how to create json object in scala/spark

I have Row (org.apache.spark.sql.Row) which has the following schema StructField(testPref,StringType,true) , this "testPref" is in Json format which has value

{
   "testPref":{
      "institutionId":"001",
      "currency":{
         "default":"",
         "padding":{
            "direction":"left",
            "value":" "
         }
      }
   }
}

I am trying to read the value like below

val pref = row.getAs[String]("testPref")

My requirement is to convert to JSON format and parse it and access keys and values. How can i do this ?

Update :

I am able to convert it to JsonObject like below

val pref = row.getAs[String]("testPref") 
val json: JsonObject = new JsonParser().parse(pref).getAsJsonObject
json.getAsJsonObject("currency").get("default").getAsString

to access json object