1.用戶發(fā)送請求至前端控制器DispatcherServlet 2.DispatcherServlet收到請求調(diào)用處理器映射器HandlerMapping。 3.處理器映射器根據(jù)請求url找到具體的處理器，生成處理器執(zhí)行鏈HandlerExecutionChain(包括處理器對象和處理器攔截器)一并返回給DispatcherServlet。 4.DispatcherServlet根據(jù)處理器Handler獲取處理器適配器HandlerAdapter 5.DispatcherServlet通過HandlerAdapter處理器適配器調(diào)用處理器 6.執(zhí)行處理器(Controller，也叫頁面控制器)。 7.Controller執(zhí)行完成返回ModelAndView 8.HandlerAdapter將controller執(zhí)行結(jié)果ModelAndView返回 9.DispatcherServlet將ModelAndView傳給ViewReslover視圖解析器 10.ViewReslover解析后返回具體View 11.DispatcherServlet對View進(jìn)行渲染視圖（即將模型數(shù)據(jù)填充至視圖中）。 12.DispatcherServlet響應(yīng)用戶。
1.DispatcherServlet：前端控制器。用戶請求到達(dá)前端控制器，它就相當(dāng)于mvc模式中的c，dispatcherServlet是整個流程控制的中心，由它調(diào)用其它組件處理用戶的請求，dispatcherServlet的存在降低了組件之間的耦合性。由框架實(shí)現(xiàn) 2.HandlerMapping：處理器映射器。HandlerMapping負(fù)責(zé)根據(jù)用戶請求找到Handler即處理器，sPRingmvc提供了不同的映射器實(shí)現(xiàn)不同的映射方式，例如：配置文件方式，實(shí)現(xiàn)接口方式，注解方式等。由框架實(shí)現(xiàn) 3.Handler：處理器。Handler 是繼DispatcherServlet前端控制器的后端控制器，在DispatcherServlet的控制下Handler對具體的用戶請求進(jìn)行處理。由于Handler涉及到具體的用戶業(yè)務(wù)請求，所以一般情況需要程序員根據(jù)業(yè)務(wù)需求開發(fā)Handler。 4.HandlAdapter：處理器適配器。通過HandlerAdapter對處理器進(jìn)行執(zhí)行，這是適配器模式的應(yīng)用，通過擴(kuò)展適配器可以對更多類型的處理器進(jìn)行執(zhí)行。由框架實(shí)現(xiàn)。 5.ViewResolver：視圖解析器。ViewResolver負(fù)責(zé)將處理結(jié)果生成View視圖，ViewResolver首先根據(jù)邏輯視圖名解析成物理視圖名即具體的頁面地址，再生成View視圖對象，最后對View進(jìn)行渲染將處理結(jié)果通過頁面展示給用戶。 springmvc框架提供了很多的View視圖類型，包括：jstlView、freemarkerView、pdfView等。一般情況下需要通過頁面標(biāo)簽或頁面模版技術(shù)將模型數(shù)據(jù)通過頁面展示給用戶，需要由程序員根據(jù)業(yè)務(wù)需求開發(fā)具體的頁面。
1.請求到達(dá)前端控制器的第一站，先做些準(zhǔn)備工作
/** * Exposes the DispatcherServlet-specific request attributes and delegates to {@link #doDispatch} * for the actual dispatching. */@Overrideprotected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception { if (logger.isDebugEnabled()) { String requestUri = urlPathHelper.getRequestUri(request); logger.debug("DispatcherServlet with name '" + getServletName() + "' processing " + request.getMethod() + " request for [" + requestUri + "]"); } //保護(hù)現(xiàn)場 // 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)) { logger.debug("Taking snapshot of request attributes before include"); attributesSnapshot = new HashMap<String, Object>(); Enumeration<?> attrNames = request.getAttributeNames(); while (attrNames.hasMoreElements()) { String attrName = (String) attrNames.nextElement(); if (this.cleanupAfterInclude || attrName.startsWith("org.springframework.web.servlet")) { attributesSnapshot.put(attrName, request.getAttribute(attrName)); } } } //將框架相關(guān)信息存儲至request，方便后面的處理器和視圖用到 // 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); //請求分發(fā) try { doDispatch(request, response); } finally { // Restore the original attribute snapshot, in case of an include. if (attributesSnapshot != null) { restoreAttributesAfterInclude(request, attributesSnapshot); } }}2.開始處理請求 //通過url查找HandlerMap中最相近的key(url)，然后由key獲取HandlerMapping對象 //通過處理器映射器獲取處理器； //通過查詢處理器適配器獲得
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception { HttpServletRequest processedRequest = request; HandlerExecutionChain mappedHandler = null; int interceptorIndex = -1; try { ModelAndView mv; boolean errorView = false; try { processedRequest = checkMultipart(request); // Determine handler for the current request //步驟3.1~3.4用于獲取包含處理器Handler和攔截器AdapterIntercepters的處理器執(zhí)行鏈HandlerExecutionChain mappedHandler = getHandler(processedRequest, false); if (mappedHandler == null || mappedHandler.getHandler() == null) { noHandlerFound(processedRequest, response); return; } // Determine handler adapter for the current request. //步驟4.1~4.2,根據(jù)HandlerExecutionChain中的處理器Handler獲取處理器適配器 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()) { String requestUri = urlPathHelper.getRequestUri(request); logger.debug("Last-Modified value for [" + requestUri + "] is: " + lastModified); } if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) { return; } } // Apply preHandle methods of registered interceptors. HandlerInterceptor[] interceptors = mappedHandler.getInterceptors(); if (interceptors != null) { for (int i = 0; i < interceptors.length; i++) { HandlerInterceptor interceptor = interceptors[i]; if (!interceptor.preHandle(processedRequest, response, mappedHandler.getHandler())) { triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null); return; } interceptorIndex = i; } } // Actually invoke the handler. //5.1~5.3通過處理器適配器HandlerApapter來調(diào)用處理器完成對請求的處理 mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); // Do we need view name translation? if (mv != null && !mv.hasView()) { mv.setViewName(getDefaultViewName(request)); } // Apply postHandle methods of registered interceptors. if (interceptors != null) { for (int i = interceptors.length - 1; i >= 0; i--) { HandlerInterceptor interceptor = interceptors[i]; interceptor.postHandle(processedRequest, response, mappedHandler.getHandler(), mv); } } } catch (ModelAndViewDefiningException ex) { logger.debug("ModelAndViewDefiningException encountered", ex); mv = ex.getModelAndView(); } catch (Exception ex) { Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null); mv = processHandlerException(processedRequest, response, handler, ex); errorView = (mv != null); } // Did the handler return a view to render? if (mv != null && !mv.wasCleared()) { render(mv, processedRequest, 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"); } } // Trigger after-completion for successful outcome. triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null); } catch (Exception ex) { // Trigger after-completion for thrown exception. triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, ex); throw ex; } catch (Error err) { ServletException ex = new NestedServletException("Handler processing failed", err); // Trigger after-completion for thrown exception. triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, ex); throw ex; } finally { // Clean up any resources used by a multipart request. if (processedRequest != request) { cleanupMultipart(processedRequest); } }}3.1 getHandler(HttpServletRequest request)，經(jīng)由HandlerMapping對象獲取HandlerExecutionChain(處理器和攔截器)
/** * Return the HandlerExecutionChain for this request. * <p>Tries all handler mappings in order. * @param request current HTTP request * @return the HandlerExecutionChain, or <code>null</code> if no handler could be found */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;}3.2.1 getHandler(HttpServletRequest request)，經(jīng)由request獲取處理器，獲取處理器Handler后，再獲取攔截器，最后組成HandlerExecutionChain
/** * 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 */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); } return getHandlerExecutionChain(handler, request);}3.2.2 根據(jù)查找到的處理器Handler和request獲取包含Handler和AdaptedInterceptors的HandlerExecutionChain
protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) { HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain) ? (HandlerExecutionChain) handler : new HandlerExecutionChain(handler); chain.addInterceptors(getAdaptedInterceptors()); String lookupPath = urlPathHelper.getLookupPathForRequest(request); for (MappedInterceptor mappedInterceptor : mappedInterceptors) { if (mappedInterceptor.matches(lookupPath, pathMatcher)) { chain.addInterceptor(mappedInterceptor.getInterceptor()); } } return chain;}/** * Return the adapted interceptors as HandlerInterceptor array. * @return the array of HandlerInterceptors, or <code>null</code> if none */protected final HandlerInterceptor[] getAdaptedInterceptors() { int count = adaptedInterceptors.size(); return (count > 0) ? adaptedInterceptors.toArray(new HandlerInterceptor[count]) : null;}3.3.getHandlerInternal(HttpServletRequest request)獲取Handler
/** * Look up a handler for the URL path of the given request. * @param request current HTTP request * @return the handler instance, or <code>null</code> if none found */@Overrideprotected Object getHandlerInternal(HttpServletRequest request) throws Exception { String lookupPath = getUrlPathHelper().getLookupPathForRequest(request); Object handler = lookupHandler(lookupPath, request); if (handler == null) { // We need to care for the default handler directly, since we need to // expose the PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE for it as well. Object rawHandler = null; if ("/".equals(lookupPath)) { rawHandler = getRootHandler(); } if (rawHandler == null) { rawHandler = getDefaultHandler(); } if (rawHandler != null) { // Bean name or resolved handler? if (rawHandler instanceof String) { String handlerName = (String) rawHandler; rawHandler = getApplicationContext().getBean(handlerName); } validateHandler(rawHandler, request); handler = buildPathExposingHandler(rawHandler, lookupPath, lookupPath, null); } } if (handler != null && logger.isDebugEnabled()) { logger.debug("Mapping [" + lookupPath + "] to " + handler); } else if (handler == null && logger.isTraceEnabled()) { logger.trace("No handler mapping found for [" + lookupPath + "]"); } return handler;}3.4 lookupHandler(lookupPath, request)根據(jù)給定url path和request獲取Handler
protected Object lookupHandler(String urlPath, HttpServletRequest request) throws Exception { // Direct match? Object handler = this.handlerMap.get(urlPath); if (handler != null) { // Bean name or resolved handler? if (handler instanceof String) { String handlerName = (String) handler; handler = getApplicationContext().getBean(handlerName); } validateHandler(handler, request); return buildPathExposingHandler(handler, urlPath, urlPath, null); } // Pattern match? List<String> matchingPatterns = new ArrayList<String>(); for (String registeredPattern : this.handlerMap.keySet()) { if (getPathMatcher().match(registeredPattern, urlPath)) { matchingPatterns.add(registeredPattern); } } String bestPatternMatch = null; Comparator<String> patternComparator = getPathMatcher().getPatternComparator(urlPath); if (!matchingPatterns.isEmpty()) { Collections.sort(matchingPatterns, patternComparator); if (logger.isDebugEnabled()) { logger.debug("Matching patterns for request [" + urlPath + "] are " + matchingPatterns); } bestPatternMatch = matchingPatterns.get(0); } if (bestPatternMatch != null) { handler = this.handlerMap.get(bestPatternMatch); // Bean name or resolved handler? if (handler instanceof String) { String handlerName = (String) handler; handler = getApplicationContext().getBean(handlerName); } validateHandler(handler, request); String pathWithinMapping = getPathMatcher().extractPathWithinPattern(bestPatternMatch, urlPath); // There might be multiple 'best patterns', let's make sure we have the correct URI template variables // for all of them Map<String, String> uriTemplateVariables = new LinkedHashMap<String, String>(); for (String matchingPattern : matchingPatterns) { if (patternComparator.compare(bestPatternMatch, matchingPattern) == 0) { uriTemplateVariables .putAll(getPathMatcher().extractUriTemplateVariables(matchingPattern, urlPath)); } } if (logger.isDebugEnabled()) { logger.debug("URI Template variables for request [" + urlPath + "] are " + uriTemplateVariables); } return buildPathExposingHandler(handler, bestPatternMatch, pathWithinMapping, uriTemplateVariables); } // No handler found... return null;}4.1 HandlerAdapter getHandlerAdapter(Object handler)，根據(jù)Handler獲取HandlerAdapter
/** * Return the HandlerAdapter for this handler object. * @param handler the handler object to find an adapter for * @throws ServletException if no HandlerAdapter can be found for the handler. This is a fatal error. */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 + "]: Does your handler implement a supported interface like Controller?");}4.2 supports(Object handler)
public boolean supports(Object handler) { return (handler instanceof Controller);}5.1 使用處理器完成對請求的處理
public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { ((Servlet) handler).service(request, response); return null;}public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException{ HttpServletRequest request; HttpServletResponse response; if (!(req instanceof HttpServletRequest && res instanceof HttpServletResponse)) { throw new ServletException("non-HTTP request or response"); } request = (HttpServletRequest) req; response = (HttpServletResponse) res; service(request, response);}5.2 service(HttpServletRequest req, HttpServletResponse resp)
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException{ String method = req.getMethod(); if (method.equals(METHOD_GET)) { long lastModified = getLastModified(req); if (lastModified == -1) { // servlet doesn't support if-modified-since, no reason // to go through further expensive logic doGet(req, resp); } else { long ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE); if (ifModifiedSince < lastModified) { // If the servlet mod time is later, call doGet() // Round down to the nearest second for a proper compare // A ifModifiedSince of -1 will always be less 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 { // // Note that this means NO servlet supports whatever // method was requested, anywhere on this server. // 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); }}5.3 doGet(HttpServletRequest req, HttpServletResponse resp)
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException{ String protocol = req.getProtocol(); String msg = lStrings.getString("http.method_get_not_supported"); if (protocol.endsWith("1.1")) { resp.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, msg); } else { resp.sendError(HttpServletResponse.SC_BAD_REQUEST, msg); }}參考：http://jinnianshilongnian.iteye.com/blog/1602617
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