This can be done without GSON or any other third party library:

@Throws(JSONException::class)
fun JSONObject.toMap(): Map<String, Any> {
    val map = mutableMapOf<String, Any>()
    val keysItr: Iterator<String> = this.keys()
    while (keysItr.hasNext()) {
        val key = keysItr.next()
        var value: Any = this.get(key)
        when (value) {
            is JSONArray -> value = value.toList()
            is JSONObject -> value = value.toMap()
        }
        map[key] = value
    }
    return map
}

@Throws(JSONException::class)
fun JSONArray.toList(): List<Any> {
    val list = mutableListOf<Any>()
    for (i in 0 until this.length()) {
        var value: Any = this[i]
        when (value) {
            is JSONArray -> value = value.toList()
            is JSONObject -> value = value.toMap()
        }
        list.add(value)
    }
    return list
}

Usage to convert JSONArray to List:

val jsonArray = JSONArray(jsonArrStr)
val list = jsonArray.toList()

Usage to convert JSONObject to Map:

val jsonObject = JSONObject(jsonObjStr)
val map = jsonObject.toMap()

More info is here

[{
  "description":"My expense to others",
  "items":["aaa","bbb"],
  "name":"My Expense"
 },
 {
  "description":"My expense to others","
  items":["aaa","bbb"],
  "name":"My Expense"
 }]

Kotlin Code

val gson = GsonBuilder().create()
val Model= gson.fromJson(body,Array<GroupModel>::class.java).toList()

Gradle

implementation 'com.google.code.gson:gson:2.8.5'

put adds the list as an element to the JSONArray. Thats not what you want. You want your JSONArray to represent the list.

JSONArray offers a constructor for that:

val jsonArray = JSONArray(listOf(1, 2, 3))

But there is a much easier way. You don't need to worry about single properties. Just pass the whole POJO.

Let's say you have this:

class QuoteData(val id: Int, val quoteId: Int, travellerId: Int?)
class TravelerData(val userQuoteTravellers: List<QuoteData>)

val travelerData = TravelerData(listOf(QuoteData(1354, 546, null)))

You just have to pass travelerData to the JSONArray constructor:

val travelerDataJson = JSONArray(travelerData)

and it will be represented like this:

"userQuoteTravellers": [ { "id": 1354, "quoteId": 526, "travellerId": null } ]

You could try doing this instead:

val objectList = gson.fromJson(json, Array<SomeObject>::class.java).asList()

EDIT [14th January 2020]: You should NOT be using GSON anymore. Jake Wharton, one of the projects maintainers, suggests using Moshi, Jackson or kotlinx.serialization.

As far as it seems, there is no builtin method to convert JSONArray to List. However, You can use Kotlin tricks to make the java code much shorter:

fun JSONArray.toMutableList(): MutableList<JSONObject> = MutableList(length(), this::getJSONObject)

Note that JSONArray may have values that are not JSONObject (but JSONArray for example). If you are not sure the array contains just object, use the following method:

fun JSONArray.toMutableList(): MutableList<Any> = MutableList(length(), this::get)

If you are using the JSON-java library and not the android one, then you can use JSONArray.toList() which returns a list you can modify.

Array<String> and ArrayList<String> are 2 different types.

What you need to provide is Array<String> but what you are actually providing is ArrayList<String>.

val list = Array(pics.length()) {
    pics.getString(it)
}

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
    }

Maybe this is the kotlin code you want, converted from your Java code:

val gson = GsonBuilder().create()
val theList = gson.fromJson<ArrayList<String>>(stringObject, object :TypeToken<ArrayList<String>>(){}.type)

Instead of using List

val list: List<String> = gson.fromJson(jsonString, Array<String>::class.java).asList()

Use Map (This will parse your json data into map)

val map = gson.fromJson<Map<String, String>>(jsonString, MutableMap::class.java)

Gson().toJson(myList) returns a String.

You should build a JSONArray and add its elements. Then add this true array. This just works:

JsonArray array = new JsonArray();
array.add("test1");
array.add("test2");
JsonObject object = new JsonObject();
object.add("arr", array);

You also seam to be messing up JSON and GSON objects. Here I just used Gson objects.