Regex DATE format validation on Java

Question

Hello!

I'm just wondering if there is a way (maybe with REGEX) to validate that an input on a java desktop app is exactly an string formated as: "YYYY-MM-DD".

I've search but with no success.

Thank you

Answer 1

Use the following regular expression:

^\d{4}-\d{2}-\d{2}$

as in

if (str.matches("\\d{4}-\\d{2}-\\d{2}")) {
    ...
}

With the matches method, the anchors ^ and $ (beginning and end of string, respectively) are present implicitly.

Answer 2

Check out this example

Answer 3

You want more than a regex, for example "9999-99-00" isn't a valid date. There's a SimpleDateFormat class that's built to do this. More heavyweight, but more comprehensive-

e.g.

SimpleDateFormat format = new SimpleDateFormat("YYYY-MM-dd");

boolean isValidDate(string input)
{
  try{ format.parse(input);return true;}
  catch(ParseException e){ return false; }
}

Unfortunately, SimpleDateFormats are both heavyweight and not threadsafe.

Answer 4

Construct a SimpleDateFormat with the mask, and then call: SimpleDateFormat.parse(String s, ParsePosition p)

Answer 5

For fine control, consider an InputVerifier using the SimpleDateFormat("YYYY-MM-dd") suggested by Steve B.

Answer 6

Putting it all together:

• REGEX doesn't validate values (like "2010-19-19")
• SimpleDateFormat does not check format ("2010-1-2", "1-0002-003" are accepted)

it's necessary to use both to validate format and value:

public static boolean isValid(String text) {
    if (text == null || !text.matches("\\d{4}-[01]\\d-[0-3]\\d"))
        return false;
    SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");
    df.setLenient(false);
    try {
        df.parse(text);
        return true;
    } catch (ParseException ex) {
        return false;
    }
}

---

A ThreadLocal can be used to avoid the creation of a new SimpleDateFormat for each call.
It is needed in a multithread context since the SimpleDateFormat is not thread safe:

private static final ThreadLocal<SimpleDateFormat> format = new ThreadLocal<SimpleDateFormat>() {
    @Override
    protected SimpleDateFormat initialValue() {
        SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");
        df.setLenient(false);
        System.out.println("created");
        return df;
    }
};

public static boolean isValid(String text) {
    if (text == null || !text.matches("\\d{4}-[01]\\d-[0-3]\\d"))
        return false;
    try {
        format.get().parse(text);
        return true;
    } catch (ParseException ex) {
        return false;
    }
}

(same can be done for a Matcher, that also is not thread safe)