Date Time Java 8
(JSR-310)
ilJUG – July 2014
By: Eyal Golan
Tech Lead at eBay

A word before starting…
The intent of this presentation is to be
basic source and starting point to the
new Java Date Time API (JSR-310)
2

Agenda
• Old vs. New
• JSR 310
• Examples by code
• Resources
3

Old Issues
• Date is not a date, nor time. It’s an
instant in time (by epoch)
• Calendar is Date and Time
• Month is 0 (zero) based
• Mutability
4

Example – Issues
5

Example – Issues
6

Example – Issues
7
First try=1274 , second try=0
Use (Calendar)start.clone();

Calendar
• YEAR, MONTH,
DAY_OF_MONTH…
• Fields start at 0
• Calendar is mutable
• Methods (set, add…) change the state of
Calendar
8

Example – The New Way
9
1274

Example – The New Way
10
1274

Example – The New Way
11
1274

Example – The New Way
12
Today 2014-07-29 and next year 2015-07-29

Modeling
• Different date/time scenarios
• Class starts at 12:30
• ilJUG is on 29th July
• The presentation is 1 hour long
• I’ve been working at eBay for 3 years and 6
months
13

Example – Issues
14

Example – The New Way
15

Example – The New Way
16

Amount of Time
• How many milliseconds it took
between request to response?
• Set time 10 seconds after now
• Calculate time that passed between
two events
17

Example – Old Calculation
18
now Tue Jul 29 01:48:56 IDT 2014 and later Thu Jan 01 04:20:00 IST 1970

Example – Old Calculation
19
119 days 6 hours 13 minutes 24 seconds 543 ms
Example taken from stackoverflow

Duration and Period
20

Duration – Machine Time
21
now 2014-07-28T23:17:40.898Z and later 2014-07-29T01:47:40.898Z
150
2014-07-28T23:17:53.898Z
9000000

Period – Human Time
22

Guidelines
• Clear
• Fluent
• DSL
• Immutability
• Amount of time, different
representations for different cases
• Human (year, month, day)
• Machine time
24

Packages
• java.time
• java.time.chrono
• java.time.format
• java.time.temporal
• java.time.zone
25

Some (not all) Classes
• Temporal – Basic interface for DateTime classes
• LocalDate / LocalTime / LocalDateTime …
• Instant
• Start of nanoseconds in timeline. Useful for timestamp
• Clock
• Allowing Temporal creation with alternate clock
• TemporalAmount – Basic interface for classes
that represent amount of time
• Duration
• Period
26

Methods Naming Conventions
of Static Creates an instance with validation
to Instance Converts to another type (truncate fields)
at Instance Combines this object with another
(expands)
from Static Converts input parameters to an instance
get Instance Part of the state of the object
27

Methods Naming Conventions
is Instance Queries state of an object
with Instance Returns a copy of an object with one
changed element
plus /
minus
instance Returns a copy of an object with amount of
added / subtracted time
parse Static Parses input string to an instance
format Instance Uses formatter to format the object’s values
to produce a string
28

Source Code
30
https://github.com/eyalgo/java8-datetime

General
31
SystemClock[Asia/Jerusalem]
2014-07-29T05:54:23.337
2014-07-29T08:54:23.338
SystemClock[Asia/Jerusalem]
SystemClock[Europe/Berlin]
2014-7-29

General
32
SystemClock[Asia/Jerusalem]
2014-07-29T05:54:23.337
2014-07-29T08:54:23.338
SystemClock[Asia/Jerusalem]
SystemClock[Europe/Berlin]
2014-7-29

General
33
SystemClock[Asia/Jerusalem]
2014-07-29T05:54:23.337
2014-07-29T08:54:23.338
SystemClock[Asia/Jerusalem]
SystemClock[Europe/Berlin]
2014-7-29

The Basics
34

Basic Date and Time
35

Partial Dates & Information
36

Information, Clear API
37

Fluent Operations
38

Time Zone
39

Using Zone
40

Instant
41
From Javadoc:
"This class models a single instantaneous point on the time-line.
This might be used to record event time-stamps in the application...
"...number of seconds that can be held in a long. This is greater than the current
estimated age of the universe...
"...The instant is stored to nanosecond resolution..."

Adjusters
• Take Temporal value and adjust it
• Pre defined
• firstDayOfMonth
• firstDayOfYear
• lastInMonth
• Look at TemoralAdjusters
• Custom adjusters
42

Adjusters
43

Custom Adjusters
44
2014-08-05
2009-09-01

Queries – Retrieve Information
45

Custom Queries
46

Custom Queries
47

Parsing and Formatting
• DateTimeFormatter
• Many pre defined formats
• http://docs.oracle.com/javase/8/docs/api/java/time/format/DateTimeFormatter.html#predefined
• Immutable
• DateTimeFormatterBuilder
• All classes use the same way
• DateTimeParseException (runtime)
48

Parsing and Formatting
49
07**2014--16

Legacy Date Time Integration
50

52
https://github.com/eyalgo/java8-datetime
http://docs.oracle.com/javase/tutorial/datetime/iso/index.html
http://docs.oracle.com/javase/tutorial/datetime/index.html
https://jcp.org/en/jsr/detail?id=310
http://www.oracle.com/technetwork/articles/java/jf14-date-time-2125367.html
http://www.mscharhag.com/2014/02/java-8-datetime-api.html
http://geekmonkey.org/articles/24-a-new-date-and-time-api-for-jdk-8
https://today.java.net/pub/a/today/2008/09/18/jsr-310-new-java-date-time-api.html

egolan74@gmail.com
https://www.linkedin.com/in/egolan74
http://eyalgo.com/
@eyalgo_egolan