• Overview

• Maven Coordinates

• Usage

• Configuration

• Cron

• Fixed Rate

• Task Management

• Examples

• Reference

Scheduling is an essential feature for the Enterprise. Helidon has its own implementation of Scheduling functionality based on Cron-utils.

To enable Scheduling, add the following dependency to your project’s pom.xml (see Managing Dependencies).

<dependency>
    <groupId>io.helidon.scheduling</groupId>
    <artifactId>helidon-scheduling</artifactId>
</dependency>

For scheduling periodic tasks, it is possible to choose a fixed rate or a Cron expression.

Fixed rate

FixedRate.builder()
        .delay(10)
        .initialDelay(5)
        .timeUnit(TimeUnit.MINUTES)
        .task(inv -> System.out.println("Every 10 minutes, first invocation 5 minutes after start"))
        .build();

FixedRate.builder()
        .delay(10)
        .task(inv -> System.out.println("Method invoked " + inv.description()))
        .build();

Cron

Cron.builder()
        .expression("0 15 8 ? * *")
        .task(inv -> System.out.println("Executer every day at 8:15"))
        .build();

Cron.builder()
        .expression("0 0 9 * * ?")
        .zone(ZoneId.of("America/New_York"))
        .task(inv -> System.out.println("Executes every day at 9:00 AM Eastern Time"))
        .build();

Cron expression syntax

Cron expression

<seconds> <minutes> <hours> <day-of-month> <month> <day-of-week> <year>

Scheduling is configurable with Helidon Config.

FixedRate.builder()
        .config(Config.create(() -> ConfigSources.create(
                """
                        delay: 4
                        delay-type: SINCE_PREVIOUS_END
                        initial-delay: 1
                        time-unit: SECONDS
                        """,
                MediaTypes.APPLICATION_X_YAML)))
        .task(inv -> System.out.println("Every 4 minutes, first invocation 1 minutes after start"))
        .build();

A io.helidon.scheduling.TaskManager can be used to manage tasks that are started within Helidon. When using imperative programming model, you can either provide a custom implementation of this interface to task builder (method taskManager), or you can use the "default" one that can be obtained by invoking io.helidon.service.registry.Services.get(TaskManager.class). When using the default TaskManager from io.helidon.service.registry.Services, there is no need to explicitly register it with the task builders.

When using declarative programming model, the TaskManager can be injected. It is a Singleton service that will be used by all scheduled tasks in the current application.

Fixed Rate Example

FixedRate.builder()
        .delay(10)
        .initialDelay(5)
        .timeUnit(TimeUnit.MINUTES)
        .task(inv -> System.out.println("Every 10 minutes, first invocation 5 minutes after start"))
        .build();

FixedRate.builder()
        .delay(10)
        .task(inv -> System.out.println("Method invoked " + inv.description()))
        .build();

• Cron-utils GitHub page

• Helidon Scheduling JavaDoc