ThreadLocal线程安全

ThreadLocal原理:

1、查看ThreadLocal的set方法可以看到getMap方法通过当前线程获取当前线程的ThreadLocalMap

 public void set(T value) {
        Thread t = Thread.currentThread();
        ThreadLocalMap map = getMap(t);
        if (map != null)
            map.set(this, value);
        else
            createMap(t, value);
    }

2、在Thread中有

public class Thread{

    ThreadLocal.ThreadLocalMap threadLocals = null;

}

ThreadLocal.ThreadLocalMap是Thread中的变量，也就是说每个Thread有唯一的ThreadLocalMap（在初次set数据的时候创建），而ThreadLocalMap的key为当前操作的ThreadLocal，value为设置的value

以下代码是ThreadLocal保证3个线程各自生成数据

package com.gcl.threadlocal;

class Res

{

    private int count;

    private ThreadLocal threadLocal = new ThreadLocal()

    {

        protected Integer initialValue() {

            return 0;

        };

    };

    public int getNum()

    {

        count = threadLocal.get() + 1;

        threadLocal.set(count);

        return count;

    }

}

class ThreadLocalThread implements Runnable

{

    private Res res;

    public ThreadLocalThread(Res res)

    {

        this.res = res;

    }

    @Override

    public void run()

    {

        for(int i = 0; i < 3; i++) {

            System.out.println(Thread.currentThread().getName() + ":" + res.getNum());

        }

    }

}

public class ThreadLocalDemo

{

    public static void main(String[] args)

    {

        Res res = new Res();

        ThreadLocalThread localThread = new ThreadLocalThread(res);

        Thread thread1 = new Thread(localThread,"thread1");

        Thread thread2 = new Thread(localThread,"thread2");

        Thread thread3 = new Thread(localThread,"thread3");

        thread1.start();

        thread2.start();

        thread3.start();

    }

}