如何将一年中的几周转换为LocalDate [英] How to convert weeks of year to LocalDate

问题描述

我都有一个年份周的字符串，例如"2015-40"和年月格式，例如"2015-08"，希望在Scala中转换为LocalDate.

I have a string with both year-week e.g. "2015-40" and year-month formats e.g. "2015-08", that would like to transform into LocalDate in Scala.

我尝试使用

val date = "2015-40"
val formatter = DateTimeFormatter.ofPattern("yyyy-ww") 
LocalDate.parse(date, formatter)

，但最终出现DateTimeParseException错误.希望对执行此操作有任何帮助

but end up with DateTimeParseException error. Would appreciate any help on how to do this

预先感谢

推荐答案

    String date = "2015-40";
    DateTimeFormatter formatter = new DateTimeFormatterBuilder()
            .appendPattern("YYYY-ww")
            .parseDefaulting(ChronoField.DAY_OF_WEEK, DayOfWeek.MONDAY.getValue())
            .toFormatter(Locale.FRANCE);
    LocalDate ld = LocalDate.parse(date, formatter);
    
    System.out.println(ld);

对不起，我只能写Java，我相信您可以将其翻译成Scala.输出为:

Sorry that I can write only Java, I trust you to translate to Scala. Output is:

2015-09-28

2015-09-28

您为什么要例外?我们缺少将2015-40解析为LocalDate的几件事:

Why were you getting an exception? There were a couple of things missing for us to parse 2015-40 into a LocalDate:

• A LocalDate是日历日期，第40周由7天组成. Java不知道您要在那7天中的哪一天，因此拒绝为您做出选择.在上面的代码中，我指定了星期一.一周中的其他任何一天都可以使用.
• 有点微妙.尽管对于人类来说，2015年和第40周是明确的，但新年前后并非总是如此，因为第1周可能在新年之前开始，或者第52或53周在新年之后开始.因此，日历年和星期数并不总是定义一个特定的星期.取而代之的是，我们需要一个周年或基于周的年的概念.一周的年份从第1周开始(包括第1周)，无论这意味着它在新年前后的几天开始.它持续到上周的最后一天，通常是在新年前后的几天.要告诉DateTimeFormatter我们要解析(或打印)一周的年份，我们需要使用大写的YYYY而不是小写的yyyy(或uuuu).

• A LocalDate is a calendar date, and week 40 consists of 7 days. Java doesn’t know which of those 7 days you want and refuses to make the choice for you. In my code above I have specified Monday. Any other day of the week should work.
• A bit subtler. While to a human year 2015 and week 40 is unambiguous, the same is not always the case around New Year where week 1 may begin before New Year or week 52 or 53 extend after New Year. So a calendar year and a week number don’t always define one specific week. Instead we need the concept of a week year or week-based year. A week year lasts from week 1 inclusive no matter if that means it begins a few days before or after New Year. And it lasts until the last day of the last week, again most often a few days before or after New Year. To tell a DateTimeFormatter that we want to parse (or print) the week year we need to use upper case YYYY instead of lower case yyyy (or uuuu).

顺便说一句，如果可以影响格式，请考虑将2015-W40与W一起使用.这是年份和星期的ISO 8601格式.在ISO中，2015-12表示年份和月份，许多人会这样阅读.因此，要消除歧义并避免误读.

As an aside, if you can influence the format, consider 2015-W40 with a W. This is ISO 8601 format for year and week. In ISO 2015-12 denotes year and month, and many will read it this way. So to disambiguate and avoid misreading.

在我的解释中，我假设使用ISO周计划(星期一是一周的第一天，而第1周定义为新年中至少有4天的第一周).您可以将不同的语言环境传递给格式化程序生成器，以获得不同的星期计划.

In my explanation I have assumed ISO week scheme (Monday is the first day of week and week 1 is defined as the first week having at least 4 days in the new year). You may pass a different locale to the formatter builder to obtain a different week scheme.

如果您确定自己的星期符合ISO标准，那么安德烈亚斯(Andreas)在评论中的建议就足够了，我们希望将其作为答案的一部分:

If you are sure that your weeks follow ISO, Andreas’ suggestion in the comment is good enough that we want as part of the answer:

或者，添加 ThreeTen Extra 库，以便您可以使用 YearWeek 类，具有很好的

Alternatively, add the ThreeTen Extra library, so you can use the YearWeek class, that has a nice atDay​(DayOfWeek dayOfWeek) method for getting a LocalDate.

链接: 维基百科文章:ISO 8601

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