SpringBoot--解决子线程无法获得HttpServletRequest的attribute的问题

​

简介

        本文介绍解决SpringBoot子线程无法获得HttpServletRequest的attribute的问题。

        在SpringBoot请求中，如果创建了子线程获取request的attribute，会无法获取到。比如：我想记录日志，将日志放到了request的attribute中：request.setAttribute("logContent", "日志内容")，然后创建子线程去获取logContent，然后进行处理。

问题复现

代码

package com.knife.controller;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.context.request.RequestContextHolder;
import org.springframework.web.context.request.ServletRequestAttributes;

import javax.servlet.http.HttpServletRequest;
import java.time.LocalDateTime;

@RestController
public class HelloController {

    @GetMapping("/test")
    public String test() {
        ServletRequestAttributes servletRequestAttributes =
                (ServletRequestAttributes)RequestContextHolder.getRequestAttributes();
        HttpServletRequest request = servletRequestAttributes.getRequest();
        request.setAttribute("logContent", "日志内容：" + LocalDateTime.now());

        Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
                ServletRequestAttributes servletRequestAttributes =
                        (ServletRequestAttributes)RequestContextHolder.getRequestAttributes();
                HttpServletRequest request = servletRequestAttributes.getRequest();

                System.out.println("子线程运行。获取到的attribute为："
                        + request.getAttribute("logContent"));
            }
        });
        thread.start();

        return "test success";
    }
}      

结果（getRequestAttributes返回null）

Exception in thread "Thread-131" java.lang.NullPointerException
  at com.knife.controller.HelloController$1.run(HelloController.java:26)
  at java.lang.Thread.run(Thread.java:748)      

解决方案

创建子线程之前调用如下代码：

RequestContextHolder.setRequestAttributes(servletRequestAttributes, true);      

代码

package com.knife.controller;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.context.request.RequestContextHolder;
import org.springframework.web.context.request.ServletRequestAttributes;

import javax.servlet.http.HttpServletRequest;
import java.time.LocalDateTime;

@RestController
public class HelloController {

    @GetMapping("/test")
    public String test() {
        ServletRequestAttributes servletRequestAttributes =
                (ServletRequestAttributes)RequestContextHolder.getRequestAttributes();
        HttpServletRequest request = servletRequestAttributes.getRequest();
        request.setAttribute("logContent", "日志内容：" + LocalDateTime.now());

        RequestContextHolder.setRequestAttributes(servletRequestAttributes, true);

        Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
                ServletRequestAttributes servletRequestAttributes =
                        (ServletRequestAttributes)RequestContextHolder.getRequestAttributes();
                HttpServletRequest request = servletRequestAttributes.getRequest();

                System.out.println("子线程运行。获取到的attribute为："
                        + request.getAttribute("logContent"));
            }
        });
        thread.start();

        return "test success";
    }
}      

结果（可以获取到属性）

子线程运行。获取到的attribute为：日志内容：2022-09-03T16:43:18.463      

线程安全性

        上边的解决方案是否有线程安全问题呢？我在子线程里延时5秒模拟长时间请求，然后多次请求，看结果。如果值都是不一样的话，应该是线程安全的。（本处我无法百分百确定，实际开发中不太建议这么写。实际开发中建议将日志内容作为线程的参数传入，与attribute剥离开）。

代码

package com.knife.controller;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.context.request.RequestContextHolder;
import org.springframework.web.context.request.ServletRequestAttributes;

import javax.servlet.http.HttpServletRequest;
import java.time.LocalDateTime;

@RestController
public class HelloController {

    @GetMapping("/test")
    public String test() {
        ServletRequestAttributes servletRequestAttributes =
                (ServletRequestAttributes)RequestContextHolder.getRequestAttributes();
        HttpServletRequest request = servletRequestAttributes.getRequest();
        request.setAttribute("logContent", "日志内容：" + LocalDateTime.now());

        RequestContextHolder.setRequestAttributes(servletRequestAttributes, true);

        Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
                ServletRequestAttributes servletRequestAttributes =
                        (ServletRequestAttributes)RequestContextHolder.getRequestAttributes();
                HttpServletRequest request = servletRequestAttributes.getRequest();

                System.out.println("子线程运行。获取到的attribute为："
                        + request.getAttribute("logContent"));

                try {
                    Thread.sleep(5000);
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }
            }
        });
        thread.start();

        return "test success";
    }
}      

结果（日志内容是新的，应该是线程安全的）

子线程运行。获取到的attribute为：日志内容：2022-09-03T16:46:42.242
子线程运行。获取到的attribute为：日志内容：2022-09-03T16:46:42.799
子线程运行。获取到的attribute为：日志内容：2022-09-03T16:46:43.359
子线程运行。获取到的attribute为：日志内容：2022-09-03T16:46:43.877
子线程运行。获取到的attribute为：日志内容：2022-09-03T16:46:44.392
子线程运行。获取到的attribute为：日志内容：2022-09-03T16:46:44.804
子线程运行。获取到的attribute为：日志内容：2022-09-03T16:46:45.247
子线程运行。获取到的attribute为：日志内容：2022-09-03T16:46:45.610
子线程运行。获取到的attribute为：日志内容：2022-09-03T16:46:46.010
子线程运行。获取到的attribute为：日志内容：2022-09-03T16:46:46.433      

其他网址