SpringBoot--解決子線程無法獲得HttpServletRequest的attribute的問題

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簡介

        本文介紹解決SpringBoot子線程無法獲得HttpServletRequest的attribute的問題。

        在SpringBoot請求中，如果建立了子線程擷取request的attribute，會無法擷取到。比如：我想記錄日志，将日志放到了request的attribute中：request.setAttribute("logContent", "日志内容")，然後建立子線程去擷取logContent，然後進行處理。

問題複現

代碼

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("子線程運作。擷取到的attribute為："
                        + request.getAttribute("logContent"));
            }
        });
        thread.start();

        return "test success";
    }
}      

結果（getRequestAttributes傳回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)      

解決方案

建立子線程之前調用如下代碼：

RequestContextHolder.setRequestAttributes(servletRequestAttributes, true);      

代碼

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("子線程運作。擷取到的attribute為："
                        + request.getAttribute("logContent"));
            }
        });
        thread.start();

        return "test success";
    }
}      

結果（可以擷取到屬性）

子線程運作。擷取到的attribute為：日志内容：2022-09-03T16:43:18.463      

線程安全性

        上邊的解決方案是否有線程安全問題呢？我在子線程裡延時5秒模拟長時間請求，然後多次請求，看結果。如果值都是不一樣的話，應該是線程安全的。（本處我無法百分百确定，實際開發中不太建議這麼寫。實際開發中建議将日志内容作為線程的參數傳入，與attribute剝離開）。

代碼

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("子線程運作。擷取到的attribute為："
                        + request.getAttribute("logContent"));

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

        return "test success";
    }
}      

結果（日志内容是新的，應該是線程安全的）

子線程運作。擷取到的attribute為：日志内容：2022-09-03T16:46:42.242
子線程運作。擷取到的attribute為：日志内容：2022-09-03T16:46:42.799
子線程運作。擷取到的attribute為：日志内容：2022-09-03T16:46:43.359
子線程運作。擷取到的attribute為：日志内容：2022-09-03T16:46:43.877
子線程運作。擷取到的attribute為：日志内容：2022-09-03T16:46:44.392
子線程運作。擷取到的attribute為：日志内容：2022-09-03T16:46:44.804
子線程運作。擷取到的attribute為：日志内容：2022-09-03T16:46:45.247
子線程運作。擷取到的attribute為：日志内容：2022-09-03T16:46:45.610
子線程運作。擷取到的attribute為：日志内容：2022-09-03T16:46:46.010
子線程運作。擷取到的attribute為：日志内容：2022-09-03T16:46:46.433      

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