code: static byte[] encode(int count) {
          // 计算需要填充的位数
          int amountToPad = BLOCK_SIZE - (count % BLOCK_SIZE);
          if (amountToPad == 0) {
              amountToPad = BLOCK_SIZE;
          }
          // 获得补位所用的字符
          char padChr = chr(amountToPad);
          StringBuilder tmp = new StringBuilder();
          for (int index = 0; index < amountToPad; index++) {
              tmp.append(padChr);
          }
          return tmp.toString().getBytes(CHARSET);
      }
docs: 获得对明文进行补位填充的字节.
  
  @param count 需要进行填充补位操作的明文字节个数
  @return 补齐用的字节数组