1，再当前日期上进行累加

   /**
     * 当前日期加减多少天
     */
    public static String getNowDateString(int day){
        return LocalDate.now().plusDays(day).format(DateTimeFormatter.ofPattern("yyyy-MM-dd"));
    }

    /**
     * 当前日期加减多少月
     */
    public static Date getNowYmdString(int month) {
        return Date.from(LocalDate.now().plusMonths(month).atStartOfDay(ZoneOffset.ofHours(8)).toInstant());
    }

    /**
     * 当前日期加减多少年后凌晨的日期+时间字符串
     */
    public static String getBeginOfYear(int year) {
        LocalDate localDate = LocalDate.now().plusYears(year);
        LocalDateTime dateTime = LocalDateTime.of(localDate.getYear(), localDate.getMonth(), localDate.getDayOfMonth(), 0, 0, 0);
        return dateTime.format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
    }

    /**
     * 当前日期加减多少天后凌晨的日期+时间字符串
     */
    public static String getBeginOfDay(int day) {
        LocalDate localDate = LocalDate.now().plusDays(day);
        LocalDateTime dateTime = LocalDateTime.of(localDate.getYear(), localDate.getMonth(), localDate.getDayOfMonth(), 0, 0, 0);
        return dateTime.format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
    }

2，获取月初周初的时间

   /**
     * 获取周初第一天的时间字符串
     */
    public static String getFirstOfWeek() {
        LocalDateTime localDate = LocalDateTime.now().with(DayOfWeek.MONDAY);
        return localDate.format(DateTimeFormatter.ofPattern("yyyy-MM-dd 00:00:00"));
    }

    /**
     * 获取周末的时间字符串
     */
    public static String getEndOfWeek() {
        LocalDateTime localDate = LocalDateTime.now().with(DayOfWeek.SUNDAY);
        return localDate.format(DateTimeFormatter.ofPattern("yyyy-MM-dd 23:59:59"));
    }

    /**
     * 获取月初第一天的时间字符串
     */
    public static String getFirstOfMonth() {
        LocalDateTime localDate = LocalDateTime.now().with(TemporalAdjusters.firstDayOfMonth());
        return localDate.format(DateTimeFormatter.ofPattern("yyyy-MM-dd 00:00:00"));
    }

    /**
     * 获取月末的时间字符串
     */
    public static String getEndOfMonth() {
        LocalDateTime localDate = LocalDateTime.now().with(TemporalAdjusters.lastDayOfMonth());
        return localDate.format(DateTimeFormatter.ofPattern("yyyy-MM-dd 23:59:59"));
    }

    /**
     * 当前日期加减多少月后的月初日期时间戳
     */
    public static long getFirstOfMonth(int lastMonth) {
        return LocalDate.now()
                .minusMonths(lastMonth)
                .with(TemporalAdjusters.firstDayOfMonth())
                .atStartOfDay(ZoneId.systemDefault())
                .toInstant()
                .toEpochMilli();
    }

    /**
     * 当前日期加减多少月后的月尾日期时间戳
     */
    public static long getLastOfMonth(int lastMonth) {
        return LocalDate.now()
                .minusMonths(lastMonth)
                .with(TemporalAdjusters.firstDayOfNextMonth())
                .atStartOfDay(ZoneId.systemDefault())
                .toInstant()
                .toEpochMilli() - 1;
    }

3，获取日期区间内月份列表 ["2022-01","2022-02"]

   /**
     * 获取日期区间内月份列表 ["2022-01","2022-02"]
     */
    public static List<String> getRankingNeedMonth(String beginTime, String endTime) {
        List<String> ymList = Lists.newArrayList();
        int intervalMonth = (int)LocalDate.parse(endTime).until(LocalDate.parse(beginTime), ChronoUnit.MONTHS);
        if (0 == intervalMonth) {
            return ymList;
        }
        for (int i = intervalMonth; i < 0; i++) {
            ymList.add(LocalDate.now().plusMonths((i + 1)).format(DateTimeFormatter.ofPattern("yyyy-MM")));
        }
        return ymList;
    }

4，计算两个日期间隔了日，时，分，秒

    /**
     * 时间转换
     */
    public static Date str2Date(String time) {
        try {
            return new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").parse(time);
        } catch (ParseException e) {
            return new Date();
        }
    }

    /**
     * 计算参数与当前时间间隔多少天多少小时多少分钟多少秒
     */
    public static String calIntervalStr(String time) {
        Date now = new Date();
        Date before = str2Date(time);
        long diff = now.getTime() - before.getTime();
        long days = diff / (1000 * 60 * 60 * 24);
        long hours = (diff - days * (1000 * 60 * 60 * 24)) / (1000* 60 * 60);
        long minutes = (diff - days * (1000 * 60 * 60 * 24) - hours * (1000 * 60 * 60)) / (1000* 60);
        long second = (diff / 1000 - days * 24 * 60 * 60 - hours * 60 * 60 - minutes * 60);
        return days + "天" + hours + "小时" + minutes + "分钟" + second + "秒";
    }