Micronaut & Kotlin Demo with a REST API

Demo Micronaut application written in Kotlin exposing a REST API to enable performing of CRUD operations on an entity. The application stores entities in memory.

Figure 1: Micronaut application with REST API

Demonstrates using both a standard JVM-based application and a native image using GraalVM. GraalVM compiles the Kotlin application ahead of time into a platform-specific native binary executable. This native executable does not require a Java runtime environment to execute. Instead, it can be executed directly on the target platform. This can lead to faster startup times and reduced memory footprint compared to running on the JVM.

The companion project, with the application written in Java instead of Kotlin, is available here: https://github.com/lydtechconsulting/micronaut-rest-java

Running The Demo

The project requires Java 21 to build.

Build and test the Micronaut application, and then run, with:

./gradlew clean test
./gradlew run

Alternatively, following tests, build a native executable with GraalVM (version 21) - install instructions - and then run the executable:

./gradlew clean test
./gradlew nativeCompile
./gradlew nativeRun

The standard test task is used as the unit tests are using mocks via the mockk test lib, and these are not supported via the nativeTestCompile task. Mocks typically rely on runtime features such as reflection which are not fully supported with Kotlin/Native.

In a terminal window use curl request to create (which returns a location header), retrieve, update and delete an item:

curl -i -X POST localhost:9001/v1/items -H "Content-Type: application/json" -d '{"name": "test-item"}'
curl -i -X GET localhost:9001/v1/items/653d06f08faa89580090466e
curl -i -X PUT localhost:9001/v1/items/653d06f08faa89580090466e -H "Content-Type: application/json" -d '{"name": "test-item-update"}'
curl -i -X DELETE localhost:9001/v1/items/653d06f08faa89580090466e

Component Tests

The component tests bring up the application in a docker container and hit this via the REST API to create, retrieve, update, and delete an item.

For more on the component tests see: https://github.com/lydtechconsulting/component-test-framework

First ensure the Project module paths are set to Inherit project compile output path to ensure the fat jar is built in ./build/libs. Then build the Micronaut application jar, followed by the Docker container:

./gradlew clean build
docker build -t ct/micronaut-rest-kotlin:latest .

Alternatively, build a native executable with GraalVM, followed by the Docker container:

./gradlew clean nativeCompile
./gradlew dockerBuildNative

Run component tests:

./gradlew componentTest --rerun-tasks

Run tests leaving containers up:

./gradlew componentTest --rerun-tasks -Dcontainers.stayup=true

Note that --rerun-tasks is required for subsequent runs when no change has happened between test runs.

Docker Clean Up

Manual clean up (if left containers up):

docker rm -f $(docker ps -aq)