Java的日期时间类基本使用1

获取某日的零点和末点、获取指定天数前的日期、获取指定某年或某月的天数

获取某日的零点和末点

   //获取某天的零点
   public String findStartTimeByDay(String day) throws ParseException {
       Calendar instance = Calendar.getInstance();
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
       Date parse = sdf.parse(day);
       instance.setTime(parse);
       instance.set(Calendar.HOUR_OF_DAY,0);
       instance.set(Calendar.MINUTE,0);
       instance.set(Calendar.SECOND,0);
       instance.set(Calendar.MILLISECOND,0);
       Date time = instance.getTime();
       String startTime = sdf.format(time);
       return startTime;
   }
//获取某天的末点(23:59:59.999)
   public String findEndTimeByDay(String day) throws ParseException {
       Calendar instance = Calendar.getInstance();
       SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
       Date parse = sdf.parse(day);
       instance.setTime(parse);
       instance.set(Calendar.HOUR_OF_DAY,23);
       instance.set(Calendar.MINUTE,59);
       instance.set(Calendar.SECOND,59);
       instance.set(Calendar.MILLISECOND,999);
       Date time = instance.getTime();
       String endTime = sdf.format(time);
       return endTime;
   }    

获取指定天数前的日期

//获取7天前的时间
Calendar now = Calendar.getInstance();
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
now.add(Calendar.DAY_OF_MONTH,-7);
String passWeekDate = sdf.format(now.getTime());

获取指定某年或某月的天数

//获取指定月份的天数
public static Integer getDayNumOfMonth(Date date) {
    Calendar calendar = Calendar.getInstance();
    calendar.setTime(date);
    Integer actualMaximum = calendar.getActualMaximum(Calendar.DAY_OF_MONTH);
    return actualMaximum;
}

// 获取今年的天数 
int daysOfThisYear = LocalDate.now().lengthOfYear(); 

// 获取指定某年的天数 
LocalDate.of(2011, 1, 1).lengthOfYear();

//使用Calendar的枚举来指代月份
Calendar.FEBRUARY
Calendar.MARCH