查找今天日期之前和之后的日期

分类：编程问答

如何解决查找今天日期之前和之后的日期

我已经创建了一个财务应用程序，并且希望该应用程序向用户显示财务月份。财务月通常代表用户获得薪水或最高收入的日子。那天可能是一个月的第一天，该月的最后一天，或者仅仅是每个月的15号。 该值可以在设置中配置。

我尝试运行在ViewModel中调用的两个方法getFirstDayOfMonth和getLastDayOfMonth

为了更好地理解上下文，这里有一些示例，我们将以今天的日期作为参考。 2020年9月9日。“输入值”是我从设置中读取的值（用户可以从中选择），它是1到31之间的一个数字。

示例：输入：5输出：2020年9月5日开始于00：00，2020年10月4日在结束23:59:59

================

输入：31输出：2020年8月31日开始00:00和2020年9月30日23:59:59

要注意的是，如果月份中没有该天，它将获得最左侧的日期，例如，如果选择第一天为31，并且该月份有30天，则将计算30天。第一天，也包括结束日期，如果选择了31天并且我们在2月，并且只有28天，那么将会选择28天。

直到现在我有了这段代码，但是我认为它可以改进，并且无法按预期工作。

fun getFirstDayOfMonth(date: LocalDateTime): Long {
    var tempDate = date
    val firstDayOfMonth = lastDay?.filter { it.isDigit() }!!.toInt()

    if (firstDayOfMonth < tempDate.dayOfMonth) {
        tempDate = tempDate.withDayOfMonth(firstDayOfMonth)
    } else if (firstDayOfMonth > tempDate.dayOfMonth) {
        tempDate = tempDate.minusMonths(1)
        if (tempDate.monthValue == 12) {
//I don't know why minusMonths does not work in the same way as plusMonths,when I write .plusMonths(1) it also change the year if I am in december,with minusMonths if I am in January it does not change the year to minus one year.
            tempDate = tempDate.minusYears(1)
        }

        if (firstDayOfMonth > tempDate.with(TemporalAdjusters.lastDayOfMonth()).dayOfMonth) {
            tempDate.withDayOfMonth(tempDate.with(TemporalAdjusters.lastDayOfMonth()).dayOfMonth)
        } else {
            tempDate = tempDate.withDayOfMonth(firstDayOfMonth)
        }
    }

    return tempDate.atZone(ZoneId.systemDefault()).toInstant().toEpochMilli()
}

fun getLastDayOfMonth(date: LocalDateTime): Long {
    var tempDate = date
    val firstDayOfMonth = lastDay?.filter { it.isDigit() }!!.toInt()

    if (firstDayOfMonth > tempDate.dayOfMonth && firstDayOfMonth <= tempDate.with(
            TemporalAdjusters.lastDayOfMonth()
        ).dayOfMonth
    ) {
        tempDate = tempDate.withDayOfMonth(firstDayOfMonth).minusDays(1)
    } else {
        tempDate = tempDate.plusMonths(1)
        if (firstDayOfMonth > tempDate.with(TemporalAdjusters.lastDayOfMonth()).dayOfMonth) {
            tempDate.withDayOfMonth(tempDate.with(TemporalAdjusters.lastDayOfMonth()).dayOfMonth)
        } else {
            tempDate = tempDate.withDayOfMonth(firstDayOfMonth).minusDays(1)
        }
    }

    return tempDate.atZone(ZoneId.systemDefault()).toInstant().toEpochMilli()
}

作为一个例子，我编写了一个测试，该测试运行今天的日期，只将月份从1月更改为12月。这是当前算法的输出。 每月的第一天是用户选择的日期，该日期也在应用程序中默认设置。

Todays date 09.01.2020
Running for month January
Running for 1 st of the month
01.01.2020
31.01.2020
===========================================
Todays date 09.02.2020
Running for month February
Running for 1 st of the month
01.02.2020
29.02.2020
===========================================
Todays date 09.03.2020
Running for month March
Running for 1 st of the month
01.03.2020
31.03.2020
===========================================
Todays date 09.04.2020
Running for month April
Running for 1 st of the month
01.04.2020
30.04.2020
===========================================
Todays date 09.05.2020
Running for month May
Running for 1 st of the month
01.05.2020
31.05.2020
===========================================
Todays date 09.06.2020
Running for month June
Running for 1 st of the month
01.06.2020
30.06.2020
===========================================
Todays date 09.07.2020
Running for month July
Running for 1 st of the month
01.07.2020
31.07.2020
===========================================
Todays date 09.08.2020
Running for month August
Running for 1 st of the month
01.08.2020
31.08.2020
===========================================
Todays date 09.09.2020
Running for month September
Running for 1 st of the month
01.09.2020
30.09.2020
===========================================
Todays date 09.10.2020
Running for month October
Running for 1 st of the month
01.10.2020
31.10.2020
===========================================
Todays date 09.11.2020
Running for month November
Running for 1 st of the month
01.11.2020
30.11.2020
===========================================
Todays date 09.12.2020
Running for month December
Running for 1 st of the month
01.12.2020
31.12.2021
===========================================

Process finished with exit code 0

也选择了31个

Todays date 09.01.2020
Running for month January
Running for 31 th of the month
31.12.2019
30.01.2020
===========================================
Todays date 09.02.2020
Running for month February
Running for 31 th of the month
31.01.2020
30.03.2020
===========================================
Todays date 09.03.2020
Running for month March
Running for 31 th of the month
09.02.2020
30.03.2020
===========================================
Todays date 09.04.2020
Running for month April
Running for 31 th of the month
31.03.2020
30.05.2020
===========================================
Todays date 09.05.2020
Running for month May
Running for 31 th of the month
09.04.2020
30.05.2020
===========================================
Todays date 09.06.2020
Running for month June
Running for 31 th of the month
31.05.2020
30.07.2020
===========================================
Todays date 09.07.2020
Running for month July
Running for 31 th of the month
09.06.2020
30.07.2020
===========================================
Todays date 09.08.2020
Running for month August
Running for 31 th of the month
31.07.2020
30.08.2020
===========================================
Todays date 09.09.2020
Running for month September
Running for 31 th of the month
31.08.2020
30.10.2020
===========================================
Todays date 09.10.2020
Running for month October
Running for 31 th of the month
09.09.2020
30.10.2020
===========================================
Todays date 09.11.2020
Running for month November
Running for 31 th of the month
31.10.2020
30.12.2021
===========================================
Todays date 09.12.2020
Running for month December
Running for 31 th of the month
09.11.2020
30.12.2021
===========================================

Process finished with exit code 0

解决方法

您的计算中有一些错误，一旦您理解了以下给出的解决方案，就可以很容易地发现它们。我在代码中添加了足够的注释，可以帮助您快速理解。

import java.time.Instant;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.Month;
import java.time.YearMonth;
import java.time.ZoneOffset;
import java.time.temporal.ChronoUnit;
import java.time.temporal.TemporalAdjusters;

public class Main {
    public static void main(String[] args) {
        // Test for 31
        int startDay = 31;

        System.out.println(Instant.ofEpochMilli(getFirstDayOfMonth(startDay,YearMonth.of(2020,Month.SEPTEMBER))));
        System.out.println(Instant.ofEpochMilli(getLastDayOfMonth(startDay,Month.SEPTEMBER))));
        
        System.out.println(Instant.ofEpochMilli(getFirstDayOfMonth(startDay,Month.FEBRUARY))));
        System.out.println(Instant.ofEpochMilli(getLastDayOfMonth(startDay,Month.FEBRUARY))));
        
        // Test for 30
        startDay = 30;
        System.out.println();
        System.out.println(Instant.ofEpochMilli(getFirstDayOfMonth(startDay,Month.FEBRUARY))));
                
        // Test for 28
        startDay = 28;
        System.out.println();
        System.out.println(Instant.ofEpochMilli(getFirstDayOfMonth(startDay,Month.FEBRUARY))));
    }

    static long getFirstDayOfMonth(int startDay,YearMonth ym) {
        // Get last day of the month
        int lastDayOfTheMonth = ym.getMonth().length(ym.isLeapYear());

        // Start of the day and on the first day of the month
        LocalDateTime ldt = LocalDate.of(ym.getYear(),ym.getMonth(),1)
                            .atStartOfDay();

        if (startDay > lastDayOfTheMonth) {
            ldt = ldt.minusMonths(1) // Go back to the last month
                    .with(TemporalAdjusters.lastDayOfMonth()); // Adjust to the last day of the obtained month
        }
        return ldt.toInstant(ZoneOffset.UTC).toEpochMilli();
    }

    static long getLastDayOfMonth(int startDay,YearMonth ym) {
        return Instant.ofEpochMilli(getFirstDayOfMonth(startDay,ym))// Get the point to start with
                .plus(ym.getMonth().length(ym.isLeapYear()),ChronoUnit.DAYS)// Add the no. of days of the given month
                .atOffset(ZoneOffset.UTC)// Get OffsetDateTime in order to get LocalDate
                .toLocalDate()// Convert to LocalDate
                .atTime(LocalTime.of(23,59,59))// At 23:59:59
                .toInstant(ZoneOffset.UTC)// Convert to Instant
                .toEpochMilli();
    }
}

输出： 

2020-08-31T00:00:00Z
2020-09-30T23:59:59Z
2020-01-31T00:00:00Z
2020-02-29T23:59:59Z

2020-09-01T00:00:00Z
2020-10-01T23:59:59Z
2020-01-31T00:00:00Z
2020-02-29T23:59:59Z

2020-09-01T00:00:00Z
2020-10-01T23:59:59Z
2020-02-01T00:00:00Z
2020-03-01T23:59:59Z
,

该LocalDateTime类似乎具有您需要内置的所有功能。检查minusDays和plusDays方法。

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