code: private static String getUUID(int length, UUID uuid) {
          int groupLength = 32 / length;
          StringBuilder sb = new StringBuilder();
          String id = uuid.toString().replace("-", "");
          for (int i = 0; i < length; i++) {
              String str = id.substring(i * groupLength, i * groupLength + groupLength);
              int x = Integer.parseInt(str, 16);
              sb.append(chars[x % 0x3E]);
          }
          return sb.toString();
      }
docs: 生成指定长度的uuid