kotlin jackson

import com.fasterxml.jackson.annotation.JsonTypeInfo
import com.fasterxml.jackson.module.kotlin.jacksonObjectMapper

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME)
sealed class Principal
object AnonymousUser : Principal() {
  val _empty: String? = null
}

// other implementations of Principal

fun main() {
  // jacksonObjectMapper() is a function in jackson which creates an object mapper with the Kotlin module
  val input = jacksonObjectMapper().writeValueAsString(AnonymousUser)
  val principal = jacksonObjectMapper().readValue(input, Principal::class.java)
  println(principal)
}