前言

? ? 這一篇，將著手介紹一次請求的處理。用到了?HandlerMapping、HandlerAdapter?知識，如果遇到不是太了解，可以回顧下。

?

源碼分析

? ? 其實 DispatcherServlet 也只是 Servlet 的一個實現，只不過它集成了 SpringMVC 的幾個功能組件（例如視圖解析器），對請求及響應進行加工處理，所以探索一個 Servlet 實現，先從它的 service 方法實現開始，來看下?javax.servlet.http.HttpServlet 的實現。

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");}// 向下轉型service(request, response);}protected void service(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {String method = req.getMethod();// 根據請求方式調用不同的 doXxx方法if (method.equals(METHOD_GET)) {// 固定返回-1，說明緩存機制交由子類擴展long lastModified = getLastModified(req);if (lastModified == -1) {doGet(req, resp);} else {/*** 緩存機制：首次請求后添加 “Last-Modefied” 的響應頭，* 第二次請求發送請求頭 If-Modified-Since* 如果服務端內容沒有變化，則自動返回 304狀態碼*/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 {// 對于不支持請求方式，通過響應流輸出錯誤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 就是做了向下轉型，調用了 service(HttpServletRequest req, HttpServletResponse resp)。然后在里面根據請求方式，調用不同的 doXxx 方法。以上屬于 servlet-api 自身的實現，接下來看看 SpringMVC 如何在此基礎上改造。

// HttpServletBean是 HttpServlet子類
public abstract class FrameworkServlet extends HttpServletBean implements ApplicationContextAware {// 覆蓋 service方法@Overrideprotected void service(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {HttpMethod httpMethod = HttpMethod.resolve(request.getMethod());// 支持 Patch請求或沒有指定請求方法if (httpMethod == HttpMethod.PATCH || httpMethod == null) {// 不管什么請求，都會調用公共的處理方法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 {// 請求開始時間，用于計算請求耗時long startTime = System.currentTimeMillis();Throwable failureCause = null;LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();// 通過"accept-language"請求頭構造 LocaleContextLocaleContext localeContext = buildLocaleContext(request);// 獲取當前線程請求的 RequestAttributesRequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);// 異步請求管理器WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());// 將 LocaleContext、ServletRequestAttributes與當前線程綁定initContextHolders(request, localeContext, requestAttributes);try {// 該類定義的抽象方法，子類 DispatcherServlet實現doService(request, response);}.....// 省略 catch處理finally{resetContextHolders(request, previousLocaleContext, previousAttributes);if (requestAttributes != null) {requestAttributes.requestCompleted();}.....// 省略日志publishRequestHandledEvent(request, response, startTime, failureCause);}}// 發布 ServletRequestHandledEvent事件private void publishRequestHandledEvent( HttpServletRequest request, HttpServletResponse response, long startTime, Throwable failureCause) {// 默認為 trueif (this.publishEvents) {// 請求耗時long processingTime = System.currentTimeMillis() - startTime;// 響應碼int statusCode = (responseGetStatusAvailable ? response.getStatus() : -1);// 封裝了 請求的 url、remoteAddr、請求方式、sessionId、處理時間、響應碼等信息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 種請求外，另外支持了 PATCH 方式請求。這里只是列舉了 doGet、doPost，其實最終都調用了 processRequest 方法。

? ? processRequest 方法通過調用?doService 來處理請求，在處理結束后發布了 ServletRequestHandledEvent 事件，可以自定義 ApplicationListener 來監聽此事件。

?

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”，保留屬性的快照// 用于支持 <jsp:incluede>Map<String, Object> attributesSnapshot = null;if (WebUtils.isIncludeRequest(request)) {attributesSnapshot = new HashMap<>();// 獲取屬性枚舉Enumeration<?> attrNames = request.getAttributeNames();while (attrNames.hasMoreElements()) {String attrName = (String) attrNames.nextElement();if (this.cleanupAfterInclude || attrName.startsWith(DEFAULT_STRATEGIES_PREFIX)) {// 將屬性壓入map中attributesSnapshot.put(attrName, request.getAttribute(attrName));}}}// 設置上下文、解析器等屬性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());// 取出上一個請求的 FlashMap并給賦值給當前請求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 {// 關注此方法doDispatch(request, response);} finally {if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {// 還原屬性快照if (attributesSnapshot != null) {restoreAttributesAfterInclude(request, attributesSnapshot);}}}}
}

? ? DispatcherServlet 來進行主要的處理實現。doService 進行一些屬性的設置之后，調用 doDispatch 方法進行處理

?

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 {/*** 調用我們配置的 MultipartResolver判斷是否需要處理，如果沒配置不會處理* 以 CommonsMultipartResolver為例* 檢測 contentType是否為 multipart/form-data且必須是 POST請求*/processedRequest = checkMultipart(request);// 如果滿足上述條件，會包裝成 DefaultMultipartHttpServletRequest// 所以 multipartRequestParsed 為 truemultipartRequestParsed = (processedRequest != request);// 根據 request找到對應的 HandlermappedHandler = getHandler(processedRequest);if (mappedHandler == null) {// 沒找到 Handler，通過response響應 404錯誤信息noHandlerFound(processedRequest, response);return;}// 根據 Handler找到對應的適配器HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());// 對 last-modified 頭支持：只有 Get 和 Head請求支持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// 對于緩存邏輯的判斷，見 ServletWebRequest.checkNotModifiedif (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {// 滿足條件直接返回return;}}// 調用攔截器的 preHandle，返回true才能通過if (!mappedHandler.applyPreHandle(processedRequest, response)) {return;}// 調用 HandlerAdapter.handle返回處理后的 ModelAndViewmv = ha.handle(processedRequest, response, mappedHandler.getHandler());if (asyncManager.isConcurrentHandlingStarted()) {return;}// 如果沒有 ModelAndView返回，則根據請求默認給出一個視圖名稱applyDefaultViewName(processedRequest, mv);// 調用攔截器的 postHandlemappedHandler.applyPostHandle(processedRequest, response, mv);} catch (Exception ex) {dispatchException = ex;} catch (Throwable err) {dispatchException = new NestedServletException("Handler dispatch failed", err);}// 視圖處理（包含異常視圖），最后會調用攔截器的 triggerAfterCompletionprocessDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);} catch (Exception ex) {// 調用攔截器的 triggerAfterCompletiontriggerAfterCompletion(processedRequest, response, mappedHandler, ex);} catch (Throwable err) {// 調用攔截器的 triggerAfterCompletiontriggerAfterCompletion(processedRequest, response, mappedHandler,new NestedServletException("Handler processing failed", err));} finally {if (asyncManager.isConcurrentHandlingStarted()) {if (mappedHandler != null) {// 調用 AsyncHandlerInterceptor.afterConcurrentHandlingStarted// 用于在異步請求處理開始之后回調mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);}} else {// 如果是文件上傳請求，需要清理資源if (multipartRequestParsed) {cleanupMultipart(processedRequest);}}}}

????通過層層的調用，終于來到了 doDispatch ，這個方法大致能夠看到請求的處理步驟概覽：

• 首先判斷是否為文件上傳的請求：和普通的請求不一樣，這種請求需要在請求結束后清理文件解析過程中創建的 MultipartFile （可能會在磁盤上保留有臨時數據）；
• 獲取 Handler ：從 HandlerMapping初始化建立的映射關系中找出；
• 攔截器 HandlerInterceptor.preHandle 調用；
• HandlerAdapter 適配：從 HandlerAdapter 初始化注冊的所有適配器中，找到支持對應 Handler 的適配器，調用 handle 方法處理（見 HandlerAdapter）
• 攔截器 HandlerInterceptor.postHandle 調用；
• 調用 processDispatchResult 進行視圖處理；
• 攔截器?HandlerInterceptor.afterCompletion 調用（異常同樣會觸發，并且會作為參數傳入）

? ? 接下來我們來看幾個主要步驟的解析。

?

getHandler

    @Nullableprotected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {if (this.handlerMappings != null) {// 遍歷所有注冊的 HandlerMappingfor (HandlerMapping hm : this.handlerMappings) {....// 省略日志// 找到匹配的HandlerExecutionChain（不為null）HandlerExecutionChain handler = hm.getHandler(request);if (handler != null) {return handler;}}}return null;}

? ? 調用 HandlerMapping.getHandler 獲取請求對應的 Handler。來看實現：

public abstract class AbstractHandlerMapping extends WebApplicationObjectSupport implements HandlerMapping, Ordered {@Override@Nullablepublic final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {// 根據 request獲取對應的 Handler（子類實現）Object handler = getHandlerInternal(request);// 如果沒有找到對應 Handler，使用默認Handlerif (handler == null) {handler = getDefaultHandler();}// 如果默認的 Handler沒有，則返回 nullif (handler == null) {return null;}// Handler為 String類型，說明是beanName，調用 getBean獲取if (handler instanceof String) {String handlerName = (String) handler;handler = obtainApplicationContext().getBean(handlerName);}// 執行鏈構造：Handler和攔截器HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);// 判斷跨域請求：是否帶有“Origin”請求頭if (CorsUtils.isCorsRequest(request)) {// 全局跨域配置CorsConfiguration globalConfig = this.globalCorsConfigSource.getCorsConfiguration(request);// 單個 Handler配置（注解 @CrossOrigin其實就是對單個 Handler的配置）CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);// 配置合并CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);// 添加 CorsInterceptor攔截器（使用合并后的配置）executionChain = getCorsHandlerExecutionChain(request, executionChain, config);}return executionChain;}// 執行鏈構造protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?(HandlerExecutionChain) handler : new HandlerExecutionChain(handler));String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);// 遍歷 List<HandlerInterceptor>for (HandlerInterceptor interceptor : this.adaptedInterceptors) {if (interceptor instanceof MappedInterceptor) {MappedInterceptor mappedInterceptor = (MappedInterceptor) interceptor;if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) {// 將匹配的 MappedInterceptor加入處理鏈chain.addInterceptor(mappedInterceptor.getInterceptor());}} else {// 其他的直接加入chain.addInterceptor(interceptor);}}return chain;}// 跨域攔截器加入protected HandlerExecutionChain getCorsHandlerExecutionChain(HttpServletRequest request,HandlerExecutionChain chain, CorsConfiguration config) {// 條件：帶有“Origin”、“Access-Control-Request-Method”請求頭的 options請求if (CorsUtils.isPreFlightRequest(request)) {HandlerInterceptor[] interceptors = chain.getInterceptors();// 使用 PreFlightHandler替代原本的 Handler處理請求chain = new HandlerExecutionChain(new PreFlightHandler(config), interceptors);} else {// 添加 CorsInterceptor攔截器（攔截器末尾）chain.addInterceptor(new CorsInterceptor(config));}return chain;}
}

? ? 抽象父類?AbstractHandlerMapping 實現了?執行鏈的構造?以及 “跨域”相關處理（攔截器），查找 Handler 的邏輯交由子類實現（getHandlerInternal）。回想一下 HandlerMapping 注冊 Handler 的邏輯分為了兩個分支?AbstractUrlHandlerMapping?和?AbstractHandlerMethodMapping （見 HandlerMapping 初始化），因此查找邏輯也隨注冊邏輯不同而不同。

?

AbstractUrlHandlerMapping?分支

public abstract class AbstractUrlHandlerMapping extends AbstractHandlerMapping implements MatchableHandlerMapping {@Overrideprotected Object getHandlerInternal(HttpServletRequest request) throws Exception {// 這一步我們會取到截取后的請求相對地址String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);// 根據相對地址找到對應的 HandlerObject handler = lookupHandler(lookupPath, request);if (handler == null) {// 沒有的話，依次查詢根 Handler、默認 HandlerObject rawHandler = null;if ("/".equals(lookupPath)) {rawHandler = getRootHandler();}if (rawHandler == null) {rawHandler = getDefaultHandler();}if (rawHandler != null) {// 如果 Handler是 beanName，調用 getBean獲取if (rawHandler instanceof String) {String handlerName = (String) rawHandler;rawHandler = getApplicationContext().getBean(handlerName);}// 校驗：由 DefaultAnnotationHandlerMapping實現// 看請求是否滿足 @RequestMapping指定的 method、param、headervalidateHandler(rawHandler, request);// 使用 Handler創建執行鏈，鏈頭添加 PathExposingHandlerInterceptor攔截器handler = buildPathExposingHandler(rawHandler, lookupPath, lookupPath, null);}}....// 省略日志return handler;}protected Object lookupHandler(String urlPath, HttpServletRequest request) throws Exception {// 從映射關系中找出請求對應的 Handler（直接路徑）// 映射關系的初始化見 HandlerMapping初始化Object handler = this.handlerMap.get(urlPath);if (handler != null) {// beanName以及 Handler校驗，上面講過了if (handler instanceof String) {String handlerName = (String) handler;handler = getApplicationContext().getBean(handlerName);}validateHandler(handler, request);// 構造執行鏈return buildPathExposingHandler(handler, urlPath, urlPath, null);}// 直接路徑中未找到，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校驗，上面講過了if (handler instanceof String) {String handlerName = (String) handler;handler = getApplicationContext().getBean(handlerName);}validateHandler(handler, request);String pathWithinMapping = getPathMatcher().extractPathWithinPattern(bestMatch, urlPath);// 可能存在多個“最佳模式”，讓我們確保所有這些模式都有正確的URI模板變量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// 構造執行鏈return buildPathExposingHandler(handler, bestMatch, pathWithinMapping, uriTemplateVariables);}// 沒有匹配的 Handler返回 nullreturn null;}
}

? ? 首先調用 UrlPathHelper.getLookupPathForRequest 獲取請求的相對路徑。以 Tomcat 舉例，配置的 <Context path="xxx"> 項目根路徑，那么對應的 web 應用所有的請求，都要添加 “xxx” 前綴，但我們的應用對此是無感知的，所以框架層面要把這些截取后，再去查找 Handler。來看下截取邏輯：

public class UrlPathHelper {public String getLookupPathForRequest(HttpServletRequest request) {// 默認為 falseif (this.alwaysUseFullPath) {return getPathWithinApplication(request);}String rest = getPathWithinServletMapping(request);if (!"".equals(rest)) {return rest;} else {return getPathWithinApplication(request);}}public String getPathWithinServletMapping(HttpServletRequest request) {// 獲取截取后的相對地址String pathWithinApp = getPathWithinApplication(request);// 獲取的 <servlet>指定的 <url-pattern>（移除通配符后）String servletPath = getServletPath(request);// 把 pathWithinApp中的“//”替換成“/”String sanitizedPathWithinApp = getSanitizedPath(pathWithinApp);String path;// 這一步主要就是對請求地址中多余的“/”進行移除匹配if (servletPath.contains(sanitizedPathWithinApp)) {// 同樣的，把請求的相對地址中，servletPath截取掉path = getRemainingPath(sanitizedPathWithinApp, servletPath, false);} else {// 同樣的，把請求的相對地址中，servletPath截取掉path = getRemainingPath(pathWithinApp, servletPath, false);}if (path != null) {return path;} else {// 如果請求不在 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) {// 獲取的項目根路徑String contextPath = getContextPath(request);// 獲取請求的相對地址String requestUri = getRequestUri(request);// 把請求的相對地址中的項目根路徑截去String path = getRemainingPath(requestUri, contextPath, true);if (path != null) {return (StringUtils.hasText(path) ? path : "/");} else {return requestUri;}}
}

? ? （getPathWithinServletMapping）首先會在配置的 DispatcherServlet 范圍內查找，對于同一個請求 “http://localhost/a/b” 來說：

• <url-pattern>/*</url-pattern>， 返回的就是 “/a/b”；
• <url-pattern>/a/*</url-pattern>，那么返回的就是 “/b”。如果請求為 “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時才會在 Application 范圍內查找，對于用一個請求“http://localhost/context/a” 來說：

• <Context path="/context">，返回的就是 “/a”；
• <Context path="/">，返回的就是 “/context/a”。如果請求為 “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 {// 同樣使用 UrlPathHelper.getLookupPathForRequestString lookupPath = getUrlPathHelper().getLookupPathForRequest(request);if (logger.isDebugEnabled()) {logger.debug("Looking up handler method for path " + lookupPath);}this.mappingRegistry.acquireReadLock();try {// 根據請求 url找到對應的 HandlerMethodHandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);....// 省略日志// createWithResolvedBean目的是確保 HandlerMethod中持有的是被調用的實例 bean// 而不是 beanName，如果是會調用了 getBean獲取實例后創建新的 HandleMethod// 因為這個實例 bean會用于反射調用方法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，通過相對路徑查找對應的 List<RequestMappingInfo>// 見 AbstractHandlerMethodMapping的注冊邏輯List<T> directPathMatches = this.mappingRegistry.getMappingsByUrl(lookupPath);if (directPathMatches != null) {// 不為 null，說明 @RequestMapping指定的是非通配符路徑// 找到匹配條件的填充 matchesaddMatchingMappings(directPathMatches, matches, request);}if (matches.isEmpty()) {// 如果通過直接路徑找不到，就在所有注冊的映射路徑中查找// 找到匹配條件的填充 matchesaddMatchingMappings(this.mappingRegistry.getMappings().keySet(), matches, request);}if (!matches.isEmpty()) {// 因為可能會有多個匹配方法，需要根據定義的優先級排序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) {// 條件：帶有“Origin”、“Access-Control-Request-Method”請求頭的 options請求if (CorsUtils.isPreFlightRequest(request)) {// 返回 EmptyHandler封裝的 HandlerMethod// 調用會拋出異常 UnsupportedOperationExceptionreturn PREFLIGHT_AMBIGUOUS_MATCH;}// 有兩個相同優先級的匹配結果，會拋異常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 + "}");}}// 調用 setAttribute設置一些屬性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);}}
}

? ? 同樣使用的是?UrlPathHelper.getLookupPathForRequest 獲取請求的相對路徑。之后根據相對路徑找到對應的 HandlerMethod 。涉及到了一個請求地址對應了多個匹配結果的篩選：

    private void addMatchingMappings(Collection<T> mappings, List<Match> matches, HttpServletRequest request) {for (T mapping : mappings) {// 獲取滿足條件的 RequestMappingInfoT match = getMatchingMapping(mapping, request);// 只有滿足返回的才不為 null，這一步會篩選掉不符合條件的// 例如：請求路徑不匹配、header頭不匹配等等if (match != null) {// 通過 MappingRegistry維護的 mappingLookup找到對應的 HandlerMethod// 使用 RequestMappingInfo和 HandlerMethod創建 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) {// 調用 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);// 這一步基本不會，因為 @RequestMapping都有默認值if (methods == null || params == null || headers == null || consumes == null || produces == null) {return null;}// 對于 @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;}// 對于 @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());}
}

? ? 以上的源碼，就是用滿足請求條件的（指定的 method、header等） RequestMappingInfo 以及對應的 HandlerMethod 封裝成 Match，?并填充到 matches 的邏輯。

????這一步可能會篩選出多個匹配項，接下來就需要靠?MatchComparator 排序后挑選出最匹配項，邏輯見?RequestMappingInfo.compareTo，這里不展開分析。

?

getHandlerAdapter

    protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {if (this.handlerAdapters != null) {// 遍歷所有注冊的 HandlerAdapterfor (HandlerAdapter ha : this.handlerAdapters) {if (logger.isTraceEnabled()) {logger.trace("Testing handler adapter [" + ha + "]");}// 調用 HandlerAdapter.supports看是否支持適配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");}

? ? 這里調用的 supports 獲取到支持適配的 HandlerAdapter，之后調用其 handle 方法執行處理邏輯，具體源碼上篇已分析，見 “HandlerAdapter”。

? ? 執行完之后，就獲取到了 ModelAndView 返回，接著就是對視圖的處理（processDispatchResult），放在下節分析。

?

總結

? ? 本篇分析的就是一個請求從接收到處理的全過程，目前進度已經獲取到了 ModelAndView，至于請求地址如何找到對應的?Handler、Handler 如何調用并返回 ModelAndView ，前幾篇已作講解。下篇將分析 “視圖處理” 源碼。