BetterSingletonSerializer.scala

import scala.collection._
import org.json4s._

object SingletonSerializer extends Serializer[Any] {
  private[this] var memoizedSingletons: mutable.Map[(Class[_], String), Any] = mutable.Map.empty

  private def isValidSingleton(clazz: Class[_], classIdentifier: String) = {
    if (memoizedSingletons.contains((clazz, classIdentifier))) {
      true
    } else if (classIdentifier.endsWith("$")) {
      val singlesonClass = Class.forName(classIdentifier)
      clazz.isAssignableFrom(singlesonClass)
    } else {
      false
    }
  }

  def deserialize(implicit format: Formats): PartialFunction[(TypeInfo, JValue), Any] = {
    case (TypeInfo(clazz, _), json) if json.extractOpt[String].map(isValidSingleton(clazz, _)).getOrElse(false) =>
      memoizedSingletons.getOrElseUpdate((clazz, json.extract[String]), {
        val className = json.extract[String]
        Class.forName(className).getField("MODULE$").get()
      })

  }

  def serialize(implicit format: Formats) = {
    case possibleSingleton if possibleSingleton.getClass.getName().endsWith("$") =>
      JString(possibleSingleton.getClass.getName())
  }
}