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Android: How to parse nested json array with different data type objects using retrofit - moshi?

I want to parse nested json using retrofit moshi. The json data i'm having is an array, inside array first element is string & second is again an array.
I don't want to parse first element in the array ("list"), just want to parse second element from the array (i.e. Inner array).
But i'm facing challenges exactly here with the data object to be use.
Obviously we can use Any type in kotlin with list, but again will loose type of the object inside the list.
Json Format:
{
"results": [
"list",
[
{
//jsonobj
},
{
//jsonobj
}
]
]
}
I want to parse json with this Data class that i have created without parsing first element & parse directly second element.
#JsonClass(generateAdapter = true)
data class ResponseModel(
#Json(name = "results")
val results: List<Results?>?,
) {
#JsonClass(generateAdapter = true)
data class Results(
#Json(name = "reference")
val reference: String?,
#Json(name = "enabled")
val enabled: Boolean,
)
}
fromJson overridden function
#Throws(IOException::class)
override fun fromJson(reader: JsonReader): C {
val result = newCollection()
reader.beginArray()
while (reader.hasNext()) {
result?.add(elementAdapter.fromJson(reader)!!)
}
reader.endArray()
return result
}
This is throwing an exception saying EXPECTED_OBJECT but it was STRING when trying to parse first element ("list").
i'm stuck here & not able to proceed further.
So can somebody plz help me to get out from here? any help will be appreciated.

More efficient way to model JSON data using retrofit - Kotlin

The data that I want to use has this structure:
{
"1": {
"id": 1,
"name": "Bulbasaur"
},
"2": {
"id": 2,
"name": "Ivysaur"
},
"3": {
"id": 3,
"name": "Venusaur"
}
}
Note:
The number labeling each object matches the id of the Pokémon, not the number of Pokémon
My problem is that when I try to create data classes for this it ends up creating a data class for each object. Not one data class that fits each object. I believe this is due to the number labeling the object(Pokémon) being different for each object.
Is there a way I can format this data in maybe one or two data classes and not over 800?
Ideally I would like the data to be structured like this but it does not work when run.
data class ReleasedPokemonModel(
val id: Int,
val name: String
)

When parsing Json to Object with this special case, you should custom Json Deserializer yourself.
Here I use Gson library to parse Json to Object.
First, create a custom Json Deserializer with Gson. As follows:
PokemonResponse.kt
data class PokemonResponse(
val pokemonMap: List<StringReleasedPokemonModel>
)
data class ReleasedPokemonModel(
val id: Int,
val name: String
)
GsonHelper.kt
object GsonHelper {
fun create(): Gson = GsonBuilder().apply {
registerTypeAdapter(PokemonResponse::class.java, PokemonType())
setLenient()
}.create()
private class PokemonType : JsonDeserializer<PokemonResponse> {
override fun deserialize(
json: JsonElement?,
typeOfT: Type?,
context: JsonDeserializationContext?
): PokemonResponse {
val list = mutableListOf<ReleasedPokemonModel>()
// Get your all key
val keys = json?.asJsonObject?.keySet()
keys?.forEach { key ->
// Get your item with key
val item = Gson().fromJson<ReleasedPokemonModel>(
json.asJsonObject[key],
object : TypeToken<ReleasedPokemonModel>() {}.type
)
list.add(item)
}
return PokemonResponse(list)
}
}
}
Next I will create a GsonConverterFactory so that I can addConvertFactory to Retrofit.
val gsonConverterFactory = GsonConverterFactory.create(GsonHelper.create())
And now I will add retrofit.
val retrofit = Retrofit.Builder()
// Custom your Retrofit
.addConverterFactory(gsonConverterFactory) // Add GsonConverterFactoty
.build()
Finally in ApiService, your response will now return type PokemonResponse.
interface ApiService {
#GET("your_link")
suspend fun getGenres(): PokemonResponse
}

The problem is that there's no JSON array there. it's literally one JSON object with each Pokemon listed as a property. I would recommend that you reformat the JSON beforehand to look like this:
[
{
"id": 1,
"name": "Bulbasaur"
},
{
"id": 2,
"name": "Ivysaur"
},
{
"id": 3,
"name": "Venusaur"
}
]
And then you could model it like this:
data class ReleasedPokemonModel(
val id: Int,
val name: String
)
data class Response(
val items: List<ReleasedPokemonModel>
)
See more here.
And see here for discussion about reformatting the data before handing it to Retrofit.

You can use Map to store the key like the following
data class PokemonResponse(
val pokemonMap:Map<String,ReleasedPokemonModel>
)
data class ReleasedPokemonModel(
val id: Int,
val name: String
)

Moshi map nested JSON value to field

Is there any way to map nested JSON value to field without additional classes? I have a JSON response
{
"title": "Warriors",
"artist": "Imagine Dragons",
"apple_music": {
"url": "https://music.apple.com/us/album/warriors/1440831203?app=music&at=1000l33QU&i=1440831624&mt=1",
"discNumber": 1,
"genreNames": [
"Alternative",
"Music"
],
}
}
But from apple_music I need only url value. So I decided to create Kotlin data class and tried option with #Json annotation
data class Song(
val title: String,
val artist: String,
#Json(name = "apple_music.url")
val appleMusicUrl: String
)
However, this doesn't work.
It throws an exception at runtime
Required value 'appleMusicUrl' (JSON name 'apple_music.url') missing at $
The code below is working
data class Song(
val title: String,
val artist: String,
#Json(name = "apple_music")
val appleMusic: AppleMusic
)
data class AppleMusic(val url: String)
I have several nested values and creating extra classes for them is quite overblowing. Is there any better ways than creating nested class for apple_music node?

One way you can do this is with alternate type adapters using #JsonQualifier. For example:
#Retention(RUNTIME)
#JsonQualifier
annotation class AppleMusicUrl
data class Song(
val title: String,
val artist: String,
#AppleMusicUrl
val appleMusicUrl: String
)
#FromJson
#AppleMusicUrl
fun fromJson(json: Map<String, Any?>): String {
return json.getValue("url") as String
}

How can I deserialize this?

I have a JSON response of an API REST call that I am not pretty sure how should I deserialize...
{
.....
"date": "10-10-19",
"rates": {
"GBP" : 101.01,
"EUR" : 102.01,
"AUD" : 103.4,
......
}
}
I would like to know How could I deserialize the "rates" object?. I think it was a Map object so using Gson I make the next POJO:
class POJO(
private val base: String,
private val date: Date,
private val rates: Rate
)
And my Rate class is
class Rate ( private val currency : Map <String, Double> )
It doesn't make any problem unless I try to use this Map in my class. When I try to access to this variable for example here :
view?.converterBinder!!.setCurrencyList(it.data!!.rates.currency)
currency is null because I think Gson doesn't know how to resolve it. I don't know if I had to deserialize it manually or there are any solution for this using Gson.
Any thoughts??

The provided Json is completely wrong, this is how it should be formatted
{
"date": "10-10-19",
"rates": {
"GBP": 101.01,
"EUR": 102.01
}
}
Please check with https://jsonlint.com to confirm the validity of a Json.
So you have a json object with a String "date", then you have another json object called "rates" containing 2 numeric Doubles "GBP" and "EUR".
Each Json should be represented by a class, so to parse it create the following object containing the 2 classes
object Models {
data class Rates(#SerializedName("GBP") val gbp: Double,
#SerializedName("EUR") val eur: Double)
data class ExchangeRates(#SerializedName("date") val date: String,
#SerializedName("rates") val rates: Rates)
}
Now you pass the class ExchangeRates to Gson to deserialize your object and you should have all the data in place.

Android App crashes as Json element is empty String ("") and not Object

I am working on an android project and using RxAndroid, Retrofit to make API call and retrieve json. The json looks something like following :
{
"result": [
{
"parent": "jhasj",
"u_deviation": "skasks",
"caused_by": "ksks",
"u_owner_mi": {
"link": "https://gddhdd.service-now.com/api/now/v1/table/sys_user/ghtytu",
"value": "ghtytu"
},
"impact": "",
}
]
}
I am using gson to parse the Json. The problem is "u_owner_mi" sometimes reruns empty string "" when there is no value assigned to it. I don't have access to change the return type to null. This is making my app crash as I am expecting an object here.
I get the following error :
Expected BEGIN_OBJECT but was STRING

If you can't modify the server, try replacing the offending line in the server response before passing it to the Gson parser. Something like:
String safeResponse = serverResponse.replace("\"u_owner_mi\": \"\"", "\"u_owner_mi\": null");

Your app (client) code is expecting an object according to a contract specified in the class that you pass to GSON. Your app behaves as it should and crashes loudly. You should consider having your server return "u_owner_mi" : null instead of an empty string, assuming you have control over that. The u_owner_mi field on the client side would have to be a nullable type.
If you don't have the ability to fix the api, you could also write a custom deserializer.
Suppose your result class and sub-object are:
data class Result(
val parent: String,
val owner: Any?
)
data class Owner(
val link: String,
val value: String
)
The deserializer could be:
class ResultDeserializer : JsonDeserializer<Result> {
override fun deserialize(json: JsonElement, typeOfT: Type?, context: JsonDeserializationContext?): Result {
val jsonObject = json.asJsonObject
val ownerProperty = jsonObject.get("owner")
return Result(
parent = jsonObject.get("parent").asString,
owner = if (ownerProperty.isJsonObject) context?.deserialize<Owner>(ownerProperty.asJsonObject, Owner::class.java)
else ownerProperty.asString
)
}
}
Finally, to add the deserializer:
#Test
fun deserialization() {
val gson = GsonBuilder().registerTypeAdapter(Result::class.java, ResultDeserializer()).create()
val result1 = gson.fromJson<Result>(jsonWithObject, Result::class.java)
val result2 = gson.fromJson<Result>(jsonWithEmpty, Result::class.java)
}