ThreadLocal实例

ThreadLocal基于线程的数据存储结构。ThreadLocal是类型于Map的一种数据结构，它以当前线程的ThreadLocal为key，来实现当前线程范围内的局部变量对象的共享。其保存和获取的方法是set（Object）和get（）。
应用实例：

/**
 * <br>
 * do what you want to do and never stop it.
 * <br>
 */
package com.luch.thread;

import java.util.Random;

/**
 * @author Jack
 * Jul 7, 2014
 * <br>
 */
public class ThreadScopeShareData {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		for(int i =0; i < 2; i++) {
		new Thread(new Runnable(){
			public void run() {
				int data = new Random().nextInt();
				System.out.println(Thread.currentThread().getName() + " has put count:" +data);
				MyThreadScopeData.getInstance().setName("name"+data);
				System.out.println(Thread.currentThread().getName() +" MyThreadScopeData: " + MyThreadScopeData.getInstance());
				new A().get();
				new B().get();
			}
			
		}).start();
		}
	}
	
	static class A{
		public void get(){
			System.out.println("A " + Thread.currentThread().getName() + " Singlton: " + MyThreadScopeData.getInstance());
			System.out.println("A " + Thread.currentThread().getName() + " has get count:" +MyThreadScopeData.getInstance().getName());
		}
	}
	
	static class B{
		public void get(){
			System.out.println("B " + Thread.currentThread().getName() + " Singlton: "+MyThreadScopeData.getInstance());
			System.out.println("B " + Thread.currentThread().getName() + " has get count:" +MyThreadScopeData.getInstance().getName());
		}
	}
	
	
	static class MyThreadScopeData{
		private String name;
		private int age;
		private MyThreadScopeData(){}
	    //private static volatile MyThreadScopeData instance;
		
		public static /*synchronized*/ MyThreadScopeData getInstance(){
			MyThreadScopeData instance = map.get();
			if (instance == null) {
				instance = new MyThreadScopeData();
				map.set(instance);
			}
			return instance;
		}
		public static ThreadLocal<MyThreadScopeData> map = new ThreadLocal<MyThreadScopeData>();
		
		public String getName() {
			System.out.println("getName:" + Thread.currentThread().getName() + " name=" + name + " this.name=" + this.name + " " + this.toString());
			return name;
		}
		public synchronized  void setName(String name) {
			this.name = name;
			System.out.println("setName:" + Thread.currentThread().getName() + " name=" + name + " this.name=" + this.name + " " + this.toString());
		}
		public int getAge() {
			return age;
		}
		public void setAge(int age) {
			this.age = age;
		}
	}

}

此实例就通过ThreadLocal这个对象来达到MyThreadScopeData 实例对象在当前线程范围内（这里是Module A和Module B）共享同一个对象。并且通过单例的模式，很好的屏蔽了ThreadLocal对外部模块的可见性。


Set(T)的源代码如下：

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

把要保存的对象保存到ThreadLocalMap这个对象中，并且以ThreadLocal本身作为key，如果此Map一开始不存在，就去初始化一个Map，然后保存值Value。