Play Framework: How to sort JSON alphabetically

Question

Given the following JSON...

{
   "z": 100,
   "b": 50,
   "q": 12
}

How do I sort the keys alphabetically?

Answer 1

Simple enough, but (obviously) we need to make sure we have a JsObject.

val js = Json.parse("""{
   "z": 100,
   "b": 50,
   "q": 12
}""")

val jsObject = js.as[JsObject] // Not actually safe, but bear with me

The fields are simply stored in a field called fields as a Seq[(String, JsValue)].

scala> jsObject.fields
res5: Seq[(String, play.api.libs.json.JsValue)] = ListBuffer((z,100), (b,50), (q,12))

We can make a new JsObject with the same fields, except sorted.

scala> JsObject(jsObject.fields.sortBy(_._1))
res6: play.api.libs.json.JsObject = {"b":50,"q":12,"z":100}

Earlier, I mentioned using as[JsObject] is unsafe, because if our JsValue is actually an array or string, it will throw an exception. The safer way to handle a JsValue here would be to pattern match on JsObject and sort it, and do nothing to any other type. It is simple enough to create a method that recursively sorts all keys:

def sortJs(js: JsValue): JsValue = js match {
    case JsObject(fields) => JsObject(fields.sortBy(_._1).map { case (k, v) => (k, sortJs(v)) })
    case _ => js
}

val js = Json.parse("""{
   "z": 100,
   "b": {"k": 1, "j": 3, "i": 98},
   "q": 12
}""")

scala> sortJs(js)
res8: play.api.libs.json.JsValue = {"b":{"i":98,"j":3,"k":1},"q":12,"z":100}