Introduction to Java 8 Date Time APIfiles.meetup.com/3189882/Java Date and Time API and... · How...

Introduction to Java 8 Date Time API

Nadeesh T V

ORACLE India Pvt Ltd

19 Dec 2015

Bangalore JUG Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.

Outline

1 Why do we need a new API?

2 JSR 310

3 Chronology

4 TimeZone

5 Summary

6 What to look for in java 9


Drawbacks of existing APIutil.Date, util.Calendar ..

What is the output of following code?

C a l e n d a r c a l = new G r e g o r i a n C a l e n d a r (1970 , 12 , 19 , 11 , 3 0 ) ;

SimpleDateFormat dateFormat = new SimpleDateFormat ( ” yyyy−MM−dd HH:mm: s s ” ) ;

System . out . p r i n t l n ( dateFormat . fo rmat ( c a l . getTime ( ) ) ) ;



What is the output of following code?

C a l e n d a r c a l = new G r e g o r i a n C a l e n d a r (1970 , 12 , 19 , 11 , 3 0 ) ;

SimpleDateFormat dateFormat = new SimpleDateFormat ( ” yyyy−MM−dd HH:mm: s s ” ) ;

System . out . p r i n t l n ( dateFormat . fo rmat ( c a l . getTime ( ) ) ) ;

Expected: 1970-12-19 11:30:00 Actual : 1971-01-19 11:30:00

Months are zero indexed :)

How to model Date without time component? eg: 19 Dec 2015

How to model Time without a date? eg: 10.30

How to model Month without a day? eg: credit card expiry date



How to model Duration? eg: 2H 15 minute

How to find number of days between 2 dates?

Both Date and Calendar are mutable


JSR 310 : Date Time API

Started in 2007

Feature Completed in 2013

JSR 310 is not joda time

Adopted from joda time

Goals

Immutable

Fluent and Clear

Pluggable or Extensible


JSR 310 : LocalDate

Stores year-month-day

19 Dec 2015

Start day, End day etc

date1 = Loca lDate . now ( ) ;

date2 = Loca lDate . o f (2015 , 12 , 3 1 ) ;

date2 . i s A f t e r ( date1 ) ;

date2 . i s L e a p Y e a r ( ) ;

date2 . lengthOfMonth ( ) ;

Manipulation - yet immutable

date2 . p l u s D a y s ( 3 ) ;

date2 . minusMonths ( 2 ) ;

date2 . withDayOfMonth ( 1 2 ) ;


JSR 310 : LocalDate

More complex alteration use TemporalAdjuster

Eg: Change to last day of month

Change to next Tuesday

Change to 3rdFriDay

TemporalAdjuster - yet immutable

date2 . w i t h ( T e m p o r a l A d j u s t e r s . f i r s tDayOfMonth ( ) ) ;

date2 . w i t h ( T e m p o r a l A d j u s t e r s . n e x t ( DayOfWeek .TUESDAY ) ) ;

date2 . w i t h ( T e m p o r a l A d j u s t e r s . n e x t (3 r d F r i d a y ) ;


JSR 310 : LocalTime

Storeshour-minute-seconds-nano

10:30

Wall clock time, openingtime etc

t ime1 = LocalTime . now ( ) ;

t ime2 = LocalTime . o f (2015 , 12 , 3 1 ) ;

t ime2 . i s A f t e r ( t ime1 ) ;

t ime2 . getHour ( ) ;


t ime . withNano ( 0 ) ;

t ime . p l u s H o u r s ( 2 ) ;

t ime . t r u n c a t e d T o ( ChronoUnit . SECONDS)


JSR 310 : LocalDateTime

Stores LocalDate and LocalTime

19 Dec 2015 10:30

Wall clock time, opening time etc


dateTime1 = LocalDateTime . now ( ) ;

dateTime2 = LocalDateTime . o f (2015 , 12 , 3 1 , 1 1 , 3 0 , 1 2 ) ;

dateTime1 . i s A f t e r ( dateTime12 ) ;

dateTime1 . p l u s D a y s ( 3 ) . p l u s H o u r s ( 2 ) ;

dateTime1 . w i t h ( T e m p o r a l A d j u s t e r s . f i r s tDayOfMonth ( ) ) ;


Chronology

Chronlogy - Calendar System

Currently support 5 Chronologies

ISo 8601, Hijrah, Japanese, Minguo, ThaiBudhist

Pluggable

ChronloLocalDate, ChronoLocalTime, ChronoLocalDateTime etc


TimeZone

World is divided into different time zones

JSR 310 uses tzdb

To figure out TimeOffset, DST rules etc

3 Classes - ZoneOffset, ZoneId, ZoneRules


JSR 310 : ZonedDateTime

Stores LocalDateTime, ZoneOffset, ZoneId

19 Dec 2015 10:30 +05:30[Asia/Calcutta]


ZonedDateTime . now ( ) ;

ZoneId zone= ZoneId . o f ( ” A s i a / C a l c u t t a ” ) ;

ZonedDateTime . o f ( l o c a l d a t e T i m e , zone ) ;

z d t . p l u s D a y s ( 3 ) . p l u s H o u r s ( 2 ) ;


JSR 310 : Instant

Represent instantaneous point in time

Stores nano seconds from 1970-1-1Z

Equivalent to Machine Time


I n s t a n t i n s t a n t 1 = I n s t a n t . now ( ) ;

i n s t a n t 1 . p l u s M i l l i s ( 2 0 ) ;

i n s t a n t 1 . i s A f t e r ( i n s t a n t 2 ) ;


JSR 310 : Duration

Represent amount of time

Stores seconds and nano seconds

Eg: 24.3 seconds


D u r a t i o n dur = D u r a t i o n . o f S e c o n d s ( 1 2 , 2 1 ) ;

dur . p l u s H o u r s ( 2 ) ;

dur . m u l t i p l i e d B y ( 1 0 ) ;

LocalDateTime . now ( ) . p l u s ( dur ) ;


JSR 310 : Period

date based amount

years , months , days

Eg: 2 year 1 month


P e r i o d p e r i o d = P e r i o d . o f ( y e a r s , onths , days ) ;

p e r i o d . p l u s D a y s ( 2 ) ;

LocalDateTime . now ( ) . p l u s ( p e r i o d ) ;


JSR 310 : Class Summary

LocalDate 2015-12-19

LocalTime 11:30

LocalDateTime 2015-12-19T11:30

ZonedDateTime 2015-12-19T11:30+5:30 Asia/Calcutta

Instant 12202 seconds

Duration PT24.3 seconds

Period PT1Y2M


Convertions

// Loca lDate / LocalTime <−> LocalDateTimeLoca lDate d a t e = Loca lDate . now ( ) ;

LocalTime t ime = LocalTime . now ( ) ;

LocalDateTime dateTimeFromDateAndTime = LocalDateTime . o f ( date , t ime ) ;

Loca lDate dateFromDateTime = LocalDateTime . now ( ) . t o L o c a l D a t e ( ) ;

LocalTime timeFromDateTime = LocalDateTime . now ( ) . toLoca lT ime ( ) ;

// I n s t a n t <−> LocalDateTimeI n s t a n t i n s t a n t = I n s t a n t . now ( ) ;

LocalDateTime dateTimeFromInstant = LocalDateTime .o f I n s t a n t ( i n s t a n t , ZoneId . o f ( ” America / L o s A n g e l e s ” ) ) ;

I n s t a n t instantFromDateTime = LocalDateTime . now ( ) .t o I n s t a n t ( Z o n e O f f s e t . o fHours ( −2));

// conv e r t o l d date / c a l e n d a r / t imezone c l a s s e sI n s t a n t i n s t a n t F r o m D a t e = new Date ( ) . t o I n s t a n t ( ) ;

I n s t a n t i n s t a n t F r o m C a l e n d a r = C a l e n d a r . g e t I n s t a n c e ( ) . t o I n s t a n t ( ) ;

ZoneId z o n e I d = TimeZone . g e t D e f a u l t ( ) . to Z on e Id ( ) ;

ZonedDateTime zonedDateTimeFromGregor ianCalendar = new G r e g o r i a n C a l e n d a r ( ). toZonedDateTime ( ) ;

// conv e r t to o l d c l a s s e sDate d a t e F r o m I n s t a n t = Date . from ( I n s t a n t . now ( ) ) ;

TimeZone timeZone = TimeZone . getTimeZone ( ZoneId . o f ( ” America / L o s A n g e l e s ” ) ) ;

G r e g o r i a n C a l e n d a r g r e g o r i a n C a l e n d a r = G r e g o r i a n C a l e n d a r . from ( ZonedDateTime . now ( ) ) ;


What to look for in java 9

Duration - toHourParts(),toMinutesPart(),dividedBY(Duarion)

LocalDate - ofInstant(Instant,Zone), toEpochSecond()

Julian Chronolgy(may be)

Additional patterns in DateTimeFormatter

Optimize implemenations of certain method implmentaion inLocalDate, LocalTime

etc ...


References

1. http://www.threeten.org

2. https://jcp.org/en/jsr/detail?id=310

3.www.javacodegeeks.com/2014/03/a-deeper-look-into-the-java-8-date-and-time-api.html


Thank you


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