SQL：优化查询以进行少量IO操作(SQL : Optimizing query to have few IO operations)

 您可以使用ScheduledExecutorService进行此操作。 从示例文档中： 
 
import static java.util.concurrent.TimeUnit.*;
class BeeperControl {
  private final ScheduledExecutorService scheduler =
    Executors.newScheduledThreadPool(1);

  public void beepForAnHour() {
    final Runnable beeper = new Runnable() {
      public void run() { System.out.println("beep"); }
    };
    final ScheduledFuture<?> beeperHandle =
      scheduler.scheduleAtFixedRate(beeper, 10, 10, SECONDS);
    scheduler.schedule(new Runnable() {
      public void run() { beeperHandle.cancel(true); }
    }, 60 * 60, SECONDS);
  }
}
 
 您可以创建此ExecutorService的实例，并告诉它以某个时间间隔刷新令牌。 
 
 但也许更简单的解决方案是使用线程同步来确保在多个线程争用它时只发生一次令牌刷新。 可以使用ReentrantLock或Semaphore确保只有一个线程刷新令牌。 

You could use a ScheduledExecutorService for this. From the example docs:
 
import static java.util.concurrent.TimeUnit.*;
class BeeperControl {
  private final ScheduledExecutorService scheduler =
    Executors.newScheduledThreadPool(1);

  public void beepForAnHour() {
    final Runnable beeper = new Runnable() {
      public void run() { System.out.println("beep"); }
    };
    final ScheduledFuture<?> beeperHandle =
      scheduler.scheduleAtFixedRate(beeper, 10, 10, SECONDS);
    scheduler.schedule(new Runnable() {
      public void run() { beeperHandle.cancel(true); }
    }, 60 * 60, SECONDS);
  }
}
 
You could create an instance of this ExecutorService and tell it to refresh the token at some interval.
 
But perhaps a simpler solution is to use thread synchronization to ensure only one token refresh happens when multiple threads are contesting for it. ReentrantLock or Semaphore could be used to ensure only one thread is refreshing the token.