springMVC中获取request和response对象的几种方式（RequestContextHolder）

Posted 2021-06-27 Yan Yang

springMVC中获取request和response对象的几种方式

• • 1.最简单方式：参数
  • 2.加入监听器，然后在代码里面获取

原文链接：https://blog.csdn.net/weixin_43052839/article/details/82426735

---

1.最简单方式：参数

@RequestMapping("/test")
@ResponseBody
public void saveTest(HttpServletRequest req, HttpServletResponse resp){
　　
}

2.加入监听器，然后在代码里面获取

在Spring API中提供了一个非常便捷的工具类 RequestContextHolder，能够在Controller中获取request对象和response对象，使用方法如下：

public class TestRequest {
    public HttpServletRequest getRequest() {
        HttpServletRequest request=((ServletRequestAttributes)RequestContextHolder.getRequestAttributes()).getRequest();
        HttpServletResponse response=((ServletRequestAttributes)RequestContextHolder.getRequestAttributes()).getResponse();
        return request;
    }
}

tips:需要注意的是如果直接使用这个工具类，则会抛出一个空指针异常。原因是需要先在web.xml配置RequestContextListener监听器:

<listener>
   <listener-class>
         org.springframework.web.context.request.RequestContextListener
   </listener-class>
</listener>

原理
RequestContextListener实现了 ServletRequestListener ,在其覆盖的requestInitialized(ServletRequestEvent requestEvent)方法中,将request最终设置到了RequestContextHolder中

import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.http.HttpServletRequest;

import org.springframework.context.i18n.LocaleContextHolder;
import org.springframework.web.context.request.RequestContextHolder;
import org.springframework.web.context.request.ServletRequestAttributes;

public class RequestContextListener implements ServletRequestListener {
    private static final String REQUEST_ATTRIBUTES_ATTRIBUTE =
        RequestContextListener.class.getName() + ".REQUEST_ATTRIBUTES";
    public void requestInitialized(ServletRequestEvent requestEvent) {
        if (!(requestEvent.getServletRequest() instanceof HttpServletRequest)) {
            throw new IllegalArgumentException(
           "Request is not an HttpServletRequest: " + requestEvent.getServletRequest());
        }
        HttpServletRequest request = (HttpServletRequest) requestEvent.getServletRequest();//从事件对象中获取request对象
        ServletRequestAttributes attributes = new ServletRequestAttributes(request);//将request设置到servletRequestAttributes中
        request.setAttribute(REQUEST_ATTRIBUTES_ATTRIBUTE, attributes);//反过来将servletRequestAttributes设置到request中
        LocaleContextHolder.setLocale(request.getLocale());
        RequestContextHolder.setRequestAttributes(attributes);//再将servletRequestAttributes设置到requestContextHolder中
    }
    public void requestDestroyed(ServletRequestEvent arg0) {
        // TODO Auto-generated method stub
    }
}