Parsing a date’s ordinal indicator ( st, nd, rd, th ) in a date-time string

Java's SimpleDateFormat doesn't support an ordinal suffix, but the ordinal suffix is just eye candy - it is redundant and can easily be removed to allow a straightforward parse:

Date date = new SimpleDateFormat("MMM dd yyyy hh:mma")
    .parse(str.replaceAll("(?<=\\d)(st|nd|rd|th)", ""));

The replace regex is so simple because those sequences won't appear anywhere else in a valid date.

---

To handle any language that appends any length of ordinal indicator characters from any language as a suffix:

Date date = new SimpleDateFormat("MMM dd yyyy hh:mma")
    .parse(str.replaceAll("(?<=\\d)(?=\\D* \\d+ )\\p{L}+", ""));

Some languages, eg Mandarin, prepend their ordinal indicator, but that could be handled too using an alternation - left as an exercise for the reader :)

Java 8 answer (and Java 6 and 7) (because when this question was asked in 2015, the replacement for SimpleDateFormat was already out):

    DateTimeFormatter parseFormatter = DateTimeFormatter
            .ofPattern("MMM d['st']['nd']['rd']['th'] uuuu h:mma", Locale.ENGLISH);
    LocalDateTime dateTime = LocalDateTime.parse(dateTimeString, parseFormatter);

With the sample date from the question this yiedls:

2015-02-13T09:00

In the format pattern [] denotes optional parts and '' denotes literal parts. So the pattern says that the number may be followed by st, nd, rd or th.

To use this in Java 6 or 7 you need ThreeTen Backport. Or for Android ThreeTenABP.

Since those suffixes are special for English, and other languages/locales have completely other usages for writing dates and times (also they don’t use AM/PM), I believe that unless you have other requirements, you should try to implement this for English dates and times only. Also you should give an English speaking locale explicitly so it will work independently of the locale setting of your computer or JVM.

I have tried to combine the best parts of answers by Hugo and myself to a duplicate question. Under that duplicate question there are still more java 8 answers. One limitation of the above code is it doesn’t have very strict validation: you will get away with Feb 13rd and even Feb 13stndrdth.

Edit: My own favourite among my answers on ordinal indicators is this one. It’s about formatting, but the formatter I present there works fine for parsing too.

In case someone finds it useful: DateTimeFormatter builder. This formatter allows you to format and to parse UK dates with ordinal suffixes (eg. "1st January 2017"):

public class UkDateFormatterBuilder
{
    /**
     * The UK date formatter that formats a date without an offset, such as '14th September 2020' or '1st January 2017'.
     * @return an immutable formatter which uses the {@link ResolverStyle#SMART SMART} resolver style. It has no override chronology or zone.
     */
    public DateTimeFormatter build()
    {
        return new DateTimeFormatterBuilder()
                .parseCaseInsensitive()
                .parseLenient()
                .appendText(DAY_OF_MONTH, dayOfMonthMapping())
                .appendLiteral(' ')
                .appendText(MONTH_OF_YEAR, monthOfYearMapping())
                .appendLiteral(' ')
                .appendValue(YEAR, 4)
                .toFormatter(Locale.UK);
    }

    private Map<Long, String> monthOfYearMapping()
    {
        Map<Long, String> monthOfYearMapping = new HashMap<>();
        monthOfYearMapping.put(1L, "January");
        monthOfYearMapping.put(2L, "February");
        monthOfYearMapping.put(3L, "March");
        monthOfYearMapping.put(4L, "April");
        monthOfYearMapping.put(5L, "May");
        monthOfYearMapping.put(6L, "June");
        monthOfYearMapping.put(7L, "July");
        monthOfYearMapping.put(8L, "August");
        monthOfYearMapping.put(9L, "September");
        monthOfYearMapping.put(10L, "October");
        monthOfYearMapping.put(11L, "November");
        monthOfYearMapping.put(12L, "December");
        return monthOfYearMapping;
    }

    private Map<Long, String> dayOfMonthMapping()
    {
        Map<Long, String> suffixes = new HashMap<>();
        for (int day=1; day<=31; day++)
        {
            suffixes.put((long)day, String.format("%s%s", (long) day, dayOfMonthSuffix(day)));
        }
        return suffixes;
    }

    private String dayOfMonthSuffix(final int day)
    {
        Preconditions.checkArgument(day >= 1 && day <= 31, "Illegal day of month: " + day);
        if (day >= 11 && day <= 13)
        {
            return "th";
        }
        switch (day % 10)
        {
            case 1:  return "st";
            case 2:  return "nd";
            case 3:  return "rd";
            default: return "th";
        }
    }
}

Plus a fragment of the test class:

public class UkDateFormatterBuilderTest
{
    DateTimeFormatter formatter = new UkDateFormatterBuilder().build();

    @Test
    public void shouldFormat1stJanuaryDate()
    {
        final LocalDate date = LocalDate.of(2017, 1, 1);

        final String formattedDate = date.format(formatter);

        Assert.assertEquals("1st January 2017", formattedDate);
    }

    @Test
    public void shouldParse1stJanuaryDate()
    {
        final String formattedDate = "1st January 2017";

        final LocalDate parsedDate = LocalDate.parse(formattedDate, formatter);

        Assert.assertEquals(LocalDate.of(2017, 1, 1), parsedDate);
    }
}

PS. I used Greg Mattes' solution for ordinal suffixes from here: How do you format the day of the month to say "11th", "21st" or "23rd" in Java? (ordinal indicator)