Kotlin Controller

@RestController
private class JsonController {
    @GetMapping("anonymous")
    fun anonymous() = object {
        val a = 1
        val b = "b"
        val nested = object {
            val c = Math.PI
            val d = DayOfWeek.MONDAY
        }
        val list = (1..10).map { it * it }
    }

    class Data(val value: Int)

    @PostMapping("data")
    fun data(@RequestBody data: Data) = data
}