Java输出json

public ActionForward gettuanjson(ActionMapping mapping, ActionForm form,
			HttpServletRequest request, HttpServletResponse response) {
		
		//处理城市id
		String cityNamePinYin=request.getParameter("city");
		if(cityNamePinYin==null||cityNamePinYin.equals(""))cityNamePinYin=Constants.PHONE_DEFAULT_CITY;
		City city=cityManager.getCityByCityNamePinYin(cityNamePinYin);
		int cid=Constants.PHONE_DEFAULT_CITY_ID;
		if(city!=null)cid=city.getId();
		
		//处理目录
		Integer category=this.getInt(request, "category", Constants.PHONE_DEFAULT_CATEGORY);
		//处理页数
		int pageNo = this.getInt(request, "pageno", Constants.PHONE_DEFAULT_PAGENO);
		//处理顺序
		int order=this.getInt(request, "order", Constants.ORDER_WEIGHT);
		
		List tuanList=tuanManager.getTuanList(cid, category, order,Constants.PHONE_DEFAULT_PAGESIZE,pageNo );
		Gson gson = new Gson(); 
		String listToJson = gson.toJson(tuanList);
		outPrintText(response,listToJson);
		return null;
	}