Regex and Date pattern matching

Question

Below is the regex I am have:

Pattern ddpat = Pattern.compile( "(\\d{1,2}/\\d{1,2}/\\d{4})" );

For an invalid date pattern 02/29/1975 (Since it is not a leap year), when I try the above REGEX on this invalid date, I don't want my REGEX to match this invalid date.

Please suggest is there some way to achieve this.

that is not possible with Regex, you have to code these type validations — Dalorzo
– Dalorzo, Commented Jul 30, 2014 at 16:52
Theoretically (!!!) you can create a regular expression enumerating (!!!) all valid dates, with factoring to reduce repetitions, (stopping today or at some point in the future). This will be a big regex, but it would be a "way to achieve this". (THIS IS NOT MEANT SERIOUSLY.) — laune
– laune, Commented Jul 30, 2014 at 16:57
Regex is the wrong tool for this job (checking validity of dates). The issue is not only with leap year, this regex will accept: 99/99/9999 as well ;) — Nir Alfasi
– Nir Alfasi, Commented Jul 30, 2014 at 16:58
I agree with this. But since this is an existing code working for years in production, I won't be able to change it any way, hence just trying to do something and let it work as of now. — WhoAmI
– WhoAmI, Commented Jul 30, 2014 at 17:00

gtgaxiola · Accepted Answer · 2014-07-30 16:55:02Z

2

You will have to use DateFormatter in order to validate dates.

Not only that, you will have to set the DateFormat's setLenient to false in order to catch those kinds of errors

public static void main(String[] args) throws ParseException {
    String d = "02/29/1975";
    DateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");
    sdf.setLenient(false);
    Date date = sdf.parse(d);
    System.out.println(date);
}

You will see that it throws the ParseException

If you don't set up the leniency, then the DateFormat will attempt to parse it to a convenient albeit arbitrary Date for example:

02/29/1975 could be converted to 03/01/1975

answered Jul 30, 2014 at 16:55

gtgaxiola

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7 Comments

WhoAmI Over a year ago

I am having an array of Date format something like this:DateFormat[] format = new DateFormat[]{ new SimpleDateFormat("MM/dd/yyyy"), new SimpleDateFormat("dd/MM/yy") }; In this case, how to use the setLenient ?

gtgaxiola Over a year ago

@WhoAmI loop over your format array and setLenient(false); before you use it

WhoAmI Over a year ago

Rather than looping, is there any shortcut so that I can set it while declaring the array? I just want to optimize the code. Please suggest.

gtgaxiola Over a year ago

@WhoAmI seriously, is a three line code (if you separate the braces) for(DateFormat f : format) { f.setLenient(false);}

gtgaxiola Over a year ago

Let us continue this discussion in chat.

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