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简介 分析请求从Servlet容器交到SpringMVC一直到DispatcherServlet具体处理请求之前都做了些什么
1. HttpServletBean
主要参与了创建工作，并没有涉及到请求的处理
2. Servlet的处理过程
首先从Servlet的service方法开始，然后在HttpServlet的service方法中根据请求的类型不同将请求路由到doGet、doHead、doPost、doPut、doDelete、doOptions、doTrace七种方法中；在FrameworkServlet中重写了除doHead，在service方法中增加了对PATCH类型请求的处理，其他类型的请求直接交给了父类进行处理；以POST请求为例，FrameworkServlet实现了HttpServlet中的doPost方法进行具体处理．
package org.springframework.web.servlet.FrameworkServlet;/*** Override the parent class implementation in order to intercept PATCH requests.*/@Overrideprotected void service(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {HttpMethod httpMethod = HttpMethod.resolve(request.getMethod());if (httpMethod == HttpMethod.PATCH || httpMethod == null) {processRequest(request, response);}else {//若是post请求，进入下面的doPost方法super.service(request, response);}}/*** 实现了HttpServlet的doPost方法*/@Overrideprotected final void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {processRequest(request, response);}/*** Process this request, publishing an event regardless of the outcome.* <p>The actual event handling is performed by the abstract* {@link #doService} template method.*/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LocaleContextLocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();//获取当前请求的LocaleContextLocaleContext localeContext = buildLocaleContext(request);//获取RequestContextHolder中原来保存的RequestAttributesRequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();//获取当前请求的ServletRequestAttributesServletRequestAttributes 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RequestAttributes设置到LocaleContextHolder和RequestContextHolderinitContextHolders(request, localeContext, requestAttributes);try {//实际处理请求入口，在DispatcherServlet中具体实现doService(request, response);}catch (ServletException | IOException ex) {failureCause = ex;throw ex;}catch (Throwable ex) {failureCause = ex;throw new NestedServletException("Request processing failed", ex);}finally {//恢复原来的LocaleContext和RequestAttributes设置到LocaleContextHolder和RequestContextHolder．因为在servlet外面可能还有别的操作，如Filter等resetContextHolders(request, previousLocaleContext, previousAttributes);if (requestAttributes != null) {requestAttributes.requestCompleted();}if (logger.isDebugEnabled()) {if (failureCause != null) {this.logger.debug("Could not complete request", failureCause);}else {if (asyncManager.isConcurrentHandlingStarted()) {logger.debug("Leaving response open for concurrent processing");}else {this.logger.debug("Successfully completed request");}}}//发布ServletRequestHandledEventpublishRequestHandledEvent(request, response, startTime, failureCause);}}
processRequest主要功能：
1）异步请求
2）调用doService方法具体处理请求
3）对LocaleContext(用于获取Locale)和RequestAttributes(用于管理requesthesession属性)的设置及恢复
4）处理完后发布ServletRequestHandledEvent消息
总结FrameworkServlet处理请求：
首先在service方法里添加了对PATCH的处理，并将所有需要自己处理的请求都集中到了processRequest方法进行统一处理，人后就是processRequest方法．
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