JDK8日期时间操作小汇总

统一使用java.time.*包下的类

1、获取当前的日期、时间、日期加时间

LocalDate todayDate = LocalDate.now(); //今天的日期

LocalTime now = LocalTime.now(); //此刻的时间--精确到毫秒

LocalDateTime now = LocalDateTime.now(); //此刻时间--年-月-日-时-分-秒-毫秒

2、获取单独年日月时分秒

LocalDateTime now = LocalDateTime.now();
System.out.println("年:"+now.getYear());
System.out.println("月:"+now.getMonthValue());
System.out.println("日:"+now.getDayOfMonth());
System.out.println("时:"+now.getHour());
System.out.println("分:"+now.getMinute());
System.out.println("秒:"+now.getSecond());
System.out.println("该日期是该年的第"+now.getDayOfYear()+"天");

3、将特定的时间转成LocalDate、LocalTime、LocalDateTime  都有很多的重载的方法

LocalDate of1 = LocalDate.of(2019, 1, 16);
System.out.println(of1);
LocalTime of2 = LocalTime.of(9, 25, 36);
System.out.println(of2);
LocalDateTime of3 = LocalDateTime.of(of1, of2);
System.out.println(of3);
LocalDateTime of4 = LocalDateTime.of(2019, 1, 14, 9, 26, 25);
System.out.println(of4);

4、判断时间是否相等（日期、时间、日期加时间）时间的比较精确到纳秒，可以先将时间进行格式化，然后比较，可以控制精度问题

// 日期
LocalDate date1 = LocalDate.of(2019, 1, 17);
LocalDate date2 = LocalDate.now();
if (date1.equals(date2)) {
    System.out.println("日期相等");
} else {
    System.out.println("日期不相等");
}
// 时间
LocalTime date1 = LocalTime.of(9, 46);
LocalTime date2 = LocalTime.now();
if (date1.equals(date2)) {
    System.out.println("时间相等");
} else {
    System.out.println("时间不相等");
}
// 时间加日期
LocalDateTime date1 = LocalDateTime.of(2019,1,17,9,47);
LocalTime date2 = LocalTime.now();
if (date1.equals(date2)) {
    System.out.println("时间加日期相等");
} else {
    System.out.println("时间加日期不相等");
}

5、检查周几这种周期性的事件

DayOfWeek of = DayOfWeek.THURSDAY;
DayOfWeek from = DayOfWeek.from(LocalDate.now());
if (from.equals(of)) {
    System.out.println("今天是周四");
} else {
    System.out.println("今天不是周四");
}
DayOfWeek from1 = DayOfWeek.from(LocalDate.of(2019, 1, 10));
if (from1.equals(of)) {
    System.out.println("该日期是周四");
} else {
    System.out.println("该日期不是周四");
}

6、指定时间之后或之前XXX的时间

LocalDateTime now = LocalDateTime.now();
System.out.println("当前时间"+now);
System.out.println("当前时间之前2天:"+now.minusDays(2));
System.out.println("当前时间之后2天:"+now.plusDays(2));
System.out.println("当前时间之前2周:"+now.minusWeeks(2));
System.out.println("当前时间之后2周:"+now.plusWeeks(2));
System.out.println("当前时间之前2月:"+now.minusMonths(2));
System.out.println("当前时间之后2月:"+now.plusMonths(2));
System.out.println("当前时间之前2年:"+now.minusYears(2));
System.out.println("当前时间之后2年:"+now.plusYears(2));
System.out.println("当前时间之前2小时:"+now.minusHours(2));
System.out.println("当前时间之后2小时:"+now.plusHours(2));
System.out.println("当前时间之前2分钟:"+now.minusMinutes(2));
System.out.println("当前时间之后2分钟:"+now.plusMinutes(2));
System.out.println("当前时间之前2秒:"+now.minusSeconds(2));
System.out.println("当前时间之后2秒:"+now.plusSeconds(2));

7、比较时间的先后

LocalDateTime now = LocalDateTime.now();
System.out.println("当前时间:"+now);
LocalDateTime appointTime = LocalDateTime.of(2019, 1, 17, 9, 32, 12);
System.out.println("指定时间:"+appointTime);
System.out.println(now.isAfter(appointTime));
System.out.println(now.isBefore(appointTime));

8、格式化时间格式及按照一定格式解析

LocalDateTime now = LocalDateTime.now();
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
DateTimeFormatter formatter2 = DateTimeFormatter.ofPattern("yyyy-MM-dd");
DateTimeFormatter formatter3 = DateTimeFormatter.ofPattern("HH:mm:ss");
//格式化
String format = now.format(formatter);
String format2 = now.format(formatter2);
String format3 = now.format(formatter3);
System.out.println("格式化1:" + format);
System.out.println("格式化2:" + format2);
System.out.println("格式化3:" + format3);
//解析
LocalDateTime localDateTime = LocalDateTime.parse(format, formatter);
LocalDate localDate = LocalDate.parse(format2, formatter2);
LocalTime localTime = LocalTime.parse(format3, formatter3);
System.out.println("解析1:" + localDateTime);
System.out.println("解析2:" + localDate);
System.out.println("解析3:" + localTime);

9、根据指定的毫秒数获取LocalDateTime对象

Long nowMilli = new Date().getTime();
LocalDateTime localDateTime = Instant.ofEpochMilli(nowMilli).atZone(ZoneId.of("+8")).toLocalDateTime();
System.out.println(localDateTime);

注：+8 表示东八区，即常说的北京时间

10、通过LocalDateTime对象获取毫秒数

LocalDateTime now = LocalDateTime.now();
long l = now.atZone(ZoneId.of("+8")).toInstant().toEpochMilli();
System.out.println(l);

注：+8 表示东八区，即常说的北京时间

11、通过LocalDateTime对象获取秒数

LocalDateTime now = LocalDateTime.now();
long second = now.toEpochSecond(ZoneOffset.of("+8"));
System.out.println(second);

注：+8 表示东八区，即常说的北京时间

12、判断指定日期是否是闰年（只LocalDate）

LocalDate now = LocalDate.now();
if (now.isLeapYear()) {
    System.out.println("now是闰年");
} else {
    System.out.println("now不是闰年");
}

13、使用默认格式解析时间（LocalDateTime对象可解析的格式yyyy-MM-ddTHH:mm:ss）--不是空格了，是T

LocalDateTime dateTime = LocalDateTime.parse("2019-01-14T12:04:12");
int monthValue = dateTime.getMonthValue();
int minute = dateTime.getMinute();
System.out.println(monthValue+":"+minute);
LocalTime time = LocalTime.parse("19:14:25");
int hour = time.getHour();
System.out.println(hour);
LocalDate date = LocalDate.parse("2019-01-12");
int year = date.getYear();
System.out.println(year);

14、总结

jdk8中提供三个类（LocalDate，LocalTime，LocalDateTime），它们分别对年月日、时分秒和年月日时分秒进行单独的处理，使用时可以根据自己的实际情况进行选择，它们的API类似。

Date与LocalDateTime、LocalDate、LocalTime互转参考：  https://www.cnblogs.com/exmyth/p/6425878.html