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 convert between old Date and Calendar object with the new Java 8 Date Time?

In this example we will learn how to convert the old java.util.Date and java.util.Calendar objects to the new Date Time introduced in Java 8. The first method in the code snippet below dateToNewDate() show conversion of java.util.Date while the calendarToNewDate() show the conversion of java.util.Calendar.

The java.util.Date and java.util.Calendar provide a toInstant() method to convert the objects to the new Date Time API class of the java.time.Instant. To convert the old date into the Java 8 LocalDate, LocalTime and LocalDateTime we first can create an instance of ZonedDateTime using the atZone() method of the Instant class.

ZonedDateTime zonedDateTime = instant.atZone(ZoneId.systemDefault());

From an instance of ZonedDateTime class we can call the toLocalDate(), toLocalTime() and toLocalDateTime() to get instance of LocalDate, LocalTime and LocalDateTime.

To convert back from the new Java 8 date to the old java.util.Date we can use the Date.from() static factory method and passing and instance of java.time.Instant that we can obtains by calling the following code.

Instant instant1 = dateTime.atZone(ZoneId.systemDefault()).toInstant();
Date now1 = Date.from(instant1);

Here are the complete code snippet to convert java.util.Date to the new Java 8 Date Time.

private static void dateToNewDate() {
    Date now = new Date();
    Instant instant = now.toInstant();

    ZonedDateTime zonedDateTime = instant.atZone(ZoneId.systemDefault());

    LocalDate date = zonedDateTime.toLocalDate();
    LocalTime time = zonedDateTime.toLocalTime();
    LocalDateTime dateTime = zonedDateTime.toLocalDateTime();

    Instant instant1 = dateTime.atZone(ZoneId.systemDefault()).toInstant();
    Date now1 = Date.from(instant1);

    System.out.println("java.util.Date          = " + now);
    System.out.println("java.time.LocalDate     = " + date);
    System.out.println("java.time.LocalTime     = " + time);
    System.out.println("java.time.LocalDateTime = " + dateTime);
    System.out.println("java.util.Date          = " + now1);
    System.out.println();
}

The steps for converting from the java.util.Calendar to the new Java 8 date can be seen in the code snippet below. As with java.util.Date the Calendar class provide toInstant() method to convert the calendar to java.time.Instant object.

Using the LocalDateTime.ofInstant() method we can create a LocalDateTime object from the instant object. By having the LocalDateTime object we can then get an instance of LocalDate and LocalTime by calling the toLocalDate() and toLocalTime() method.

Finally to convert back to java.util.Calendar we can use the GregorianCalendar.from() static factory method which require an instance of ZonedDateTime to be passed as a parameter. To get an instance of ZonedDateTime we can call LocalDateTime.atZone() method. You can see the complete code in the code snippet below.

private static void calendarToNewDate() {
    Calendar now = Calendar.getInstance();

    LocalDateTime dateTime = LocalDateTime.ofInstant(now.toInstant(),
            ZoneId.systemDefault());

    LocalDate date = dateTime.toLocalDate();
    LocalTime time = dateTime.toLocalTime();

    ZonedDateTime zonedDateTime = dateTime.atZone(ZoneId.systemDefault());
    Calendar now1 = GregorianCalendar.from(zonedDateTime);

    System.out.println("java.util.Calendar      = " + now);
    System.out.println("java.time.LocalDateTime = " + dateTime);
    System.out.println("java.time.LocalDate     = " + date);
    System.out.println("java.time.LocalTime     = " + time);
    System.out.println("java.util.Calendar      = " + now1);
}

Below is the main Java class to run the code snippet. You must place the above methods inside this class to run the code snippet.

package org.kodejava.example.datetime;

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

public class LegacyDateCalendarToNewDateExample {
    public static void main(String[] args) {
        dateToNewDate();
        calendarToNewDate();
    }
}

Here are the result of the code snippet above. The first group is conversion the java.util.Date to the new Date Time API. The second group is conversion from the java.util.Calendar to the new Date Time API.

java.util.Date          = Mon Feb 01 11:09:55 WITA 2016
java.time.LocalDate     = 2016-02-01
java.time.LocalTime     = 11:09:55.746
java.time.LocalDateTime = 2016-02-01T11:09:55.746
java.util.Date          = Mon Feb 01 11:09:55 WITA 2016

java.util.Calendar      = java.util.GregorianCalendar[time=1454296195871,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=sun.util.calendar.ZoneInfo[id="Asia/Makassar",offset=28800000,dstSavings=0,useDaylight=false,transitions=5,lastRule=null],firstDayOfWeek=1,minimalDaysInFirstWeek=1,ERA=1,YEAR=2016,MONTH=1,WEEK_OF_YEAR=6,WEEK_OF_MONTH=1,DAY_OF_MONTH=1,DAY_OF_YEAR=32,DAY_OF_WEEK=2,DAY_OF_WEEK_IN_MONTH=1,AM_PM=0,HOUR=11,HOUR_OF_DAY=11,MINUTE=9,SECOND=55,MILLISECOND=871,ZONE_OFFSET=28800000,DST_OFFSET=0]
java.time.LocalDateTime = 2016-02-01T11:09:55.871
java.time.LocalDate     = 2016-02-01
java.time.LocalTime     = 11:09:55.871
java.util.Calendar      = java.util.GregorianCalendar[time=1454296195871,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=sun.util.calendar.ZoneInfo[id="Asia/Makassar",offset=28800000,dstSavings=0,useDaylight=false,transitions=5,lastRule=null],firstDayOfWeek=2,minimalDaysInFirstWeek=4,ERA=1,YEAR=2016,MONTH=1,WEEK_OF_YEAR=5,WEEK_OF_MONTH=1,DAY_OF_MONTH=1,DAY_OF_YEAR=32,DAY_OF_WEEK=2,DAY_OF_WEEK_IN_MONTH=1,AM_PM=0,HOUR=11,HOUR_OF_DAY=11,MINUTE=9,SECOND=55,MILLISECOND=871,ZONE_OFFSET=28800000,DST_OFFSET=0]

How do I convert string date to long value?

package org.kodejava.example.util;

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class StringDateToLong {
    public static void main(String[] args) {
        // Here we have a string date and we want to covert it to long value
        String today = "13/10/2017";

        // Create a SimpleDateFormat which will be use to convert the string to
        // a date object.
        DateFormat formatter = new SimpleDateFormat("dd/MM/yyyy");
        try {
            // The SimpleDateFormat parse the string and return a date object.
            // To get the date in long value just call the getTime method of
            // the Date object.
            Date date = formatter.parse(today);
            long dateInLong = date.getTime();

            System.out.println("Date         = " + date);
            System.out.println("Date in Long = " + dateInLong);
        } catch (ParseException e) {
            e.printStackTrace();
        }
    }
}

The result of the code snippet:

Date         = Fri Oct 13 00:00:00 WITA 2017
Date in Long = 1507824000000