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.
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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.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
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
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
minus*() methods for manipulating the components of
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
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
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!
Published at DZone with permission of Mohamed Sanaulla, DZone MVB. See the original article here.
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