Parsing of weekdays not working for locale german

Question

I'm trying to use java.time.format.DateTimeFormatter to parse time strings but ran into a problem parsing german short day of week names.

Given the following program

import java.time.DayOfWeek;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeFormatterBuilder;
import java.time.format.TextStyle;
import java.util.Locale;

var locale = Locale.forLanguageTag("de");
var dtf = new DateTimeFormatterBuilder()
        .appendOptional(DateTimeFormatter.ofPattern("eeee"))
        .appendOptional(DateTimeFormatter.ofPattern("eee"))
        .toFormatter(locale);
var input1 = DayOfWeek.TUESDAY.getDisplayName(TextStyle.FULL, locale);
var input2 = DayOfWeek.TUESDAY.getDisplayName(TextStyle.SHORT_STANDALONE, locale);
System.out.printf("input: %s, parsed: %s\n", input1, dtf.parse(input1));
System.out.printf("input: %s, parsed: %s\n", input2, dtf.parse(input2));

the output I would expect is

input: Dienstag, parsed: {DayOfWeek=2},ISO
input: Di, parsed: {DayOfWeek=2},ISO

but I actually get

input: Dienstag, parsed: {DayOfWeek=2},ISO
Exception in thread "main" java.time.format.DateTimeParseException: Text 'Di' could not be parsed, unparsed text found at index 0
    at java.base/java.time.format.DateTimeFormatter.parseResolved0(DateTimeFormatter.java:2049)
    at java.base/java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1874)
    at org.rksm.Main.main(Main.java:22)

Note that when I change the locale to Locale.forLanguageTag("en") it works and the output is

input: Tuesday, parsed: {DayOfWeek=2},ISO
input: Tue, parsed: {DayOfWeek=2},ISO

What am I doing wrong?

Does it work with [`Locale.GERMANY`](https://docs.oracle.com/javase/8/docs/api/java/util/Locale.html#GERMANY) (or `GERMAN`)? — Andy Turner, Jul 23 '19 at 15:20
Note that `eee` stands for `TextStyle.SHORT`, WHILE `ccc` stands for `TextStyle.SHORT_STANDALONE`. Have you tried `ccc`? — RealSkeptic, Jul 23 '19 at 15:24
RealSkeptic: Indeed, TextStyle.SHORT_STANDALONE / ccc is the way to go. If you post it as an answer I mark it as such. Thank you! — robertkrahn, Jul 23 '19 at 15:30

score 5 · Accepted Answer · answered Jul 23 '19 at 15:39

Although in English there is no difference between the name of the day when it is used alone and the name as it is used within the context of a date, in German, apparently, there is.

The pattern eee corresponds to TextStyle.SHORT, while the pattern ccc corresponds to TextStyle.SHORT_STANDALONE. Thus, if you try to parse a day name that was created by TextStyle.SHORT_STANDALONE with eee in the languages where it matters, the parsing will fail.

The way to go is ccc for the standalone version.

The documentation mentioning this is actually in the DateTimeFormatterBuilder API rather than DateTimeFormatter's.

That’s true: `TextStyle.SHORT` gives `Di.` with a dot, `SHORT_STANDALONE` just `Di` without the dot (on my Java 11 with default settings; I suspect that setting the system property `java.locale.providers` would change the results). — Ole V.V., Jul 24 '19 at 14:37

Parsing of weekdays not working for locale german

1 Answers1