public static String getDateBefore(int day) {　　SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");　　Calendar now = Calendar.getInstance(); 
　　now.setTime(new Date()); 
　　now.add(Calendar.DATE, day); //day=-1表示得到昨天日期
　　return sdf.format(now.getTime()) ;
}