ScheduledExecutorService 替代 Timer

import java.util.Timer;
import java.util.TimerTask;

public class TimerTest {
    private Timer timer = new Timer();

    // 启动计时器 延迟3s,每0.5s执行1次
    public void launchTimer() {
        timer.schedule(new TimerTask() {
            public void run() {
                System.out.println("hello world-1:" + System.currentTimeMillis());
                throw new RuntimeException();
            }
        }, 1000 * 3, 500);
    }

    // 向计时器添加一个任务，延迟1s，每5s执行一次
    public void addOneTask() {
        System.out.println("hello world-2-1:" + System.currentTimeMillis());
        timer.schedule(new TimerTask() {
            public void run() {
                System.out.println("hello world-2-2:" + System.currentTimeMillis());
            }
        }, 1000 * 1, 1000 * 5);
    }

    public static void main(String[] args) throws Exception {
        TimerTest test = new TimerTest();
        test.launchTimer();
        Thread.sleep(1000 * 5);// 5秒钟之后添加一个新任务
        test.addOneTask();
    }
}

输出：

hello world-1:1623314074261
Exception in thread "Timer-0" java.lang.RuntimeException
    at com.company.TimerTest$1.run(TimerTest.java:14)
    at java.util.TimerThread.mainLoop(Timer.java:555)
    at java.util.TimerThread.run(Timer.java:505)
hello world-2-1:1623314076261
Exception in thread "main" java.lang.IllegalStateException: Timer already cancelled.
    at java.util.Timer.sched(Timer.java:397)
    at java.util.Timer.schedule(Timer.java:248)
    at com.company.TimerTest.addOneTask(TimerTest.java:22)
    at com.company.TimerTest.main(TimerTest.java:34)

分析：定时任务1执行完，输出，会抛出运行时异常。此时timer已经是cancelled状态。再执行定时任务2，就会抛出Timer already cancelled异常。
解决的办法：1.定时任务里捕获异常 2.使用ScheduledExecutorService

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

public class Main {

    public ScheduledExecutorService scheduleExec = Executors.newScheduledThreadPool(1);

    //启动计时器
    public void launchTimer() {
        Runnable task = new Runnable() {
            public void run() {
                System.out.println("hello world-1:" + System.currentTimeMillis());
                throw new RuntimeException();
            }
        };
        scheduleExec.scheduleWithFixedDelay(task, 1000 * 5, 1000 * 10, TimeUnit.MILLISECONDS);
    }

    //添加新任务
    public void addOneTask() {
        System.out.println("hello world-2-1:" + System.currentTimeMillis());
        Runnable task = new Runnable() {
            public void run() {
                System.out.println("hello world-2-2:" + System.currentTimeMillis());
            }
        };
        scheduleExec.scheduleWithFixedDelay(task, 1000 * 1, 1000, TimeUnit.MILLISECONDS);
    }

    public static void main(String[] args) throws Exception {
        Main test = new Main();
        test.launchTimer();
        Thread.sleep(1000 * 5);//5秒钟之后添加新任务
        test.addOneTask();
    }
}

输出：

hello world-2-1:1623313863678
hello world-1:1623313863679
hello world-2-2:1623313864679
hello world-2-2:1623313865681
hello world-2-2:1623313866682
...