为什么JDK建议ThreadLocal定义为private static？ThreadLocal内存泄漏

1.ThreadLocal是什么

ThreadLocal用于保存某个线程共享变量：对于同一个static ThreadLocal，不同线程只能从中get，set，remove自己的变量，而不会影响其他线程的变量。

1、ThreadLocal.get: 获取ThreadLocal中当前线程共享变量的值。

2、ThreadLocal.set: 设置ThreadLocal中当前线程共享变量的值。

3、ThreadLocal.remove: 移除ThreadLocal中当前线程共享变量的值。

4、ThreadLocal.initialValue: ThreadLocal没有被当前线程赋值时或当前线程刚调用remove方法后调用get方法，返回此方法值。

关键点：线程变量，即每个线程自己都拥有一个该变量，而不影响其他线程中的ThreadLocal

2.代码示例

public class ThreadLocalTest {

    public static void main(String[] args) {
        final ThreadLocal threadLocal1 = new ThreadLocal<>();
        final ThreadLocal threadLocal2 = new ThreadLocal<>();

        new Thread(new Runnable() {
            @Override
            public void run() {
                threadLocal1.set("A");
                threadLocal2.set(1);
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getName());
                System.out.println(threadLocal1.get());
                System.out.println(threadLocal2.get());
            }
        }).start();


        new Thread(new Runnable() {
            @Override
            public void run() {
                threadLocal1.set("B");
                threadLocal2.set(2);
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getName());
                System.out.println(threadLocal1.get());
                System.out.println(threadLocal2.get());
            }
        }).start();


        new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println(Thread.currentThread().getName());
                System.out.println(threadLocal1.get());
                System.out.println(threadLocal2.get());
            }
        }).start();
    }
}

输出结果

Thread-2
null
null
Thread-1
B
2
Thread-0
A
1