如何从今天开始获取最后两个星期五的日期？

Question

我需要使用今天的日期来获取最近两个星期五的日期。这是我当前使用的公共类GetDate {

public static void main(String[] args) {
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
    Date dt = new Date();
    Calendar c = Calendar.getInstance();
    c.setTime(dt);
    System.out.println("today : " + sdf.format(dt));
    while (c.get(Calendar.DAY_OF_WEEK) != 6) {
        c.add(Calendar.DATE, -1);
    }
    Date lastFri=c.getTime();
    System.out.println("last fri : "+sdf.format(lastFri));
    c.add(Calendar.DATE, -7);
    Date prevFri = c.getTime();
    System.out.println("previous friday : "+sdf.format(prevFri));

    }


}

有什么方法可以优化此代码？

Answer 1

在Java 8，如果你没有使用日历API，你可以使用一个TemporalAdjuster ：

LocalDate today = LocalDate.now();
LocalDate prevFriday = today.with(previous(FRIDAY));
LocalDate prevPrevFriday = prevFriday.with(previous(FRIDAY));

_{注意：需要以下静态导入
import static java.time.temporal.TemporalAdjusters.previous;
import static java.time.DayOfWeek.FRIDAY;}

Answer 2

您可以这样获得最后一个星期五：

Calendar cal = Calendar.getInstance();
cal.add(Calendar.WEEK_OF_YEAR, -1);
cal.set(Calendar.DAY_OF_WEEK, Calendar.FRIDAY);

通过减去一个星期并将星期几设置为星期五，可以得到最后一个星期五。

Answer 3

尝试类似：

cal.add(Calendar.WEEK_OF_YEAR, -1);
cal.set(Calendar.DAY_OF_WEEK, Calendar.FRIDAY);
Date lastFriday = cal.getTime();
cal.add(Calendar.WEEK_OF_YEAR, -1);
cal.set(Calendar.DAY_OF_WEEK, Calendar.FRIDAY);
Date lastToLastFriday = cal.getTime();

Answer 4

此行应有帮助：

calendar.add(Calendar.DATE, Calendar.FRIDAY - 7 - c.get(Calendar.DAY_OF_WEEK));

因此，这段代码正在解决您的问题：

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
Calendar c = GregorianCalendar.getInstance();
c.add(Calendar.DATE, Calendar.FRIDAY - 7 - c.get(Calendar.DAY_OF_WEEK));
System.out.println(sdf.formate(c.getTime()));
c.add(Calendar.DATE, Calendar.FRIDAY - 14 - c.get(Calendar.DAY_OF_WEEK));
System.out.println(sdf.formate(c.getTime()));