All-open compiler plugin

By default, classes and the functions in Kotlin are final. In order to make a particular class or function non-final you need to use the open keyword. It is one of the pain points of using Kotlin with Spring as the classes for external configuration properties (Spring beans proxified with CGLIB like @Configuration classes) are required to be open.

Fortunately, with Kotlin v1.0.6, there is a Kotlin-Spring plugin that tells the compiler to open classes and their member functions for classes annotated or meta-annotated with one of the following annotations: 

• @Component
• @Async
• @Transactional
• @Cacheable
• Also, classes annotated with @Configuration, @Controller, @RestController, @Service, or @Repository are automatically opened since these annotations are meta-annotated with @Component

In a nutshell, it becomes much easier to open the required configuration classes by using Spring.