SpringMVC源码分析（3）DispatcherServlet的请求处理流程

<springmvc源码分析（2）dispatcherservlet的初始化>初始化DispatcherServlet的多个组件。

本文继续分析DispatcherServlet解析请求的过程。

概览

　　①：DispatcherServlet是springmvc中的前端控制器(front controller),负责接收request并将request转发给对应的处理组件.

　　②：HanlerMapping是springmvc中完成url到controller映射的组件.DispatcherServlet接收request,然后从HandlerMapping查找处理request的controller.

　　③：Cntroller处理request,并返回ModelAndView对象,Controller是springmvc中负责处理request的组件(类似于struts2中的Action),ModelAndView是封装结果视图的组件.

　　④ ⑤ ⑥：视图解析器解析ModelAndView对象并返回对应的视图给客户端.

要点

维护url和controller的映射

这部分工作由DefaultAnnotationHandlerMapping.setApplicationContext的父类

org.springframework.web.servlet.handler.AbstractDetectingUrlHandlerMapping.initApplicationContext实现。具体方法为detectHandlers

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protectedvoiddetectHandlers()throwsBeansException{ if (logger.isDebugEnabled()){ logger.debug( "LookingforURLmappingsinapplicationcontext:" +getApplicationContext()); } String[]beanNames=( this .detectHandlersInAncestorContexts? BeanFactoryUtils.beanNamesForTypeIncludingAncestors(getApplicationContext(),Object. class ): getApplicationContext().getBeanNamesForType(Object. class ));   //TakeanybeannamethatwecandetermineURLsfor. for (StringbeanName:beanNames){ String[]urls=determineUrlsForHandler(beanName); if (!ObjectUtils.isEmpty(urls)){ //URLpathsfound:Let'sconsideritahandler. registerHandler(urls,beanName); } else { if (logger.isDebugEnabled()){ logger.debug( "Rejectedbeanname'" +beanName+ "':noURLpathsidentified" ); } } } }

2.准确定位处理请求的具体方法（在AnnotationMethodHandlerAdapter中实现）

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protectedModelAndViewinvokeHandlerMethod(HttpServletRequestrequest,HttpServletResponseresponse,Objecthandler) throwsException{   ServletHandlerMethodResolvermethodResolver=getMethodResolver(handler); MethodhandlerMethod=methodResolver.resolveHandlerMethod(request); //具体实现方法的匹配 ServletHandlerMethodInvokermethodInvoker=newServletHandlerMethodInvoker(methodResolver); ServletWebRequestwebRequest=newServletWebRequest(request,response); ExtendedModelMapimplicitModel=newBindingAwareModelMap();   Objectresult=methodInvoker.invokeHandlerMethod(handlerMethod,handler,webRequest,implicitModel); ModelAndViewmav= methodInvoker.getModelAndView(handlerMethod,handler.getClass(),result,implicitModel,webRequest); methodInvoker.updateModelAttributes(handler,(mav!= null ?mav.getModel(): null ),implicitModel,webRequest); returnmav; }

1.请求入口

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@Override protectedfinalvoiddoGet(HttpServletRequestrequest,HttpServletResponseresponse) throwsServletException,IOException{   processRequest(request,response); }   /** *DelegatePOSTrequeststo{@link#processRequest}. *@see#doService */ @Override protectedfinalvoiddoPost(HttpServletRequestrequest,HttpServletResponseresponse) throwsServletException,IOException{   processRequest(request,response); }   protectedfinalvoidprocessRequest(HttpServletRequestrequest,HttpServletResponseresponse) throwsServletException,IOException{   longstartTime=System.currentTimeMillis(); ThrowablefailureCause= null ;   //ExposecurrentLocaleResolverandrequestasLocaleContext. LocaleContextpreviousLocaleContext=LocaleContextHolder.getLocaleContext(); LocaleContextHolder.setLocaleContext(buildLocaleContext(request), this .threadContextInheritable); //ExposecurrentRequestAttributestocurrentthread. RequestAttributespreviousRequestAttributes=RequestContextHolder.getRequestAttributes(); ServletRequestAttributesrequestAttributes= null ; if (previousRequestAttributes== null ||previousRequestAttributes.getClass().equals(ServletRequestAttributes. class )){ requestAttributes=newServletRequestAttributes(request); RequestContextHolder.setRequestAttributes(requestAttributes, this .threadContextInheritable); }   if (logger.isTraceEnabled()){ logger.trace( "Boundrequestcontexttothread:" +request); }   try { doService(request,response); } catch (ServletExceptionex){ failureCause=ex; throwex; } catch (IOExceptionex){ failureCause=ex; throwex; } catch (Throwableex){ failureCause=ex; thrownewNestedServletException( "Requestprocessingfailed" ,ex); }   finally { //Clearrequestattributesandresetthread-boundcontext. LocaleContextHolder.setLocaleContext(previousLocaleContext, this .threadContextInheritable); if (requestAttributes!= null ){ RequestContextHolder.setRequestAttributes(previousRequestAttributes, this .threadContextInheritable); requestAttributes.requestCompleted(); } if (logger.isTraceEnabled()){ logger.trace( "Clearedthread-boundrequestcontext:" +request); }   if (failureCause!= null ){ this .logger.debug( "Couldnotcompleterequest" ,failureCause); } else { this .logger.debug( "Successfullycompletedrequest" ); } if ( this .publishEvents){ //Whetherornotwesucceeded,publishanevent. longprocessingTime=System.currentTimeMillis()-startTime; this .webApplicationContext.publishEvent( newServletRequestHandledEvent( this , request.getRequestURI(),request.getRemoteAddr(), request.getMethod(),getServletConfig().getServletName(), WebUtils.getSessionId(request),getUsernameForRequest(request), processingTime,failureCause)); } } }

processRequest方法主要做4项工作。

1. 得到当前线程的LocaleContext和RequestAttributes，创建新的LocaleContext和RequestAttributes并重新绑定到当前线程。

   调用子类实现的doService()

   重置当前线程的LocaleContext和RequestAttributes

   执行成功后，发布ServletRequestHandledEvent事件。

   2.DispatcherServlet自定义的doService方法

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   protectedvoiddoService(HttpServletRequestrequest,HttpServletResponseresponse)throwsException{ if (logger.isDebugEnabled()){ StringrequestUri=urlPathHelper.getRequestUri(request); logger.debug( "DispatcherServletwithname'" +getServletName()+ "'processing" +request.getMethod()+ "requestfor[" +requestUri+ "]" ); }   //Keepasnapshotoftherequestattributesincaseofaninclude, //tobeabletorestoretheoriginalattributesaftertheinclude. Map<string,object>attributesSnapshot= null ; if (WebUtils.isIncludeRequest(request)){ logger.debug( "Takingsnapshotofrequestattributesbeforeinclude" ); attributesSnapshot=newHashMap<string,object>(); EnumerationattrNames=request.getAttributeNames(); while (attrNames.hasMoreElements()){ StringattrName=(String)attrNames.nextElement(); if ( this .cleanupAfterInclude||attrName.startsWith( "org.springframework.web.servlet" )){ attributesSnapshot.put(attrName,request.getAttribute(attrName)); } } }   //Makeframeworkobjectsavailabletohandlersandviewobjects. 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());   try { doDispatch(request,response); } finally { //Restoretheoriginalattributesnapshot,incaseofaninclude. if (attributesSnapshot!= null ){ restoreAttributesAfterInclude(request,attributesSnapshot); } } }</string,object></string,object>

   主要做两部分工作

   1. 如果是include请求，先保存一份request域数据的快照，doDispatch执行过后，将会用快照数据恢复。

      调用doDispatch方法，完成请求转发。

      3.doDispatch方法

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      protectedvoiddoDispatch(HttpServletRequestrequest,HttpServletResponseresponse)throwsException{ HttpServletRequestprocessedRequest=request; HandlerExecutionChainmappedHandler= null ; intinterceptorIndex=- 1 ;   try { ModelAndViewmv; booleanerrorView= false ;   try { //1.检查是否是文件上传的请求 processedRequest=checkMultipart(request);   //Determinehandlerforthecurrentrequest. //2.取得处理当前请求的controller,这里也称为hanlder,处理器,第一个步骤的意义就在这里体现了. //这里并不是直接返回controller,而是返回的HandlerExecutionChain请求处理器链对象,该对象封装了handler和interceptors. mappedHandler=getHandler(processedRequest, false ); if (mappedHandler== null ||mappedHandler.getHandler()== null ){ noHandlerFound(processedRequest,response); return ; }   //Determinehandleradapterforthecurrentrequest. //3.获取处理request的处理器适配器handleradapter HandlerAdapterha=getHandlerAdapter(mappedHandler.getHandler());   //Processlast-modifiedheader,ifsupportedbythehandler. Stringmethod=request.getMethod(); booleanisGet= "GET" .equals(method); if (isGet|| "HEAD" .equals(method)){ longlastModified=ha.getLastModified(request,mappedHandler.getHandler()); if (logger.isDebugEnabled()){ StringrequestUri=urlPathHelper.getRequestUri(request); logger.debug( "Last-Modifiedvaluefor[" +requestUri+ "]is:" +lastModified); } if (newServletWebRequest(request,response).checkNotModified(lastModified)&&isGet){ return ; } }   //ApplypreHandlemethodsofregisteredinterceptors. //4.拦截器的预处理方法 HandlerInterceptor[]interceptors=mappedHandler.getInterceptors(); if (interceptors!= null ){ for (inti= 0 ;i<interceptors.length;i++){ actuallyinvokethehandler.= "" applyposthandlemethodsofregisteredinterceptors.= "" handlerinterceptorinterceptor= "interceptors[i];" interceptorindex= "i;" inti= "interceptors.length-1;i" mv= "ha.handle(processedRequest,response,mappedHandler.getHandler());" >= 0 ;i--){ HandlerInterceptorinterceptor=interceptors[i]; interceptor.postHandle(processedRequest,response,mappedHandler.getHandler(),mv); } } } catch (ModelAndViewDefiningExceptionex){ logger.debug( "ModelAndViewDefiningExceptionencountered" ,ex); mv=ex.getModelAndView(); } catch (Exceptionex){ Objecthandler=(mappedHandler!= null ?mappedHandler.getHandler(): null ); mv=processHandlerException(processedRequest,response,handler,ex); errorView=(mv!= null ); }   //Didthehandlerreturnaviewtorender? if (mv!= null &&!mv.wasCleared()){ render(mv,processedRequest,response); if (errorView){ WebUtils.clearErrorRequestAttributes(request); } } else { if (logger.isDebugEnabled()){ logger.debug( "NullModelAndViewreturnedtoDispatcherServletwithname'" +getServletName()+ "':assumingHandlerAdaptercompletedrequesthandling" ); } }   //Triggerafter-completionforsuccessfuloutcome. triggerAfterCompletion(mappedHandler,interceptorIndex,processedRequest,response, null ); }   catch (Exceptionex){ //Triggerafter-completionforthrownexception. triggerAfterCompletion(mappedHandler,interceptorIndex,processedRequest,response,ex); throwex; } catch (Errorerr){ ServletExceptionex=newNestedServletException( "Handlerprocessingfailed" ,err); //Triggerafter-completionforthrownexception. triggerAfterCompletion(mappedHandler,interceptorIndex,processedRequest,response,ex); throwex; }   finally { //Cleanupanyresourcesusedbyamultipartrequest. if (processedRequest!=request){ cleanupMultipart(processedRequest); } } }</interceptors.length;i++){>

      很明显这儿是SpringMVC核心。

      1.根据请求的路径找到HandlerMethod(带有Method反射属性，也就是对应Controller中的方法)（DispatcherServlet.getHandler完成）

      2.匹配路径对应的拦截器（DispatcherServlet.getHandler完成）

      3.获得HandlerExecutionChain对象（DispatcherServlet.getHandler完成）

      4.通过HandlerAdapter对象进行处理得到ModelAndView对象（HandlerAdapter.handle）

      5.调用HandlerInterceptor.preHandle

      6.调用HandlerInterceptor.postHandle

      7. 渲染

      4.总结

      

      简单粗暴的总结下

      step1-6: 获取controller

      step5-15 :调用controller方法

      step17-20:渲染view

      其他：aop方式处理拦截统一处理。