如何使用改进的rxjava仅在第一次api调用失败时进行另一次api调用

Observable.create(new ObservableOnSubscribe<String>() {
    @Override
    public void subscribe(ObservableEmitter<String> emitter) throws Exception {
        // 执行API调用，这里假设调用失败
        emitter.onError(new Exception("API调用失败"));
    }
})
.retryWhen(new Function<Observable<Throwable>, ObservableSource<?>>() {
    @Override
    public ObservableSource<?> apply(Observable<Throwable> throwableObservable) throws Exception {
        // 定义重试条件和行为
        return throwableObservable.zipWith(Observable.range(1, 3), new BiFunction<Throwable, Integer, Integer>() {
            @Override
            public Integer apply(Throwable throwable, Integer retryCount) throws Exception {
                // 判断是否需要重试
                if (retryCount <= 3 && throwable instanceof Exception) {
                    return retryCount;
                } else {
                    throw Exceptions.propagate(throwable);
                }
            }
        }).flatMap(new Function<Integer, ObservableSource<?>>() {
            @Override
            public ObservableSource<?> apply(Integer retryCount) throws Exception {
                // 进行重试操作
                return Observable.timer(retryCount, TimeUnit.SECONDS);
            }
        });
    }
})
.subscribe(new Consumer<String>() {
    @Override
    public void accept(String result) throws Exception {
        // 处理API调用成功的结果
    }
}, new Consumer<Throwable>() {
    @Override
    public void accept(Throwable throwable) throws Exception {
        // 处理API调用失败的情况
    }
});