Kotlin - resource decorator issue with controllers returning a Kotlin data class

[dcoraboeuf]

Given a data class like:

data class MyType(val key: String, val name: String)

a controller returning this type:

@RestController
class MyController {
   @GetMapping("/my-type/{key}")
   fun getMyType(@PathVariable key: String): MyType {
      ...
   }
}

a resource decorator:

@Component
class MyTypeResourceDecorator : AbstractResourceDecorator<MyType>(MyType::class.java) {
    override fun links(myType: MyType, resourceContext: ResourceContext): List<Link> {
        return resourceContext.links()
                .self(on(MyTypeController::class.java).getMyType(myType.key))
    }
}

When tested, the call will fail because of:

Cannot subclass final class MyType

A current workaround is to adapt the controller to return a Resource instead:

@RestController
class MyController {
   @GetMapping("/my-type/{key}")
   fun getMyType(@PathVariable key: String): Resource<MyType> {
      ...
   }
}

[dcoraboeuf]

Other (and simpler) workaround, using an open instead of a data class:

open class MyType(val key: String, val name: String)

Of course, this is not very satisfying, but some fix might be available in a future Spring Kotlin extension - see https://github.com/sdeleuze/spring-kotlin