LocalDate, LocalTime, LocalDateTime

  • LocalDate,LocalTime,LocalDateTimeInstances of the class are immutable objects representing the date, time, date, and time using the ISO-8601 calendar system, respectively. 
     @Test
  public void localDateTimeTest(a) {
    // Get the current date and time
    LocalDateTime now = LocalDateTime.now();
    System.out.println(now); / / the T10:2021-03-21 saith. 018324300
    // Set the specified date and time to get a new LocalDateTime
    LocalDateTime dateTime = LocalDateTime.of(2021.3.20.23.27.0);
    System.out.println(dateTime);  // 2021-03-20T23:27
    / / modify LocalDateTime
    LocalDateTime plusYears = dateTime.plusYears(10);
    System.out.println(plusYears);  // 2031-03-20T23:27
    LocalDateTime plusMonths = dateTime.plusMonths(10);
    System.out.println(plusMonths);  // 2022-01-20T23:27
    LocalDateTime plusDays = dateTime.plusDays(10);
    System.out.println(plusDays);  // 2021-03-30T23:27
    LocalDateTime plusHours = dateTime.plusHours(10);
    System.out.println(plusHours);  // 2021-03-21T09:27
    LocalDateTime plusMinutes = dateTime.plusMinutes(10);
    System.out.println(plusMinutes);  // 2021-03-20T23:37
    LocalDateTime plusSeconds = dateTime.plusSeconds(10);
    System.out.println(plusSeconds);  // 2021-03-20T23:27:10

    LocalDateTime minusDays = dateTime.minusDays(10);
    System.out.println(minusDays);  // 2021-03-10T23:27

    LocalDateTime plus = dateTime.plus(Duration.ofDays(1));
    System.out.println(plus);  // 2021-03-21T23:27

    LocalDateTime withDayOfMonth = dateTime.withDayOfMonth(1);  // Change to the first day of the month
    System.out.println(withDayOfMonth);  // 2021-03-01T23:27
    LocalDateTime withDayOfYear = dateTime.withDayOfYear(1);  // Change to the first day of the year
    System.out.println(withDayOfYear);  // 2021-01-01T23:27
    LocalDateTime withMonth = dateTime.withMonth(1);  // Change the month to January, other unchanged
    System.out.println(withMonth);  // 2021-01-20T23:27
    LocalDateTime withYear = dateTime.withYear(1);  // Change the year
    System.out.println(withYear);  // 0001-03-20T23:27
    // Get information
    int dayOfMonth = dateTime.getDayOfMonth();  // Get the current date
    System.out.println(dayOfMonth);  / / 20
    int dayOfYear = dateTime.getDayOfYear();  // Get the current day of the year
    System.out.println(dayOfYear);  / / 79
    DayOfWeek dayOfWeek = dateTime.getDayOfWeek();  // Get the day of the week
    System.out.println(dayOfWeek);  // SATURDAY
    Month month = dateTime.getMonth();  // Get the month
    System.out.println(month);  // MARCH
    int monthValue = dateTime.getMonthValue();  // Get the month int value
    System.out.println(monthValue);    / / 3
    int year = dateTime.getYear();  // Get the year
    System.out.println(year);  / / 2021

    // Compare dates
    boolean after = dateTime.isAfter(now);
    System.out.println(after);  // false
    boolean before = dateTime.isBefore(now);
    System.out.println(before);  // true
  }
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    The same applies to LocalTime and LocalDate

Instant timestamp

  • It is based on a description of what happened in the first year of Unix (traditionally set at midnight on January 1, 1970 in the UTC time zone) 
      @Test
  public void InstantTest(a) {
    Instant now = Instant.now();  // According to standard time, not local time
    System.out.println(now);  / / the 2021-03-21 T05:22:02. 162907300 z

    OffsetDateTime offsetDateTime = now.atOffset(ZoneOffset.ofHours(8));
    System.out.println(offsetDateTime);  / / the T13:2021-03-21 22:02. 162907300 + 08:00

    long epochSecond = now.getEpochSecond();  // How many seconds have been offset since 1970
    System.out.println(epochSecond);  / / 1616304122

    Instant ofEpochSecond = Instant.ofEpochSecond(1);  // Since 1970, offset by one second
    System.out.println(ofEpochSecond);  // 1970-01-01T00:00:01Z
  }
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Duration and Period

  • Duration: used to calculate two “time” intervals; Period: Used to calculate two “date” intervals 
      @Test
  public void DurationTest(a) {
    Instant now = Instant.now();
    try {
      Thread.sleep(100);
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
    Instant now1 = Instant.now();
    // Calculate the time difference
    Duration duration = Duration.between(now, now1);
    System.out.println(duration);  / / PT0.1126982 S

    LocalDateTime now2 = LocalDateTime.now();
    try {
      Thread.sleep(100);
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
    LocalDateTime now3 = LocalDateTime.now();
    // Calculate the time difference
    Duration between = Duration.between(now2, now3);
    System.out.println(between);  / / PT0.1067149 S

    // Calculate the date difference
    Period between1 = Period.between(now2.toLocalDate(), now3.toLocalDate());
    System.out.println(between1);

    Period between2 = Period.between(LocalDate.of(2010.10.1), LocalDate.now());
    System.out.println(between2);
  }
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4. Date manipulation

  • TemporalAdjuster: Time corrector. Sometimes we may need to get. For example, change the date to next Sunday
  • TemporalAdjusters: This class provides a lot of common usage through static methodsTemporalAdjusterThe implementation of the 
      @Test
  public void temporalAdjusterTest(a) {
    LocalDateTime now = LocalDateTime.now();
    LocalDateTime nextDayOfWeekFRIDAY = now.with(TemporalAdjusters.next(DayOfWeek.FRIDAY));  / / next Friday
    System.out.println(nextDayOfWeekFRIDAY);

    LocalDateTime firstDayOfMonth = now.with(TemporalAdjusters.firstDayOfMonth());  // The first day of the month
    System.out.println(firstDayOfMonth);
  }
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Parse and format

  • java.time.format.DateTimeFormatterClass: This class provides three formatting methods:
    • Predefined standard formats
    • Locale-specific formats
    • Custom format
      @Test
  public void DateTimeFormatterTest(a) {
    DateTimeFormatter isoWeekDate = DateTimeFormatter.ISO_LOCAL_DATE;  // Predefined standard format
    LocalDateTime now = LocalDateTime.now();
    String format = now.format(isoWeekDate);  // Convert to String
    System.out.println(format);

    DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");  // Define the format
    String format1 = now.format(formatter);  // Convert to String
    System.out.println(format1);

    LocalDateTime parse = LocalDateTime.parse("The 2020-01-01 10:10:10", formatter);  / / parsing
    System.out.println(parse);
  }
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Six, time zone processing

  • Java8 has added support for time zones, with time zones as follows:ZonedDate,ZonedTime,ZonedDateTime
  • Each time zone corresponds to an ID. The region ID is in the format of {region}/{city}, for example:Asia/Shanghai 等
  • ZoneId: This class contains all time zone information
    • getAvailableZoneIds(): You can obtain the time zone information of all time zones
    • of(id): Obtain the value with the specified time zone informationZoneIdobject
      @Test
  public void ZoneIdTest(a) {
    Set<String> availableZoneIds = ZoneId.getAvailableZoneIds();
    availableZoneIds.forEach(System.out::println);  // Get all time zones

    LocalDateTime now = LocalDateTime.now(ZoneId.of("Asia/Shanghai"));
    System.out.println(now);  / / the 2021-03-21 T13: time. 184581100
    ZonedDateTime now1 = ZonedDateTime.now(ZoneId.of("Asia/Shanghai"));
    System.out.println(now1);  // 2021-03-21T13:17:21.184581100+08:00[Asia/Shanghai] Bring the local time of the time zone
  }
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