New feature of JDK8: date time related API

Problems with old version date time API:

1. Poor design: in java.tilogjava Sq| has date classes in its packages, java.util.Date Contains both date and time, and java.sql.Date Only. Contains the date. In addition, the classes used for formatting and parsing are java.text Defined in the package.
2. Non thread safety: java.util.Date It is non thread safe. All date classes are mutable, which is one of the biggest problems of Java date classes.
3. Time zone processing trouble: the date class does not provide internationalization, and there is no time zone support. So ava introduced java.util.Calendar And java.util.TimeZone Class, but they also have all of the above problems.

New date time API introduction

A new set of date time API has been added in JDK 8, which is reasonably designed and thread safe.

java.time -Base package containing value objects
java.time.chrono -Provide access to different calendar systems
java.time.format -Format and parse time and date
java.time.temporal -Includes underlying framework and extension features
java.time.zone -Classes with time zone support

The new date and time API is located at java.time In the package, the following are some key classes:

LocalDate: refers to the date, including MM DD YY. The format is 2019-10-16
LocalTime: time, including time, minute and second, in the format of 16:38:54.158549300
LocalDateTime: indicates the date time, including mm / DD / yyyy, HHM / s, in the format of 2018-09-06T15:33:56.750
DateTimeFormatter: date time format class.
Instant: time stamp, indicating a specific time instant.
Duration: used to calculate the distance of 2 times (local time, hour minute second)
Period: used to calculate the distance between two dates
zonedDaterime: time with time zone

The calendar used in Java is the ISO 8601 calendar system, which is the world's civil calendar, which is what we call the Gregorian calendar. There are 365 days in a normal year and 366 in a leap year. In addition, ava 8 also provides four other calendars, namely:

Thai buddhistdate: Buddhist calendar of Thailand
MinguoDate: calendar of the Republic of China
JapaneseDate: Japanese calendar
HijrahDate: Islamic calendar

Common methods of LocalDateTime, LocalDate and LocalTime

LocalDateTime = LocalDate + LocalTime

(1.) get the current time of the default time zone

LocalDate localdate  = LocalDate.now();  --Date of acquisition:
LocalTime localtime  = LocalTime.now();  --Get time: hours, minutes and seconds
LocalDateTime localdatetime  = LocalDateTime.now();  --Acquisition time: mm / DD / yyyy, HHM / S

--result:
localdate = 2020-06-16
localtime = 17:35:13.788
localdatetime = 2020-06-16T17:35:13.789

(2) Specify specific date and time

LocalDateTime dateTime = LocalDateTime.of(2089, 12, 25, 12, 30, 30); -- Mm / DD / yyyy HHM / S
LocalDate date = LocalDate.of(2089, 12, 25); -- specific date
LocalTime time1 = LocalTime.of(12, 30); -- time
LocalTime time2 = LocalTime.of(12, 30, 30); -- Hour minute second
LocalTime time3 = LocalTime.of(12, 30, 30, 150); -- Hour minute second nanosecond

-- result
dateTime: 2089-12-25T12:30:30
date: 2089-12-25
time1: 12:30
time2: 12:30:30
time3: 12:30:30.000000150

(3) Get specific month, day, hour, minute, second, week, day, etc

Here, LocalDate and LocalTime can be used separately or directly

LocalDate of = LocalDate.now();
System.out.println("year = " + of.getYear());
System.out.println("Month (English) = " + of.getMonth());
System.out.println("Month (number) = " + of.getMonthValue());
System.out.println("Day of the month = " + of.getDayOfMonth());
System.out.println("Day of the year = " + of.getDayOfYear());
System.out.println("week = " + of.getDayOfWeek());

LocalTime nowTime = LocalTime.now();
System.out.println("When:" + nowTime.getHour());
System.out.println("Points:" + nowTime.getMinute());
System.out.println("Seconds:" + nowTime.getSecond());
System.out.println("Nanosecond:" + nowTime.getNano());

(4) Date size judgment

The comparison between isBefore and isAfter here is the latter minus the former. If the latter is large, it returns a positive number, otherwise it is a negative number

LocalDate date1 = LocalDate.of(2020, 11, 30);
LocalDate date2 = LocalDate.of(2089, 12, 25);

System.out.println(date1.isBefore(date2));
System.out.println(date1.isAfter(date2));
System.out.println(date1.equals(date2));
System.out.println(date.isLeapYear()); -- Leap year or not

(5) How many days in a month or a year

System.out.println(date1.lengthOfMonth()); -- judge the number of days in this month
 System.out.println(date1.lengthOfYear()); -- judge the days of the year

(6) Directly modify, add, and reduce month, day, hour, minute and second

-- modify
LocalDateTime dateTime1 = LocalDateTime.of(2089, 12, 25, 12, 30, 30);
System.out.println("Set year:" + dateTime1.withYear(1991));
System.out.println("Set month:" + dateTime1.withMonth(5));
System.out.println("Set hours:" + dateTime1.withHour(3));
System.out.println("Set minutes:" + dateTime1.withMinute(25));
System.out.println("Set seconds:" + dateTime1.withSecond(26));
System.out.println("Set the day of the month:" + dateTime1.withDayOfMonth(20));
System.out.println("Set the day of the year:" + dateTime1.withDayOfYear(100));

-- increase
System.out.println("Year added:" + dateTime1.plusYears(3));
System.out.println("Add month:" + dateTime1.plusMonths(5));
System.out.println("Add days:" + dateTime1.plusDays(3));
System.out.println("Add hours:" + dateTime1.plusHours(2));
System.out.println("Add minutes:" + dateTime1.plusMinutes(26));
System.out.println("Increase seconds:" + dateTime1.plusSeconds(20));

-- reduce
System.out.println("Juvenile reduction:" + dateTime1.minusYears(3));
System.out.println("Decrease month:" + dateTime1.minusMonths(5));
System.out.println("Decrease days:" + dateTime1.minusDays(3));
System.out.println("Reduce hours:" + dateTime1.minusHours(2));
System.out.println("Reduce minutes:" + dateTime1.minusMinutes(26));
System.out.println("Reduce seconds:" + dateTime1.minusSeconds(20));

(7) Time type conversion

LocalDateTime dateTime1 = LocalDateTime.of(2089, 12, 25, 12, 30, 30);
LocalDate date = LocalDate.of(2089, 12, 25);
LocalTime time= LocalTime.of(12, 30, 30);

System.out.println(dateTime1.toLocalTime()); -- LocalDateTime turn LocalTime
System.out.println(dateTime1.toLocalDate()); -- LocalDateTime turn LocalDate
System.out.println(date.atTime(time)); -- LocalDate and LocalTime turn LocalDateTime
System.out.println(time.atDate(date)); -- LocalDate and LocalTime turn LocalDateTime

-- result
12:30:30
2089-12-25
2089-12-25T12:30:30
2089-12-25T12:30:30

Date parsing and formatting: DateTimerFormatter

LocalDateTime dateTime = LocalDateTime.of(2089, 12, 25, 12, 30, 30);
DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");

-- Both positive and negative can be called format method
String date1 = dateTime.format(dtf);
System.out.println(date1);
String date2 = dtf.format(dateTime);
System.out.println(date2);

-- result
2089-12-25 12:30:30
2089-12-25 12:30:30

Calculate date time difference Duration and Period

Duration

LocalDateTime today = LocalDateTime.now();
LocalDateTime dateTime = LocalDateTime.of(2089, 12, 25, 12, 30, 30);

Duration duration = Duration.between(today, dateTime); 
System.out.println(duration.toDays());    -- Days of difference
System.out.println(duration.toHours());   -- Hours of difference
System.out.println(duration.toMinutes()); -- Minutes difference
System.out.println(duration.toMillis());  -- Millisecond difference
System.out.println(duration.toNanos());   -- Nanosecond difference

Period

LocalDate today = LocalDate.now();
LocalDate date = LocalDate.of(2089, 12, 25);

Period period = Period.between(today, date);
System.out.println(period.getYears());  -- How many years is the difference
System.out.println(period.getMonths()); -- How many months is the difference
System.out.println(period.getDays());   -- How many days is the difference

Time adjusters: TemporalAdjusters and TemporalAdjusters

TemporalAdjuster is a functional interface, which can be customized;
TemporalAdjusters is a tool class for TemporalAdjusters, with many built-in methods

example:

-- Adjust to the first day of the next year
LocalDateTime dateTime = LocalDateTime.of(2089, 12, 25, 12, 30, 30);
LocalDateTime with = dateTime.with(TemporalAdjusters.firstDayOfNextYear());
System.out.println("with = " + with);

-- result
with = 2090-01-01T12:30:30

Time stamp: Instant

Instant instant = Instant.now(); -- Get the current time to 1970-01-01 00:00:00 MS value of
System.out.println(instant);
System.out.println("Seconds:" + instant .getEpochSecond());
System.out.println("Msec :" + instant .toEpochMilli());

there Instant.now() method uses UTC time by default instead of system default time. Click the source code to see

Time zone related: ZoneID, zonedatetime

--Get a collection of time zones in different parts of the world
ZoneId.getAvailableZoneIds().forEach(System.out::println);

ZonedDateTime now = ZonedDateTime.now();-- System default time zone
ZonedDateTime now1 = ZonedDateTime.now(Clock.systemUTC());-- time zone UTC
ZonedDateTime now2 = ZonedDateTime.now(ZoneId.of("Asia/Shanghai"));--adopt ZoneId Specify time zone
System.out.println("now = " + now);
System.out.println("now1 = " + now1);
System.out.println("now2 = " + now2);

Keywords: Java SQL JDK

Added by Iceman18 on Wed, 17 Jun 2020 07:06:02 +0300

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New feature of JDK8: date time related API