java获取这周的开始时间

public static void main(String[] args) {
        Calendar c=Calendar.getInstance();
        SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");
        //今天
        String today=df.format("今天时间："+c.getTime());
        System.out.println(today);
        //今天是周几
        int dayOfWeek = c.get(Calendar.DAY_OF_WEEK);
               //
        dayOfWeek-=2;
        //今天-1天（昨天）
        c.add(Calendar.DAY_OF_MONTH, -dayOfWeek);
        String yesterday=df.format(c.getTime());
        System.out.println("周一时间   "+yesterday);
        System.out.println("今天周几   "+dayOfWeek);
    }