时间戳
long currentTimeMillis = System.currentTimeMillis(); // 毫秒级时间戳
long currentTimestamp = System.currentTimeMillis()/1000; // 秒级时间戳
从 Java 8 开始加入的 Instant 类也可以获取秒级时间戳：
import java.time.Instant;
public class Main {
public static void main(String[] args) {
long currentTimestamp1 = System.currentTimeMillis()/1000; // 秒级时间戳
long currentTimestamp2 = Instant.now().getEpochSecond(); // 这个也是秒级时间戳
System.out.println("当前秒级时间戳：" + currentTimestamp1);
System.out.println("当前秒级时间戳：" + currentTimestamp2);
}
}
java.time.LocalDateTime
LocalDatetime 类从 Java 8 开始引入。
该类的一个显著特点是，月从1开始，而不是从0开始，年也不用像 java.util.Date 那样加一个 1900。
获取当前日期和时间
import java.time.LocalDateTime;
public class Main {
public static void main(String[] args) {
LocalDateTime localDateTime = LocalDateTime.now();
System.out.println(localDateTime);
}
}
运行结果示例：
2019-06-22T21:50:20.760
分表获取当前年月日时分秒
import java.time.LocalDateTime;
public class Main {
public static void main(String[] args) {
LocalDateTime localDateTime = LocalDateTime.now();
System.out.printf("%s-%s-%s %s:%s:%s\n",
localDateTime.getYear(), localDateTime.getMonth().getValue(), localDateTime.getDayOfMonth(),
localDateTime.getHour(), localDateTime.getMinute(), localDateTime.getSecond());
}
}
运行结果示例：
2019-6-22 21:51:46
将秒级时间戳转换为 LocalDateTime
import java.time.Instant;
import java.time.LocalDateTime;
import java.time.ZoneId;
public class Main {
public static void main(String[] args) {
LocalDateTime localDateTime = LocalDateTime.ofInstant(Instant.ofEpochSecond(1561211629L), ZoneId.systemDefault());
System.out.printf("%s-%s-%s %s:%s:%s\n",
localDateTime.getYear(), localDateTime.getMonth().getValue(), localDateTime.getDayOfMonth(),
localDateTime.getHour(), localDateTime.getMinute(), localDateTime.getSecond());
}
}
将 LocalDateTime 转换成时间戳
import java.time.Instant;
import java.time.LocalDateTime;
import java.time.ZoneId;
public class Main {
public static void main(String[] args) {
LocalDateTime localDateTime = LocalDateTime.of(2019, 6, 23, 9, 0);
System.out.println(localDateTime);
Instant instant = localDateTime.atZone(ZoneId.systemDefault()).toInstant();
System.out.println(instant.getEpochSecond()); // 秒级时间戳
System.out.println(instant.toEpochMilli()); // 毫秒级时间戳
}
}
运行结果示例：
2019-06-23T09:00
1561251600
1561251600000
也可以像下面这样获取秒级时间戳：
import java.time.LocalDateTime;
import java.time.ZoneId;
public class Main {
public static void main(String[] args) {
LocalDateTime localDateTime = LocalDateTime.of(2019, 6, 23, 9, 0);
System.out.println( localDateTime.atZone(ZoneId.systemDefault()).toEpochSecond() );;
}
}
格式化 LocalDateTime
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.time.format.FormatStyle;
public class Main {
public static void main(String[] args) {
LocalDateTime localDateTime = LocalDateTime.now();
System.out.println( localDateTime.format(DateTimeFormatter.ISO_DATE) );
System.out.println( localDateTime.format(DateTimeFormatter.ofLocalizedDate(FormatStyle.FULL)) );
System.out.println( localDateTime.format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")) );
}
}
运行结果示例：
2019-06-22
2019年6月22日 星期六
2019-06-22 22:02:38
字符串转换为 LocalDateTime
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
public class Main {
public static void main(String[] args) {
DateTimeFormatter df = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
LocalDateTime localDateTime = LocalDateTime.parse("2019-06-18 12:00:00", df);
System.out.println( localDateTime );
}
}
模式可以在 DateTimeFormatter 的源码注释中找到：
* Symbol Meaning Presentation Examples
* ------ ------- ------------ -------
* G era text AD; Anno Domini; A
* u year year 2004; 04
* y year-of-era year 2004; 04
* D day-of-year number 189
* M/L month-of-year number/text 7; 07; Jul; July; J
* d day-of-month number 10
*
* Q/q quarter-of-year number/text 3; 03; Q3; 3rd quarter
* Y week-based-year year 1996; 96
* w week-of-week-based-year number 27
* W week-of-month number 4
* E day-of-week text Tue; Tuesday; T
* e/c localized day-of-week number/text 2; 02; Tue; Tuesday; T
* F week-of-month number 3
*
* a am-pm-of-day text PM
* h clock-hour-of-am-pm (1-12) number 12
* K hour-of-am-pm (0-11) number 0
* k clock-hour-of-am-pm (1-24) number 0
*
* H hour-of-day (0-23) number 0
* m minute-of-hour number 30
* s second-of-minute number 55
* S fraction-of-second fraction 978
* A milli-of-day number 1234
* n nano-of-second number 987654321
* N nano-of-day number 1234000000
*
* V time-zone ID zone-id America/Los_Angeles; Z; -08:30
* z time-zone name zone-name Pacific Standard Time; PST
* O localized zone-offset offset-O GMT+8; GMT+08:00; UTC-08:00;
* X zone-offset 'Z' for zero offset-X Z; -08; -0830; -08:30; -083015; -08:30:15;
* x zone-offset offset-x +0000; -08; -0830; -08:30; -083015; -08:30:15;
* Z zone-offset offset-Z +0000; -0800; -08:00;
*
* p pad next pad modifier 1
*
* ' escape for text delimiter
* '' single quote literal '
* [ optional section start
* ] optional section end
* # reserved for future use
* { reserved for future use
* } reserved for future use
获取某个时间对应的月份有多少天
import java.time.LocalDateTime;
public class Main {
public static void main(String[] args) {
LocalDateTime localDateTime = LocalDateTime.now();
System.out.println(localDateTime.toLocalDate().lengthOfMonth());
}
}
toLocalDate 用于获取 LocalDate 对象。
lengthOfMonth 方法返回的是 int 类型。
运行结果示例：
30
获取一段时间前的时间
import java.time.LocalDateTime;
import java.time.temporal.ChronoUnit;
public class Main {
public static void main(String[] args) {
LocalDateTime localDateTime1 = LocalDateTime.now();
System.out.println(localDateTime1);
LocalDateTime localDateTime2 = localDateTime1.minus(32, ChronoUnit.DAYS); // 32天前的时间
System.out.println(localDateTime1); // localDateTime1 保持不变
System.out.println(localDateTime2);
}
}
运行结果示例：
2019-06-22T22:11:59.322
2019-06-22T22:11:59.322
2019-05-21T22:11:59.322
获取一段时间后的时间
import java.time.LocalDateTime;
import java.time.temporal.ChronoUnit;
public class Main {
public static void main(String[] args) {
LocalDateTime localDateTime1 = LocalDateTime.now();
System.out.println("localDateTime1: " + localDateTime1);
LocalDateTime localDateTime2 = localDateTime1.plus(32, ChronoUnit.HOURS); // 32小时后的时间
System.out.println("localDateTime1: " + localDateTime1); // localDateTime1 保持不变
System.out.println("localDateTime2: " + localDateTime2);
}
}
运行结果示例：
localDateTime1: 2019-06-23T08:48:14.321
localDateTime1: 2019-06-23T08:48:14.321
localDateTime2: 2019-06-24T16:48:14.321
指定时间
import java.time.LocalDateTime;
public class Main {
public static void main(String[] args) {
LocalDateTime localDateTime1 = LocalDateTime.of(2019, 6, 23, 9, 0);
System.out.println("localDateTime1: " + localDateTime1);
LocalDateTime localDateTime2 = localDateTime1.withHour(20); // 将 hour 改成 20
System.out.println("localDateTime1: " + localDateTime1); // localDateTime1 保持不变
System.out.println("localDateTime2: " + localDateTime2);
}
}
运行结果示例：
localDateTime1: 2019-06-23T09:00
localDateTime1: 2019-06-23T09:00
localDateTime2: 2019-06-23T20:00
获取当天最早的时间、最晚的时间
import java.time.LocalDateTime;
import java.time.LocalTime;
public class Main {
public static void main(String[] args) {
LocalDateTime localDateTime = LocalDateTime.of(2019, 6, 23, 9, 0);
System.out.println(LocalDateTime.of(localDateTime.toLocalDate(), LocalTime.MIN)); // 当前最早的时间
System.out.println(LocalDateTime.of(localDateTime.toLocalDate(), LocalTime.MAX)); // 当天最晚的时间
}
}
运行结果示例：
2019-06-23T00:00
2019-06-23T23:59:59.999999999
LocalDateTime 转换为 Date
import java.time.LocalDateTime;
import java.time.ZoneId;
import java.util.Date;
public class Main {
public static void main(String[] args) {
LocalDateTime localDateTime = LocalDateTime.of(2019, 6, 23, 9, 0);
Date date = Date.from(localDateTime.atZone(ZoneId.systemDefault()).toInstant());
System.out.println(date);
System.out.println(date.getTime()); // 毫秒级时间戳
}
}
运行结果示例：
Sun Jun 23 09:00:00 CST 2019
1561251600000
判断两个 LocalDateTime 的时间先后关系
import java.time.LocalDateTime;
public class Main {
public static void main(String[] args) {
LocalDateTime localDateTime01 = LocalDateTime.of(2019, 6, 18, 12, 0);
LocalDateTime localDateTime02 = LocalDateTime.of(2019, 6, 1, 12, 0);
System.out.println( localDateTime01.isAfter(localDateTime02) ); // 类似的，还有 isBefore 等方法
}
}
运行结果：
true
获取两个 LocalDateTime 之间的间隔
import java.time.Duration;
import java.time.LocalDateTime;
import java.time.temporal.ChronoUnit;
public class Main {
public static void main(String[] args) {
LocalDateTime localDateTime01 = LocalDateTime.of(2019, 6, 18, 12, 0);
LocalDateTime localDateTime02 = LocalDateTime.of(2019, 6, 18, 13, 0);
Duration duration = Duration.between(localDateTime01, localDateTime02);
System.out.println( duration.get(ChronoUnit.SECONDS) );
System.out.println( duration.getSeconds() );
}
}
运行结果：
3600
3600
java.time.LocalDate
LocalDate 类从 Java 8 开始引入。相对于 LocalDateTime，LocalDate 仅处理年月日这三个维度。
获取当前年月日对应的 LocalDate
import java.time.LocalDate;
public class Main {
public static void main(String[] args) {
LocalDate localDate = LocalDate.now();
System.out.println(localDate);
System.out.printf("%s-%s-%s\n", localDate.getYear(), localDate.getMonthValue(), localDate.getDayOfMonth());
}
}
运行结果示例：
2019-06-24
2019-6-24
生成指定时间的 LocalDate
import java.time.LocalDate;
public class Main {
public static void main(String[] args) {
LocalDate localDate = LocalDate.of(2019, 6, 18);
System.out.println(localDate);
System.out.printf("%s-%s-%s\n", localDate.getYear(), localDate.getMonthValue(), localDate.getDayOfMonth());
}
}
运行结果：
2019-06-18
2019-6-18
获取指定时间是当年的第几天
import java.time.LocalDate;
public class Main {
public static void main(String[] args) {
LocalDate localDate = LocalDate.of(2019, 6, 18);
System.out.println(localDate.getDayOfYear());
}
}
运行结果：
169
将当年的第几天转换为 LocalDate
import java.time.LocalDate;
public class Main {
public static void main(String[] args) {
LocalDate localDate = LocalDate.ofYearDay(2019, 169);
System.out.println(localDate);
}
}
运行结果：
2019-06-18
计算两个 LocalDate 之间间隔的时间
import java.time.LocalDate;
import java.time.Period;
import java.time.temporal.ChronoUnit;
public class Main {
public static void main(String[] args) {
LocalDate localDate01 = LocalDate.of(2019, 6, 18);
LocalDate localDate02 = LocalDate.of(2019, 6, 12);
Period period = Period.between(localDate01, localDate02);
System.out.println( period.get(ChronoUnit.DAYS) );
}
}
运行结果：
-6
java.time.LocalTime
LocalTime 类从 Java 8 开始引入。相对于 LocalDateTime，LocalDate 仅处理时分秒这三个维度。秒，可以精确到纳秒。1秒等于10^9（10的9次方）纳秒。
获取当前时间对应的 LocalTime
import java.time.LocalTime;
public class Main {
public static void main(String[] args) {
LocalTime localTime = LocalTime.now();
System.out.println( localTime );
System.out.printf("%s:%s:%s %s\n", localTime.getHour(), localTime.getMinute(), localTime.getSecond(), localTime.getNano());
}
}
运行结果示例：
23:42:15.555
23:42:15 555000000
生成指定时间的 LocalTime
import java.time.LocalTime;
public class Main {
public static void main(String[] args) {
LocalTime localTime = LocalTime.of(10, 25, 59);
System.out.println( localTime );
}
}
运行结果：
10:25:59
获取当前时间是当日的第几秒
import java.time.LocalTime;
public class Main {
public static void main(String[] args) {
LocalTime localTime = LocalTime.of(10, 25, 59);
System.out.println(localTime.toSecondOfDay());
}
}
运行结果：
37559
将当日的第几秒转换为 LocalTime
import java.time.LocalTime;
public class Main {
public static void main(String[] args) {
LocalTime localTime = LocalTime.ofSecondOfDay(37559);
System.out.println(localTime);
}
}
运行结果：
10:25:59
java.util.Date
获取当前时间
import java.util.Date;
public class Main {
public static void main(String[] args) {
Date date = new Date(); // 当前时间
System.out.println("年: " + (1900+date.getYear())); // 要加上 1900
System.out.println("月: " + (1+date.getMonth())); // 要加上 1
System.out.println("日: " + date.getDate());
System.out.println("时: " + date.getHours());
System.out.println("分: " + date.getMinutes());
System.out.println("秒: " + date.getSeconds());
}
}
注意，上面用到的 get 开头的方法，已经被废弃了。
运行结果示例：
年: 2019
月: 6
日: 23
时: 10
分: 10
秒: 46
时间戳转换为 Date
import java.time.Instant;
import java.util.Date;
public class Main {
public static void main(String[] args) {
// 方法1
Date date1 = new Date(1561256015L*1000); // 要使用毫秒级
System.out.println(date1);
// 方法2
Date date2 = Date.from(Instant.ofEpochSecond(1561256015L));
System.out.println(date2);
}
}
运行结果示例：
Sun Jun 23 10:13:35 CST 2019
Sun Jun 23 10:13:35 CST 2019
Date 转换为时间戳
import java.util.Date;
public class Main {
public static void main(String[] args) {
Date date = new Date();
System.out.println(date.toInstant().getEpochSecond()); // 返回 long 类型
}
}
运行结果示例：
1561256111
格式化 Date
import java.text.SimpleDateFormat;
import java.util.Date;
public class Main {
public static void main(String[] args) {
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
Date date = new Date();
System.out.println( df.format(date) );
}
}
运行结果示例：
2019-06-24 06:53:56
注意，SimpleDateFormat 是线程不安全的，也就是不要在多线程中共享一个 SimpleDateFormat 实例。
字符串转换为 Date
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
public class Main {
public static void main(String[] args) throws ParseException {
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
Date date = df.parse("2019-06-18 12:00:00");
System.out.println( date );
}
}
运行结果：
Tue Jun 18 00:00:00 CST 2019
java.sql.Date
java.sql.Date 继承自 java.util.Date。不同的是，只支持年月日，不支持时分秒。
不支持时分秒
import java.sql.Date;
public class Main {
public static void main(String[] args) {
Date date = new Date(2019-1900, 6,18);
System.out.println(date);
System.out.println(date.getMinutes()); // 抛出异常
}
}
运行时会抛出异常：
2019-07-18
Exception in thread "main" java.lang.IllegalArgumentException
at java.sql.Date.getMinutes(Date.java:200)
at Main.main(Main.java:9)
java.sql.Date 与时间戳互相转换
import java.sql.Date;
public class Main {
public static void main(String[] args) {
// 时间戳到 Date
Date date = new Date(1561256015L*1000); // 毫秒级时间戳
System.out.println(date);
// Date 到时间戳
System.out.println(date.getTime());
}
}
运行结果：
2019-06-23
1561256015000
java.sql.Date 转换为 Instant、LocalDate
import java.sql.Date;
import java.time.Instant;
import java.time.LocalDate;
public class Main {
public static void main(String[] args) {
Date date = new Date(2019-1900, 6,18);
Instant instant = date.toInstant(); // 转换为 Instant
LocalDate localDate = date.toLocalDate(); // 转换为 LocalDate
}
}
从字符串解析时间
import java.sql.Date;
public class Main {
public static void main(String[] args) {
Date date = Date.valueOf("2019-06-18");
Date date2 = Date.valueOf("2019-6-18");
System.out.println(date);
System.out.println(date2);
}
}
执行结果：
2019-06-18
2019-06-18
java.util.Calendar
查看 Calender 实例内容
import java.util.Calendar;
public class Main {
public static void main(String[] args) {
Calendar calendar = Calendar.getInstance();
System.out.println(calendar);
}
}
运行结果示例：
java.util.GregorianCalendar[time=1561343283169,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=sun.util.calendar.ZoneInfo[id="Asia/Shanghai",offset=28800000,dstSavings=0,useDaylight=false,transitions=19,lastRule=null],firstDayOfWeek=1,minimalDaysInFirstWeek=1,ERA=1,YEAR=2019,MONTH=5,WEEK_OF_YEAR=26,WEEK_OF_MONTH=5,DAY_OF_MONTH=24,DAY_OF_YEAR=175,DAY_OF_WEEK=2,DAY_OF_WEEK_IN_MONTH=4,AM_PM=0,HOUR=10,HOUR_OF_DAY=10,MINUTE=28,SECOND=3,MILLISECOND=169,ZONE_OFFSET=28800000,DST_OFFSET=0]
MONTH 是从 0 开始算的，所以实际使用中要加1。周日是一周的第一天。
从 Calendar 中获取年月日时分秒
import java.util.Calendar;
public class Main {
public static void main(String[] args) {
Calendar calendar = Calendar.getInstance();
System.out.printf("%s-%s-%s %s:%s:%s \n",
calendar.get(Calendar.YEAR), calendar.get(Calendar.MONTH) + 1, calendar.get(Calendar.DAY_OF_MONTH),
calendar.get(Calendar.HOUR_OF_DAY), calendar.get(Calendar.MINUTE), calendar.get(Calendar.SECOND)
);
}
}
运行结果示例：
2019-6-24 10:34:31
Calendar 转换为时间戳
import java.util.Calendar;
public class Main {
public static void main(String[] args) {
Calendar calendar = Calendar.getInstance();
calendar.set(2019, 6, 18, 18, 0, 0);
// 转换为秒级时间戳
System.out.println( calendar.toInstant().getEpochSecond() );
// 转换为毫秒级时间戳
System.out.println( calendar.getTimeInMillis() );
}
}
运行结果：
1563444000
1563444000591
时间戳转换为 Calender
import java.util.Calendar;
public class Main {
public static void main(String[] args) {
Calendar calendar = Calendar.getInstance();
calendar.setTimeInMillis(1563444000L*1000L);
System.out.printf("%s-%s-%s %s:%s:%s \n",
calendar.get(Calendar.YEAR), calendar.get(Calendar.MONTH) + 1, calendar.get(Calendar.DAY_OF_MONTH),
calendar.get(Calendar.HOUR_OF_DAY), calendar.get(Calendar.MINUTE), calendar.get(Calendar.SECOND)
);
}
}
Calender 转换为 Date
import java.util.Calendar;
import java.util.Date;
public class Main {
public static void main(String[] args) {
Calendar calendar = Calendar.getInstance();
Date date = calendar.getTime();
System.out.println( date );
}
}
运行结果示例：
Mon Jun 24 18:49:57 CST 2019
Date 转换为 Calender
import java.util.Calendar;
import java.util.Date;
public class Main {
public static void main(String[] args) {
Date date = new Date();
Calendar calendar = Calendar.getInstance();
calendar.setTime(date);
System.out.printf("%s-%s-%s %s:%s:%s \n",
calendar.get(Calendar.YEAR), calendar.get(Calendar.MONTH)+1, calendar.get(Calendar.DAY_OF_MONTH),
calendar.get(Calendar.HOUR_OF_DAY), calendar.get(Calendar.MINUTE), calendar.get(Calendar.SECOND)
);
}
}