SpringMVC执行流程及源码解析
tppb4955
8年前
<p>在SpringMVC中主要是围绕着DispatcherServlet来设计，可以把它当做指挥中心。这里先说明一下SpringMVC文档给出的执行流程，然后是我们稍微具体的执行流程，最后是流程大致的源码跟踪。关于很很很详细的源码解析，这里暂先不做。</p> <p><strong>官方文档中的流程</strong></p> <p>首先看下SpringMVC文档上给的流程图：</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/44245573e0c5d1ff460cb32da9e29893.png"></p> <p>这张图片给了我们大概的执行流程：</p> <ul> <li>用户请求首先发送到前端控制器DispatcherServlet，DispatcherServlet根据请求的信息来决定使用哪个页面控制器Controller（也就是我们通常编写的Controller）来处理该请求。找到控制器之后，DispatcherServlet将请求委托给控制器去处理。</li> <li>接下来页面控制器开始处理用户请求，页面控制器会根据请求信息进行处理，调用业务层等等，处理完成之后，会把结果封装成一个ModelAndView返回给DispatcherServlet。</li> <li>前端控制器DispatcherServlet接到页面控制器的返回结果后，根据返回的视图名选择相应的试图模板，并根据返回的数据进行渲染。</li> <li>最后前端控制器DispatcherServlet将结果返回给用户。</li> </ul> <p><strong>更具体的流程</strong></p> <p>上面只是总体流程，接下来我们稍微深入一点，看下更具体的流程，这里没有图，只有步骤解析：</p> <ul> <li>用户请求发送到前端控制器DispatcherServlet。</li> <li>前端控制器DispatcherServlet接收到请求后，DispatcherServlet会使用HandlerMapping来处理，HandlerMapping会查找到具体进行处理请求的Handler对象。</li> <li>HandlerMapping找到对应的Handler之后，并不是返回一个Handler原始对象，而是一个Handler执行链，在这个执行链中包括了拦截器和处理请求的Handler。HandlerMapping返回一个执行链给DispatcherServlet。</li> <li>DispatcherServlet接收到执行链之后，会调用Handler适配器去执行Handler。</li> <li>Handler适配器执行完成Handler（也就是我们写的Controller）之后会得到一个ModelAndView，并返回给DispatcherServlet。</li> <li>DispatcherServlet接收到Handler适配器返回的ModelAndView之后，会根据其中的视图名调用视图解析器。</li> <li>视图解析器根据逻辑视图名解析成一个真正的View视图，并返回给DispatcherServlet。</li> <li>DispatcherServlet接收到视图之后，会根据上面的ModelAndView中的model来进行视图渲染完成之后，DispatcherServlet就可以将结果返回给用户了。</li> </ul> <p><strong>源码</strong></p> <p>DispatcherServlet是一个Servlet，我们知道在Servlet在处理一个请求的时候会交给service方法进行处理，这里也不例外，DispatcherServlet继承了FrameworkServlet，首先进入FrameworkServlet的service方法：</p> <pre> <code class="language-java">protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //请求方法 String method = request.getMethod(); //PATCH方法单独处理 if (method.equalsIgnoreCase(RequestMethod.PATCH.name())) { processRequest(request, response); } else {//其他的请求类型的方法经由父类，也就是HttpServlet处理 super.service(request, response); } }</code></pre> <p>HttpServlet中会根据请求类型的不同分别调用doGet或者doPost等方法，FrameworkServlet中已经重写了这些方法，在这些方法中会调用processRequest进行处理，在processRequest中会调用doService方法，这个doService方法就是在DispatcherServlet中实现的。下面就看下DispatcherServlet中的doService方法的实现。</p> <p><strong>请求到达DispatcherServlet</strong> <strong>doService方法：</strong></p> <pre> <code class="language-java">protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception { //给request中的属性做一份快照 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)); } } } //如果我们没有配置类似本地化或者主题的处理器之类的 //SpringMVC会使用默认的值 //默认配置文件是DispatcherServlet.properties 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 { //开始处理 doDispatch(request, response); } finally { if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) { return; } // Restore the original attribute snapshot, in case of an include. if (attributesSnapshot != null) { restoreAttributesAfterInclude(request, attributesSnapshot); } } }</code></pre> <p>DispatcherServlet开始真正的处理， <strong>doDispatch方法</strong> ：</p> <pre> <code class="language-java">protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception { HttpServletRequest processedRequest = request; HandlerExecutionChain mappedHandler = null; boolean multipartRequestParsed = false; //SpringMVC中异步请求的相关知识，暂先不解释 WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request); try { ModelAndView mv = null; Exception dispatchException = null; try { //先检查是不是Multipart类型的，比如上传等 //如果是Multipart类型的，则转换为MultipartHttpServletRequest类型 processedRequest = checkMultipart(request); multipartRequestParsed = processedRequest != request; //获取当前请求的Handler mappedHandler = getHandler(processedRequest, false); if (mappedHandler == null || mappedHandler.getHandler() == null) { noHandlerFound(processedRequest, response); return; } //获取当前请求的Handler适配器 HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler()); // 对于header中last-modified的处理 String method = request.getMethod(); boolean isGet = "GET".equals(method); if (isGet || "HEAD".equals(method)) { long lastModified = ha.getLastModified(request, mappedHandler.getHandler()); if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) { return; } } //拦截器的preHandle方法进行处理 if (!mappedHandler.applyPreHandle(processedRequest, response)) { return; } try { //真正调用Handler的地方 mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); } finally { if (asyncManager.isConcurrentHandlingStarted()) { return; } } //处理成默认视图名，就是添加前缀和后缀等 applyDefaultViewName(request, mv); //拦截器postHandle方法进行处理 mappedHandler.applyPostHandle(processedRequest, response, mv); } catch (Exception ex) { dispatchException = ex; } //处理最后的结果，渲染之类的都在这里 processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException); } catch (Exception ex) { triggerAfterCompletion(processedRequest, response, mappedHandler, ex); } catch (Error err) { triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err); } finally { if (asyncManager.isConcurrentHandlingStarted()) { // Instead of postHandle and afterCompletion mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response); return; } // Clean up any resources used by a multipart request. if (multipartRequestParsed) { cleanupMultipart(processedRequest); } } }</code></pre> <p>可以看到大概的步骤还是按照我们上面分析的走的。</p> <p><strong>查找请求对应的Handler对象</strong></p> <p>对应着这句代码mappedHandler = getHandler(processedRequest, false);，看下具体的getHandler方法：</p> <pre> <code class="language-java">protected HandlerExecutionChain getHandler(HttpServletRequest request, boolean cache) throws Exception { return getHandler(request); }</code></pre> <p>继续往下看getHandler：</p> <pre> <code class="language-java">protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception { //遍历所有的handlerMappings进行处理 //handlerMappings是在启动的时候预先注册好的 for (HandlerMapping hm : this.handlerMappings) { HandlerExecutionChain handler = hm.getHandler(request); if (handler != null) { return handler; } } return null; }</code></pre> <p>继续往下看getHandler，在AbstractHandlerMapping类中：</p> <pre> <code class="language-java">public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception { //根据request获取handler Object handler = getHandlerInternal(request); if (handler == null) { //如果没有找到就使用默认的handler handler = getDefaultHandler(); } if (handler == null) { return null; } //如果Handler是String，表明是一个bean名称 //需要超照对应bean if (handler instanceof String) { String handlerName = (String) handler; handler = getApplicationContext().getBean(handlerName); } //封装Handler执行链 return getHandlerExecutionChain(handler, request); }</code></pre> <p><strong>根据requrst获取handler</strong></p> <p>首先看下根据requrst获取handler步骤getHandlerInternal方法，在AbstractHandlerMethodMapping中：</p> <pre> <code class="language-java">protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception { //获取request中的url，用来匹配handler String lookupPath = getUrlPathHelper().getLookupPathForRequest(request); //根据路径寻找Handler HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request); //根据handlerMethod中的bean来实例化Handler并添加进HandlerMethod return (handlerMethod != null) ? handlerMethod.createWithResolvedBean() : null; }</code></pre> <p>看下根据路径寻找handler的方法lookupHandlerMethod：</p> <pre> <code class="language-java">protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception { List<Match> matches = new ArrayList<Match>(); //直接匹配 List<T> directPathMatches = this.urlMap.get(lookupPath); //如果有匹配的，就添加进匹配列表中 if (directPathMatches != null) { addMatchingMappings(directPathMatches, matches, request); } //还没有匹配的，就遍历所有的处理方法查找 if (matches.isEmpty()) { // No choice but to go through all mappings addMatchingMappings(this.handlerMethods.keySet(), matches, request); } //找到了匹配的 if (!matches.isEmpty()) { Comparator<Match> comparator = new MatchComparator(getMappingComparator(request)); Collections.sort(matches, comparator); //排序之后，获取第一个 Match bestMatch = matches.get(0); //如果有多个匹配的，会找到第二个最合适的进行比较一下 if (matches.size() > 1) { 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 + "}"); } } //设置request参数 handleMatch(bestMatch.mapping, lookupPath, request); //返回匹配的url的处理的方法 return bestMatch.handlerMethod; } else {//最后还没有找到，返回null return handleNoMatch(handlerMethods.keySet(), lookupPath, request); } }</code></pre> <p><strong>获取默认Handler</strong></p> <p>如果上面没有获取到Handler，就会获取默认的Handler。如果还获取不到就返回null。</p> <p><strong>处理String类型的Handler</strong></p> <p>如果上面处理完的Handler是String类型的，就会根据这个handlerName获取bean。</p> <p><strong>封装Handler执行链</strong></p> <p>上面获取完Handler，就开始封装执行链了，就是将我们配置的拦截器加入到执行链中去，getHandlerExecutionChain：</p> <pre> <code class="language-java">protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) { //如果当前Handler不是执行链类型，就使用一个新的执行链实例封装起来 HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain) ? (HandlerExecutionChain) handler : new HandlerExecutionChain(handler); //先获取适配类型的拦截器添加进去拦截器链 chain.addInterceptors(getAdaptedInterceptors()); //当前的url String lookupPath = urlPathHelper.getLookupPathForRequest(request); //遍历拦截器，找到跟当前url对应的，添加进执行链中去 for (MappedInterceptor mappedInterceptor : mappedInterceptors) { if (mappedInterceptor.matches(lookupPath, pathMatcher)) { chain.addInterceptor(mappedInterceptor.getInterceptor()); } } return chain; }</code></pre> <p><strong>获取对应请求的Handler适配器</strong></p> <p>getHandlerAdapter：</p> <pre> <code class="language-java">protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException { //遍历所有的HandlerAdapter，找到和当前Handler匹配的就返回 //我们这里会匹配到RequestMappingHandlerAdapter for (HandlerAdapter ha : this.handlerAdapters) { if (ha.supports(handler)) { return ha; } } }</code></pre> <p><strong>缓存的处理</strong></p> <p>也就是对last-modified的处理</p> <p><strong>执行拦截器的preHandle方法</strong></p> <p>就是遍历所有的我们定义的interceptor，执行preHandle方法</p> <p><strong>使用Handler适配器执行当前的Handler</strong></p> <p>ha.handle执行当前Handler，我们这里使用的是RequestMappingHandlerAdapter，首先会进入AbstractHandlerMethodAdapter的handle方法：</p> <pre> <code class="language-java">public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { return handleInternal(request, response, (HandlerMethod) handler); }</code></pre> <p>handleInternal方法，在RequestMappingHandlerAdapter中：</p> <pre> <code class="language-java">protected final ModelAndView handleInternal(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod) throws Exception { if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) { // Always prevent caching in case of session attribute management. checkAndPrepare(request, response, this.cacheSecondsForSessionAttributeHandlers, true); } else { // Uses configured default cacheSeconds setting. checkAndPrepare(request, response, true); } // Execute invokeHandlerMethod in synchronized block if required. if (this.synchronizeOnSession) { HttpSession session = request.getSession(false); if (session != null) { Object mutex = WebUtils.getSessionMutex(session); synchronized (mutex) { return invokeHandleMethod(request, response, handlerMethod); } } } //执行方法，封装ModelAndView return invokeHandleMethod(request, response, handlerMethod); }</code></pre> <p><strong>组装默认视图名称</strong></p> <p>前缀和后缀名都加上</p> <p><strong>执行拦截器的postHandle方法</strong></p> <p>遍历intercepter的postHandle方法。</p> <p><strong>处理最后的结果，渲染之类的</strong></p> <p>processDispatchResult方法：</p> <pre> <code class="language-java">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) { 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()) { //渲染 render(mv, request, response); if (errorView) { WebUtils.clearErrorRequestAttributes(request); } } else { } if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) { // Concurrent handling started during a forward return; } if (mappedHandler != null) { mappedHandler.triggerAfterCompletion(request, response, null); } }</code></pre> <p>重点看下render方法，进行渲染：</p> <pre> <code class="language-java">protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception { //设置本地化 Locale locale = this.localeResolver.resolveLocale(request); response.setLocale(locale); View view; if (mv.isReference()) { //解析视图名，得到视图 view = resolveViewName(mv.getViewName(), mv.getModelInternal(), locale, request); } 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() + "'"); } } //委托给视图进行渲染 view.render(mv.getModelInternal(), request, response); } view.render就是进行视图的渲染，然后跳转页面等处理。</code></pre> <p>到这里大概的流程就走完了。其中涉及到的东西还有很多，暂先不做详细处理。</p> <p> </p> <p>来自：http://www.iteye.com/news/32332</p> <p> </p>