Creating your first Micronaut Graal application

Learn how to create a Hello World Micronaut GraalVM application.

Authors: Iván López, Sergio del Amo

Micronaut Version: 3.7.3

1. Getting Started

In this guide, we will create a Micronaut application written in Kotlin with GraalVM support.

2. What you will need

To complete this guide, you will need the following:

  • Some time on your hands

  • A decent text editor or IDE

  • JDK 1.8 or greater installed with JAVA_HOME configured appropriately

3. 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.

4. Writing the Application

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

mn create-app example.micronaut.micronautguide \
    --features=graalvm,serialization-jackson \
    --build=maven --lang=kotlin
If you don’t specify the --build argument, Gradle is used as the build tool.
If you don’t specify the --lang argument, Java is used as the language.

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

If you use Micronaut Launch, select Micronaut Application as application type and add graalvm, and serialization-jackson features.

If you have an existing Micronaut application and want to add the functionality described here, you can view the dependency and configuration changes from the specified features and apply those changes to your application.

4.1. Enable annotation Processing

If you use Java or Kotlin and IntelliJ IDEA, make sure to enable annotation processing.


4.2. Service

Create a POJO Conference:

package example.micronaut

import io.micronaut.serde.annotation.Serdeable;

@Serdeable (1)
data class Conference(val name: String)
1 Declare the @Serdeable annotation at the type level in your source code to allow the type to be serialized or deserialized.

Create a Service:

package example.micronaut

import java.util.Random
import jakarta.inject.Singleton

@Singleton (1)
class ConferenceService {

    fun randomConf(): Conference = CONFERENCES[Random().nextInt(CONFERENCES.size)] (2)

    companion object {
        private val CONFERENCES = listOf(
                Conference("GR8Conf EU"),
                Conference("Micronaut Summit"),
                Conference("Devoxx Belgium"),
                Conference("Oracle Code One"),
                Conference("Codemotion Madrid")
1 Use jakarta.inject.Singleton to designate a class as a singleton.
2 Return a random conference.

4.3. Controller

Create a Controller with a method that returns a Conference. The Micronaut framework will convert it automatically to JSON in the response:

package example.micronaut

import io.micronaut.http.annotation.Controller
import io.micronaut.http.annotation.Get

@Controller("/conferences") (1)
class ConferenceController(private val conferenceService: ConferenceService) { (2)

    @Get("/random") (3)
    fun randomConf(): Conference = conferenceService.randomConf() (4)
1 The class is defined as a controller with the @Controller annotation mapped to the path /conferences.
2 Constructor injection
3 The @Get annotation maps the index method to an HTTP GET request on /random.
4 Return a Conference.

5. Generate a Micronaut Application Native Executable with GraalVM

We will use GraalVM, the polyglot embeddable virtual machine, to generate a native executable of our Micronaut application.

Compiling native executables ahead of time with GraalVM improves startup time and reduces the memory footprint of JVM-based applications.

Only Java and Kotlin projects support using GraalVM’s native-image tool. Groovy relies heavily on reflection, which is only partially supported by GraalVM.

5.1. Native executable generation

The easiest way to install GraalVM on Linux or Mac is to use

Java 11
sdk install java 22.1.0.r11-grl
If you still use Java 8, use the JDK11 version of GraalVM.
Java 17
sdk install java 22.1.0.r17-grl

For installation on Windows, or for manual installation on Linux or Mac, see the GraalVM Getting Started documentation.

After installing GraalVM, install the native-image component, which is not installed by default:

gu install native-image

To generate a native executable using Maven, run:

./mvnw package -Dpackaging=native-image

The native executable is created in the target directory and can be run with target/micronautguide.

5.2. Creating native executable inside Docker

The output following this approach is a Docker image that runs the native executable of your application. You don’t need to install any additional dependencies.

Building GraalVM native executable with Maven
./mvnw package -Dpackaging=docker-native

5.3. Running the native executable

Execute the application by either running the executable or starting the Docker container.

Executing the native executable
10:29:46.845 [main] INFO  io.micronaut.runtime.Micronaut - Startup completed in 12ms. Server Running: http://localhost:8080

We can see that the application starts in only 12ms.

5.4. Sending a request

Start the application either using Docker or the native executable. You can run a few cURL requests to test the application:

time curl localhost:8080/conferences/random
real    0m0.016s
user    0m0.005s
sys     0m0.004s
time curl localhost:8080/conferences/random
{"name":"GR8Conf EU"}
real    0m0.014s
user    0m0.005s
sys     0m0.004s

6. Next steps

Read more about GraalVM Support inside the Micronaut framework.

Take a look at the Micronaut Gradle plugin and Micronaut Maven Plugin documentation.

7. Help with the Micronaut Framework

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