如何正确停止线程

使用 interrupt 来通知，而不是强制

1：普通情况停止线程

public class RightWayStopThreadWithoutSleep implements Runnable {

    @Override
    public void run() {
        int num = 0;
        while (!Thread.currentThread().isInterrupted() && num <= Integer.MAX_VALUE / 2) {
            if (num % 10000 == 0) {
                System.out.println(num + "是1W的倍数");
            }
            num++;
        }
        System.out.println("任务运行结束！");
    }

    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread(new RightWayStopThreadWithoutSleep());
        thread.start();
        Thread.sleep(1000);
        // 通知停止线程
        thread.interrupt();
    }
}

通知停止线程
thread.interrupt();
并且线程需要配合
Thread.currentThread().isInterrupted()
运行结果：

……
……
221730000是1W的倍数
221740000是1W的倍数
221750000是1W的倍数
221760000是1W的倍数
221770000是1W的倍数
221780000是1W的倍数
221790000是1W的倍数
221800000是1W的倍数
任务运行结束！

Process finished with exit code 0

2：线程可能被阻塞情况下停止线程

public class RightWayStopThreadWithSleep {
    public static void main(String[] args) throws InterruptedException {
        Runnable runnable = () -> {
            int num = 0;
            while (num <= 300 && !Thread.currentThread().isInterrupted()) {
                if (num % 100 == 0) {
                    System.out.println(num + "是100的倍数");
                }
                num++;
            }
            try {
                // 等个1秒，模拟阻塞
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                System.out.println("线程已停止！！");
                e.printStackTrace();
            }
        };

        Thread thread = new Thread(runnable);
        thread.start();
        // 等待时间要小于上面设置的1秒，不然线程都运行结束了，才执行到下面的thread.interrupt();代码
        Thread.sleep(500);
        // 通知停止线程
        thread.interrupt();
    }
}

线程在sleep 1秒的过程中，收到interrupt信号被打断，
线程正在sleep过程中响应中断的方式就是抛出 InterruptedException 异常
运行结果：

0是100的倍数
100是100的倍数
200是100的倍数
300是100的倍数
线程已停止！！
java.lang.InterruptedException: sleep interrupted
    at java.lang.Thread.sleep(Native Method)
    at stopthreads.RightWayStopThreadWithSleep.lambda$main$0(RightWayStopThreadWithSleep.java:19)
    at java.lang.Thread.run(Thread.java:748)

Process finished with exit code 0

3：线程在每次迭代后都阻塞的情况下停止线程

public class RightWayStopThreadWithSleepEveryLoop {
    public static void main(String[] args) throws InterruptedException {
        Runnable runnable = () -> {
            int num = 0;
            try {
                while (num <= 10000) {
                    if (num % 100 == 0) {
                        System.out.println(num + "是100的倍数");
                    }
                    num++;
                    // 每次循环都要等待10毫秒，模拟阻塞
                    Thread.sleep(10);
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        };

        Thread thread = new Thread(runnable);
        thread.start();
        // 5秒后通知停止线程
        Thread.sleep(5000);
        thread.interrupt();
    }
}

当每次迭代都会让线程阻塞一段时间的时候，在while/for循环条件判断时，是不需要判断线程是否中断的Thread.currentThread().isInterrupted()

如果将上述代码的 try/catch 放在 while 循环内

public class RightWayStopThreadWithSleepEveryLoop {
    public static void main(String[] args) throws InterruptedException {
        Runnable runnable = () -> {
            int num = 0;
            while (num <= 10000) {
                if (num % 100 == 0) {
                    System.out.println(num + "是100的倍数");
                }
                num++;
                try {
                    Thread.sleep(10);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        };

        Thread thread = new Thread(runnable);
        thread.start();
        Thread.sleep(5000);
        thread.interrupt();
    }
}

运行结果：

0是100的倍数
100是100的倍数
200是100的倍数
300是100的倍数
400是100的倍数
java.lang.InterruptedException: sleep interrupted
    at java.lang.Thread.sleep(Native Method)
    at stopthreads.RightWayStopThreadWithSleepEveryLoop.lambda$main$0(RightWayStopThreadWithSleepEveryLoop.java:18)
    at java.lang.Thread.run(Thread.java:748)
500是100的倍数
600是100的倍数
700是100的倍数
……
……

会发现虽然抛出了异常，但是程序并没有停止，还在继续输出，
即使在while条件判断处添加 !Thread.currentThread().isInterrupted() 条件，依然不能停止程序！
原因：
java语言在设计sleep函数时，有这样一个理念：就是当它一旦响应中断，便会把interrupt标记位清除。
也就是说虽然线程在sleep过程中收到了interrupt中断通知，并且也捕获到了异常打印了异常信息，但是由于sleep设计理念，导致Thread.currentThread().isInterrupted()标记位会被清除，所以才会导致程序不能退出。

两种停止线程最佳方法

1. 捕获了InterruptedException之后的优先选择：在方法签名中抛出异常

public class RightWayStopThreadInProd implements Runnable {

    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread(new RightWayStopThreadInProd());
        thread.start();
        Thread.sleep(1000);
        thread.interrupt();
    }

    @Override
    public void run() {
        while (true) {
            System.out.println("go...");
            try {
                throwInMethod();
            } catch (InterruptedException e) {
                // 捕获异常，进行保存日志、停止程序等操作
                System.out.println("stop");
                e.printStackTrace();
            }
        }
    }

    /**
     * 如果方法内要抛出异常，最好是将异常抛出去，由顶层的调用方去处理，而不是try/catch
     * 这样调用方才能捕获异常并作出其它操作
     * @throws InterruptedException
     */
    private void throwInMethod() throws InterruptedException {
        Thread.sleep(2000);
    }
}

如果方法内要抛出异常，最好是将异常抛出去，由顶层的调用方去处理，而不是try/catch
这样调用方才能捕获异常并做出其它操作。

2. 在catch中调用Thread.currentThread().interrupt();来恢复设置中断状态

public class RightWayStopThreadInProd2 implements Runnable {

    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread(new RightWayStopThreadInProd2());
        thread.start();
        Thread.sleep(1000);
        thread.interrupt();
    }

    @Override
    public void run() {
        while (true) {
            if (Thread.currentThread().isInterrupted()) {
                System.out.println("程序运行结束");
                break;
            }
            reInterrupt();
        }
    }

    private void reInterrupt() {
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
            e.printStackTrace();
        }
    }
}