例子1（scheduleAtFixedRate）：延遲2秒後，每隔3秒執行1次

ScheduledExecutorService es = Executors.newScheduledThreadPool(5);
        log.info("開始時間");
        Runnable syncRunnable = new Runnable() {
            @Override
            public void run() {
                log.info(Thread.currentThread().getName());
            }
        };
        es.scheduleAtFixedRate(syncRunnable, 
 
2000, 3000, TimeUnit.MILLISECONDS);

運行結果：

            10:49:22.495 開始時間
            10:49:24.500 pool-1-thread-1
            10:49:27.499 pool-1-thread-1
            10:49:30.500 pool-1-thread-2
            10:49:33.500 pool-1-thread-1
            10:49:36.501 pool-1-thread-3
            10:49:39.500 pool-1-thread-2
            10:49:42.500 pool-1-thread-2
            10:49:45.500 pool-1-thread-1
            10:49:48.501 pool-1-thread-1
            10:49:51.501 pool-1-thread-1
            10:49:54.501 pool-1-thread-4
            10:49:57.501 pool-1-thread-2
            10:50:00.502 pool-1-thread-2
            10:50:03.502 pool-1-thread-3
            10:50:06.502 pool-1-thread-3
            10:50:09.502 pool-1-thread-3
            10:50:12.503 pool-1-thread-5
            10:50:15.503 pool-1-thread-5
            10:50:18.503 pool-1-thread-5
            10:50:21.503 pool-1-thread-5
            10:50:24.503 pool-1-thread-3
            10:50:27.503 pool-1-thread-2
            10:50:30.503 pool-1-thread-1
            10:50:33.504 pool-1-thread-4
            10:50:36.504 pool-1-thread-5
            10:50:39.504 pool-1-thread-5
            10:50:42.504 pool-1-thread-2

例子2（scheduleWithFixedDelay）：延遲5秒後，每個任務執行完後延遲3秒在執行1次

ScheduledExecutorService es = Executors.newScheduledThreadPool(5);
        log.info("開始時間");
        Runnable syncRunnable = new Runnable() {
            @Override
            public void run() {
                log.info(Thread.currentThread().getName());
                
 
try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        };
        es.scheduleWithFixedDelay(syncRunnable, 5000, 3000, TimeUnit.MILLISECONDS);

運行結果：

            11:10:27.773 開始時間
            11:10:32.778 pool-1-thread-1
            11:10:36.779 pool-1-thread-1
            11:10:40.780 pool-1-thread-2
            11:10:44.781 pool-1-thread-1
            11:10:48.783 pool-1-thread-3
            11:10:52.785 pool-1-thread-3
            11:10:56.785 pool-1-thread-4
            11:11:00.787 pool-1-thread-4
            11:11:04.788 pool-1-thread-4
            11:11:08.789 pool-1-thread-4
            11:11:12.790 pool-1-thread-3
            11:11:16.792 pool-1-thread-1

本來是每隔3秒執行的，但是，由於某個任務處理時間過長，導致延後。本例是延後1秒，即4秒。

總結：scheduleAtFixedRate與scheduleWithFixedDelay區別

scheduleAtFixedRate：不管任務是否執行完了，在3秒內必須執行
scheduleWithFixedDelay：等任務執行完了，在等3秒後執行
因此，scheduleWithFixedDelay 非常有用。

線程池（5）Executors.newScheduledThreadPool