how do we check if a date is a valid date

Question

I am trying to set a next schedule date for a process to run. This scheduler needs to display up a Vf page when the user logs in or when he loads up a page. I am running a scheduled batch process to populate a field for the next scheduled date. If the user chooses a monthly schedule where in it needs to run on a particular date of every month.

I am unsure of how to calculate the date for the days 29,30 and 31 as they are not there for every month of the year. If i try to create a new date instance for the months these days are not valid then it would throw an exception.

If these days are not available for the month then i need to somehow have it set it to the next valid date.

Any thoughts on how to approach this

public DateTime getmonthlyNextscheduleDate(String day, String times)
 {
    Date monthDate;
    Datetime monthDateTime;
    DateTime nextScheduleDate;
    if(day == '29' || day =='30' || day =='31')
    {

    }
    else
    {
    monthDate = Date.newInstance(Integer.valueof(day),Date.today().month(),Date.today().year());
    monthDateTime = Datetime.newInstance(monthDate, gettimes(times));
    if(monthDateTime > Datetime.now())
    {
        nextScheduleDate = monthDateTime.addMonths(1);
    }
    else
    {
        nextScheduleDate = monthDateTime;
    }
    }
    return nextScheduleDate;
 }

Answer 1

An ugly way would be just catching the exception and calling your function recursively with day - 1. A bit more elegant way would use daysInMonth function like this.

Integer daysInMonth = Date.daysInMonth(Date.today().month());
while( day > daysInMonth){
      day--;
}