Very simple + untidy json flattener.

JsonFlatten.scala

import play.api.libs.json.{JsObject, JsValue, Json}

implicit class JsonFlatten(v: JsValue) {

  def toMap(pref: String = ""): Map[String, String] = if (v.isIterable) v.validate[Seq[JsObject]] map { jsons =>
    jsons.foldLeft(Map.empty[String, String]) {
      case (acc, json) => acc ++ json.toMap(pref)
    }
  } getOrElse Map.empty[String, String] else v.validate[Map[String, JsValue]] map { mp =>
    mp.foldLeft(Map.empty[String, String]) {
      case (acc, (k, value)) if value.isFlat => acc + (s"$pref.$k" -> value.toString)
      case (acc, (k, value)) => acc ++ value.toMap(s"$pref.$k")
    }
  } getOrElse Map.empty[String, String]
  def isFlat = !(v.isNestable || v.isIterable)
  def isNestable = v.validate[JsObject].isSuccess
  def isIterable = v.validate[Seq[JsValue]].isSuccess

}