常不为空且是ModelAndViewDefiningException类型的异常，那么把视图解析成ModelAndViewDefiningException特定的视图。如果异常不为空且不是ModelAndViewDefiningException类型的异常，那么调用 processHandlerException()让HandlerExceptionResovlers中的异常处理器来处理。

processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);

	/**
	 * Handle the result of handler selection and handler invocation, which is
	 * either a ModelAndView or an Exception to be resolved to a ModelAndView.
	 */
	private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
			HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception {

		boolean errorView = false;

		if (exception != null) {
			if (exception instanceof ModelAndViewDefiningException) {
				logger.debug("ModelAndViewDefiningException encountered", exception);
				mv = ((ModelAndViewDefiningException) exception).getModelAndView();
			}
			else {
				Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
				mv = processHandlerException(request, response, handler, exception);
				errorView = (mv != null);
			}
		}

		// Did the handler return a view to render?
		if (mv != null && !mv.wasCleared()) {
			render(mv, request, response);
			if (errorView) {
				WebUtils.clearErrorRequestAttributes(request);
			}
		}
		else {
			if (logger.isDebugEnabled()) {
				logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() +
						"': assuming HandlerAdapter completed request handling");
			}
		}

		if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
			// Concurrent handling started during a forward
			return;
		}

		if (mappedHandler != null) {
			mappedHandler.triggerAfterCompletion(request, response, null);
		}
	}

processHandlerException()内部实现是遍历DispatcherServlet中的handlerExceptionResolvers(程序异常解析器集合)，如果当前有异常解析器能够处理这个异常且处理完毕后返回的ModelAndView不为空，那么跳出循环。然后继续判断，如果ModelAndView中的model属性并且view属性都为空的话，把异常信息放到request中(EXCEPTION_ATTRIBUTE的值是 DispatcherServlet.class.getName() + ".EXCEPTION")，直接返回null。

protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,
			Object handler, Exception ex) throws Exception {

		// Check registered HandlerExceptionResolvers...
		ModelAndView exMv = null;
		for (HandlerExceptionResolver handlerExceptionResolver : this.handlerExceptionResolvers) {
			exMv = handlerExceptionResolver.resolveException(request, response, handler, ex);
			if (exMv != null) {
				break;
			}
		}
		if (exMv != null) {
			if (exMv.isEmpty()) {
				request.setAttribute(EXCEPTION_ATTRIBUTE, ex);
				return null;
			}
			// We might still need view name translation for a plain error model...
			if (!exMv.hasView()) {
				exMv.setViewName(getDefaultViewName(request));
			}
			if (logger.isDebugEnabled()) {
				logger.debug("Handler execution resulted in exception - forwarding to resolved error view: " + exMv, ex);
			}
			WebUtils.exposeErrorRequestAttributes(request, ex, getServletName());
			return exMv;
		}

		throw ex;
	}

同时我们也可以看看HandlerExceptionResolverComposite中的resolveException()方法。通过遍历已配置的异常解析器列表来解决处理异常，如果处理返回的ModelAndView实例不为空，那么直接返回ModelAndView实例。

@Override
	public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response,
			Object handler,Exception ex) {

		if (this.resolvers != null) {
			for (HandlerExceptionResolver handlerExceptionResolver : this.resolvers) {
				ModelAndView mav = handlerExceptionResolver.resolveException(request, response, handler, ex);
				if (mav != null) {
					return mav;
				}
			}
		}
		return null;
	}

回到DispatcherServlet中的processDispatchResult()，如果ModelAndView实例不为空且modelAndView中的model和view属性不为空，那么进行render()操作。render()操作之后，判断errorView是否为true，如果为true，代表已经有错误视图去响应错误，那么就可以清理request中一些关于错误的属性(status_code、exception_type、message、exception、request_uri、servlet_name)。

private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
			HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception {

		boolean errorView = false;
            ....
		// Did the handler return a view to render?
		if (mv != null && !mv.wasCleared()) {
			render(mv, request, response);
			if (errorView) {
				WebUtils.clearErrorRequestAttributes(request);
			}
		}
		else {
			if (logger.isDebugEnabled()) {
				logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() +
						"': assuming HandlerAdapter completed request handling");
			}
		}

		if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
			// Concurrent handling started during a forward
			return;
		}

		if (mappedHandler != null) {
			mappedHandler.triggerAfterCompletion(request, response, null);
		}
	}

//WebUtils

	/**
	 * Standard Servlet 2.3+ spec request attributes for error pages.
	 * <p>To be exposed to JSPs that are marked as error pages, when forwarding
	 * to them directly rather than through the servlet container's error page
	 * resolution mechanism.
	 */
	public static final String ERROR_STATUS_CODE_ATTRIBUTE = "javax.servlet.error.status_code";
	public static final String ERROR_EXCEPTION_TYPE_ATTRIBUTE = "javax.servlet.error.exception_type";
	public static final String ERROR_MESSAGE_ATTRIBUTE = "javax.servlet.error.message";
	public static final String ERROR_EXCEPTION_ATTRIBUTE = "javax.servlet.error.exception";
	public static final String ERROR_REQUEST_URI_ATTRIBUTE = "javax.servlet.error.request_uri";
	public static final String ERROR_SERVLET_NAME_ATTRIBUTE = "javax.servlet.error.servlet_name";

	/**
	 * Clear the Servlet spec's error attributes as {@link javax.servlet.http.HttpServletRequest}
	 * attributes under the keys defined in the Servlet 2.3 specification:
	 * {@code javax.servlet.error.status_code},
	 * {@code javax.servlet.error.exception_type},
	 * {@code javax.servlet.error.message},
	 * {@code javax.servlet.error.exception},
	 * {@code javax.servlet.error.request_uri},
	 * {@code javax.servlet.error.servlet_name}.
	 * @param request current servlet request
	 */
	public static void clearErrorRequestAttributes(HttpServletRequest request) {
		request.removeAttribute(ERROR_STATUS_CODE_ATTRIBUTE);
		request.removeAttribute(ERROR_EXCEPTION_TYPE_ATTRIBUTE);
		request.removeAttribute(ERROR_MESSAGE_ATTRIBUTE);
		request.removeAttribute(ERROR_EXCEPTION_ATTRIBUTE);
		request.removeAttribute(ERROR_REQUEST_URI_ATTRIBUTE);
		request.removeAttribute(ERROR_SERVLET_NAME_ATTRIBUTE);
	}

看看render()里面是干嘛的，它实际上是为了呈现ModelAndView，这是处理请求的最后一步，里面涉及到将逻辑视图转换成真正的物理视图。

protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
		// Determine locale for request and apply it to the response.
		Locale locale = this.localeResolver.resolveLocale(request);
		response.setLocale(locale);

		View view;
		if (mv.isReference()) {
			// We need to resolve the view name.
			view = resolveViewName(mv.getViewName(), mv.getModelInternal(), locale, request);
			if (view == null) {
				throw new ServletException("Could not resolve view with name '" + mv.getViewName() +
						"' in servlet with name '" + getServletName() + "'");
			}
		}
		else {
			// No need to lookup: the ModelAndView object contains the actual View object.
			view = mv.getView();
			if (view == null) {
				throw new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a " +
						"View object in servlet with name '" + getServletName() + "'");
			}
		}

		// Delegate to the View object for rendering.
		if (logger.isDebugEnabled()) {
			logger.debug("Rendering view [" + view + "] in DispatcherServlet with name '" + getServletName() + "'");
		}
		try {
			if (mv.getStatus() != null) {
				response.setStatus(mv.getStatus().value());
			}
			view.render(mv.getModelInternal(), request, response);
		}
		catch (Exception ex) {
			if (logger.isDebugEnabled()) {
				logger.debug("Error rendering view [" + view + "] in DispatcherServlet with name '" +
						getServletName() + "'", ex);
			}
			throw ex;
		}
	}

resolveViewName()其实将视图名称转换成真正的视图对象。通过遍历当前所有的viewResolvers，如果视图解析器解析后的view对象不为空的话，那么直接返回当前view对象。

protected View resolveViewName(String viewName, Map<String, Object> model, Locale locale,
			HttpServletRequest request) throws Exception {

		for (ViewResolver viewResolver : this.viewResolvers) {
			View view = viewResolver.resolveViewName(viewName, locale);
			if (view != null) {
				return view;
			}
		}
		return null;
	}

进入到ContentNegotiatingViewResolver。ContentNegotiatingViewResolver根据请求头中的Accept属性或者是请求文件名来解析视图。它本身不提供解析视图，而是通过viewResolvers集合中的视图解析器来解析视图。resolveViewName()这个方法，通过请求头中的Accept属性获取requestMediaTypes，由此获取与之兼容的view对象集合。再通过兼容的view对象集合获得最佳匹配的view对象(AbstractMessageConverterMethodProcessor也用了类似的方法，获得最佳的selectedMediaType)。

@Override
	public View resolveViewName(String viewName, Locale locale) throws Exception {
		RequestAttributes attrs = RequestContextHolder.getRequestAttributes();
		Assert.state(attrs instanceof ServletRequestAttributes, "No current ServletRequestAttributes");
		List<MediaType> requestedMediaTypes = getMediaTypes(((ServletRequestAttributes) attrs).getRequest());
		if (requestedMediaTypes != null) {
			List<View> candidateViews = getCandidateViews(viewName, locale, requestedMediaTypes);
			View bestView = getBestView(candidateViews, requestedMediaTypes, attrs);
			if (bestView != null) {
				return bestView;
			}
		}
		if (this.useNotAcceptableStatusCode) {
			if (logger.isDebugEnabled()) {
				logger.debug("No acceptable view found; returning 406 (Not Acceptable) status code");
			}
			return NOT_ACCEPTABLE_VIEW;
		}
		else {
			logger.debug("No acceptable view found; returning null");
			return null;
		}
	}

获取到合适的view对象，那么调用其本身的render()方法，将model对象填充到到view对象中，完成渲染操作。

if (mv.getStatus() != null) {
				response.setStatus(mv.getStatus().value());
			}
			view.render(mv.getModelInternal(), request, response);

尾言

对于一个框架，我们不仅要做到熟练使用，还用知其然知其所以然。以后我再写关于框架源码分析的文章，会尽量切割，缩小篇幅。