Gradual Migration of 3 Java Projects to Kotlin (feat. Lombok Support)

Amid Java's high adoption rate, Kotlin is an attractive alternative that boosts productivity through excellent expressiveness, null safety, extension functions, and more.

The biggest obstacle when converting an early Java project to Kotlin was Lombok. Kotlin cannot directly recognize code generated by Lombok, which meant the hassle of having to delombok every dependent Java file and manually fix it.

For a stable migration, it is efficient to proceed in the following order:

• Strengthen tests (Unit, Integration, E2E)
• Convert the build script to gradle.kts
• Convert low-dependency Entity, Repository, Util classes first
• Sequentially convert Controller and Service classes

Starting with Kotlin 1.7.20, Lombok began to be supported as a plugin, greatly lowering the difficulty of migration. Now, instead of having to individually modify every dependent Java file, you can gradually migrate by converting only the necessary classes to Kotlin one at a time.

For practical application, you should first update to Spring Boot 2.5.2 or higher and add build configuration for Kotlin 1.8.0 or higher.