日期格式的模式匹配：dd.MM.yyyy，MM.yyyy和yyyy

Question

I need to check a date for a given string. The string that I get isn't regular and I don't want to use Dateformat or something like this. I'm trying to avoid getting multiple exceptions. I need a regex for dd.MM.yyyy and MM.yyyy and yyyy . At first I had

\\d+\\.?\\d+\\.?\\d+ 

but this isn't working.

Answer 1

If you really want to use a regex , here is a basic working example:

String regex = "([0-9]{2}\\.){0,2}([0-9]{4})";
assert "03.2017".matches(regex);
assert "31.03.2017".matches(regex);
assert "2017".matches(regex);
assert !"23-2017".matches(regex);

Note that:

• it will only check that there are digits at the right place
• it won't detect incorrect years (for example 0013 ) or incorrect days/months (day 45 or month 15)

To really check for dates, I suggest you use libraries especially made for this, like DateFormat , JodaTime or apache's DateUtils .

---

Using DateTimeFormatter :

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("[[dd.]MM.]yyyy");
// correct dates
assert formatter.parse("31.12.2017") != null;
assert formatter.parse("12.2017") != null;
assert formatter.parse("2017") != null;
// wrong date
assert formatter.parse("31.2017") == null;

---

Using DateUtils ( maven link ):

String[] acceptedFormats = {"dd.MM.yyyy", "dd.MM.yyyy", "dd/MM/yyyy"};

// correct dates
assert DateUtils.parseDate("07.12.2017", acceptedFormats) != null;
assert DateUtils.parseDate("07.2017", acceptedFormats) != null;
assert DateUtils.parseDate("2017", acceptedFormats) != null;
assert DateUtils.parseDate("2017", acceptedFormats) != null;
// wrong dates
assert DateUtils.parseDate("123.2012", acceptedFormats) == null;
assert DateUtils.parseDate("01.13.2012", acceptedFormats) == null;

Answer 2

Could you try the below

String regex = "([0-9]{2})-([0-9]{2})-([0-9]{4})";

which will match the date dd-mm-yyyy