Retrofit's service generator with change Api Url implementation

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import okhttp3.OkHttpClient;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;

/**
 * Created by mladenrakonjac on 01/06/16.
 */
public class ServiceGenerator {

    public static String apiBaseUrl = Constants.BASE_API_URL;
    private static Retrofit retrofit;

    private static OkHttpClient.Builder httpClient = new OkHttpClient.Builder();

    private static Gson gson = new GsonBuilder()
            .setDateFormat("yyyy-MM-dd'T'HH:mm:ss")
            .create();

    private static Retrofit.Builder builder =
            new Retrofit.Builder()
                    .baseUrl(apiBaseUrl)
                    .addConverterFactory(GsonConverterFactory.create(gson));

    public static void changeApiBaseUrl(String newApiBaseUrl) {
        apiBaseUrl = newApiBaseUrl;

        builder = new Retrofit.Builder()
                .addConverterFactory(GsonConverterFactory.create())
                .baseUrl(apiBaseUrl);
    }

    public static <S> S createService(Class<S> serviceClass) {
        Retrofit retrofit = builder.client(httpClient.build()).build();
        return retrofit.create(serviceClass);
    }
}