WeatherDataService.java

public class WeatherService {

    private WeatherListener mListener;

    public WeatherService(WeatherListener listener) {
        this.mListener = listener;
    }

    public void getWeather(String cityName) {
        RestAdapter adapter = new RestAdapter.Builder().setEndpoint("http://api.openweathermap.org").build();
        OpenWeatherService openWeatherService = adapter.create(OpenWeatherService.class);

        openWeatherService.getWeatherData(cityName, "imperial", new Callback<WeatherData>() {
            @Override
            public void success(WeatherData weatherData, Response response) {
                mListener.onWeatherData(weatherData);
            }

            @Override
            public void failure(RetrofitError error) {
                mListener.onNoWeatherData();
            }
        });
    }
}