Java ScheduledExecutorServiceの例

投稿日: 2019-11-05 2019-11-05
タグ: Concurrency, Java, scheduler

Javaでは、
ScheduledExecutorService`を使用して、タスクを定期的に、または
TimeUnit`によって定義済みの遅延の後に1回実行することができます。

1.タスクを1回実行する

ScheduledExecutorService`は
Runnable`と `Callable`タスクの両方を受け入れます。

1.1 5秒の初期遅延後に `Runnable`タスクを実行します。

ScheduledExecutorExample.java

package com.mkyong.concurrency.executor.scheduler;

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

public class ScheduledExecutorRunnable {

    public static void main(String[]args) {

        ScheduledExecutorService ses = Executors.newScheduledThreadPool(1);

        Runnable task2 = () -> System.out.println("Running task2...");

        task1();

       //run this task after 5 seconds, nonblock for task3
        ses.schedule(task2, 5, TimeUnit.SECONDS);

        task3();

        ses.shutdown();

    }

    public static void task1() {
        System.out.println("Running task1...");
    }

    public static void task3() {
        System.out.println("Running task3...");
    }

}

出力

Running task1...
Running task3...
Running task2...//display after 5 seconds

1.2 5秒の初期遅延後に `Callable`タスクを実行します。

ScheduledExecutorExample.java

package com.mkyong.concurrency.executor.scheduler;

import java.util.concurrent.** ;

public class ScheduledExecutorCallable {

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

        ScheduledExecutorService ses = Executors.newScheduledThreadPool(1);

        Callable<Integer> task2 = () -> 10;

        task1();

       //run this task after 5 seconds, nonblock for task3, returns a future
        ScheduledFuture<Integer> schedule = ses.schedule(task2, 5, TimeUnit.SECONDS);

        task3();

       //block and get the result
        System.out.println(schedule.get());

        System.out.println("shutdown!");

        ses.shutdown();

    }

    public static void task1() {
        System.out.println("Running task1...");
    }

    public static void task3() {
        System.out.println("Running task3...");
    }

}

出力

Running task1...
Running task3...
10                 //display after 5 seconds
shutdown!

2.定期的にタスクを実行する

定期的にタスクを実行するには、 `scheduleAtFixedRate`を使います。

2.1 5秒の初期遅延の後、1秒ごとに `Runnable`タスクを実行します。

ScheduledExecutorExample.java

package com.mkyong.concurrency.executor.scheduler;

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

public class ScheduledExecutorRepeat {

    private static int count = 0;

    public static void main(String[]args) throws InterruptedException {

        ScheduledExecutorService ses = Executors.newScheduledThreadPool(1);

        Runnable task1 = () -> {
            count++;
            System.out.println("Running...task1 - count : " + count);
        };

       //init Delay = 5, repeat the task every 1 second
        ScheduledFuture<?> scheduledFuture = ses.scheduleAtFixedRate(task1, 5, 1, TimeUnit.SECONDS);

        while (true) {
            System.out.println("count :" + count);
            Thread.sleep(1000);
            if (count == 5) {
                System.out.println("Count is 5, cancel the scheduledFuture!");
                scheduledFuture.cancel(true);
                ses.shutdown();
                break;
            }
        }

    }
}

出力

count :0
count :0
count :0
count :0
count :0
Running...task1 - count : 1
count :1
Running...task1 - count : 2
count :2
Running...task1 - count : 3
count :3
Running...task1 - count : 4
count :4
Running...task1 - count : 5
Count is 5, cancel the scheduledFuture!