前言

    这一篇，将着手介绍一次请求的处理。用到了 HandlerMapping、HandlerAdapter 知识，如果遇到不是太了解，可以回顾下。

 

源码分析

    其实 DispatcherServlet 也只是 Servlet 的一个实现，只不过它集成了 SpringMVC 的几个功能组件（例如视图解析器），对请求及响应进行加工处理，所以探索一个 Servlet 实现，先从它的 service 方法实现开始，来看下 javax.servlet.http.HttpServlet 的实现。

public abstract class HttpServlet extends GenericServlet {@Overridepublic void service(ServletRequest req, ServletResponse res)throws ServletException, IOException {HttpServletRequest request;HttpServletResponse response;try {request = (HttpServletRequest) req;response = (HttpServletResponse) res;} catch (ClassCastException e) {throw new ServletException("non-HTTP request or response");}// 向下转型service(request, response);}protected void service(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {String method = req.getMethod();// 根据请求方式调用不同的 doXxx方法if (method.equals(METHOD_GET)) {// 固定返回-1，说明缓存机制交由子类扩展long lastModified = getLastModified(req);if (lastModified == -1) {doGet(req, resp);} else {/*** 缓存机制：首次请求后添加 “Last-Modefied” 的响应头，* 第二次请求发送请求头 If-Modified-Since* 如果服务端内容没有变化，则自动返回 304状态码*/long ifModifiedSince;try {ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);} catch (IllegalArgumentException iae) {ifModifiedSince = -1;}if (ifModifiedSince < (lastModified / 1000 * 1000)) {maybeSetLastModified(resp, lastModified);doGet(req, resp);} else {resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);}}} else if (method.equals(METHOD_HEAD)) {long lastModified = getLastModified(req);maybeSetLastModified(resp, lastModified);doHead(req, resp);} else if (method.equals(METHOD_POST)) {doPost(req, resp);} else if (method.equals(METHOD_PUT)) {doPut(req, resp);} else if (method.equals(METHOD_DELETE)) {doDelete(req, resp);} else if (method.equals(METHOD_OPTIONS)) {doOptions(req, resp);} else if (method.equals(METHOD_TRACE)) {doTrace(req, resp);} else {// 对于不支持请求方式，通过响应流输出错误String errMsg = lStrings.getString("http.method_not_implemented");Object[] errArgs = new Object[1];errArgs[0] = method;errMsg = MessageFormat.format(errMsg, errArgs);resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);}}
}

    可以看到 service 就是做了向下转型，调用了 service(HttpServletRequest req, HttpServletResponse resp)。然后在里面根据请求方式，调用不同的 doXxx 方法。以上属于 servlet-api 自身的实现，接下来看看 SpringMVC 如何在此基础上改造。

// HttpServletBean是 HttpServlet子类
public abstract class FrameworkServlet extends HttpServletBean implements ApplicationContextAware {// 覆盖 service方法@Overrideprotected void service(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {HttpMethod httpMethod = HttpMethod.resolve(request.getMethod());// 支持 Patch请求或没有指定请求方法if (httpMethod == HttpMethod.PATCH || httpMethod == null) {// 不管什么请求，都会调用公共的处理方法processRequest(request, response);} else {super.service(request, response);}}@Overrideprotected final void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {processRequest(request, response);}@Overrideprotected final void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {processRequest(request, response);}protected final void processRequest(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {// 请求开始时间，用于计算请求耗时long startTime = System.currentTimeMillis();Throwable failureCause = null;LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();// 通过"accept-language"请求头构造 LocaleContextLocaleContext localeContext = buildLocaleContext(request);// 获取当前线程请求的 RequestAttributesRequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);// 异步请求管理器WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());// 将 LocaleContext、ServletRequestAttributes与当前线程绑定initContextHolders(request, localeContext, requestAttributes);try {// 该类定义的抽象方法，子类 DispatcherServlet实现doService(request, response);}.....// 省略 catch处理finally{resetContextHolders(request, previousLocaleContext, previousAttributes);if (requestAttributes != null) {requestAttributes.requestCompleted();}.....// 省略日志publishRequestHandledEvent(request, response, startTime, failureCause);}}// 发布 ServletRequestHandledEvent事件private void publishRequestHandledEvent( HttpServletRequest request, HttpServletResponse response, long startTime, Throwable failureCause) {// 默认为 trueif (this.publishEvents) {// 请求耗时long processingTime = System.currentTimeMillis() - startTime;// 响应码int statusCode = (responseGetStatusAvailable ? response.getStatus() : -1);// 封装了 请求的 url、remoteAddr、请求方式、sessionId、处理时间、响应码等信息this.webApplicationContext.publishEvent(new ServletRequestHandledEvent(this,request.getRequestURI(), request.getRemoteAddr(),request.getMethod(), getServletConfig().getServletName(),WebUtils.getSessionId(request), getUsernameForRequest(request),processingTime, failureCause, statusCode));}}
}

    除了支持 servlet 自身支持的 7 种请求外，另外支持了 PATCH 方式请求。这里只是列举了 doGet、doPost，其实最终都调用了 processRequest 方法。

    processRequest 方法通过调用 doService 来处理请求，在处理结束后发布了 ServletRequestHandledEvent 事件，可以自定义 ApplicationListener 来监听此事件。

 

doService

public class DispatcherServlet extends FrameworkServlet {@Overrideprotected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {.....// 省略日志// 如果 attributes含有 “javax.servlet.include.request_uri”，保留属性的快照// 用于支持 <jsp:incluede>Map<String, Object> attributesSnapshot = null;if (WebUtils.isIncludeRequest(request)) {attributesSnapshot = new HashMap<>();// 获取属性枚举Enumeration<?> attrNames = request.getAttributeNames();while (attrNames.hasMoreElements()) {String attrName = (String) attrNames.nextElement();if (this.cleanupAfterInclude || attrName.startsWith(DEFAULT_STRATEGIES_PREFIX)) {// 将属性压入map中attributesSnapshot.put(attrName, request.getAttribute(attrName));}}}// 设置上下文、解析器等属性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());// 取出上一个请求的 FlashMap并给赋值给当前请求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 {// 关注此方法doDispatch(request, response);} finally {if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {// 还原属性快照if (attributesSnapshot != null) {restoreAttributesAfterInclude(request, attributesSnapshot);}}}}
}

    DispatcherServlet 来进行主要的处理实现。doService 进行一些属性的设置之后，调用 doDispatch 方法进行处理

 

doDispatch

    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 {/*** 调用我们配置的 MultipartResolver判断是否需要处理，如果没配置不会处理* 以 CommonsMultipartResolver为例* 检测 contentType是否为 multipart/form-data且必须是 POST请求*/processedRequest = checkMultipart(request);// 如果满足上述条件，会包装成 DefaultMultipartHttpServletRequest// 所以 multipartRequestParsed 为 truemultipartRequestParsed = (processedRequest != request);// 根据 request找到对应的 HandlermappedHandler = getHandler(processedRequest);if (mappedHandler == null) {// 没找到 Handler，通过response响应 404错误信息noHandlerFound(processedRequest, response);return;}// 根据 Handler找到对应的适配器HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());// 对 last-modified 头支持：只有 Get 和 Head请求支持String method = request.getMethod();boolean isGet = "GET".equals(method);if (isGet || "HEAD".equals(method)) {long lastModified = ha.getLastModified(request, mappedHandler.getHandler());....// 省略日志// 对于缓存逻辑的判断，见 ServletWebRequest.checkNotModifiedif (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {// 满足条件直接返回return;}}// 调用拦截器的 preHandle，返回true才能通过if (!mappedHandler.applyPreHandle(processedRequest, response)) {return;}// 调用 HandlerAdapter.handle返回处理后的 ModelAndViewmv = ha.handle(processedRequest, response, mappedHandler.getHandler());if (asyncManager.isConcurrentHandlingStarted()) {return;}// 如果没有 ModelAndView返回，则根据请求默认给出一个视图名称applyDefaultViewName(processedRequest, mv);// 调用拦截器的 postHandlemappedHandler.applyPostHandle(processedRequest, response, mv);} catch (Exception ex) {dispatchException = ex;} catch (Throwable err) {dispatchException = new NestedServletException("Handler dispatch failed", err);}// 视图处理（包含异常视图），最后会调用拦截器的 triggerAfterCompletionprocessDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);} catch (Exception ex) {// 调用拦截器的 triggerAfterCompletiontriggerAfterCompletion(processedRequest, response, mappedHandler, ex);} catch (Throwable err) {// 调用拦截器的 triggerAfterCompletiontriggerAfterCompletion(processedRequest, response, mappedHandler,new NestedServletException("Handler processing failed", err));} finally {if (asyncManager.isConcurrentHandlingStarted()) {if (mappedHandler != null) {// 调用 AsyncHandlerInterceptor.afterConcurrentHandlingStarted// 用于在异步请求处理开始之后回调mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);}} else {// 如果是文件上传请求，需要清理资源if (multipartRequestParsed) {cleanupMultipart(processedRequest);}}}}

    通过层层的调用，终于来到了 doDispatch ，这个方法大致能够看到请求的处理步骤概览：

• 首先判断是否为文件上传的请求：和普通的请求不一样，这种请求需要在请求结束后清理文件解析过程中创建的 MultipartFile （可能会在磁盘上保留有临时数据）；
• 获取 Handler ：从 HandlerMapping初始化建立的映射关系中找出；
• 拦截器 HandlerInterceptor.preHandle 调用；
• HandlerAdapter 适配：从 HandlerAdapter 初始化注册的所有适配器中，找到支持对应 Handler 的适配器，调用 handle 方法处理（见 HandlerAdapter）
• 拦截器 HandlerInterceptor.postHandle 调用；
• 调用 processDispatchResult 进行视图处理；
• 拦截器 HandlerInterceptor.afterCompletion 调用（异常同样会触发，并且会作为参数传入）

    接下来我们来看几个主要步骤的解析。

 

getHandler

    @Nullableprotected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {if (this.handlerMappings != null) {// 遍历所有注册的 HandlerMappingfor (HandlerMapping hm : this.handlerMappings) {....// 省略日志// 找到匹配的HandlerExecutionChain（不为null）HandlerExecutionChain handler = hm.getHandler(request);if (handler != null) {return handler;}}}return null;}

    调用 HandlerMapping.getHandler 获取请求对应的 Handler。来看实现：

public abstract class AbstractHandlerMapping extends WebApplicationObjectSupport implements HandlerMapping, Ordered {@Override@Nullablepublic final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {// 根据 request获取对应的 Handler（子类实现）Object handler = getHandlerInternal(request);// 如果没有找到对应 Handler，使用默认Handlerif (handler == null) {handler = getDefaultHandler();}// 如果默认的 Handler没有，则返回 nullif (handler == null) {return null;}// Handler为 String类型，说明是beanName，调用 getBean获取if (handler instanceof String) {String handlerName = (String) handler;handler = obtainApplicationContext().getBean(handlerName);}// 执行链构造：Handler和拦截器HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);// 判断跨域请求：是否带有“Origin”请求头if (CorsUtils.isCorsRequest(request)) {// 全局跨域配置CorsConfiguration globalConfig = this.globalCorsConfigSource.getCorsConfiguration(request);// 单个 Handler配置（注解 @CrossOrigin其实就是对单个 Handler的配置）CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);// 配置合并CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);// 添加 CorsInterceptor拦截器（使用合并后的配置）executionChain = getCorsHandlerExecutionChain(request, executionChain, config);}return executionChain;}// 执行链构造protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?(HandlerExecutionChain) handler : new HandlerExecutionChain(handler));String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);// 遍历 List<HandlerInterceptor>for (HandlerInterceptor interceptor : this.adaptedInterceptors) {if (interceptor instanceof MappedInterceptor) {MappedInterceptor mappedInterceptor = (MappedInterceptor) interceptor;if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) {// 将匹配的 MappedInterceptor加入处理链chain.addInterceptor(mappedInterceptor.getInterceptor());}} else {// 其他的直接加入chain.addInterceptor(interceptor);}}return chain;}// 跨域拦截器加入protected HandlerExecutionChain getCorsHandlerExecutionChain(HttpServletRequest request,HandlerExecutionChain chain, CorsConfiguration config) {// 条件：带有“Origin”、“Access-Control-Request-Method”请求头的 options请求if (CorsUtils.isPreFlightRequest(request)) {HandlerInterceptor[] interceptors = chain.getInterceptors();// 使用 PreFlightHandler替代原本的 Handler处理请求chain = new HandlerExecutionChain(new PreFlightHandler(config), interceptors);} else {// 添加 CorsInterceptor拦截器（拦截器末尾）chain.addInterceptor(new CorsInterceptor(config));}return chain;}
}

    抽象父类 AbstractHandlerMapping 实现了 执行链的构造 以及 “跨域”相关处理（拦截器），查找 Handler 的逻辑交由子类实现（getHandlerInternal）。回想一下 HandlerMapping 注册 Handler 的逻辑分为了两个分支 AbstractUrlHandlerMapping 和 AbstractHandlerMethodMapping （见 HandlerMapping 初始化），因此查找逻辑也随注册逻辑不同而不同。

 

AbstractUrlHandlerMapping 分支

public abstract class AbstractUrlHandlerMapping extends AbstractHandlerMapping implements MatchableHandlerMapping {@Overrideprotected Object getHandlerInternal(HttpServletRequest request) throws Exception {// 这一步我们会取到截取后的请求相对地址String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);// 根据相对地址找到对应的 HandlerObject handler = lookupHandler(lookupPath, request);if (handler == null) {// 没有的话，依次查询根 Handler、默认 HandlerObject rawHandler = null;if ("/".equals(lookupPath)) {rawHandler = getRootHandler();}if (rawHandler == null) {rawHandler = getDefaultHandler();}if (rawHandler != null) {// 如果 Handler是 beanName，调用 getBean获取if (rawHandler instanceof String) {String handlerName = (String) rawHandler;rawHandler = getApplicationContext().getBean(handlerName);}// 校验：由 DefaultAnnotationHandlerMapping实现// 看请求是否满足 @RequestMapping指定的 method、param、headervalidateHandler(rawHandler, request);// 使用 Handler创建执行链，链头添加 PathExposingHandlerInterceptor拦截器handler = buildPathExposingHandler(rawHandler, lookupPath, lookupPath, null);}}....// 省略日志return handler;}protected Object lookupHandler(String urlPath, HttpServletRequest request) throws Exception {// 从映射关系中找出请求对应的 Handler（直接路径）// 映射关系的初始化见 HandlerMapping初始化Object handler = this.handlerMap.get(urlPath);if (handler != null) {// beanName以及 Handler校验，上面讲过了if (handler instanceof String) {String handlerName = (String) handler;handler = getApplicationContext().getBean(handlerName);}validateHandler(handler, request);// 构造执行链return buildPathExposingHandler(handler, urlPath, urlPath, null);}// 直接路径中未找到，使用通配符匹配List<String> matchingPatterns = new ArrayList<String>();for (String registeredPattern : this.handlerMap.keySet()) {if (getPathMatcher().match(registeredPattern, urlPath)) {matchingPatterns.add(registeredPattern);} else if (useTrailingSlashMatch()) {if (!registeredPattern.endsWith("/") && getPathMatcher().match(registeredPattern + "/", urlPath)) {matchingPatterns.add(registeredPattern + "/");}}}String bestMatch = null;// 使用模式匹配后，查找最匹配的 HandlerComparator<String> patternComparator = getPathMatcher().getPatternComparator(urlPath);if (!matchingPatterns.isEmpty()) {Collections.sort(matchingPatterns, patternComparator);....// 省略日志bestMatch = matchingPatterns.get(0);}if (bestMatch != null) {handler = this.handlerMap.get(bestMatch);if (handler == null) {if (bestMatch.endsWith("/")) {handler = this.handlerMap.get(bestMatch.substring(0, bestMatch.length() - 1));}if (handler == null) {throw new IllegalStateException("Could not find handler for best pattern match [" + bestMatch + "]");}}// beanName以及 Handler校验，上面讲过了if (handler instanceof String) {String handlerName = (String) handler;handler = getApplicationContext().getBean(handlerName);}validateHandler(handler, request);String pathWithinMapping = getPathMatcher().extractPathWithinPattern(bestMatch, urlPath);// 可能存在多个“最佳模式”，让我们确保所有这些模式都有正确的URI模板变量Map<String, String> uriTemplateVariables = new LinkedHashMap<String, String>();for (String matchingPattern : matchingPatterns) {if (patternComparator.compare(bestMatch, matchingPattern) == 0) {Map<String, String> vars = getPathMatcher().extractUriTemplateVariables(matchingPattern, urlPath);Map<String, String> decodedVars = getUrlPathHelper().decodePathVariables(request, vars);uriTemplateVariables.putAll(decodedVars);}}....// 省略日志// 构造执行链return buildPathExposingHandler(handler, bestMatch, pathWithinMapping, uriTemplateVariables);}// 没有匹配的 Handler返回 nullreturn null;}
}

    首先调用 UrlPathHelper.getLookupPathForRequest 获取请求的相对路径。以 Tomcat 举例，配置的 <Context path="xxx"> 项目根路径，那么对应的 web 应用所有的请求，都要添加 “xxx” 前缀，但我们的应用对此是无感知的，所以框架层面要把这些截取后，再去查找 Handler。来看下截取逻辑：

public class UrlPathHelper {public String getLookupPathForRequest(HttpServletRequest request) {// 默认为 falseif (this.alwaysUseFullPath) {return getPathWithinApplication(request);}String rest = getPathWithinServletMapping(request);if (!"".equals(rest)) {return rest;} else {return getPathWithinApplication(request);}}public String getPathWithinServletMapping(HttpServletRequest request) {// 获取截取后的相对地址String pathWithinApp = getPathWithinApplication(request);// 获取的 <servlet>指定的 <url-pattern>（移除通配符后）String servletPath = getServletPath(request);// 把 pathWithinApp中的“//”替换成“/”String sanitizedPathWithinApp = getSanitizedPath(pathWithinApp);String path;// 这一步主要就是对请求地址中多余的“/”进行移除匹配if (servletPath.contains(sanitizedPathWithinApp)) {// 同样的，把请求的相对地址中，servletPath截取掉path = getRemainingPath(sanitizedPathWithinApp, servletPath, false);} else {// 同样的，把请求的相对地址中，servletPath截取掉path = getRemainingPath(pathWithinApp, servletPath, false);}if (path != null) {return path;} else {// 如果请求不在 servlet指定的 <url-pattern>下String pathInfo = request.getPathInfo();if (pathInfo != null) {return pathInfo;}if (!this.urlDecode) {path = getRemainingPath(decodeInternal(request, pathWithinApp), servletPath, false);if (path != null) {return pathWithinApp;}}return servletPath;}}public String getPathWithinApplication(HttpServletRequest request) {// 获取的项目根路径String contextPath = getContextPath(request);// 获取请求的相对地址String requestUri = getRequestUri(request);// 把请求的相对地址中的项目根路径截去String path = getRemainingPath(requestUri, contextPath, true);if (path != null) {return (StringUtils.hasText(path) ? path : "/");} else {return requestUri;}}
}

    （getPathWithinServletMapping）首先会在配置的 DispatcherServlet 范围内查找，对于同一个请求 “http://localhost/a/b” 来说：

• <url-pattern>/*</url-pattern>， 返回的就是 “/a/b”；
• <url-pattern>/a/*</url-pattern>，那么返回的就是 “/b”。如果请求为 “http://localhost/a” ，那么返回的就是空字符串了。

    （getPathWithinApplication）只有在上一步返回空字符串时才会在 Application 范围内查找，对于用一个请求“http://localhost/context/a” 来说：

• <Context path="/context">，返回的就是 “/a”；
• <Context path="/">，返回的就是 “/context/a”。如果请求为 “http://localhost” ，那么返回的就是 “/”了。

 

AbstractHandlerMethodMapping 分支

public abstract class AbstractHandlerMethodMapping<T> extends AbstractHandlerMapping implements InitializingBean {@Overrideprotected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {// 同样使用 UrlPathHelper.getLookupPathForRequestString lookupPath = getUrlPathHelper().getLookupPathForRequest(request);if (logger.isDebugEnabled()) {logger.debug("Looking up handler method for path " + lookupPath);}this.mappingRegistry.acquireReadLock();try {// 根据请求 url找到对应的 HandlerMethodHandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);....// 省略日志// createWithResolvedBean目的是确保 HandlerMethod中持有的是被调用的实例 bean// 而不是 beanName，如果是会调用了 getBean获取实例后创建新的 HandleMethod// 因为这个实例 bean会用于反射调用方法return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);} finally {this.mappingRegistry.releaseReadLock();}}protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {List<Match> matches = new ArrayList<Match>();// 使用 MappingRegistry.getMappingsByUrl，通过相对路径查找对应的 List<RequestMappingInfo>// 见 AbstractHandlerMethodMapping的注册逻辑List<T> directPathMatches = this.mappingRegistry.getMappingsByUrl(lookupPath);if (directPathMatches != null) {// 不为 null，说明 @RequestMapping指定的是非通配符路径// 找到匹配条件的填充 matchesaddMatchingMappings(directPathMatches, matches, request);}if (matches.isEmpty()) {// 如果通过直接路径找不到，就在所有注册的映射路径中查找// 找到匹配条件的填充 matchesaddMatchingMappings(this.mappingRegistry.getMappings().keySet(), matches, request);}if (!matches.isEmpty()) {// 因为可能会有多个匹配方法，需要根据定义的优先级排序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);}// 取出最匹配的Match bestMatch = matches.get(0);if (matches.size() > 1) {// 条件：带有“Origin”、“Access-Control-Request-Method”请求头的 options请求if (CorsUtils.isPreFlightRequest(request)) {// 返回 EmptyHandler封装的 HandlerMethod// 调用会抛出异常 UnsupportedOperationExceptionreturn PREFLIGHT_AMBIGUOUS_MATCH;}// 有两个相同优先级的匹配结果，会抛异常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 + "}");}}// 调用 setAttribute设置一些属性handleMatch(bestMatch.mapping, lookupPath, request);// 返回匹配的 HandlerMethodreturn bestMatch.handlerMethod;} else {// 未匹配return handleNoMatch(this.mappingRegistry.getMappings().keySet(), lookupPath, request);}}
}

    同样使用的是 UrlPathHelper.getLookupPathForRequest 获取请求的相对路径。之后根据相对路径找到对应的 HandlerMethod 。涉及到了一个请求地址对应了多个匹配结果的筛选：

    private void addMatchingMappings(Collection<T> mappings, List<Match> matches, HttpServletRequest request) {for (T mapping : mappings) {// 获取满足条件的 RequestMappingInfoT match = getMatchingMapping(mapping, request);// 只有满足返回的才不为 null，这一步会筛选掉不符合条件的// 例如：请求路径不匹配、header头不匹配等等if (match != null) {// 通过 MappingRegistry维护的 mappingLookup找到对应的 HandlerMethod// 使用 RequestMappingInfo和 HandlerMethod创建 Match// 用于 MatchComparator的排序matches.add(new Match(match, this.mappingRegistry.getMappings().get(mapping)));}}}

public abstract class RequestMappingInfoHandlerMapping extends AbstractHandlerMethodMapping<RequestMappingInfo> {@Overrideprotected RequestMappingInfo getMatchingMapping(RequestMappingInfo info, HttpServletRequest request) {// 调用 RequestMappingInfo.getMatchingConditionreturn info.getMatchingCondition(request);}
}

public final class RequestMappingInfo implements RequestCondition<RequestMappingInfo> {@Overridepublic 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);// 这一步基本不会，因为 @RequestMapping都有默认值if (methods == null || params == null || headers == null || consumes == null || produces == null) {return null;}// 对于 @RequestMapping指定的 path/value匹配（直接地址匹配、通配符匹配）PatternsRequestCondition patterns = this.patternsCondition.getMatchingCondition(request);if (patterns == null) {return null;}// 对于 @RequestMapping指定的 method、param、header、consumes、produces的匹配RequestConditionHolder custom = this.customConditionHolder.getMatchingCondition(request);if (custom == null) {return null;}return new RequestMappingInfo(this.name, patterns,methods, params, headers, consumes, produces, custom.getCondition());}
}

    以上的源码，就是用满足请求条件的（指定的 method、header等） RequestMappingInfo 以及对应的 HandlerMethod 封装成 Match， 并填充到 matches 的逻辑。

    这一步可能会筛选出多个匹配项，接下来就需要靠 MatchComparator 排序后挑选出最匹配项，逻辑见 RequestMappingInfo.compareTo，这里不展开分析。

 

getHandlerAdapter

    protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {if (this.handlerAdapters != null) {// 遍历所有注册的 HandlerAdapterfor (HandlerAdapter ha : this.handlerAdapters) {if (logger.isTraceEnabled()) {logger.trace("Testing handler adapter [" + ha + "]");}// 调用 HandlerAdapter.supports看是否支持适配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");}

    这里调用的 supports 获取到支持适配的 HandlerAdapter，之后调用其 handle 方法执行处理逻辑，具体源码上篇已分析，见 “HandlerAdapter”。

    执行完之后，就获取到了 ModelAndView 返回，接着就是对视图的处理（processDispatchResult），放在下节分析。

 

总结

    本篇分析的就是一个请求从接收到处理的全过程，目前进度已经获取到了 ModelAndView，至于请求地址如何找到对应的 Handler、Handler 如何调用并返回 ModelAndView ，前几篇已作讲解。下篇将分析 “视图处理” 源码。