Java – Stream of Dates

Date and Time handling always been a pain area for java developers. The new Date-Time API added in Java 8 changed the way, you interact with dates in java. It was a very powerful and much-needed improvement. The only thing missing was, getting a stream of dates having some common difference between two subsequent dates (though it was possible but there was no easy way).

Java 9 has introduced a new method LocalDate.datesUntil() which can give a stream on dates. Using datesUntil() makes it easy to create dates streams with fixed offset.

1. Syntax of LocalDate.datesUntil()

This method has two overloaded forms:

Stream<LocalDate> datesUntil(LocalDate end)
Stream<LocalDate> datesUntil(LocalDate end, Period step)

The first version (i.e. without a Period) internally calls the second method with Period.ofDays(1) and generates stream of dates with difference of 1 day in between.

Date Stream Example with LocalDate.datesUntil()

Creating a stream of dates is very simple and straightforward.

import java.time.LocalDate;
import java.time.Period;
import java.util.List;
import java.util.stream.Collectors;

public class Java9StreamExamples {

    public static void main(String[] args) {
        System.out.println( getDaysInJava9(LocalDate.now(), LocalDate.now().plusDays(10)) );
        System.out.println( getDaysInJava9Weeks(LocalDate.now(), LocalDate.now().plusWeeks(10)) );
    }
    
    //Stream of dates with 1 day difference
    public static List<LocalDate> getDaysInJava9(LocalDate start, LocalDate end) {
        return start.datesUntil(end).collect(Collectors.toList());
    }
    
    //Stream of dates with 1 week difference
    public static List<LocalDate> getDaysInJava9Weeks(LocalDate start, LocalDate end) {
        return start.datesUntil(end, Period.ofWeeks(1)).collect(Collectors.toList());
    }
}


Output:

[2017-07-31, 2017-08-01, 2017-08-02, 2017-08-03, 2017-08-04, 
2017-08-05, 2017-08-06, 2017-08-07, 2017-08-08, 2017-08-09]

[2017-07-31, 2017-08-07, 2017-08-14, 2017-08-21, 2017-08-28, 
2017-09-04, 2017-09-11, 2017-09-18, 2017-09-25, 2017-10-02]

2. Date Stream in Java 8

If you have still not adapted Java 9, then you can use given below method to generate Date streams. This code is compatible to Java 8.

import java.time.LocalDate;
import java.time.Period;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class Java9StreamExamples {

    public static void main(String[] args) 
    {
        System.out.println( getDaysInJava8(LocalDate.now(), 10) );
    }

    //Stream of dates with 1 day difference
    public static List<LocalDate> getDaysInJava8(LocalDate start, int days) 
    {
        return Stream.iterate(start, date -> date.plusDays(1))
                .limit(days)
                .collect(Collectors.toList());
    }
}

Output:

[2017-07-31, 2017-08-01, 2017-08-02, 2017-08-03, 2017-08-04, 
2017-08-05, 2017-08-06, 2017-08-07, 2017-08-08, 2017-08-09]

Drop me your questions in the comments section.

Happy Learning !!