DateTimeFormatter month pattern letter “L” fails

Question

I noticed that java.time.format.DateTimeFormatter is not able to parse out as expected. See below:

import java.time.L         


        

Answer 1

While the other answers give excellent information on pattern letter L and date parsing, I should like to add that you should really avoid the problem altogether. Don’t get date (and time) as string from your database. Instead use an appropriate datetime object.

    String sql = "select sysdate as dt from dual;"
    PreparedStatement stmt = yourDatabaseConnection.prepareStatement(sql);
    ResultSet rs = stmt.executeQuery();
    if (rs.next()) {
        LocalDateTime dateTime = rs.getObject("dt", LocalDateTime.class);
        // do something with dateTime
    }

(Not tested since I haven’t got an Oracle database at hand. Please forgive any typo.)

Answer 2

“stand-alone” month name

I believe 'L' is meant for languages that use a different word for the month itself versus the way it is used in a date. For example:

Locale russian = Locale.forLanguageTag("ru");

asList("MMMM", "LLLL").forEach(ptrn -> 
    System.out.println(ptrn + ": " + ofPattern(ptrn, russian).format(Month.MARCH))
);

Output:

MMMM: марта
LLLL: Март

There shouldn't be any reason to use 'L' instead of 'M' when parsing a date.

I tried the following to see which locales support stand-alone month name formatting:

Arrays.stream(Locale.getAvailableLocales())
    .collect(partitioningBy(
                loc -> "3".equals(Month.MARCH.getDisplayName(FULL_STANDALONE, loc)),
                mapping(Locale::getDisplayLanguage, toCollection(TreeSet::new))
    )).entrySet().forEach(System.out::println);

The following languages get a locale-specific stand-alone month name from 'LLLL':

Catalan, Chinese, Croatian, Czech, Finnish, Greek, Hungarian, Italian, Lithuanian, Norwegian, Polish, Romanian, Russian, Slovak, Turkish, Ukrainian

All other languages get "3" as a stand-alone name for March.

Answer 3

According to the javadocs:

Pattern letters 'L', 'c', and 'q' specify the stand-alone form of the text styles.

However, I couldn't find much about what the "stand-alone" form is supposed to be. In looking at the code I see that using 'L' selects TextStyle.SHORT_STANDALONE and according to that javadoc:

Short text for stand-alone use, typically an abbreviation. For example, day-of-week Monday might output "Mon".

However, that isn't how it seems to work. Even with three letters I get numerical output from this code:

DateTimeFormatter pattern = DateTimeFormatter.ofPattern ("dd-LLL-yyyy");
System.out.println (pattern.format (LocalDate.now ()));

Edit

After further investigation it seems (as near as I can tell) that the "stand-alone" versions of these codes are for when you want to load your own locale-independent data, presumably using DateTimeFormatterBuilder. As such, by default DateTimeFormatter has no entries loaded for TextStyle.SHORT_STANDALONE.