How do I convert java.util.TimeZone to java.time.ZoneId?

The following code snippet will show you how to convert the old java.util.TimeZone to java.time.ZoneId introduced in Java 8. In the first line of our main() method we get the default timezone using the TimeZone.getDefault() and convert it to ZoneId by calling the toZoneId() method. In the second example we create the TimeZone object by calling the getTimeZone() and pass the string of timezone id. To convert it to ZoneId we call the toZoneId() method.

package org.kodejava.example.datetime;

import java.time.ZoneId;
import java.util.TimeZone;

public class TimeZoneToZoneId {
    public static void main(String[] args) {
        ZoneId zoneId = TimeZone.getDefault().toZoneId();
        System.out.println("zoneId = " + zoneId);

        TimeZone timeZoneUsPacific = TimeZone.getTimeZone("US/Pacific");
        ZoneId zoneIdUsPacific = timeZoneUsPacific.toZoneId();
        System.out.println("zoneIdUsPacific = " + zoneIdUsPacific);
    }
}

This snippet prints the following output:

zoneId = Asia/Shanghai
zoneIdUsPacific = US/Pacific

To convert the other way around you can do it like the following code snippet. Below we convert the ZoneId to TimeZone by using the TimeZone.getTimeZone() method and pass the ZoneId.systemDefault() which return the system default timezone. Or we can create ZoneId using the ZoneId.of() method and specify the timezone id and then pass it to the getTimeZone() method of the TimeZone class.

package org.kodejava.example.datetime;

import java.time.ZoneId;
import java.util.TimeZone;

public class ZoneIdToTimeZone {
    public static void main(String[] args) {
        TimeZone timeZone = TimeZone.getTimeZone(ZoneId.systemDefault());
        System.out.println("timeZone = " + timeZone.getDisplayName());

        TimeZone timeZoneUsPacific = TimeZone.getTimeZone(ZoneId.of("US/Pacific"));
        System.out.println("timeZoneUsPacific = " + timeZoneUsPacific.getDisplayName());
    }
}

And here are the output of the code snippet above:

timeZone = China Standard Time
timeZoneUsPacific = Pacific Standard Time

How do I get a list of all TimeZones Ids using Java 8?

To retrieve a list of all available time zones ids we can call the java.time.ZoneId static method getAvailableZoneIds(). This method return a Set of string of all zone ids. The format of the zone id are “{area}/{city}”. You can use this ids of string to create the ZoneId object using the ZoneId.of() static method.

package org.kodejava.example.datetime;

import java.time.ZoneId;
import java.time.format.TextStyle;
import java.util.Locale;
import java.util.Set;

public class GetAllTimeZoneIds {
    public static void main(String[] args) {
        Set<String> zoneIds = ZoneId.getAvailableZoneIds();
        for (String id : zoneIds) {
            ZoneId zoneId = ZoneId.of(id);
            System.out.println("id          = " + id);
            System.out.println("displayName = " + 
                zoneId.getDisplayName(TextStyle.FULL, Locale.US));
        }
    }
}

Here are some of zone IDs printed out to the console:

id          = Asia/Aden
displayName = Arabian Time
id          = America/Cuiaba
displayName = Amazon Time
id          = Etc/GMT+9
displayName = GMT-9:00
id          = Etc/GMT+8
displayName = GMT-8:00
id          = Africa/Nairobi
displayName = Eastern Africa Time
...
...
...
id          = Europe/Nicosia
displayName = Eastern European Time
id          = Pacific/Guadalcanal
displayName = Solomon Is. Time
id          = Europe/Athens
displayName = Eastern European Time
id          = US/Pacific
displayName = Pacific Time
id          = Europe/Monaco
displayName = Central European Time

How do I modified the value of LocalDate and LocalTime object?

The easiest way to modify the value of a LocalDate, LocalTime or LocalDateTime object is to use the with() method of the corresponding object. These methods will return a modified version of the object, it doesn’t change the attribute of the original object. All the methods, like withYear(), withDayOfMonth() or the with(ChronoField) of the LocalDate object will return a new object with the modified attribute.

With the LocalTime object you can use the withHour(), withMinute(), withSecond() or the more generic with(ChronoField) method to modified the attribute of a LocalTime object. You can also modified a LocalDateTime object using these with() method. Let’s see the example in the code snippet below.

package org.kodejava.example.datetime;

import java.time.LocalDate;
import java.time.LocalTime;
import java.time.temporal.ChronoField;

public class ManipulatingDateTime {
    public static void main(String[] args) {
        LocalDate date1 = LocalDate.of(2020, 4, 21);
        System.out.println("date1 = " + date1);
        LocalDate date2 = date1.withYear(2019);
        System.out.println("date2 = " + date2);
        LocalDate date3 = date2.withDayOfMonth(10);
        System.out.println("date3 = " + date3);
        LocalDate date4 = date3.with(ChronoField.MONTH_OF_YEAR, 12);
        System.out.println("date4 = " + date4);

        LocalTime time1 = LocalTime.of(1, 5, 10);
        System.out.println("time1 = " + time1);
        LocalTime time2 = time1.withHour(6);
        System.out.println("time2 = " + time2);
        LocalTime time3 = time2.withMinute(45);
        System.out.println("time3 = " + time3);
        LocalTime time4 = time3.with(ChronoField.SECOND_OF_MINUTE, 25);
        System.out.println("time4 = " + time4);

        LocalDate now1 = LocalDate.now();
        System.out.println("now1 = " + now1);
        LocalDate now2 = now1.plusWeeks(1);
        System.out.println("now2 = " + now2);
        LocalDate now3 = now2.minusMonths(2);
        System.out.println("now3 = " + now3);
        LocalDate now4 = now3.plus(15, ChronoUnit.DAYS);
        System.out.println("now4 = " + now4);
    }
}

The output of this code snippet are:

date1 = 2020-04-21
date2 = 2019-04-21
date3 = 2019-04-10
date4 = 2019-12-10
time1 = 01:05:10
time2 = 06:05:10
time3 = 06:45:10
time4 = 06:45:25
now1 = 2020-04-21
now2 = 2020-04-28
now3 = 2020-02-28
now4 = 2020-03-14

These with() methods is the counterpart of the get() methods. Where the get() methods will give you the value of the corresponding LocalDate or LocalTime attribute, the with() method will change the attribute value and return a new object. It didn’t call set because the object is immutable, which means it value cannot be changed.

While with the with() method you can change the value of date time attribute in an absolute way using the plus() or minus() method can help you change the date and time attribute in a relative way. The plus() and minus() method allows you to move a Temporal back or forward a give amount of time, defined by a number plus a TemporalUnit, in this case we use the ChronoUnit enumeration which implements this interface.

How do I use TemporalField to access date time value?

The LocalDate and LocalTime are probably the first two classes from the Java 8 Date and Time API that you will work with. An instance of the LocalDate object is an immutable object representing a date without the time of the day and on the other way around the LocalTime object is an immutable object representing a time without the date information.

The LocalDate object have methods to get information related to date such as getYear(), getMonth(), getDayOfMonth(). While the LocalTime object have methods to get information related to time such as getHour(), getMinute(), getSecond(). Beside using those methods we can also access the value of these object using the TemporalField interface. We can pass a TemporalField to the get() method of LocalDate and LocalTime objects. TemporalField is an interface, one of its implementation that we can use to get the value is the ChronoField enumerations.

Let’s see some examples in the code snippet below:

package org.kodejava.example.datetime;

import java.time.LocalDate;
import java.time.LocalTime;
import java.time.temporal.ChronoField;

public class DateTimeValueTemporalField {
    public static void main(String[] args) {
        LocalDate date = LocalDate.now();
        System.out.println("Date = " + date);
        System.out.println("Year = " + date.getYear());
        System.out.println("Year = " + date.get(ChronoField.YEAR));

        System.out.println("Month= " + date.getMonth().getValue());
        System.out.println("Month= " + date.get(ChronoField.MONTH_OF_YEAR));

        System.out.println("Date = " + date.getDayOfMonth());
        System.out.println("Date = " + date.get(ChronoField.DAY_OF_MONTH));

        System.out.println("DOW  = " + date.getDayOfWeek().getValue());
        System.out.println("DOW  = " + date.get(ChronoField.DAY_OF_WEEK) + "\n");

        LocalTime time = LocalTime.now();
        System.out.println("Time  = " + time);
        System.out.println("Hour  = " + time.getHour());
        System.out.println("Hour  = " + time.get(ChronoField.HOUR_OF_DAY));

        System.out.println("Minute= " + time.getMinute());
        System.out.println("Minute= " + time.get(ChronoField.MINUTE_OF_HOUR));

        System.out.println("Second= " + time.getSecond());
        System.out.println("Second= " + time.get(ChronoField.SECOND_OF_MINUTE));

        System.out.println("Nano  = " + time.getNano());
        System.out.println("Nano  = " + time.get(ChronoField.NANO_OF_SECOND));
    }
}

The output of the code snippet above are:

Date = 2020-04-20
Year = 2020
Year = 2020
Month= 4
Month= 4
Date = 20
Date = 20
DOW  = 1
DOW  = 1

Time  = 16:06:11.389185
Hour  = 16
Hour  = 16
Minute= 6
Minute= 6
Second= 11
Second= 11
Nano  = 389185000
Nano  = 389185000

How do I get all Sundays of the year in Java?

You need the create a holiday calendar for your application. One of the functionality is to include all Sundays of the year as a holiday for your calendar. The following code snippet will show you how to get all Sundays of the given year. First we need to find the first Sunday of the year using the first 3 lines of code in the main() method. After getting the first Sunday we just need to loop to add 7 days using the Period.ofDays() to the current Sunday to get the next Sunday. We stop the loop when the year of the Sunday is different to the current year.

package org.kodejava.example.datetime;

import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.Month;
import java.time.Period;
import java.time.format.DateTimeFormatter;
import java.time.format.FormatStyle;

import static java.time.temporal.TemporalAdjusters.firstInMonth;

public class FindAllSundaysOfTheYear {
    public static void main(String[] args) {
        // Create a LocalDate object that represent the first day of the year.
        int year = 2020;
        LocalDate now = LocalDate.of(year, Month.JANUARY, 1);
        // Find the first Sunday of the year
        LocalDate sunday = now.with(firstInMonth(DayOfWeek.SUNDAY));

        do {
            // Loop to get every Sunday by adding Period.ofDays(7) the the current Sunday.
            System.out.println(sunday.format(DateTimeFormatter.ofLocalizedDate(FormatStyle.FULL)));
            sunday = sunday.plus(Period.ofDays(7));
        } while (sunday.getYear() == year);
    }
}

The output of this code snippet are:

Sunday, January 5, 2020
Sunday, January 12, 2020
Sunday, January 19, 2020
Sunday, January 26, 2020
Sunday, February 2, 2020
Sunday, February 9, 2020
Sunday, February 16, 2020
Sunday, February 23, 2020
...
Sunday, December 6, 2020
Sunday, December 13, 2020
Sunday, December 20, 2020
Sunday, December 27, 2020

How do I get the first Sunday of the year in Java?

The following code snippet help you to find the first Sunday of the year or you can replace it with any day that you want. To achieve this we can use the TemporalAdjusters.firstInMonth adjusters, this adjusters returns a new date in the same month with the first matching day-of-week. This is used for expressions like ‘first Sunday in January’.

Because we want to get the first Sunday of the year first we create a LocalDate which represent the 1st January of 2020. Then we call the with() method and pass the firstInMonth adjusters with the DayOfWeek.SUNDAY to find. Beside using Java 8 date time API, you can also use the old java.util.Calendar class as also shown in the code snippet below. But using the new date time API give you a more readable, simpler and less code to write.

package org.kodejava.example.datetime;

import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.Month;
import java.time.ZoneId;
import java.util.Calendar;

import static java.time.temporal.TemporalAdjusters.firstInMonth;

public class FirstSundayOfTheYear {
    public static void main(String[] args) {
        // Get the first Sunday of the year using Java 8 date time
        LocalDate now = LocalDate.of(2020, Month.JANUARY, 1);
        LocalDate sunday = now.with(firstInMonth(DayOfWeek.SUNDAY));
        System.out.println("The first Sunday of 2020 falls on: " + sunday);

        // Get the first Sunday of the year using the old java.util.Calendar
        Calendar calendar = Calendar.getInstance();
        calendar.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);
        calendar.set(Calendar.DAY_OF_WEEK_IN_MONTH, 1);
        calendar.set(Calendar.MONTH, Calendar.JANUARY);
        calendar.set(Calendar.YEAR, 2020);
        System.out.println("The first Sunday of 2020 falls on: " + calendar.getTime());
        System.out.println("The first Sunday of 2020 falls on: " +
            LocalDate.ofInstant(calendar.getTime().toInstant(), ZoneId.systemDefault()));
    }
}

This code snippet will print out the following output:

The first Sunday of 2020 falls on: 2020-01-05
The first Sunday of 2020 falls on: Sun Jan 05 04:39:59 CST 2020
The first Sunday of 2020 falls on: 2020-01-05

How to convert java.time.LocalDate to java.util.Date?

The following code snippet demonstrate how to convert java.time.LocalDate to java.util.Date and vice versa. In the first part of the code snippet we convert LocalDate to Date and back to LocalDate object. On the second part we convert LocalDateTime to Date and back to LocalDateTime object.

package org.kodejava.example.datetime;

import java.time.*;
import java.util.Date;

public class LocalDateToDate {
    public static void main(String[] args) {
        // Convert java.time.LocalDate to java.util.Date and back to
        // java.time.LocalDate
        LocalDate localDate = LocalDate.now();
        System.out.println("LocalDate = " + localDate);

        Date date1 = Date.from(localDate.atStartOfDay(ZoneId.systemDefault()).toInstant());
        System.out.println("Date      = " + date1);

        localDate = date1.toInstant().atZone(ZoneId.systemDefault()).toLocalDate();
        System.out.println("LocalDate = " + localDate);
        System.out.println();

        // Convert java.time.LocalDateTime to java.util.Date and back to
        // java.time.LocalDateTime
        LocalDateTime localDateTime = LocalDateTime.now();
        System.out.println("LocalDateTime = " + localDateTime);

        Date date2 = Date.from(localDateTime.atZone(ZoneId.systemDefault()).toInstant());
        System.out.println("Date          = " + date2);

        localDateTime = date2.toInstant().atZone(ZoneId.systemDefault()).toLocalDateTime();
        System.out.println("LocalDateTime = " + localDateTime);
    }
}

The result of the code snippet:

LocalDate = 2017-02-14
Date      = Tue Feb 14 00:00:00 WITA 2017
LocalDate = 2017-02-14

LocalDateTime = 2017-02-14T10:34:49.562
Date          = Tue Feb 14 10:34:49 WITA 2017
LocalDateTime = 2017-02-14T10:34:49.562

How do I create a custom TemporalAdjuster?

In this example we are going to learn how to implement a custom TemporalAdjuster. We are going to create TemporalAdjuster to find the next working day from a specified date. We will use 5 working days, from Monday to Friday.

The custom temporal adjuster class should implement the TemporalAdjuster interface, which define a single method that we must implement, the adjustInto(Temporal) method.

package org.kodejava.example.datetime;

import java.time.DayOfWeek;
import java.time.temporal.ChronoField;
import java.time.temporal.ChronoUnit;
import java.time.temporal.Temporal;
import java.time.temporal.TemporalAdjuster;

public class NextWorkingDayAdjuster implements TemporalAdjuster {
    @Override
    public Temporal adjustInto(Temporal temporal) {
        int field = temporal.get(ChronoField.DAY_OF_WEEK);
        DayOfWeek dayOfWeek = DayOfWeek.of(field);

        int daysToAdd = 1;
        if (DayOfWeek.FRIDAY.equals(dayOfWeek)) {
            daysToAdd = 3;
        } else if (DayOfWeek.SATURDAY.equals(dayOfWeek)) {
            daysToAdd = 2;
        }
        return temporal.plus(daysToAdd, ChronoUnit.DAYS);
    }
}

The NextWorkingDayAdjuster move the temporal object a day forward. Except if it is on Friday or Saturday, which will move the temporal object three days or two days forward respectively. This will make it return Monday as the next working day.

After creating the custom adjuster, now let’s create an example that use the NextWorkingDayAdjuster class.

package org.kodejava.example.datetime;

import java.time.LocalDate;
import java.time.Month;
import java.time.temporal.TemporalAdjuster;

public class NextWorkingDayAdjusterDemo {
    public static void main(String[] args) {
        TemporalAdjuster nextWorkingDay = new NextWorkingDayAdjuster();

        LocalDate now = LocalDate.now();
        LocalDate nextDay = now.with(nextWorkingDay);
        System.out.println("now            = " + now);
        System.out.println("nextWorkingDay = " + nextDay);

        LocalDate friday = LocalDate.of(2016, Month.MARCH, 11);
        nextDay = friday.with(nextWorkingDay);
        System.out.println("friday         = " + friday);
        System.out.println("nextWorkingDay = " + nextDay);

        LocalDate saturday = LocalDate.of(2016, Month.MARCH, 12);
        nextDay = saturday.with(nextWorkingDay);
        System.out.println("saturday       = " + saturday);
        System.out.println("nextWorkingDay = " + nextDay);
    }
}

And here are the results of our code:

now            = 2016-03-10
nextWorkingDay = 2016-03-11
friday         = 2016-03-11
nextWorkingDay = 2016-03-14
saturday       = 2016-03-12
nextWorkingDay = 2016-03-14

How do I manipulate LocalDate object using TemporalAdjuster?

In the previous example we manipulate the value of LocalDate by adding or subtracting the value of date object by days, months, years using methods like plusMonths() or minusDays(). Or by changing the year or the month of the date object using methods like withYear() or withMonth().

But there are times that we want to manipulate the date object so that we can get the first day of the month or the last day of the month. We want to manipulate the date value to advance the date to the first Monday after the current day or the last the of the year.

To manipulate the date object in this way we can use the with() method and pass a TemporalAdjuster object as an argument. Fortunately, the Date and Time API already provide some commonly used TemporalAdjuster. These TemporalAdjuster are provided as a static factory methods that we can find in the java.time.temporal.TemporalAdjusters class.

The following example is a code snippet to manipulate the date object using TemporalAdjuster / TemporalAdjusters class.

package org.kodejava.example.datetime;

import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.temporal.TemporalAdjusters;

public class DateManipulationWithTemporalAdjuster {
    public static void main(String[] args) {
        LocalDate date = LocalDate.now();
        System.out.println("Current date       = " + date);

        LocalDate date1 = date.with(TemporalAdjusters.firstDayOfMonth());
        System.out.println("First day of month = " + date1);

        LocalDate date2 = date.with(TemporalAdjusters.lastDayOfMonth());
        System.out.println("Last day of month  = " + date2);

        LocalDate date3 = date.with(TemporalAdjusters.next(DayOfWeek.MONDAY));
        System.out.println("Next Monday        = " + date3);

        LocalDate date4 = date.with(TemporalAdjusters.lastDayOfYear());
        System.out.println("Last day of year   = " + date4);
    }
}

The result of the code snippet are:

Current date       = 2016-03-06
First day of month = 2016-03-01
Last day of month  = 2016-03-31
Next Monday        = 2016-03-07
Last day of year   = 2016-12-31

The table below shows the complete of static factory method provided by the TemporalAdjusters class.

Method Name Method Description
dayOfWeekInMonth Returns a new date in the same month with the ordinal day-of-week.
firstDayOfMonth Returns a new date set to the first day of the current month.
firstDayOfNextMonth Returns a new date set to the first day of the next month.
firstDayOfNextYear Returns a new date set to the first day of the next year.
firstDayOfYear Returns a new date set to the first day of the current year.
firstInMonth Returns a new date in the same month with the first matching day-of-week.
lastDayOfMonth Returns a new date set to the last day of the current month.
lastDayOfYear Returns a new date set to the last day of the current year.
lastInMonth Returns a new date in the same month with the last matching day-of-week.
next Returns the next day-of-week adjuster.
nextOrSame Returns the next-or-same day-of-week adjuster.
ofDateAdjuster Returns user-written adjuster.
previous Returns the previous day-of-week adjuster.
previousOrSame Returns the previous-or-same day-of-week adjuster.

How do I manipulate the value of LocalDate object?

In the following example we will learn how to manipulate a LocalDate object. There are many methods available for us to change the value of a LocalDate object. For example we can change the year, month and day of LocalDate object. We can use methods like withYear(), withDayOfMonth(), plusYears(), minusMonths(), etc. All these methods will return a new LocalDate object, the original LocalDate will stay unchanged.

Let’s see the following code example for demonstration on how to manipulate the value of LocalDate object.

package org.kodejava.example.datetime;

import java.time.LocalDate;
import java.time.Month;
import java.time.temporal.ChronoField;
import java.time.temporal.ChronoUnit;

public class LocalDateManipulation {
    public static void main(String[] args) {
        absoluteAttributeManipulations();
        relativeAttributeManipulations();
    }

    private static void relativeAttributeManipulations() {
        System.out.println("LocalDateManipulation.relativeAttributeManipulations");
        LocalDate date1 = LocalDate.of(2015, Month.AUGUST, 17);
        LocalDate date2 = date1.minusYears(70);
        LocalDate date3 = date2.plusMonths(10);
        LocalDate date4 = date3.minusDays(15);
        LocalDate date5 = date4.plusWeeks(52);
        LocalDate date6 = date5.minus(52, ChronoUnit.WEEKS);

        System.out.println("of(2015, Month.AUGUST, 17)        => " + date1);
        System.out.println("date1.minusYears(70)              => " + date2);
        System.out.println("date1.plusMonths(10)              => " + date3);
        System.out.println("date3.minusDays(15)               => " + date4);
        System.out.println("date4.plusWeeks(52)               => " + date5);
        System.out.println("date5.minus(52, ChronoUnit.WEEKS) => " + date6);

    }

    private static void absoluteAttributeManipulations() {
        System.out.println("LocalDateManipulation.absoluteAttributeManipulations");
        LocalDate date1 = LocalDate.of(2016, Month.JANUARY, 1);
        LocalDate date2 = date1.withYear(2010);
        LocalDate date3 = date2.withMonth(Month.DECEMBER.getValue());
        LocalDate date4 = date3.withDayOfMonth(15);
        LocalDate date5 = date4.with(ChronoField.DAY_OF_YEAR, 100);

        System.out.println("of(2016, Month.JANUARY, 1)                 => " + date1);
        System.out.println("date1.withYear(2010)                       => " + date2);
        System.out.println("date2.withMonth(Month.DECEMBER.getValue()) => " + date3);
        System.out.println("date3.withDayOfMonth(15)                   => " + date4);
        System.out.println("date4.with(ChronoField.DAY_OF_YEAR, 100)   => " + date5);
    }
}

The results of this code snippet are:

LocalDateManipulation.absoluteAttributeManipulations
of(2016, Month.JANUARY, 1)                 => 2016-01-01
date1.withYear(2010)                       => 2010-01-01
date2.withMonth(Month.DECEMBER.getValue()) => 2010-12-01
date3.withDayOfMonth(15)                   => 2010-12-15
date4.with(ChronoField.DAY_OF_YEAR, 100)   => 2010-04-10

LocalDateManipulation.relativeAttributeManipulations
of(2015, Month.AUGUST, 17)        => 2015-08-17
date1.minusYears(70)              => 1945-08-17
date1.plusMonths(10)              => 1946-06-17
date3.minusDays(15)               => 1946-06-02
date4.plusWeeks(52)               => 1947-06-01
date5.minus(52, ChronoUnit.WEEKS) => 1946-06-02