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<String> local = new ThreadLocal<String>();
work(local);
}

public void testInheritableThreadLocal() {
final ThreadLocal<String> local = new InheritableThreadLocal<String>();
work(local);
}

private void work(final ThreadLocal<String> 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。