Code from the following Kotlin demos published on the "Kotlin by JetBrains" YouTube channel. This is a complete code version but uses Maven instead of Gradle.
Part 1 : Spring Time in Kotlin. Getting Started https://www.youtube.com/watch?v=gf-kjD2ZmZk
Part 2 : Kotlin Extensions in Spring Framework https://www.youtube.com/watch?v=0jWo3o7r-W4
Part 3 : Testing a Spring application with JUnit and Kotlin. Tutorial https://www.youtube.com/watch?v=lCBjvlAyuiY