Question

Does anyone know of a DateFormatter in Java that isn’t so picky? By that I mean I could provide it multiple formats the date could be written in and if I provide it a format such as:

yyyy-MM-dd HH:mm:ss Z

A user could enter:

2010-11-02 10:46:05 -0600
or
2010-11-02 10:46:05
or
2010-11-02 10:46
or
2010-11-02
or
2010-11-02 -0600

I could create an implementation of DataFormat that is configured with a List of DateFormat objects and make my implementation run through each in the List until one is able to parse the date. So, I really am just curios if someone is aware of an existing date formatting library that is less picky/more flexible then what Java provides.

Answer 1

It looks like you have a pretty regular format for each part, it’s just that the parts are optional. I would use a regex that has each part (some being optional). Match on that regex and get the groups for each part. Then put them together in the most complete form (“2010-11-02 10:46:05 -0600”) and have the DateFormatter parse that. This way you also get to control the defaults for the parts if they are missing.

Here is some code:

    Pattern p = Pattern
            .compile("(\\d{4}-\\d{2}-\\d{2})\\s*(\\d{2}:\\d{2})?(:\\d{2})?\\s*(\\+|-\\d{4})?");
    String[] strs = { "2010-11-02 10:46:05 -0600", "2010-11-02 10:46:05",
            "2010-11-02 10:46", "2010-11-02", "2010-11-02 -0600" };
    SimpleDateFormat format = new SimpleDateFormat("yyy-MM-dd HH:mm:ss Z");
    for (String s : strs) {
        Matcher m = p.matcher(s);
        if (m.matches()) {
            String hrmin = m.group(2) == null ? "00:00" : m.group(2);
            String sec = m.group(3) == null ? ":00" : m.group(3);
            String z = m.group(4) == null ? "+0000" : m.group(4);
            String t = String.format("%s %s%s %s", m.group(1), hrmin, sec,
                    z);
            System.out.println(s + " : " + format.parse(t));
        }
    }

Output:

2010-11-02 10:46:05 -0600 : Tue Nov 02 11:46:05 CDT 2010
2010-11-02 10:46:05 : Tue Nov 02 05:46:05 CDT 2010
2010-11-02 10:46 : Tue Nov 02 05:46:00 CDT 2010
2010-11-02 : Mon Nov 01 19:00:00 CDT 2010
2010-11-02 -0600 : Tue Nov 02 01:00:00 CDT 2010