Contents

Overview

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

Maven Coordinates

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

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

Usage

For scheduling tasks in Helidon you can choose from @Scheduling.Cron or @Scheduling.FixedRate annotations by required complexity of invocation interval. All you need is to define a method with one of the annotations in an application scoped bean.

Fixed rate

For simple fixed rate invocation interval, the @Scheduling.FixedRate is the easiest way to schedule task invocation.

@Scheduling.FixedRate(delayBy = "PT5M", value = "PT10M")

All values defined with the annotation can be overridden from config.

Overriding annotated values from config
fully.qualified.ClassName.methodName:
  schedule:
    initial-delay: 5
    delay: 15
    time-unit: HOURS

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

@Scheduling.FixedRate(delayBy = "PT5M", value = "PT10M")

Cron expression

For more complicated interval definition, cron expression can be leveraged with @Scheduling.Cron annotation.

@Scheduling.Cron(value = "0 15 8 ? * *", concurrent = false)
public void methodName() { /* ... */ }

Cron expression

Cron expression format
<seconds> <minutes> <hours> <day-of-month> <month> <day-of-week> <year>
Table 1. 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
Table 2. 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

initial 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
Table 3. 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 injected as method parameter.

@Scheduling.Cron("0 15 8 ? * *")
public void methodName(CronInvocation inv) {
    { /* ... */ }
}

Configuration

Scheduled annotation properties can be overridden using application.yaml properties

Overriding annotated values from config
fully.qualified.ClassName.methodName:
  schedule:
    cron: "* * * * * ?"
    concurrent: false
Table 4. Configuration properties
Property Description

cron

String containing cron setup

concurrent

Boolean, equivalent concurrent property of @Scheduling.Cron. Defaults to true.

Examples

Fixed rate

Example of scheduling with fixed rate
@Scheduling.FixedRate(delayBy = "PT5M", value = "PT10M")
public void methodName() {
    System.out.println("Every 10 minutes, first invocation 5 minutes after start");
}

FixedRate Metadata Injection

Example with invocation metadata
@Scheduling.FixedRate(delayBy = "PT5M", value = "PT10M")
public void methodName(FixedRateInvocation inv) {
    System.out.println("Method invoked " + inv.description());
}

Cron expression

Example of scheduling with cron expression
@Scheduling.Cron(value = "0 15 8 ? * *", concurrent = false)
public void methodName() {
    System.out.println("Executer every day at 8:15");
}

Scheduled Metadata Injection.

Example with invocation metadata
@Scheduling.Cron("0 15 8 ? * *")
public void methodName(CronInvocation inv) {
    System.out.println("Method invoked " + inv.description());
}

Reference