code: public static byte[] md5Bytes(byte[] bs) {
          if (bs == null) return null;
          MessageDigest md5;
          try {
              md5 = MessageDigest.getInstance("MD5");
          } catch (NoSuchAlgorithmException ex) {
              throw new RuntimeException(ex);
          }
          return md5.digest(bs);
      }
docs: MD5加密
  
  @param bs 待加密数据
  
  @return md5值