Retrofit2+RxJava如何从服务器获取自定义错误？

public interface ApiService {
    @GET("data")
    Observable<ResponseData> getData();
}

public class ApiManager {
    private static final String BASE_URL = "http://example.com/api/";
    private static final int TIMEOUT = 30;

    private ApiService apiService;

    public ApiManager() {
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(BASE_URL)
                .addConverterFactory(GsonConverterFactory.create())
                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .build();

        apiService = retrofit.create(ApiService.class);
    }

    public Observable<ResponseData> getData() {
        return apiService.getData()
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .onErrorResumeNext(new Function<Throwable, ObservableSource<? extends ResponseData>>() {
                    @Override
                    public ObservableSource<? extends ResponseData> apply(Throwable throwable) throws Exception {
                        // 在这里处理错误，可以根据服务器返回的错误码进行判断和处理
                        // 返回一个自定义的错误响应对象
                        return Observable.error(new CustomErrorException(throwable.getMessage()));
                    }
                });
    }
}

ApiManager apiManager = new ApiManager();
apiManager.getData()
        .subscribe(new Observer<ResponseData>() {
            @Override
            public void onSubscribe(Disposable d) {
                // 可以在这里进行一些初始化操作
            }

            @Override
            public void onNext(ResponseData responseData) {
                // 处理服务器返回的数据
            }

            @Override
            public void onError(Throwable e) {
                // 处理自定义的错误信息
                if (e instanceof CustomErrorException) {
                    CustomErrorException customError = (CustomErrorException) e;
                    String errorMessage = customError.getMessage();
                    // 显示错误信息给用户或进行其他操作
                } else {
                    // 处理其他类型的错误
                }
            }

            @Override
            public void onComplete() {
                // 请求完成后的操作
            }
        });