Spring Boot - Scheduling Tasks

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Scheduling tasks in spring boot

Enable Scheduling

To enable Scheduling annotation, add @EnableScheduling to one of your @Configuration class.

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@Configuration
@EnableScheduling
public class AppConfig {
}

@Scheduled Annotation

Fix rate

we can execute a task on a fixed period. add @Scheduled annotation and set fixedRate attribute.

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@Scheduled(fixedRate = 2000L)
public void someJob() throws InterruptedException {
	System.out.println("Current Time is " + LocalDateTime.now().format(DateTimeFormatter.ofPattern("HH:mm:ss")));
}

Delay

fixedDelay - Execute the annotated method with a fixed period between the end of the last invocation and the start of the next.

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@Scheduled(initialDelay = 1000L, fixedDelay = 2000L)
public void someJob() throws InterruptedException {
	System.out.println("Current Time is " + LocalDateTime.now().format(DateTimeFormatter.ofPattern("HH:mm:ss")));
}

Cron Expression

Cron expression used by @Scheduled is NOT the same as cron in Linux. There are 6 fields in a cron expression. Each has its own range of valid values.

For testing cron expressions check https://crontab.guru/. Note that second is not in standard Linux Cron.

Cron expression consiste of six fields:

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second, minute, hour, day of the month, month, day(s) of week

cron meaning and valid values

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┌───────────── second (0-59)
│ ┌───────────── minute (0 - 59)
│ │ ┌───────────── hour (0 - 23)
│ │ │ ┌───────────── day of the month (1 - 31)
│ │ │ │ ┌───────────── month (1 - 12) (or JAN-DEC)
│ │ │ │ │ ┌───────────── day of the week (0 - 7)
│ │ │ │ │ │          (0 or 7 is Sunday, or MON-SUN)
│ │ │ │ │ │
* * * * * *

Please see Cron Expression Documentation for more details and examples.

To run at 8:00, 8:30, 9:00 9:30 every day

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@Scheduled(cron = "* */30 8-9 * * *", zone = "America/New_York")
public void someJob() throws InterruptedException {
	System.out.println("Current Time is " + LocalDateTime.now().format(DateTimeFormatter.ofPattern("HH:mm:ss")));
}

To run at 11:00PM every day

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@Scheduled(cron = "0 0 23 * * *", zone = "America/New_York")
public void someJob() throws InterruptedException {
	System.out.println("Current Time is " + LocalDateTime.now().format(DateTimeFormatter.ofPattern("HH:mm:ss")));
}

To avoid hard coding the cron value, we can use Spring Expression to externalize the configuration of the task.

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@Scheduled(cron = "${myTask.cron}", zone = "America/New_York")
public void someJob() throws InterruptedException {
	System.out.println("Current Time is " + LocalDateTime.now().format(DateTimeFormatter.ofPattern("HH:mm:ss")));
}

application.properties file

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myTask.cron=*/10 * 0 * * *

Setting Scheduler’s pool size

The default size is 1

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spring.task.scheduling.pool.size=5

ShedLock

ShedLock makes sure that your scheduled tasks are executed at most once at the same time. If a task is being executed on one node, it acquires a lock which prevents execution of the same task from another node (or thread). Please note, that if one task is already being executed on one node, execution on other nodes does not wait, it is simply skipped.

Reference