java线程之InheritableThreadLocal

ThreadLocal和InheritableThreadLocal区别，可以用代码测试一下：

package com.lang;

import junit.framework.TestCase;

import static java.lang.System.out;

public class TestInheritableThreadLocal extends TestCase {

	public void testThreadLocal() {
		final ThreadLocal local = new ThreadLocal();
		work(local);
	}
	
	public void testInheritableThreadLocal() {
		final ThreadLocal local = new InheritableThreadLocal();
		work(local);
	}
	
	private void work(final ThreadLocal local) {
		local.set("a");
		out.println(Thread.currentThread() + "," + local.get());
		Thread t = new Thread(new Runnable() {
			
			@Override
			public void run() {
				out.println(Thread.currentThread() + "," + local.get());
				local.set("b");
				out.println(Thread.currentThread() + "," + local.get());
			}
		});
		
		t.start();
		try {
			t.join();
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		
		out.println(Thread.currentThread() + "," + local.get());
	}
}

运行testThreadLocal，输出：

Thread[main,5,main],a
Thread[Thread-0,5,main],null
Thread[Thread-0,5,main],b
Thread[main,5,main],a

运行testInheritableThreadLocal，输出：

Thread[main,5,main],a
Thread[Thread-0,5,main],a
Thread[Thread-0,5,main],b
Thread[main,5,main],a

比较后，看到ThreadLocal里的值，子线程里不能获得；InheritableThreadLocal里的值，子线程可以获得。