Java 8 LocalDate - How do I get all dates between

问题:

Is there a usablility to get all dates between two dates in the new java.time API?

Let's say I have this part of code:

@Test
public void testGenerateChartCalendarData() {
    LocalDate startDate = LocalDate.now();

    LocalDate endDate = startDate.plusMonths(1);
    endDate = endDate.withDayOfMonth(endDate.lengthOfMonth());
}

Now I need all dates between startDate and endDate.

I was thinking to get the daysBetween of the two dates and iterate over:

long daysBetween = ChronoUnit.DAYS.between(startDate, endDate);

for(int i = 0; i <= daysBetween; i++){
    startDate.plusDays(i); //...do the stuff with the new date...
}

Is there a better way to get the dates?

回答1:

Assuming you mainly want to iterate over the date range, it would make sense to create a DateRange class that is iterable. That would allow you to write:

for (LocalDate d : DateRange.between(startDate, endDate)) ...

Something like:

public class DateRange implements Iterable<LocalDate> {

  private final LocalDate startDate;
  private final LocalDate endDate;

  public DateRange(LocalDate startDate, LocalDate endDate) {
    //check that range is valid (null, start < end)
    this.startDate = startDate;
    this.endDate = endDate;
  }

  @Override
  public Iterator<LocalDate> iterator() {
    return stream().iterator();
  }

  public Stream<LocalDate> stream() {
    return Stream.iterate(startDate, d -> d.plusDays(1))
                 .limit(ChronoUnit.DAYS.between(startDate, endDate) + 1);
  }

  public List<LocalDate> toList() { //could also be built from the stream() method
    List<LocalDate> dates = new ArrayList<> ();
    for (LocalDate d = startDate; !d.isAfter(endDate); d = d.plusDays(1)) {
      dates.add(d);
    }
    return dates;
  }
}

It would make sense to add equals & hashcode methods, getters, maybe have a static factory + private constructor to match the coding style of the Java time API etc.

回答2:

First you can use a TemporalAdjuster to get the last day of the month. Next the Stream API offers Stream::iterate which is the right tool for your problem.

LocalDate start = LocalDate.now();
LocalDate end = LocalDate.now().plusMonths(1).with(TemporalAdjusters.lastDayOfMonth());
List<LocalDate> dates = Stream.iterate(start, date -> date.plusDays(1))
    .limit(ChronoUnit.DAYS.between(start, end))
    .collect(Collectors.toList());
System.out.println(dates.size());
System.out.println(dates);

回答3:

Java 9

In Java 9, the LocalDate class was enhanced with the LocalDate.datesUntil(LocalDate endExclusive) method, which returns all dates within a range of dates as a Stream<LocalDate>.

List<LocalDate> dates = startDate.datesUntil(endDate).collect(Collectors.toList());

回答4:

You can use the .isAfter and .plusDays to do this over a loop. I would not say better as I haven't done a huge amount of research into the topic but I can confidently say it uses the Java 8 API and is a slight alternative.

LocalDate startDate = LocalDate.now();
LocalDate endDate = startDate.plusMonths(1);
while (!startDate.isAfter(endDate)) {
 System.out.println(startDate);
 startDate = startDate.plusDays(1);
}

Output

2016-07-05
2016-07-06
...
2016-08-04
2016-08-05

Example Here

回答5:

You could create a stream of LocalDate objects. I had this problem too and I published my solution as java-timestream on github.

Using your example...

LocalDateStream
    .from(LocalDate.now())
    .to(1, ChronoUnit.MONTHS)
    .stream()
    .collect(Collectors.toList());

It's more or less equivalent to other solutions proposed here, but it takes care of all of the date math and knowing when to stop. You can provide specific or relative end dates, and tell it how much time to skip each iteration (the default above is one day).

回答6:

The ThreeTen-Extra library has a LocalDateRange class that can do exactly what you're requesting:

LocalDateRange.ofClosed(startDate, endDate).stream()
        .forEach(/* ...do the stuff with the new date... */);

回答7:

In my time library Time4J, I have written an optimized spliterator to construct a stream of calendar dates with good parallelization characteristics. Adapted to your use-case:

LocalDate start = ...;
LocalDate end = ...;

Stream<LocalDate> stream = 
  DateInterval.between(start, end) // closed interval, else use .withOpenEnd()
    .streamDaily()
    .map(PlainDate::toTemporalAccessor);

This short approach can be an interesting start point if you are also interested in related features like clock intervals per calendar date (partitioned streams) or other interval features and want to avoid awkward hand-written code, see also the API of DateInterval.

回答8:

tl;dr

Expanding on the good Answer by Singh, using a stream from datesUntil in Java 9 and later.

today                                 // Determine your beginning `LocalDate` object.
.datesUntil(                          // Generate stream of `LocalDate` objects.
    today.plusMonths( 1 )             // Calculate your ending date, and ask for a stream of dates till then.
)                                     // Returns the stream.
.collect( Collectors.toList() )       // Collect your resulting dates in a `List`. 
.toString()                           // Generate text representing your found dates.

[2018-09-20, 2018-09-21, 2018-09-22, 2018-09-23, 2018-09-24, 2018-09-25, 2018-09-26, 2018-09-27, 2018-09-28, 2018-09-29, 2018-09-30, 2018-10-01, 2018-10-02, 2018-10-03, 2018-10-04, 2018-10-05, 2018-10-06, 2018-10-07, 2018-10-08, 2018-10-09, 2018-10-10, 2018-10-11, 2018-10-12, 2018-10-13, 2018-10-14, 2018-10-15, 2018-10-16, 2018-10-17, 2018-10-18, 2018-10-19]

LocalDate::datesUntil stream

As of Java 9, you can ask for a stream of dates. Call LocalDate::datesUntil.

Start by determining today's date. That requires a time zone. For any given moment, the date varies around the globe by zone.

ZoneId z = ZoneId.of( "Pacific/Auckland" ) ;
LocalDate today = LocalDate.now( z ) ;

Determine your ending date.

LocalDate stop = today.plusMonths( 1 ) ;

Ask for stream of dates from beginning to ending.

Stream< LocalDate > stream = today.datesUntil( today.plusMonths( 1 ) );

Pull the dates from that stream, collecting them into a List.

List< LocalDate > datesForMonthFromToday = stream.collect( Collectors.toList() );

Print our list of dates, generating text in standard ISO 8601 format.

System.out.println( datesForMonthFromToday );

---

About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.

The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.

To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.

You may exchange java.time objects directly with your database. Use a JDBC driver compliant with JDBC 4.2 or later. No need for strings, no need for java.sql.* classes.

Where to obtain the java.time classes?

• Java SE 8, Java SE 9, Java SE 10, Java SE 11, and later - Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and Java SE 7
  • Most of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
• Android
  • Later versions of Android bundle implementations of the java.time classes.
  • For earlier Android (<26), the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). See How to use ThreeTenABP….

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.

回答9:

You could use the Range functionality in Google's Guava library. After defining the DiscreteDomain over LocalDate instances you could get a ContiguousSet of all dates in the range.

LocalDate d1 = LocalDate.parse("2017-12-25");
LocalDate d2 = LocalDate.parse("2018-01-05");

DiscreteDomain<LocalDate> localDateDomain = new DiscreteDomain<LocalDate>() {
    public LocalDate next(LocalDate value) { return value.plusDays(1); }
    public LocalDate previous(LocalDate value) { return value.minusDays(1); }
    public long distance(LocalDate start, LocalDate end) { return start.until(end, ChronoUnit.DAYS); }
    public LocalDate minValue() { return LocalDate.MIN; }
    public LocalDate maxValue() { return LocalDate.MAX; }
};

Set<LocalDate> datesInRange = ContiguousSet.create(Range.closed(d1, d2), localDateDomain);