Java8 new features of the time and date API

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Java8 includes a new time and date API, which is placed under the java.time package. This new time-date API is immutable and thread-safe (This class is immutable and thread-safe).

Local time: LocalDate, LocalTime, LocalDateTime

Instances of the classes localDate, LocalTime, and LocalDateTime are immutable objects that represent the date, time, date, and time, respectively, using the ISO-8601 calendar system. They provide a simple date or time and do not contain current time information. Nor do they contain information related to the time zone.

localDate, LocalTime, and LocalDateTime are used in exactly the same way.

Take localDateTime as an example.

// Get the current date and time
LocalDateTime nowDateTime = LocalDateTime.now();
System.out.println(nowDateTime);
// Get the specified date and time
LocalDateTime assignDateTime = LocalDateTime.of(2017, 11, 22, 15, 23, 55);
System.out.println(assignDateTime);
// current time plus two years
LocalDateTime nowDateTimePlus2Years = nowDateTime.plusYears(2);
System.out.println(nowDateTimePlus2Years);
// Current time minus two years
LocalDateTime nowDateTimeMinus2Years = nowDateTime.minusYears(2);
System.out.println(nowDateTimeMinus2Years);

Output result.

2018-05-13T16:56:04.346 2017-11-22T15:23:55 2020-05-13T16:56:04.346 2016-05-13T16:56:04.346

Timestamp : Instant

Instant : Timestamp, starting at 00:00:00 on January 1, 1970 and ending at a certain time in milliseconds.

// Get UTC time zone by default (UTC: Universal Time)
Instant instant1 = Instant.now();
System.out.println(instant1);
// Get the timestamp
long milli = instant1.toEpochMilli();
System.out.println(milli);
// with offset operation: offset by 8 hours: Beijing time
OffsetDateTime offsetDateTime = instant1.atOffset(ZoneOffset.ofHours(8));
System.out.println(offsetDateTime);

// add 60 seconds to the time stamp
Instant instant2 = Instant.ofEpochSecond(60);
System.out.println(instant2);

Output result.

2018-05-13T11:54:33.717Z 1526212473717 2018-05-13T19:54:33.717+08:00 1970-01-01T00:01:00Z

Calculation interval: Duration, Period

Duration : Calculates the interval between two “times”.

Period: Calculates the interval between two “dates”.

Calculates the interval between two “times”.

Instant instant1 = Instant.now();
try {
  Thread.sleep(1000);
} catch (InterruptedException e) {
  e.printStackTrace();
}
Instant instant2 = Instant.now();

Duration duration = Duration.between(instant1, instant2);
System.out.println(duration.toMillis());

System.out.println("==================");

LocalTime time1 = LocalTime.now();
try {
  Thread.sleep(1000);
} catch (InterruptedException e) {
  e.printStackTrace();
}
LocalTime time2 = LocalTime.now();
System.out.println(Duration.between(time1, time2).toMillis());

1 4 12

Difference of 1 year, 4 months and 12 days.

Time corrector: TemporalAdjuster

TemporalAdjuster : A time corrector, sometimes we may need to get, for example, to adjust the date to “next week as” and so on.

TemporalAdjusters: This class provides a number of common TemporalAdjuster implementations via static methods.

For example.

LocalDateTime dateTime = LocalDateTime.now();
// Specify the date
LocalDateTime dateTimeWithDayOfMonth = dateTime.withDayOfMonth(10);
// Specify the time using the time corrector: the next weekend
LocalDateTime dateTimeNextSunday = dateTime.with(TemporalAdjusters.next(DayOfWeek.SUNDAY));
System.out.println(dateTimeNextSunday);

// Custom time corrector: get the next weekday
LocalDateTime dateTime1 = dateTime.with((temporal) -> {
  LocalDateTime time = (LocalDateTime)temporal;
  DayOfWeek dayOfWeek = time.getDayOfWeek();
  if (dayOfWeek.equals(DayOfWeek.FRIDAY)) {
    return time.plusDays(3);
  } else if (dayOfWeek.equals(DayOfWeek.SATURDAY)) {
    return time.plusDays(2);
  } else {
    return time.plusDays(1);
  }
});
System.out.println(dateTime1);

Time and date formatting: dateTimeFormatter

// Use the ISO standard date format
DateTimeFormatter formatter = DateTimeFormatter.ISO_DATE_TIME;
LocalDateTime dateTime = LocalDateTime.now();
// Formatting method for LocalDateTime
String dateStr = dateTime.format(formatter);
System.out.println(dateStr);

// Using a custom date format
DateTimeFormatter formatter1 = DateTimeFormatter.ofPattern("yyyy year MM month dd day HH:mm:ss");
// DateTimeFormatter's formatting method
String dateStr2 = formatter1.format(dateTime);
System.out.println(dateStr2);

Handling of time zones: ZonedDate, ZonedTime, ZonedDateTime

Take LocalDateTime as an example.

Use the static LocalDateTime now(ZoneId zone) method of LocalDateTime to specify the time zone.

LocalDateTime dateTime = LocalDateTime.now(ZoneId.of("America/Los_Angeles"));

Result: 2018-05-13T06:24:47.349. shows the time in the Los Angeles time zone, USA.

To convert to ZonedDateTime (time date object with time zone) using the ZonedDateTime atZone(ZoneId zone) method of LocalDateTime.

LocalDateTime dateTime2 = LocalDateTime.now();
ZonedDateTime zonedDateTime = dateTime2.atZone(ZoneId.of("America/Los_Angeles"));
System.out.println(zonedDateTime);

Result: 2018-05-13T06:24:47.446-07:00 [America/Los_Angeles] ZonedDateTime is the time date with time zone.