java Calendar获取某个时间上个月的时间

java8的时间api很好用,但有的场景用Calendar也是很合适的

 

 /**
     * 从当前时间获取上个月的第一天和最后一天
     */
    private void getPreMonthDate(String startDate) throws Exception {
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
        Calendar c = getPreMonth(startDate);

        //获取某月最小天数
        int firstDay = c.getActualMinimum(Calendar.DAY_OF_MONTH);
        //设置日历中月份的最小天数
        c.set(Calendar.DAY_OF_MONTH, firstDay);
        // 上个月第一天
        String startTime = format.format(c.getTime());

        
        Calendar c2 = getPreMonth(startDate);
        int lastDay = c2.getActualMaximum(Calendar.DAY_OF_MONTH);
        c2.set(Calendar.DAY_OF_MONTH, lastDay);
        String endTime = format.format(c2.getTime());


    }

    /**
     * 从当前时间"yyyy-MM-dd"格式获取上个月的时间
     */
    private Calendar getPreMonth(String startDate) throws Exception{
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
        Calendar c = Calendar.getInstance();
        Date date = format.parse(startDate);
        c.setTime(date);
        c.add(Calendar.MONTH, -1);
        return c;
    }

获取上周的时间也是一个道理
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
Calendar c = Calendar.getInstance();
Date date = format.parse("2020-05-01");
c.setTime(date);
c.add(Calendar.DATE, -7);
format.format(c.getTime());

获取当前星期内星期*的date

LocalDate currentDate = LocalDate.now();
// 获取本周星期*的date
LocalDate mondayLocalDate = currentDate.with(DayOfWeek.MONDAY);
DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyyMMdd");
mondayLocalDate.format(dateTimeFormatter);
// 获取上周内 「星期*」的 date
LocalDate previousDate = currentDate.with(TemporalAdjusters.previousOrSame(DayOfWeek.SUNDAY));

获取当天0点10位时间戳

Long time = LocalDateTime.now().withHour(0).withMinute(0).withSecond(0).toEpochSecond(ZoneOffset.of("+8"));

String format = String.format("local:time:%s", time);

根据时间戳和日期格式转化成日期字符串

        String date =getDateStringByTimestamp(1234567890, "yyyyMMdd");


public static String getDateStringByTimestamp(Integer timestamp, String format) {
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern(format);
        return formatter.format(LocalDateTime.ofInstant(Instant.ofEpochSecond(timestamp), ZoneOffset.of("+8")));
    }

获取当月第一天的时间

    //获取当月第一天
    public static LocalDate getCurMonthFirstDay() {
        LocalDate currentDate = LocalDate.now();
        return currentDate.with(TemporalAdjusters.firstDayOfMonth());
    }

获取某个月第一天

 /**
     * 获得某月第一天
     * @param year 2019
     * @param month 10
     * @return
     */
    public static String getFirstDayOfMonth(int year,int month){
        Calendar cal = Calendar.getInstance();
        Integer nowYear = cal.get(Calendar.YEAR);
        Integer nowMonth = cal.get(Calendar.MONTH) + 1;
        //设置年份
        cal.add(Calendar.YEAR,year - nowYear);
        //设置月份
        cal.add(Calendar.MONTH, month - nowMonth);
        //获取某月最小天数
        int firstDay = cal.getActualMinimum(Calendar.DAY_OF_MONTH);
        //设置日历中月份的最小天数
        cal.set(Calendar.DAY_OF_MONTH, firstDay);
        //格式化日期
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        String firstDayOfMonth = sdf.format(cal.getTime());
        return firstDayOfMonth;
    }