[SOLVED] Calculate previous calendar period

Calculate previous calendar period

I have two timestamps: start/end of period (calendar month, week or day).

I need to calculate previous period (previous month, week etc.). I tried to do it using LocalDateTime functions. E.g. using getMonthOfYear() - 1 for month period but what to do with last day (beforeDayTo)?

E.g. september's getDayOfMonth() returns 30, but for previous period (august) I need 31 etc.

Long fromDateMillis = 1440277200000L;
Long toDateMillis = 1440363599000L;

LocalDateTime fromLocalDate = new LocalDateTime(fromDateMillis);
LocalDateTime toLocalDate = new LocalDateTime(toDateMillis)

int beforeYear = fromLocalDate.getYear();
int beforeMonthFrom = fromLocalDate.getMonthOfYear() - 1;
int beforeMonthTo = toLocalDate.getMonthOfYear() - 1;
int beforeDayFrom = fromLocalDate.getDayOfMonth();
int beforeDayTo = toLocalDate.getDayOfMonth();
Timestamp prevFromDate = Timestamp
        .valueOf(java.time.LocalDateTime.of(beforeYear, beforeMonthFrom, 1, 0, 0, 0));
Timestamp prevToDate = Timestamp
        .valueOf(java.time.LocalDateTime.of(beforeYear, beforeMonthTo, beforeDayTo, 0, 0, 0));

How to solve this issue?

Solution

You are getting the number of Day of the current month.

Calendar cal = Calendar.getInstance();
cal.setTimeInMillis(timestamp);
cal.add(Calendar.MONTH, -1);
cal.set(Calendar.DAY_OF_MONTH, cal.getActualMaximum(Calendar.DAY_OF_MONTH));
cal.getTimeInMillis();

The last line give you the timestanp as a Long. So you can do it :

Timestamp timestamp = new Timestamp(cal.getTimeInMillis());

Calendar alow you to do all what you want to do. Take a look to this http://docs.oracle.com/javase/7/docs/api/java/util/Calendar.html