How to localize Java Calendar class?

Question

是否可以本地化Java日历类以将当前系统日期转换为例如Jalali（波斯）日期？

Answer 1

例如，创建实例时，您可以传递Locale 。

Calendar.getInstance(Locale.US);

Answer 2

Localize

How to localize Java Calendar class?

You don't. Instead, you localize a ZonedDateTime object.

The terrible Calendar class, actually GregorianCalendar , was supplanted years by the ZonedDateTime class. All the awful old date-time classes from the earliest versions of Java ( Date , Calendar , SimpleDateFormat , java.sql.Timestamp , java.sql.Date , etc.) were all outmoded by the modern java.time classes.

You can easily convert from the legacy classes to the modern by calling new methods added to the old classes.

ZonedDateTime zdt = ( ( GregorianCalendar ) myCalendar ).toZonedDateTime() ;

Now let DateTimeFormatter automatically localize while generating a String representing textually the date-time value.

To localize, specify:

• FormatStyle to determine how long or abbreviated should the string be.
• Locale to determine:
  • The human language for translation of name of day, name of month, and such.
  • The cultural norms deciding issues of abbreviation, capitalization, punctuation, separators, and such.

Example:

Locale l = Locale.CANADA_FRENCH ; 
DateTimeFormatter f = DateTimeFormatter.ofLocalizedDateTime( FormatStyle.FULL )
                                       .withLocale( l ) ;
String output = zdt.format( f ) ;

Jalali calendar

convert current system date to for example Jalali (Persian) date ?

Java does come bundled with an implementation of Chronology for the Hijrah calendar system: HijrahChronology . Perhaps that might meet your needs (I know next-to-nothing about chronologies other than ISO 8601 ).

You might learn more about this by searching Stack Overflow .

If that implementation does not meet your needs, you might find one elsewhere or develop your own. Besides the several open-source chronologies bundled with Java, you will find several more in the ThreeTen-Extra project, all open-source. You might find others from other sources.

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About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date , Calendar , & SimpleDateFormat .

The Joda-Time project, now in maintenance mode , advises migration to the java.time classes.

To learn more, see the Oracle Tutorial . And search Stack Overflow for many examples and explanations. Specification is JSR 310 .

You may exchange java.time objects directly with your database. Use a JDBC driver compliant with JDBC 4.2 or later. No need for strings, no need for java.sql.* classes.

Where to obtain the java.time classes?

• Java SE 8 , Java SE 9 , Java SE 10 , Java SE 11 , and later - Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and Java SE 7
  • Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport .
• Android
  • Later versions of Android bundle implementations of the java.time classes.
  • For earlier Android (<26), the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). See How to use ThreeTenABP… .

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval , YearWeek , YearQuarter , and more .