//假设传过来一个字符串日期time,形式如：2011-07-21
String strs[] = time.split("-");
                Calendar calendar = Calendar.getInstance();
                int year = Integer.parseInt(strs[0]);
                int month = Integer.parseInt(strs[1]) - 1;
                calendar.set(year, month, 1);
                int maxDay = calendar.getMaximum(Calendar.DAY_OF_MONTH);
                SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
                List<Object> datas = new ArrayList<Object>();
                for (int j=1; j<=maxDay; j++) {
                    calendar.set(year, month, j);
                    time = sdf.format(calendar.getTime());
                    datas.add(time);
                }

------解决方案--------------------

探讨

闰年的月份天数也不一样，1 3 5 7 8 10 12 这些都是特殊的月数，要做好都得考虑进去