How can I make a leading zero in DateTime-Pattern optional

John Du :

I have a user input field and would like to parse his date, whatever he puts in.

The user might provide his date with a leading zero or without one, so I wanna be able to parse an input like this

02.05.2019

and also this

2.5.2019

But as far as I can tell there is no way to make the leading zero optional, either always have 2 digits like 01, 03, 12 and so on, or only have the necessary digits like 1, 3, 12.

So apparently I have to decide whether to allow leading zeros or not, but is there seriously no way to make the leading zero optional ?

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Well, I tested a pattern that included a leading zero dd.MM.uuuu and I tested a pattern that did not include a leading zero d.M.uuuu and when I parsed the wrong input with the wrong pattern exceptions were thrown.

Therefore my question is if there is a way to make the leading zero optional.

Ole V.V. :

This is trivial when you know it. One pattern letter, for example d or M, will accept either one or two digits (or for year up to 9 digits).

    DateTimeFormatter dateFormatter = DateTimeFormatter.ofPattern("d.M.u");
    System.out.println(LocalDate.parse("02.05.2019", dateFormatter));
    System.out.println(LocalDate.parse("3.5.2019", dateFormatter));
    System.out.println(LocalDate.parse("4.05.2019", dateFormatter));
    System.out.println(LocalDate.parse("06.5.2019", dateFormatter));
    System.out.println(LocalDate.parse("15.12.2019", dateFormatter));

Output:

2019-05-02
2019-05-03
2019-05-04
2019-05-06
2019-12-15

I searched for this information in the documentation and didn’t find it readily. I don’t think it is well documented.