CODEWITHSUNDEEP
jsonscalaplayframeworkjson-deserializationjson4s
Sarthak Maheshwari
Sarthak Maheshwari

Reputation: 45

json4s MappingException does not show up when throwing from my CustomSerializer

I have a Tag.scala file in my Play Framework app with TagKeys and TagValues defined. I want to throw a MappingException when the json is misformatted or the keys/values passed do not belong to TagKey and TagValue.

The json I'm expecting is "tags": [{"key": "Key1", "value": "Value1"}, ....] and it will get converted into a Option[Seq[Tag]]

I want to throw an error for misformatted json or for invalid keys/values, but the MappingException seems to be getting lost somewhere and the Serializer returns an empty Sequence.

Also, when I don't catch the NoSuchElementException and just do the conversion without any try catch, I get a org.json4s.package$MappingException: unknown error

case class Tag(tagKey: TagKey, tagValue: TagValue)

sealed abstract class TagKey

object TagKey {
  case object Key1 extends TagKey
  case object Key2 extends TagKey
}

sealed abstract class TagValue

object TagValue {
  case object Value1 extends TagValue
  case object Value2 extends TagValue
}

object TagSerializer extends CustomSerializer[Tag](_ =>
  (
    {
      case JObject(List(("key", JString(k)), ("value", JString(v)))) =>
        try Tag(TagKey(k), TagValue(v))
        catch {
          case ex: java.util.NoSuchElementException =>
            throw new MappingException(s"Invalid key/value for tags. Error: $ex")
        }
      case unknownJson: Any => throw new MappingException("Invalid Json")
    },

    { case x: Tag =>
      JObject(List(("key", JString(x.tagKey)), ("value", JString(x.tagValue))))
    }
  )
)

I then add this TagSerializer to the formats in my custom body parser. The serialization deserialization works fine.

What am I doing wrong here? Why isn't the error showing up?

Upvotes: 1

Views: 64

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