Java / Gradle

Micronaut AWS Lambda and a Cron Job

Learn how to use a scheduled expression with an EventBridge trigger to execute a Micronaut AWS Lambda every 5 minutes

Sergio del Amo
On this guide
In this section

Getting Started

In this guide, we will create a Micronaut application written in Java.

What you will need

To complete this guide, you will need the following:

Solution

We recommend that you follow the instructions in the next sections and create the application step by step. However, you can go right to the completed example.

Writing the App

Create an application using the Micronaut Command Line Interface or with Micronaut Launch.

mn create-function-app example.micronaut.micronautguide \
    --features=aws-lambda-scheduled-event \
    --build=gradle \
    --lang=java
Note
 If you don’t specify the --build argument, Gradle with the Kotlin DSL is used as the build tool.
If you don’t specify the --lang argument, Java is used as the language.
If you don’t specify the --test argument, JUnit is used for Java and Kotlin, and Spock is used for Groovy.

If you use Micronaut Launch, select serverless function as the application type and add the aws-lambda-scheduled-event feature.

The previous command creates a Micronaut application with the default package example.micronaut in a directory named micronautguide.

Setup IntelliJ IDEA to develop Micronaut Applications.

Handler

Micronaut Launch/Micronaut CLI generates the following handler when you select the feature aws-lambda-scheduled-event. The handler receives an EventBridge (CloudWatch Events) notification event. Add a log statement.

java/src/main/java/example/micronaut/FunctionRequestHandler.java
package example.micronaut;
import io.micronaut.function.aws.MicronautRequestHandler;
import com.amazonaws.services.lambda.runtime.events.ScheduledEvent;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class FunctionRequestHandler extends MicronautRequestHandler<ScheduledEvent, Void> {
    private static final Logger LOG = LoggerFactory.getLogger(FunctionRequestHandler.class);
    @Override
    public Void execute(ScheduledEvent input) {
        LOG.info("input: {}", input);
        return null;
    }
}

Logback

Replace src/main/resources/logback.xml with the following content to get a more verbose output:

src/main/resources/logback.xml
<configuration>
    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <pattern>%d{yyyy-MM-dd HH:mm:ss} %X{AWSRequestId} %X{AWSFunctionName} %X{AWSFunctionVersion} %X{AWSFunctionArn} %X{AWSFunctionMemoryLimit}  %X{AWSFunctionRemainingTime} %X{AWS-XRAY-TRACE-ID} %-5p %c{1} - %m%n</pattern>
        </encoder>
    </appender>
    <root level="info">
        <appender-ref ref="STDOUT" />
    </root>
</configuration>

Lambda

Create a Lambda Function. As a runtime, select Java 17, Java 21, or Java 25.

create function

Triggers

Create a trigger that fires every 5 minutes:

eventbridgetrigger

Upload Code

Create an executable jar including all dependencies:

./gradlew shadowJar

Upload it:

upload function code

Handler

In the AWS console, as Handler, set:

example.micronaut.FunctionHandler

Test

After you upload the code, wait for 5 minutes and you should see CloudWatch log output such as:

TRACE c.s.e.f.d.Handler - {version=0, id=ed9bd6b2-0429-9b03-742b-fe294946f272, detail-type=Scheduled Event, source=aws.events, account=1234567899, time=2021-05-19T09:03:02Z, region=us-east-1, resources=[arn:aws:events:us-east-1:1234567899:rule/5minutes], detail={}}
2021-05-19 09:03:31 b4e05b4e-ae9f-4844-b7fb-5e70016b41fd eurorates-daily-java11 $LATEST arn:aws:lambda:us-east-1:1234567899:function:micronautguide-java11 512 14990 1-60a4d463-1fa098426b0ff44e24a69bf8 TRACE c.s.e.f.d.Handler - {version=0, id=ed9bd6b2-0429-9b03-742b-fe294946f272, detail-type=Scheduled Event, source=aws.events, account=1234567899, time=2021-05-19T09:03:02Z, region=us-east-1, resources=[arn:aws:events:us-east-1:1234567899:rule/5minutes], detail={}}

Read more about:

Help with the Micronaut Framework

The Micronaut Foundation sponsored the creation of this Guide. A variety of consulting and support services are available.

License

Note
 All guides are released with an Apache License 2.0 for the code and a Creative Commons Attribution 4.0 license for the writing and media (images).