Micronaut provides powerful support for task scheduling using the @Scheduled annotation. Whether it’s sending emails, clearing temporary files, or syncing data, scheduled tasks can be a game-changer for automating backend operations.
This guide explains how to create scheduled tasks in Micronaut using Maven, with clean examples and explanations that even beginners can follow.
π¦ Project Setup
Use the Micronaut Launch tool or manually configure your project.
pom.xml (important dependencies)
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<dependency> <groupId>io.micronaut</groupId> <artifactId>micronaut-runtime</artifactId> </dependency> <dependency> <groupId>io.micronaut</groupId> <artifactId>micronaut-inject</artifactId> </dependency> <dependency> <groupId>io.micronaut</groupId> <artifactId>micronaut-scheduling</artifactId> </dependency> |
Make sure to have a JDK version 17 or later and enable annotation processing in your IDE (e.g., IntelliJ, Eclipse).
π§ What is @Scheduled?
The @Scheduled annotation allows you to declare tasks that run automatically based on a fixed delay, fixed rate, or a cron expression.
You can annotate methods in singleton beans, and Micronaut will invoke them according to the schedule.
π§ Configuration
Make sure the scheduling feature is enabled. In most setups, this is enabled by default.
You can explicitly enable it in application.yml:
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micronaut: application: name: scheduler-demo |
No special scheduler config is needed unless you are tweaking advanced thread pool settings.
β Example 1: Fixed Delay Execution
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package com.kscodes.micronaut.advanced; import io.micronaut.scheduling.annotation.Scheduled; import jakarta.inject.Singleton; @Singleton public class FixedDelayTask { @Scheduled(fixedDelay = "10s") // runs every 10 seconds public void runTask() { System.out.println("Fixed delay task executed at: " + System.currentTimeMillis()); } } |
This method runs 10 seconds after the previous execution ends.
β Example 2: Fixed Rate Execution
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package com.kscodes.micronaut.advanced; import io.micronaut.scheduling.annotation.Scheduled; import jakarta.inject.Singleton; @Singleton public class FixedRateTask { @Scheduled(fixedRate = "5s") // runs exactly every 5 seconds public void heartbeat() { System.out.println("Fixed rate heartbeat at: " + System.currentTimeMillis()); } } |
This task runs every 5 seconds, regardless of the duration of the previous task execution.
β Example 3: Cron Expression
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package com.kscodes.micronaut.advanced; import io.micronaut.scheduling.annotation.Scheduled; import jakarta.inject.Singleton; @Singleton public class CronBasedTask { @Scheduled(cron = "0 0/1 * * *") // every minute at 0 seconds public void cleanupJob() { System.out.println("Cleanup job executed!"); } } |
You can use standard UNIX cron expressions for precise scheduling control.
π Error Handling in Scheduled Tasks
If an exception occurs inside a scheduled task, it will be logged by Micronaut, but wonβt stop future executions.
You can add try-catch blocks to ensure graceful recovery:
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@Scheduled(fixedDelay = "15s") public void safeJob() { try { // risky operation } catch (Exception e) { System.err.println("Error occurred: " + e.getMessage()); } } |
π Testing the Scheduler
Run your application using:
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./mvnw mn:run |
Watch the logs in the console. Youβll see timestamps every time a scheduled method executes.
π§° Tips for Real-World Usage
- Keep long-running tasks async or in separate threads to avoid blocking.
- Use cron expressions for complex schedules (e.g., every Monday at 9 AM).
- Schedule tasks based on environment profiles (e.g., only in production).
- Use
@Scheduled(initialDelay = "5s", fixedRate = "30s")for a delayed start.
π Monitoring Scheduled Tasks
Micronaut doesn’t provide out-of-the-box visibility into scheduled task metrics, but you can use Micrometer to monitor method invocation counts, timings, etc.
π Conclusion
Scheduling background tasks is essential for most backend services. Micronaut makes this incredibly easy and expressive using just the @Scheduled annotation. From cron expressions to fixed-rate execution, you can automate tasks efficiently without external schedulers.
Start small with simple tasks, and grow into advanced scheduling scenarios using Micronaut’s powerful features.