public static String checksum(File file) throws IOException, NoSuchAlgorithmException {
        MessageDigest digest = MessageDigest.getInstance("SHA-256");
        BufferedInputStream bis = new BufferedInputStream(new FileInputStream(file));
        byte[] buff = new byte[bis.available()];
        bis.read(buff, 0, buff.length);
        byte[] hash = digest.digest(buff);
        return new BASE64Encoder().encode(hash);
    }