lift-jsonのextractで痒いところに手を伸ばす

1.scala

sealed trait Carrier
case object PC extends Carrier
case object Mobile extends Carrier
case object Smartphone extends Carrier

2.scala

import net.liftweb.json._

lazy val CarrierSerializer = new Serializer[Carrier] {
  override def deserialize(implicit format: Formats) = {
    case (TypeInfo(c, _), JInt(i)) if c == classOf[Carrier] && i == 0 => PC
    case (TypeInfo(c, _), JInt(i)) if c == classOf[Carrier] && i == 1 => Mobile
    case (TypeInfo(c, _), JInt(i)) if c == classOf[Carrier] && i == 2 => Smartphone
  }
  override def serialize(implicit format: Formats) = {
    case PC => JInt(0)
    case Mobile => JInt(1)
    case Smartphone => JInt(2)
  }
}

3.scala

import net.liftweb.json._

val jsonStr = """[0, 1, 2]"""

implicit lazy val myformats = DefaultFormats + CarrierSerializer // 自作Serializerの組み込み

val result = parse(jsonStr).extract[List[Carrier]] // List(PC, Mobile, Smartphone)

4.scala

import net.liftweb.json._

val arrange: PartialFunction[JValue, JValue] = {
  case JObject(List(JField("Item", item))) => item
  case JField("Items", items) => JField("items", items)
}

def extract(jsonStr: String) =
  parse(jsonStr)
    .transform(arrange)
    .extract[Result]