獲取本週一時間，然後+/-1就是下週/上週一的時間

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
 
public class DateTest {
    public static Date geLastWeekMonday(Date date) {
        Calendar cal = Calendar.getInstance();
        cal.setTime(getThisWeekMonday(date));
        cal.add(Calendar.DATE, 
 
-7);
        return cal.getTime();
    }
 
    public static Date getThisWeekMonday(Date date) {
        Calendar cal = Calendar.getInstance();
        cal.setTime(date);
        // 獲得當前日期是一個星期的第幾天
        int dayWeek = cal.get(Calendar.DAY_OF_WEEK);
        if (1 == dayWeek) {
            cal.add(Calendar.DAY_OF_MONTH, 
 
-1);
        }
        // 設定一個星期的第一天，按中國的習慣一個星期的第一天是星期一
        cal.setFirstDayOfWeek(Calendar.MONDAY);
        // 獲得當前日期是一個星期的第幾天
        int day = cal.get(Calendar.DAY_OF_WEEK);
        // 根據日曆的規則，給當前日期減去星期幾與一個星期第一天的差值
        cal.add(Calendar.DATE, cal.getFirstDayOfWeek() - day);
        return cal.getTime();
    }
 
    
 
public static Date getNextWeekMonday(Date date) {
        Calendar cal = Calendar.getInstance();
        cal.setTime(getThisWeekMonday(date));
        cal.add(Calendar.DATE, 7);
        return cal.getTime();
    }
 
    public static void main(String[] args) {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        try {
            Date date = sdf.parse("2017-09-10");
            System.out.println("今天是" + sdf.format(date));
            System.out.println("上週一" + sdf.format(geLastWeekMonday(date)));
            System.out.println("本週一" + sdf.format(getThisWeekMonday(date)));
            System.out.println("下週一" + sdf.format(getNextWeekMonday(date)));
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

輸出結果：

今天是2017-09-10
上週一2017-08-28
本週一2017-09-04
下週一2017-09-11