Getting started with Vertx in Kotlin

Published on 19 May 2017

This time I decided to take a good look at Vertx, and as I had a plan to learn Kotlin anyways, I decided to give them a spin together.

Project setup

First let’s just create a new Gradle project:

gradle init --type java-library

Then edit the build.gradle file to have kotlin and java support, along with slf4j and logback support, targeting Java 8. At the end it should look similar to this:

plugins {
    id 'java'
    id 'idea'
    id 'application'
    id 'org.jetbrains.kotlin.jvm' version '1.1.2-2'
    id 'com.github.johnrengelman.shadow' version '2.0.0'


sourceCompatibility = '1.8'
targetCompatibility = '1.8'

mainClassName = "io.github.sandornemeth.abeona.AbeonaAppKt"

def vertx_version = '3.4.1'
def jackson_version = '2.8.7'
def logback_version = '1.2.2'

compileKotlin {
    kotlinOptions.jvmTarget = '1.8'

repositories {

dependencies {
    // kotlin dependencies
    compile 'org.jetbrains.kotlin:kotlin-stdlib-jre8'
    compile 'org.jetbrains.kotlin:kotlin-reflect'

    // vertx
    compile "io.vertx:vertx-core:$vertx_version"
    compile "io.vertx:vertx-web:$vertx_version"

    // Jackson
    compile "com.fasterxml.jackson.core:jackson-databind:$jackson_version"
    compile "com.fasterxml.jackson.module:jackson-module-kotlin:$jackson_version"

    // Logging
    compile "ch.qos.logback:logback-classic:$logback_version"

    // Utilities
    compile 'org.javassist:javassist:3.21.0-GA'

    // Testing
    testCompile 'org.jetbrains.kotlin:kotlin-test'
    testCompile 'org.jetbrains.kotlin:kotlin-test-junit'
    testCompile 'junit:junit:4.12'
    testCompile "io.vertx:vertx-unit:$vertx_version"
    testCompile 'org.assertj:assertj-core:3.7.0'

I also use the shadow plugin from johnrengelman/shadow to package the complete application into a single fat-jar.

Now that we are all set up, let’s get started with the application. First create an entry point for the application:

fun main(args: Array<String>) {

    val vertx = Vertx.vertx()

Here 2 things are happening:

Then create the verticle itself:

class ApiVerticle : AbstractVerticle() {

    companion object {
        val log = loggerFor(javaClass)

    override fun start(startFuture: Future<Void>?) {
        val router = createRouter()
        val port = config().getInteger("http.port", 8080)

                .requestHandler { router.accept(it) }
                .listen(port, { result ->
                    if (result.succeeded()) {
              "Listening on port $port")
                    } else {

    private fun createRouter() = Router.router(vertx).apply {

    val handlerRoot = Handler<RoutingContext> { req ->
        req.response().end("Hello world!")

There are a couple of things happening here:

And finally let’t test the application. Run the build with gradle build, and then run it: java -jar build/libs/abeona-backend-all.jar.

We can now send our first request:

# curl -XGET http://localhost:8080
Hello world!