scala spray json with error

sealed trait Obj
  case class Error(error:String) extends Obj
  case class DataA(a1:String, a2: Int) extends Obj
  case class DataB(b1:String, b2: Boolean) extends Obj

  val strA = """{"a1":"foo", "a2": 1}"""
  val strB = """{"b1":"bar", "b2": false}"""
  val srtE = """{"error": "oops"}"""

  object JsonProtocols extends DefaultJsonProtocol {
    implicit val errorFormat = jsonFormat1(Error)
    implicit val dataAFormat = jsonFormat2(DataA)
    implicit val dataBFormat = jsonFormat2(DataB)
  }

  import JsonProtocols._
  val result:Obj = strA.parseJson.convertTo[Either[DataA,Error]] match {
    case Left(dataA) => dataA
    case Right(error) => error
  }