Automagic content negotiation with playframework (version >= 2.1). If called with Accept: application/json => { "firstName": "Erik", "surName": "Fried", "age": 34 } Accept: text/xml => <person> <firstName>Erik</firstName> <surName>Fried</surName> <age>34</age> </person>

Controller.scala

package controllers

import play.api.mvc._
import play.api.libs.json.{Writes, Json}

import test.PersonRepository
import scala.xml.Elem


object PersonResource extends Controller with ContentNegotiation {

  def getPerson(id: Int) = Action { implicit request =>
    //The ContentNegotiation trait provides the XmlOrJson function.
    XmlOrJson {
      PersonRepository.get(id)
    }
  }
}

// Define a base "interface" for all classes that can be serialized to XML.
trait XmlSerializable {
  def toXML: Elem
}

trait ContentNegotiation {
  //Self type annotation -> trait must be mixed in into Controller (thus, has access to render, Accepts and Ok)
  self : Controller =>

  //Serializes the provided value according to the Accept headers of the (implicitly) provided request
  def XmlOrJson[A <: XmlSerializable](value: A)(implicit request: Request[AnyContent], writes: Writes[A]) : Result = {
    render {
      case Accepts.Xml() => Ok(value.toXML)
      case Accepts.Json() => Ok(Json.toJson(value))
    }
  }
}

Domain.scala

package test

import play.api.libs.json.Json
import controllers.XmlSerializable

case class Person(firstName: String, surName: String, age: Int) extends XmlSerializable{
  //The XML serialization is (for good and bad) defined explicitly
  override def toXML =
    <person>
      <firstName>{firstName}</firstName>
      <surName>{surName}</surName>
      <age>{age}</age>
    </person>
}
object Person {
  // We define the Json Writes in the companion object,
  // so it will be automatically inferred whenever we want to write this class
  implicit val personWrites = Json.writes[Person]
}


// Pretend this is for real...
object PersonRepository {
  def get(id: Int) = Person("Erik", "Fried", 34)
}

routes

GET     /person/:id                controllers.PersonResource.getPerson(id: Int)