Java多线程中的ThreadLocal，可继承，可修改。

package test;

import java.util.Date;

public class InheritableThreadLocalExt  extends InheritableThreadLocal<Object>{
	@Override
	
	protected Object initialValue() {
		return new Date().getTime();
	}
	
	@Override
	protected Object childValue(Object parentValue) {
		return parentValue + " insert at child thread.";
	}

}

package test;

public class Tools  {
	public static InheritableThreadLocalExt tl = new InheritableThreadLocalExt();

}

package test;

public class ThreadA extends Thread {
	
	@Override
	public void run() {
		try {
			for (int i = 0; i < 10; i++) {
				System.out.println("from ThreadA get value=" + Tools.tl.get());
				Thread.sleep(100);
			}
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}

}

package test;

public class Run {
	


	public static void main(String[] args) {
		try {
			for (int i = 0; i < 10; i++) {
				System.out.println("from Main get value=" + Tools.tl.get());
				Thread.sleep(100);
			}
			Thread.sleep(5000L);
			ThreadA a = new ThreadA();
			a.start();
			
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}

}

输出：

from Main get value=1514531585175
from Main get value=1514531585175
from Main get value=1514531585175
from Main get value=1514531585175
from Main get value=1514531585175
from Main get value=1514531585175
from Main get value=1514531585175
from Main get value=1514531585175
from Main get value=1514531585175
from Main get value=1514531585175
from ThreadA get value=1514531585175 insert at child thread.
from ThreadA get value=1514531585175 insert at child thread.
from ThreadA get value=1514531585175 insert at child thread.
from ThreadA get value=1514531585175 insert at child thread.
from ThreadA get value=1514531585175 insert at child thread.
from ThreadA get value=1514531585175 insert at child thread.
from ThreadA get value=1514531585175 insert at child thread.
from ThreadA get value=1514531585175 insert at child thread.
from ThreadA get value=1514531585175 insert at child thread.
from ThreadA get value=1514531585175 insert at child thread.