ThreadLocal

package com.itheima;

public class ThreadLocalTest {

    private static ThreadLocal<String> local = new ThreadLocal<>();
    public static void main(String[] args) {
        local.set("Main Message");
        System.out.println(Thread.currentThread().getName()+":" + local.get());
        new Thread(new Runnable() {
            @Override
            public void run() {
                local.set("sub Message");
                System.out.println(Thread.currentThread().getName()+":" + local.get());
            }
        }).start();
        local.remove();
        System.out.println(Thread.currentThread().getName()+":" + local.get());
    }
}

result:

用ThreadLocal来获取当前的员工id