How to obtain the start time and end time of a day?

Handling edge cases and advanced tricks

Juggling multiple time zones

If you're managing time zones, it's worth pinpointing ZoneId. Check the code below:

import java.time.ZoneId;
import java.time.ZonedDateTime;

ZoneId zoneId = ZoneId.of("America/New_York"); // New Yorkers, rejoice! 🗽
ZonedDateTime zonedStartOfDay = LocalDate.now().atStartOfDay(zoneId);
ZonedDateTime zonedEndOfDay = zonedStartOfDay.plusDays(1).minusNanos(1);

System.out.println("Zoned Start: " + zonedStartOfDay); // NYC is waking up ☕
System.out.println("Zoned End: " + zonedEndOfDay); // NYC falls asleep 🌃
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Navigating the old Java sea

For those sailing in the Java 7 and earlier sea, use robust libraries like Apache Commons Lang, or stick to manual setting:

import org.apache.commons.lang3.time.DateUtils;
import java.util.Calendar;

Calendar start = Calendar.getInstance();
start.setTime(DateUtils.truncate(start.getTime(), Calendar.DAY_OF_MONTH)); // Day has just started!

Calendar end = (Calendar) start.clone();
end.add(Calendar.DAY_OF_MONTH, 1);
end.add(Calendar.MILLISECOND, -1); // You've got 1 ms to midnight!

System.out.println("Legacy Start: " + start.getTime());
System.out.println("Legacy End: " + end.getTime());
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To the millisecond and beyond!

For those applications craving for millisecond precision, here's how to quench their thirst:

LocalDateTime endOfDayMillis = LocalDate.now().atTime(23, 59, 59, 999_999_999);
System.out.println("End with Milliseconds: " + endOfDayMillis); // It's milli milli exciting!
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Maintaining consistency across all apps

For accurate and consistent time tracking, all applications should follow the same definitions:

• Stick to LocalTime.MIN and LocalTime.MAX
• Stick to standard zone offsets for global applications
• Stick to using Instant for applications logged and timestamped across systems

Handling intervals like a boss

To ace your period management game, go with the Interval class:

import java.time.*;
import java.time.temporal.ChronoUnit;

Instant startInstant = LocalDate.now().atStartOfDay().toInstant(ZoneOffset.UTC);
Instant endInstant = LocalDate.now().plusDays(1).atStartOfDay().minusNanos(1).toInstant(ZoneOffset.UTC);

Duration dayDuration = Duration.between(startInstant, endInstant); // Oh, the times we've shared!
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Checking if a date falls within a certain period

Determine if a specific date is within certain bounds as shown below:

boolean isWithinToday = !date.isBefore(startOfDay) && date.isBefore(endOfDay.plusSeconds(1));
// "Is it today yet?" -me, every Monday morning
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