final String regex = "(\\d{1,2}).(\\d{1,2}).(\\d{2,2}$)";
        final String string = "12.02.16";

        final Pattern pattern = Pattern.compile(regex, Pattern.MULTILINE);
        final Matcher matcher = pattern.matcher(string);

        matcher.find();
        StringBuilder sbuf = new StringBuilder();
        Formatter fmt = new Formatter(sbuf);
        fmt.format("%02d-%02d-20%02d ", Integer.parseInt(matcher.group(1)), Integer.parseInt(matcher.group(2)), Integer.parseInt(matcher.group(3)));
        System.out.print(sbuf.toString());

    enum Mon {
        xx, jan, feb, mar, apr, may, june, july, aug, sept, oct, nov, dec
    }

    public static void main(String[] args) {

        final String regex = "((\\d{1,2}).(?<xx>[a-zA-Z]{3}|\\d{1,2}).(\\d{4}))";
        final String string = "12-May-2016";

        final Pattern pattern = Pattern.compile(regex, Pattern.MULTILINE);
        final Matcher matcher = pattern.matcher(string);

        matcher.find();
        StringBuilder sbuf = new StringBuilder();
        Formatter fmt = new Formatter(sbuf);
        int num;
        if (matcher.group("xx").length() <= 2) {
            num = Integer.parseInt(matcher.group("xx"));
        } else {
            num = Mon.valueOf(matcher.group("xx").toLowerCase()).ordinal();
        }
        fmt.format("%4d-%02d-%02d", Integer.parseInt(matcher.group(4)), num, Integer.parseInt(matcher.group(2)));
        System.out.println(sbuf.toString());

    }