通过RequestContextHolder直接获取HttpServletRequest对象

男娘i 2023-10-11 19:07 1阅读 0赞

朋友遇到一个问题：他想在Service方法中使用的API，但是又不想把对象当作这个Service方法的参数传过来，原因是这个方法被N多Controller调用，加一个参数就得改一堆代码。一句话：就是他懒。不过，这个问题该这么解决呢？

不把当作参数传过来，这意味着要在Service的方法中直接获取到对象。

我们知道，一次请求，Web应用服务器就会分配一个线程去处理。也就是说，在Service方法中获取到的对象需要满足：线程内共享，线程间隔离。

这恰恰是的应用场景。

那么，就需要在请求执行之前获取到，把它到某个类的类型的静态成员中，使用的时候直接通过静态方式访问到这个对象，调用它的方法，即可获取到线程隔离的了。最后，在请求结束后，要调用的方法，清理资源引用。

![cc46366f90ceeaa103118c1025273093.gif][]![4a17894252cb8b4fdac8b16ad76da0f0.gif][]

import javax.servlet.ServletRequestEvent;

import javax.servlet.ServletRequestListener;

import javax.servlet.http.HttpServletRequest;

public class RequestHolder implements ServletRequestListener \{

private static ThreadLocal httpServletRequestHolder= new ThreadLocal ();

@Override

public void requestInitialized(ServletRequestEvent requestEvent) \{

HttpServletRequest request = (HttpServletRequest) requestEvent.getServletRequest();

httpServletRequestHolder.set(request); // 绑定到当前线程

@Override

public void requestDestroyed(ServletRequestEvent requestEvent) \{

httpServletRequestHolder.remove(); // 清理资源引用

public static HttpServletRequest getHttpServletRequest() \{

return httpServletRequestHolder.get();

![0b42f94eab3db00b5ec0204589d3f770.gif][]![f2b7799a3671af43b62c7370368cfecd.gif][]

import java.io.IOException;

import javax.servlet.Filter;

import javax.servlet.FilterChain;

import javax.servlet.FilterConfig;

import javax.servlet.ServletException;

import javax.servlet.ServletRequest;

import javax.servlet.ServletResponse;

import javax.servlet.http.HttpServletRequest;

public class RequestHolder implements Filter \{

private static ThreadLocal httpServletRequestHolder= new ThreadLocal ();

@Override

public void init(FilterConfig filterConfig) throws ServletException \{

@Override

public void doFilter(ServletRequest request, ServletResponse response,

FilterChain chain) throws IOException, ServletException \{

httpServletRequestHolder.set((HttpServletRequest) request); // 绑定到当前线程

try \{

chain.doFilter(request, response);

\} catch (Exception e) \{

throw e;

\} finally \{

httpServletRequestHolder.remove(); // 清理资源引用

@Override

public void destroy() \{

public static HttpServletRequest getHttpServletRequest() \{

return httpServletRequestHolder.get();

![efc0902050ce8bebeafe834e2e19bae8.gif][]![5a5f387675c57b759e6e3727c13f3668.gif][]

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import org.springframework.web.servlet.handler.HandlerInterceptorAdapter;

public class RequestHolder extends HandlerInterceptorAdapter \{

private static ThreadLocal httpServletRequestHolder= new ThreadLocal ();

@Override

public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)

throws Exception \{

httpServletRequestHolder.set(request); // 绑定到当前线程

return true;

@Override

public void afterCompletion(HttpServletRequest request, HttpServletResponse response,

Object handler, Exception ex)

throws Exception \{

httpServletRequestHolder.remove(); // 清理资源引用

public static HttpServletRequest getHttpServletRequest() \{

return httpServletRequestHolder.get();

无论是哪种方式，都可以直接在Service的方法中执行

HttpServletRequest request=RequestHolder.getHttpServletRequest();

即可直接获取到线程隔离的了。

类似的功能，在SpringMVC中就有开箱即用的实现。代码是

HttpServletRequest request=

((ServletRequestAttributes) RequestContextHolder.getRequestAttributes()).getRequest();

那么SpringMVC是如何实现的呢？

先看一下的源码(精简了一下)

![1a8b8188816d2bf15755e0e89ce2823f.gif][]![5d0d4a2e679497a782d396461e096315.gif][]

public abstract class RequestContextHolder \{

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

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

public static void resetRequestAttributes() \{

requestAttributesHolder.remove(); // 重点

inheritableRequestAttributesHolder.remove();

public static void setRequestAttributes(RequestAttributes attributes) \{

setRequestAttributes(attributes, false);

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

if (attributes==null) \{

resetRequestAttributes();

else \{

if (inheritable) \{

inheritableRequestAttributesHolder.set(attributes);

requestAttributesHolder.remove();

else \{

requestAttributesHolder.set(attributes); // 重点

inheritableRequestAttributesHolder.remove();

public static RequestAttributes getRequestAttributes() \{

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

if (attributes==null) \{

attributes = inheritableRequestAttributesHolder.get();

return attributes;

主要代码就是把对象化，然后提供了、等静态方法，来放入或取出中线程隔离的。

接下来看一下方法是在什么时候调用的呢？

![setRequestAttributes()][setRequestAttributes]

可以看到被调用，又被调用，而在每次请求时都会被调用，无论是GET、POST、PUT、DELETE还是TRACE、OPTIONS等等。

先来看一下方法

![c688e5661bed49e78385c6d8ccc3678c.gif][]![4ca16447dbc400d058418d8894519a14.gif][]

protected final void processRequest(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException \{

long startTime= System.currentTimeMillis();

Throwable failureCause =null;

LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();

LocaleContext localeContext = buildLocaleContext(request);

RequestAttributes previousAttributes =RequestContextHolder.getRequestAttributes(); // 重点1

ServletRequestAttributes requestAttributes=

buildRequestAttributes(request, response, previousAttributes); // 重点2

WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());

initContextHolders(request, localeContext, requestAttributes); // 重点3

try \{

doService(request, response); // 执行请求

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 \{

resetContextHolders(request, previousLocaleContext, previousAttributes); // 重点4

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");

publishRequestHandledEvent(request, startTime, failureCause); // 发布请求处理完成事件

在之前就先，通常为。

直接看方法的实现

![46c0f8f79210e6b0439d039405dae056.gif][]![a8dc28511eb2b2cef01f363b6fe5f091.gif][]

protected ServletRequestAttributes buildRequestAttributes(HttpServletRequest request, HttpServletResponse response,

RequestAttributes previousAttributes) \{

if (previousAttributes==null || previousAttributes instanceof ServletRequestAttributes) \{

return new ServletRequestAttributes(request); // 重点

else \{

return null; // preserve the pre-bound RequestAttributes instance

的代码不再去看了，它就是接口的实现类，只是对对象(还有)的一个包装。

直接看方法的实现

![9b983ecc49e8c25e648f1afd18b53029.gif][]![072e4e35da3db4743af00d41fe748a76.gif][]

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); // 重点

if (logger.isTraceEnabled()) \{

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

调用方法，把对象放入。默认是。

即把的封装对象与当前线程绑定。

![9ba3486ba5c6659594e4ad8484e61ccf.gif][]![3e867674e85f47318938ecdb4175b99d.gif][]

private void resetContextHolders(HttpServletRequest request, LocaleContext prevLocaleContext,

RequestAttributes previousAttributes) \{

LocaleContextHolder.setLocaleContext(prevLocaleContext, this.threadContextInheritable);

RequestContextHolder.setRequestAttributes(previousAttributes, this.threadContextInheritable); // 重点

if (logger.isTraceEnabled()) \{

logger.trace("Cleared thread-bound request context: " + request);

在请求执行完毕后，再次调用，但由于为，所以，这里相当于调用。

再回顾一下方法。

![6a9940a2a100cb835e5df8afaa136ccc.gif][]![6358d0ff1be4b4ff22741c76dbbf0c40.gif][]

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

if (attributes==null) \{

resetRequestAttributes();

else \{

if (inheritable) \{

inheritableRequestAttributesHolder.set(attributes);

requestAttributesHolder.remove();

else \{

requestAttributesHolder.set(attributes);

inheritableRequestAttributesHolder.remove();

参数为，就会调用，来清理当前线程引用的。

至此，SpringMVC是如何实现直接获取对象的源码，就分析完了。和我们自己实现的思路差不多，只不过多绕了几个弯而已。

原文链接：https://my.oschina.net/ojeta/blog/801640

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