ThreadLocal 线程局部变量

ThreadLocal线程局部变量

与之前写的Unsafe一样，都是为了解决并发访问变量的问题。与synchronized等加锁不同的，ThreadLocal完全不提供锁，而是利用空间换时间，为每个线程都提供了变量的独立副本，保障线程安全。

package com.chen.thread;

import java.text.SimpleDateFormat;
import java.util.Random;

/**
 * Created by CHEN on 2016/9/28.
 */
public class ThreadLocalExample implements Runnable {
    //建立一个SimpleDateFormat的本地线程变量
    private static final ThreadLocal<SimpleDateFormat> formatter =
            new ThreadLocal<SimpleDateFormat>() {
        //初始化
                @Override
        protected SimpleDateFormat initialValue() {
            return new SimpleDateFormat("yyyyMMdd HHmm");
        }
    };

    public static void main(String[] args) throws InterruptedException {
        ThreadLocalExample obj = new ThreadLocalExample();
        for (int i = 0; i < 10; i++) {
            Thread t = new Thread(obj, "" + i);
            Thread.sleep(new Random().nextInt(1000));
            t.start();
        }
    }

    @Override
    public void run() {
        //输出构造时的变量值
        System.out.println("Thread Name= " + Thread.currentThread().getName() + " default Formatter = " + formatter.get().toPattern());
        try {
            Thread.sleep(new Random().nextInt(1000));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //对当前线程造成影响
        formatter.set(new SimpleDateFormat());
        //影响之后的结果
        System.out.println("Thread Name= " + Thread.currentThread().getName() + " formatter = " + formatter.get().toPattern());
    }

}