Using RetroFit in Android apps

ApiClient.java

import retrofit.RestAdapter;

/**
 * Created by NODER on 3/4/2015.
 */
public class ApiClient {
    private static UserApiInterface userApiInterface;
    
    public static RestAdapter getRestAdapter(){
        return DemoApplication.getInstance().getRestAdapter();
    }
    
    public static UserApiInterface getUserApiInterface(){
        if(userApiInterface==null){
            userApiInterface = getRestAdapter().create(UserApiInterface.class);
        }
        return userApiInterface;
    }
    
    public interface ErrorCodes{
        public static final int ERR_CODE_UNAME_EXIST = 43;
        public static final int ERR_CODE_EMAIL_EXIST = 44;
        public static final int ERR_INTERNAL_SERVER = 500;
        public static final int ERR_EMAIL_DOES_NOT_EXIST = 46;
    }
}

DemoApplication.java

import android.app.Application;
/**
 * Created by NODER on 3/4/2015.
 */
public class DemoApplication extends Application {

    private OkHttpClient okHttpClient;
    private RestAdapter restAdapter;
   
  @Override
	public void onCreate() {
		super.onCreate();
		    okHttpClient = new OkHttpClient();
	}
    public OkHttpClient getOkHttpClient(){
        return okHttpClient;
    }

    public RestAdapter getRestAdapter(){
        if(restAdapter==null){
            restAdapter = new RestAdapter.Builder()
                    .setEndpoint("URL")
                    .build();
        }
        return restAdapter;
    }

}

UserApiInterface.java

import retrofit.Callback;
import retrofit.RetrofitError;
import retrofit.http.Field;
import retrofit.http.FormUrlEncoded;
import retrofit.http.GET;
import retrofit.http.POST;
import retrofit.http.Path;

/**
 * Created by NODER on 3/4/2015.
 */
public interface UserApiInterface {

    @GET("/user/search/{query}")
    public void search(@Path("query") String query, Callback<String> cb);
    
    @GET("/user/login")
    public Response login(@Query("email") String email, @Query("password") String password);
}

UserIntentService.java

/**
 * Created by NODER on 3/4/2015.
 */
public class UserIntentService extends IntentService{
    public UploadService2() {
        super("");
    }

    @Override
    protected void onHandleIntent(Intent intent) {
        Response response = ApiClient.getUserApiInterface().login("email", "password");
    }
}