Date and time

LocalDate

Create a LocalDate object and read its value

// According to the date of establishment
LocalDate date1 = LocalDate.of(2014, 3, 18);

// read
System.out.println(date1.getYear()); // 2014
System.out.println(date1.getMonth()); // MARCH
System.out.println(date1.getMonth().getValue()); // 3
System.out.println(date1.getDayOfMonth()); // 18
System.out.println(date1.lengthOfMonth()); // 31
System.out.println(date1.isLeapYear()); // false

// current date
LocalDate now = LocalDate.now();
System.out.println(now); // 2018-08-14

// Get date from date object
System.out.println(now.get(ChronoField.YEAR)); // 2018
System.out.println(now.get(ChronoField.MONTH_OF_YEAR)); // 8
System.out.println(now.get(ChronoField.DAY_OF_MONTH)); // 14

LocalTime

Create LocalTime and read value

// Create time based on hours, minutes and seconds
LocalTime time1 = LocalTime.of(13, 45, 20);
System.out.println(time1.getHour()); // 13
System.out.println(time1.getMinute()); // 45
System.out.println(time1.getSecond()); // 20

// Create a date or time from a date or time string
LocalDate date2 = LocalDate.parse("2014-03-18");
LocalTime time2 = LocalTime.parse("13:45:20");

LocalDateTime

Create a LocalDateTime object directly or by merging dates and times

// Direct creation date time
LocalDateTime lt1 = LocalDateTime.of(2014, Month.MARCH, 18, 13, 45, 20);

// Created by date and time
LocalDate date1 = LocalDate.of(2014, 3, 18);
LocalTime time1 = LocalTime.of(13, 45, 20);
LocalDateTime lt2 = LocalDateTime.of(date1, time1);
LocalDateTime lt3 = date1.atTime(13, 45, 20);
LocalDateTime lt4 = date1.atTime(time1);
LocalDateTime lt5 = time1.atDate(date1);

// Extract date and time from datetime
LocalDate date2 = lt1.toLocalDate();
LocalTime time2 = lt1.toLocalTime();

Instant

Date and time format of the machine

// Get the current time stamp
System.out.println(Instant.now().toEpochMilli()); // 1534255959679

Time slot

Duration & Period

The unit of interval is hour, minute and second, and the unit of interval is year, month and day

Create Duration and Period objects

LocalDate date1 = LocalDate.parse("2018-08-12");
LocalDate date2 = LocalDate.parse("2018-08-11");
LocalTime time1 = LocalTime.parse("12:45:20");
LocalTime time2 = LocalTime.parse("12:45:21");
Instant instant1 = Instant.ofEpochSecond(22);
Instant instant2 = Instant.ofEpochSecond(11);

// Time interval is time seconds
Duration d2 = Duration.between(time1, time2); // time2 - time1
Duration d3 = Duration.between(instant1, instant2); // instant2 - instant1
Duration d4 = Duration.ofMinutes(3); // Create a 3 minute time period
System.out.println(d2.getSeconds()); // 1
System.out.println(d4.getSeconds()); // 180

// Time interval is MM DD YY
Period p1 = Period.between(date1, date2); // date2 - date1
Period p2 = Period.ofDays(10);
System.out.println(p1.getDays()); // -1
System.out.println(p2.getDays()); // 10

Manipulating, parsing, and formatting dates

Modify LocalDate object properties

LocalDate date1 = LocalDate.of(2014, 3, 18);

// Modify in a more intuitive way
LocalDate date1 = date1.withYear(2011); // Revision year
LocalDate date1 = date1.withMonth(11); // Revision month
LocalDate date1 = date1.withDayOfMonth(25); // Revision date

// Modify in a relative way
date1.minusYears(1); // Reduction of 1 years
date1.plusYears(2); // Plus two years
date1.plus(3, ChronoUnit.MONTHS); // Plus March
date1.plus(22, ChronoUnit.DAYS); // Plus 22 days

TemporalAdjuster

LocalDate date1 = LocalDate.of(2014, 3, 18);

// The first Sunday after the current date including the current date
System.out.println(date1.with(nextOrSame(DayOfWeek.SUNDAY))); // 2014-03-23

// First Sunday of the month
System.out.println(date1.with(firstInMonth(DayOfWeek.SUNDAY))); // 2014-03-02
// Last Sunday of the month
System.out.println(date1.with(lastInMonth(DayOfWeek.SUNDAY))); // 2014-03-30
// First day of the month
System.out.println(date1.with(firstDayOfMonth())); // 2014-03-01
// Last day of the month
System.out.println(date1.with(lastDayOfMonth())); // 2014-03-31

// The first day of the year
System.out.println(date1.with(firstDayOfYear())); // 2014-01-01
// The first day of next year
System.out.println(date1.with(firstDayOfNextYear())); // 2015-01-01

Customize a temporaladjuster

Next working day

Scheme 1: implement a TemporalAdjuster class

public class NextWorkingDay implements TemporalAdjuster {
    @Override
    public Temporal adjustInto(Temporal temporal) {
        // What day of the week is the current date
        DayOfWeek dow =
                DayOfWeek.of(temporal.get(ChronoField.DAY_OF_WEEK));
        // Judge how many days to move back
        int dayToAdd = 1;
        if (dow == DayOfWeek.FRIDAY) dayToAdd = 3;
        else if (dow == DayOfWeek.SATURDAY) dayToAdd = 2;
        return temporal.plus(dayToAdd, ChronoUnit.DAYS);
    }
}

Scheme 2: use Lambda directly

LocalDate nextWorkingDate = LocalDate.now()
    .with(temporal -> {
        // What day of the week is the current date
        DayOfWeek dow =
            DayOfWeek.of(temporal.get(ChronoField.DAY_OF_WEEK));
        // Judge how many days to move back
        int dayToAdd = 1;
        if (dow == DayOfWeek.FRIDAY) dayToAdd = 3;
        else if (dow == DayOfWeek.SATURDAY) dayToAdd = 2;
        return temporal.plus(dayToAdd, ChronoUnit.DAYS);
    });

Scheme 3: using Lambda to implement a TemporalAdjuster

TemporalAdjuster nextWorkingDay = TemporalAdjusters.ofDateAdjuster(
    temporal -> {
        // What day of the week is the current date
        DayOfWeek dow =
            DayOfWeek.of(temporal.get(ChronoField.DAY_OF_WEEK));
        // Judge how many days to move back
        int dayToAdd = 1;
        if (dow == DayOfWeek.FRIDAY) dayToAdd = 3;
        else if (dow == DayOfWeek.SATURDAY) dayToAdd = 2;
        return temporal.plus(dayToAdd, ChronoUnit.DAYS);
    }
);

Output and analyze date and time objects

LocalDate date1 = LocalDate.of(2014, 3, 18);
System.out.println(date1.format(DateTimeFormatter.BASIC_ISO_DATE)); // 20140318
System.out.println(date1.format(DateTimeFormatter.ISO_LOCAL_DATE)); // 2014-03-18

LocalDate date2 = LocalDate.parse("20140318", DateTimeFormatter.BASIC_ISO_DATE);
LocalDate date3 = LocalDate.parse("2014-03-18", DateTimeFormatter.ISO_LOCAL_DATE);

// Create a DateTimeFormatter based on a pattern
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy/MM/dd");
System.out.println(date1.format(formatter)); // 2014/03/18
LocalDate date4 = LocalDate.parse("2018/08/14", formatter);

// Create a localized DateTimeFormatter
DateTimeFormatter italianFormatter =
    DateTimeFormatter.ofPattern("d. MMMM yyyy", Locale.ITALIAN);
System.out.println(date1.format(italianFormatter)); // 18. marzo 2014
LocalDate date5 = LocalDate.parse("18. marzo 2014", italianFormatter);

Time zone and calendar

ZoneId

// Print all time zones
ZoneId.getAvailableZoneIds().stream()
	.forEach(System.out::println);

// Create a time zone in the format {region} / {City}
ZoneId romeZone = ZoneId.of("Europe/Rome");

// Convert old time zone object to ZoneId
ZoneId newZoneId = TimeZone.getDefault().toZoneId();

//  Get current time zone
ZoneId defaultZoneId = ZoneId.systemDefault();
System.out.println(defaultZoneId); // Asia/Shanghai

ZonedDateTime

Add time zone information for a point in time

ZoneId romeZone = ZoneId.of("Europe/Rome");

// Add time zone information for a point in time
LocalDate date1 = LocalDate.now();
ZonedDateTime zdt1 = date1.atStartOfDay(romeZone);

LocalDateTime dateTime1 = LocalDateTime.now();
ZonedDateTime zdt2 = dateTime1.atZone(romeZone);

Instant instant1 = Instant.now();
ZonedDateTime zdt3 = instant1.atZone(romeZone);

// Convert LocalDateTime to Instant
Instant instantFromDateTime = dateTime1.toInstant(ZoneOffset.ofHours(0));
// Convert Instant to LocalDateTime
LocalDateTime dateTimeFromInstant = LocalDateTime.ofInstant(instant1, romeZone);

ZoneOffset

Time zone calculation using a fixed deviation from UTC / Greenwich mean time

// Not recommended
// New York is five hours behind London
ZoneOffset newYorkOffset = ZoneOffset.of("-05:00");
System.out.println(newYorkOffset);
OffsetDateTime dateTimeInNewYork = OffsetDateTime.of(LocalDateTime.now(), newYorkOffset);

Other calendar systems

ISO-8601 calendar system is the fact standard of world civilization calendar system. Java 8 also provides four other calendar systems, namely

ThaiBuddhistDate
MinguoDate
JapaneseDate
HijrahDate  // Islamic calendar

All these classes and LocalDate implement the chronololocaldate interface.

LocalDate date1 = LocalDate.now();
JapaneseDate japaneseDate = JapaneseDate.from(date1);
System.out.println(japaneseDate); // Japanese Heisei 30-08-14

Chronology japaneseChronology = Chronology.ofLocale(Locale.JAPAN);
ChronoLocalDate now = japaneseChronology.dateNow();
System.out.println(now); // 2018-08-14