如何在Java中获取两个日期之间的月份列表

Question

我试图获取 Java 中两个日期之间的月份列表（实际上是这些月份的第一天），但我没有得到预期的结果。

开始日期为“3/17/2020”，结束日期为“3/17/2021”，预期结果如下：

"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码：

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);
       }
   }
}

通过上面的代码我得到以下结果：

"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"

请帮助我理解这个问题并提出与 java 7 相同的解决方案。

Answer 1

我建议您使用现代 java.time日期时间 API 和相应的格式化 API（包，java.time.format）来完成此操作。从Trail: Date Time中了解有关现代日期时间 API 的更多信息。日期java.util时间 APISimpleDateFormat已经过时且容易出错。如果您不使用 Java-8，您仍然可以通过ThreeTenABP库使用 Java-8 日期时间 API。

如果您在 Android 中执行此操作，并且您的 Android API 级别仍然不符合 Java8，请通过 desugaring 检查可用的 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());
    }
}

输出：

[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]

使用旧版 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;
    }
}

输出：

[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]