获取日期的当月有多少天和当前是周几

String str = "2020年08月08日";

SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日");

Date date = sdf.parse(str);

Calendar instance = Calendar.getInstance();

System.out.println(instance.getActualMaximum(Calendar.DATE));

System.out.println(instance.get(Calendar.DAY_OF_WEEK)-1);