JavaはYYYYMMDD形式で1年のすべての稼働日を取得します

私の日曜日の課題は、特定の年の稼働日を取得してCSVなどのファイルに保存することです。

次のコードがあり、私が直面している問題は、特定の形式で日付を印刷する方法です。つまり、コードは現在、Sat Jan 19 00:00:00 CET 2019のようなものを印刷するため、YYYYMMDDです。

また、週末を除外できる場合、および一般的にJava 8ではるかに短いコードを記述するより良い方法がある場合。

import java.io.*;
import java.util.*;
import java.text.SimpleDateFormat;

public class DatesInYear
{

    public static SimpleDateFormat dateFormat = new SimpleDateFormat("yyyyMMdd");

    public static void main (String[] args) throws java.lang.Exception
    {

        Date dt = new Date();
        System.out.println(dt);

        List<Date> dates = printDates("20190101","20191231");


        Collections.reverse(dates);
        System.out.println(dates.size());
        for(Date date:dates)
        {
            SimpleDateFormat format1 = new SimpleDateFormat("yyyyMMdd");
            System.out.println(format1.format(date));

        }
    }
    public static List<Date> printDates(String fromDate, String toDate)
    {
        ArrayList<Date> dates = new ArrayList<Date>();

        try {

            Calendar fromCal = Calendar.getInstance();
            fromCal.setTime(dateFormat .parse(fromDate));

            Calendar toCal = Calendar.getInstance();
            toCal.setTime(dateFormat .parse(toDate));

            while(!fromCal.after(toCal))
            {
                dates.add(fromCal.getTime());
                fromCal.add(Calendar.DATE, 1);
            }


        } catch (Exception e) {
            System.out.println(e);
        }
        return dates;
    }
}

あなたの問題に対する2つのわずかに異なるテイクがあります：

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

public class DatesInYear {

    public static void main(final String[] args) throws Exception {

        listWorkingDays(2020).forEach(System.out::println);
    }

    private static List<LocalDate> listWorkingDays(final int year) {

        IntStream
            .rangeClosed(1,      LocalDate.ofYearDay(year + 1, 1).minusDays(1).getDayOfYear())
            .mapToObj   (day  -> LocalDate.ofYearDay(year, day))
            .filter     (date -> date.getDayOfWeek().getValue() <= 5)
            .forEach    (System.out::println);

        return IntStream
            .rangeClosed(1,      LocalDate.ofYearDay(year + 1, 1).minusDays(1).getDayOfYear())
            .mapToObj   (day  -> LocalDate.ofYearDay(year, day))
            .filter     (date -> date.getDayOfWeek().getValue() <= 5)
            .collect    (Collectors.toList());
    }
}

2020年なので、実際にはjava.time.*API を採用する必要があります。

「営業」日を日付に変換する本当にきちんとした方法があると私は確信していますが、私はブルートフォースメソッドに行きました...

LocalDate ld = LocalDate.of(2020, Month.JANUARY, 1);
LocalDate endDate = ld.plusYears(1);

// You don't "have" to put into a list, but I like to seperate my
// code responsbilities ;)
List<LocalDate> workDays = new ArrayList<>(365);
System.out.println(endDate);
while (ld.isBefore(endDate)) {
    // This would be a good place for a delegate to determine if we want the specific day
    // as it could then take into account public holidays
    if (ld.getDayOfWeek() == DayOfWeek.SATURDAY || ld.getDayOfWeek() == DayOfWeek.SUNDAY) {
        // NOOP
    } else {
        workDays.add(ld);
    }
    ld = ld.plusDays(1);
}

次に、単純にa DateTimeFormatterを使用して、を必要な形式にフォーマットできLocalDateます。たとえば...

DateTimeFormatter format = DateTimeFormatter.ofPattern("yyyyMMdd");
List<String> formats = workDays.stream().map(value -> value.format(format)).collect(Collectors.toList());

for (String value : formats) {
    System.out.println(value);
}

    Set<DayOfWeek> weekend = EnumSet.of(DayOfWeek.SATURDAY, DayOfWeek.SUNDAY);
    LocalDate.of(2019, Month.JANUARY, 1)
             .datesUntil(LocalDate.of(2020, Month.DECEMBER, 31), Period.ofDays(1))
             .filter(x -> !weekend.contains(x.getDayOfWeek()))
             .forEachOrdered(System.out::println);

Java 8と最新の日時APIを使用して日付範囲のすべての平日を表示する明快な方法は次のとおりです。

import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.time.temporal.ChronoUnit;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class Main {
    public static void main(String[] args) {
        List<LocalDate> dates = getDates("2019-01-01", "2019-12-31");
        for (LocalDate date : dates) {
            System.out.println(DateTimeFormatter.BASIC_ISO_DATE.format(date));
        }
    }

    public static List<LocalDate> getDates(String fromDate, String toDate) {
        LocalDate startDate = LocalDate.parse(fromDate);
        LocalDate endDate = LocalDate.parse(toDate).plusDays(1);
        long range = ChronoUnit.DAYS.between(startDate, endDate);
        return Stream.iterate(startDate, date -> date.plusDays(1)).limit(range)
                .filter(d -> !(d.getDayOfWeek() == DayOfWeek.SATURDAY || d.getDayOfWeek() == DayOfWeek.SUNDAY))
                .collect(Collectors.toList());
    }
}

出力：

20190101
20190102
20190103
20190104
20190107
20190108
...
...
...
20191226
20191227
20191230
20191231

import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.time.temporal.ChronoUnit;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class Main {
public static void main(String[] args) {
    List<LocalDate> dates = getDates("2019-01-01", "2019-12-31");
    for (LocalDate date : dates) {
        System.out.println(DateTimeFormatter.BASIC_ISO_DATE.format(date));
    }
}

public static List<LocalDate> getDates(String fromDate, String toDate) {
    LocalDate startDate = LocalDate.parse(fromDate);
    LocalDate endDate = LocalDate.parse(toDate).plusDays(1);
    long range = ChronoUnit.DAYS.between(startDate, endDate);
    return Stream.iterate(startDate, date -> date.plusDays(1)).limit(range)
            .filter(d -> !(d.getDayOfWeek() == DayOfWeek.SATURDAY || d.getDayOfWeek() == DayOfWeek.SUNDAY))
            .collect(Collectors.toList());
}

}

これを試して：

// Java 8を使用

 DateTimeFormatter oldPattern = DateTimeFormatter
        .ofPattern("yyyy-MM-dd HH:mm:ss");
    DateTimeFormatter newPattern = DateTimeFormatter.ofPattern("yyyy-MM-dd");

    LocalDateTime datetime = LocalDateTime.parse(input, oldPattern);
    output = datetime.format(newPattern);

    System.out.println("old format date: " + input);
    System.out.println("new format date : " + output);