Java8新特性之日期时间API的介绍和具体使用

long times = System.currentTimeMillis();
		//返回的是当前时间与1970年1月1月1日0分0秒之间以毫秒为单位的时间差
		//称为时间戳
		System.out.println(times);

	//将java.util.Date 对象转换为java.sql.Date对象
		Date date1 = new Date();
		java.sql.Date date2 = new java.sql.Date(date1.getTime());

SimpleDateFormat sfd = new SimpleDateFormat();
		Date date = new Date();
		System.out.println(date);
		String formateDate = sfd.format(date);
		System.out.println(formateDate);

Date date = new Date();
		System.out.println(date);
		SimpleDateFormat sfd = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
		String formateDate = sfd.format(date);
		System.out.println(formateDate);

String str = "2021/4/12 下午10:16";
	    SimpleDateFormat sfd = new SimpleDateFormat();
		Date date2 = sfd.parse(str);
		System.out.println(date2);

public static void testExper() throws ParseException {
		String s = "2021-04-13";
		SimpleDateFormat sfd = new SimpleDateFormat("yyyy-MM-dd");
		Date date = sfd.parse(s);
		java.sql.Date date2 = new java.sql.Date(date.getTime());
		System.out.println(date2);
	}

	Calendar calendar = Calendar.getInstance();
		System.out.println(calendar.getClass()); //java.util.GregorianCalendar，其实还是子类类型的对象

Calendar calendar = Calendar.getInstance();
//		System.out.println(calendar.getClass()); //java.util.GregorianCalendar
		//get()
		int days = calendar.get(calendar.DAY_OF_MONTH);//获取当前日期是这个月的第几天
		System.out.println(days); //13
		//set()
		calendar.set(calendar.DAY_OF_MONTH, 22);//重新设置
	    days = calendar.get(calendar.DAY_OF_MONTH);//在重新获取
		System.out.println(days); //22
		//add()
		calendar.add(calendar.DAY_OF_MONTH, 3);
		days = calendar.get(calendar.DAY_OF_MONTH);
		System.out.println(days); //25

		//getTime():日历类----> Date类
		Date date = calendar.getTime();
		System.out.println(date); //Sun Apr 25 13:14:59 CST 2021

		//setTime():Date类----> 日历类
		Date date2 = new Date();
		calendar.setTime(date2);
		days = calendar.get(calendar.DAY_OF_MONTH);
		System.out.println(days); //13

LocalDate localDate = LocalDate.now();
		LocalTime localTime = LocalTime.now();
		LocalDateTime localDateTime = LocalDateTime.now();
		System.out.println(localDate);
		System.out.println(localTime);
		System.out.println(localDateTime);

//of():设置指定时间的年、月、日、时、分。没有偏移量。
		LocalDateTime localDateTime2 = LocalDateTime.of(2021, 4, 13, 15, 20);
		System.out.println(localDateTime2);

//now():获取本初子午线对应的标准时间
		Instant instant = Instant.now();
		System.out.println(instant);
		//添加时间的偏移量
		OffsetDateTime offsetDateTime = instant.atOffset(ZoneOffset.ofHours(8));
		System.out.println(offsetDateTime);

long milli = instant.toEpochMilli();
		System.out.println(milli);

//通过给定的毫秒数，获取Instant实例
		Instant instant2 = Instant.ofEpochMilli(1618300028028l);
		System.out.println(instant2);

DateTimeFormatter formatter = DateTimeFormatter.ISO_LOCAL_DATE_TIME;
		LocalDateTime localDateTime = LocalDateTime.now();
		String str = formatter.format(localDateTime);//注意类型变化
		System.out.println(localDateTime);
		System.out.println(str);

	DateTimeFormatter formatter = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.SHORT);
		LocalDateTime localDateTime = LocalDateTime.now();
		String str = formatter.format(localDateTime);
		System.out.println(localDateTime);
		System.out.println(str);

//自定义格式。如：
		DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd hh:mm:ss");
		String string = formatter.format(LocalDateTime.now());
		System.out.println(string);