How to get delimiter from a date string?

Question

24.03.2018 02:34:22 how can I get the delimiter ('.') from a that kind of date string? Format can be different and delimiter can be these '.','-','/' also. Is there a way to do it with Java's date format classes?

Answer 1

To answer this, we'll have to make a few assumptions:

• As you've said, the delimiter can be -, /, or ., so I will be assuming no other delimiter is allowed.
• From your only example in your question, we're looking for the delimiter of the date and not the time.
• From your example, we'll assume that the date is always listed before the time.

Therefore, we should be able to solve this by looking for the first occurrence of any of those three characters:

public static Optional<Character> findDelimiter(String formattedDate) {
    for (char c : formattedDate.toCharArray()) {
        switch (c) {
            case '.':
            case '/':
            case '-':
                return Optional.of(c);
            case ' ':
            case '\t':
                return Optional.empty();
        }
    }

    return Optional.empty();
}

This will stop at the first instance of a space or a tab, assuming neither of those is the delimiter.

Answer 2

Basically you have 2 options :

1. Find the delimiter, and choose how to parse with this infomartion :

   private static LocalDateTime stringToDate(String str) {
       char delimiter = str.charAt(2);
       switch (delimiter) {
           case '.':
               return LocalDateTime.parse(str, DateTimeFormatter.ofPattern("dd.MM.yyyy HH:mm:ss"));
           case '/':
               return LocalDateTime.parse(str, DateTimeFormatter.ofPattern("dd/MM/yyyy HH:mm:ss"));
           case '-':
               return LocalDateTime.parse(str, DateTimeFormatter.ofPattern("dd-MM-yyyy HH:mm:ss"));
           default:
               throw new DateTimeParseException("Bad String", str, 0);
       }
   }
   

2. Find the delimiter and build the pattern with it :

   private static LocalDateTime stringToDate(String str) {
       String delimiter = str.substring(2, 3);
       if (delimiter.matches("[-\\.\\/]")) {
           return LocalDateTime.parse(str, DateTimeFormatter
                      .ofPattern("dd" + delimiter + "MM" + delimiter + "yyyy HH:mm:ss"));
       } else {
           throw new DateTimeParseException("Bad String " + str, str, 0);
       }
   }
   

---

Use :

String strdate1 = "04-03-2018 02:34:22";
LocalDateTime date1 = stringToDate(strdate1);

Answer 3

From the format string I would use a regular expression for taking out the longest substring that starts and ends with y, M or d and in between hasn’t got other letters. If more such substrings I’d take them all in turn. This should give you the yyyy-MM-dd or corresponding part of the format. Then from this substring (these substrings) I would take out all chars that are neither letters nor whitespace (use a regexp again). Or maybe also whitespace. There you’ve got your delimiter/s. Consider the case when they are none or there are more than one.

It may be a bit more complicated than what others have said, but I think it’s also a bit safer if you really don’t know what the format can look like.

There may be a special case: the usual formatters (DateTimeFormatter and SimpleDateFormat) allow punctuation to be enclosed in apostrophes. For example yyyy'.'MM'.'dd means the same as yyyy.MM.dd. Maybe you want to take it into account. If one really wanted apostrophe as delimiter, it should be doubled: yyyy''MM''dd.