mn create-app example.micronaut.micronautguide \
--features=graalvm \
--build=maven \
--lang=kotlin \
--test=junit
Creating your first Micronaut Graal application
Learn how to create a Hello World Micronaut GraalVM application.
Authors: Iván López, Sergio del Amo
Micronaut Version: 4.6.3
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 (e.g. IntelliJ IDEA)
-
JDK 17 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.
-
Download and unzip the source
4. Writing the Application
Create an application using the Micronaut Command Line Interface or with Micronaut Launch.
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.
|
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
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. 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("Greach"),
Conference("GR8Conf EU"),
Conference("Micronaut Summit"),
Conference("Devoxx Belgium"),
Conference("Oracle Code One"),
Conference("CommitConf"),
Conference("Codemotion Madrid")
)
}
}
1 | Use jakarta.inject.Singleton to designate a class as a singleton. |
2 | Return a random conference. |
4.2. 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. GraalVM installation
sdk install java 21.0.5-graal
sdk use java 21.0.5-graal
For installation on Windows, or for manual installation on Linux or Mac, see the GraalVM Getting Started documentation.
The previous command installs Oracle GraalVM, which is free to use in production and free to redistribute, at no cost, under the GraalVM Free Terms and Conditions.
Alternatively, you can use the GraalVM Community Edition:
sdk install java 21.0.2-graalce
sdk use java 21.0.2-graalce
5.2. Native executable generation
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
.
5.3. 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.
./mvnw package -Dpackaging=docker-native
5.4. Running the native executable
Execute the application by either running the executable or starting the Docker container.
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.
5.5. 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
{"name":"Greach"}
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.
8. License
All guides are released with an Apache license 2.0 license for the code and a Creative Commons Attribution 4.0 license for the writing and media (images…). |