Datetime java 8

Datetime java 8 DEFAULT

Java 8 - New Date/Time API



With Java 8, a new Date-Time API is introduced to cover the following drawbacks of old date-time API.

  • Not thread safe − java.util.Date is not thread safe, thus developers have to deal with concurrency issue while using date. The new date-time API is immutable and does not have setter methods.

  • Poor design − Default Date starts from 1900, month starts from 1, and day starts from 0, so no uniformity. The old API had less direct methods for date operations. The new API provides numerous utility methods for such operations.

  • Difficult time zone handling − Developers had to write a lot of code to deal with timezone issues. The new API has been developed keeping domain-specific design in mind.

Java 8 introduces a new date-time API under the package java.time. Following are some of the important classes introduced in java.time package.

  • Local − Simplified date-time API with no complexity of timezone handling.

  • Zoned − Specialized date-time API to deal with various timezones.

Local Date-Time API

LocalDate/LocalTime and LocalDateTime classes simplify the development where timezones are not required. Let's see them in action.

Create the following java program using any editor of your choice in, say, C:\> JAVA.

Java8Tester.java

Live Demo

import java.time.LocalDate; import java.time.LocalTime; import java.time.LocalDateTime; import java.time.Month; public class Java8Tester { public static void main(String args[]) { Java8Tester java8tester = new Java8Tester(); java8tester.testLocalDateTime(); } public void testLocalDateTime() { // Get the current date and time LocalDateTime currentTime = LocalDateTime.now(); System.out.println("Current DateTime: " + currentTime); LocalDate date1 = currentTime.toLocalDate(); System.out.println("date1: " + date1); Month month = currentTime.getMonth(); int day = currentTime.getDayOfMonth(); int seconds = currentTime.getSecond(); System.out.println("Month: " + month +"day: " + day +"seconds: " + seconds); LocalDateTime date2 = currentTime.withDayOfMonth(10).withYear(2012); System.out.println("date2: " + date2); //12 december 2014 LocalDate date3 = LocalDate.of(2014, Month.DECEMBER, 12); System.out.println("date3: " + date3); //22 hour 15 minutes LocalTime date4 = LocalTime.of(22, 15); System.out.println("date4: " + date4); //parse a string LocalTime date5 = LocalTime.parse("20:15:30"); System.out.println("date5: " + date5); } }

Verify the Result

Compile the class using javac compiler as follows −

C:\JAVA>javac Java8Tester.java

Now run the Java8Tester as follows −

C:\JAVA>java Java8Tester

It should produce the following output −

Current DateTime: 2014-12-09T11:00:45.457 date1: 2014-12-09 Month: DECEMBERday: 9seconds: 45 date2: 2012-12-10T11:00:45.457 date3: 2014-12-12 date4: 22:15 date5: 20:15:30

Zoned Date-Time API

Zoned date-time API is to be used when time zone is to be considered. Let us see them in action.

Create the following Java program using any editor of your choice in, say, C:\> JAVA.

Java8Tester.java

Live Demo

import java.time.ZonedDateTime; import java.time.ZoneId; public class Java8Tester { public static void main(String args[]) { Java8Tester java8tester = new Java8Tester(); java8tester.testZonedDateTime(); } public void testZonedDateTime() { // Get the current date and time ZonedDateTime date1 = ZonedDateTime.parse("2007-12-03T10:15:30+05:30[Asia/Karachi]"); System.out.println("date1: " + date1); ZoneId id = ZoneId.of("Europe/Paris"); System.out.println("ZoneId: " + id); ZoneId currentZone = ZoneId.systemDefault(); System.out.println("CurrentZone: " + currentZone); } }

Verify the Result

Compile the class using javac compiler as follows −

C:\JAVA>javac Java8Tester.java

Now run the Java8Tester as follows −

C:\JAVA>java Java8Tester

It should produce the following output −

date1: 2007-12-03T10:15:30+05:00[Asia/Karachi] ZoneId: Europe/Paris CurrentZone: Etc/UTC

Chrono Units Enum

java.time.temporal.ChronoUnit enum is added in Java 8 to replace the integer values used in old API to represent day, month, etc. Let us see them in action.

Create the following Java program using any editor of your choice in, say, C:\> JAVA.

Java8Tester.java

Live Demo

import java.time.LocalDate; import java.time.temporal.ChronoUnit; public class Java8Tester { public static void main(String args[]) { Java8Tester java8tester = new Java8Tester(); java8tester.testChromoUnits(); } public void testChromoUnits() { //Get the current date LocalDate today = LocalDate.now(); System.out.println("Current date: " + today); //add 1 week to the current date LocalDate nextWeek = today.plus(1, ChronoUnit.WEEKS); System.out.println("Next week: " + nextWeek); //add 1 month to the current date LocalDate nextMonth = today.plus(1, ChronoUnit.MONTHS); System.out.println("Next month: " + nextMonth); //add 1 year to the current date LocalDate nextYear = today.plus(1, ChronoUnit.YEARS); System.out.println("Next year: " + nextYear); //add 10 years to the current date LocalDate nextDecade = today.plus(1, ChronoUnit.DECADES); System.out.println("Date after ten year: " + nextDecade); } }

Verify the Result

Compile the class using javac compiler as follows −

C:\JAVA>javac Java8Tester.java

Now run the Java8Tester as follows −

C:\JAVA>java Java8Tester

It should produce the following result −

Current date: 2014-12-10 Next week: 2014-12-17 Next month: 2015-01-10 Next year: 2015-12-10 Date after ten year: 2024-12-10

Period and Duration

With Java 8, two specialized classes are introduced to deal with the time differences.

  • Period − It deals with date based amount of time.

  • Duration − It deals with time based amount of time.

Let us see them in action.

Create the following Java program using any editor of your choice in, say, C:\> JAVA.

Java8Tester.java

Live Demo

import java.time.temporal.ChronoUnit; import java.time.LocalDate; import java.time.LocalTime; import java.time.Duration; import java.time.Period; public class Java8Tester { public static void main(String args[]) { Java8Tester java8tester = new Java8Tester(); java8tester.testPeriod(); java8tester.testDuration(); } public void testPeriod() { //Get the current date LocalDate date1 = LocalDate.now(); System.out.println("Current date: " + date1); //add 1 month to the current date LocalDate date2 = date1.plus(1, ChronoUnit.MONTHS); System.out.println("Next month: " + date2); Period period = Period.between(date2, date1); System.out.println("Period: " + period); } public void testDuration() { LocalTime time1 = LocalTime.now(); Duration twoHours = Duration.ofHours(2); LocalTime time2 = time1.plus(twoHours); Duration duration = Duration.between(time1, time2); System.out.println("Duration: " + duration); } }

Verify the Result

Compile the class using javac compiler as follows −

C:\JAVA>javac Java8Tester.java

Now run the Java8Tester as follows −

C:\JAVA>java Java8Tester

It should produce the following output −

Current date: 2014-12-10 Next month: 2015-01-10 Period: P-1M Duration: PT2H

Temporal Adjusters

TemporalAdjuster is used to perform the date mathematics. For example, get the "Second Saturday of the Month" or "Next Tuesday". Let us see them in action.

Create the following Java program using any editor of your choice in, say, C:\> JAVA.

Java8Tester.java

Live Demo

import java.time.LocalDate; import java.time.temporal.TemporalAdjusters; import java.time.DayOfWeek; public class Java8Tester { public static void main(String args[]) { Java8Tester java8tester = new Java8Tester(); java8tester.testAdjusters(); } public void testAdjusters() { //Get the current date LocalDate date1 = LocalDate.now(); System.out.println("Current date: " + date1); //get the next tuesday LocalDate nextTuesday = date1.with(TemporalAdjusters.next(DayOfWeek.TUESDAY)); System.out.println("Next Tuesday on : " + nextTuesday); //get the second saturday of next month LocalDate firstInYear = LocalDate.of(date1.getYear(),date1.getMonth(), 1); LocalDate secondSaturday = firstInYear.with(TemporalAdjusters.nextOrSame( DayOfWeek.SATURDAY)).with(TemporalAdjusters.next(DayOfWeek.SATURDAY)); System.out.println("Second Saturday on : " + secondSaturday); } }

Verify the Result

Compile the class using javac compiler as follows −

C:\JAVA>javac Java8Tester.java

Now run the Java8Tester as follows −

C:\JAVA>java Java8Tester

It should produce the following result −

Current date: 2014-12-10 Next Tuesday on : 2014-12-16 Second Saturday on : 2014-12-13

Backward Compatibility

A toInstant() method is added to the original Date and Calendar objects, which can be used to convert them to the new Date-Time API. Use an ofInstant(Insant,ZoneId) method to get a LocalDateTime or ZonedDateTime object. Let us see them in action.

Create the following Java program using any editor of your choice in, say, C:\> JAVA.

Java8Tester.java

Live Demo

import java.time.LocalDateTime; import java.time.ZonedDateTime; import java.util.Date; import java.time.Instant; import java.time.ZoneId; public class Java8Tester { public static void main(String args[]) { Java8Tester java8tester = new Java8Tester(); java8tester.testBackwardCompatability(); } public void testBackwardCompatability() { //Get the current date Date currentDate = new Date(); System.out.println("Current date: " + currentDate); //Get the instant of current date in terms of milliseconds Instant now = currentDate.toInstant(); ZoneId currentZone = ZoneId.systemDefault(); LocalDateTime localDateTime = LocalDateTime.ofInstant(now, currentZone); System.out.println("Local date: " + localDateTime); ZonedDateTime zonedDateTime = ZonedDateTime.ofInstant(now, currentZone); System.out.println("Zoned date: " + zonedDateTime); } }

Verify the Result

Compile the class using javac compiler as follows −

C:\JAVA>javac Java8Tester.java

Now run the Java8Tester as follows −

C:\JAVA>java Java8Tester

It should produce the following output −

Current date: Wed Dec 10 05:44:06 UTC 2014 Local date: 2014-12-10T05:44:06.635 Zoned date: 2014-12-10T05:44:06.635Z[Etc/UTC]
Sours: https://www.tutorialspoint.com/java8/java8_datetime_api.htm

New Date-Time API in Java 8

New date-time API is introduced in Java 8 to overcome the following drawbacks of old date-time API : 

  1. Not thread safe : Unlike old java.util.Date which is not thread safe the new date-time API is immutable and doesn’t have setter methods.
  2. Less operations : In old API there are only few date operations but the new API provides us with many date operations.

Java 8 under the package java.time introduced a new date-time API, most important classes among them are :  

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  1. Local : Simplified date-time API with no complexity of timezone handling.
  2. Zoned : Specialized date-time API to deal with various timezones.
  • LocalDate/LocatTime and LocalDateTime API : Use it when time zones are NOT required.

Java

 
Outputthe current date is 2021-09-23 the current time is 20:52:39.954238 current date and time : 2021-09-23T20:52:39.956909 in formatted manner 23-09-2021 20:52:39 Month : SEPTEMBER day : 23 seconds : 39 the republic day :1950-01-26 specific date with current time : 2016-09-24T20:52:39.956909
  • Zoned date-time API : Use it when time zones are to be considered

Java

 
 
 
 
 
 
 
 
Output: 

formatted current Date and Time : 09-04-2018 06:21:13 the current zone is Etc/UTC tokyo time zone is 2018-04-09T15:21:13.220+09:00[Asia/Tokyo] formatted tokyo time zone 09-04-2018 15:21:13

 

  • Period and Duration classes : 
    Period : It deals with date based amount of time. 
    Duration : It deals with time based amount of time.

Java

Outputgap between dates is a period of P6Y6M25D the current time is 18:34:24.813548 after adding five hours of duration 23:34:24.813548 duration gap between time1 & time2 is PT-5H
  • ChronoUnits Enum : java.time.temporal.ChronoUnit enum is added in Java 8 to replace integer values used in old API to represent day, month etc.

Java

 
 
 
 
 
 
 
 
 
 
 
Output: current date is :2018-04-09 next to next year is 2020-04-09 the next month is 2018-05-09 next week is 2018-04-16 20 years after today 2038-04-09

 

  • TemporalAdjuster : It is used to perform various date related operations.

Java

 
 
 
 
 
Outputthe current date is 2021-07-09 firstDayOfNextMonth : 2021-08-01 next saturday from now is 2021-07-10 firstDayOfMonth : 2021-07-01 lastDayOfMonth : 2021-07-31

 




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The main API for dates, times, instants, and durations.

The classes defined here represent the principle date-time concepts, including instants, durations, dates, times, time-zones and periods. They are based on the ISO calendar system, which is the de facto world calendar following the proleptic Gregorian rules. All the classes are immutable and thread-safe.

Each date time instance is composed of fields that are conveniently made available by the APIs. For lower level access to the fields refer to the package. Each class includes support for printing and parsing all manner of dates and times. Refer to the package for customization options.

The package contains the calendar neutral API , , and . This is intended for use by applications that need to use localized calendars. It is recommended that applications use the ISO-8601 date and time classes from this package across system boundaries, such as to the database or across the network. The calendar neutral API should be reserved for interactions with users.

Dates and Times

is essentially a numeric timestamp. The current Instant can be retrieved from a . This is useful for logging and persistence of a point in time and has in the past been associated with storing the result from .

stores a date without a time. This stores a date like '2010-12-03' and could be used to store a birthday.

stores a time without a date. This stores a time like '11:30' and could be used to store an opening or closing time.

stores a date and time. This stores a date-time like '2010-12-03T11:30'.

stores a date and time with a time-zone. This is useful if you want to perform accurate calculations of dates and times taking into account the , such as 'Europe/Paris'. Where possible, it is recommended to use a simpler class without a time-zone. The widespread use of time-zones tends to add considerable complexity to an application.

Duration and Period

Beyond dates and times, the API also allows the storage of periods and durations of time. A is a simple measure of time along the time-line in nanoseconds. A expresses an amount of time in units meaningful to humans, such as years or days.

Additional value types

stores a month on its own. This stores a single month-of-year in isolation, such as 'DECEMBER'.

stores a day-of-week on its own. This stores a single day-of-week in isolation, such as 'TUESDAY'.

stores a year on its own. This stores a single year in isolation, such as '2010'.

stores a year and month without a day or time. This stores a year and month, such as '2010-12' and could be used for a credit card expiry.

stores a month and day without a year or time. This stores a month and day-of-month, such as '--12-03' and could be used to store an annual event like a birthday without storing the year.

stores a time and offset from UTC without a date. This stores a date like '11:30+01:00'. The is of the form '+01:00'.

stores a date and time and offset from UTC. This stores a date-time like '2010-12-03T11:30+01:00'. This is sometimes found in XML messages and other forms of persistence, but contains less information than a full time-zone.

Package specification

Unless otherwise noted, passing a null argument to a constructor or method in any class or interface in this package will cause a to be thrown. The Javadoc "@param" definition is used to summarise the null-behavior. The "@throws " is not explicitly documented in each method.

All calculations should check for numeric overflow and throw either an or a .

Design notes (non normative)

The API has been designed to reject null early and to be clear about this behavior. A key exception is any method that takes an object and returns a boolean, for the purpose of checking or validating, will generally return false for null.

The API is designed to be type-safe where reasonable in the main high-level API. Thus, there are separate classes for the distinct concepts of date, time and date-time, plus variants for offset and time-zone. This can seem like a lot of classes, but most applications can begin with just five date/time types.

  • - a timestamp
  • - a date without a time, or any reference to an offset or time-zone
  • - a time without a date, or any reference to an offset or time-zone
  • - combines date and time, but still without any offset or time-zone
  • - a "full" date-time with time-zone and resolved offset from UTC/Greenwich

is the closest equivalent class to . is the closest equivalent class to .

Where possible, applications should use , and to better model the domain. For example, a birthday should be stored in a code . Bear in mind that any use of a time-zone, such as 'Europe/Paris', adds considerable complexity to a calculation. Many applications can be written only using , and , with the time-zone added at the user interface (UI) layer.

The offset-based date-time types and , are intended primarily for use with network protocols and database access. For example, most databases cannot automatically store a time-zone like 'Europe/Paris', but they can store an offset like '+02:00'.

Classes are also provided for the most important sub-parts of a date, including , , , and . These can be used to model more complex date-time concepts. For example, is useful for representing a credit card expiry.

Note that while there are a large number of classes representing different aspects of dates, there are relatively few dealing with different aspects of time. Following type-safety to its logical conclusion would have resulted in classes for hour-minute, hour-minute-second and hour-minute-second-nanosecond. While logically pure, this was not a practical option as it would have almost tripled the number of classes due to the combinations of date and time. Thus, is used for all precisions of time, with zeroes used to imply lower precision.

Following full type-safety to its ultimate conclusion might also argue for a separate class for each field in date-time, such as a class for HourOfDay and another for DayOfMonth. This approach was tried, but was excessively complicated in the Java language, lacking usability. A similar problem occurs with periods. There is a case for a separate class for each period unit, such as a type for Years and a type for Minutes. However, this yields a lot of classes and a problem of type conversion. Thus, the set of date-time types provided is a compromise between purity and practicality.

The API has a relatively large surface area in terms of number of methods. This is made manageable through the use of consistent method prefixes.

  • - static factory method
  • - static factory method focussed on parsing
  • - gets the value of something
  • - checks if something is true
  • - the immutable equivalent of a setter
  • - adds an amount to an object
  • - subtracts an amount from an object
  • - converts this object to another type
  • - combines this object with another, such as

Multiple calendar systems is an awkward addition to the design challenges. The first principle is that most users want the standard ISO calendar system. As such, the main classes are ISO-only. The second principle is that most of those that want a non-ISO calendar system want it for user interaction, thus it is a UI localization issue. As such, date and time objects should be held as ISO objects in the data model and persistent storage, only being converted to and from a local calendar for display. The calendar system would be stored separately in the user preferences.

There are, however, some limited use cases where users believe they need to store and use dates in arbitrary calendar systems throughout the application. This is supported by , however it is vital to read all the associated warnings in the Javadoc of that interface before using it. In summary, applications that require general interoperation between multiple calendar systems typically need to be written in a very different way to those only using the ISO calendar, thus most applications should just use ISO and avoid .

The API is also designed for user extensibility, as there are many ways of calculating time. The field and unit API, accessed via and provide considerable flexibility to applications. In addition, the and interfaces provide day-to-day power, allowing code to read close to business requirements:

LocalDate customerBirthday = customer.loadBirthdayFromDatabase(); LocalDate today = LocalDate.now(); if (customerBirthday.equals(today)) { LocalDate specialOfferExpiryDate = today.plusWeeks(2).with(next(FRIDAY)); customer.sendBirthdaySpecialOffer(specialOfferExpiryDate); }
Since:
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Sours: https://docs.oracle.com/javase/8/docs/api/java/time/package-summary.html
Curso Java Completo - Aula 208: Java 8 Nova API DateTime, Trabalhando com Time Zones

Java Date and Time

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The java.time, java.util, java.sql and java.text packages contains classes for representing date and time. Following classes are important for dealing with date in Java.

Java 8 Date/Time API

Java has introduced a new Date and Time API since Java 8. The java.time package contains Java 8 Date and Time classes.

Classical Date/Time API

But classical or old Java Date API is also useful. Let's see the list of classical Date and Time classes.

Formatting Date and Time

We can format date and time in Java by using the following classes:

Java Date and Time APIs

Java provide the date and time functionality with the help of two packages java.time and java.util. The package java.time is introduced in Java 8, and the newly introduced classes tries to overcome the shortcomings of the legacy java.util.Date and java.util.Calendar classes.

Classical Date Time API Classes

The primary classes before Java 8 release were:

Java.lang.System: The class provides the currentTimeMillis() method that returns the current time in milliseconds. It shows the current date and time in milliseconds from January 1st 1970.

java.util.Date: It is used to show specific instant of time, with unit of millisecond.

java.util.Calendar: It is an abstract class that provides methods for converting between instances and manipulating the calendar fields in different ways.

java.text.SimpleDateFormat: It is a class that is used to format and parse the dates in a predefined manner or user defined pattern.

java.util.TimeZone: It represents a time zone offset, and also figures out daylight savings.

Drawbacks of existing Date/Time API's

  1. Thread safety: The existing classes such as Date and Calendar does not provide thread safety. Hence it leads to hard-to-debug concurrency issues that are needed to be taken care by developers. The new Date and Time APIs of Java 8 provide thread safety and are immutable, hence avoiding the concurrency issue from developers.
  2. Bad API designing: The classic Date and Calendar APIs does not provide methods to perform basic day-to-day functionalities. The Date and Time classes introduced in Java 8 are ISO-centric and provides number of different methods for performing operations regarding date, time, duration and periods.
  3. Difficult time zone handling: To handle the time-zone using classic Date and Calendar classes is difficult because the developers were supposed to write the logic for it. With the new APIs, the time-zone handling can be easily done with Local and ZonedDate/Time APIs.

New Date Time API in Java 8

The new date API helps to overcome the drawbacks mentioned above with the legacy classes. It includes the following classes:

java.time.LocalDate: It represents a year-month-day in the ISO calendar and is useful for representing a date without a time. It can be used to represent a date only information such as a birth date or wedding date.

java.time.LocalTime: It deals in time only. It is useful for representing human-based time of day, such as movie times, or the opening and closing times of the local library.

java.time.LocalDateTime: It handles both date and time, without a time zone. It is a combination of LocalDate with LocalTime.

java.time.ZonedDateTime: It combines the LocalDateTime class with the zone information given in ZoneId class. It represent a complete date time stamp along with timezone information.

java.time.OffsetTime: It handles time with a corresponding time zone offset from Greenwich/UTC, without a time zone ID.

java.time.OffsetDateTime: It handles a date and time with a corresponding time zone offset from Greenwich/UTC, without a time zone ID.

java.time.Clock : It provides access to the current instant, date and time in any given time-zone. Although the use of the Clock class is optional, this feature allows us to test your code for other time zones, or by using a fixed clock, where time does not change.

java.time.Instant : It represents the start of a nanosecond on the timeline (since EPOCH) and useful for generating a timestamp to represent machine time. An instant that occurs before the epoch has a negative value, and an instant that occurs after the epoch has a positive value.

java.time.Duration : Difference between two instants and measured in seconds or nanoseconds and does not use date-based constructs such as years, months, and days, though the class provides methods that convert to days, hours, and minutes.

java.time.Period : It is used to define the difference between dates in date-based values (years, months, days).

java.time.ZoneId : It states a time zone identifier and provides rules for converting between an Instant and a LocalDateTime.

java.time.ZoneOffset : It describe a time zone offset from Greenwich/UTC time.

java.time.format.DateTimeFormatter : It comes up with various predefined formatter, or we can define our own. It has parse() or format() method for parsing and formatting the date time values.


Next TopicJava LocalDate class



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Sours: https://www.javatpoint.com/java-date

Java 8 datetime

Java Date Time Tutorial

The Java date and time API can be rather confusing when you first try to figure out how to use it. Therefore I have put together this little trail on Java's date and time classes. Hopefully that will help you get an overview of Java's date and time classes. I also hope it may clear up some of the confusion Sun has created with Java's many date and time classes.

Actually, the Java date time API has been changed (cleaned up) in Java 8 with the introduction of a whole new set of classes. This tutorial will explain both the Java 8 date time API and the Java 7 date time API.

Java 8 Date Time API

In Java 8 a whole new date time API was added. The new Java date time API is located in the Java package which is part of the standard Java 8 class library.

The main change in the Java 8 date time API is that date and time is now no longer represented by a single number of milliseconds since Jan. 1st 1970, but by the number of seconds and nanoseconds since Jan. 1st 1970. The number of seconds can be both positive and negative and is represented by a . The number of nanoseconds is always positive and is represented by an . You will see this new date and time representation in many of the classes in the new Java date time API.

The package also contains a set of subpackages which contain more utilities etc. For instance the contains classes to work with Japanese, Thai, Taiwanese and Islamic calendars. The package contains classes used to parse and format dates from and to strings.

The core of the Java 8 date time API consists of the following classes:

Represents an instant in time on the time line. In the Java 7 date time API an instant was typically represented by a number of millseconds since Jan. 1st. 1970. In Java 8 the class represents an instant in time represented by a number of seconds and a number of nanoseconds since Jan. 1st 1970.
Represents a duration of time, for instance the time between two instants. Like the class a represents its time as a number of seconds and nanoseconds.
Represents a date without time zone information - e.g. a birthday, official holiday etc.
Represents a date and time without time zone information
Represents a local time of day without time zone information.
Represents a date and time including time zone information
Formats date time objects as Strings. For instance a or a .

Java 7 Date Time API

Java 7 has the following date and time classes and methods. Each of these classes are also explained in their own pages, later. See the links at the bottom of this page, or at the top right of every page.


A static method that returns the current date and time as milliseconds since January 1st 1970
A class that represents a date and time. Most methods in this class are deprecated.
A class that represents a date. All time information cut off. This date class is used with JDBC.
A class that represents a date and time. This date and time class is used with JDBC.
A base class for calendar classes. Has methods to do date and time arithmethics like adding a day or month to another date.
A concrete class subclassing java.util.Calendar, representing the Gregorian calendar which is used in most of the western world today. Has all the methods from java.util.Calendar to do date and time arithmethics.
The Java TimeZone class is a class that represents time zones, and is helpful when doing calendar arithmetics across time zones.
A class that can help you parse String's into Date's, and format Date's as String's.

So, which of all these classes should you use? Well, that depends on what you are trying to do.

If you need to do simple timing the method will do just fine.

If you just need an object to hold a date, for instance as a property in a simple domain model object, you can use the class.

If you need to read and write the date and time to a database, use the and classes.

If you need to do date calculations like adding days or months to another date, or check what weekday (monday, tuesday etc.) a given date is, or convert dates and times between time zones, use the and classes.

Here is a list of the texts in this Java date and time tutorial. This list also available in the upper right side of all pages, so you can easily navigate between them.

Next: Java System.currentTimeMillis()

Sours: http://tutorials.jenkov.com/java-date-time/index.html
Curso Java Completo - Aula 203: Java 8 Nova API DateTime LocalDate, LocalTime, LocalDateTime

Nowadays, several applications still use the and APIs, including libraries to make our lives easier working with these types, for example, JodaTime. Java 8, however, introduced new APIs to handle date and time, which allow us to have more fine-grained control over our date and time representation, handing us immutable datetime objects, a more fluent API and in most cases a performance boost, without using additional libraries. Let’s take a look at the basics.

LocalDate/LocalTime/LocalDateTime

Let’s start off with the APIs that are most related to : , a date API that represents a date without time; , a time representation without a date; and , which is a combination of the previous two. All of these types represent the local date and/or time for a region, but, just like , they contain zero information about the zone in which it is represented, only a representation of the date and time in your current timezone.

First of all, these APIs support an easy instantiation:

It’s easy to convert between them:

Aside from that, it’s incredibly easy to perform operations on our date and time representations, using the `plus` and `minus` methods as well as some utility functions:

Now how would we move from to and its variants? Well, that’s simple: We can convert from a Date type to the Instant type, which is a representation of the time since the epoch of 1 January 1970, and then we can instantiate a using the Instant and the current zone.

To convert back to a date, we can simply use the Instant that the Java 8 time type represents. One thing to take note of, though, is that although , and do not contain any Zone or Offset information, they do represent the local date and/or time in a specific region, and as such they do hold the offset present in that region. Thus, we are required to provide an offset to correctly convert the specific type to an Instant.

Difference in Time: Duration and Period

As you’ve noticed, in one of the above examples we’ve used a object. and are two representations of time between two dates, the former representing the difference of time in seconds and nanoseconds, the latter in days, months and years.

When should you use these? when you need to know the difference in time between two representations:

when you’re looking for a difference between a representation that holds time information:

When outputting or using , a special format will be used based on ISO-8601 standard. The pattern used for a Period is PnYnMnD, where n defines the number of years, months or days present within the period. This means that P1Y2M3D defines a period of 1 year, 2 months, and 3 days. The ‘P’ in the pattern is the period designator, which tells us that the following format represents a period. Using the pattern, we can also create a period based on a string using the method.

When using , we move away slightly from the ISO-8601 standard, as Java 8 does not use the same patterns. The pattern defined by ISO-8601 is PnYnMnDTnHnMn.nS. This is basically the pattern, extended with a time representation. In the pattern, T is the time designator, so the part that follows defines a duration specified in hours, minutes and seconds.

Java 8 uses two specific patterns for , namely PnDTnHnMn.nS when parsing a String to a , and PTnHnMn.nS when calling the method on a instance.

Last but not least, we can also retrieve the various parts of a period or duration, by using the corresponding method on a type. However, it’s important to know that the various datetime types also support this through the use of enumeration type. Let’s take a look at some examples:

Working With Zones and Offsets: ZondedDateTime and OffsetDateTime

Thus far, we’ve shown how the new date APIs have made a few things a little easier. What really makes a difference, however, is the ability to easily use date and time in a timezone context. Java 8 provides us with and , the first one being a with information for a specific Zone (e.g. Europe/Paris), the second one being a with an offset. What’s the difference? uses a fixed time difference between UTC/Greenwich and the date that is specified, whilst specifies the zone in which the time is represented, and will take daylight saving time into account.

Converting to either of these types is very easy:


When switching between them, you have to keep in mind that converting from a to will take daylight saving time into account, while converting in the other direction, from to , means you will not have information about the region of the zone, nor will there be any rules applied for daylight saving time. That is because an offset does not define any time zone rules, nor is it bound to a specific region.

Now, what if we would like to know what the time for a specific zone or offset is in our own timezone? There are some handy functions defined for that as well!

It would be a hassle if we would have to manually convert between these types all the time to get the one we need. This is where Spring Framework comes to our aid. Spring provides us with quite a few datetime converters out of the box, which are registered on the and can be found in the class.

When using these converters, it is important to know that it will not convert time between regions or offsets. The , for example, will return the for the zone it was specified in, not the that it would represent in the region of your application.

Last but not least, you can consult to find all the available time zones, or use the map , which contains an abbreviated version for a few time zones such as EST, CST and more.

Formatting - Using the DateTimeFormatter

Of course, various regions in the world use different formats to specify the time. One application might use MM-dd-yyyy, whilst another uses dd/MM/yyyy. Some applications want to remove all confusion and represent their dates by yyyy-MM-dd. When using , we would quickly move to using multiple formatters. The class, however, provides us with optional patterns, so that we can use a single formatter for several formats! Let’s take a look using some examples.

The square brackets in a pattern define an optional part in the pattern. By making our various formats optional, the first pattern that matches the string will be used to convert our date representation. This might get quite difficult to read when you’re using multiple patterns, so let’s take a look at creating our using the builder pattern.

These are the basics to include multiple patterns, but what if our patterns only differ slightly? Let’s take a look at yyyy-MM-dd and yyyy-MMM-dd.

However, you should not use a formatter that supports multiple formats when converting to a string, because when we would use our formatter to format our date to a string representation, it will also use the optional patterns.

Since we’re in the 21st century, obviously we have to take globalization into account, and we’ll want to offer localized dates for our users. To ensure that your returns a specific locale, you can simply do the following:

To find which Locales are available, you can use .

Now it could be that the date pattern you receive holds more information than the type you’re using. A will throw an exception as soon as a provided date representation isn’t in accords with the pattern. Let’s take a closer look at the issue and how to work around it.

Let’s create a formatter that can handle the ISO date, time, and datetime patterns.

Now we can perfectly execute all of the following:

LocalDateTime? What if you’d expect a LocalTime and you are given a date representation or vice versa?

For these last two cases, there is no single correct solution, but it depends on what you require, or what those dates and times represent or could represent. The magic is found in the use of , which you can use to create default values for a part of the pattern.

If we start with a , and you just want the or , you’ll receive the corresponding part of the . To create a , we’ll need default values for the date and time it is holding. Let’s say that if you do not provide information about a date, we’ll return today’s date, and if you don’t provide a time, we’ll assume you meant the start of the day.

Since we’re returning a , it won’t be parsed to a or , so let’s use the to get the correct type.

Using allows us to check which information is present and to provide defaults for any information that is missing, enabling us to easily convert to the required type, using the logic that makes sense in our application.

To learn how to compose valid time patterns, check out the documentation.

Conclusion

Most new features require some time to understand and get used to, and the Java 8 Date/Time API is no different. The APIs provide us with better access to the correct format necessary, as well as a more standardized and readable manner of working with date time operations. Using these tips and tricks, we can pretty much cover all of our use cases.

Sours: https://dzone.com/articles/java-8-date-and-time

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