Micronaut app using Micronaut Data and GraalVM (written in Kotlin)

Sample of a simple Micronaut CRUD application using Micronaut Data and supporting Oracle's GraalVM/SubstrateVM.

• Scenario
• Setup
• Building and executing the application
  • Running on the JVM
  • Using the native image
• Further hints
  • Install GraalVM
  • Setup PostgreSQL with Docker
  • Fixing possible errors

Scenario

The example contains a Footballmanager microservice which accesses a PostgreSQL and provides the data via REST/JSON.

To create a new Footballer a POST request needs to be submitted to the REST endpoint http://localhost:8080/footballers:

{
  "firstName": "Toni",
  "lastName": "Kroos",
  "position": "Midfield"
}

All existing Footballers can be retrieved be sending a GET request to http://localhost:8080/footballers.

With the optional request parameter position all Footballers of a certain position are determined (e.g. http://localhost:8080/footballers?position=Midfield).

Setup

The PostgreSQL should be running on jdbc:postgresql://localhost:5432/footballerdb. See below how to setup a dockerized PostgreSQL.

Building and executing the application

Running on the JVM

Building the Fat-/Uber-Jar with Gradle:

./gradlew clean shadowJar

Executing the JAR via:

java -jar build/libs/footballermanager-0.1-all.jar

(Or you just start the Application.kt in your IDE).

Using the native image

How to build a native image of the application with GraalVM/SubstrateVM (installation see below).

Using GraalVM’s native-image tool:

sdk use java 21.2.0.r11-grl

./gradlew clean assemble

native-image --no-server -cp build/libs/footballermanager-0.1-all.jar

Executing the native image via:

./footballermanager 

Using Micronaut's Gradle Plugin:

Since Micronaut 2.1.0 you can delegate the native image generation to Micronaut's Gradle Plugin:

sdk use java 21.2.0.r11-grl

./gradlew nativeImage  

Executing the native image via:

./build/native-image/application 

Further hints

Install GraalVM

To manage SDK versions on your local machine SDKMAN! is a very helpful tool. Oracle's GraalVM can be installed with sdk install java 21.2.0.r11-grl (or appropriate version).

If you don't want to use Micronaut's Gradle Plugin you have to install GraalVM’s native-image tool with the command gu install native-image.

Setup PostgreSQL with Docker

Execute the following steps:

docker pull postgres  

docker run -p 5432:5432 --name postgres-db -e POSTGRES_PASSWORD=mysecretpassword -d postgres

docker exec -it postgres-db bash
psql -U postgres
CREATE DATABASE footballerdb;

Fixing possible errors

Problem: The first request after starting the app results in an error like this:

{
   "message": "Internal Server Error: SQL Error executing Query: ERROR: relation \"footballer\" does not exist\n  Position: 102"
}

Solution: Please make sure these properties are set in the application.yaml so that the table footballer is created:

datasources:
  default:
    schema-generate: CREATE  # or CREATE_DROP if you want the table to be re-created with each app start
    dialect: postgres