* 本月第一天
*/
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");
GregorianCalendar gc2 = (GregorianCalendar) Calendar.getInstance();
Calendar calendar2 = Calendar.getInstance();
gc2.setTime(new Date());
gc2.set(Calendar.DAY_OF_MONTH, 1); //設置該月的第一天
String b_day_first = df.format(gc2.getTime());
StringBuffer str_b = new StringBuffer().append(b_day_first).append(" 00:00:00");//拼接 時分秒
b_day_first = str_b.toString();
/**
* 本月最後一天
*/
calendar2.add(Calendar.MONTH, 1); //加一個月
calendar2.set(Calendar.DATE, 1); //設置爲該月第一天
calendar2.add(Calendar.DATE, -1); //再減一天即爲上個月最後一天
String b_day_last= df.format(calendar2.getTime());
StringBuffer endStrb = new StringBuffer().append(b_day_last).append(" 23:59:59"); //拼接 時分秒
b_day_last = endStrb.toString();