code: public static String toFixdLengthString(long num, int fixdlenth) {
  		StringBuffer sb = new StringBuffer();
  		String strNum = String.valueOf(num);
  		if (fixdlenth - strNum.length() >= 0) {
  			sb.append(generateZeroString(fixdlenth - strNum.length()));
  		} else {
  			throw new RuntimeException("将数字" + num + "转化为长度为" + fixdlenth + "的字符串发生异常！");
  		}
  		sb.append(strNum);
  		return sb.toString();
  	}
docs: 根据数字生成一个定长的字符串，长度不够前面补0
  
  @param num 数字
  @param fixdlenth 字符串长度
  @return 定长的字符串