20191227 Java8 日期时间API
背景
Java 8通过发布新的Date-Time API (JSR 310)来进一步加强对日期与时间的处理。
在旧版的 Java 中，日期时间 API 存在诸多问题，其中有：
- 非线程安全 − java.util.Date 是非线程安全的，所有的日期类都是可变的，这是Java日期类最大的问题之一。
- 设计很差 − Java的日期/时间类的定义并不一致，在java.util和java.sql的包中都有日期类，此外用于格式化和解析的类在java.text包中定义。java.util.Date同时包含日期和时间，而java.sql.Date仅包含日期，将其纳入java.sql包并不合理。另外这两个类都有相同的名字，这本身就是一个非常糟糕的设计。
- 时区处理麻烦 − 日期类并不提供国际化，没有时区支持，因此Java引入了java.util.Calendar和java.util.TimeZone类，但他们同样存在上述所有的问题。
Java 8 在 java.time 包下提供了很多新的 API。以下为两个比较重要的 API：
- Local(本地) − 简化了日期时间的处理，没有时区的问题。
- Zoned(时区) − 通过制定的时区处理日期时间。
新的java.time包涵盖了所有处理日期，时间，日期/时间，时区，时刻（instants），过程（during）与时钟（clock）的操作。
LocalDateTime, LocalDate, LocalTime
这三者是本地化日期时间API
- LocalDateTime 包含日期和时间，比如：2018-09-24 10:32:10
- LocalDate 只包含日期，比如：2018-09-24
- LocalTime 只包含时间，比如：10:32:10
private void testLocalDateTime() {
System.out.println("=================== testLocalDateTime ============================");
// 获取当前的日期时间
LocalDateTime localDateTime = LocalDateTime.now();
System.out.println("当前日期时间: " + localDateTime);
System.out.println("当前日期: " + localDateTime.toLocalDate());
System.out.println("当前时间: " + localDateTime.toLocalTime());
System.out.println(",================== get =============================");
// get
// 获取日期时间的单项值
int year = localDateTime.get(ChronoField.YEAR);
Month month = localDateTime.getMonth();
int monthValue = localDateTime.getMonthValue();
int dayOfYear = localDateTime.getDayOfYear();
int dayOfMonth = localDateTime.getDayOfMonth();
DayOfWeek dayOfWeek = localDateTime.getDayOfWeek();
int hour = localDateTime.getHour();
int minute = localDateTime.getMinute();
int seconds = localDateTime.getSecond();
int nano = localDateTime.getNano();
System.out.println("year：" + year);
System.out.println("month：" + month);
System.out.println("monthValue：" + monthValue);
System.out.println("dayOfYear：" + dayOfYear);
System.out.println("dayOfMonth：" + dayOfMonth);
System.out.println("dayOfWeek：" + dayOfWeek);
System.out.println("hour：" + hour);
System.out.println("minute：" + minute);
System.out.println("seconds：" + seconds);
System.out.println("nano：" + nano);
System.out.println(",================== with, plus, minus =============================");
LocalDateTime withDateTime = localDateTime.with(ChronoField.YEAR, 2000).withMonth(10);
System.out.println("withDateTime: " + withDateTime);
LocalDateTime plusLocalDateTime = localDateTime.plus(1, ChronoUnit.MONTHS);
System.out.println("plusLocalDateTime: " + plusLocalDateTime);
LocalDateTime minusLocalDateTime = localDateTime.minusDays(1);
System.out.println("minusLocalDateTime: " + minusLocalDateTime);
System.out.println(",================== of =============================");
// of
// 通过指定值获取指定日期
LocalDateTime ofLocalDateTime = LocalDateTime.of(2019, 12, 27, 15, 8, 7);
System.out.println("ofLocalDateTime：" + ofLocalDateTime);
LocalDate ofLocalDate = LocalDate.of(2014, Month.DECEMBER, 12);
System.out.println("ofLocalDate: " + ofLocalDate);
LocalTime ofLocalTime = LocalTime.of(22, 15);
System.out.println("ofLocalTime: " + ofLocalTime);
System.out.println(",================== parse =============================");
// parse
// 将字符串解析为日期、时间
LocalDateTime parseDateTime = LocalDateTime.parse("2019-11-01T20:15:30.001");
System.out.println("parseDateTime: " + parseDateTime);
LocalDate parseDate = LocalDate.parse("2019-11-01");
System.out.println("parseDate: " + parseDate);
LocalTime parseTime = LocalTime.parse("20:15:30");
System.out.println("parseTime: " + parseTime);
System.out.println(",================== isAfter, isBefore =============================");
boolean isAfter = localDateTime.isAfter(localDateTime.minusDays(1));
System.out.println("isAfter: " + isAfter);
boolean isBefore = localDateTime.isBefore(localDateTime.minusDays(1));
System.out.println("isBefore: " + isBefore);
System.out.println("================== LocalDate =============================");
LocalDate localDate = LocalDate.now();
System.out.println("localDate：" + localDate);
int lengthOfMonth = localDate.lengthOfMonth();
System.out.println("该月天数：" + lengthOfMonth);
boolean isLeapYear = localDate.isLeapYear(); // false
System.out.println("是否闰年：" + isLeapYear);
LocalDateTime dateTime = localDate.atTime(5, 6);
System.out.println("转为LocalDateTime：" + dateTime);
System.out.println("================== LocalTime =============================");
LocalTime localTime = LocalTime.now();
System.out.println("localTime：" + localTime);
LocalDateTime localDateTime1 = localTime.atDate(localDate);
System.out.println("转为LocalDateTime：" + localDateTime1);
}
ZonedDateTime
带时区的日期时间
private void testZonedDateTime() {
System.out.println("=================== testZonedDateTime ============================");
// 获取当前时间日期
ZonedDateTime date1 = ZonedDateTime.parse("2015-12-03T10:15:30+05:30[Asia/Shanghai]");
System.out.println("date1: " + date1);
ZoneId id = ZoneId.of("Europe/Paris");
System.out.println("ZoneId: " + id);
ZoneId currentZone = ZoneId.systemDefault();
System.out.println("当期时区: " + currentZone);
}
MonthDay
MonthDay只包含月日信息，可以用于存放类似于生日，结婚纪念日等信息。
private void testMonthDay() {
System.out.println("=================== testMonthDay ============================");
LocalDate birthday = LocalDate.of(1999, 12, 27);
MonthDay monthDay = MonthDay.of(birthday.getMonth(), birthday.getDayOfMonth());
System.out.println("monthDay：" + monthDay);
MonthDay fromMonthDay = MonthDay.from(LocalDate.now());
System.out.println("MonthDay.from(LocalDate.now())：" + fromMonthDay);
if (fromMonthDay.equals(monthDay)) {
System.out.println("happy birthday!");
} else {
System.out.println("not birthday!");
}
}
Period
Period用于计算两个LocalDate之间的时长。
private void testPeriod() {
System.out.println("=================== testPeriod ============================");
LocalDate date1 = LocalDate.of(2018, 9, 30);
LocalDate date2 = LocalDate.of(2018, 10, 31);
Period period = Period.between(date1, date2);
System.out.println("period：" + period);
List<TemporalUnit> units = period.getUnits();
System.out.println("units：" + units);
int months = period.getMonths();
int days = period.getDays();
System.out.println("months：" + months);
System.out.println("days：" + days);
}
Duration
Duration用于计算两个LocalTime或者LocalDateTime的时间差。
private void testDuration() {
System.out.println("=================== testDuration ============================");
LocalDateTime dateTime1 = LocalDateTime.now();
LocalDateTime dateTime2 = LocalDateTime.now().plusSeconds(60 * 60 * 2 + 1).minusNanos(1000000);
Duration duration = Duration.between(dateTime1, dateTime2);
System.out.println("duration：" + duration);
List<TemporalUnit> units = duration.getUnits();
System.out.println("duration.getUnits()：" + units);
long seconds = duration.getSeconds();
System.out.println("duration.getSeconds()：" + seconds);
long nano = duration.getNano();
System.out.println("duration.getNano()：" + nano);
boolean isZero = duration.isZero();
System.out.println("duration.isZero()：" + isZero);
long hours = duration.toHours();
System.out.println("duration.toHours()：" + hours);
Duration abs = duration.abs();
System.out.println("duration.abs()：" + abs);
boolean isNegative = duration.isNegative();
System.out.println("duration.isNegative()：" + isNegative);
Duration withDuration = duration.withSeconds(5);
System.out.println("duration.withSeconds(5)：" + withDuration);
Duration plusNanos = duration.plusNanos(1000000);
System.out.println("duration.plusNanos(1000000)：" + plusNanos);
}
Instant
时间戳。
private void testInstant() {
System.out.println("=================== testInstant ============================");
Instant instant = Instant.now();
System.out.println("instant：" + instant);
// 获取毫秒数
long toEpochMilli = instant.toEpochMilli();
System.out.println("toEpochMilli：" + toEpochMilli);
}
Clock
Clock 通过指定一个时区，然后就可以获取到当前的时刻，日期与时间。可以替代 System.currentTimeMillis() 与 TimeZone.getDefault() 。
private void testClock() {
System.out.println("=================== testClock ============================");
Clock clock = Clock.systemDefaultZone();
System.out.println("Clock.systemDefaultZone()：" + clock);
Instant instant = clock.instant();
System.out.println("clock.instant()：" + instant);
}
ZoneId, ZoneOffset, ZoneRegion
对时区的操作。
ZoneId是抽象类，是ZoneOffset和ZoneRegion的父类。
private void testZone() {
System.out.println("=================== testZone ============================");
System.out.println(",=================== ZoneId ============================");
Set<String> set = ZoneId.getAvailableZoneIds();
System.out.println("ZoneId.getAvailableZoneIds()：" + Arrays.toString(set.toArray()));
System.out.println(",,=================== ZoneOffset ============================");
ZoneId systemDefaultZoneId = ZoneId.systemDefault();
System.out.println("ZoneId.systemDefault()：" + systemDefaultZoneId);
ZoneId ofZoneId = ZoneId.of("Asia/Aden");
System.out.println("ofZoneId.getClass()：" + ofZoneId.getClass());
System.out.println("ZoneId.of(\"Asia/Aden\")：" + ofZoneId);
System.out.println(",,=================== ZoneRegion ============================");
ZoneId ofZoneRegion = ZoneId.of("+8");
System.out.println("ofZoneRegion.getClass()：" + ofZoneRegion.getClass());
System.out.println("ZoneId.of(\"+8\")：" + ofZoneRegion);
}
TemporalAdjuster, TemporalAdjusters
用于调整日期时间。
TemporalAdjuster 是函数式接口，TemporalAdjusters 是工具类。
private void testTemporalAdjusters() {
System.out.println("=================== testTemporalAdjusters ============================");
LocalDateTime localDateTime = LocalDateTime.now();
System.out.println("当前时间：" + localDateTime);
TemporalAdjuster temporalAdjuster = null;
System.out.println("=================== first, last ============================");
temporalAdjuster = TemporalAdjusters.firstInMonth(DayOfWeek.FRIDAY);
this.adjustDateTime("当月的第一个星期五", temporalAdjuster);
temporalAdjuster = TemporalAdjusters.firstDayOfMonth();
this.adjustDateTime("当月的第一天", temporalAdjuster);
temporalAdjuster = TemporalAdjusters.firstDayOfNextMonth();
this.adjustDateTime("下个月的第一天", temporalAdjuster);
temporalAdjuster = TemporalAdjusters.lastInMonth(DayOfWeek.FRIDAY);
this.adjustDateTime("当月的最后一个星期五", temporalAdjuster);
temporalAdjuster = TemporalAdjusters.lastDayOfMonth();
this.adjustDateTime("当月的最后一天", temporalAdjuster);
temporalAdjuster = TemporalAdjusters.lastDayOfYear();
this.adjustDateTime("当年的最后一天", temporalAdjuster);
System.out.println("=================== next, previous ============================");
// next：如果当天是周五，返回下一个周五
// nextOrSame：如果当天是周五，返回当天
temporalAdjuster = TemporalAdjusters.next(DayOfWeek.FRIDAY);
this.adjustDateTime("下一个周五", temporalAdjuster);
temporalAdjuster = TemporalAdjusters.nextOrSame(DayOfWeek.FRIDAY);
this.adjustDateTime("下一个周五", temporalAdjuster);
// previous：如果当天是周五，返回上一个周五
// previousOrSame：如果当天是周五，返回当天
temporalAdjuster = TemporalAdjusters.previous(DayOfWeek.FRIDAY);
this.adjustDateTime("上一个周五", temporalAdjuster);
temporalAdjuster = TemporalAdjusters.previousOrSame(DayOfWeek.FRIDAY);
this.adjustDateTime("上一个周五", temporalAdjuster);
System.out.println("=================== dayOfWeekInMonth ============================");
temporalAdjuster = TemporalAdjusters.dayOfWeekInMonth(3, DayOfWeek.SUNDAY);
this.adjustDateTime("当月的第三个星期日", temporalAdjuster);
System.out.println("=================== ofDateAdjuster ============================");
temporalAdjuster = TemporalAdjusters.ofDateAdjuster(localDate -> localDate.minusDays(1));
this.adjustDateTime("昨天", temporalAdjuster);
}
private void adjustDateTime(String desc, TemporalAdjuster temporalAdjuster) {
LocalDateTime localDateTime = LocalDateTime.now();
LocalDateTime with = localDateTime.with(temporalAdjuster);
System.out.println(desc + "：" + with);
}
DateTimeFormatter
用于格式化日期时间
private void testDateTimeFormatter() {
System.out.println("=================== testDateTimeFormatter ============================");
DateTimeFormatter dateTimeFormatter = null;
System.out.println(",=================== ofLocalizedDateTime ============================");
// FormatStyle.FULL 带时区信息，不能用于 LocalDateTime
dateTimeFormatter = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.FULL);
this.formatDateTime("ofLocalizedDateTime(FormatStyle.FULL)：", dateTimeFormatter);
dateTimeFormatter = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.LONG);
this.formatDateTime("ofLocalizedDateTime(FormatStyle.LONG)：", dateTimeFormatter);
dateTimeFormatter = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.MEDIUM);
this.formatDateTime("ofLocalizedDateTime(FormatStyle.MEDIUM)：", dateTimeFormatter);
dateTimeFormatter = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.SHORT);
this.formatDateTime("ofLocalizedDateTime(FormatStyle.SHORT)：", dateTimeFormatter);
System.out.println(",=================== ofPattern ============================");
dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy MM dd");
this.formatDateTime("ofPattern(\"yyyy MM dd\")：", dateTimeFormatter);
System.out.println(",=================== 静态常量 DateTimeFormatter ============================");
dateTimeFormatter = DateTimeFormatter.BASIC_ISO_DATE;
this.formatDateTime("BASIC_ISO_DATE：", dateTimeFormatter);
dateTimeFormatter = DateTimeFormatter.ISO_DATE_TIME;
this.formatDateTime("ISO_DATE_TIME：", dateTimeFormatter);
}
private void formatDateTime(String desc, DateTimeFormatter dateTimeFormatter) {
ZonedDateTime zonedDateTime = ZonedDateTime.now();
String format = zonedDateTime.format(dateTimeFormatter);
System.out.println(desc + "：" + format);
}
与 java.util.Date 的相互转换
private void testConvert() {
System.out.println("=================== testConvert ============================");
System.out.println(",=================== LocalDateTime 转 java.util.Date ============================");
LocalDateTime localDateTime = LocalDateTime.now();
System.out.println("localDateTime：" + localDateTime);
Instant instant = localDateTime.atZone(ZoneId.systemDefault()).toInstant();
Date fromDate = Date.from(instant);
System.out.println("fromDate：" + fromDate);
System.out.println(",=================== java.util.Date 转 LocalDateTime ============================");
Date date = new Date();
System.out.println("date：" + date);
Instant toInstant = date.toInstant();
LocalDateTime ofLocalDateTime = LocalDateTime.ofInstant(toInstant, ZoneId.systemDefault());
System.out.println("ofLocalDateTime：" + ofLocalDateTime);
}
