20191227 Java8 date and time API

background

Java 8 to further enhance the processing of the date and time by issuing new Date-Time API (JSR 310).

In older versions of Java, there are many problems date and time API, including:

• Non-thread-safe - java.util.Date non-thread-safe, all the dates are variable class, which is one of the biggest problems date Java classes.
• Poor design - defined Java date / time is not the same class, and in java.util package java.sql class includes the date, in addition to formatting and parsing the class definition java.text package. java.util.Date contains the date and time, and contains only java.sql.Date date will be incorporated into the package java.sql unreasonable. In addition these two classes have the same name, which itself is a very bad design.
• Time zone handling trouble - Date class does not offer international, no time zone support, so the introduction of Java and java.util.TimeZone java.util.Calendar class, but they are all above problems also exist.

Java 8 in java.timeproviding a lot of new API under the package. The following are two of the more important API:

• Local (Local) - simplifies the handling of date and time, no problem time zone.
• Zoned (time zone) - the processing date and time established by time zone.

Java.time new packet covers all the processing date, time, date / time, time zone, time (Instants), the process (During) with the clock (Clock) operation.

localdateti me, LOCALDATE, localtime

These three are localized date and time API

• LocalDateTime contains the date and time, for example: 2018-09-24 10:32:10
• LocalDate only contains the date, for example: 2018-09-24
• LocalTime contains only time such as: 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

Date and time with time zone

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 contain only day of information, it can be used to store like birthdays, wedding anniversaries and other information.

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 duration between the two used to calculate LocalDate.

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 used to calculate two or LocalTime LocalDateTime time difference.

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

Timestamp.

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 by specifying a time zone, and then you can obtain the current time, date and time. Can replace System.currentTimeMillis () and 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

Operation of the time zone.

ZoneId is an abstract class, it is ZoneOffset and ZoneRegion parent.

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

Used to adjust the date and time.

TemporalAdjuster is a function interface, TemporalAdjusters are tools.

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

Used to format date and time

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);
}

And conversion of java.util.Date

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);
}

Reference material

• Java 8 Date Time API - rookie Tutorial
• [Java8 new features] new date and time API
• Java8 date and time of the operation
• Java8 Instant timestamp
• LocalDate transformation and Date
• Java8 new time zone handling characteristics -018-