Java Obtenga todos los días hábiles en un año en formato AAAAMMDD

Mi desafío del domingo es obtener y persistir días hábiles en un año en particular en un archivo CSV, etc.

Tengo el siguiente código y el problema al que me enfrento es: cómo imprimir fechas en un formato específico, es decir, AAAAMMDD, ya que el código actualmente imprime algo como Sábado 19 de enero 00:00:00 CET 2019.

Además, si puedo excluir los fines de semana y, en general, si hay una mejor manera de escribir un código mucho más corto en Java 8.

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;
    }
}

Aquí hay 2 tomas ligeramente diferentes de su problema:

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());
    }
}

Como es 2020, realmente debería estar adoptando la java.time.*API.

Si bien estoy seguro de que probablemente haya una forma realmente ordenada de obtener los días "laborables" entre fechas, he optado por el método de fuerza bruta ...

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);
}

Luego, simplemente puede usar a DateTimeFormatterpara formatear el LocalDateformato que desee, por ejemplo ...

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);

Una forma lúcida de mostrar todos los días de la semana en un rango de fechas utilizando Java 8 y la API moderna de fecha y hora es la siguiente:

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());
    }
}

Salida:

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());
}

}

prueba esto:

// Usando Java 8

 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);