Kotlin data class create dynamically json of its fields using GSON - serialization

Question

I have a data class like this:
data class TestModel(
val id: Int,
val description: String,
val picture: String)
If I create JSON from this data class using GSON and it generates a result like this
{"id":1,"description":"Test", "picture": "picturePath"}
What to do if I need the following JSON from my data class:
{"id":1, "description":"Test"}
And other times:
`{"id":1, "picture": "picturePath"}
`
Thanks in advance!

Answer 1

You can solve this problem with writing custom adapter and with optional types:
import com.google.gson.Gson
import com.google.gson.GsonBuilder
import com.google.gson.TypeAdapter
import com.google.gson.stream.JsonReader
import com.google.gson.stream.JsonToken
import com.google.gson.stream.JsonWriter
data class TestModel(
val id: Int,
val description: String? = "",
val picture: String? = "")
class TesModelTypeAdapter : TypeAdapter<TestModel>() {
override fun read(reader: JsonReader?): TestModel {
var id: Int? = null
var picture: String? = null
var description: String? = null
reader?.beginObject()
while (reader?.hasNext() == true) {
val name = reader.nextName()
if (reader.peek() == JsonToken.NULL) {
reader.nextNull()
continue
}
when (name) {
"id" -> id = reader.nextInt()
"picture" -> picture = reader.nextString()
"description" -> description = reader.nextString()
}
}
reader?.endObject()
return when {
!picture.isNullOrBlank() && description.isNullOrBlank() -> TestModel(id = id ?: 0, picture = picture)
!description.isNullOrBlank() && picture.isNullOrBlank() -> TestModel(id = id ?: 0, description = description)
else -> TestModel(id ?: 0, picture, description)
}
}
override fun write(out: JsonWriter?, value: TestModel?) {
out?.apply {
beginObject()
value?.let {
when {
!it.picture.isNullOrBlank() && it.description.isNullOrBlank() -> {
name("id").value(it.id)
name("picture").value(it.picture)
}
!it.description.isNullOrBlank() && it.picture.isNullOrBlank() -> {
name("id").value(it.id)
name("description").value(it.description)
}
else -> {
name("id").value(it.id)
name("picture").value(it.picture)
name("description").value(it.description)
}
}
}
endObject()
}
}
}
class App {
companion object {
#JvmStatic fun main(args: Array<String>) {
val tm = TestModel(12, description = "Hello desc")
val tm2 = TestModel(23, picture = "https://www.pexels.com/photo/daylight-forest-glossy-lake-443446/")
val tm3 = TestModel(12, "Hello desc", "https://www.pexels.com/photo/daylight-forest-glossy-lake-443446/")
val gson = GsonBuilder().registerTypeAdapter(TestModel::class.java, TesModelTypeAdapter()).create()
System.out.println(gson.toJson(tm))
System.out.println(gson.toJson(tm2))
System.out.println(gson.toJson(tm3))
}
}
}

Answer 2

Here is actually a way to ignore fields, that are not marked via #Exposed annotation. In order for this to work, special configuration should be used when instantiating Gson. Here is how you can to this.
Easy way is to mark the field as #Transient. Then it would not be either serialized and deserialized.

Answer 3

I want to give you alternative ways without manually serialization/deserialization.
data class TestModel(
val id: Int,
val description: String? = null,
val picture: String? = null)
When you create json from data class
val params = TestModel(id = 1, description = "custom text")
or
val params = TestModel(id = 1, picture = "picture path")
If one of them field is null of data class GSON skips that field
automatically.