Micronaut Kotlin Integrations

Includes extensions to Micronaut for Kotlin

Version: 1.0.0.M2

1 Introduction

This project provides various extensions and improvements to the Micronaut and Kotlin experience.

Release History


  • Support for auto config of Jackson Kotlin Module even if module scan is disabled

  • Improved separation of route and application building in Kotr support

  • Dependency Upgrades


  • Initial Milestone

2 Kotlin Runtime Support

The micronaut-kotlin-runtime dependency adds the following features:

  • Support for defining configuration with config4k.

  • A runtime dependency on jackson-module-kotlin

To enable the above features add the dependency to your build:

compile 'io.micronaut.kotlin:micronaut-kotlin-runtime:1.0.0.M2'

Config4k Support

Config4k is a type safe configuration format for Kotlin based on HOCON (Human-Optimized Config Object Notation). Configuration files are defined using the conf extension. The following an example configuration file:

An Example src/main/resources/application.conf
micronaut {
  server {
    port = 8081

3 Ktor Support

Ktor is a Kotlin framework for building connected applications. The micronaut-ktor module includes support for using Ktor as the server instead of Micronaut’s native HTTP server.

This allows users familiar with Ktor to use Micronaut features such as Dependency Injection, AOP, configuration management and so on.

See the Example application which demonstrates how to setup a Micronaut Ktor application

3.1 The KtorApplication class

The entry point for a Micronaut Ktor application is an Application class. An example class can be seen below:

Example Application class
import io.ktor.server.netty.NettyApplicationEngine
import io.micronaut.ktor.*
import org.slf4j.LoggerFactory
import javax.inject.Singleton

class Application : KtorApplication<NettyApplicationEngine.Configuration>({ (1)
    applicationEngineEnvironment { (2)
        log = LoggerFactory.getLogger(Application::class.java)

    applicationEngine { (3)
        workerGroupSize = 10

fun main(args: Array<String>) { (4)
1 The Application class extends io.micronaut.ktor.KtorApplication and provides the server type (in this case Netty).
2 You can optionally configure the ApplicationEngineEnvironment.
3 You can optionally configure the ApplicationEngine. In this case NettyApplicationEngine instance’s workerGroupSize is set to 10
4 A main method is defined for running the application within a runnable JAR

3.2 Defining Ktor Modules

To define Ktor modules you can create classes that subclass io.micronaut.ktor.KtorApplicationBuilder to install features or io.micronaut.ktor.KtorRoutingBuilder to configure routes.

For example, the following will install the Jackson feature (when ktor-jackson is on the classpath):

Installing Features
import com.fasterxml.jackson.databind.SerializationFeature
import io.ktor.application.install
import io.ktor.features.ContentNegotiation
import io.ktor.jackson.jackson
import io.micronaut.ktor.KtorApplicationBuilder
import javax.inject.Singleton

class GreetingConfiguration : KtorApplicationBuilder({ (1)
    install(ContentNegotiation) { (2)
        jackson {
1 The class subclasses KtorApplicationBuilder.
2 The ContentNegotiation feature is installed and Jackson configured.

To build application routes you can use the KtorRoutingBuilder:

Defining Routes
import io.ktor.application.call
import io.ktor.request.receive
import io.ktor.response.respond
import io.ktor.routing.*
import io.micronaut.ktor.KtorRoutingBuilder
import javax.inject.Singleton

class GreetingRoutes(private val greetingService: GreetingService) : KtorRoutingBuilder({ (1)
    get("/") {

    post("/") {
        val name = call.receive<CustomGreetingRequest>().name


data class CustomGreetingRequest(val name: String)
1 The class subclasses KtorRoutingBuilder and uses dependency injection to reference GreetingService.
2 The routing DSL is used to build the application routes.