Since Google announced Kotlin as the official language for Andriod development, it is getting prevalent in mobile development. It has a lot more features that are very good for server-side development as well. If you are a new developer, I would highly recommend learning Kotlin over Java. As it is effortless to mix Java and Kotlin in one project, you can try Kotlin in a project step by step. With a lot of requests from our users, we have developed a Kotlin OpenAPI generator in light-codegen and created an example application. The Kotlin code is much simpler than Java for the same handlers and tests.