play-json

import play.api.libs.json._
import play.api.libs.functional.syntax._

case class User(id: Long, name: String, friends: Seq[User] = Seq.empty)
object User {

 // In this format, an undefined friends property is mapped to an empty list
 implicit val format: Format[User] = (
   (__ \ "id").format[Long] and
   (__ \ "name").format[String] and
   (__ \ "friends").lazyFormatNullable(implicitly[Format[Seq[User]]])
     .inmap[Seq[User]](_ getOrElse Seq.empty, Some(_))
 )(User.apply, unlift(User.unapply))
}

object MyController extends play.api.mvc.Controller {
  def displayUserAsJson(id: String) = Action {
     Ok(Json.toJson(User(id.toLong, "myName")))
  }

  def saveUser(jsonString: String)= Action {
    val user = Json.parse(jsonString).as[User]
    //myDataStore.save(user)
    Ok
  }
}