获取指定月份天数和指定月份的第一天和最后一天

 public static final String DF_YYYY_MM = "yyyyMM";
    private static SimpleDateFormat sdf=new SimpleDateFormat("yyyyMM");
    /**
     * 校验时间格式yyyyMM
     * @param str
     * @return
     */
    public static boolean timeForm(String str ) {
        String MONTH_REGEX = "^([1-9]\\d{3})(([0]{0,1}[1-9])|([1][0-2]))$";
        boolean matches = Pattern.matches(MONTH_REGEX, str);
        return matches;
    }
    /**
     * 获取指定月份天数
     */
    public static int getDayOfMonth(String month){
        try {
            Date nowDate=sdf.parse(month);
            Calendar calendar = Calendar.getInstance();
            calendar.setTime(nowDate);
            calendar.set(Calendar.DAY_OF_MONTH, calendar.getActualMaximum(Calendar.DAY_OF_MONTH));
            int i = calendar.get(Calendar.DATE);
            return i;
        } catch (ParseException e) {
            e.printStackTrace();
        }
        return 0 ;

    }
    /**
     * 获取某月最后一天
     */
    public static Date getMaxDateMonth(String month){
        try {
            Date nowDate=sdf.parse(month);
            Calendar calendar = Calendar.getInstance();
            calendar.setTime(nowDate);
            calendar.set(Calendar.DAY_OF_MONTH, calendar.getActualMaximum(Calendar.DAY_OF_MONTH));
            calendar.set(Calendar.HOUR_OF_DAY,23);
            calendar.set(Calendar.MINUTE,59);
            calendar.set(Calendar.SECOND,59);
            return calendar.getTime();
        } catch (ParseException e) {
            e.printStackTrace();
        }
        return null;
    }
    /**
     * 获取某月开始时间
     */
    public static Date getMinDateMonth(String month){
        try {
            Date nowDate=sdf.parse(month);
            Calendar 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;
    }