Java 8 – TemporalAdjusters

Learn to use Java 8 TemporalAdjusters where we want to deal with recurring dates such as processing weekly reports, sending automated monthly report outs, etc.

1. TemporalAdjuster interface

The TemporalAdjuster interface and the TemporalAdjusters factory class provide many useful inbuilt adjusters for handling recurring events. The names of most of these tell you directly what they do.

If there are any specific business requirements not solved by provided adjusters, we can build our own custom TemporalAdjuster.

We can apply then to any temporal object with the with() method of that date/time object.

For example, in a team, there is always a weekly meeting every Monday. We want to get the list of dates for the next 5 meetings.

import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.temporal.TemporalAdjusters;
import java.util.ArrayList;
import java.util.List;

public class TemporalAdjusterExamples 
{
	public static void main(String[] args) 
	{
		LocalDate localDate = LocalDate.of(2020, 5, 9);
		
		List<LocalDate> meetingDates = getWeeklyMeetingDates(localDate, 5);
		System.out.println(meetingDates);
	}
	
	private static List<LocalDate> 
			getWeeklyMeetingDates(LocalDate localDate, int count) 
	{
		List<LocalDate> dates = new ArrayList<>();
		for(int i = 0; i < count; i++)
		{
			localDate = localDate
				.with(TemporalAdjusters.next(DayOfWeek.MONDAY));
			dates.add(localDate);
		}
	    return dates;
	}
}

Program output.

[2020-05-11, 
2020-05-18, 
2020-05-25, 
2020-06-01, 
2020-06-08]

2. Builtin Adjusters

This is the list of defualt provided adjusters for easy use. Visit official Java Doc for detailed information.

3. Creating Custom TemporalAdjuster

Create a custom adjuster which can be used to get recurring dates adjusted to some business logic. It can be done in two ways:

• Implement TemporalAdjuster interface
• Inline Lambda expression

  >

  //Custom temporal adjuster with lambda
  TemporalAdjuster temporalAdjuster = t -> t.plus(Period.ofDays(7));
  
  
  //Custom temporal adjuster with TemporalAdjuster interface
  class NextBirthDay implements TemporalAdjuster 
  {
      @Override
      public Temporal adjustInto(Temporal temporal) 
      {
          return temporal.with(ChronoField.MONTH_OF_YEAR, 11)
          				.with(ChronoField.DAY_OF_MONTH, 22);
      }
  }
  

  Drop me your questions and suggestions related using Java 8 TemporalAdjuster for date manipulation in comments.

  Happy Learning !!

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