Java中通过日期类获取某个日期是当月的第几周，如今天（2017-12-19），应该返回4

Question

1、用Java新增的java.time.LocalDate
LocalDate.now().get(ChronoField.ALIGNED_WEEK_OF_MONTH); // 3

2、用java.util.Calendar
Calendar.getInstance().get(Calendar.DAY_OF_WEEK_IN_MONTH); // 3

以上两种方法返回的都是3，但是我看日历今天（2017-12-19）明明是12月的第4周才对啊！！！

查阅官方文档：
For example, in a calendar systems with a seven day week, the first aligned-week-of-year starts on day-of-year 1, the second aligned-week starts on day-of-year 8, and so on. Thus, day-of-year values 1 to 7 are in aligned-week 1, while day-of-year values 8 to 14 are in aligned-week 2, and so on.

1到7为第一周，8到14为第二周......扑街，感觉就是除以7再向上取整啊！

请问：**_按照我的计算方式_，有大神知道Java中有自带的API直接获取周数的吗？或者说有什么方法可以很机智快捷地算出当天对应的周数吗？**

Answer 1

public static int getWeek(String str) throws Exception{
SimpleDateFormat sdf= new SimpleDateFormat("yyyy-MM-dd");
Date date =sdf.parse(str);
Calendar calendar = Calendar.getInstance();
calendar.setTime(date);
//第几周
int week = calendar.get(Calendar.WEEK_OF_MONTH);
//第几天，从周日开始
int day = calendar.get(Calendar.DAY_OF_WEEK);
return week;
}