Play 2.0 Json <-> Object Binding/Marshalling/Unmarshalling

Play.scala

// taken from http://www.playframework.org/documentation/api/2.0/scala/play/api/libs/json/package.html 

case class User(id: Long, name: String, friends: List[User])

implicit object UserFormat extends Format[User] {
  def reads(json: JsValue): User = User(
    (json \ "id").as[Long],
    (json \ "name").as[String],
    (json \ "friends").asOpt[List[User]].getOrElse(List()))
  def writes(u: User): JsValue = JsObject(List(
    "id" -> JsNumber(u.id),
    "name" -> JsString(u.name),
    "friends" -> JsArray(u.friends.map(fr => JsObject(List("id" -> JsNumber(fr.id),
    "name" -> JsString(fr.name)))))))
}

//then in a controller:
object MyController extends Controller {
   def displayUserAsJson(id: String) = Action {
      Ok(toJson( User(id.toLong, "myName", friends: List())))
   }
   def saveUser(jsonString: String)= Action {
     val user = play.api.libs.json.parse(jsonString).as[User]
     myDataStore.save(user)
     Ok
   }
}