JDK Tutorials - Herong's Tutorial Examples - v6.32, by Herong Yang
Converting java.util.GregorianCalendar to java.time.ZonedDateTime
This section provides a tutorial example how to migrate Java code from the old java.util.GregorianCalendar class to the new java.time.ZonedDateTime class.
If you are currently using the old java.util.GregorianCalendar class to manipulate time measured as date, time, and timezone component, you should migrate your code to use the new java.time.ZonedDateTime class.
If you are using both classes in your code, you may use two new methods provided on java.util.GregorianCalendar class:
The following sample program provides some comparison between java.util.GregorianCalendar and java.time.ZonedDateTime and might be helpful to you in migrating your code:
/* CalendarClassMigration.java
* Copyright (c) HerongYang.com. All Rights Reserved.
*/
import java.util.GregorianCalendar;
import java.time.ZonedDateTime;
import java.util.Calendar;
import java.time.temporal.ChronoField;
class CalendarClassMigration {
public static void main(String[] a) {
java.io.PrintStream out = System.out;
GregorianCalendar oCalendar = new GregorianCalendar();
ZonedDateTime oDateTime = ZonedDateTime.now();
out.println();
out.println("Epoch seconds:");
out.println("GregorianCalendar class: "
+ (long) oCalendar.getTimeInMillis()/1000);
out.println("ZonedDateTime class: "
+ oDateTime.getLong(ChronoField.INSTANT_SECONDS));
out.println();
out.println("Epoch milliseconds:");
out.println("GregorianCalendar class: "
+ oCalendar.getTimeInMillis());
out.println("ZonedDateTime class: "
+ (oDateTime.getLong(ChronoField.INSTANT_SECONDS)*1000
+oDateTime.getLong(ChronoField.MILLI_OF_SECOND)));
out.println();
out.println("Nanoseconds-of-Second:");
out.println("GregorianCalendar class: Not supported");
out.println("ZonedDateTime class: " + oDateTime.getNano());
out.println();
out.println("Calendar date:");
out.println("GregorianCalendar class: "
+ oCalendar.get(Calendar.YEAR) + "-"
+ (oCalendar.get(Calendar.MONTH)+1) + "-"
+ oCalendar.get(Calendar.DAY_OF_MONTH));
out.println("ZonedDateTime class: "
+ oDateTime.getLong(ChronoField.YEAR) + "-"
+ oDateTime.getLong(ChronoField.MONTH_OF_YEAR) + "-"
+ oDateTime.getLong(ChronoField.DAY_OF_MONTH));
out.println();
out.println("Timezone ID:");
out.println("GregorianCalendar class: "
+ oCalendar.getTimeZone().getID());
out.println("ZonedDateTime class: "
+ oDateTime.getZone());
out.println();
out.println("UTC offset:");
out.println("GregorianCalendar class: "
+ (oCalendar.get(Calendar.ZONE_OFFSET)
+oCalendar.get(Calendar.DST_OFFSET))/(60*60*1000));
out.println("ZonedDateTime class: "
+ oDateTime.getOffset());
out.println();
out.println("String presentation:");
out.println("GregorianCalendar class: "
+ oCalendar.getTime().toString());
out.println("ZonedDateTime class: " + oDateTime.toString());
out.println();
out.println("Converting GregorianCalendar to ZonedDateTime:");
ZonedDateTime cDateTime = oCalendar.toZonedDateTime();
out.println("GregorianCalendar class: "
+ oCalendar.getTime().toString());
out.println("ZonedDateTime class: " + cDateTime.toString());
out.println();
out.println("Converting GregorianCalendar from ZonedDateTime:");
GregorianCalendar cCalendar = GregorianCalendar.from(oDateTime);
out.println("GregorianCalendar class: "
+ cCalendar.getTime().toString());
out.println("ZonedDateTime class: " + oDateTime.toString());
}
}
When running CalendarClassMigration.java, I got the following output:
herong> java CalendarClassMigration.java Epoch seconds: GregorianCalendar class: 1708372665 ZonedDateTime class: 1708372665 Epoch milliseconds: GregorianCalendar class: 1708372665235 ZonedDateTime class: 1708372665244 Nanoseconds-of-Second: GregorianCalendar class: Not supported ZonedDateTime class: 244850000 Calendar date: GregorianCalendar class: 2024-2-19 ZonedDateTime class: 2024-2-19 Timezone ID: GregorianCalendar class: America/Argentina/Buenos_Aires ZonedDateTime class: America/Argentina/Buenos_Aires UTC offset: GregorianCalendar class: -3 ZonedDateTime class: -03:00 String presentation: GregorianCalendar class: Mon Feb 19 16:57:45 ART 2024 ZonedDateTime class: 2024-02-19T16:57:45.244850-03:00[America/...] Converting GregorianCalendar to ZonedDateTime: GregorianCalendar class: Mon Feb 19 16:57:45 ART 2024 ZonedDateTime class: 2024-02-19T16:57:45.235-03:00[America/...] Converting GregorianCalendar from ZonedDateTime: GregorianCalendar class: Mon Feb 19 16:57:45 ART 2024 ZonedDateTime class: 2024-02-19T16:57:45.244850-03:00[America/...]
Table of Contents
java.time.Instant - Representing a Moment of Time
java.time.Instant Usage Examples
java.time.Instant - get(INSTANT_SECONDS) Error
Converting java.util.Date to java.time.Instant
java.time.ZonedDateTime - Calendar and Timezone
java.time.ZonedDateTime Usage Examples
►Converting java.util.GregorianCalendar to java.time.ZonedDateTime
java.time.OffsetDateTime - Calendar and UTC Offset
java.time.OffsetDateTime Usage Examples
java.time.LocalDateTime - Local Date and time without Timezone
Partial Date and Time Objects and Classes
java.time.format.DateTimeFormatter - Date-Time Strings
java.time.Duration - Time Durations
java.time.Duration Usage Examples
java.time.Period - Periods in Days and Months
java.time.Period Usage Examples
Date, Time and Calendar Classes
Date and Time Object and String Conversion
Number Object and Numeric String Conversion
Locales, Localization Methods and Resource Bundles
Calling and Importing Classes Defined in Unnamed Packages
HashSet, Vector, HashMap and Collection Classes
Character Set Encoding Classes and Methods
Encoding Conversion Programs for Encoded Text Files
Datagram Network Communication
DOM (Document Object Model) - API for XML Files
DTD (Document Type Definition) - XML Validation
XSD (XML Schema Definition) - XML Validation
XSL (Extensible Stylesheet Language)
Message Digest Algorithm Implementations in JDK
Private key and Public Key Pair Generation
PKCS#8/X.509 Private/Public Encoding Standards
Digital Signature Algorithm and Sample Program
"keytool" Commands and "keystore" Files
KeyStore and Certificate Classes
Secret Key Generation and Management
Cipher - Encryption and Decryption
The SSL (Secure Socket Layer) Protocol
SSL Socket Communication Testing Programs