SpringMVC中RequestContextHolder获取请求信息的方法

超、凢脫俗 2023-09-24 08:06 117阅读 0赞

![SpringMVC中RequestContextHolder获取请求信息的方法][SpringMVC_RequestContextHolder]

RequestContextHolder的作用是：

在Service层获取获取request和response信息

代码示例：

ServletRequestAttributes attrs=(ServletRequestAttributes)RequestContextHolder.getRequestAttributes();

HttpServletRequest request=attrs.getRequest();

源码分析：

定义了两个ThreadLocal变量用来存储Request

private static final ThreadLocal requestAttributesHolder=new NamedThreadLocal("Request attributes");

private static final ThreadLocal inheritableRequestAttributesHolder=new NamedInheritableThreadLocal("Request context");

设置方法

public static void setRequestAttributes(@Nullable RequestAttributes attributes) \{

setRequestAttributes(attributes, false);

public static void setRequestAttributes(@Nullable RequestAttributes attributes, boolean inheritable) \{

if (attributes==null) \{

resetRequestAttributes();

\} else if (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

private void initContextHolders(HttpServletRequest request, @Nullable LocaleContext localeContext, @Nullable RequestAttributes requestAttributes) \{

if (localeContext !=null) \{

LocaleContextHolder.setLocaleContext(localeContext, this.threadContextInheritable);

if (requestAttributes !=null) \{

RequestContextHolder.setRequestAttributes(requestAttributes, this.threadContextInheritable);

if (this.logger.isTraceEnabled()) \{

this.logger.trace("Bound request context to thread: " + request);

再看一下请求信息怎么获取

@Nullable

public static RequestAttributes getRequestAttributes() \{

RequestAttributes attributes=(RequestAttributes)requestAttributesHolder.get();

if (attributes==null) \{

attributes=(RequestAttributes)inheritableRequestAttributesHolder.get();

return attributes;

解决疑问

1 request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

private static final ThreadLocal requestAttributesHolder=new NamedThreadLocal ("Request attributes");

//可被子线程继承的request

private static final ThreadLocal inheritableRequestAttributesHolder=new NamedInheritableThreadLocal ("Request context");

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.

public static RequestAttributes getRequestAttributes() \{

RequestAttributes attributes=requestAttributesHolder.get();

if (attributes==null) \{

attributes=inheritableRequestAttributesHolder.get();

return attributes;

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

protected final void processRequest(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException \{

long startTime=System.currentTimeMillis();

Throwable failureCause=null;

//获取上一个请求保存的LocaleContext

LocaleContext previousLocaleContext=LocaleContextHolder.getLocaleContext();

//建立新的LocaleContext

LocaleContext localeContext=buildLocaleContext(request);

//获取上一个请求保存的RequestAttributes

RequestAttributes previousAttributes=RequestContextHolder.getRequestAttributes();

//建立新的RequestAttributes

ServletRequestAttributes requestAttributes=buildRequestAttributes(request,

response, previousAttributes);

WebAsyncManager asyncManager=WebAsyncUtils.getAsyncManager(request);

asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(),

new RequestBindingInterceptor());

//具体设置的方法

initContextHolders(request, localeContext, requestAttributes);

try \{

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 \{

//恢复

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.

private void initContextHolders(HttpServletRequest request,

LocaleContext localeContext,

RequestAttributes requestAttributes) \{

if (localeContext !=null) \{

LocaleContextHolder.setLocaleContext(localeContext,

this.threadContextInheritable);

if (requestAttributes !=null) \{

RequestContextHolder.setRequestAttributes(requestAttributes,

this.threadContextInheritable);

if (logger.isTraceEnabled()) \{

logger.trace("Bound request context to thread: " + 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.