并发问题引出ThreadLocal

package cn.itcast.thread;

import java.util.HashMap;
import java.util.Map;

import org.junit.Test;

public class Demo1 {

    @Test
    public void fun1(){
        final ThreadLocal<String> t1=new ThreadLocal<String>();
        t1.set("hello");
        System.out.println(t1.get());
        t1.remove();
        System.out.println(t1.get());
    }
    @Test
    public void fun2(){
        final ThreadLocal<String> t1=new ThreadLocal<String>();
        
        new Thread(){
            public void run(){
                t1.set("内部类");
                System.out.println(t1.get());
            }
        }.start();
        
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(t1.get());
    }
    @Test
    public void fun3(){
        final Map<Thread,String> map=new HashMap<Thread,String>();
        map.put(Thread.currentThread(), "hello");
        System.out.println(map.get(Thread.currentThread()));
        
        new Thread(){
            public void run(){
                System.out.println(Thread.currentThread().getName());
                System.out.println(map.get(Thread.currentThread()));
            }
        }.start();
    }
}

/**
 * 它内部是一个Map
 */
class TL<T>{
    private Map<Thread,T> map=new HashMap<Thread,T>();
    
    public void set(T data){
        map.put(Thread.currentThread(),data);
    }
    
    public T get(){
        return map.get(Thread.currentThread());
    }
    
    public void remove(){
        map.remove(Thread.currentThread());
    }
}
/**
 * ThreadLocal通常用在一个类的成员上
 * 多个线程访问它时，每个线程都有自己的副本，互不干扰
 * Hibernate中把Session放到了ThreadLocal中！
 */
class User{
    private ThreadLocal<String> usernameT1=new ThreadLocal<String>();
}