1、ScheduledThreadPool简介

ScheduledThreadPool是核心线程数量固定，非核心线程数量无限，执行完闲置 10ms 后回收，任务队列为延时阻塞队列。一般是用在执行定时或周期性任务的使用场景。相对于通过使用 ThreadPoolExecutor 的方式，使用ScheduledThreadPool更方便，有些参数可能不需要设置，可以根据实现情况使用。

2、newFixedThreadPool源码

private static final long DEFAULT_KEEPALIVE_MILLIS = 10L;
 
public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) {
    return new ScheduledThreadPoolExecutor(corePoolSize);
}
public ScheduledThreadPoolExecutor(int corePoolSize) {
    super(corePoolSize, Integer.MAX_VALUE,
          DEFAULT_KEEPALIVE_MILLIS, MILLISECONDS,
          new DelayedWorkQueue());
}
 
public static ScheduledExecutorService newScheduledThreadPool(
        int corePoolSize, ThreadFactory threadFactory) {
    return new ScheduledThreadPoolExecutor(corePoolSize, threadFactory);
}
public ScheduledThreadPoolExecutor(int corePoolSize,
                                   ThreadFactory threadFactory) {
    super(corePoolSize, Integer.MAX_VALUE,
          DEFAULT_KEEPALIVE_MILLIS, MILLISECONDS,
          new DelayedWorkQueue(), threadFactory);
}

3、使用示例

import java.util.concurrent.*;
import java.util.Date; 
import java.text.DateFormat;
import java.text.SimpleDateFormat;

public class Main {
  public static void main(String[] args) throws Exception {
    
    
    ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(5);
    // 需执行的任务
    Runnable task =new Runnable(){
      public void run() {
              Date date=new Date();
              DateFormat dateFormat=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
              System.out.println(" 当前时间为："+dateFormat.format(date));
      }
    };
    //添加任务
    scheduledThreadPool.schedule(task, 1, TimeUnit.SECONDS); // 延迟1s后执行任务
    scheduledThreadPool.scheduleAtFixedRate(task,10,1000,TimeUnit.MILLISECONDS);// 延迟10ms后、每隔1000ms执行任务

    scheduledThreadPool.awaitTermination(10000, TimeUnit.MILLISECONDS);
    System.exit(0); //success
  }
}