Spring boot with dynamically change cron expression in #Scheduler - spring-boot

Question

I'M trying to run my app by implementing scheduler with cron expression. To run my application I have three conditions:-
First condition is :
I have some time slots like
LocalTime [] slots = {LocalTime.of(0, 0), LocalTime.of(7, 0), LocalTime.of(13, 0), LocalTime.of(19, 0)}
Now the condition is when JVM start it will first check the time duration from current time and the given time slot. Below is the method to check the duration:-
public static Duration findNextSlotDuration(LocalTime now, LocalTime [] slots) {
Duration duration = null;
if(slots != null)
{
if(slots.length == 1)
{
duration = Duration.between(now, slots[0]);
}else if(slots.length > 1)
{
for (int i = 0; i < slots.length-1; i++) {
if(isBetween(now, slots[i], slots[i+1]))
{
duration = Duration.between(now, slots[i+1]);
break;
}
}
}
if(duration != null && !duration.isNegative())
return duration;
else
{
Duration d1 = Duration.between(now, LocalTime.of(23, 59)).plusMinutes(1);
Duration d2 = Duration.between(LocalTime.of(0, 0), slots[0]);
return d1.plus(d2);
}
}
return Duration.ofMinutes(5);
}
private static boolean isBetween(LocalTime candidate, LocalTime start, LocalTime end) {
return !candidate.isBefore(start) && !candidate.isAfter(end); // Inclusive.
}
For example if JVM start at 17PM today then it will first check the time slot and it will get slot between 13 to 19 PM and duration will be 2 hours as per method findNextSlotDuration , so the scheduler will start after 2 hour means at 19 PM. Another scenario, if JVM start today at 19 Hr 00 Min 29 Sec then it will not get the slot so, the duration will be 6 Hr 00 Min 29 Sec then the scheduler start at 00:00:29 O'Clock.
Now the second condition is:
If the JVM is still running after completing my task then it will again run my task after every 6 hours.
The Last condition is:
It will run only from Monday to Saturday
So any idea how I can implement #Scheduler with Cron or any better approach in Spring boot.

Answer 1

Firstly, I will try to give some suggestions to you if I understand correctly. I hope it will be helpful for you
You can catch application ready event as below and also you can implement whenever you want to perform. Also you can trigger your method by using this approach.
#Component
public class AppReadyComponent implements ApplicationListener<ApplicationReadyEvent> {
#Override
public void onApplicationEvent(ApplicationReadyEvent event) {
// some logic
}
}
Lastly, you can dynamically calculate cron values and use it to trigger your scheduled method as below.
#SpringBootApplication
public class MainApp {
#Bean
public String getCronValue() {
// here you may calculate cron value dynamically and return it as a string
return cronValue;
}
}
Here is your scheduled method
#Scheduled(cron = "#{#getCronValue}")
public void process() {
// some logic
}