RequestCallback - a subclass of Retrofit's Callback class. Makes things simpler by taking care of showing and hiding progress view (for example animated spinner) and providing higher level of abstraction with its callbacks.

HttpStatus.java

public enum HttpStatus {
    UNAUTHORIZED(401),
    FORBIDDEN(403),
    NOT_FOUND(404),

    OTHER_ERROR(null);

    private static HashMap<Integer, HttpStatus> map;
    private Integer code;

    HttpStatus(Integer code) {
        this.code = code;
    }

    public static HttpStatus getStatusByCode(Integer code) {
        if (map == null) {
            initializeMapping();
        }
        if (map.containsKey(code)) {
            return map.get(code);
        }

        HttpStatus otherError = OTHER_ERROR;
        OTHER_ERROR.setCode(code);
        return otherError;
    }

    private static void initializeMapping() {
        map = new HashMap<Integer, HttpStatus>();
        for (HttpStatus httpStatus : HttpStatus.values()) {
            map.put(httpStatus.code, httpStatus);
        }
    }

    public Integer getCode() {
        return code;
    }

    private void setCode(Integer code) {
        this.code = code;
    }
}

LoadingUI.java

public interface LoadingUI {

    void showProgressView();

    void hideProgressView();

    void onNetworkErrorOccurred();

    void onGenericErrorOccurred();
}

RequestCallback.java

public abstract class RequestCallback <T> implements Callback<T> {
    private LoadingUI ui;
    private boolean shouldUseProgressView = true;

    public RequestCallback(LoadingUI ui) {
        this.ui = ui;
    }

    public RequestCallback(LoadingUI ui, boolean shouldUseProgressView) {
        this.ui = ui;
        this.shouldUseProgressView = shouldUseProgressView;
    }

    public abstract void onSuccess(T body, Response response);

    public abstract void onErrorOccurred(HttpStatus statusCode);


    @Override
    public final void onResponse(Response<T> response, Retrofit retrofit) {
        if (response.isSuccess()) {
            onSuccess(response.body(), response);
        } else {
            onErrorOccurred(HttpStatus.getStatusByCode(response.code()));
        }

        tryHideProgressView();
    }

    protected void tryHideProgressView() {
        if (shouldUseProgressView) {
            ui.hideProgressView();
        }
    }

    @Override
    public final void onFailure(Throwable throwable) {
        if (throwable instanceof IOException) {
            onNetworkErrorOccurred();
        } else {
            onGenericErrorOccurred();
        }
        tryHideProgressView();

    }

    protected void onNetworkErrorOccurred() {
        ui.onNetworkErrorOccurred();
    }

    protected void onGenericErrorOccurred() {
        ui.onGenericErrorOccurred();
    }

}