Parsing dates entered in different formats

[Serge Glaeser]

Hello

I'm having a hard time parsing dates that are entered in different formats. Is there a general way to do that? I have a text field where the user can enter a date (so obviously he can enter any format) ex.

10102010
101010
10.10.2010
10.10.10
or the date can be invalid (505002 or anything else)

Is there a general approach on how to handle things like that? i found the classes simpledateformatter and dateformatter, but they can handle only one format.

any tips appreciated.

thanks

[Martin Vanyavchich]

Take a look at setLenient. Combibig this and a set of formats might do the trick for you.

[Garrett Rowe]

The best way would probably be to not let the user enter the date via a text field. That way you can more easily control the format of the date entered. If this is a swing app, you could possibly use a JComboBox to constrain the possible inputs.

[Rob Spoor]

A JSpinner with a SpinnerDateModel is better than a JComboBox or JTextField. It still allows free typing but performs validation on the entered text.

[Serge Glaeser]

thanks for all the replies. Spinners and combos are not an option unfortunately (and we're using SWT not swing).

this setLenient sounds interesting. I'll have a look at that.

thanks

[Serge Glaeser]

well lenient seems to be more forgiving if someone misspells a date (ex. 32.01.2010 would become 01.02.2010 instead of throwing an exception) but doesn't help with the formatting.

any other ideas? anyone done anything similar?

[Rob Spoor]

Use a number of allowed formats, then check each of them:

DateFormat[] formats = { ... };
for (DateFormat format: formats)
{
    ParsePosition position = new ParsePosition(0);
    Date date = format.parse(input, position); // returns null rather than throw a ParseException
    if (date != null /* no error */ && position.getIndex() == input.length() /* trailing chars, e.g. 01/01/2010abc */)
    {
        return date;
    }
}
// not valid for any of the formats

The order is quite important here; if MM/dd/yyyy comes before dd/MM/yyyy then 01/02/2010 will be January 2nd. If the order is the other way around then it's February 1st.

[Vinoth Kumar Kannan]

Rob Prime wrote:
Date date = format.parse(input, position); // returns null rather than throw a ParseException

Rob, one question...
The DateFormat class defines - public abstract Date parse(String source, ParsePosition pos)
then for format.parse(input, position) to work, format must be a SimpleDateFormat class object,right?

[Rob Spoor]

It doesn't need to be. It can be any DateFormat subclass. SimpleDateFormat is mostly chosen but others are also possible.

[Jesper de Jong]

This is not a simple problem for which there is a simple solution, because there are numerous ways to enter a date in an ambiguous way.

For example, what if I enter "020310"? Does that mean 2 March 2010 (ddmmyy), 3 February 2010 (mmddyy), 10 March 2002 (yymmdd) or some other possible combination? You'll have to think about what inputs you're going to accept and how the different possibilities should be interpreted.

There's no standard method in the standard Java library to parse any "arbitrary format" string into a date.

[Vinoth Kumar Kannan]

Is there any difference between format.parse(String,ParsePosition) and parse(String), other than the first returning null instead of a ParseException by the second?

[Rob Spoor]

No. In fact, in the current implementation parse(String) calls parse(String, ParseException), then either returns the parsed Date or throws a ParseException:

    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;
    }

By the way, these two fields of ParsePosition have package visibility; we must use the matching getters and setters.