如何在Scala / Play中将JSON转换为简单的旧数据（Map，List，String，Int等）

Question

I have a JsValue corresponding to the following JSON object:

{"foo": [{"id": 1, value: "bar"}, {"id": 2, "value": "baz"}, ...]}

Is there some easy way to turn this into a Map(String, List(Map(String, Either(String, Int)))) or some other structure of regular ol' data?

I want to query the JSON for whether <anonymous outermost value>["foo"] contains {"id": 42, "value": "Towel"} . This would be easy for me if I could convert the JsValue object to plain old collections*. Is there some other straightforward way to do so on JsValue objects?

(*) I think it'd be something like anonymous_outermost_value("foo") contains Map("id" -> Left(42), "value" -> Right("Towel")) .

(In this particular application, I would be OK with converting all the IDs to strings and turning the Either(String, Int) into just String , if that makes stuff easier.)

Answer 1

Work with Map , List etc is not easier than work with Playframework Json. If you want use the usual way to work with data, JSON basics helps you.

You must implement converters Json <-> Plain objects with Json Reads[T] and Writes[T]

For example Json object {"id": 1, value: "bar"} represented with case class A(id: Long, value: String) and {"foo": [{"id": 1, value: "bar"}.. represented with case class B(foo: List[A]) . The simplest way for implement converter Json <-> Plain objects is Json.format[T] macros.

implicit val aFormat = Json.format[A]
implicit val bFormat = Json.format[A]

Then you may use Json.toJson[T](o: T) <-> Json.fromJson[T](json: JsValue) for converting T <-> JsValue

Answer 2

You could convert the JsValue to a JsObject (which is simply a wrapper around a Map[String, JsValue] ), extracting the foo property as a JsArray (which is a wrapper around a Seq[JsValue] ) and so on. But I think it's really easier to simply use the Json functions:

for {
  foo <- (json \ "foo").validate[Seq[JsObject]]
  obj <- foo
  id <- (obj \ "id").validate[Int]
  value <- (obj \ "value").validate[String]
  if id == 42 && value == "Towel"
} {
  // do something
}