A JSR-310 Date: Beyond JODA Time

A brief look at JSR-310, and why it exists at all.

1. B E Y O N D J O D A T I M E A JSR-310 DATE
2. IN THIS PRESENTATION •  What is JSR-310? •  What’s wrong with Date, Calendar and DateFormat? •  Why not JODA Time? •  JSR-310 Overview
3. • What does it mean? • What does it have? WHAT IS JSR-310?
4. WHAT DOES JSR-310 MEANS? •  A Java Specification Request included on Java 8
5. WHAT DOES JSR-310 MEANS? •  A Java Specification Request included on Java 8 •  A library to handle dates and times
6. WHAT DOES JSR-310 MEANS? •  A Java Specification Request included on Java 8 •  A library to handle dates and times •  A set of packages: •  java.time.* •  java.time.chrono.* •  java.time.format.* •  java.time.temporal.* •  java.time.zone.*
7. WHAT DOES JSR-310 HAVE? •  Instants (timestamps) •  Date and Time •  Partial Date and Time •  Parser and Formatter •  Time zones •  Different chronologies (calendars)
8. • Bad Naming • Historical Issues • Design Problems • Deficiencies WHAT’S WRONG WITH THE EXISTING CLASSES?
9. BAD NAMING •  Horrible naming decisions
10. BAD NAMING •  Horrible naming decisions •  Date is not a date, it is an instant in time (a timestamp)
11. BAD NAMING •  Horrible naming decisions •  Date is not a date, it is an instant in time (a timestamp) •  Date is not a time •  The time field manipulation methods are deprecated
12. BAD NAMING •  Horrible naming decisions •  Date is not a date, it is an instant in time (a timestamp) •  Date is not a time •  The time field manipulation methods are deprecated •  Calendar is not a calendar, it is a date and time
13. HISTORICAL ISSUES •  Date has no support for I18N or L10N
14. HISTORICAL ISSUES •  Date has no support for I18N or L10N •  So Sun added IBM-donated (through Taligent) code •  Calendar •  TimeZone •  SimpleDateFormat
15. HISTORICAL ISSUES •  Date has no support for I18N or L10N •  So Sun added IBM-donated (through Taligent) code •  Calendar •  TimeZone •  SimpleDateFormat •  Which don’t even play well together •  SimpleDateFormat can’t be used to convert from or to Calendar
16. HISTORICAL ISSUES •  Date has no support for I18N or L10N •  So Sun added IBM-donated (through Taligent) code •  Calendar •  TimeZone •  SimpleDateFormat •  Which don’t even play well together •  SimpleDateFormat can’t be used to convert from or to Calendar •  And still kept months 0-based •  (but at least made years 0-based instead of 1900-based)
17. DESIGN PROBLEMS •  They are mutable!
18. DESIGN PROBLEMS •  They are mutable! •  On core, excluding tests, SimpleDateTime is: •  instantiated in 225 places •  a field in 77 places •  usually synchronized (if correct) •  a local variable in 103 places •  Which could be replaced with a dozen immutable static constants
19. DESIGN PROBLEMS •  They are mutable! •  On core, excluding tests, SimpleDateTime is: •  instantiated in 225 places •  a field in 77 places •  usually synchronized (if correct) •  a local variable in 103 places •  Which could be replaced with a dozen immutable static constants •  Calendar stores redundant representations, and recomputes lazily depending on the method being called
20. DEFICIENCIES •  They are limited •  My alarm clock rings at 6:30 AM
21. DEFICIENCIES •  They are limited •  My alarm clock rings at 6:30 AM (time without date or tz) •  I was born March 23, 1971
22. DEFICIENCIES •  They are limited •  My alarm clock rings at 6:30 AM (time without date or tz) •  I was born March 23, 1971(date without time) •  My birthday is March 23
23. DEFICIENCIES •  They are limited •  My alarm clock rings at 6:30 AM (time without date or tz) •  I was born March 23, 1971(date without time) •  My birthday is March 23 (date without year) •  This presentation is one hour long
24. DEFICIENCIES •  They are limited •  My alarm clock rings at 6:30 AM (time without date or tz) •  I was born March 23, 1971(date without time) •  My birthday is March 23 (date without year) •  This presentation is one hour long (a duration) •  A year has twelve months
25. DEFICIENCIES •  They are limited •  My alarm clock rings at 6:30 AM (time without date or tz) •  I was born March 23, 1971(date without time) •  My birthday is March 23 (date without year) •  This presentation is one hour long (a duration) •  A year has twelve months (a period)
26. • Why JODA Time? • Too Flexible • Bad Internal Representation • Null-happy • JODA Time & JSR-310 WHY NOT JODA TIME?
27. WHY JODA TIME? •  JODA Time addresses all these issues: •  It is composed of immutable classes •  It handles Instants, Date&Time, Partials, and Durations •  It is flexible •  It is well designed
28. TOO FLEXIBLE •  Every class is prepared to handle the most obscure calendar systems (pluggable chronology) •  But code usually assumes Gregorian Calendar •  (have you ever written code that handles 13 months?) •  int month = dateTime.getMonthOfDay(); •  It lacks type safety
29. BAD INTERNAL REPRESENTATION •  Represents dates as instants •  But a date&time may correspond to more than one instant •  Overlap hour when daylight savings end •  As well as not have any instant that corresponds to it at all •  Gap hour when daylight starts •  Has to perform complex computations for simple operations
30. NULL-HAPPY •  Accepts nulls as valid values on most of its methods •  Leads to subtle bugs
31. JODA TIME AND JSR-310 •  JODA Time is Not Broken •  But the lessons learned led to a new time library design •  JSR-310 is inspired by JODA Time, but simpler and more robust
32. • Basic classes • Now • Clocks and Testing • Parsing and Printing • Fields and Units • Java 7 Backport JSR-310 OVERVIEW
33. BASIC INTERFACES Interface •  TemporalAccessor •  Temporal •  TemporalField •  TemporalAmount •  TemporalUnit •  TemporalQuery •  TemporalAdjuster Purpose •  Readable date&time •  Modifiable date&time •  Date&time component •  Amount of time •  Unit of amount of time •  Queries date&time •  Modifies date&time
34. TEMPORALACCESSOR
35. TEMPORAL
36. TEMPORALFIELD
37. TEMPORALAMOUNT
38. TEMPORALUNIT
39. TEMPORALQUERY
40. TEMPORALADJUSTER
41. BASIC CLASSES Class •  Instant •  Clock •  LocalDateTime •  OffsetDateTime •  ZonedDateTime •  Duration •  Period Purpose •  Moment in time •  Instant Factory •  Arbitrary Date and Time •  Date & Time with UTC offset •  Date & Time with TZ •  Difference between instants •  Duration in time units
42. INSTANT •  A point in time •  Time since 1970-01-01 00:00:00 UTC •  Useful for timestamps •  Nanosecond resolution •  Temporal, TemporalAccessor, TemporalAdjuster •  Before/After •  To/From seconds, milliseconds •  Creates OffsetDateTime & ZonedDateTime
43. LOCALDATETIME •  A time in years, months, days, hours, minutes and seconds •  No timezone •  Does not have an instant associated with it •  ISO-8601 Calendar System, not Gregorian •  Temporal, TemporalAccessor, TemporalAdjuster •  Before/After •  Manipulate with years, months, weeks, days, hours, minutes, seconds and nanos •  Creates OffsetDateTime & ZonedDateTime
44. ZONEDDATETIME/OFFSETDATETIME •  A date and time associated with either a particular time zone, or a particular time zone offset •  OffsetDateTime always have an associated instant •  ZonedDateTime have gaps and overlaps •  One can get a ZDT that returns either the earlier or the later time in an overlap •  Temporal, TemporalAccessor •  Before/After
45. DURATION & PERIOD •  Represent amounts of time •  Duration is an amount of nanoseconds •  Period is an amount of years, months and days •  Can be computed in absolute terms •  Duration.ofMinutes(10) •  Can be computed from dates and instants •  Period.between(LocalDate.now(), birthDay) •  Can be added of subtracted from instants, dates and times
46. PARTIAL DATES AND TIMES •  LocalDate •  LocalTime •  DayOfWeek •  Month •  MonthDay •  YearMonth •  Year
47. WHAT TIME IS IT NOW? •  Instant.now() •  default timezone •  Instant.now(ZoneId zone) •  time at a specific time zone •  Instant.now(Clock clock) •  time as generated by a specific clock •  LocalTime.now() •  MonthDay.now(clock) •  ZonedDateTime(zone) •  etc
48. CLOCK AND TESTING •  Clocks can be injected •  Clocks can be created with various properties •  Static clocks •  Mocked clocks •  Low-precision clocks (whole seconds, whole minutes, etc) •  Clocks can be created with specific time zones •  Clock.system(Zone.of(“America/Los_Angeles”)) •  Makes code handling date and time testable •  Makes tests independent of timezone
49. PRINTING & PARSING •  DateTimeFormatter replaces SimpleDateFormat •  Immutable, so reusable and thread-safe •  Many pre-defined styles •  DateTimeFormatterBuilder •  All instant, date and time classes use it the same way: •  Instant t = Instant.parse(input, dateTimeFormatter); •  String ts = ZonedDateTime.format(dateTimeFormatter); •  Duration, Period and other classes have fixed formats: •  Duration d = Duration.parse(repr);
50. JSR-310 BACKPORT TO JAVA 7 •  Fork of the original implementation of JSR-310, under the BSD license, before it got added to JDK 8 •  Presently equivalent to milestone 7 of JDK 1.8 •  When JDK 1.8 comes out, a new release of the backport will be made •  Presently diverging from JDK 1.8 •  org.threeten, threetenbp, 8.1 •  package org.threeten.bp instead of java.time
51. BENEFITS OF ADOPTING THE BACKPORT •  Much superior to existing Java classes •  Closer to Java 8 than JODA, and less prone to bugs •  Easy transition to Java 8 •  Superior testability
52. TRIVIAL EXAMPLE
53. COMPLEX EXAMPLE 1
54. COMPLEX EXAMPLE 2