Get first and last day of month using threeten, LocalDate

java

date-manipulation

temporal-adjusters

localdate

byNikita Barsukov·Dec 9, 2024

Fetch the first and last day of a month using LocalDate and YearMonth:

localDate.withDayOfMonth(1): Retrieves the month's initial day.
yearMonth.atEndOfMonth(): Procures the month's final day.

import org.threeten.bp.LocalDate;
import org.threeten.bp.YearMonth;

LocalDate today = LocalDate.now();
LocalDate firstDay = today.withDayOfMonth(1); // Not an astrology sign, but rather the first day
LocalDate lastDay = YearMonth.from(today).atEndOfMonth(); // The last dance with the month

These expressions provide the current month's start and end dates perfect for any LocalDate manipulation.

Digging deeper: A touch of `TemporalAdjusters`

Enhance date manipulations with TemporalAdjusters:

import org.threeten.bp.temporal.TemporalAdjusters;

LocalDate firstDayAdjusted = today.with(TemporalAdjusters.firstDayOfMonth()); // Favouring TemporalAdjusters since it's the first in the month
LocalDate lastDayAdjusted = today.with(TemporalAdjusters.lastDayOfMonth()); // Last call! Courtesy of TemporalAdjusters

Improve readability and maintainability with static imports:

import static org.threeten.bp.temporal.TemporalAdjusters.firstDayOfMonth;
import static org.threeten.bp.temporal.TemporalAdjusters.lastDayOfMonth;

LocalDate firstDayClean = today.with(firstDayOfMonth()); // Cleaned up nicely for the first date
LocalDate lastDayClean = today.with(lastDayOfMonth()); // Out with a bang using lastDayOfMonth

Leap years got you leaping? These methods got you covered for February's extra day.

For a change, consider using YearMonth:

YearMonth yearMonthInstance = YearMonth.from(today);
LocalDate firstDayYearMonth = yearMonthInstance.atDay(1); // Nothing tricky - it's day one 
LocalDate lastDayYearMonth = yearMonthInstance.atEndOfMonth(); // YearMonth sends regards for the last day

YearMonth handles monthly cycles like a charm, particularly in business logic.

Navigating the edge: Advanced usage and edge cases

Crafting the last day from known lengths

Knowing the month's length? plusDays() has your back:

LocalDate lastDayKnownLength = firstDay.plusDays(monthLength - 1); // The last crusader from the known lengths kingdom

Remember, we start at day one, thus the reminder to subtract one from the known monthLength.

Designing date manually

When precision is key, and you need to manually set a specific date, not related to today:

LocalDate firstDaySpecific = LocalDate.of(year, month, 1); // The wizard has constructed the first day
LocalDate lastDaySpecific = firstDaySpecific.withDayOfMonth(
  firstDaySpecific.lengthOfMonth() // A specific wizard's tool to get the very last day 
);

Always cross-check date operations with business rules for avoiding surprises.