Creating Reads / Writes for Java Enum Fieldless

Question

With the JSON library of the Play Framework, how can I create Reads and Writes to list Java without fields?

public enum EnumNoFields { RED, WHITE, BLUE }

 implicit val EnumNoFieldsReads: Reads[EnumNoFields] = ? implicit val EnumNoFieldsWrites: Writes[EnumNoFields] = ? 

Answer 1

I just used Enum # name .

  implicit val EnumNoFieldsReads: Reads[EnumNoFields] = (JsPath \ "displayValue").read[String].map{x: String => EnumNoFields.valueOf(x)} implicit val EnumNoFieldsWrites: Writes[EnumNoFields] = (JsPath \ "displayValue").write[String].contramap{x:EnumNoFields => x.name} 

Answer 2

The general solution would look like this:

 def javaEnumFormat[E <: Enum[E] : ClassTag] = new Format[E] { override def reads(json: JsValue): JsResult[E] = json.validate[String] match { case JsSuccess(value, _) => try { val clazz = implicitly[ClassTag[E]].runtimeClass.asInstanceOf[Class[E]] JsSuccess(Enum.valueOf(clazz, value)) } catch { case _: IllegalArgumentException => JsError("enumeration.unknown.value") } case JsError(_) => JsError("enumeration.expected.string") } override def writes(o: E): JsValue = JsString(o.toString) } 

which you can use as follows:

implicit val enumNoFieldsFormat = javaEnumFormat[EnumNoFields]