/**
   * Converts the byte array to hex string.
   *
   * @param raw the data.
   * @return the hex string.
   */
  private String getHex(byte[] raw) {
    if (raw == null) return null;

    StringBuilder hex = new StringBuilder(2 * raw.length);
    Formatter f = new Formatter(hex);
    try {
      for (byte b : raw) f.format("%02x", b);
    } finally {
      f.close();
    }
    return hex.toString();
  }
 /**
  * Calculates the hash of the certificate known as the "thumbprint" and returns it as a string
  * representation.
  *
  * @param cert The certificate to hash.
  * @param algorithm The hash algorithm to use.
  * @return The SHA-1 hash of the certificate.
  * @throws CertificateException
  */
 private static String getThumbprint(X509Certificate cert, String algorithm)
     throws CertificateException {
   MessageDigest digest;
   try {
     digest = MessageDigest.getInstance(algorithm);
   } catch (NoSuchAlgorithmException e) {
     throw new CertificateException(e);
   }
   byte[] encodedCert = cert.getEncoded();
   StringBuilder sb = new StringBuilder(encodedCert.length * 2);
   Formatter f = new Formatter(sb);
   try {
     for (byte b : digest.digest(encodedCert)) f.format("%02x", b);
   } finally {
     f.close();
   }
   return sb.toString();
 }