问题

输入列表：

1. 起始日期 例如) 2020-10-01
2. 终止日期 例如) 2020-10-30
3. 列表 [星期几] 例如) [周日, 周一....]
4. 列表 [周数] 例如) [1, 4, 5]

我想知道如何在两个日期之间获取特定的星期几。
谢谢。

答案1

得分: 1

> from date ex) 2020-10-01 to date ex) 2020-10-30

您提供的输入字符串已经是 ISO8601 日期格式，因此可以在不显式提供 `DateTimeFormatter` 的情况下进行解析。如果要以自定义格式（例如 `yyyy-MM-dd`）获取输出字符串，则需要使用 `DateTimeFormatter` 格式化日期对象。

```java
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;

public class Main {
    public static void main(String[] args) {
        String inputStrDate = "2020-10-01";
        LocalDate date = LocalDate.parse(inputStrDate);

        String outputStrDate = date.format(DateTimeFormatter.ofPattern("yyyy-MM-dd"));
        System.out.println(outputStrDate);
    }
}

输出:

2020-10-01

但是，如果您的输入是其他格式，则需要使用 DateTimeFormatter 将其解析为日期对象。

import java.time.LocalDate;
import java.time.format.DateTimeFormatter;

public class Main {
    public static void main(String[] args) {
        // 输入字符串的格式化程序
        DateTimeFormatter inputFormat = DateTimeFormatter.ofPattern("dd-MM-yyyy");

        String inputStrDate = "10-01-2020";
        LocalDate date = LocalDate.parse(inputStrDate, inputFormat);

        // 输出字符串的格式化程序
        DateTimeFormatter outputFormat = DateTimeFormatter.ofPattern("yyyy-MM-dd");

        String outputStrDate = date.format(outputFormat);
        System.out.println(outputStrDate);
    }
}

输出:

2020-10-01

了解更多有关日期时间 API 的信息，可参阅 Trail: Date Time。

<details>
<summary>英文:</summary>

&gt; from date ex) 2020-10-01 to date ex) 2020-10-30

Your input string is already in the ISO8601 format for date and therefore it can be parsed without providing a `DateTimeFormatter` explicitly. In order to get the output string in a custom format (e.g. `yyyy-MM-dd`), you need to format the date object using `DateTimeFormatter`.

    import java.time.LocalDate;
    import java.time.format.DateTimeFormatter;
    
    public class Main {
    	public static void main(String[] args) {
    		String inputStrDate = &quot;2020-10-01&quot;;
    		LocalDate date = LocalDate.parse(inputStrDate);
    
    		String outputStrDate = date.format(DateTimeFormatter.ofPattern(&quot;yyyy-MM-dd&quot;));
    		System.out.println(outputStrDate);
    	}
    }
**Output:**

    2020-10-01

However, if your input is some other format, you will need to use `DateTimeFormatter` in order to parse it to a date object.

    import java.time.LocalDate;
    import java.time.format.DateTimeFormatter;
    
    public class Main {
    	public static void main(String[] args) {
    		// Formatter for input string
    		DateTimeFormatter inputFormat = DateTimeFormatter.ofPattern(&quot;dd-MM-yyyy&quot;);
    
    		String inputStrDate = &quot;10-01-2020&quot;;
    		LocalDate date = LocalDate.parse(inputStrDate, inputFormat);
    
    		// Formatter for output string
    		DateTimeFormatter outputFormat = DateTimeFormatter.ofPattern(&quot;yyyy-MM-dd&quot;);
    
    		String outputStrDate = date.format(outputFormat);
    		System.out.println(outputStrDate);
    	}
    }

**Output:**

    2020-10-01

Learn more about date-time API from **[Trail: Date Time](https://docs.oracle.com/javase/tutorial/datetime/index.html)**.



</details>



# 答案2
**得分**: 1

```java
for (LocalDate d = fromDate; !d.isAfter(toDate); d = d.plusDays(1)) { // Loop from start to end date
    for (Integer wf : weekOfMonth) {
        for (Integer df : dayOfWeek) {
            offDay = d.with(fieldWeek, wf)
                       .with(fieldDay, df);

            if (d.getMonth() == offDay.getMonth() && !offDays.contains(offDay)) {
                offDays.add(offDay);
            }
        }
    }
}

抱歉我之前问了错误的问题。
非常感谢。

我已经完成了，但我还是研究了你的代码。

for(LocalDate d = fromDate; !d.isAfter(toDate); d = d.plusDays(1)) { // 일정 시작 ~ 끝 loop
        for (Integer wf : weekOfMonth) {
            for (Integer df : dayOfWeek) {
                offDay = d.with(fieldWeek, wf)
                        .with(fieldDay, df);

                
                if (d.getMonth() == offDay.getMonth() && !offDays.contains(offDay)) {
                    offDays.add(offDay);
                }
            }
        }
    }

答案3

得分: 0

java.time

我也建议您使用java.time，这是现代的Java日期和时间API，用于处理日期。我的建议是：

	LocalDate fromDate = LocalDate.of(2020, Month.OCTOBER, 1);
	LocalDate toDate = LocalDate.of(2020, Month.OCTOBER, 30);
	List<DayOfWeek> daysOfWeek = List.of(DayOfWeek.SUNDAY, DayOfWeek.MONDAY);
	List<Integer> weeks = List.of(1, 4, 5);
	
	if (! YearMonth.from(fromDate).equals(YearMonth.from(toDate))) {
		throw new IllegalStateException("Covering more than one month is not yet supported");
	}
	
	WeekFields wf = WeekFields.SUNDAY_START;
	for (int week : weeks) {
		for (DayOfWeek dow : daysOfWeek) {
			LocalDate date = fromDate.with(wf.weekOfMonth(), week)
					.with(wf.dayOfWeek(), dow.get(wf.dayOfWeek()));
			// Is date inside interval?
			if (! (date.isBefore(fromDate)  || date.isAfter(toDate))) {
				System.out.println(date);
			}
		}
	}

输出：

>     2020-10-18
>     2020-10-19
>     2020-10-25
>     2020-10-26

打印的日期是美国方式定义的十月第4和第5周的星期日和星期一，其中星期从星期日开始（因为您在示例列表中首先提到了星期日），第1周是10月1日的一周。第1周的星期日和星期一没有打印出来，因为它们在10月1日之前，也就是在九月份。

请考虑您需要哪种周计数方案。您可以使用`WeekFields.ISO`或`WeekFields.of(Locale.getDefault())`等方式。

我首先查找周，然后查找星期几，因为对我来说这是自然的方式。我需要使用`WeekFields`对象进行两次调整，以确保选择的周计数方案得到遵守。

如果您需要跨越一个以上的日历月份，请遍历各个月份，并为每个月份执行相同的操作。还要检查结果日期是否在该月份内，以忽略在月份边界附近的重复日期。

	LocalDate fromDate = LocalDate.of(2020, Month.OCTOBER, 1);
LocalDate toDate = LocalDate.of(2020, Month.OCTOBER, 30);
List<DayOfWeek> daysOfWeek = List.of(DayOfWeek.SUNDAY, DayOfWeek.MONDAY);
List<Integer> weeks = List.of(1, 4, 5);
if (! YearMonth.from(fromDate).equals(YearMonth.from(toDate))) {
throw new IllegalStateException("Covering more than one month is not yet supported");
}
WeekFields wf = WeekFields.SUNDAY_START;
for (int week : weeks) {
for (DayOfWeek dow : daysOfWeek) {
LocalDate date = fromDate.with(wf.weekOfMonth(), week)
.with(wf.dayOfWeek(), dow.get(wf.dayOfWeek()));
// Is date inside interval?
if (! (date.isBefore(fromDate)  || date.isAfter(toDate))) {
System.out.println(date);
}
}
}