Someone

 // Create a calendar object of the desired month
  out.println(dateSplit[2]);
  out.println(dateSplit[0]);
  out.println(dateSplit[1]);
    Calendar cal = new GregorianCalendar(Integer.parseInt(dateSplit[2]), Integer.parseInt(dateSplit[0]), Integer.parseInt(dateSplit[1]));
    
    // Get the number of days in that month
    int days = cal.getActualMaximum(Calendar.DAY_OF_MONTH); // 28
    out.println("days: "+days);