InheritableThreadLocal用法与ThreadLocal的区别

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public class TestThreadLocal {static final String VALUE01 = "test01";static final String VALUE02 = "test02";public static void main(String[] args) throws InterruptedException {ThreadLocal<String> threadLocal = new ThreadLocal<String>();threadLocal.set(VALUE01);InheritableThreadLocal<String> inheritableThreadLocal = new InheritableThreadLocal<String>();inheritableThreadLocal.set(VALUE01);Thread thread_1 = new Thread_TestThreadLocal(threadLocal, inheritableThreadLocal);thread_1.setName("Thread01");thread_1.start();thread_1.join();System.out.println(Thread.currentThread().getName() + "******************************************");System.out.println(Thread.currentThread().getName() + "\tThreadLocal: " + threadLocal.get());System.out.println(Thread.currentThread().getName() + "\tInheritableThreadLocal: " + inheritableThreadLocal.get());}}class Thread_TestThreadLocal extends Thread {ThreadLocal<String> threadLocal;InheritableThreadLocal<String> inheritableThreadLocal;public Thread_TestThreadLocal(ThreadLocal<String> threadLocal,InheritableThreadLocal<String> inheritableThreadLocal) {super();this.threadLocal = threadLocal;this.inheritableThreadLocal = inheritableThreadLocal;}public void run() {// 下面的输出就是说是了InheritableThreadLocal的用法，这里threadLocal输出的是null，因是这是一个新的线程。//而InheritableThreadlocal不是空，它把原来线程的初始化值携带过来了。System.out.println(Thread.currentThread().getName() + "\tThreadLocal: " + threadLocal.get());System.out.println(Thread.currentThread().getName() + "\tInheritableThreadLocal: " + inheritableThreadLocal.get());}}

打印结果：

Thread01 ThreadLocal: null

Thread01 InheritableThreadLocal: test01
main******************************************
main ThreadLocal: test01

main InheritableThreadLocal: test01

InheritableThreadLocal

该类扩展了 ThreadLocal，为子线程提供从父线程那里继承的值：在创建子线程时，子线程会接收所有可继承的线程局部变量的初始值，以获得父线程所具有的值。通常，子线程的值与父线程的值是一致的；但是，通过重写这个类中的 childValue 方法，子线程的值可以作为父线程值的一个任意函数。

当必须将变量（如用户 ID 和事务 ID）中维护的每线程属性（per-thread-attribute）自动传送给创建的所有子线程时，应尽可能地采用可继承的线程局部变量，而不是采用普通的线程局部变量。

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