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 obtain 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 language-java">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 language-java">package org.kodejava.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 = Tue Nov 16 08:44:51 CST 2021 java.time.LocalDate = 2021-11-16 java.time.LocalTime = 08:44:51.031 java.time.LocalDateTime = 2021-11-16T08:44:51.031 java.util.Date = Tue Nov 16 08:44:51 CST 2021 java.util.Calendar = java.util.GregorianCalendar[time=1637023491089,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=sun.util.calendar.ZoneInfo[id="Asia/Shanghai",offset=28800000,dstSavings=0,useDaylight=false,transitions=31,lastRule=null],firstDayOfWeek=1,minimalDaysInFirstWeek=1,ERA=1,YEAR=2021,MONTH=10,WEEK_OF_YEAR=47,WEEK_OF_MONTH=3,DAY_OF_MONTH=16,DAY_OF_YEAR=320,DAY_OF_WEEK=3,DAY_OF_WEEK_IN_MONTH=3,AM_PM=0,HOUR=8,HOUR_OF_DAY=8,MINUTE=44,SECOND=51,MILLISECOND=89,ZONE_OFFSET=28800000,DST_OFFSET=0] java.time.LocalDateTime = 2021-11-16T08:44:51.089 java.time.LocalDate = 2021-11-16 java.time.LocalTime = 08:44:51.089 java.util.Calendar = java.util.GregorianCalendar[time=1637023491089,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=sun.util.calendar.ZoneInfo[id="Asia/Shanghai",offset=28800000,dstSavings=0,useDaylight=false,transitions=31,lastRule=null],firstDayOfWeek=2,minimalDaysInFirstWeek=4,ERA=1,YEAR=2021,MONTH=10,WEEK_OF_YEAR=46,WEEK_OF_MONTH=3,DAY_OF_MONTH=16,DAY_OF_YEAR=320,DAY_OF_WEEK=3,DAY_OF_WEEK_IN_MONTH=3,AM_PM=0,HOUR=8,HOUR_OF_DAY=8,MINUTE=44,SECOND=51,MILLISECOND=89,ZONE_OFFSET=28800000,DST_OFFSET=0] A programmer, recreational runner and diver, live in the island of Bali, Indonesia. Programming in Java, Spring, Hibernate / JPA. You can support me working on this project, buy me a cup of coffee ☕ every little bit helps, thank you 🙏
Java Convert Calendar to Date
In this Java core tutorial we learn how to convert a java.util.Calendar object to java.util.Date or java.sql.Date object in Java programming language.
Table of contents
How to Convert Calendar to java.util.Date
To convert a Calendar object to java.util.Date object we can use the Calendar.getTime() method to return Date object from a Calendar object as Java code below.
import java.util.Calendar; import java.util.Date; public class ConvertCalendarToDateExample1 public static void main(String. args) Calendar calendar = Calendar.getInstance(); // convert Calendar to java.util.Date Date date = calendar.getTime(); System.out.println(date); > >Sat Apr 16 13:26:58 ICT 2022How to Convert Calendar to java.sql.Date
To convert a Calendar object to java.sql.Date object we can use the Calendar.getTimeInMillis() to get milliseconds value of Calendar object and use it to instantiate a java.sql.Date object as following Java program.
import java.util.Calendar; import java.sql.Date; public class ConvertCalendarToDateExample2 public static void main(String. args) Calendar calendar = Calendar.getInstance(); // Convert Calendar to java.sql.Date long milliseconds = calendar.getTimeInMillis(); Date sqlDate = new Date(milliseconds); System.out.println(sqlDate); > >Guide to java.util.Date Class
Learn to create new date, get current date, parse date to string or format Date object using java.util.Date class. These usecases are frequently required, and having them in one place will help in saving time for many of us.
It is worth noting that there is no timezone information associated with Date instance. A Date instance represents the time spent since Epach in milliseconds. If we print the date instance, it always prints the default or local timezone of the machine. So the timezone information printed in Date.toString() method should not misguide you.
1. Formatting a Date to String
Java program of formatting Date to string using SimpleDateFormat.format() . Please note that SimpleDateFormat is not a thread-safe class, so we should not share its instance with multiple threads.
SimpleDateFormat sdf = new SimpleDateFormat("dd/M/yyyy"); String date = sdf.format(new Date());Refer SimpleDateFormat JavaDoc for detailed date and time patterns. Below is a list of the most common pattern letters you can use.
y = year (yy or yyyy) M = month (MM) d = day in month (dd) h = hour (0-12) (hh) H = hour (0-23) (HH) m = minute in hour (mm) s = seconds (ss) S = milliseconds (SSS) z = time zone text (e.g. Pacific Standard Time. ) Z = time zone, time offset (e.g. -0800)| Pattern | Example |
|---|---|
| yyyy-MM-dd (ISO) | “2018-07-14” |
| dd-MMM-yyyy | “14-Jul-2018” |
| dd/MM/yyyy | “14/07/2018” |
| E, MMM dd yyyy | “Sat, Jul 14 2018” |
| h:mm a | “12:08 PM” |
| EEEE, MMM dd, yyyy HH:mm:ss a | “Saturday, Jul 14, 2018 14:31:06 PM” |
| yyyy-MM-dd’T’HH:mm:ssZ | “2018-07-14T14:31:30+0530” |
| hh ‘o»clock’ a, zzzz | “12 o’clock PM, Pacific Daylight Time” |
| K:mm a, z | “0:08 PM, PDT” |
2. Parsing a String to Date
Java program of parsing a string to Date instance using SimpleDateFormat.parse() method.
SimpleDateFormat sdf = new SimpleDateFormat("dd-M-yyyy hh:mm:ss"); String dateInString = "15-10-2015 10:20:56"; Date date = sdf.parse(dateInString);3. Getting Current Date and Time
java.util.Date class represents the date and time elapsed since the epoch. Given below are the Java programs for getting the current date and time and printing in a given format.
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss"); Date date = new Date(); System.out.println(dateFormat.format(date)); For reference, since Java 8, we can use LocalDate , LocalTime and LocalDateTime classes.
LocalDate today = LocalDate.now(); System.out.println("Today's Local date : " + today); LocalTime time = LocalTime.now(); System.out.println("local time now : " + time);4. Convert between Date and Calendar
4.1. Converting Calendar to Date
Calendar calendar = Calendar.getInstance(); Date date = calendar.getTime();4.2. Converting Date to Calendar
SimpleDateFormat sdf = new SimpleDateFormat("dd-M-yyyy hh:mm:ss"); String dateInString = "27-04-2016 10:22:56"; Date date = sdf.parse(dateInString); Calendar calendar = Calendar.getInstance(); calendar.setTime(date); We can compare two two date instances using its compareTo() method. It returns an integer value representing given date is before or after another date.
The comparison date1.CompareTo(date2) will return:
- a value 0 if date2 is equal to date1;
- a value less than 0 if date1 is before date2;
- a value greater than 0 if date1 is after date2.
Date date1 = new Date(); Date date2 = new Date(); int comparison = date1.compareTo(date2);6. Extracting Days, Months and Years
Java program to get date parts such as year, month, etc separately.
The methods to get the year, month, day of the month, hour, etc. are deprecated. If you need to get or set the year, month, day of the month, etc. use a java.util.Calendar instead.
Calendar calendar = Calendar.getInstance(); calendar.setTime(new Date()); int year = calendar.get(Calendar.YEAR); int month = calendar.get(Calendar.MONTH); int dayOfMonth = calendar.get(Calendar.DAY_OF_MONTH); // Jan = 0, not 1 int dayOfWeek = calendar.get(Calendar.DAY_OF_WEEK); int weekOfYear = calendar.get(Calendar.WEEK_OF_YEAR); int weekOfMonth= calendar.get(Calendar.WEEK_OF_MONTH); int hour = calendar.get(Calendar.HOUR); // 12 hour clock int hourOfDay = calendar.get(Calendar.HOUR_OF_DAY); // 24 hour clock int minute = calendar.get(Calendar.MINUTE); int second = calendar.get(Calendar.SECOND); int millisecond= calendar.get(Calendar.MILLISECOND);