1
Date now = new Date();
2
System.out.println("当前时间: " + now);
3

4
long timestamp = now.getTime(); // 时间戳，这个最常用

1
Calendar calendar = Calendar.getInstance();
2
calendar.set(2023, 1, 1); // 这是2月1日！不是1月1日！
3
calendar.set(2023, Calendar.JANUARY, 1); // 正确做法：用常量

1
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
2

3
// 错误用法：多个线程共用同一个sdf实例
4
// 会出现各种奇怪的结果，比如月份变成13、时间错乱
5

6
// 正确用法：每次new一个，或者用ThreadLocal包装

1
// 创建
2
LocalDate now = LocalDate.now();
3
LocalDate specific = LocalDate.of(2023, 1, 1); // 月份是1，不是0！舒服了
4
LocalDate parsed = LocalDate.parse("2023-01-01");
5

6
// 获取字段
7
int year = now.getYear();
8
int month = now.getMonthValue(); // 1-12，不用+1了
9
int day = now.getDayOfMonth();
10

11
// 日期计算
12
LocalDate nextWeek = now.plusDays(7);
13
LocalDate lastMonth = now.minusMonths(1);
14

15
// 日期比较
16
boolean isAfter = now.isAfter(specific);
17
boolean isBefore = now.isBefore(specific);
18

19
// 计算天数差
20
long daysBetween = ChronoUnit.DAYS.between(specific, now);
21

22
// 闰年判断
23
boolean isLeapYear = now.isLeapYear();

1
LocalTime now = LocalTime.now();
2
LocalTime specific = LocalTime.of(12, 0, 0);
3
LocalTime parsed = LocalTime.parse("12:00:00");
4

5
int hour = now.getHour();
6
int minute = now.getMinute();
7
int second = now.getSecond();
8

9
LocalTime plusHours = now.plusHours(1);
10
LocalTime minusMinutes = now.minusMinutes(30);
11

12
long minutesBetween = ChronoUnit.MINUTES.between(specific, now);

1
LocalDateTime now = LocalDateTime.now();
2
LocalDateTime specific = LocalDateTime.of(2023, 1, 1, 12, 0, 0);
3

4
// 拆分
5
LocalDate date = now.toLocalDate();
6
LocalTime time = now.toLocalTime();

1
// 当前时间（系统时区）
2
ZonedDateTime now = ZonedDateTime.now();
3

4
// 指定时区
5
ZonedDateTime newYork = ZonedDateTime.now(ZoneId.of("America/New_York"));
6

7
// 时区转换
8
ZonedDateTime shanghai = now.withZoneSameInstant(ZoneId.of("Asia/Shanghai"));

1
Instant now = Instant.now();
2
long epochMilli = now.toEpochMilli(); // 毫秒时间戳
3
long epochSecond = now.getEpochSecond(); // 秒时间戳

1
LocalDateTime now = LocalDateTime.now();
2

3
// 预定义格式
4
DateTimeFormatter isoFormatter = DateTimeFormatter.ISO_LOCAL_DATE_TIME;
5

6
// 自定义格式
7
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
8
String formatted = now.format(formatter); // 2023-01-01 12:00:00
9

10
// 解析
11
LocalDateTime parsed = LocalDateTime.parse("2023-01-01 12:00:00", formatter);

1
// Duration：时间间隔（时分秒）
2
LocalTime start = LocalTime.of(10, 0);
3
LocalTime end = LocalTime.of(12, 30);
4
Duration duration = Duration.between(start, end);
5
long hours = duration.toHours(); // 2
6
long minutes = duration.toMinutes(); // 150
7

8
// Period：日期间隔（年月日）
9
LocalDate startDate = LocalDate.of(2020, 1, 1);
10
LocalDate endDate = LocalDate.of(2023, 6, 15);
11
Period period = Period.between(startDate, endDate);
12
int years = period.getYears(); // 3
13
int months = period.getMonths(); // 5
14
int days = period.getDays(); // 14