Loading/Content/Error object for RxJava

Lce.java

import android.support.annotation.Nullable;

import io.reactivex.ObservableTransformer;
import lombok.AccessLevel;
import lombok.AllArgsConstructor;
import lombok.Getter;
import lombok.ToString;
import retrofit2.HttpException;
import retrofit2.Response;

/**
 * Idea comes from: https://tech.instacart.com/lce-modeling-data-loading-in-rxjava-b798ac98d80
 * An Lce contains either the loading flag, content, or an error.
 */

@ToString
@Getter
@AllArgsConstructor(access = AccessLevel.PRIVATE)
public class Lce<D> {

    private final boolean error;

    @Nullable
    private final Throwable errorData;

    private final boolean loading;

    @Nullable
    private final String loadingSource;

    @Nullable
    private final D data;


    public static <D> Lce<D> error(@Nullable Throwable errorData) {
        return new Lce<>(true, errorData, false, null, null);
    }

    public static <D> Lce<D> loading(@Nullable String source) {
        return new Lce<>(false, null, true, source, null);
    }

    public static <D> Lce<D> data(D data) {
        return new Lce<>(false, null, false, null, data);
    }

    /**
     * Used to transform a common Observable&lt;Response&gt; retrofit api response
     * into Observable&lt;Lce&gt;
     *
     * @param <D> The data type that the Response and Lce hold.
     * @return An observable that will emit Lce objects based on the response.
     */
    public static <D> ObservableTransformer<Response<D>, Lce<D>> transformRequestToLce() {
        return transformRequestToLce(null);
    }

    public static <D> ObservableTransformer<Response<D>, Lce<D>> transformRequestToLce(@Nullable String loadingSource) {
        return upstream -> upstream
                .map(response -> response.isSuccessful() ?
                        Lce.data(response.body()) :
                        Lce.<D>error(new HttpException(response)))
                .startWith(Lce.loading(loadingSource))
                .onErrorReturn(Lce::error);
    }
}