How to execute tasks regularly in java

How to execute a method regularly in java

There are many ways to implement the timing function in java. Here are 3 methods:

1. Create a thread.

import java.util.Date;
public class ThreadTest {
    public static void main(String[] args) {
        // 设置执行周期
        final long timeInterval = 3000;
        
        Runnable runnable = new Runnable() {
            public void run() {
                while (true) {
                    System.out.println("Task Run ... " + new Date());
                    
                    try {
                        Thread.sleep(timeInterval);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        };
        Thread thread = new Thread(runnable);
        thread.start();
    }
}

2. Use the API Timer and TaskTimer that come with the JDK.

What is the difference between this method and the first simple and crude method? It is mainly reflected in the fact that the API can be used to start the task at a specified time, and the execution of the first task can be postponed. It can also be set A certain time interval, but the principle is the same. A thread is still started in the background. It should be said that there is only one thread executing the task, no matter how many Tasks we start. So there will be problems. For example, if one task is not completed and another task starts to be executed, concurrency problems may occur. Also, if an error is reported in a task, the thread will be stopped.

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;

public class MyTask extends TimerTask{

    private String name;
    
    public MyTask(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public void run() {
        SimpleDateFormat sf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String format = sf.format(new Date());
        System.out.println("exec MyTask ... 当前时间为：" + format);
        System.out.println(this.name +" 正在执行！" + sf.format(new Date()));
    }
    
    public static void main(String[] args) {
        Timer timer = new Timer();
        TimerTask task1 = new MyTask("Tasks 1");
        TimerTask task2 = new MyTask("Tasks 2");
        
        Calendar calendar1 = Calendar.getInstance();
        calendar1.add(Calendar.SECOND, 3);
        Calendar calendar2 = Calendar.getInstance();
        calendar2.add(Calendar.SECOND, 5);
        
        SimpleDateFormat sf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String format = sf.format(new Date());
        System.out.println("当前时间为：" + format);
        
        timer.schedule(task1, calendar1.getTime(), 3000L);
        timer.schedule(task2, calendar2.getTime(), 3000L);
    }

}

In fact, Timer encapsulates a Task queue and Time thread object. Our custom Task reference will be placed in the queue waiting for execution.

It is roughly the relationship Timer - TimerThread - TaskQueue - MyTask - run Of course, the final execution method must be the run method in our custom task. Because our custom task has inherited TimeTask, and this class has implemented the Runnable interface.

3. Use ScheduledExecutorService

ScheduledExecutorService was introduced as a concurrent tool class. This is the most ideal way to implement scheduled tasks.

1. Compared with Timer's single thread, it executes tasks through a thread pool.

2. You can flexibly set the delay time for the first task execution.

3. Provides a good convention to set the execution interval.

import java.util.Date;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
public class qwe {
    public static void main(String[] args) {
        //新建定时任务
        Runnable runnable = new Runnable() {
            //run方法中是定时执行的操作
            public void run() {
                System.out.println(new Date());
            }
        };
        ScheduledExecutorService service = Executors.newSingleThreadScheduledExecutor();
        /*
         * 参数一:command：执行线程
         * 参数二:initialDelay：初始化延时
         * 参数三:period：两次开始执行最小间隔时间
         * 参数四:unit：计时单位
         */
        service.scheduleAtFixedRate(runnable, 0, 60, TimeUnit.SECONDS);
    }
}

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