生成无重复随机token

 public static void main(String[] args) {        String token = System.currentTimeMillis() + new Random(999999999).nextInt() + "";        MessageDigest md = null;        try {            // 进行MD5加密            md = MessageDigest.getInstance("md5");            byte[] md5 = md.digest(token.getBytes());            // 进行base64转换            BASE64Encoder encoder = new BASE64Encoder();            String result = encoder.encode(md5);            System.out.println(result);        } catch (NoSuchAlgorithmException e) {            e.printStackTrace();        }    }