Using Gson in Kotlin to parse JSON array

Question

Trying to parse JSON array in Kotlin, made it work for single JSON object to a WeatherObject object (code snippet below)

{ "coord": {     "lon": -2.93,     "lat": 43.26 },  "weather": [{     "id": 802,     "main": "Clouds",     "description": "scattered clouds",     "icon": "03d" }],  "main": {     "temp": 283.681,     "temp_min": 283.681,     "temp_max": 283.681,     "pressure": 991.72,     "sea_level": 1034.92,     "grnd_leve": 991.72,     "humidity": 98 }, "wind": {     "speed": 1.07,     "deg": 144.001 },  "dt": 1429773245, "id": 3128026, "name": "Bilbao", "cod": 200 

}

but not sure how to do the same if the JSON is a array of same JSON object, i.e.

from json array [ {}, {} …] to ArrayList<WeatherObject >

something like:

fun getWeatherObjectArrayFromJson(jsonStr: String): ArrayList<WeatherObject &gt 

having problem with gsonBuilder.registerTypeAdapter(ArrayList<WeatherObject &gt::class.java, WeatherDeserializer())

class WeatherObject {      var main: String = ""     var description: String = ""     var temp: Float = 0.0f     var tempMax: Float = 0.0f     var tempMin: Float = 0.0f     var humidity: Int = 0     var wind: WindObject? = null  }  class WeatherDeserializer : JsonDeserializer<WeatherObject> {      override fun deserialize(json: JsonElement?, typeOfT: Type?, context: JsonDeserializationContext?): WeatherObject? {         val jsonObj = json as JsonObject          val wheather = WeatherObject()         val wind = WindObject()          val jsonWeatherArray = jsonObj.getAsJsonArray("weather").get(0)         val jsonMainObj = jsonObj.getAsJsonObject("main")         val jsonWindObj = jsonObj.getAsJsonObject("wind")          wheather.main = jsonWeatherArray.asJsonObject.get("main").asString         wheather.description = jsonWeatherArray.asJsonObject.get("description").asString         wheather.temp = jsonMainObj.get("temp").asFloat         wheather.tempMax = jsonMainObj.get("temp_max").asFloat         wheather.tempMin = jsonMainObj.get("temp_min").asFloat         wheather.humidity = jsonMainObj.get("humidity").asInt         wind.speed = jsonWindObj.get("speed").asFloat         wind.deg = jsonWindObj.get("deg").asFloat         wheather.wind = wind          return wheather      } }  fun getWeatherObjectFromJson(jsonStr: String): WeatherObject {          var stringReader: StringReader = StringReader(jsonStr)         var jsonReader: JsonReader = JsonReader(stringReader)          val gsonBuilder = GsonBuilder().serializeNulls()         gsonBuilder.registerTypeAdapter(WeatherObject::class.java, WeatherDeserializer())         val gson = gsonBuilder.create()          val weather: WeatherObject = gson.fromJson(jsonReader, WeatherObject::class.java)          return weather     } 

Update:

tried the solution from chandil03, IT IS WORKING! put the testing json array data and the function here:

tried

fun getWeatherObjectFromJsonArray(jsonArrayStr: String): List<WeatherObject> {          var stringReader: StringReader = StringReader(jsonStr)         //var jsonReader: JsonReader = JsonReader(stringReader)          val gsonBuilder = GsonBuilder().serializeNulls()         gsonBuilder.registerTypeAdapter(WeatherObject::class.java, WeatherDeserializer())         val gson = gsonBuilder.create()          val weatherList: List<WeatherObject> = gson.fromJson(stringReader , Array<WeatherObject>::class.java).toList()         //val weatherList: List<WeatherObject> = gson.fromJson(jsonReader, Array<WeatherObject>::class.java).toList          return weatherList     } 

got exception at

val weatherList: List<WeatherObject> = gson.fromJson(stringReader , Array<WeatherObject>::class.java).toList()  com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_ARRAY but was BEGIN_OBJECT at line 1 column 2 path $ 

the json array data is like:

[ {   "coord": {     "lon": -2.93,     "lat": 43.26   },    "weather": [{     "id": 802,     "main": "Clouds",     "description": "scattered clouds",     "icon": "03d"   }],    "main": {     "temp": 283.681,     "temp_min": 283.681,     "temp_max": 283.681,     "pressure": 991.72,     "sea_level": 1034.92,     "grnd_leve": 991.72,     "humidity": 98   },   "wind": {     "speed": 1.07,     "deg": 144.001   },   "clouds": {     "all": 36   },   "dt": 1429773245,   "id": 3128026,   "name": "Bilbao",   "cod": 200 },   {   "coord": {     "lon": -2.93,     "lat": 43.26   },    "weather": [{     "id": 802,     "main": "Clouds",     "description": "scattered clouds",     "icon": "03d"   }],    "main": {     "temp": 283.681,     "temp_min": 283.681,     "temp_max": 283.681,     "pressure": 991.72,     "sea_level": 1034.92,     "grnd_leve": 991.72,     "humidity": 98   },   "wind": {     "speed": 1.07,     "deg": 144.001   },   "clouds": {     "all": 36   },   "dt": 1429773245,   "id": 3128026,   "name": "Bilbao",   "cod": 200 } ] 

Answer 1

You need to change parameter in your fromJson() function call like following:

val weatherList: List<WeatherObject> = gson.fromJson(stringReader , Array<WeatherObject>::class.java).toList() 

You need to pass Array<WeatherObject>::class.java for class type and then convert result into List. No need to change registerTypeAdapter() function call.

Check following code:

fun getWeatherObjectFromJson(jsonStr: String): List<WeatherObject> {          var stringReader: StringReader = StringReader(jsonStr)         var jsonReader: JsonReader = JsonReader(stringReader)          val gsonBuilder = GsonBuilder().serializeNulls()         gsonBuilder.registerTypeAdapter(WeatherObject::class.java, WeatherDeserializer())         val gson = gsonBuilder.create()         val weatherList: List<WeatherObject> = gson.fromJson(stringReader , Array<WeatherObject>::class.java).toList()          return weatherList     }