Scala code for conversion of arbitrary nested data structures (list, maps, sets, values) to a JSON string. This involves converting the nested Scala collections (mutable/immutable Maps, Sets, Iterables, etc) to their Java counterparts., which is done with a a distinct function in the gist (toJava).

GsonJson.scala

import com.google.gson.Gson
import scala.collection.JavaConversions

val gson = new Gson()

val mapPrototype = new java.util.HashMap[String,Any]()
def parseJson(json: String): Map[String,Any] = {
  // Note: mapAsScalaMap is a wrapper, the data is NOT copied
  scala.collection.JavaConversions.mapAsScalaMap(gson.fromJson(json, mapPrototype.getClass)).toMap
}

val sampleJson="{\"k1\":\"v1\",\"k2\":10, \"k3\":[1,2,3]}"

def toJava(x: Any): Any = {
  import scala.collection.JavaConverters._
  x match {
    case y: scala.collection.MapLike[_, _, _] => 
      y.map { case (d, v) => toJava(d) -> toJava(v) } asJava
    case y: scala.collection.SetLike[_,_] => 
      y map { item: Any => toJava(item) } asJava
    case y: Iterable[_] => 
      y.map { item: Any => toJava(item) } asJava
    case y: Iterator[_] => 
      toJava(y.toIterable)
    case _ => 
      x
  }
}

def scalaToJson(x: Any): String = {
  gson.toJson(toJava(x))
}

val result = parseJson(sampleJson)

println(result.get("k3").get)
println(result.get("doesnt exist"))

val r2 = result + ("baz"-> Seq(Seq("a", "b"), scala.collection.mutable.Map("abc"->1.0))) + ("quux"->Seq(Map("x"->1))) + ("zet"->Set(1,2,Seq(3,4)))

scalaToJson(r2)