由开始日期和有效天数算截止日期

String days = "40";//40天
Calendar  endDate =   Calendar.getInstance();//截止日期
endDate.add(endDate.DATE, Integer.parseInt(days));

 	if(request.getParameter("search_date")!=null && !request.getParameter("search_date").equals("")){
		search_date=request.getParameter("search_date");
		search_date_yuan = search_date;
		strDate.add(strDate.YEAR, -Integer.parseInt( search_date));  
		search_date = new SimpleDateFormat("yyyyMMddHHmmss").format(strDate.getTime());
		criteria.put("search_date", search_date_yuan);
	}