de.ipcon.tools

Class ForceIsoWeekNumber

java.lang.Object

java.util.spi.LocaleServiceProvider

java.util.spi.CalendarDataProvider

de.ipcon.tools.ForceIsoWeekNumber

public class ForceIsoWeekNumber
extends java.util.spi.CalendarDataProvider

As of Java 23, the COMPAT locale provider was removed https://bugs.openjdk.org/browse/JDK-8325568 . This provider could be used by specifying -Djava.locale.providers=COMPAT,... at startup, to fix the week number rules which, while formerly correct, starting with JRE9 by using the CLDR data from the Unicode Consortium, were objectively wrong (which means equal to the US's rules).

Not using the COMPAT provider would result in having wrong week numbers in SimpleDateFormat and DateTimeFormat, as they use the 'local' definition instead of the ISO definition, which just counts Thursdays: https://en.wikipedia.org/wiki/ISO_week_date

Although the java.time code knows about the ISO rules, using the formatters will always pick the wrong definition, ignoring users relying on the formatters.

This CalendarDataProvider will force ISO week number rule for any locale known by the current JVM.

This is unnecessarily complicated and intrusive; as the official way, where we have to give a list of supported Locales before the JVM has this list available for us. This provider works by checking files within /modules/jdk.localedata/sun/text/resources/cldr to accomplish that task without using static lists. This class needs two additional things to do it's work:

• in one of the loaded jars, a file named META-INF/services/CalenderDataProvider with the fully qualified class name of this class as it's content
• a JVM started with -Djava.locale.providers=SPI,CLDR

Constructor Summary

Constructors

Constructor and Description
ForceIsoWeekNumber() no args constructor as needed by SPI

Method Summary

Modifier and Type	Method and Description
java.util.Locale[]	getAvailableLocales() This method will be called by the JVM so early, that the call to Locale::getAvailableLocales will result in an NPE caused the the not yet instantiated internal pool.
int	getFirstDayOfWeek(java.util.Locale l) Return the first day of the week according to CLDR data, which we extracted during
int	getMinimalDaysInFirstWeek(java.util.Locale l) Return the the minimal days in the first week, which, if we translate that to the ISO rule, just means how many days from week start until thursday.
boolean	isSupportedLocale(java.util.Locale l) Returns true as it will only be asked for Locales returned in getAvailableLocales, which we supplied already in the first place.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ForceIsoWeekNumber

public ForceIsoWeekNumber()

no args constructor as needed by SPI

Method Detail

getAvailableLocales

public java.util.Locale[] getAvailableLocales()

This method will be called by the JVM so early, that the call to Locale::getAvailableLocales will result in an NPE caused the the not yet instantiated internal pool. Instead, this method will use the jrt file system to scan through sun/text/resources/cldr to find valid combinations if language and country and build a list from that. We need to supply an exaustive list as the JVM will only ask us once and never again. Further, the method will check sun.util.resources.cldr.CalendarData for local week start data, as we need to adjust the value of MinimalDaysInFirstWeek according to that, so that local week start is still according to CLDR data, just the week counting is ISO.

Specified by:

getAvailableLocales in class java.util.spi.LocaleServiceProvider

Returns:

all known locale/country combinations this JVM supports

isSupportedLocale

public boolean isSupportedLocale(java.util.Locale l)

Returns true as it will only be asked for Locales returned in getAvailableLocales, which we supplied already in the first place.

Overrides:

isSupportedLocale in class java.util.spi.LocaleServiceProvider

Parameters:

l - the locale to check for

Returns:

true

getFirstDayOfWeek

public int getFirstDayOfWeek(java.util.Locale l)

Return the first day of the week according to CLDR data, which we extracted during

Specified by:

getFirstDayOfWeek in class java.util.spi.CalendarDataProvider

Parameters:

l - the locale to get the first day of the week for

Returns:

int representing weekday: 1: sunday, 2: monday, ...

See Also:

.

getMinimalDaysInFirstWeek

public int getMinimalDaysInFirstWeek(java.util.Locale l)

Return the the minimal days in the first week, which, if we translate that to the ISO rule, just means how many days from week start until thursday.

Specified by:

getMinimalDaysInFirstWeek in class java.util.spi.CalendarDataProvider

Parameters:

l - the locale to get the minimal days in first week for

Returns:

int representing the amount of days until Thursday, including.