Java 如何获取一周的日期（我知道周数）？

How to get dates of a week (I know week number)?

提问by Mellon

I know the week number of the year, a week is start from Sunday, then Monday, Tuesday...,Saturday.

我知道一年中的周数，一周是从星期日开始，然后是星期一，星期二......，星期六。

Since I know the week number, what's the efficient way to get the dates of the specific week by using Java code??

既然我知道周数，那么使用 Java 代码获取特定周日期的有效方法是什么？

采纳答案by bungrudi

If you don't want external library, just use calendar.

如果您不想要外部库，只需使用日历。

SimpleDateFormat sdf = new SimpleDateFormat("MM dd yyyy");
Calendar cal = Calendar.getInstance();
cal.set(Calendar.WEEK_OF_YEAR, 23);        
cal.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
System.out.println(sdf.format(cal.getTime()));    

回答by Alois Cochard

You can use the joda timelibrary

您可以使用joda 时间库

int weekNumber = 10;
DateTime weekStartDate = new DateTime().withWeekOfWeekyear(weekNumber);
DateTime weekEndDate = new DateTime().withWeekOfWeekyear(weekNumber + 1);

回答by mezzie

You did not mention what return type do you exactly need but this code should prove useful to you. sysouts and formatter are just to show you the result.

您没有提到您究竟需要什么返回类型，但这段代码应该对您有用。sysouts 和 formatter 只是为了向您展示结果。

Calendar cal = Calendar.getInstance();
cal.setTime(new Date());
cal.set(Calendar.WEEK_OF_YEAR, 30);
SimpleDateFormat formatter = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
cal.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);
System.out.println(formatter.format(cal.getTime()));
cal.add(Calendar.DAY_OF_WEEK, 6);
System.out.println(formatter.format(cal.getTime()));

回答by Mateusz Szulc

Pure Java 8 / java.time solution

纯 Java 8 / java.time 解决方案

Based on this:

基于此：

final long calendarWeek = 34;
LocalDate desiredDate = LocalDate.now()
            .with(IsoFields.WEEK_OF_WEEK_BASED_YEAR, calendarWeek)
            .with(TemporalAdjusters.previousOrSame(DayOfWeek.MONDAY));

回答by Ashish

This answer is pretty much same as others. But, here it goes:

这个答案与其他答案几乎相同。但是，这里是：

int year = 2018;
int week = 27;
int day = 1; //assuming week starts from sunday
Calendar calendar = Calendar.getInstance();
calendar.setWeekDate(year, week, day);
System.out.println(calendar.getTime());