Spring scheduler - getting time of next event - spring-boot

Question

I've got a SpringBoot Scheduler that looks like this:
#Scheduled(cron = "*/10 * * * * * ") // Every 10 seconds
public void scheduleTaskUsingCronExpression() {
long now = System.currentTimeMillis() / 1000;
System.out.println("schedule tasks using cron jobs - " + now);
}
I'd like to get the time of the next event, so I can print it out at the end of each event. I've read about using CronExpression, which has a next() method, but not sure how I get the CronExpression. OR do I create a CronExpression and somehow pass it in instead of using the #Scheduled annotation?

Answer 1

I'm not sure I can get accurate interval time but I can get roughly correct next running time from following code.
#Value("${cron.schedule}") String schedule;
#Scheduled(cron = "${cron.schedule}") // Every 10 seconds
public void scheduleTaskUsingCronExpression() {
var expression = CronExpression.parse(schedule);
var result = expression.next(LocalDateTime.now());
System.out.println("schedule tasks using cron jobs - " + result);
}

Answer 2

You can define your cron string (that you use in the #Scheduled annotation) as a final field of your class, and then create CronExpression from it to find out the next trigger date.
Also, instead of using #Scheduled annotation, you can take a look at Spring's TaskScheduler (from the package org.springframework.scheduling). It has the method TaskScheduler#schedule with two arguments: a Runnable that will run in background and a CronTrigger to set the cron expression and and the timezone of executing background tasks.
UPD. One other way to reuse your cron is set it in your application.properties and use within #Value and #Scheduled annotations, e.g. #Scheduled(cron = ${property.from.file}). In this case you can also change the cron expression before running your application if needed.