Java:如何在相应的一周内对所有Java日期进行分组？

Question

问题:

我有很多日期,我需要按周安排.

问题: 如何按日期的一周对日期进行分组？

示例数据集

Date date = new SimpleDateFormat.parse("04/01/2015")
Date date = new SimpleDateFormat.parse("04/02/2015")
Date date = new SimpleDateFormat.parse("04/03/2015")
Date date = new SimpleDateFormat.parse("04/04/2015")
Date date = new SimpleDateFormat.parse("04/05/2015")
Date date = new SimpleDateFormat.parse("04/06/2015")
Date date = new SimpleDateFormat.parse("04/07/2015")
Date date = new SimpleDateFormat.parse("04/08/2015")
Date date = new SimpleDateFormat.parse("04/09/2015")

期望的输出

HashMap<Date, Date> hashMap = groupByWeek(ArrayList<Date> dates);

printWeeklyGroupedDates();

Week 1:
04/01/2015
04/02/2015
04/03/2015
04/04/2015
04/05/2015
04/06/2015
04/07/2015
Week 2:
04/08/2015
04/09/2015

我试过的

public Date getWhichYearlyWeek(Date date){

  Calendar cal = Calendar.getInstance();
  cal.setTime(date);
  cal.get(Calendear.WEEK_OF_YEAR);

  //Need to return this as 'Date' but indicate which week this is for the TreeMap functionality below          

  return cal.getTime();
}


public TreeMap<Date, ArrayList<Date>> getWeeklyMappedDates(ArrayList<Date> dateArray){

  TreeMap<Date, ArrayList<Date>> treeMap = new TreeMap<Date, ArrayList<Date>>

  for(Date i : dateArray){

    Date date = getWhichYearlyWeek(date);

    if(!treeMap.containsKey(date))
      treeMap.get(date).add(date);
    else
      treeMap.put(date, new ArrayList<Date>());
  }

  return treeMap;
}

Answer 1

如果Java 8可用:

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("MM/dd/yyyy");
TemporalField weekOfYear = WeekFields.of(Locale.getDefault()).weekOfYear();

Stream.of(
      "04/01/2015"
    , "04/02/2015"
    , "04/03/2015"
    , "04/04/2015"
    , "04/05/2015"
    , "04/06/2015"
    , "04/07/2015"
    , "04/08/2015"
    , "04/09/2015"
)
.collect(Collectors.groupingBy(
    d -> LocalDate.parse(d, formatter).get(weekOfYear),
    LinkedHashMap::new,
    Collectors.toList()
))
.forEach((week, dates) -> {
    System.out.println("Week " + week + ":");

    dates.forEach(System.out::println);
});

打印(使用de_CH我的计算机上的区域设置)

Week 14:
04/01/2015
04/02/2015
04/03/2015
04/04/2015
04/05/2015
Week 15:
04/06/2015
04/07/2015
04/08/2015
04/09/2015

Answer 2

您可以简单地使用自定义List对Dates 进行排序Comparator。下面的示例按年份和日期对日期进行排序，不知道您是否想要第二部分，但这是一个很好的演示......

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Calendar;
import java.util.Collections;
import java.util.Comparator;
import java.util.Date;
import java.util.List;

public class Test {

    public static void main(String[] args) {
        try {
            SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");
            List<Date> dates = new ArrayList<Date>(25);
            dates.add(sdf.parse("04/01/2015"));
            dates.add(sdf.parse("04/02/2015"));
            dates.add(sdf.parse("04/03/2015"));
            dates.add(sdf.parse("04/04/2015"));
            dates.add(sdf.parse("04/05/2015"));
            dates.add(sdf.parse("04/06/2015"));
            dates.add(sdf.parse("04/07/2015"));
            dates.add(sdf.parse("04/08/2015"));
            dates.add(sdf.parse("04/09/2015"));

            int week = 0;
            int woy = -1;
            Collections.sort(dates, new WeekComparator());
            for (Date date : dates) {
                if (woy != getWeekOfYear(date)) {
                    woy = getWeekOfYear(date);
                    week++;
                    System.out.println("Week " + week + ":");
                }
                System.out.println(date);
            }

        } catch (ParseException exp) {
            exp.printStackTrace();
        }
    }

    public static class WeekComparator implements Comparator<Date> {

        @Override
        public int compare(Date o1, Date o2) {
            int result = getWeekOfYear(o1) - getWeekOfYear(o2);
            if (result == 0) {
                result = o1.compareTo(o2);
            }
            return result;
        }

    }

    protected static int getWeekOfYear(Date date) {
        Calendar cal = Calendar.getInstance();
        cal.setTime(date);
        return cal.get(Calendar.WEEK_OF_YEAR);
    }

}

哪些输出

Week 1:
Wed Apr 01 00:00:00 EST 2015
Thu Apr 02 00:00:00 EST 2015
Fri Apr 03 00:00:00 EST 2015
Sat Apr 04 00:00:00 EST 2015
Week 2:
Sun Apr 05 00:00:00 EST 2015
Mon Apr 06 00:00:00 EST 2015
Tue Apr 07 00:00:00 EST 2015
Wed Apr 08 00:00:00 EST 2015
Thu Apr 09 00:00:00 EST 2015

Java 8 时间 API

只是因为我需要练习...

import java.text.SimpleDateFormat;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.time.temporal.WeekFields;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Locale;

public class Test {

    public static void main(String[] args) {
        SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("MM/dd/yyyy");

        List<LocalDate> dates = new ArrayList<LocalDate>(25);
        dates.add(LocalDate.parse("04/01/2015", dtf));
        dates.add(LocalDate.parse("04/02/2015", dtf));
        dates.add(LocalDate.parse("04/03/2015", dtf));
        dates.add(LocalDate.parse("04/04/2015", dtf));
        dates.add(LocalDate.parse("04/05/2015", dtf));
        dates.add(LocalDate.parse("04/06/2015", dtf));
        dates.add(LocalDate.parse("04/07/2015", dtf));
        dates.add(LocalDate.parse("04/08/2015", dtf));
        dates.add(LocalDate.parse("04/09/2015", dtf));

        int week = 0;
        int woy = -1;
        Collections.sort(dates, new WeekComparator());
        for (LocalDate date : dates) {
            if (woy != getWeekOfYear(date)) {
                woy = getWeekOfYear(date);
                week++;
                System.out.println("Week " + week + ":");
            }
            System.out.println(date);
        }
    }

    public static class WeekComparator implements Comparator<LocalDate> {

        @Override
        public int compare(LocalDate o1, LocalDate o2) {
            int result = getWeekOfYear(o1) - getWeekOfYear(o2);
            if (result == 0) {
                result = o1.compareTo(o2);
            }
            return result;
        }

    }

    protected static int getWeekOfYear(LocalDate date) {
        WeekFields wf = WeekFields.of(Locale.getDefault());
        return date.get(wf.weekOfYear());
    }

}

哪些输出

Week 1:
2015-04-01
2015-04-02
2015-04-03
2015-04-04
Week 2:
2015-04-05
2015-04-06
2015-04-07
2015-04-08
2015-04-09

在任何一种情况下，您都可以将每个日期映射到Map按周键控的日期中，但这取决于您