public class calender {

    public static class DateUtil {
        private static SimpleDateFormat sdf = new SimpleDateFormat("yyyyMM");
        private static Calendar calendar = Calendar.getInstance();

        /*
        输入日期字符串比如201703，返回当月第一天的Date
        */        public static Date getMinDateMonth(String month) {
            try {
                Date nowDate = sdf.parse(month);
                calendar = Calendar.getInstance();
                calendar.setTime(nowDate);
                calendar.set(Calendar.DAY_OF_MONTH, calendar.getActualMinimum(Calendar.DAY_OF_MONTH));
                return calendar.getTime();
            } catch (ParseException e) {
                e.printStackTrace();
            }
            return null;
        }

        /*
        输入日期字符串，返回当月最后一天的Date
        */        public static Date getMaxDateMonth(String month) {
            try {
                Date nowDate = sdf.parse(month);
                calendar = Calendar.getInstance();
                calendar.setTime(nowDate);
                calendar.set(Calendar.DAY_OF_MONTH, calendar.getActualMaximum(Calendar.DAY_OF_MONTH));
                return calendar.getTime();
            } catch (ParseException e) {
                e.printStackTrace();
            }
            return null;
        }

        public static void main(String[] args) throws ParseException {
            String month = "201705";
            System.out.println(getMinDateMonth(month));
            System.out.println(getMaxDateMonth(month));
        }
    }
}
  

 代码执行结果：
Mon May 01 00:00:00 CST 2017
Wed May 31 00:00:00 CST 2017