Kotlin Spring Boot

A solid reference for modern Kotlin/Spring Boot 3.x patterns that shows you the right way to structure REST APIs with dependency injection, services, and controllers. It covers the full stack from build.gradle.kts setup through data classes, validation DTOs, OpenAPI interfaces, and exception handling. The service pattern example uses NEVER propagation for transaction control and implements idempotency checks, which is practical advice you don't see in every tutorial. Also includes Kotlin idioms like avoiding the !! operator and preferring when expressions. Good for anyone building backend services who wants to see clean patterns rather than figuring out Spring Boot conventions from scratch.