指定日期的前后几天的日期或者月份

1 

 public static String asd(int past, String time, Integer type) {
        //time  yyyy-MM-dd
        LocalDate now = LocalDate.now();
        Integer year = Integer.valueOf(time.substring(0, 4));
        Integer month = Integer.valueOf(time.substring(5, 7));
        if (type == 1) {
            //天
            Integer day = Integer.valueOf(time.substring(8, 10));
            LocalDate localDate = LocalDate.of(year, month, day);
            LocalDate localTimeDay = localDate.minusDays(past);
            return localTimeDay.toString();
        } else if (type == 2) {
            Integer day = 01;
            //月
            LocalDate localDate = LocalDate.of(year, month, day);
            LocalDate localTimeMonth = localDate.minusMonths(past);
            return localTimeMonth.toString().substring(0, 7);
        }
        return now.toString();
    }

但是这种也不算是很完美  按照下标截取还是很不保险 ，测试的时候就发现 有人传 2021-6-2  这种不是标准格式的。

所以有第二种方式。

2 

/**
 * 获取指定日期的前几天或月份的日期
 *
 * @param past
 * @return
 */
public static String getPastDate(int past, String time, Integer type) {
    //改为以- 截取 防止出现 不是标准时间格式
    LocalDate now = LocalDate.now();
    int index = time.indexOf("-");
    Integer month =0;
    int indexOf=0;
    if(time.length()>7){
        indexOf = time.indexOf("-", index + 1);
         month = Integer.valueOf(time.substring(index + 1, indexOf));
    }else {
        String str=time.substring(0, time.indexOf("-"));
        String bb=time.substring(str.length()+1, time.length());
       month = Integer.valueOf(bb);
    }
    Integer year = Integer.valueOf(time.substring(0, time.indexOf("-")));
    if (type == 1) {
        //天
        Integer day = Integer.valueOf(time.substring(indexOf + 1));
        LocalDate localDate = LocalDate.of(year, month, day);
        LocalDate localTimeDay = localDate.minusDays(past);
        return localTimeDay.toString();
    } else if (type == 2) {
        Integer day = 01;
        //月
        LocalDate localDate = LocalDate.of(year, month, day);
        LocalDate localTimeMonth = localDate.minusMonths(past);
        return localTimeMonth.toString().substring(0, 7);
    }
    return now.toString();
}