//定义最大位数
    private final Integer DIGIT_LENGTH = 5;
    //格式化num
    if (id.length() < DIGIT_LENGTH) {
        NumberFormat nf = NumberFormat.getInstance();
        nf.setGroupingUsed(false);
        nf.setMaximumIntegerDigits(DIGIT_LENGTH);
        nf.setMinimumIntegerDigits(DIGIT_LENGTH);
        id = nf.format(num);
    }