docs: private void setDbCodeCollection() {
          dbCodeCollection = new ArrayList<String>(shardingNum);
          int codeLength = Integer.toBinaryString(shardingNum - 1).length();
          for (int i = 0; i < shardingNum; i++) {
              String dbcode = Integer.toBinaryString(i);
              for (int j = dbcode.length(); j < codeLength; j++) {
                  dbcode = "0" + dbcode;
              }
              dbCodeCollection.add(i, dbcode);
          }
      }