为什么scanner.next返回null？

Question

 public static String getResponseFromHttpUrl(URL url) throws IOException {
    HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
    try {
        InputStream in = urlConnection.getInputStream();
        Scanner scanner = new Scanner(in);
        scanner.useDelimiter("\\A");
        boolean hasInput = scanner.hasNext();
        if (hasInput) {
            return scanner.next();
        } else {
            return null;
        }
    }
    finally {
        urlConnection.disconnect();
    }
}

我正在mainActivity的doinbackground方法内的异步任务中调用此函数，但它始终返回null。当我尝试调试时，hasInput为true ..任何建议?? TIA。