Deserialize complex JSON in Kotlin

Question

I would like to deserialize the following JSON:

{
   "participants": {
      "0": {
         "layout": "layout1"
      }
   },
   "layouts": {
      "layout1": {
         "width": 100,
         "height": 100
      }
   }
}

Into the following structure:

@Serializable
data class Layout(val width: Int, val height: Int)
    
@Serializable
data class Participant(val index: Int, val layout: Layout)
    
@Serializable
data class ViewData(val participants: MutableMap<Int, Participant>, val layouts: MutableMap<Int, Layout>)

What I'm particularly struggling with is how to create the correct relationship between participant's layout using the key "layout1" in the "layouts" hash.

Thanks!

What exactly are you trying to do? Unfortunately, I don't understand :( — Mateusz, Jul 28 '22 at 19:57
Would like to transform my data from the json into the classes above — Nahum Bazes, Jul 29 '22 at 02:23

score 0 · Answer 1 · answered Jul 29 '22 at 10:48

You have to create the classes that matches the json string

        data class Layout(
            val width: Int,
            val height: Int
        )

        data class Participant(
            val layout: String
        )

        data class ViewData(
            val participants: Map<String, Participant>,
            val layouts: Map<String, Layout>
        )

It is not possible (by default) to deserialize map<String, Any> to map<Int, Any> and it is not possible to add magical val index: Int

then create a function that will help you get layout by participant name

        data class ViewData(
            val participants: Map<String, Participant>,
            val layouts: Map<String, Layout>
        ) {

            fun getLayoutForParticipant(participantId: String): Layout? {
                val layoutId = participants[participantId]?.layout
                return layoutId?.let { layouts[it] }
            }
        }



        val json: String = """
            {
                "participants": {
                    "0": {
                        "layout": "layout1"
                    }
                },
                "layouts": {
                    "layout1": {
                        "width": 100,
                        "height": 100
                    }
                }
            }

        """

        val deserialized: ViewData = objectMapper.readValue(json, ViewData::class.java)

        println(deserialized)
        println(deserialized.getLayoutForParticipant("0"))

result:

ViewData(participants={0=Participant(layout=layout1)}, layouts={layout1=Layout(width=100, height=100)})
Layout(width=100, height=100)

Thank you very much for this. I was thinking about some sort of a custom serializer. Is this possible somehow? — Nahum Bazes, Jul 29 '22 at 12:44
yup, it is possible, but depends on what deserializer you use. But I'm not sure that it is a better or simpler way — Mateusz, Jul 29 '22 at 16:39
Mateusz, what is the objectMapper you are using? Is it standard in Kotlin? Can it be used in MKP? — Nahum Bazes, Jul 30 '22 at 08:30

Deserialize complex JSON in Kotlin

1 Answers1