// Java SDK 获取Root证书SN  AntCertificationUtil.getRootCertSN();
/**
 * 从公钥证书中提取公钥序列号
 *
 * @param certPath 公钥证书存放路径，例如:/home/admin/cert.crt
 * @return 公钥证书序列号
 * @throws AlipayApiException
 */
public static String getCertSN(String certPath) throws AlipayApiException {
    InputStream inputStream = null;
    try {
        inputStream = new FileInputStream(certPath);
        CertificateFactory cf = CertificateFactory.getInstance("X.509");
        X509Certificate cert = (X509Certificate) cf.generateCertificate(inputStream);
        MessageDigest md = MessageDigest.getInstance("MD5");
        md.update((cert.getIssuerX500Principal().getName() + cert.getSerialNumber()).getBytes());
        String certSN = new BigInteger(1, md.digest()).toString(16);
        //BigInteger会把0省略掉，需补全至32位
        certSN = fillMD5(certSN);
        return certSN;

    } catch (NoSuchAlgorithmException e) {
        throw new AlipayApiException(e);
    } catch (IOException e) {
        throw new AlipayApiException(e);
    } catch (CertificateException e) {
        throw new AlipayApiException(e);
    } finally {
        try {
            if (inputStream != null) {
                inputStream.close();
            }
        } catch (IOException e) {
            throw new AlipayApiException(e);
        }
    }
}

// Java SDK 获取证书SN  AlipaySignature.getCertSN();
/**
 * 获取根证书序列号
 *
 * @param rootCertContent
 * @return
 */
public static String getRootCertSN(String rootCertContent) {
    String rootCertSN = null;
    try {
        X509Certificate[] x509Certificates = readPemCertChain(rootCertContent);
        MessageDigest md = MessageDigest.getInstance("MD5");
        for (X509Certificate c : x509Certificates) {
            if (c.getSigAlgOID().startsWith("1.2.840.113549.1.1")) {
                md.update((c.getIssuerX500Principal().getName() + c.getSerialNumber()).getBytes());
                String certSN = new BigInteger(1, md.digest()).toString(16);
                //BigInteger会把0省略掉，需补全至32位
                certSN = fillMD5(certSN);
                if (StringUtils.isEmpty(rootCertSN)) {
                    rootCertSN = certSN;
                } else {
                    rootCertSN = rootCertSN + "_" + certSN;
                }
            }

        }
    } catch (Exception e) {
        AlipayLogger.logBizError(("提取根证书失败"));
    }
    return rootCertSN;

}

private static String fillMD5(String md5) {
    return md5.length() == 32 ? md5 : fillMD5("0" + md5);
}