如何在Java中獲取兩個日期之間的月份列表

Question

我試圖在 Java 中獲取兩個日期之間的月份列表（實際上是這些月份的第一天），但我沒有得到預期的結果。

開始日期為“3/17/2020”，結束日期為“3/17/2021”，預期結果如下：

"01-Mar-2020"
"01-Apr-2020"
"01-May-2020"
"01-Jun-2020"
"01-Jul-2020"
"01-Aug-2020"
"01-Sep-2020"
"01-Oct-2020"
"01-Nov-2020"
"01-Dec-2020"
"01-Jan-2021"
"01-Feb-2021"
"01-Mar-2021"

下面是我正在使用的代碼：

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;

public class Main {
   public static void main(String[] args) {
       String date1 = "3/17/2020";
       String date2 = "3/17/2021";

    DateFormat formater = new SimpleDateFormat("MM/dd/yyyy");

    Calendar beginCalendar = Calendar.getInstance();
    Calendar finishCalendar = Calendar.getInstance();

    try {
        beginCalendar.setTime(formater.parse(date1));
        finishCalendar.setTime(formater.parse(date2));
    } catch (ParseException e) {
        e.printStackTrace();
    }
  DateFormat formaterYd = new SimpleDateFormat("01-MMM-YYYY");


    while (beginCalendar.before(finishCalendar)) {
        // add one month to date per loop
        String date =    formaterYd.format(beginCalendar.getTime()).toUpperCase();
        System.out.println(date);
        beginCalendar.add(Calendar.MONTH, 1);
       }
   }
}

使用上面的代碼，我得到以下結果：

"01-Jan-2020"
"01-Feb-2020"
"01-Mar-2020"
"01-Apr-2020"
"01-May-2020"
"01-Jun-2020"
"01-Jul-2020"
"01-Aug-2020"
"01-Sep-2020"
"01-Oct-2020"
"01-Nov-2020"
"01-Dec-2020"

請幫助我理解這個問題，並建議任何與 java 7 相同的解決方案。

Answer 1

我建議您使用現代java.time日期時間 API 和相應的格式化 API（包， java.time.format ）來執行此操作。 從Trail: Date Time 中了解有關現代日期時間 API 的更多信息。 java.util日期時間 API 和SimpleDateFormat已過時且容易出錯。 如果您沒有使用 Java-8，您仍然可以通過ThreeTenABP庫使用 Java-8 日期時間 API。

如果您在 Android 中執行此操作並且您的 Android API 級別仍然不符合 Java8，請檢查 通過 desugaring 可用的 Java 8+ API 。

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) {
        // Test
        System.out.println(getDateList("3/17/2020",  "3/17/2021"));
    }

    static List<String> getDateList(String strStartDate, String strEndDate) {
        // Formatter for the input
        DateTimeFormatter inputFormatter = DateTimeFormatter.ofPattern("M/d/u");
        
        // Formatter for the output
        DateTimeFormatter outputFormatter = DateTimeFormatter.ofPattern("dd-MMM-uuuu");

        // Parse strings to LocalDate instances
        LocalDate startDate = LocalDate.parse(strStartDate, inputFormatter);
        LocalDate endDate = LocalDate.parse(strEndDate, inputFormatter);

        return Stream.iterate(startDate.withDayOfMonth(1), date -> date.plusMonths(1))
                .limit(ChronoUnit.MONTHS.between(startDate, endDate.plusMonths(1)))
                .map(date -> date.format(outputFormatter))
                .collect(Collectors.toList());
    }
}

輸出：

[01-Mar-2020, 01-Apr-2020, 01-May-2020, 01-Jun-2020, 01-Jul-2020, 01-Aug-2020, 01-Sep-2020, 01-Oct-2020, 01-Nov-2020, 01-Dec-2020, 01-Jan-2021, 01-Feb-2021, 01-Mar-2021]

使用舊版 API：

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

public class Main {
    public static void main(String[] args) throws ParseException {
        // Test
        System.out.println(getDateList("3/17/2020", "3/17/2021"));
    }

    static List<String> getDateList(String strStartDate, String strEndDate) throws ParseException {
        // List to be populated and returned
        List<String> dateList = new ArrayList<>();

        // Formatter for the input
        DateFormat inputFormatter = new SimpleDateFormat("M/d/yyyy");

        // Formatter for the output
        DateFormat outputFormatter = new SimpleDateFormat("dd-MMM-yyyy");

        // Parse strings to LocalDate instances
        Date startDate = inputFormatter.parse(strStartDate);
        Date endDate = inputFormatter.parse(strEndDate);

        // Calendar to start with
        Calendar startWith = Calendar.getInstance();
        startWith.setTime(startDate);
        startWith.set(Calendar.DAY_OF_MONTH, 1);

        for (Calendar calendar = startWith; calendar.getTime().getTime() <= endDate.getTime(); calendar
                .add(Calendar.MONTH, 1)) {
            dateList.add(outputFormatter.format(calendar.getTime()));
        }

        return dateList;
    }
}

輸出：

[01-Mar-2020, 01-Apr-2020, 01-May-2020, 01-Jun-2020, 01-Jul-2020, 01-Aug-2020, 01-Sep-2020, 01-Oct-2020, 01-Nov-2020, 01-Dec-2020, 01-Jan-2021, 01-Feb-2021, 01-Mar-2021]

Answer 2

使用java.time.LocalDate ：

public static List<LocalDate> diff(LocalDate start, LocalDate end) {
    return start
            .datesUntil(end)
            .filter(e -> e.getDayOfMonth() == 1)
            .collect(Collectors.toList());
}

diff(LocalDate.now(), LocalDate.of(2020, 12, 20))

輸出：

[2020-10-01, 2020-11-01, 2020-12-01]

您可以使用DateTimeFormatter字符串日期到LocalDate ，反之亦然。

編輯
僅使用 java 7（修改了有問題的給定代碼）：

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


    String date1 = "3/17/2020";
    String date2 = "3/17/2021";

    DateFormat formater = new SimpleDateFormat("MM/dd/yyyy");

    Calendar beginCalendar = Calendar.getInstance();
    Calendar finishCalendar = Calendar.getInstance();

    try {
        beginCalendar.setTime(formater.parse(date1));
        finishCalendar.setTime(formater.parse(date2));
    } catch (ParseException e) {
        e.printStackTrace();
    }
    DateFormat formaterYd = new SimpleDateFormat("dd-MMM-YYYY");
    

    // mind this condition in while
    while (beginCalendar.compareTo(finishCalendar) <= 0) {
        Calendar tmp = (Calendar)beginCalendar.clone();
        tmp.set(Calendar.DAY_OF_MONTH, 1);
        String date = formaterYd.format(tmp.getTime()).toUpperCase();
        System.out.println(date);
        beginCalendar.add(Calendar.MONTH, 1);
    }
}

Answer 3

Java7解決方案：

public static void main(String[] args) throws ParseException {
    DateFormat df1 = new SimpleDateFormat("MM/dd/yyyy", Locale.US);
    Date dateFrom = df1.parse("3/17/2020");
    Date dateTo = df1.parse("3/17/2021");
    final Locale locale = Locale.US;

    DateFormat df2 = new SimpleDateFormat("MMM-yyyy", Locale.US);
    List<String> months = getListMonths(dateFrom, dateTo, locale, df2);

    for (String month : months)
        System.out.println(month.toUpperCase(locale));
}

public static List<String> getListMonths(Date dateFrom, Date dateTo, Locale locale, DateFormat df) {
    Calendar calendar = Calendar.getInstance(locale);
    calendar.setTime(dateFrom);

    List<String> months = new ArrayList<>();

    while (calendar.getTime().getTime() <= dateTo.getTime()) {
        months.add(df.format(calendar.getTime()));
        calendar.add(Calendar.MONTH, 1);
    }

    return months;
}

輸出：

MAR-2020
APR-2020
MAY-2020
JUN-2020
JUL-2020
AUG-2020
SEP-2020
OCT-2020
NOV-2020
DEC-2020
JAN-2021
FEB-2021
MAR-2021