build.sbt

libraryDependencies += "com.typesafe.play" %% "play-json" % "2.3.7"

resolvers += "typesafe" at "http://typesafe.artifactoryonline.com/typesafe/releases"

scalaVersion := "2.11.4"

EitherReadsExample.scala

import JsEither._

case class Page(id: Int, name: String, screen_name: String, is_closed: Int, photo_50: String, photo_100: String, photo_200: String)
object Page {
  implicit val format = Json.format[Page]
}

case class Profile(id: Int, first_name: String, last_name: String)
object Profile {
  implicit val format = Json.format[Profile]
}

object EitherReadsExample {
  def main(args: Array[String]): Unit = {
    println(json.validate[Seq[Either[Profile, Page]]])
  }
}

JsEither.scala

import play.api.libs.json._

// https://groups.google.com/d/topic/play-framework/anYvYB-8GYs/discussion

implicit object JsEither {
  implicit def eitherReads[A, B](implicit A: Reads[A], B: Reads[B]): Reads[Either[A, B]] =
    Reads[Either[A, B]] { json =>
      A.reads(json) match {
        case JsSuccess(value, path) => JsSuccess(Left(value), path)
        case JsError(e1) => B.reads(json) match {
          case JsSuccess(value, path) => JsSuccess(Right(value), path)
          case JsError(e2) => JsError(JsError.merge(e1, e2))
        }
      }
    }

  implicit def eitherWrites[A, B](implicit A: Writes[A], B: Writes[B]): Writes[Either[A,B]] =
    Writes[Either[A, B]] {
      case Left(a) => A.writes(a)
      case Right(b) => B.writes(b)
    }

  implicit def eitherFormat[A, B](implicit A: Format[A], B: Format[B]): Format[Either[A,B]] =
    Format(eitherReads, eitherWrites)
}