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测试 ThreadLocal

每个 Thread 都有一个 ThreadLocalMap 的对象,存储时以 ThreadLocal 变量为 key,set() 的参数作为 value,这样同一个 ThreadLocal 变量在不同的线程中就可以存储不同的数据。

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public class ThreadLocalTest {
private static ThreadLocal<String> foo = new ThreadLocal<>();
public static void main(String[] args) throws Exception {
new Thread(() -> {
await(300);
System.out.println(Thread.currentThread().getName() + ": " + foo.get()); // [2] 输出: Thread-1: null
foo.set("1"); // [3]
await(1000);
System.out.println(Thread.currentThread().getName() + ": " + foo.get()); // [5] 输出: Thread-1: 1
}, "Thread-1").start();
new Thread(() -> {
foo.set("2"); // [1]
await(600);
System.out.println(Thread.currentThread().getName() + ": " + foo.get()); //[4] 输出: Thread-2: 2
}, "Thread-2").start();
}
public static void await(long timeout) {
try { Thread.sleep(timeout); } catch (InterruptedException e) {}
}
}

输出:

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3
Thread-1: null
Thread-2: 2
Thread-1: 1

ThreadLocal 的变量一般定义为 private static 的。