Overview

Maven Coordinates

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>

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Scheduling

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

Fixed rate

For simple fixed rate invocation use .

Example of scheduling with fixed rate use Scheduling.fixedRateBuilder() builder.

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

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Metadata like human-readable interval description or configured values are available through FixedRateInvocation provided as task parameter.

Example with ivocation metadata

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

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Cron expression

For more complicated interval definition, cron expression can be leveraged with Scheduling.cronBuilder() builder.

Example of scheduling with cron expression

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

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Cron expression format

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

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Cron expression fields

Order	Name	Supported values	Supported field format	Optional
1	seconds	0-59	CONST, LIST, RANGE, WILDCARD, INCREMENT	false
2	minutes	0-59	CONST, LIST, RANGE, WILDCARD, INCREMENT	false
3	hours	0-23	CONST, LIST, RANGE, WILDCARD, INCREMENT	false
4	day-of-month	1-31	CONST, LIST, RANGE, WILDCARD, INCREMENT, ANY, LAST, WEEKDAY	false
5	month	1-12 or JAN-DEC	CONST, LIST, RANGE, WILDCARD, INCREMENT	false
6	day-of-week	1-7 or SUN-SAT	CONST, LIST, RANGE, WILDCARD, INCREMENT, ANY, NTH, LAST	false
7	year	1970-2099	CONST, LIST, RANGE, WILDCARD, INCREMENT	true

Field formats

Name	Regex format	Example	Description
CONST	\d+	12	exact value
LIST	\d+,\d+(,\d+)*	1,2,3,4	list of constants
RANGE	\d+-\d+	15-30	range of values from-to
WILDCARD	\*	*	all values withing the field
INCREMENT	\d+\/\d+	0/5	inital number / increments, 2/5 means 2,7,9,11,16,…
ANY	\?	?	any day(apply only to day-of-week and day-of-month)
NTH	\#	1#3	nth day of the month, 2#3 means third monday of the month
LAST	\d*L(+\d+\|\-\d+)?	3L-3	last day of the month in day-of-month or last nth day in the day-of-week
WEEKDAY	\#	1#3	nearest weekday of the nth day of month, 1W is the first monday of the week

Examples

Cron expression	Description
* * * * * ?	Every second
0/2 * * * * ? *	Every 2 seconds
0 45 9 ? * *	Every day at 9:45
0 15 8 ? * MON-FRI	Every workday at 8:15

Metadata like human-readable interval description or configured values are available through CronInvocation provided as task parameter.

Example with ivocation metadata

Scheduling.cronBuilder()
    .expression("0 15 8 ? * *")
    .task(inv -> System.out.println("Method invoked " + inv.description()))
    .build();

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