java正則判斷日期字符串

public static boolean isDateTime(String timeStr) {
        String format = "((19|20)[0-9]{2})-(0?[1-9]|1[012])-(0?[1-9]|[12][0-9]|3[01]) "
                + "([01]?[0-9]|2[0-3]):[0-5][0-9]:[0-5][0-9]";
        Pattern pattern = Pattern.compile(format);
        Matcher matcher = pattern.matcher(timeStr);
        if (matcher.matches()) {
            pattern = Pattern.compile("(\\d{4})-(\\d+)-(\\d+).*");
            matcher = pattern.matcher(timeStr);
            if (matcher.matches()) {
                int y = Integer.valueOf(matcher.group(1));
                int m = Integer.valueOf(matcher.group(2));
                int d = Integer.valueOf(matcher.group(3));
                if (d > 28) {
                    Calendar c = Calendar.getInstance();
                    c.set(y, m-1, 1);
                    int lastDay = c.getActualMaximum(Calendar.DAY_OF_MONTH);
                    return (lastDay >= d);
                }
            }
            return true;
        }
        return false;
    }

    public static void main(String[] args) {
        System.out.println(DateUtils.isDateTime("2019-05-08 12:00:20"));
        System.out.println(DateUtils.isDateTime("2019-06-08 12:00:020"));
        System.out.println(DateUtils.isDateTime("2019-06-08 12:00"));
    }

結果：

true
false
false