How to get queue and pool size from ScheduledExecutorService

Question

I am create a scheduler and schedule a job with 2 sec delay. But before schedule specific jobs i want to check ScheduledExecutorService's pool size and queue size but i couldn't found any way for that. Can anyone suggest to me how can i check ScheduledExecutorService's pool size and queue size before schedule any job .

   //here i have created ScheduledExecutorService 
private static final ScheduledExecutorService SCHEDULED_EXECUTOR_SERVICE;


static {
     //initialized  ScheduledExecutorService with 30 pool size
    Scheduled_Executor_Service = (ThreadPoolExecutor) Executors.newScheduledThreadPool(30);
}


public void addTaskTOSchedule(){

  //Here i want to check poolsize and queue size of SCHEDULED_EXECUTOR_SERVICE if 
  //ScheduledExecutorService already used more then specific number thread then i will not schedule job

SCHEDULED_EXECUTOR_SERVICE.schedule(() -> {
                    User user = new User();
                    SCHEDULED_EXECUTOR_SERVICE.execute(user);
                }, 2000, TimeUnit.MILLISECONDS);
}

Answer 1

ScheduledExecutorService interface doesn't allow to access the internal queue. You would have to cast the service to implementation class to get the size of the queue like this:

ScheduledExecutorService Scheduled_Executor_Service = Executors.newScheduledThreadPool(30);
        if (Scheduled_Executor_Service instanceof ScheduledThreadPoolExecutor) {
            ScheduledThreadPoolExecutor implementation = (ScheduledThreadPoolExecutor) Scheduled_Executor_Service;
            int size = implementation.getQueue().size();

        }