Working With LocalDate, LocalTime, and LocalDateTime

Source: https://dzone.com/articles/working-with-localdate-localtime-and-localdatetime

Java 8 introduced a major change for date and time APIs. Let's take a look at these changes and how to implement them in your project.

by

Mohamed Sanaulla

Java 8 had a major change for the date and time APIs, which was the inclusion of Joda Time APIs into the JDK under the JSR 310: Date and Time API. This JSR was lead by Stephen Colebourne, the creator of Joda Time.
There are many amazing APIs for working with date and time. In this article I will look at the most commonly used ones: java.time.LocalDate, java.time.LocalTime, and java.time.LocalDateTime. These represent the date and time values independent of the timezone. So, they rely on the system clock to capture the values.

Creating an Instance

Let's look at the ways to create their instances using the now() method and the factory method of():

jshell> LocalDate.now()

$46 ==> 2018-07-07

jshell> LocalDate.of(2018, 3, 30)

$47 ==> 2018-03-30

jshell> LocalTime.now()

$48 ==> 00:32:06.883656

jshell> LocalTime.of(12,43,12,33333);

$49 ==> 12:43:12.000033333

jshell> LocalDateTime.now()

$50 ==> 2018-07-07T00:32:30.335562400

jshell> LocalDateTime.of(2018, 12, 30, 12,33)

$51 ==> 2018-12-30T12:33

jshell> LocalDateTime.of(LocalDate.now(), LocalTime.now())

$52 ==> 2018-07-07T00:40:38.198318200

Manipulating Date and Time

Let's look at how to manipulate or modify the date and time instances created:

jshell> LocalDate d = LocalDate.now()

d ==> 2018-07-07

jshell> d.plusDays(12)

$54 ==> 2018-07-19

jshell> d

d ==> 2018-07-07

jshell> d.plusMonths(2)

$56 ==> 2018-09-07

jshell> d.minusDays(5)

$57 ==> 2018-07-02

jshell> d.minusWeeks(4)

$58 ==> 2018-06-09

These plus*() and minus*() methods are 

immutable and return a new date and time instance. In the above example,
 we saw few methods to manipulate the components of java.time.LocalDate. On similar lines, there are plus*() and minus*() methods for manipulating the components of java.time.LocalTime and java.time.LocalDateTime.

Comparing Date and Time Instances

We would want to know if the given date and time is before or after another, and in such cases, we will make use of the isBefore() and isAfter() methods, as shown below:

jshell> var d1 = LocalDate.of(2018, 7, 6)

d1 ==> 2018-07-06

jshell> var d2 = LocalDate.of(2018, 7, 7)

d2 ==> 2018-07-07

jshell> d1.isAfter(d2)

$64 ==> false

jshell> d1.isBefore(d2)

$65 ==> true

jshell> var dt1 = LocalDateTime.of(2018, 7, 7, 12, 30)

dt1 ==> 2018-07-07T12:30

jshell> var dt2 = LocalDateTime.of(2018, 7, 7, 14, 30)

dt2 ==> 2018-07-07T14:30

jshell> dt1.isBefore(dt2)

$68 ==> true

jshell> dt1.isAfter(dt2)

$69 ==> false

Converting Between String and Date Object Representations

Often, we have had the need to convert a String representation of date and time to its corresponding object and also convert the object into a String representation. With older date class java.util.Date, we use java.text.SimpleDateFormat to parse a string to date and vice-versa. In the new date time API, a new class —java.time.format.DateTimeFormatter — has been introduced for the same task.
If you follow the ISO standard of converting the date between its string and object representations, a lot of the integrations between layers and applications become seamless due to the predefined ISO formats available in the java.time.format.DateTimeFormatter. Let's see this in action:

jshell> import java.time.*

jshell> LocalDateTime ldt = LocalDateTime.now()

ldt ==> 2018-09-26T22:58:32.229096300

jshell> import java.time.format.*

jshell> ldt.format(DateTimeFormatter.ISO_DATE)

$4 ==> "2018-09-26"

jshell> ldt.format(DateTimeFormatter.ISO_DATE_TIME)

$5 ==> "2018-09-26T22:58:32.2290963"

jshell> ldt.format(DateTimeFormatter.ISO_LOCAL_DATE_TIME)

$9 ==> "2018-09-26T22:58:32.2290963"

jshell> ldt.format(DateTimeFormatter.BASIC_ISO_DATE)

$10 ==> "20180926"

We can even make use of custom formatting patterns as shown below:

jshell> ldt.format(DateTimeFormatter.ofPattern("d-M-y"));

$11 ==> "26-9-2018"

jshell> ldt.format(DateTimeFormatter.ofPattern("d-MM-y hh:mm:ss"));

$12 ==> "26-09-2018 10:58:32"

jshell> ldt.format(DateTimeFormatter.ofPattern("d/MMM/y hh:mm:ss"));

$13 ==> "26/Sep/2018 10:58:32"

jshell> ldt.format(DateTimeFormatter.ofPattern("d-MMM-y hh:mm:ss"));

$14 ==> "26-Sep-2018 10:58:32"

jshell> ldt.format(DateTimeFormatter.ofPattern("d-MMM-y hh:mm:ss"));

$15 ==> "26-Sep-2018 10:58:32"

jshell> ldt.format(DateTimeFormatter.ofPattern("d-MMM-y HH:mm:ss"));

$16 ==> "26-Sep-2018 22:58:32"

The different rules for creating the patterns can be found in the Javadoc for java.time.format.DateTimeFormatter.
Let us look at converting a valid String representation of date and time to LocalDateTime and its related objects:

<br />jshell> LocalDate ld = LocalDate.parse("2018-09-26")

ld ==> 2018-09-26

jshell> LocalDateTime ldt = LocalDateTime.parse("2018-09-26T22:24:33")

ldt ==> 2018-09-26T22:24:33

You can see that in the above code we are not providing the pattern for parsing the string. Instead, it is making use of the default ISO formats. This approach is very useful when exchanging the date and time values via APIs.
With this, I have shown some basic things that you can do with the new date and time instances, which are timezone independent. In the coming posts, I will write about timezone dependent time, finding duration, the period between time and date, and working with different calendar systems. Stay tuned!