code: public Controller keepPara(String... names) {
  		for (String name : names) {
  			String[] values = request.getParameterValues(name);
  			if (values != null) {
  				if (values.length == 1)
  					request.setAttribute(name, values[0]);
  				else
  					request.setAttribute(name, values);
  			}
  		}
  		return this;
  	}
docs: Keep parameter's value names pointed, model value can not be kept