This is a very short tutorial

If you need to learn how to setup Kotlin with Maven, please follow the beginning of our Kotlin CRUD REST API tutorial

A live demo can be found here

Dependencies

<dependency>
    <groupId>io.javalin</groupId>
    <artifactId>javalin</artifactId>
    <version>4.3.0</version>
</dependency>
<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-simple</artifactId>
    <version>1.7.32</version>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.module</groupId>
    <artifactId>jackson-module-kotlin</artifactId>
    <version>2.9.9</version>
</dependency>

Our main class

fun main(args: Array<String>) {

    var todos = arrayOf(Todo(123123123, "My very first todo", false))

    val app = Javalin.create {
        it.addStaticFiles("/public")
    }.start(7000)

    app.routes {
        get("/todos") { ctx ->
            ctx.json(todos)
        }
        put("/todos") { ctx ->
            todos = ctx.bodyAsClass<Array<Todo>>()
            ctx.status(204)
        }
    }

}

We’re use Javalin to serve our static files, as well as handle two endpoints: get and put.

Most of the work here is being done by ctx.json and ctx.bodyAsClass, which map a Todo data-class:

data class Todo(val id: Long = -1, val title: String = "", val completed: Boolean = false)

That’s it. The rest of the logic is in index.html (vue template) and todomvc.js (vue logic).
This is not a JavaScript tutorial, so please have a look at those files for yourself.