说明：  数字摘要工具类 getDigitalDigest(String fileName) 默认使用SHA1生成数字签名 getDigitalDigest(String fileName, String algorithm) 根据需要传入签名方法，如果签名方法不存在抛出NoSuchAlgorithmException
(Abstract digital tools class getDigitalDigest (String fileName) defaults to SHA1 to generate a digital signature getDigitalDigest (String fileName, String algorithm) throws NoSuchAlgorithmException If the signature method does not exist based on the need to pass the signature method,)