[android] Retrofit 2 - Dynamic URL

If you already have your code setup and you don’t want to make changes on the different interfaces you can, use the solution described in this link. The main point is the method changeApiBaseUrl that updates the URL and recreates the Retrofit builder.

public class ServiceGenerator {  
public static String apiBaseUrl = "http://futurestud.io/api";
private static Retrofit retrofit;

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

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

// No need to instantiate this class.
private ServiceGenerator() {
}

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, AccessToken token) {
    String authToken = token.getTokenType().concat(token.getAccessToken());
    return createService(serviceClass, authToken);
}

// more methods
// ...
}

You can use it as follows:

public class DynamicBaseUrlActivity extends AppCompatActivity {

public static final String TAG = "CallInstances";
private Callback<ResponseBody> downloadCallback;

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

    downloadCallback = new Callback<ResponseBody>() {
        @Override
        public void onResponse(Call<ResponseBody> call, Response<ResponseBody> response) {
            Log.d(TAG, "server contacted at: " + call.request().url());
        }

        @Override
        public void onFailure(Call<ResponseBody> call, Throwable t) {
            Log.d(TAG, "call failed against the url: " + call.request().url());
        }
    };

    // first request
    FileDownloadService downloadService = ServiceGenerator.create(FileDownloadService.class);
    Call<ResponseBody> originalCall = downloadService.downloadFileWithFixedUrl();
    originalCall.enqueue(downloadCallback);

    // change base url
    ServiceGenerator.changeApiBaseUrl("http://development.futurestud.io/api");

    // new request against new base url
    FileDownloadService newDownloadService = ServiceGenerator.create(FileDownloadService.class);
    Call<ResponseBody> newCall = newDownloadService.downloadFileWithFixedUrl();
    newCall.enqueue(downloadCallback);
    }
}