Gson Dynamic Key Deserializer

Gson Dynamic Key Deserializer.java

package me.peerapong.android_dynamicjsonkey;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;
import com.google.gson.reflect.TypeToken;

import java.lang.reflect.Type;
import java.util.HashMap;
import java.util.Map;

import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;
import retrofit2.http.GET;

public class MainActivity extends AppCompatActivity {

    private static final String TAG = MainActivity.class.getSimpleName();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Gson gson = new GsonBuilder()
                .registerTypeAdapter(new TypeToken<NumberResponse>() {
                }.getType(), new NumberResponse.NumberResponseDeserializer())
                .create();

        API api = new Retrofit.Builder()
                .baseUrl("http://172.20.10.2:8087/")
                .addConverterFactory(GsonConverterFactory.create(gson))
                .build()
                .create(API.class);
        api.getNumber().enqueue(new Callback<NumberResponse>() {
            @Override
            public void onResponse(Call<NumberResponse> call, Response<NumberResponse> response) {
                NumberResponse numberResponse = response.body();
                Log.d(TAG, "onResponse: " + numberResponse.getStringNumberMap().toString());
                /*
                OUTPUT: D/MainActivity: onResponse: {1={id=1.0, name=ONE}, 2={id=2.0, name=TWO}, 3={id=3.0, name=THREE}}
                */
            }

            @Override
            public void onFailure(Call<NumberResponse> call, Throwable t) {
                t.printStackTrace();
            }
        });
    }

    public interface API {

        /*
        {
          "1": {"id": 1, "name": "ONE"},
          "2": {"id": 2, "name": "TWO"},
          "3": {"id": 3, "name": "THREE"}
        }
         */
        @GET("/dynamic.json")
        Call<NumberResponse> getNumber();
    }

    static class NumberResponse {
        public Map<String, Number> mStringNumberMap;

        public Map<String, Number> getStringNumberMap() {
            return mStringNumberMap;
        }

        public void setStringNumberMap(Map<String, Number> stringNumberMap) {
            mStringNumberMap = stringNumberMap;
        }

        public static class Number {
            public int id;
            public String name;

            @Override
            public String toString() {
                return "Number{" +
                        "id=" + id +
                        ", name='" + name + '\'' +
                        '}';
            }
        }

        public static class NumberResponseDeserializer implements JsonDeserializer<NumberResponse> {
            @Override
            public NumberResponse deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {

                NumberResponse response = new Gson().fromJson(json, NumberResponse.class);

                Map<String, Number> map = new HashMap<>();
                map = (Map<String, Number>) new Gson().fromJson(json, map.getClass());

                response.setStringNumberMap(map);
                return response;
            }
        }
    }
}

or if you (future reader) don't mind adding a little (or a lot) performance cost (due to reflections in runtime), use TypeToken for GSON, see the article here: http://findnerd.com/list/view/Parse-Json-Object-with-dynamic-keys-using-Gson-/24094/