How to schedule a task at runtime where the frequency of the scheduler is read from the database-CodePudding

In the spring boot app, I have to call a method for a given frequency.This frequency will be read from the database. Frequent could be seconds or minutes or hours or days, etc. How do I implement this schedule for spring boot?

CodePudding user response：

for this you can use a cron with this annoation @Scheduled

Spring will schedule the annotated method to run at 10:15 AM on the 15th day of every month

@Scheduled(cron = "0 15 10 15 * ?")
public void scheduleTaskUsingCronExpression() {
 
    long now = System.currentTimeMillis() / 1000;
    System.out.println(
      "schedule tasks using cron jobs - "   now);
}

see this doc https://spring.io/guides/gs/scheduling-tasks/ and this https://spring.io/guides/gs/scheduling-tasks/

In Order to get the cron exp from the db : see this How to change Spring's @Scheduled fixedDelay at runtime?

CodePudding user response：

To give more other alternative solutions beside @Scheduled annotation.

You can use ScheduledExecutorService to execute task with fixed rate or fixed delay.

ScheduledExecutorService executorService = Executors
  .newSingleThreadScheduledExecutor();

Then you can use below function which depend on your need:

scheduleAtFixedRate
scheduleWithFixedDelay

Example:

Future<String> resultFuture = 
  executorService.schedule(callableTask, 1, TimeUnit.SECONDS);
Future<String> resultFuture = service
  .scheduleAtFixedRate(runnableTask, 100, 450, TimeUnit.MILLISECONDS);
service.scheduleWithFixedDelay(task, 100, 150, TimeUnit.MILLISECONDS);

Refer:

https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ScheduledExecutorService.html https://www.baeldung.com/java-executor-service-tutorial

PS: i highly recommend quartz framework also, it can schedule task with many different policies.

CodePudding user response：

You may use Task Exection and Sceduling API of Spring.

Your task to run in a scheduled mode

public class MyTask implements Runnable {

    public void run(){
        System.out.println("MyTask is running");
    }
}

A service to be used for dynamically creation of sceduled jobs. Inspired by this so answer.
You may add it in your library.

@Component
public class DbScheduledJobs {

    private final TaskScheduler executor;

    @Autowired
    public DbScheduledJobs(TaskScheduler taskExecutor) {
        this.executor = taskExecutor;
    }

    public void schedule(final Runnable task, String cronLike) {
        executor.schedule(task, new CronTrigger(cronLike));
    }

    public void schedule(final Runnable task, LocalDateTime runOnceAt) {
        executor.schedule(task, Date.from(runAt.atZone(ZoneId.systemDefault()).toInstant()));
    }

    public void schedulingExamples(final Runnable task) {
        // Schedule a task to run once at the given date (here in 1minute)
        executor.schedule(task, Date.from(LocalDateTime.now().plusMinutes(1)
                .atZone(ZoneId.systemDefault()).toInstant()));

        // Schedule a task that will run as soon as possible and every 1000ms
        executor.scheduleAtFixedRate(task, 1000);

        // Schedule a task that will first run at the given date and every 1000ms
        executor.scheduleAtFixedRate(task, Date.from(LocalDateTime.now().plusMinutes(1)
                .atZone(ZoneId.systemDefault()).toInstant()), 1000);

        // Schedule a task that will run as soon as possible and every 1000ms after the previous completion
        executor.scheduleWithFixedDelay(task, 1000);

        // Schedule a task that will run as soon as possible and every 1000ms after the previous completion
        executor.scheduleWithFixedDelay(task, Date.from(LocalDateTime.now().plusMinutes(1)
                .atZone(ZoneId.systemDefault()).toInstant()), 1000);

        // Schedule a task with the given cron expression
        executor.schedule(task, new CronTrigger("*/5 * * * * MON-FRI"));
    }
}

Your actual service, which reads from Db.

@Service
public class DbService {

    private final DbScheduledJobs dbScheduledJobs;

    @Autowired
    public DbService(DbScheduledJobs dbScheduledJobs) {
        this.dbScheduledJobs = dbScheduledJobs;
    }

    public void example() {
        // Read your cron like schedule from db
        String cronLikeScedule = "fetched from db"; // Ex. "*/5 * * * * MON-FRI"

        // Choose your Runnable instance - either statically or using Reflection.
        Runnable myRunnable = new MyTask();

        // Add this task to run on a schedule basis dynamically.
        this.dbScheduledJobs.schedule(myRunnable, cronLikeScedule);
    }
}

Hope that it helps, this solution is not tested.