关于 ThreadLocal 你需要知道的几点

//定义一个ThreadLocal变量用以存储不同线程的ID
ThreadLocal<Long> localVs = new ThreadLocal<>();
//线程list
List<Thread> threads = new ArrayList<>();
//初始化线程
IntStream.range(0, 5).forEach(value -> {
    Thread tmp = new Thread(() -> {
        //线程运行时（线程运行期间)，将ID放入变量
        localVs.set(Thread.currentThread().getId());
        //输出当前线程名称，ID
        System.out.println(Thread.currentThread().getName() + ": " + Thread.currentThread().getId());

        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //延迟3s，输出当前线程名称，所属ThreadLocal变量
        System.out.println(Thread.currentThread().getName() + ": " + localVs.get());
    });
    threads.add(tmp);
});

for (Thread thread : threads) {
    thread.start();
}

Thread-0: 12
Thread-2: 14
Thread-1: 13
Thread-4: 16
Thread-3: 15
Disconnected from the target VM, address: '127.0.0.1:59273', transport: 'socket'
Thread-1: 13
Thread-0: 12
Thread-2: 14
Thread-4: 16
Thread-3: 15