trying out the nice ordinal formatting and parsing code in https://stackoverflow.com/a/72557618/116639

out.txt

str = Sep 8th 2023
Exception in thread "main" java.time.format.DateTimeParseException: Text 'Sep 8th 2023' could not be parsed: Unable to obtain LocalDateTime from TemporalAccessor: {},ISO resolved to 2023-09-08 of type java.time.format.Parsed
	at java.base/java.time.format.DateTimeFormatter.createError(DateTimeFormatter.java:2023)
	at java.base/java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1958)
	at java.base/java.time.LocalDateTime.parse(LocalDateTime.java:494)
	at ParseOrdinalDate.main(ParseOrdinalDate.java:41)
Caused by: java.time.DateTimeException: Unable to obtain LocalDateTime from TemporalAccessor: {},ISO resolved to 2023-09-08 of type java.time.format.Parsed
	at java.base/java.time.LocalDateTime.from(LocalDateTime.java:463)
	at java.base/java.time.format.Parsed.query(Parsed.java:241)
	at java.base/java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1954)
	... 2 more
Caused by: java.time.DateTimeException: Unable to obtain LocalTime from TemporalAccessor: {},ISO resolved to 2023-09-08 of type java.time.format.Parsed
	at java.base/java.time.LocalTime.from(LocalTime.java:433)
	at java.base/java.time.LocalDateTime.from(LocalDateTime.java:459)
	... 4 more

ParseOrdinalDate.java

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeFormatterBuilder;
import java.time.format.TextStyle;
import java.time.temporal.ChronoField;
import java.util.HashMap;
import java.util.Locale;
import java.util.Map;

public class ParseOrdinalDate {

    static final Map<Long, String> ORDINAL_SUFFIX_MAP;

    static {
        Map<Long, String> map = new HashMap<>();
        for (int i = 1; i <= 31; i++) {
            String suffix = switch (i) {
                case 1, 21, 31 -> "st";
                case 2, 22 -> "nd";
                case 3, 23 -> "rd";
                default -> "th";
            };
            map.put((long) i, i + suffix);
        }
        ORDINAL_SUFFIX_MAP = Map.copyOf(map);
    }

    public static void main(String[] args) {
        DateTimeFormatter formatter = new DateTimeFormatterBuilder()
                .appendText(ChronoField.MONTH_OF_YEAR, TextStyle.SHORT)
                .appendLiteral(" ")
                .appendText(ChronoField.DAY_OF_MONTH, ORDINAL_SUFFIX_MAP)
                .appendLiteral(" ")
                .appendText(ChronoField.YEAR, TextStyle.SHORT)
                .toFormatter(Locale.ROOT);

        String str = formatter.format(LocalDate.now());
        System.out.println("str = " + str);

        LocalDateTime result = LocalDateTime.parse(str, formatter);
        System.out.println("result = " + result);
    }

}

ParseOrdinalDateFixed.java

import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeFormatterBuilder;
import java.time.format.TextStyle;
import java.time.temporal.ChronoField;
import java.util.Locale;
import java.util.Map;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class ParseOrdinalDateFixed {

    static final Map<Long, String> ORDINAL_SUFFIX_MAP = IntStream.rangeClosed(1, 31)
                                                                 .boxed()
                                                                 .collect(Collectors.toMap(Integer::longValue,
                                                                                           n -> n + switch ((n % 100 / 10 != 1) ? n % 10 : 0) {
                                                                                               case 1 -> "st";
                                                                                               case 2 -> "nd";
                                                                                               case 3 -> "rd";
                                                                                               default -> "th";
                                                                                           }));

    public static void main(String[] args) {
        DateTimeFormatter formatter = new DateTimeFormatterBuilder()
                .appendText(ChronoField.MONTH_OF_YEAR, TextStyle.SHORT)
                .appendLiteral(" ")
                .appendText(ChronoField.DAY_OF_MONTH, ORDINAL_SUFFIX_MAP)
                .appendLiteral(" ")
                .appendText(ChronoField.YEAR, TextStyle.SHORT)
                .toFormatter(Locale.ROOT);

        for (LocalDate date = LocalDate.of(2000, 1, 1); date.isBefore(LocalDate.of(2000, 2, 1)); date = date.plusDays(1)) {
            String str = formatter.format(date);
            LocalDate result = LocalDate.parse(str, formatter);
            boolean same = result.equals(date);
            System.out.println("date = " + date + ", str = " + str + ", result = " + result + ", same = " + same);
        }
    }

}