Java 11 time - is (long)timestamp today

I have a cronjob string saved in a mongo document field. I get the next valid (long)time by

CronExpression exp = new CronExpression(billing.getReminder());
			
long nextReminder = exp.getNextValidTimeAfter(new Date()).getTime();

My idea is to check if this "nextReminder" isToday() then create some task.
What is the best way to check it with java 11?

You could use java.time for a comparison...

There is an Instant representing a moment in time like a timestamp in epoch milliseconds does (⇒ your long nextReminder) as well as OffsetDateTime.now() for the actual moment now and LocalDate as the part describing the date-part only.

You could find out if the nextReminder is today by using a method like this:

/**
 * <p>
 * Checks if the day (or date) of a given timestamp (in epoch milliseconds)
 * is the same as <em>today</em> (the day this method is executed).<br>
 * <strong>Requires an offset in order to have a common base for comparison</strong>
 * </p>
 *
 * @param epochMillis	the timestamp in epoch milliseconds to be checked
 * @param zoneOffset	the offset to be used as base of the comparison
 * @return <code>true</code> if the dates of the parameter and today are equal,
 *         otherwise <code>false</code>
 */
public static boolean isToday(long epochMillis, ZoneOffset zoneOffset) {
	// extract the date part from the parameter with respect to the given offset
	LocalDate datePassed = Instant.ofEpochMilli(epochMillis)
								.atOffset(zoneOffset)
								.toLocalDate();
	// then extract the date part of "now" with respect to the given offset
	LocalDate today = Instant.now()
								.atOffset(zoneOffset)
								.toLocalDate();
	// then return the result of an equality check
	return datePassed.equals(today);
}

and then just call it like

boolean isNextReminderToday = isToday(nextReminder, ZoneOffset.systemDefault());

which would use the time offset of the system. Maybe, ZoneOffset.UTC could be a smart choice, too.

The answer by deHaar is correct. However, I felt to write this one because in this case, using the Zone ID (instead of Zone Offset) makes the code a bit simpler and also easier to understand.

import java.time.Instant;
import java.time.LocalDate;
import java.time.ZoneId;

public class Main {
	public static void main(String[] args) {
		// A test data
		long nextReminder = 1597754387710L;

		// Your time-zone e.g. Europe/London
		ZoneId zoneId = ZoneId.of("Europe/London");

		// Next reminder date
		Instant instant = Instant.ofEpochMilli(nextReminder);
		LocalDate nextReminderDate = instant.atZone(zoneId).toLocalDate();

		// Today at the time-zone of Europe/London
		LocalDate today = LocalDate.now(zoneId);

		if (today.equals(nextReminderDate)) {
			System.out.println("The next reminder day is today");
		}
	}
}

Output:

The next reminder day is today

Using apache commons DateUtils.isToday(nextReminder)

Using your own method.

private static final long MILLIS_PER_DAY = 86400000;

public static boolean isToday(long timestamp) {
   long now =  System.currentTimeMillis();
   long today = now.getTime() / MILLIS_PER_DAY;
   long expectedDay = timestamp / MILLIS_PER_DAY;
   return today == expectedDay;
}

Note: Consider using UTC when working with date/time.