Suggestions for date validation

[Joe Harry]

Guys,

I know that this must have been implemented a million times, but I'm here looking for ideas:

I need to validate the date for a specific format. I have both the inputs (date format and the actual date) as String objects. I can use a variety of API's to do this (Calendar, SimpleDateFormat, DateUtils etc., ) but I would like to have suggestions on the simplest one.

For example: isDateValid("DDMMYYYY", "21122010")

In all my date formats, I do not have any seperators (like . or -). It is always either DDMM or DDMMYYYY or any of that combination but always without a seperator.

[Joe Harry]

Suggestions???

[Wouter Oet]

Remember that PatienceIsAVirtue!

I would use SimpleDateFormat.

[Rob Spoor]

And remember that the pattern characters are case sensitive. YYYY is invalid, and DD returns the day of the year, not the day of the month. You want "ddMMyyyy" or "ddMM". Because yes, MM should remain uppercase as mm is reserved for minutes.

[Joe Harry]

It looks like the SimpleDateFormat would not be suitable for me:

		final SimpleDateFormat format = new SimpleDateFormat(dateFormat);		
		try {
			format.parse(date);
			format.setLenient(false);
			return true;
		}
		catch (ParseException ex) {
			return false;			
		}

	public static void main (String [] args) {
		System.out.println(isDateFormatValid("ddMMyyyy", "50212011"));	// prints true
                System.out.println(isDateFormatValid("ddMMyyyy", "50210000"));	// prints true
	}

It looks like only the date format is validated but not the date, month or year.

[Rob Spoor]

Sure it is, with a bit of tweaking:

final SimpleDateFormat format = new SimpleDateFormat(dateFormat);		
// turn leniency off before parsing!
format.setLenient(false);
// using parse(String, ParsePosition) will not throw an exception
// this is in fact used inside parse(String)
ParsePosition position = new ParsePosition(0);
Date d = format.parse(date);
// d != null means the date is valid
// the length check is to also disallow trailing data, e.g. 04042011abc
return d != null && position.getIndex() == date.length();

[Sean Clark]

Rob, your post you posted has a minor bug, should be:

Date d = format.parse(date, position);

rather than

Date d = format.parse(date);

.
Nice bit of of code though, I didn't know about this
Sean

[Joe Harry]

Nope it still prints the wrong values:

			final SimpleDateFormat format = new SimpleDateFormat(date);
                        format.setLenient(false);
			ParsePosition position = new ParsePosition(0);
			Date d = format.parse(date, position);
			
			return d != null && position.getIndex() == date.length();

            Tried the call as below:

             System.out.println(isDateFormatValid("ddMMyyyy", "32131980")); // prints true... expected to be false  :banghead: 

[Joe Harry]

It was a mistake from my side. It worked perfectly fine. Thanks!

[Rob Spoor]

Sean Clark wrote:Rob, your post you posted has a minor bug, should be:

Date d = format.parse(date, position);

rather than

Date d = format.parse(date);

.
Nice bit of of code though, I didn't know about this
Sean

You're very right of course.

[Rob Spoor]

Joe Harry wrote:It was a mistake from my side. It worked perfectly fine. Thanks!

You're welcome

[Joe Harry]

I have another question in this context. I have the date as MMyy and from this I need to get the date. Any suggestions on how this could be acheived?

[Rob Spoor]

Parse to Date, then convert to Calendar, then retrieve the information you need:

Date date = ...;
Calendar calendar = Calendar.getInstance();
calendar.setTime(date);
int year = calendar.get(Calendar.YEAR);
// etc

[Joe Harry]

Another hint to my requirement is that I need the date always to be the last date of that month and year. I hope that there should be methods like getLastDate() or similar??

[Rob Spoor]

Calendar has a method called getActualMaximum; it uses its current date/time to determine the result. So getActualMaximum(Calendar.DAY_OF_MONTH) would return 28 if the calendar's date was in February, and 30 for this month.
Don't confuse this method with getMaximum which will return the absolute maximum; getMaximum(Calendar.DAY_OF_MONTH) would return 31, whatever the calendar's date would be.

[Joe Harry]

Thanks for the suggestions. Would try that you!

[Gaurav Kr. Arora]

Joe Harry wrote:Nope it still prints the wrong values:

			final SimpleDateFormat format = new SimpleDateFormat(date);
                        format.setLenient(false);
			ParsePosition position = new ParsePosition(0);
			Date d = format.parse(date, position);
			
			return d != null && position.getIndex() == date.length();

            Tried the call as below:

             System.out.println(isDateFormatValid("ddMMyyyy", "32131980")); // prints true... expected to be false  :banghead: 

Could you please explain why position.getIndex() == date.length(); condition is needed in the return statement above? Can't we just use d!=null?
[size=9]PS: Am new user of SimpleDateFormat and might not be fully aware of its functionality.[/size]

[Rob Spoor]

Try using "01012011abc" for input, and print out both "d" and "position" after the parsing. You'll see why I added that.