Determine if a String is a valid date before parsing

Question

I have this situation where I am reading about 130K records containing dates stored as String fields. Some records contain blanks (nulls), some contain strings like this: \'

Answer 1

you could use split to determine which format to use

String[] parts = date.split("-");
df = (parts.length==3 ? format1 : format2);

That assumes they are all in one or the other format, you could improve the checking if need be

Answer 2

If you formats are exact (June 7th 1999 would be either 07-Jun-99 or 07/06/1999: you are sure that you have leading zeros), then you could just check for the length of the string before trying to parse.

Be careful with the short month name in the first version, because Jun may not be June in another language.

But if your data is coming from one database, then I would just convert all dates to the common format (it is one-off, but then you control the data and its format).

Answer 3

Assuming the patterns you gave are the only likely choices, I would look at the String passed in to see which format to apply.

public Date parseDate(final String date) {
  if (date == null) {
    return null;
  }

  SimpleDateFormat format = (date.charAt(2) == '/') ? new SimpleDateFormat("dd/MMM/yyyy")
                                                   : new SimpleDateFormat("dd-MMM-yy");
  try {
    return format.parse(date);
  } catch (ParseException e) {
    // Log a complaint and include date in the complaint
  }
  return null;
}

As others have mentioned, if you can guarantee that you will never access the DateFormats in a multi-threaded manner, you can make class-level or static instances.

Answer 4

An alternative to creating a SimpleDateFormat (or two) per iteration would be to lazily populate a ThreadLocal container for these formats. This will solve both Thread safety concerns and concerns around object creation performance.

Answer 5

In this limited situation, the best (and fastest method) is certinally to parse out the day, then based on the next char either '/' or '-' try to parse out the rest. and if at any point there is unexpected data, return NULL then.

Answer 6

A simple utility class I have written for my project. Hope this helps someone.

Usage examples:

DateUtils.multiParse("1-12-12");
DateUtils.multiParse("2-24-2012");
DateUtils.multiParse("3/5/2012");
DateUtils.multiParse("2/16/12");




public class DateUtils {

    private static List<SimpleDateFormat> dateFormats = new ArrayList<SimpleDateFormat>();



    private Utils() {
        dateFormats.add(new SimpleDateFormat("MM/dd/yy")); // must precede yyyy
        dateFormats.add(new SimpleDateFormat("MM/dd/yyyy"));
        dateFormats.add(new SimpleDateFormat("MM-dd-yy"));
        dateFormats.add(new SimpleDateFormat("MM-dd-yyyy"));            

    }
        private static Date tryToParse(String input, SimpleDateFormat format) {
        Date date  = null;
        try {
            date = format.parse(input);
        } catch (ParseException e) {

        }

        return date;
    }

        public static Date multiParse(String input)  {
        Date date = null;
        for (SimpleDateFormat format : dateFormats) {
            date = tryToParse(input, format);
            if (date != null) break;
        }
        return date;
    }
}