SpringMVC中RequestContextHolder获取请求信息的方法
RequestContextHolder的作用是:
在Service层获取获取request和response信息
代码示例:
ServletRequestAttributesattrs=(ServletRequestAttributes)RequestContextHolder.getRequestAttributes(); HttpServletRequestrequest=attrs.getRequest();
源码分析:
定义了两个ThreadLocal变量用来存储Request
privatestaticfinalThreadLocalrequestAttributesHolder=newNamedThreadLocal("Requestattributes"); privatestaticfinalThreadLocal inheritableRequestAttributesHolder=newNamedInheritableThreadLocal("Requestcontext");
设置方法
publicstaticvoidsetRequestAttributes(@NullableRequestAttributesattributes){ setRequestAttributes(attributes,false); } publicstaticvoidsetRequestAttributes(@NullableRequestAttributesattributes,booleaninheritable){ if(attributes==null){ resetRequestAttributes(); }elseif(inheritable){ inheritableRequestAttributesHolder.set(attributes); requestAttributesHolder.remove(); }else{ requestAttributesHolder.set(attributes); inheritableRequestAttributesHolder.remove(); } }
是在SpringMVC处理Servlet的类FrameworkServlet的类中,doget/dopost方法,调用processRequest方法进行初始化上下文方法中initContextHolders设置进去的
privatevoidinitContextHolders(HttpServletRequestrequest,@NullableLocaleContextlocaleContext,@NullableRequestAttributesrequestAttributes){ if(localeContext!=null){ LocaleContextHolder.setLocaleContext(localeContext,this.threadContextInheritable); } if(requestAttributes!=null){ RequestContextHolder.setRequestAttributes(requestAttributes,this.threadContextInheritable); } if(this.logger.isTraceEnabled()){ this.logger.trace("Boundrequestcontexttothread:"+request); } }
再看一下请求信息怎么获取
@Nullable publicstaticRequestAttributesgetRequestAttributes(){ RequestAttributesattributes=(RequestAttributes)requestAttributesHolder.get(); if(attributes==null){ attributes=(RequestAttributes)inheritableRequestAttributesHolder.get(); } returnattributes; }
解决疑问
1request和response怎么和当前请求挂钩?
首先分析RequestContextHolder这个类,里面有两个ThreadLocal保存当前线程下的request,关于ThreadLocal可以参考我的另一篇博文[Java学习记录--ThreadLocal使用案例]
//得到存储进去的request privatestaticfinalThreadLocalrequestAttributesHolder= newNamedThreadLocal ("Requestattributes"); //可被子线程继承的request privatestaticfinalThreadLocal inheritableRequestAttributesHolder= newNamedInheritableThreadLocal ("Requestcontext");
再看`getRequestAttributes()`方法,相当于直接获取ThreadLocal里面的值,这样就保证了每一次获取到的Request是该请求的request.
publicstaticRequestAttributesgetRequestAttributes(){ RequestAttributesattributes=requestAttributesHolder.get(); if(attributes==null){ attributes=inheritableRequestAttributesHolder.get(); } returnattributes; }
2request和response等是什么时候设置进去的?
找这个的话需要对springMVC结构的`DispatcherServlet`的结构有一定了解才能准确的定位该去哪里找相关代码.
在IDEA中会显示如下的继承关系.
左边1这里是Servlet的接口和实现类.
右边2这里是使得SpringMVC具有Spring的一些环境变量和Spring容器.类似的XXXAware接口就是对该类提供Spring感知,简单来说就是如果想使用Spring的XXXX就要实现XXXAware,spring会把需要的东西传送过来.
那么剩下要分析的的就是三个类,简单看下源码
1.HttpServletBean进行初始化工作
2.FrameworkServlet初始化WebApplicationContext,并提供service方法预处理请
3.DispatcherServlet具体分发处理.
那么就可以在FrameworkServlet查看到该类重写了service(),doGet(),doPost()...等方法,这些实现里面都有一个预处理方法`processRequest(request,response);`,所以定位到了我们要找的位置
查看`processRequest(request,response);`的实现,具体可以分为三步:
- 获取上一个请求的参数
- 重新建立新的参数
- 设置到XXContextHolder
- 父类的service()处理请求
- 恢复request
- 发布事
protectedfinalvoidprocessRequest(HttpServletRequestrequest,HttpServletResponseresponse) throwsServletException,IOException{ longstartTime=System.currentTimeMillis(); ThrowablefailureCause=null; //获取上一个请求保存的LocaleContext LocaleContextpreviousLocaleContext=LocaleContextHolder.getLocaleContext(); //建立新的LocaleContext LocaleContextlocaleContext=buildLocaleContext(request); //获取上一个请求保存的RequestAttributes RequestAttributespreviousAttributes=RequestContextHolder.getRequestAttributes(); //建立新的RequestAttributes ServletRequestAttributesrequestAttributes=buildRequestAttributes(request, response,previousAttributes); WebAsyncManagerasyncManager=WebAsyncUtils.getAsyncManager(request); asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), newRequestBindingInterceptor()); //具体设置的方法 initContextHolders(request,localeContext,requestAttributes); try{ doService(request,response); } catch(ServletExceptionex){ failureCause=ex; throwex; } catch(IOExceptionex){ failureCause=ex; throwex; } catch(Throwableex){ failureCause=ex; thrownewNestedServletException("Requestprocessingfailed",ex); } finally{ //恢复 resetContextHolders(request,previousLocaleContext,previousAttributes); if(requestAttributes!=null){ requestAttributes.requestCompleted(); } if(logger.isDebugEnabled()){ if(failureCause!=null){ this.logger.debug("Couldnotcompleterequest",failureCause); } else{ if(asyncManager.isConcurrentHandlingStarted()){ logger.debug("Leavingresponseopenforconcurrentprocessing"); } else{ this.logger.debug("Successfullycompletedrequest"); } } } //发布事件 publishRequestHandledEvent(request,response,startTime,failureCause); } }
再看initContextHolders(request,localeContext,requestAttributes)方法,把新的RequestAttributes设置进LocalThread,实际上保存的类型为ServletRequestAttributes,这也是为什么在使用的时候可以把RequestAttributes强转为ServletRequestAttributes.
privatevoidinitContextHolders(HttpServletRequestrequest, LocaleContextlocaleContext, RequestAttributesrequestAttributes){ if(localeContext!=null){ LocaleContextHolder.setLocaleContext(localeContext, this.threadContextInheritable); } if(requestAttributes!=null){ RequestContextHolder.setRequestAttributes(requestAttributes, this.threadContextInheritable); } if(logger.isTraceEnabled()){ logger.trace("Boundrequestcontexttothread:"+request); } }
因此RequestContextHolder里面最终保存的为ServletRequestAttributes,这个类相比`RequestAttributes`方法是多了很多.
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