Spring MVC 中RequestContextHolder獲取request和response

1.最簡單方式：處理方法入參

例如：

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

2.加入監聽器，然后在代碼里面獲取

在Spring API中提供了一個非常便捷的工具類RequestContextHolder，能夠在Controller中獲取request對象和response對象，使用方法如下

HttpServletRequest req = ((ServletRequestAttributes)RequestContextHolder.getRequestAttributes()).getRequest();
HttpServletResponse resp = ((ServletWebRequest)RequestContextHolder.getRequestAttributes()).getResponse();

需要注意的是如果直接使用這個工具類，則會拋出一個空指針異常。原因是需要先在web.xml配置RequestContextListener監聽器:

 

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

 

原理

RequestContextListener實現了ServletRequestListener ,在其覆蓋的requestInitialized(ServletRequestEvent requestEvent)方法中,將request最終設置到了RequestContextHolder中.

 

public class RequestContextListener implements ServletRequestListener {

    private static final String REQUEST_ATTRIBUTES_ATTRIBUTE =
            RequestContextListener.class.getName() + ".REQUEST_ATTRIBUTES";


    @Override
    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();//從事件對象中獲取request對象
        ServletRequestAttributes attributes = new ServletRequestAttributes(request);//將request設置到servletRequestAttributes中
        request.setAttribute(REQUEST_ATTRIBUTES_ATTRIBUTE, attributes);//反過來將servletRequestAttributes設置到request中
        LocaleContextHolder.setLocale(request.getLocale());
        RequestContextHolder.setRequestAttributes(attributes);//再將servletRequestAttributes設置到requestContextHolder中
    }