newScheduledThreadPool

public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) {
    return new ScheduledThreadPoolExecutor(corePoolSize);
}
    
public ScheduledThreadPoolExecutor(int corePoolSize) {
    super(corePoolSize, Integer.MAX_VALUE, 0, NANOSECONDS, new DelayedWorkQueue());
}

ScheduledThreadPoolExecutor的實現(xiàn)

獲取任務(wù)的過程

把ScheduledFutureTask放入DelayQueue中的過程

-----------------------------------------------------------------------------讀書筆記摘自 書名：Java并發(fā)編程的藝術(shù) 作者：方騰飛；魏鵬；程曉明

常見用途

參考：Executor框架的成員文章來源地址http://www.zghlxwxcb.cn/news/detail-453505.html

線程任務(wù)

public class Task implements Runnable {
    private final String name;

    public Task(String name) {
        this.name = name;
    }

    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName() + " → " + name + " Start Time = " + new Date());
        processCommand();
        System.out.println(Thread.currentThread().getName() + " → " + name + " End   Time = " + new Date());
    }

    private void processCommand() {
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

1. schedule(new Task(), 10, TimeUnit.SECONDS)

public class ScheduledThreadPool {
    public static void main(String args[]) throws InterruptedException, ExecutionException {

        System.out.println(Thread.currentThread().getName() + "線程: Start at: " + new Date());

        ScheduledThreadPoolExecutor exec = (ScheduledThreadPoolExecutor) Executors.newScheduledThreadPool(5);

        for (int i = 0; i < 10; i++) {
            System.out.println("添加了第" + i + "個線程任務(wù) " + new Date());
            exec.schedule(new Task("線程名字" + i), 10, TimeUnit.SECONDS);// 延遲10秒執(zhí)行
        }

        exec.shutdown();

        System.out.println(Thread.currentThread().getName() + "線程: 打卡" + new Date());

        while (!exec.isTerminated()) {
            // wait for all tasks to finish
        }

        System.out.println(Thread.currentThread().getName() + "線程: Finished all threads at：" + new Date());
    }
}

執(zhí)行結(jié)果分析

2. scheduleWithFixedDelay(new Task(), 2, 4, TimeUnit.SECONDS) 初始延時 2s， 固定延時4s

public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command,
                                                 long initialDelay,
                                                 long delay,
                                                 TimeUnit unit);

public class FixedDelay {
    public static void main(String args[]) throws InterruptedException, ExecutionException {
        way1();
        way2();
    }

    private static void way2() {
        System.out.println(Thread.currentThread().getName() + "線程: Start at: " + new Date());

        ScheduledThreadPoolExecutor scheduledExecutorService = new ScheduledThreadPoolExecutor(1);

        scheduledExecutorService.scheduleWithFixedDelay(() -> {
            System.out.println(Thread.currentThread().getName() + " → " + " Start Time = " + new Date());
            try {
                sleep(3000);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
            System.out.println(Thread.currentThread().getName() + " → " + " End   Time = " + new Date());
        }, 1, 4, TimeUnit.SECONDS);  // 延遲 1s，周期 4s
    }

    private static void way1() {
        System.out.println(Thread.currentThread().getName() + "線程: Start at: " + new Date());

        ScheduledExecutorService scheduledExecutorService = Executors.newScheduledThreadPool(2);

        scheduledExecutorService.scheduleWithFixedDelay(new Task("任務(wù)"), 1, 4, TimeUnit.SECONDS);  // 延遲 1s, 周期 4s
    }
}

執(zhí)行結(jié)果分析

3. scheduleAtFixedRate(new Task(), 1, 4, TimeUnit.SECONDS) 初始延時 1s， 周期4s

執(zhí)行結(jié)果分析

定時任務(wù)?每天晚上9點(diǎn)執(zhí)行一次

public class FixedRateDemo {
    public static void main(String args[]) throws InterruptedException, ExecutionException, ParseException {
        System.out.println(Thread.currentThread().getName() + "線程: Starting at: " + new Date());

        ScheduledExecutorService executor = Executors.newScheduledThreadPool(1);
        // long oneDay = 24 * 60 * 60 * 1000=86400000; // 1天24小時作為周期
        // long initDelay = getTimeMillis("21:00:00") - System.currentTimeMillis(); // 當(dāng)前時間

        long oneDayPeriod = 10000; // 正常1天=24*60*60*1000=86400000ms,這里用5s來模擬
//        long initDelay = getTimeMillis("21:00:00") - getTimeMillis("20:59:57"); // 假設(shè)模擬此時當(dāng)天的20:59:57 → 3000ms
        long initDelay = getTimeMillis("21:00:00") - getTimeMillis("21:00:03"); // 假設(shè)模擬此時當(dāng)天的21:00:03 →-3000ms

        initDelay = initDelay > 0 ? initDelay : oneDayPeriod + initDelay;

        executor.scheduleAtFixedRate(new Task("定時任務(wù)"), initDelay, oneDayPeriod, TimeUnit.MILLISECONDS);
    }


    /**
     * 獲取指定時間對應(yīng)的毫秒數(shù)
     */
    private static long getTimeMillis(String time) throws ParseException {
        DateFormat dateFormat = new SimpleDateFormat("yy-MM-dd HH:mm:ss");
        DateFormat dayFormat = new SimpleDateFormat("yy-MM-dd");
        Date curDate = dateFormat.parse(dayFormat.format(new Date()) + " " + time);
        return curDate.getTime();
    }
}

執(zhí)行結(jié)果分析

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