Json4s unable to desrialize in scala

Question

I need a help in json desrialization in scala using Json4s. I get the following error when I try to desrialize the json

scala.collection.immutable.Map$Map1 cannot be cast to 
 LocationServiceTest$$anonfun$1$LocationList$3
 java.lang.ClassCastException: scala.collection.immutable.Map$Map1 cannot be cast to 
 LocationServiceTest$$anonfun$1$LocationList$3
at LocationServiceTest$$anonfun$1.apply$mcV$sp(LocationServiceTest.scala:34)
at LocationServiceTest$$anonfun$1.apply(LocationServiceTest.scala:16)
at LocationServiceTest$$anonfun$1.apply(LocationServiceTest.scala:16)

My Json as follows :

    {
  "locations" : [
    {
      "country": "YY",
      "placeName": "YY",
      "latitude": "YY",
      "longitude": "YY"
    },
    {
      "country": "XX",
      "placeName": "XX",
      "latitude": "XX",
      "longitude": "XX"
    },

My code :

case class Location(country: String, placeName: String, latitude: Double, longitude: Double)
 val locations = parse(scala.io.Source.fromFile("input.json").mkString)
  println(locations.values.asInstanceOf[LocationList])

Using extract(format, manifest) also fails.. Can someone please help.

Could you share `LocationList` code, please? i guess that it is something like `LocationList(locations: Seq[Location])` but I'd like to confirm. — Ivan Kurchenko, Mar 06 '20 at 16:38
`extract` is the function you should use. Please, show how you use it and what is the error you get. — Suma, Mar 06 '20 at 17:01
BEWARE: Json4s is [vulnerable under DoS/DoW attacks](https://github.com/json4s/json4s/issues?utf8=%E2%9C%93&q=is%3Aissue+is%3Aopen+denial)! — Andriy Plokhotnyuk, May 06 '20 at 05:49

score 2 · Accepted Answer · answered Mar 06 '20 at 17:21

The code is shown below:

object Test extends App {
  import org.json4s._
  import org.json4s.jackson.JsonMethods._
  implicit val formats =DefaultFormats

  val str = scala.io.Source.fromFile("input.json").mkString

  case class Location(country: String, placeName: String, latitude: String, longitude: String)

  val dataObj= parse(str)
  val locObj = (dataObj \ "locations").extract[Seq[Location]]

  println(locObj)
}

The output:

List(Location(YY,YY,YY,YY), Location(XX,XX,XX,XX))

Note that in case class, latitude and longitude are string since in json, you declared them as string.

Let me know if it helps!!

score 1 · Answer 2 · edited Jun 20 '20 at 09:12

1

The parse function creates JValue (JSON representation in Scala types, like Map, Array and primitive types). That type is not in any way related to some custom type, like LocationList. For that you need to use json.extract. See https://github.com/json4s/json4s Extracting values:

Case classes can be used to extract values from parsed JSON

json.extract[Person]

edited Jun 20 '20 at 09:12

Community

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answered Mar 06 '20 at 16:48

Suma

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Json4s unable to desrialize in scala

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