Scala将Json播放到OrderdMap

Question

I'm new to scala. I'm trying to convert JSON to ordered Map which should have values in insertion order. But compiler says I can convert only to Map, not to ListMap and asking me to implement an implicit Read or format.

But I wanted to know is there any way we can directly use some existing functions as we have for JSON to Map conversion? I also checked for an option in SprayJson and other, but it looks like there are no existing functions available for JSON to ordered collection.

 import play.api.libs.json._
 import scala.collection.immutable.ListMap

object Test extends App{

 val jsonString = """{"ONE":"O", "TWO":"T", "THREE":"T", "FOUR":"F", "FIVE":"F"}"""
val jsonValue = Json.parse(jsonString).as[ListMap[String, String]]

 println("Result : " + jsonValue)
}

Expected Result ListMap(ONE -> O, TWO -> T, THREE -> T, FOUR -> F, FIVE -> F); 

Answer 1

The keys of the Json object is not ordered and Hence the keys, values of Json object can be retrived at any order and hence it is not guaranteed to be ordered. Ordering is maintained only in arrays not in objects. so you will have to change the Json object to an Json array to achieve this like shown below

scala> import scala.collection.immutable.ListMap
import scala.collection.immutable.ListMap

scala> import play.api.libs.json._
import play.api.libs.json._

scala> val jsonString = """[{"F1":{"A" : "a"}}, {"F2":{"B" : "b"}}, {"F3":{"C" : "c"}}, {"F4":{"D" : "d"}}, {"F5":{"E" : "e"}}]"""
jsonString: String = [{"F1":{"A" : "a"}}, {"F2":{"B" : "b"}}, {"F3":{"C" : "c"}}, {"F4":{"D" : "d"}}, {"F5":{"E" : "e"}}]

scala> val list = Json.parse(jsonString).as[List[Map[String, Map[String, String]]]].flatten.foldLeft(ListMap[String,Map[String, String]]())({ case (arr,(key, value)) => arr + (key -> value)})
list: scala.collection.immutable.ListMap[String,Map[String,String]] = Map(F1 -> Map(A -> a), F2 -> Map(B -> b), F3 -> Map(C -> c), F4 -> Map(D -> d), F5 -> Map(E -> e))