Call a method on a specific dates using ThreadPoolTaskExecutor - spring

Question

I have a method that I wish to run once using Spring and it needs to run on a given java.util.Date (or LocalDateTime alternatively). I am planning to persist all of the dates that the method should execute to a data source. It should run asynchronously.
One way is to check the DB every day for a date and execute the method if the date has passed and hasn't been executed. Is there a better way?
I know that Spring offers a ThreadPoolTaskScheduler and a ThreadPoolTaskExecutor. I am looking at ScheduledFuture schedule(Runnable task, Date startTime) from the TaskScheduler interface. Would I need to create a Runnable Spring managed bean just to call my method? Or is there a simpler annotation that would do this? An example would really help.
(Looked here too.)

Answer 1

By externalizing the scheduled date (to a database), the typical scheduling practices (i.e. cron based, or fixed scheduling) no longer apply. Given a target Date, you can schedule the task accurately as follows:
Date now = new Date();
Date next = ... get next date from external source ...
long delay = next.getTime() - now.getTime();
scheduler.schedule(Runnable task, delay, TimeUnit.MILLISECONDS);
What remains is to create an efficient approach to dispatching each new task.
The following has a TaskDispatcher thread, which schedules each Task based on the next java.util.Date (which you read from a database). There is no need to check daily; this approach is flexible enough to work with any scheduling scenario stored in the database.
To follow is working code to illustrate the approach.
The example Task used; in this case just sleeps for a fixed time. When the task is complete, the TaskDispatcher is signaled through a CountDownLatch.
public class Task implements Runnable {
private final CountDownLatch completion;
public Task(CountDownLatch completion) {
this.completion = completion;
}
#Override
public void run() {
System.out.println("Doing task");
try {
Thread.sleep(60*1000); // Simulate the job taking 60 seconds
} catch (InterruptedException e) {
e.printStackTrace();
}
completion.countDown(); // Signal that the job is complete
}
}
The dispatcher is responsible for reading the database for the next scheduled Date, launching a ScheduledFuture runnable, and waiting for the task to complete.
public class TaskDispatcher implements Runnable {
private static final ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);
private boolean isInterrupted = false;
#Override
public void run() {
while (!isInterrupted) {
Date now = new Date();
System.out.println("Reading database for next date");
Date next = ... read next data from database ...
//Date next = new Date(); // Used as test
//next.setTime(now.getTime()+10*1000); // Used as test
long delay = next.getTime() - now.getTime();
System.out.println("Scheduling next task with delay="+delay);
CountDownLatch latch = new CountDownLatch(1);
ScheduledFuture<?> countdown = scheduler.schedule(new Task(latch), delay, TimeUnit.MILLISECONDS);
try {
System.out.println("Blocking until the current job has completed");
latch.await();
} catch (InterruptedException e) {
System.out.println("Thread has been requested to stop");
isInterrupted = true;
}
if (!isInterrupted)
System.out.println("Job has completed normally");
}
scheduler.shutdown();
}
}
The TaskDispatcher was started as follows (using Spring Boot) - start the thread as you normally do with Spring:
#Bean
public TaskExecutor taskExecutor() {
return new SimpleAsyncTaskExecutor(); // Or use another one of your liking
}
#Bean
public CommandLineRunner schedulingRunner(TaskExecutor executor) {
return new CommandLineRunner() {
public void run(String... args) throws Exception {
executor.execute(new TaskDispatcher());
}
};
}
Let me know if this approach will work for your use case.

Answer 2

Take a look at the #Scheduled annotation. It may accomplish what you're looking for.
#Scheduled(cron="*/5 * * * * MON-FRI")
public void scheduledDateWork() {
Date date = new Date(); //or use DAO call to look up date in database
executeLogic(date);
}
Cron Expression Examples from another answer:
"0 0 * * * *" = the top of every hour of every day.
"*/10 * * * * *" = every ten seconds.
"0 0 8-10 * * *" = 8, 9 and 10 o'clock of every day.
"0 0/30 8-10 * * *" = 8:00, 8:30, 9:00, 9:30 and 10 o'clock every day.
"0 0 9-17 * * MON-FRI" = on the hour nine-to-five weekdays
"0 0 0 25 12 ?" = every Christmas Day at midnight