Java 以 YYYYMMDD 格式获取一年中的所有工作日

Question

我周日的挑战是获取特定年份的工作日并将其保存到 CSV 等文件中。

我有以下代码，我面临的问题是:如何以特定格式打印日期，即 YYYYMMDD，因为代码当前打印的内容类似于 Sat Jan 19 00:00:00 CET 2019。

另外，如果我可以排除周末，并且通常是否有更好的方法可以在 Java 8 中编写更短的代码。

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;
    }
}

Answer 1

既然是 2020 年，你真的应该拥抱 java.time.* API。

虽然我确信可能有一种非常巧妙的方法来获得日期之间的“工作日”，但我已经采用了蛮力方法......

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);
}

然后你可以简单地使用 DateTimeFormatter格式化 LocalDate转换成您想要的格式，例如...

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);
}