Java 8 – Date and Time Examples

A big part of developer community has been complaining about Date and Calendar classes. Reasons were many such as hard to understand, hard to use and not flexible. Date class has even become obsolete and java docs suggest to use Calendar class instead of Date class. And on top of all, Date comparison is buggy and I have also faced such issue in past.

Moving forward, JAVA 8 (Lambda) is expected to release the new Date and Time APIs/classes (JSR-310), also called as ThreeTen, which will simply change the way you have been doing till date. This A key part of this is providing a new API that is dramatically easier to use and less error prone.

It will provide some highly demanded features such as:

• All the key public classes are immutable and thread-safe
• Defined terminology and behavior that other areas in computing can adopt

Table of Contents

New classes to represent local date and timezone
New classes to represent timestamp and duration
Added utility classes over existing enums
Date adjusters introduced
Building dates will be easier
New class to simulate system/machine clock
Timezone handling related changes
Date formatting changes
References

New classes to represent local date and timezone

The new classes intended to replace Date class are LocalDate, LocalTime and LocalDateTime.

LocalDate

The LocalDate class represents a date. There is no representation of a time or time-zone.

LocalDate localDate = LocalDate.now();
System.out.println(localDate.toString());                //2013-05-15
System.out.println(localDate.getDayOfWeek().toString()); //WEDNESDAY
System.out.println(localDate.getDayOfMonth());           //15
System.out.println(localDate.getDayOfYear());            //135
System.out.println(localDate.isLeapYear());              //false
System.out.println(localDate.plusDays(12).toString());   //2013-05-27

LocalTime

The LocalTime class represents a time. There is no representation of a date or time-zone.

//LocalTime localTime = LocalTime.now();     //toString() in format 09:57:59.744
LocalTime localTime = LocalTime.of(12, 20);
System.out.println(localTime.toString());    //12:20
System.out.println(localTime.getHour());     //12
System.out.println(localTime.getMinute());   //20
System.out.println(localTime.getSecond());   //0
System.out.println(localTime.MIDNIGHT);      //00:00
System.out.println(localTime.NOON);          //12:00

LocalDateTime

The LocalDateTime class represents a date-time. There is no representation of a time-zone.

LocalDateTime localDateTime = LocalDateTime.now(); 
System.out.println(localDateTime.toString());      //2013-05-15T10:01:14.911
System.out.println(localDateTime.getDayOfMonth()); //15
System.out.println(localDateTime.getHour());       //10
System.out.println(localDateTime.getNano());       //911000000

If you want to use the date functionality with zone information, then Lambda provide you extra 3 classes similar to above one i.e. OffsetDate, OffsetTime and OffsetDateTime. Timezone offset can be represented in “+05:30” or “Europe/Paris” formats. This is done via using another class i.e. ZoneId.

OffsetDateTime offsetDateTime = OffsetDateTime.now();
System.out.println(offsetDateTime.toString());            	//2013-05-15T10:10:37.257+05:30

offsetDateTime = OffsetDateTime.now(ZoneId.of("+05:30"));
System.out.println(offsetDateTime.toString());            	//2013-05-15T10:10:37.258+05:30

offsetDateTime = OffsetDateTime.now(ZoneId.of("-06:30"));
System.out.println(offsetDateTime.toString());            	//2013-05-14T22:10:37.258-06:30

ZonedDateTime zonedDateTime = 
				ZonedDateTime.now(ZoneId.of("Europe/Paris"));
System.out.println(zonedDateTime.toString());     			//2013-05-15T06:45:45.290+02:00[Europe/Paris]

New classes to represent timestamp and duration

Instant

For representing the specific timestamp ant any moment, the class needs to be used is Instant. The Instant class represents an instant in time to an accuracy of nanoseconds. Operations on an Instant include comparison to another Instant and adding or subtracting a duration.

Instant instant = Instant.now();
System.out.println(instant.toString());                                 //2013-05-15T05:20:08.145Z
System.out.println(instant.plus(Duration.ofMillis(5000)).toString());   //2013-05-15T05:20:13.145Z
System.out.println(instant.minus(Duration.ofMillis(5000)).toString());  //2013-05-15T05:20:03.145Z
System.out.println(instant.minusSeconds(10).toString());				//2013-05-15T05:19:58.145Z

Duration

Duration class is a whole new concept brought first time in java language. It represents the time difference between two time stamps.

Duration duration = Duration.ofMillis(5000);
System.out.println(duration.toString());     //PT5S

duration = Duration.ofSeconds(60);
System.out.println(duration.toString());     //PT1M

duration = Duration.ofMinutes(10);
System.out.println(duration.toString());     //PT10M

duration = Duration.ofHours(2);
System.out.println(duration.toString());     //PT2H

duration = Duration.between(Instant.now(), Instant.now().plus(Duration.ofMinutes(10)));
System.out.println(duration.toString());  //PT10M

Duration deals with small unit of time such as milliseconds, seconds, minutes and hour. They are more suitable for interacting with application code.

Period

To interact with human, you need to get bigger durations which are presented with Period class.

Period period = Period.ofDays(6);
System.out.println(period.toString());    //P6D

period = Period.ofMonths(6);
System.out.println(period.toString());    //P6M

period = Period.between(LocalDate.now(), 
			LocalDate.now().plusDays(60));
System.out.println(period.toString());   //P1M29D

Added utility classes over existing enums

The current Java SE platform uses int constants for months, day-of-week and am-pm etc. Now a lot of extra utility classes have been added which work on top of these enums. I am taking an example such a class DayOfWeek. This class is a wrapper of day enums and can be used consistently with other classes also.

DayOfWeek

//day-of-week to represent, from 1 (Monday) to 7 (Sunday)
System.out.println(DayOfWeek.of(2));        			//TUESDAY 

DayOfWeek day = DayOfWeek.FRIDAY;
System.out.println(day.getValue());         			//5

LocalDate localDate = LocalDate.now();
System.out.println(localDate.with(DayOfWeek.MONDAY));  //2013-05-13  i.e. when was monday in current week ?

Other such classes are Month, MonthDay, Year, YearMonth and many more.

Date adjusters

Date adjusters are another beautiful and useful addition in date handling tools. It easily solves the problems like : How do you find last day of the month? Or the next working day? Or a week on Tuesday?

Lets see in code.

LocalDate date = LocalDate.of(2013, Month.MAY, 15);						//Today
		
LocalDate endOfMonth = date.with(TemporalAdjusters.lastDayOfMonth());
System.out.println(endOfMonth.toString()); 								//2013-05-31

LocalDate nextTue = date.with(TemporalAdjusters.next(DayOfWeek.TUESDAY));
System.out.println(nextTue.toString());									//2013-05-21

Creating date objects

Creating date objects now can be done using builder pattern also. The builder pattern allows the object you want to be built up using individual parts. This is achieved using the methods prefixed by “at”.

//Builder pattern used to make date object
 OffsetDateTime date1 = Year.of(2013)
						.atMonth(Month.MAY).atDay(15)
						.atTime(0, 0)
						.atOffset(ZoneOffset.of("+03:00"));
 System.out.println(date1);   									//2013-05-15T00:00+03:00

//factory method used to make date object
OffsetDateTime date2 = OffsetDateTime.
						of(2013, 5, 15, 0, 0, 0, 0, ZoneOffset.of("+03:00"));
System.out.println(date2);										//2013-05-15T00:00+03:00

New class to simulate system/machine clock

A new class Clock is proposed in new release. This simulates the system clock functionality. I loved this feature most of all others. The reason is while doing unit testing. you are often required to test a API in future date. For this we had been forwarding the system clock for next date, and then again restart the server and test the application.

Now, no need to do this. Use Clock class to simulate this scenario.

Clock clock = Clock.systemDefaultZone();
System.out.println(clock);						//SystemClock[Asia/Calcutta]
System.out.println(clock.instant().toString());	//2013-05-15T06:36:33.837Z
System.out.println(clock.getZone());			//Asia/Calcutta

Clock anotherClock = Clock.system(ZoneId.of("Europe/Tiraspol"));
System.out.println(anotherClock);						//SystemClock[Europe/Tiraspol]
System.out.println(anotherClock.instant().toString());	//2013-05-15T06:36:33.857Z
System.out.println(anotherClock.getZone());				//Europe/Tiraspol

Clock forwardedClock  = Clock.tick(anotherClock, Duration.ofSeconds(600));
System.out.println(forwardedClock.instant().toString());  //2013-05-15T06:30Z

Timezone Changes

Timezone related handling is done by 3 major classes. These are ZoneOffset, TimeZone, ZoneRules.

• The ZoneOffset class represents a fixed offset from UTC in seconds. This is normally represented as a string of the format “±hh:mm”.
• The TimeZone class represents the identifier for a region where specified time zone rules are defined.
• The ZoneRules are the actual set of rules that define when the zone-offset changes.

//Zone rules
System.out.println(ZoneRules.of(ZoneOffset.of("+02:00")).isDaylightSavings(Instant.now()));
System.out.println(ZoneRules.of(ZoneOffset.of("+02:00")).isFixedOffset());

Date Formatting

Date formatting is supported via two classes mainly i.e. DateTimeFormatterBuilder and DateTimeFormatter. DateTimeFormatterBuilder works on builder pattern to build custom patterns where as DateTimeFormatter provides necessary input in doing so.

DateTimeFormatterBuilder formatterBuilder = new DateTimeFormatterBuilder();
formatterBuilder.append(DateTimeFormatter.ISO_LOCAL_DATE_TIME)
				.appendLiteral("-")
				.appendZoneOrOffsetId();
DateTimeFormatter formatter = formatterBuilder.toFormatter();
System.out.println(formatter.format(ZonedDateTime.now()));

These are major changes which I was able to identify and worked on.

References

• https://docs.oracle.com/javase/tutorial/java/javaOO/lambdaexpressions.html
• http://sourceforge.net/apps/mediawiki/threeten/index.php?title=User_Guide

Happy Learning !!