ThreadLocal

线程本地存储区域。ThreadLocal能够放一个线程级别的变量，其本身能够被多个线程共享使用，并且能够达到线程安全的目的。JDK中建议ThreadLocal定义为private static。
内部存储结构类似map，key是存储信息，value是存储内容。
常用set\get\initialValue方法。

/**
 * ThreadLocal表示每个线程自身的存储区域：本地、局部区域
 */
public class ThreadLocalTest01 {
    //    private static ThreadLocal<Integer> threadLocal = new ThreadLocal();
    //    更改初始值
//    private static ThreadLocal<Integer> threadLocal = new ThreadLocal() {
//        @Override
//        protected Object initialValue() {
//            return 200;
//        }
//    };
    private static ThreadLocal<Integer> threadLocal = ThreadLocal.withInitial(() -> 200);

    public static void main(String[] args) {
        // 设置值
        threadLocal.set(99);
        System.out.println(Thread.currentThread().getName() + "-->" + threadLocal.get());   // 200
        new Thread(new ThreadLocalTest01.MyRun()).start();
    }


    public static class MyRun implements Runnable {

        @Override
        public void run() {
            threadLocal.set(11);
            System.out.println(Thread.currentThread().getName() + "-->" + threadLocal.get());   // 11
        }
    }
}

每个线程存储自身的数据，更改不会影响其他的线程。

/**
 * ThreadLocal表示每个线程自身的存储区域：本地、局部区域
 */
public class ThreadLocalTest01 {
    private static ThreadLocal<Integer> threadLocal = ThreadLocal.withInitial(() -> 1);

    public static void main(String[] args) {
        for (int i = 0; i < 5; i++) {
            new Thread(new ThreadLocalTest01.MyRun()).start();
        }
    }


    public static class MyRun implements Runnable {

        @Override
        public void run() {
            Integer integer = threadLocal.get();
            System.out.println(Thread.currentThread().getName() + "-->" + integer);   // 1
            threadLocal.set(integer - 1);
            System.out.println(Thread.currentThread().getName() + "-->" + threadLocal.get());   // 0
        }
    }
}

InheritableThreadLocal 继承上下文环境的数据,可以将数据进行共享。

public class ThreadLocalTest01 {
    private static ThreadLocal<Integer> threadLocal = new InheritableThreadLocal<>();

    public static void main(String[] args) {
        threadLocal.set(2);
        System.out.println(Thread.currentThread().getName() + "-->" + threadLocal.get());
        // 线程由main线程开辟，将数据拷贝一份给子线程
        new Thread(() -> {
            System.out.println(Thread.currentThread().getName() + "-->" + threadLocal.get());   // 2
        }).start();
    }
}