怎么获得某月的第一天和最后一天

	/**
     * 上个月第一天和最后一天
     * @param date
     * @return
     */
    public static Map<String, String> getFirstday_Lastday_Month(Date date) {
        SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        calendar.add(Calendar.MONTH, -1);
        Date theDate = calendar.getTime();
        
        //上个月第一天
        GregorianCalendar gcLast = (GregorianCalendar) Calendar.getInstance();
        gcLast.setTime(theDate);
        gcLast.set(Calendar.DAY_OF_MONTH, 1);
        String day_first = df.format(gcLast.getTime());
        StringBuffer str = new StringBuffer().append(day_first).append(" 00:00:00");
        day_first = str.toString();

        //上个月最后一天
        calendar.add(Calendar.MONTH, 1);    //加一个月
        calendar.set(Calendar.DATE, 1);        //设置为该月第一天
        calendar.add(Calendar.DATE, -1);    //再减一天即为上个月最后一天
        String day_last = df.format(calendar.getTime());
        StringBuffer endStr = new StringBuffer().append(day_last).append(" 23:59:59");
        day_last = endStr.toString();

        Map<String, String> map = new HashMap<String, String>();
        map.put("first", day_first);
        map.put("last", day_last);
        return map;
    }