Adding Kotlin sounds easy: add a module, convert a class, enjoy null safety. In real large-scale Java codebases, adding Kotlin is more complicated than that. Even though Kotlin provides excellent interoperability with Java, libraries like Hibernate and annotation processors like Lombok and MapStruct make things harder than they might seem at first glance.

This session aims to be a field guide for teams adding Kotlin into their projects without freezing Java development or taking on the risk of a big-bang rewrite. We'll walk through adding the first module, convert Lombok-backed classes into Kotlin (while highlighting potential problems), navigate persistence edge-cases, Kotlin testing and deal with Java platform types that break Kotlin's nullability guarantees.

You will see where Kotlin pays off fastest and where leaving Java alone might be wiser. Leave with a staged adoption strategy, refactoring patterns for Lombok, ideas for Kotlin test-data DSLs, discover some experimental Kotlin features worth enabling today and learn how to introduce Kotlin one well-chosen boundary at a time.