Java Monthly Recurrence

I am trying to get a monthly recurrence dates for a specific period. The code below works except when I am specifying the recurrence date of 30. Then it is generating the following error, which is normal:

Exception in thread "main" java.time.DateTimeException: Invalid date 'FEBRUARY 30'

My question is : Is there a way to set the recurrence to the last day of the month if the specified date (day) of the recurrence is higher than the last day of the month ?

Thanks !

public class MonthlyRecurrence {
    public static void main(String[] args) {

        LocalDate startDate = LocalDate.of(2020, 10, 6);
        LocalDate endDate = LocalDate.of(2021, 12, 31);
        int dayOfMonth = 30;

        List<LocalDate> reportDates = getReportDates(startDate, endDate, dayOfMonth);
        System.out.println(reportDates);
    }

    private static List<LocalDate> getReportDates(LocalDate startDate, LocalDate endDate, int dayOfMonth) {
        List<LocalDate> dates = new ArrayList<>();
        LocalDate reportDate = startDate;
        
        while (reportDate.isBefore(endDate)) {
            reportDate = reportDate.plusMonths(1).withDayOfMonth(dayOfMonth);
            dates.add(reportDate);
        }
        return dates;
    }
    }

You need to specify a TemporalAdjuster to get the specific day of the month regardless of the month's length. It is passed as the third argument to your method.

Because I wasn't quite certain what you wanted, I included two adjusters. One for a specific day and one for the last day of the month. They can be used interchangeably. However, the latter will not reach Dec 31, 2021 since the before excludes ==

LocalDate startDate = LocalDate.of(2020, 10, 6);
LocalDate endDate = LocalDate.of(2021, 12, 31);

// Adjuster for a specific day
int dayOfMonth = 30;  // must be final or effectively final
                      // as it is used in the following lambda.
TemporalAdjuster specificDay = 
        date-> {
	        LocalDate ld = (LocalDate)date;
	        int max = ld.getMonth().length(ld.isLeapYear());
	        int day = dayOfMonth > max ? max : dayOfMonth;
	        return date.with(ChronoField.DAY_OF_MONTH,day);
};
		
		
// Adjuster for the lastDay of the month.
TemporalAdjuster lastDay = TemporalAdjusters.lastDayOfMonth();
	
List<LocalDate> reportDates =
		getReportDates(startDate, endDate, specificDay);

reportDates.forEach(System.out::println);
	
private static List<LocalDate> getReportDates(LocalDate startDate,
		LocalDate endDate, TemporalAdjuster specificDay) {
	List<LocalDate> dates = new ArrayList<>();
	
	// round up start day to specificDay
    LocalDate reportDate = startDate.with(specificDay);
    
	while (reportDate.isBefore(endDate)) {
		dates.add(reportDate);
		reportDate = reportDate.plusMonths(1).with(specificDay);
	}
	return dates;
}

Prints the following depending on choice of TemporalAdjuster

SpecificDay (30th)  LastDayOfMonth
	2020-10-30        2020-10-31
	2020-11-30        2020-11-30
	2020-12-30        2020-12-31
	2021-01-30        2021-01-31
	2021-02-28        2021-02-28
	2021-03-30        2021-03-31
	2021-04-30        2021-04-30
	2021-05-30        2021-05-31
	2021-06-30        2021-06-30
	2021-07-30        2021-07-31
	2021-08-30        2021-08-31
	2021-09-30        2021-09-30
	2021-10-30        2021-10-31
	2021-11-30        2021-11-30
	2021-12-30	


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