is date valid

[chen young]

Hi,

I need to check if date is valid
This is the format of the date: ####-##-## ##:##:## ,for example2008-12-23 09:29:13
I am a bit confused with all the date objects in java
Any suggestion regarding how should I check this format ?

Thanks

[Sunil Kumar]

Use simple date format like this

  public static boolean validateDate(String dateStr, 
                                        String formatStr)
    {
         if (formatStr == null) return false; 
        SimpleDateFormat df = new SimpleDateFormat(formatStr);
        Date testDate = null;
        try
        {
            testDate = df.parse(dateStr);
        }
        catch (ParseException e)
        {
            return false;
        }

        if (!df.format(testDate).equals(dateStr)) return false;
        return true;
    }  

[Mustafa Musaji]

I'm not sure if I completely understand how you want to check the date, but you can use SimpleDateFormat to create the format of the date and then parse a date object using the formatter created. Check out the API for SimpleDateFormat or google "date format using Java". You'll find some good examples.

EDIT: Exactly how Sunil has said above! lol, beat me to it!

[chen young]

Thanks

[Mustafa Musaji]

You may also want to check out this Thread in the intermediate forum

https://coderanch.com/t/425542/Java-General-intermediate/Date-validation

[ramya narayanan]

Dear All,
I've a dummy doubt.
Please don't mind.
In the below code,

 if (!df.format(testDate).equals(dateStr)) return false;     

datestr is the original date value & testDate(in the if condition after it is executed) is the formatted date.
There is likely both may not be equal .
in that case if block becomes true right & returns false.
So the original date & validated date won't be equal right!

[Sunil Kumar]

ramya narayanan wrote:There is likely both may not be equal .

Not sure if this case exists. Did you find one?

[ramya narayanan]

No sunil, I want to know what the below code does.

if (!df.format(testDate).equals(dateStr)) return false;       

Regards

[Rob Spoor]

Sunil Kumar wrote:Use simple date format like this

  public static boolean validateDate(String dateStr, 
                                        String formatStr)
    {
         if (formatStr == null) return false; 
        SimpleDateFormat df = new SimpleDateFormat(formatStr);
        Date testDate = null;
        try
        {
            testDate = df.parse(dateStr);
        }
        catch (ParseException e)
        {
            return false;
        }

        if (!df.format(testDate).equals(dateStr)) return false;
        return true;
    }  

There are two improvements that can be made:
- turn off leniency
- check if the parsing did not ignore the trailing part of the string (ok, you're actually doing that at the end, but it can be a bit more efficient ;))

public static boolean validateDate(String dateStr, String formatStr)
{
    if (formatStr == null || formatStr.length() == 0) return false;
    if (dateStr == null || dateStr.length() == 0) return false;
    SimpleDateFormat df = new SimpleDateFormat(formatStr);
    df.setLenient(false);
    ParsePosition pos = new ParsePosition(0);
    df.parse(dateStr, pos); // ignore the output
    return pos.getIndex() == dateStr.length();
} 

If the string could not be parsed, then pos.getIndex() will still return 0. If it could be parsed but there is trailing garbage (e.g. "2009-01-13 09:34:00 Hello world!") then pos.getIndex() will be smaller than dateStr.length().

As for no exception, that's because DateFormat.parse(String) uses the same technique:

public Date parse(String source) throws ParseException
{
    ParsePosition pos = new ParsePosition(0);
    Date result = parse(source, pos);
    if (pos.index == 0)
        throw new ParseException("Unparseable date: \"" + source + "\"" ,
            pos.errorIndex);
    return result;
}

And if you can avoid an exception, you should always do so.

[Rob Spoor]

ramya narayanan wrote:No sunil, I want to know what the below code does.

if (!df.format(testDate).equals(dateStr)) return false;       

Regards

Parsing a date can remove any trailing garbage, as in the example I described above. This statement checks if the formatted date is equal to the source string. Taking my example, the formatted date would be "2009-01-13 09:34:00" which is not equal to the source.

[ramya narayanan]

Thanks Rob Prime for once again patiently explaining the best practices !
My Best Regards(to you)!

[Sunil Kumar]

Thanks Rob!