last day of month calculation

Question

I am having issues with the calculation of when the next Last Day of the Month is for a notification which is scheduled to be sent.

Here is my code:

RecurrenceFrequency recurrenceFrequency = notification.getRecurrenceFrequency();
Calendar nextNotifTime = Calendar.getInstance();

This is the line causing issues I believe:

nextNotifTime.add(recurrenceFrequency.getRecurrencePeriod(), 
                  recurrenceFrequency.getRecurrenceOffset());

How can I use the Calendar to properly set the last day of the next month for the notification?

Answer 1

Calendar.getInstance().getActualMaximum(Calendar.DAY_OF_MONTH);

This returns actual maximum for current month. For example it is February of leap year now, so it returns 29 as int.

Answer 2

java.time.temporal.TemporalAdjusters.lastDayOfMonth()

Using the java.time library built into Java 8, you can use the TemporalAdjuster interface. We find an implementation ready for use in the TemporalAdjusters utility class: lastDayOfMonth.

import java.time.LocalDate;
import java.time.temporal.TemporalAdjusters;

LocalDate now = LocalDate.now(); //2015-11-23
LocalDate lastDay = now.with(TemporalAdjusters.lastDayOfMonth()); //2015-11-30

If you need to add time information, you may use any available LocalDate to LocalDateTime conversion like

lastDay.atStartOfDay(); //2015-11-30T00:00