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JDK dateformatter parsing DayOfWeek in German locale, java8 vs java9

I have tried some code in Java 8 (1.8.0_77) and Java 9 (Java HotSpot(TM) 64-Bit Server VM (build 9+181, mixed mode))

DateTimeFormatter dtf = DateTimeFormatter.ofPattern("eee", Locale.GERMAN);
DayOfWeek mo = dtf.parse("Mo", DayOfWeek::from);
System.out.println("mo = " + mo);

I am not too familiar with details of those classes, but in Java 8 this works, printing:

mo = MONDAY

In Java 9, however it fails

Exception in thread "main" java.time.format.DateTimeParseException: Text 'Mo' could not be parsed at index 0 at java.base/java.time.format.DateTimeFormatter.parseResolved0(DateTimeFormatter.java:1988) at java.base/java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1890) at day.main(day.java:10)

Any ideas, is this reproducible?

so, when formating: using this code:

DateTimeFormatter dtf = DateTimeFormatter.ofPattern("eee", Locale.GERMAN);
String format = dtf.format(DayOfWeek.MONDAY);
System.out.println("format = " + format);

jdk1.8.0-77:

format = Mo

jdk-9 (build 9+181)

format = Mo.

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user140547 Avatar asked Sep 15 '17 17:09

user140547


2 Answers

This seems to be there in java-9 due to the current implementation of CLDR date-time-patterns with the implementation of JEP - 252 which states that

Use locale data from the Unicode Consortium's Common Locale Data Repository (CLDR) by default.

Localized patterns for the formatting and translation of display strings, such as the locale name, may be different in some locales.

To enable behavior compatible with JDK 8, set the system property java.locale.providers to a value with COMPAT ahead of CLDR.


And to second the data part of it, the international components for Unicode in German locale which has the following relevant information can justify that the behavior is intentional -

enter image description here

Edit/Note: As linked in the comments, the migration guide states a similar warning for such implementations -

If your application starts successfully, look carefully at your tests and ensure that the behavior is the same as on JDK 8. For example, a few early adopters have noticed that their dates and currencies are formatted differently. See Use CLDR Locale Data by Default.

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Naman Avatar answered Sep 23 '22 22:09

Naman


The abbreviatiions "Mo", "Di" etc. without dot have not disappeared in CLDR but are accessible via standalone-mode. You should change your pattern using the standalone format symbol "c" instead of "e":

DateTimeFormatter dtf = DateTimeFormatter.ofPattern("ccc", Locale.GERMAN);
DayOfWeek mo = dtf.parse("Mo", DayOfWeek::from);

Indeed, I consider the change of underlying data as breaking backwards compatibility (concrete as behavioural break).

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Meno Hochschild Avatar answered Sep 20 '22 22:09

Meno Hochschild