public class InheritableThreadLocal<T> extends ThreadLocal<T> {

    protected T childValue(T parentValue) {

        return parentValue;

    }

    ThreadLocalMap getMap(Thread t) {

       return t.inheritableThreadLocals;

    }

    void createMap(Thread t, T firstValue) {

        t.inheritableThreadLocals = new ThreadLocalMap(this, firstValue);

    }

}

import java.util.concurrent.atomic.AtomicInteger;

/**

 * Created by hujunzheng on 2017/6/23.

 */

class ThreadCount {

    private static final AtomicInteger nextId = new AtomicInteger(0);

    private static final ThreadLocal<Integer> threadCount =

            ThreadLocal.withInitial(() -> nextId.getAndIncrement());//返回的是重写了ThreadLocal initialValue()方法的ThreadLocal.SuppliedThreadLocal对象

    public static int get() {

        return threadCount.get();

    }

}

class ThreadSign {

    private static final AtomicInteger nextId = new AtomicInteger(0);

    private static final ThreadLocal<Integer> threadCount = new InheritableThreadLocal<Integer>() {

        @Override

        protected Integer initialValue() {

            return nextId.getAndIncrement();

        }

    };

    public static int get() {

        return threadCount.get();

    }

}

public class ThreadLocalTest {

    public static void testThreadLocal() {

        for (int i = 0; i < 5; ++i) {

            int pi = i;

            new Thread(() -> {

                System.out.println(Thread.currentThread().getName() + " count->" + ThreadCount.get());

                for (int j = 0; j < 5; ++j) {

                    new Thread(() -> System.out.println("       " + Thread.currentThread().getName() + " count->" + ThreadCount.get()), "cthread" + j + " pthread" + pi).start();

                }

            }, "pthread" + i).start();

        }

    }

    public static void testInheritableThreadLocal() {

        for(int i=0; i<5; ++i) {

            int pi = i;

            new Thread(() -> {

                System.out.println(Thread.currentThread().getName() + " sign->" + ThreadSign.get());

                for(int j=0; j<5; ++j) {

                    new Thread(() -> System.out.println("       " + Thread.currentThread().getName() + " sign->" + ThreadSign.get()), "cthread" + j + " pthread" + pi).start();

                }

            }, "pthread" + i).start();

        }

    }

    public static void main(String[] args) {

//        testThreadLocal();

        testInheritableThreadLocal();

    }

}