学习过ThreadLocal的童鞋都知道，在子线程中，是无法访问父线程通过ThreadLocal设置的变量的。

package thread;

/**
 * @author heyunlin
 * @version 1.0
 */
public class ThreadLocalExample {

    public static void main(String[] args) throws InterruptedException, NoSuchFieldException, IllegalAccessException {
        ThreadLocal<String> threadLocal = new ThreadLocal<>();

        threadLocal.set("hello");

        Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("run()...");

                /*
                 * 子线程中无法访问父线程中设置的ThreadLocal变量
                 */
                System.out.println(threadLocal.get());
            }
        });

        thread.start();
        thread.join();

        System.out.println(thread);
        System.out.println(threadLocal.get());
    }

}

运行结果：

InheritableThreadLocal就是为了解决这个不可见问题而生的~

package thread;

/**
 * @author heyunlin
 * @version 1.0
 */
public class InheritableThreadLocalExample {

    public static void main(String[] args) throws InterruptedException, NoSuchFieldException, IllegalAccessException {
        InheritableThreadLocal<String> threadLocal = new InheritableThreadLocal<>();

        threadLocal.set("hello");

        Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("run()...");
                System.out.println(threadLocal.get());
            }
        });

        thread.start();
        thread.join();

        System.out.println(thread);
        System.out.println(threadLocal.get());
    }

}

运行结果：