◀Table of Contents

Build a Micronaut Application into a Native Executable

This guide shows how to create a simple Micronaut application, and compile it into a native executable with GraalVM Native Image.

Create a sample Micronaut REST application. Go to Micronaut Launch. Select Micronaut Application as application type. Click FEATURES, search and add graalvm packaging feature. You can keep rest values as default and click Generate Project. Then Download ZIP.

Unzip the downloaded package and enter application directory:

 unzip demo.zip && cd demo

Assume you selected Maven as the build tool, Micronaut Launch would create a folder with a complete Micronaut application skeleton:

 ├── README.md
 ├── micronaut-cli.yml
 ├── mvnw
 ├── mvnw.bat
 ├── pom.xml
 └── src
     ├── main
     │   ├── java
     │   │   └── com
     │   │       └── example
     │   │           └── Application.java
     │   └── resources
     │       ├── application.yml
     │       └── logback.xml
     └── test
         └── java
             └── com
                 └── example
                     └── DemoTest.java

Now you will modify this template application and add a rest endpoint that will return a simple message.

Under src/main/java/com/example create a POJO in a file named Conference.java with the following content:
```
 package com.example;

 import io.micronaut.core.annotation.Introspected;

 @Introspected 
 public class Conference {

     private final String name;

     public Conference(String name) {
         this.name = name;
     }

     public String getName() {
         return name;
     }
 }
```
Notice the @Introspected annotation before the class name to generate BeanIntrospection metadata at compilation time. This information can be used, for example, to the render the POJO as JSON using Jackson without using reflection.

Next create a ConferenceService.java service in the same location:

 package com.example;

 import jakarta.inject.Singleton;
 import java.util.Arrays;
 import java.util.List;
 import java.util.Random;

 @Singleton 
 public class ConferenceService {

     private static final List<Conference> CONFERENCES = Arrays.asList(
             new Conference("Greach"),
             new Conference("GR8Conf EU"),
             new Conference("Micronaut Summit"),
             new Conference("Devoxx Belgium"),
             new Conference("Oracle Code One"),
             new Conference("CommitConf"),
             new Conference("Codemotion Madrid")
     );

     public Conference randomConf() { 
         return CONFERENCES.get(new Random().nextInt(CONFERENCES.size()));
     }
 }

The service returns a random conference name. Notice jakarta.inject.Singleton to designate a class as a singleton.

Finally, create a Micronaut controller as a REST endpoint that returns a Conference in a file named ConferenceController.java. The Micronaut framework will convert it automatically to JSON in the response:

 package com.example;

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

 @Controller("/conferences") 
 public class ConferenceController {

     private final ConferenceService conferenceService;

     public ConferenceController(ConferenceService conferenceService) { 
         this.conferenceService = conferenceService;
     }

     @Get("/random") 
     public Conference randomConf() { 
         return conferenceService.randomConf();
     }
 }

The class is defined as a controller with the @Controller annotation mapped to the path /conferences. The @Get annotation maps the index method to an HTTP GET request on /random.

Now since the application is ready, generate a native executable using GraalVM Native Image:
- If the application was built with Maven, specify the native-image packaging format:
```
  ./mvnw package -Dpackaging=native-image
```
- If you used using Gradle, execute the nativeImage task:
```
  ./gradlew nativeCompile
```
After some time a native executable called demo will be built into the /target directory. If you use Gradle, the executable called demo will be written to the /build/native/nativeCompile/ folder.

Execute the application by running the executable: Maven:

 ./target/demo

Gradle:

 ./build/native/nativeCompile/demo

Send a request to test it:

 time curl localhost:8080/conferences/random

Run this application regularly, from a JAR on a JVM, to compare execution time:
```
 ./mvnw mn:run
```
Notice the startup time. Deploying a Micronaut application as a native executable helps to achieve instantaneous startup, lower CPU and memory consumption, making the application cloud native and ready for cloud or on-premises deployments.

As a nice extra, you can also create a native executable inside Docker. You do not need to install any additional dependencies.

./mvnw package -Dpackaging=docker-native

The output is a platform-dependent Docker image containing a native executable of your Micronaut applocation.

Build a Micronaut Application into a Native Executable

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