Develop Reference

Consuming Polymorphic Jsons with Retrofit and Kotlin

My API sends me a polyphonic Json in with the variable addon_item can be either a String or an Array, I have spend days trying to make a CustomDezerializer for it without any success.
Here is the Json response:
({
"code": 1,
"msg": "OK",
"details": {
"merchant_id": "62",
"item_id": "1665",
"item_name": "Burrito",
"item_description": "Delicioso Burrito en base de tortilla de 30 cm",
"discount": "",
"photo": "http:\/\/www.asiderapido.cloud\/upload\/1568249379-KDKQ5789.jpg",
"item_cant": "-1",
"cooking_ref": false,
"cooking_ref_trans": "",
"addon_item": [{
"subcat_id": "144",
"subcat_name": "EXTRA",
"subcat_name_trans": "",
"multi_option": "multiple",
"multi_option_val": "",
"two_flavor_position": "",
"require_addons": "",
"sub_item": [{
"sub_item_id": "697",
"sub_item_name": "Queso cheddar",
"item_description": "Delicioso queso fundido",
"price": "36331.20",
"price_usd": null
}]
}]
}
})
Here is the Custom Dezerializer, which includes BodyConverter that removes two braces that encompassed the Json response:
'''
/**
* This class was created due to 2 issues with the current API responses:
* 1. The API JSON results where encapsulated by parenthesis
* 2. They had dynamic JSON variables, where the Details variable was coming as a String
* or as an Object depending on the error message (werer whe user and password wereh correct.
*
*/
class JsonConverter(private val gson: Gson) : Converter.Factory() {
override fun responseBodyConverter(
type: Type?, annotations: Array<Annotation>?,
retrofit: Retrofit?
): Converter<ResponseBody, *>? {
val adapter = gson.getAdapter(TypeToken.get(type!!))
return GsonResponseBodyConverter(gson, adapter)
}
override fun requestBodyConverter(
type: Type?,
parameterAnnotations: Array<Annotation>?,
methodAnnotations: Array<Annotation>?,
retrofit: Retrofit?
): Converter<*, RequestBody>? {
val adapter = gson.getAdapter(TypeToken.get(type!!))
return GsonRequestBodyConverter(gson, adapter)
}
internal inner class GsonRequestBodyConverter<T>(
private val gson: Gson,
private val adapter: TypeAdapter<T>
) : Converter<T, RequestBody> {
private val MEDIA_TYPE = MediaType.parse("application/json; charset=UTF-8")
private val UTF_8 = Charset.forName("UTF-8")
#Throws(IOException::class)
override fun convert(value: T): RequestBody {
val buffer = Buffer()
val writer = OutputStreamWriter(buffer.outputStream(), UTF_8)
val jsonWriter = gson.newJsonWriter(writer)
adapter.write(jsonWriter, value)
jsonWriter.close()
return RequestBody.create(MEDIA_TYPE, buffer.readByteString())
}
}
// Here we remove the parenthesis from the JSON response
internal inner class GsonResponseBodyConverter<T>(
gson: Gson,
private val adapter: TypeAdapter<T>
) : Converter<ResponseBody, T> {
#Throws(IOException::class)
override fun convert(value: ResponseBody): T? {
val dirty = value.string()
val clean = dirty.replace("(", "")
.replace(")", "")
try {
return adapter.fromJson(clean)
} finally {
value.close()
}
}
}
class DetalleDeProductoDeserializer : JsonDeserializer<DetallesDelItemWrapper2> {
override fun deserialize(
json: JsonElement,
typeOfT: Type,
context: JsonDeserializationContext
): DetallesDelItemWrapper2 {
if ((json as JsonObject).get("addon_item") is JsonObject) {
return Gson().fromJson<DetallesDelItemWrapper2>(json, ListaDetalleAddonItem::class.java)
} else {
return Gson().fromJson<DetallesDelItemWrapper2>(json, DetallesDelItemWrapper2.CookingRefItemBoolean::class.java)
}
}
}
companion object {
private val LOG_TAG = JsonConverter::class.java!!.getSimpleName()
fun create(detalleDeProductoDeserializer: DetalleDeProductoDeserializer): JsonConverter {
Log.e("Perfill Adapter = ", "Test5 " + "JsonConverter" )
return create(Gson())
}
fun create(): JsonConverter {
return create(Gson())
}
private fun create(gson: Gson?): JsonConverter {
if (gson == null) throw NullPointerException("gson == null")
return JsonConverter(gson)
}
}
}
Here is the RetrofitClient.class:
class RetrofitClient private constructor(name: String) {
private var retrofit: Retrofit? = null
fun getApi(): Api {
return retrofit!!.create(Api::class.java)
}
init {
if (name == "detalleDelItem") run {
retrofit = Retrofit.Builder()
.baseUrl(BASE_URL)
.addConverterFactory(JsonConverterJava.create(JsonConverterJava.DetallesDelItemDeserializer()))
// .addConverterFactory(GsonConverterFactory.create(percentDeserializer))
.client(unsafeOkHttpClient.build())
.build()
Log.e("RetrofitClient ", "Instace: " + "detalle " + name)
}
}
companion object {
//Remember this shit is https for the production server
private val BASE_URL = "http://www.asiderapido.cloud/mobileapp/api/"
private var mInstance: RetrofitClient? = null
#Synchronized
fun getInstance(name: String): RetrofitClient {
mInstance = RetrofitClient(name)
return mInstance!!
}
}
}
Finally my POJO:
open class DetallesDelItemWrapper2 {
#SerializedName("code")
val code: Int? = null
#Expose
#SerializedName("details")
var details: ItemDetails? = null
#SerializedName("msg")
val msg: String? = null
class ItemDetails {
#Expose
#SerializedName("addon_item")
val addonItem: Any? = null
#SerializedName("category_info")
val categoryInfo: CategoryInfo? = null
#SerializedName("cooking_ref")
val cookingRef: Any? = null
#SerializedName("cooking_ref_trans")
val cookingRefTrans: String? = null
}
class ListaDetalleAddonItem: DetallesDelItemWrapper2(){
#SerializedName("addon_item")
val detalleAddonItem: List<DetalleAddonItem>? = null
}
class StringDetalleAddonItem: DetallesDelItemWrapper2(){
#SerializedName("addon_item")
val detalleAddonItem: String? = null
}

I took a shot at this and came up with 2 possible ideas. I don't think they're the only way to achieve this, but I think I can share my thoughts.
First, I've reduced the problem to actually only parsing the items. So I've removed retrofit from the equation and use the following jsons:
val json = """{
"addon_item": [{
"subcat_id": "144",
"subcat_name": "EXTRA",
"subcat_name_trans": "",
"multi_option": "multiple",
"multi_option_val": "",
"two_flavor_position": "",
"require_addons": "",
"sub_item": [{
"sub_item_id": "697",
"sub_item_name": "Queso cheddar",
"item_description": "Delicioso queso fundido",
"price": "36331.20",
"price_usd": null
}]
}]
}
""".trimIndent()
(for when the addon_item is an array)
val jsonString = """{
"addon_item": "foo"
}
""".trimIndent()
(for when the addon_item is a string)
First approach
My first approach was to model addon_item as a generic JsonElement:
data class ItemDetails(
#Expose
#SerializedName("addon_item")
val addonItem: JsonElement? = null
)
(I'm using data classes because I find them more helpful, but you don't have too)
The idea here is to let gson deserialize it as a generic json element and you can then inspect it yourself. So if we add some convenience methods to the class:
data class ItemDetails(
#Expose
#SerializedName("addon_item")
val addonItem: JsonElement? = null
) {
fun isAddOnItemString() =
addonItem?.isJsonPrimitive == true && addonItem.asJsonPrimitive.isString
fun isAddOnItemArray() =
addonItem?.isJsonArray == true
fun addOnItemAsString() =
addonItem?.asString
fun addOnItemAsArray() =
addonItem?.asJsonArray
}
So as you can see, we check the addOnItem for what it contains and according to that, we can obtain its contents. Here's an example of how to use it:
fun main() {
val item = Gson().fromJson(jsonString, ItemDetails::class.java)
println(item.isAddOnItemArray())
println(item.isAddOnItemString())
println(item.addOnItemAsString())
}
I think the biggest advantage of this is that it's fairly simple and you don't require custom logic to deserialize. For me, the huge drawback is the type-safety loss.
You can get the add on as an array, but it will be an array of json elements that have to be "manually" deserialized. Hence, my 2nd approach tries to tackle this.
Second approach
The idea here is to use Kotlin's sealed classes and have 2 types of add ons:
sealed class AddOnItems {
data class StringAddOnItems(
val addOn: String
) : AddOnItems()
data class ArrayAddOnItems(
val addOns: List<SubCategory> = emptyList()
) : AddOnItems()
fun isArray() = this is ArrayAddOnItems
fun isString() = this is StringAddOnItems
}
The SubCategory class is just what was inside the list. Here's a simple version of it:
data class SubCategory(
#SerializedName("subcat_id")
val id: String
)
As you can see the AddOnItems is a sealed class that has the only 2 possible types for your use case.
Now we need a custom deserializer:
class AddOnItemsDeserializer : JsonDeserializer<AddOnItems> {
override fun deserialize(json: JsonElement?, typeOfT: Type?, context: JsonDeserializationContext?) =
when {
json?.isJsonArray == true -> {
AddOnItems.ArrayAddOnItems(context!!.deserialize(
json.asJsonArray,
TypeToken.getParameterized(List::class.java, SubCategory::class.java).type))
}
json?.isJsonPrimitive == true && json.asJsonPrimitive.isString ->
AddOnItems.StringAddOnItems(json.asJsonPrimitive.asString)
else -> throw IllegalStateException("Cannot parse $json as addonItems")
}
}
In a nutshell, this checks if add on is an array and creates the respective class and the same for string.
Here's how you can use it:
fun main() {
val item = GsonBuilder()
.registerTypeAdapter(AddOnItems::class.java, AddOnItemsDeserializer())
.create()
.fromJson(jsonString, ItemDetails::class.java)
println(item.addOnItems.isString())
println(item.addOnItemsAsString().addOn)
val item = GsonBuilder()
.registerTypeAdapter(AddOnItems::class.java, AddOnItemsDeserializer())
.create()
.fromJson(json, ItemDetails::class.java)
println(item.addOnItems.isArray())
println(item.addOnItemsAsArray().addOns[0])
}
I think the biggest advantage here is that you get to keep the types. However, you still need to check what it is before calling addOnItemsAs*.
Hope this helps

How to properly make reusable class to catch response data using retrofit?

I am new in Android development, and I am trying to get data from server. the general JSON response structure will be like this
{
"success": "1",
"data": [
{
"customers_id": 4,
"customers_gender": "0",
"customers_firstname": "TES IOS",
"customers_lastname": "TES IOS",
"customers_dob": "2018-12-27",
"email": "TES002#email.com",
"user_name": "TES002",
"customers_default_address_id": 0,
"customers_telephone
},
"message": "Successfully get user data from server"
}
the "success" and "message" field will be the same (will always be string). but the "data" can be different for other request call. It can send user data, store data or product data, or even Array/List of Products.
so I want to make general reusable class to catch that JSON response. the class will be like this, I set the "data" to be Any, and then later it will be casted back to User object:
class ServerData(successStatus: Int, data: Any, message: String) {
val isSuccessfull : Boolean
val data : Any
val message : String
init {
isSuccessfull = successStatus != 0
this.data = data
this.message = message
}
}
the interface is like this:
interface LakuinAPI {
#FormUrlEncoded
#POST("processlogin")
fun performLogin(
#Field("kode_customer") outletCode: String,
#Field("password") password: String
): Call<ServerData>
}
and then I use it in the activity, like the code below:
private fun sendLoginDataToServer(outletCode: String, password: String) {
val call = lakuinAPI.performLogin(outletCode,password)
call.enqueue(object: Callback<ServerData> {
override fun onFailure(call: Call<ServerData>, t: Throwable) {
Toast.makeText(this#LoginActivity,t.localizedMessage,Toast.LENGTH_LONG).show()
}
override fun onResponse(call: Call<ServerData>, response: Response<ServerData>) {
if (!response.isSuccessful) {
Toast.makeText(this#LoginActivity,"Code: " + response.code(),Toast.LENGTH_LONG).show()
return
}
val lakuinServerData = response.body()
val userList = lakuinServerData?.data as List<User> // the error in here
val userData = userList.first() // the error in here
println(userData)
}
})
}
but I get error message:
java.lang.ClassCastException: com.google.gson.internal.LinkedTreeMap
cannot be cast to com.ssss.lakuinkotlin.Model.User
I give comment in the code above the location of the error. I don't why it happened.
to be honest, I am not if this is the correct way to catch user data from general response JSON like the the JSON above. is there a better way ?

You can use generics to achieve it
class Response<Data> constructor() : ResponseSimple() {
#SerializedName(FIELD_DATA)
var data: Data? = null
private constructor(data: Data) : this() {
this.data = data
}
companion object {
const val FIELD_SUCCESS = "success"
const val FIELD_ERROR = "error"
const val FIELD_DATA = "data"
const val FIELD_MESSAGE = "message"
#JvmStatic
fun <Data> create(data: Data): Response<Data> {
return Response(data)
}
}
}
And ResponseSimple is
open class ResponseSimple {
#SerializedName(Response.FIELD_ERROR)
var error: String = ""
#SerializedName(Response.FIELD_SUCCESS)
var succes: Boolean = false
#SerializedName(Response.FIELD_MESSAGE)
var message:String = ""
}
Then api response should be Call<Response<ServerData>>.
And about ClassCastException, you can't convert ServerData to User just using as.
You need to use Call<Response<ArrayList<User>>> or create class converter.

Try replacing this line :
val userList = lakuinServerData?.data as List<User>
with:
val userList = lakuinServerData?.data as new TypeToken<List<User>>(){}.getType()

How To Filter Retrofit2 Json Response To Keep Only Certain Elements In ArrayList

I'm new to kotlin so this maybe a very easy issue to resolve.
What I'm trying to do is filter the json response that I receive using Retrofit2 before I display the images in a grid with a RecyclerView.
instagram.com/explore/tags/{hashtag}/?__a=1&max_id= Using Retrofit2 I'm able to get the data response fine and also display the given url images in a RecyclerView.
I have not been successful in using the filter, map, loops and conditions to remove elements from the Arraylist. I do not understand these to the fullest extent but I have searched looking for solutions and those are what I came apon.
Interface
interface InstagramDataFetcher
{
#GET("tags/{tag}/?__a=1&max_id=")
fun getInstagramData(#Path("tag") hashtag: String) : Call <InstagramResponse>
}
Where I get my response from and also get StringIndexOutOfBoundsException
class InstagramFeedFragment : Fragment()
{
private fun onResponse()
{
val service = RestAPI.retrofitInstance?.create(InstagramDataFetcher::class.java)
val call = service?.getInstagramData("hashtag")
call?.enqueue(object : Callback<InstagramResponse>
{
override fun onFailure(call: Call<InstagramResponse>, t: Throwable)
{
Log.d("FEED", " $t")
}
override fun onResponse(
call: Call<InstagramResponse>, response: Response<InstagramResponse>
)
{
//for ((index, value) in data.withIndex())
if (response.isSuccessful)
{
var data: ArrayList<InstagramResponse.InstagramEdgesResponse>? = null
val body = response.body()
data = body!!.graphql.hashtag.edge_hashtag_to_media.edges
for ((index, value) in data.withIndex())
{
if(value.node.accessibility_caption[index].toString().contains("text") ||
value.node.accessibility_caption[index].toString().contains("person"))
{
data.drop(index)
}
}
recyclerView.adapter = InstagramGridAdapter(data, parentFragment!!.context!!)
}
}
})
}
}
This is my model class
data class InstagramResponse(val graphql: InstagramGraphqlResponse)
{
data class InstagramGraphqlResponse(val hashtag: InstagramHashtagResponse)
data class InstagramHashtagResponse(val edge_hashtag_to_media: InstagramHashtagToMediaResponse)
data class InstagramHashtagToMediaResponse(
val page_info: InstagramPageInfo,
val edges: ArrayList<InstagramEdgesResponse>
)
data class InstagramPageInfo(
val has_next_page: Boolean,
val end_cursor: String
)
data class InstagramEdgesResponse(val node: InstagramNodeResponse)
data class InstagramNodeResponse(
val __typename: String,
val shortcode: String,
val display_url: String,
val thumbnail_src: String,
val thumbnail_resources: ArrayList<InstagramThumbnailResourceResponse>,
val is_video: Boolean,
val accessibility_caption: String
)
data class InstagramThumbnailResourceResponse(
val src: String,
val config_width: Int,
val config_height: Int
)
}
Simply again, I want to just remove elements from the arraylist that match certain things what I don't want. For instance. the "is_video" value that comes from the json. I want to go through the arraylist and remove all elements that have "is_video" as true.
Thanks

If you asking how to filter the list then below is the demo.
You just need to use filter on your data which is an ArrayList. I've tried keeping the same structure for the models so that you can get a better understanding.
fun main() {
val first = InstagramNodeResponse(
title = "first",
is_video = true
)
val second = InstagramNodeResponse(
title = "second",
is_video = false
)
val list: ArrayList<InstagramEdgesResponse> = arrayListOf(
InstagramEdgesResponse(node = first),
InstagramEdgesResponse(node = second)
)
val itemsWithVideo = list.filter { it.node.is_video == true }
val itemsWithoutVideo = list.filter { it.node.is_video == false }
println(itemsWithVideo.map { it.node.title }) // [first]
println(itemsWithoutVideo.map { it.node.title }) // [second]
}
// Models
data class InstagramEdgesResponse(val node: InstagramNodeResponse)
data class InstagramNodeResponse(
val title: String,
val is_video: Boolean
)

how to parse data from json

i tried to parse json data, but it kind of weird because it not show the right data but if i tried to called json on browser it has the right data.
so this is how i parse the json data
doAsync {
val url = localhost.getMovie()
val request = okhttp3.Request.Builder().url(url).build()
val client = OkHttpClient()
uiThread {
client.newCall(request).enqueue(object : Callback, okhttp3.Callback {
override fun onResponse(call: okhttp3.Call?, response: okhttp3.Response?) {
val body = response?.body()?.string()
println(body)
uiThread {
val gson = GsonBuilder().create()
val movieFeed = gson.fromJson(body, Movie2Response::class.java)
Log.v("body", ""+body)
Log.v("feed", ""+movieFeed.data)
uiThread {
}
}
}
override fun onFailure(call: okhttp3.Call?, e: IOException) {
println("failed")
}
})
}
}
movie response
class Movie2Response (val data: MutableList<Movie2>)
movie
class Movie2 (
#SerializedName("id")
var movieId: String? = null,
#SerializedName("description")
var synopsis: String? = null,
#SerializedName("release_date")
var release: String? = null,
#SerializedName("poster")
var poster: String? = null,
#SerializedName("genre")
var genre: String? = null,
#SerializedName("title")
var title: String? = null
)
and this is what i got from the json data
V/body: {"data":[{"title":"Aquaman","description":""........
V/feed: [com.mqa.android.moviereview.model.Movie2#7509e04, com.mqa.android.moviereview.model.Movie2#890afed, com.mqa.android.moviereview.model.Movie2#9834e22, com.mqa.android.moviereview.model.Movie2#f02d0b3, com.mqa.android.moviereview.model.Movie2#d3b9670, com.mqa.android.moviereview.model.Movie2#4d55de9, com.mqa.android.moviereview.model.Movie2#cac2a6e, com.mqa.android.moviereview.model.Movie2#94fc50f, com.mqa.android.moviereview.model.Movie2#d9ba99c]
it shows right in body but in the array it show like that. please help what is wrong with it. because i want to show the title data to the spinner

Your code worked pretty well as the log results showed. The real problem is the log function Log.v("feed", ""+movieFeed.data). If you want to show pretty log, you should override the toString() method in Movie2 class by:
Open Movie2 and right click in the editor -> Generate -> then click toString() to override it.
For data class in Kotlin, you can just add data before class keyword.

Everything okey with you data. You just forgot adding default realisation to log this object.
class Movie2(/*your fields*/)
just add data before class. will be something like that
data class Movie2(/*your fields*/)
Kotlin doesn't know ho toString you Movie2. If you wanna default realisation use data class

How to get GSON & Retrofit to serialize and map an array from a JSON response into a String?

I am making an API request which returns some array values. I need to serialize these array values so that I can assign them to their corresponding class attributes (which are String types).
Now I know how to use GSON to serialize and deserialize lists, but with Retrofit the mapping is done automatically. This means that if my attribute is of type String, the API call returns the error "Expected a String but received an Array instead". How do I get around this so that I can receive them as arrays without failure, and them store them as strings subsequently?
My API Response:
{
"utterances": [{
"langs": ["eng", "afr", "xho", "zul"],
"utts": [
"Have you been here before?",
"Was u al hier gewees?",
"Ingaba wakhe weza apha ngaphambili?",
"Ingabe uke weza lapha ngaphambilini?"
],
"responses": [
["Yes", "No"],
["Ja", "Nee"],
["Ewe", "Hayi"],
["Yebo", "Cha"]
]
},
{
"langs": ["eng", "afr", "xho", "zul"],
"utts": [
"How are you?",
"Hoe gaan dit met jou?",
"unjani?",
"unjani?"
],
"responses": [
["Good", "Bad"],
["Goed", "sleg"],
["ezilungileyo", "ezimbi"],
["kuhle", "kubi"]
]
}
]
}
My UtteranceResponse class:
class UtteranceResponse {
#SerializedName("status")
var status: String? = null
#SerializedName("count")
var count: Int = 0
#SerializedName("utterances")
var utterances: ArrayList<Utterance>? = null
}
My Utterance class:
class Utterance: SugarRecord {
#SerializedName ("langs")
var langs: String? = null
#SerializedName ("utts")
var utterances_text: String? = null
var utterances_tts: String? = null
#SerializedName ("responses")
var responses_text: String? = null
constructor(){
}
}
And finally the calling function:
fun getUtterancesFromWebservice (){
val apiService = ApiInterface.create()
val call = apiService.getUtteranceDetails()
call.enqueue(object: Callback<UtteranceResponse> {
override fun onResponse(call: Call<UtteranceResponse>, response: retrofit2.Response<UtteranceResponse>?) {
if (response != null) {
if (response.body()?.utterances != null){
var list: List<Utterance> = response.body()?.utterances!!
val utterances: Utterance = list[0]
//storeUtterancesFromList(list)
} else {
Log.d ("Response:", response.body().toString())
}
}else{
Log.d ("responseResult", "NULL")
}
}
override fun onFailure(call: Call<UtteranceResponse>, t: Throwable) {
Log.e("SHIT", t.toString())
}
})
}
UPDATE
My API Interface as well:
#GET("bins/1ahazo")
abstract fun getUtteranceDetails():Call<UtteranceResponse>
companion object Factory {
const val BASE_URL = "https://api.myjson.com/"
fun create(): ApiInterface {
val gson = GsonBuilder().setPrettyPrinting().create()
val retrofit = Retrofit.Builder()
.baseUrl(BASE_URL)
.addConverterFactory(GsonConverterFactory.create())
.build()
return retrofit.create(ApiInterface::class.java)
}
}

You are returning single object not list. Change Call<UtteranceResponse> in ApiInterface to
Call<List<Utterance>>
and for converting list to string list to string and string to list
class Utterance: SugarRecord {
#SerializedName ("langs")
var langs: List<String?>? = null
#SerializedName ("utts")
var utterances_text: String? = null
var utterances_tts: List<String?>? = null
#SerializedName ("responses")
var responses_tex:List<List<String?>?>? = null;
constructor(){
}
}