public class InheritableThreadLocalDemo {//    全局变量
//    static ThreadLocal<String> threadLocal = new ThreadLocal<>();static ThreadLocal<String> threadLocal = new InheritableThreadLocal<>();public static void main(String[] args) {new Thread(new Runnable() {@Overridepublic void run() {InheritableThreadLocalDemo.threadLocal.set("superWorld");new Service().call();}}).start();}
}class Service {public void call() {System.out.println("Service:" + Thread.currentThread().getName() + " : " + InheritableThreadLocalDemo.threadLocal.get());//new Dao().call();new Thread(new Runnable() {@Overridepublic void run() {new Dao().call();}}).start();}
}class Dao {public void call() {System.out.println("Dao:" + Thread.currentThread().getName() + " : " + InheritableThreadLocalDemo.threadLocal.get());}}

public class InheritableThreadLocal<T> extends ThreadLocal<T> {/*** Computes the child's initial value for this inheritable thread-local* variable as a function of the parent's value at the time the child* thread is created.  This method is called from within the parent* thread before the child is started.* <p>* This method merely returns its input argument, and should be overridden* if a different behavior is desired.** @param parentValue the parent thread's value* @return the child thread's initial value*/protected T childValue(T parentValue) {return parentValue;}/*** Get the map associated with a ThreadLocal.** @param t the current thread*/ThreadLocalMap getMap(Thread t) {return t.inheritableThreadLocals;}/*** Create the map associated with a ThreadLocal.** @param t the current thread* @param firstValue value for the initial entry of the table.*/void createMap(Thread t, T firstValue) {t.inheritableThreadLocals = new ThreadLocalMap(this, firstValue);}
}

    /*** Get the map associated with a ThreadLocal. Overridden in* InheritableThreadLocal.** @param  t the current thread* @return the map*/ThreadLocalMap getMap(Thread t) {return t.threadLocals;}/*** Create the map associated with a ThreadLocal. Overridden in* InheritableThreadLocal.** @param t the current thread* @param firstValue value for the initial entry of the map*/void createMap(Thread t, T firstValue) {t.threadLocals = new ThreadLocalMap(this, firstValue);}

if (parent.inheritableThreadLocals != null)this.inheritableThreadLocals =  ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);

     　　static ThreadLocalMap createInheritedMap(ThreadLocalMap parentMap) {return new ThreadLocalMap(parentMap);}private ThreadLocalMap(ThreadLocalMap parentMap) {Entry[] parentTable = parentMap.table;int len = parentTable.length;setThreshold(len);table = new Entry[len];for (int j = 0; j < len; j++) {Entry e = parentTable[j];if (e != null) {@SuppressWarnings("unchecked")ThreadLocal<Object> key = (ThreadLocal<Object>) e.get();if (key != null) {Object value = key.childValue(e.value);Entry c = new Entry(key, value);int h = key.threadLocalHashCode & (len - 1);while (table[h] != null)h = nextIndex(h, len);table[h] = c;size++;}}}}