README.md

Kotlin + Java/Lombok Build Demo

Using Kotlin in an existing Java project that uses Kotlin has caused a lot of problems for people, with several questions on StackOverflow & elsewhere (see 1, 2, 3, 4, 5, 6, 7)

Looking through it, there were some suggestions of it being possible using Kapt &/or Delombok, but not much of clear guidance, until I found this answer:

If you put Java and Kotlin code in different modules, it should work. Rationale: Kotlin will see whatever declarations get to the byte code, but it can’t see whatever Lombok generates on-the-fly in the source code

This project shows a Hello World app using a Gradle multi-project build, but it should also work for Maven if you split the Java & Kotlin into separate modules.

For more info on Kotlin+Lombok, see this Medium Post.

References

This hello-world app is an adapted version of JetBrains' mixed-java-kotlin-hello-world example.

See the Gradle Tutorial for more info on multi-project builds (& code on GitHub).

Kotlin - Using Gradle

Running the app

Gradle

Run Main.kt:

$ cd kotlin-lombok-integration
$ ./gradlew build
$ ./gradlew run

> Task :kotlin-subproject:run
Hi Harry and Ron and Hermione

BUILD SUCCESSFUL in 0s
4 actionable tasks: 1 executed, 3 up-to-date

Run Tests:

(  ) at Fri 1.19.18 in kotlin-lombok-integration on  master [!]
❯❯❯ ./gradlew test

> Task :kotlin-subproject:test

demo.GreetingJoinerTest > getJoinedGreeting PASSED


BUILD SUCCESSFUL in 2s
5 actionable tasks: 2 executed, 3 up-to-date

IntelliJ

Importing: Import Project -> Import project from external model -> Gradle

Note: In the IntelliJ preferences, make sure you enable the Lombok plugin & annotation processing for the project.

Open Main.kt. Click the run/start symbol & select Run demo.MainKt. Kotlin code should be able to call any Lombok-generated methods on Java classes (e.g., "${greeter.greeting} ..." in GreetingJoiner.kt).