getFirstDayOfWeek未返回一周首日：美国时区获取周日LocalDate异常排查

Ah, I see the issue here—you've run into a common gotcha with how the with(DayOfWeek) method works in Java's Date/Time API! Let's break this down:

The Root Problem #

When you call LocalDate.now().with(DayOfWeek.SUNDAY) (since Locale.US uses Sunday as the first day of the week), the method doesn't automatically "roll back" to the start of the current week. Instead, it looks for the next occurrence of that day of the week if the current date isn't already that day.

For example:

• If today is Monday, April 9th, with(DayOfWeek.SUNDAY) will jump to the next Sunday (April 15th) instead of the previous Sunday (April 8th).
• Only if today were already Sunday would it return the current date.

Your minusWeeks(1) workaround works for days after Sunday, but it's fragile: if today is Sunday, it would incorrectly return the previous week's Sunday instead of the current one.

Proper Solutions #

Here are three robust ways to get the first day of the current week (Sunday for Locale.US):

1. Use TemporalAdjusters.previousOrSame() #

This is the simplest and most readable approach. The previousOrSame adjuster returns the current date if it matches the target day of the week; otherwise, it returns the most recent prior occurrence:

import java.time.LocalDate;
import java.time.temporal.TemporalAdjusters;
import java.time.temporal.WeekFields;
import java.util.Locale;

LocalDate startDate = LocalDate.now()
    .with(TemporalAdjusters.previousOrSame(WeekFields.of(Locale.US).getFirstDayOfWeek()));

2. Explicitly Use Week Fields to Target the Current Week #

You can use WeekFields to anchor the date to the current week of the week-based year, then set it to the first day of the week:

import java.time.LocalDate;
import java.time.temporal.WeekFields;
import java.util.Locale;

WeekFields usWeekRules = WeekFields.of(Locale.US);
LocalDate today = LocalDate.now();
LocalDate startDate = today
    .with(usWeekRules.weekOfWeekBasedYear(), today.get(usWeekRules.weekOfWeekBasedYear()))
    .with(usWeekRules.getFirstDayOfWeek());

3. Build a Custom Offset Calculation #

If you prefer a more hands-on approach, you can calculate the exact number of days to subtract to reach the week's start:

import java.time.LocalDate;
import java.time.DayOfWeek;
import java.time.temporal.WeekFields;
import java.util.Locale;

WeekFields usWeekRules = WeekFields.of(Locale.US);
DayOfWeek firstDay = usWeekRules.getFirstDayOfWeek();
LocalDate today = LocalDate.now();
int daysToSubtract = (today.getDayOfWeek().getValue() - firstDay.getValue() + 7) % 7;
LocalDate startDate = today.minusDays(daysToSubtract);

All these solutions will correctly return the current week's Sunday, whether today is Sunday or any other day of the week.

内容的提问来源于stack exchange，提问作者user9633120