Date Pattern starting from 12 hours

Issue

I'm trying to convert two dates into this pattern: yyyy-MM-dd HH:mm:ss.SSS.

I need to retrieve two dates:

• Last year, same month, day 1, 00:00:00.000
• Last day of previous month, 23:59:59.999

So, as of today, I need these two values:

• 2022-11-01 00:00:00.000
• 2023-10-31 23:59:59.999

The problem is: I get 2022-11-01 12:00:00.000.

This is the code that generates last year's date.

private String getLastYear() {
    DateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS");
    Date date = new Date();
    Calendar c = Calendar.getInstance();
    c.setTime(date);
    c.add(Calendar.YEAR, -1);
    c.set(Calendar.DAY_OF_MONTH, 1);
    c.set(Calendar.HOUR, 0);
    c.set(Calendar.MINUTE, 0);
    c.set(Calendar.SECOND, 0);
    c.set(Calendar.MILLISECOND, 0);
    return format.format(c.getTime());
}

If I try adding one hour, the output will be: 2022-11-01 13:00:00.000.

Also, I can't retrieve the last day of the previous month. As I have read here, all I keep getting is the first day of the next month.

Here's the code.

private String getPreviousMonth() {
    DateFormat format = new SimpleDateFormat(DATE_PATTERN);
    Calendar c = Calendar.getInstance();
    Date date = new Date();
    c.setTime(date);
    c.add(Calendar.MONTH, -1);
    c.set(Calendar.DAY_OF_MONTH, c.getActualMaximum(Calendar.DAY_OF_MONTH));
    c.set(Calendar.HOUR, 23);
    c.set(Calendar.MINUTE, 59);
    c.set(Calendar.SECOND, 59);
    c.set(Calendar.MILLISECOND, 999);
    return format.format(c.getTime());
}

There is something I'm missing. Any help is highly appreciated!

Solution

You say any help is highly appreciated, so here's an example that uses java.time, which uses today as base and calculates the two desired results as follows:

First of current month in the last year

• subtract a year from today (2023-11-17 ⇒ 2022-11-17)
• take the first of that month (2022-11-17 ⇒ 2022-11-01)
• involve the start of the day (2022-11-01 ⇒ 2022-11-01 00:00:00.000)

Last day of last month at the end of the day

• subtract a month from today (2023-11-17 ⇒ 2023-10-17)
• go to the last day of that month (2023-10-17 ⇒ 2023-10-31)
• append the maximum time of day (2023-10-31 ⇒ 2023-10-31 23:59:59.999)

public static void main(String[] args) {
    LocalDateTime lastYearSameMonthFirstDay
                        // today (without time of day)
                        = LocalDate.now()
                                   // subtract 1 from the year
                                   .minusYears(1)
                                   // go to the first day of month 
                                   .with(TemporalAdjusters.firstDayOfMonth())
                                   // append the start of the day
                                   .atStartOfDay();
    
    LocalDateTime lastDayOfPreviousMonth
                        // today (date only as above)
                        = LocalDate.now()
                                   // subract 1 from the month value
                                   .minusMonths(1)
                                   // go to the last day of that month
                                   .with(TemporalAdjusters.lastDayOfMonth())
                                   // append the end of the day
                                   .atTime(LocalTime.MAX);
    // prepare a formatter for the output
    DateTimeFormatter dtf = DateTimeFormatter.ofPattern("uuuu-MM-dd HH:mm:ss.SSS");
    // and print both LocalDateTimes formatted as desired
    System.out.println(lastYearSameMonthFirstDay.format(dtf));
    System.out.println(lastDayOfPreviousMonth.format(dtf));
}

Output (execution date 2023-11-17):

2022-11-01 00:00:00.000
2023-10-31 23:59:59.999

Answered By - deHaar