标签：upd his bin sync service 方法 new cep original
分析 Spring MVC 是怎么处理请求的。首先分析 HttpServletBean、FrameworkServlet 和 DispatcherServlet 这三个 Servlet 的处理过程，最后分析 doDispatcher 的结构。
HttpServletBean
参与了创建工作，并没有涉及请求的处理。
FrameworkServlet
在类中的 service() 、doGet()、doPost()、doPut()、doDelete()、doOptions()、doTrace() 这些方法中可以看到都调用了一个共同的方法 processRequest() ，它是类在处理请求中最核心的方法。
protected final void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { long startTime = System.currentTimeMillis(); Throwable failureCause = null; //获取 LocaleContextHolder 中原来保存的 LocaleContext LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext(); //获取当前请求的 LocaleContext LocaleContext localeContext = buildLocaleContext(request); //获取 RequestContextHolder 中原来保存的 RequestAttributes RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes(); //获取当前请求的 ServletRequestAttributes ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes); WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request); asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor()); //将当前请求的 LocaleContext 和 ServletRequestAttributes 设置到 LocaleContextHolder 和 RequestContextHolder initContextHolders(request, localeContext, requestAttributes); try { //实际处理请求的入口，这是一个模板方法，在 Dispatcher 类中才有具体实现 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 { //将 previousLocaleContext，previousAttributes 恢复到 LocaleContextHolder 和 RequestContextHolder 中 resetContextHolders(request, previousLocaleContext, previousAttributes); if (requestAttributes != null) { requestAttributes.requestCompleted(); } //删除了日志打印代码 //发布了一个 ServletRequestHandledEvent 类型的消息 publishRequestHandledEvent(request, response, startTime, failureCause); } }
DispatcherServlet
上一章中其实还没把该类讲清楚，在这个类中，里面的智行处理的入口方法应该是 doService 方法，方法里面调用了 doDispatch 进行具体的处理，在调用 doDispatch 方法之前 doService 做了一些事情：首先判断是不是 include 请求，如果是则对 request 的 Attribute 做个快照备份，等 doDispatcher 处理完之后（如果不是异步调用且未完成）进行还原 ，在做完快照后又对 request 设置了一些属性。
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception { // 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<>(); 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 { //调用 doDispatch 方法 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() 方法：
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 { //检查是不是上传请求 processedRequest = checkMultipart(request); multipartRequestParsed = (processedRequest != request); // Determine handler for the current request. 根据 request 找到 Handler mappedHandler = getHandler(processedRequest); if (mappedHandler == null || mappedHandler.getHandler() == null) { noHandlerFound(processedRequest, response); return; } // Determine handler adapter for the current request.根据 Handler 找到对应的 HandlerAdapter HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler()); // Process last-modified header, if supported by the handler. //处理 GET 、 HEAD 请求的 LastModified 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; } } //执行相应的 Interceptor 的 preHandle if (!mappedHandler.applyPreHandle(processedRequest, response)) { return; } // Actually invoke the handler. HandlerAdapter 使用 Handler 处理请求 mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); //如果需要异步处理，直接返回 if (asyncManager.isConcurrentHandlingStarted()) { return; } //当 view 为空时，根据 request 设置默认 view applyDefaultViewName(processedRequest, mv); //执行相应 Interceptor 的 postHandler 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); } //调用 processDispatchResult 方法处理上面处理之后的结果（包括处理异常，渲染页面，发出完成通知触发 Interceptor 的 afterCompletion） 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 { //判断是否执行异步请求 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. 删除上传请求的资源 if (multipartRequestParsed) { cleanupMultipart(processedRequest); } } } }
Handler，HandlerMapping，HandlerAdapter 三个区别：
Handler：处理器，对应 MVC 的 C层，也就是 Controller 层，具体表现形式有很多种，可以是类，方法，它的类型是 Object，只要可以处理实际请求就可以是 Handler。
HandlerMapping：用来查找 Handler 的。
HandlerAdapter ：Handler 适配器，
另外 View 和 ViewResolver 的原理与 Handler 和 HandlerMapping 的原理类似。
标签：upd his bin sync service 方法 new cep original
原文地址：https://www.cnblogs.com/deityjian/p/11494557.html
