ScheduledThreadPoolExecutor使用

1.简介

1.1 继承结构

java.lang.Object
  java.util.concurrent.AbstractExecutorService
      java.util.concurrent.ThreadPoolExecutor
          java.util.concurrent.ScheduledThreadPoolExecutor

1.2 实现接口

Executor, ExecutorService, ScheduledExecutorService 

2.常用API

void execute(Runnable command)
<V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit)  
ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit)  
ScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit)  
ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit)
void shutdown()  

scheduleAtFixedRate与scheduleWithFixedDelay区别:
    scheduleAtFixedRate 按定时任务传入时间严格周期执行
    scheduleWithFixedDelay 按任务具体执行时间来周期执行

3.小栗子

3.1 void execute(Runnable command)

public static void main(String[] args) {
    ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(1);
    executor.execute(() -> {
        System.out.println("execute");
    });
    executor.shutdown();
}

3.2 <V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit)

public static void main(String[] args) {
    ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(1);
    executor.schedule(new Callable<Object>() {
        @Override
        public Object call() throws Exception {
            System.out.println("schedule Callable");
            return null;
        }
    }, 2, TimeUnit.SECONDS);
    executor.shutdown();
}   

3.3 ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit)

public static void main(String[] args) {
    ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(1);
    executor.schedule(() -> {
        System.out.println("schedule Runnable");
    }, 2, TimeUnit.SECONDS);
    executor.shutdown();
}

3.4 ScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit)

public static void main(String[] args) {
    ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(1);
    long startTime = System.currentTimeMillis() / 1000;
    executor.scheduleAtFixedRate(()->{
        try {
            long endTime = System.currentTimeMillis() / 1000;
            System.out.println("time:" + (endTime - startTime));
            Thread.sleep(1000);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }, 1, 2, TimeUnit.SECONDS);
}
result:
    time:1
    time:3
    time:5
    time:7

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

public static void main(String[] args) {
    ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(1);
    long startTime = System.currentTimeMillis() / 1000;
    executor.scheduleWithFixedDelay(()->{
        try {
            long endTime = System.currentTimeMillis() / 1000;
            System.out.println("time:" + (endTime - startTime));
            Thread.sleep(1000);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }, 1, 2, TimeUnit.SECONDS);
}
result:
    time:1
    time:4
    time:7
    time:10

4 归纳

在讲ThreadPoolExecutor时候，我们讲尽量不要直接实例化，而是使用Executors获取连接池对象。ScheduledThreadPoolExecutor是ThreadPoolExecutor子类，我们也建议不要直接实例化，工具类中有获取实例的方法。
Executors API:
    public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) 
    ...

5 总结

scheduleAtFixedRate和scheduleWithFixedDelay虽然delay一样，但是执行之间不一样，具体自己体会，其他的API就不做介绍了，个人感觉还是要多看源码。