在线程池或异步任务调用链中，ThreadLocal无法正确传递值

解决方式：

1. 线程池装饰器ThreadPoolTaskExecutor
2. 阿里开源框架ttl , TransmittableThreadLocal

核心代码

public class UserContextHolder {
    //ThreadLocal 
    private static final ThreadLocal<UserInfoContext> userContext = new ThreadLocal<>();
    
    //方式2优化： 使用ttl 存储上下文信息，可以穿透到异步线程里
    private static TransmittableThreadLocal<UserInfoContext> userContext2 = new TransmittableThreadLocal<>();

    public UserContextHolder() {
    }

    public static UserInfoContext getUserInfoContext() {
        return userContext.get();
    }

    public static void setUserInfoContext(UserInfoContext userInfoContext) {
        userContext.set(userInfoContext);
    }
    public static void remove() {
        userContext.remove();
    }


    public static UserInfoContext getUserInfoContext2() {
        return userContext2.get();
    }

    public static void setUserInfoContext2(UserInfoContext userInfoContext) {
        userContext2.set(userInfoContext);
    }
    public static void remove2() {
        userContext2.remove();
    }
}

@AllArgsConstructor
@Data
public class UserInfoContext {
    private String token;
    private String userId;
    private String userName;

}

public class UserContextInterceptor implements HandlerInterceptor, Ordered {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        String token = request.getHeader("token");
        //根据token获取用户信息，从数据库获取
        UserInfoContext userInfoContext = new UserInfoContext(token, "userId-123", "userName-lixi");

        //设置上下文信息
        UserContextHolder.setUserInfoContext(userInfoContext);

        //方式2 设置上下文信息ttl
        UserContextHolder.setUserInfoContext2(userInfoContext);

        return true;
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        //必须threadLoacl清除，防止内存泄漏
        UserContextHolder.remove();

        //ttl 也需要清除
        UserContextHolder.remove2();
    }

    @Override
    public int getOrder() {
        return 0;
    }
}

public class TestUserContextUtil {

    //默认线程池
    private static  ThreadPoolExecutor threadPoolExecutor =  null;

    //使用装饰器 线程池
    private static ThreadPoolTaskExecutor threadPoolTaskExecutor =  null;


    static {
        threadPoolExecutor = new ThreadPoolExecutor(10,
                20,
                10,
                TimeUnit.SECONDS,
                new LinkedBlockingDeque<>(100),
                new ThreadFactoryBuilder().setNameFormat("异步线程池-%d").build(),
                new ThreadPoolExecutor.AbortPolicy()
        );
        
        //方式1优化：使用ThreadPoolTaskExecutor 设置装饰器
        threadPoolTaskExecutor = new ThreadPoolTaskExecutor();
        threadPoolTaskExecutor.setCorePoolSize(10);
        threadPoolTaskExecutor.setMaxPoolSize(20);
        threadPoolTaskExecutor.setKeepAliveSeconds(10);
        threadPoolTaskExecutor.setQueueCapacity(100);
        threadPoolTaskExecutor.setThreadFactory(new ThreadFactoryBuilder().setNameFormat("异步线程池-%d").build());
        threadPoolTaskExecutor.setRejectedExecutionHandler(new ThreadPoolExecutor.AbortPolicy());
        threadPoolTaskExecutor.setTaskDecorator(new BusinessContextDecorator());
        threadPoolTaskExecutor.initialize();






    }



    public static void main(String[] args) {
        //主线程模拟 拦截器设置 用户上下文信息
        UserInfoContext userInfoContext = new UserInfoContext("token-123", "userId-123", "userName-lixi");
        UserContextHolder.setUserInfoContext(userInfoContext);

        getSubThreadContext();
        getAsyncThreadContext();
        getAsyncThreadPool();
        getAsyncThreadPool2();
    }


    //模拟 同步方法调用 获取上下文
    public static void getSubThreadContext() {

        System.out.println("同步方法调用获取上下文:"+UserContextHolder.getUserInfoContext());
    }


    //模拟 异步方法调用 获取上下文 [普通线程实现]
    public static void getAsyncThreadContext() {

        new Thread(() -> {
            try {
                TimeUnit.MICROSECONDS.sleep(500);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("异步线程 方法调用获取上下文:"+UserContextHolder.getUserInfoContext());
        }).start();

    }

    //模拟threadPoolExecutor 异步方法调用 获取上下文
    public static void getAsyncThreadPool() {

        threadPoolExecutor.execute(() -> {
            System.out.println("异步线程 方法调用获取上下文:"+UserContextHolder.getUserInfoContext());
        });


    }
    
    //测试方式1 装饰器
    //模拟threadPoolTaskExecutor 异步方法调用 获取上下文
    public static UserInfoContext getAsyncThreadPool2() {

        Future<UserInfoContext> future = threadPoolTaskExecutor.submit(() -> {
            System.out.println("异步线程-装饰器 方法调用获取上下文:" + UserContextHolder.getUserInfoContext());
            return UserContextHolder.getUserInfoContext();
        });

        try {
            UserInfoContext userInfoContext = future.get(10, TimeUnit.SECONDS);
            return userInfoContext;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    //测试方式2 ttl 
    //模拟threadPoolExecutor 异步方法调用 获取上下文, 上下文使用ttl存储
    public static UserInfoContext getAsyncThreadPool3() {

        Future<UserInfoContext> future = threadPoolTaskExecutor.submit(() -> {
            System.out.println("异步线程-ttl 方法调用获取上下文:" + UserContextHolder.getUserInfoContext2());
            return UserContextHolder.getUserInfoContext();
        });

        try {
            UserInfoContext userInfoContext = future.get(10, TimeUnit.SECONDS);
            return userInfoContext;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}

public class BusinessContextDecorator implements TaskDecorator {
    @Override
    public Runnable decorate(Runnable runnable) {
        //主线程的上下文
        UserInfoContext userContext = UserContextHolder.getUserInfoContext();
        //主线程的traceId
//        Map<String, String> copyOfContextMap = MDC.getCopyOfContextMap();
        return () -> {
            //将执行任务前，保存主线程 上下文
            UserContextHolder.setUserInfoContext(userContext);
//            MDC.setContextMap(copyOfContextMap);
            runnable.run();
        };
    }
}

测试代码

@GetMapping("/test/userContext")
public String testUserContext() {
    UserInfoContext userInfoContext = userContextService.getAsyncThreadPool();
    return userInfoContext.toString();
}

//使用ttl
@GetMapping("/test/userContext/ttl")
public String testUserContext2() {
    UserInfoContext userInfoContext = userContextService.getAsyncThreadPool3();
    return userInfoContext.toString();
}

验证效果

异步线程-装饰器 方法调用获取上下文:UserInfoContext(token=111, userId=userId-123, userName=userName-lixi)

异步线程-ttl 方法调用获取上下文:UserInfoContext(token=111, userId=userId-123, userName=userName-lixi)