ScheduledExecutorService

我们需要定期或在特定延迟后执行任务,Java提供了Timer类，通过它我们可以实现这一点，但有时我们需要并行运行类似的任务。所以创建多个Timer对象将是系统的开销，最好有一个调度任务的线程池。Java通过ScheduledThreadPoolExecutor类提供计划的线程池实现，实现ScheduledExecutorService接口。

public class WorkerThread implements Runnable{

private String command;
    
    public WorkerThread(String s){
        this.command=s;
    }

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

    private void processCommand() {
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    @Override
    public String toString(){
        return this.command;
    }
}

public class ScheduledThreadPool {

    public static void main(String[] args) throws InterruptedException {
        ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(5);
        
        
        //schedule to run after sometime
        System.out.println("Current Time = "+new Date());
        for(int i=0; i<3; i++){
            Thread.sleep(1000);
            WorkerThread worker = new WorkerThread("do heavy processing");
            scheduledThreadPool.schedule(worker, 10, TimeUnit.SECONDS);
        }
        
        //add some delay to let some threads spawn by scheduler
        Thread.sleep(30000);
        
        scheduledThreadPool.shutdown();
        while(!scheduledThreadPool.isTerminated()){
            //wait for all tasks to finish
        }
        System.out.println("Finished all threads");
    }

}