java list对象转换成json

@RequestMapping("query")
	public ModelAndView query(UserAgent userAgent, HttpServletRequest request) {
		ModelAndView modelAndView = new ModelAndView("category/list");
		Long userId = userAgent.getUserId();
		List<ProductCategory> list = productCategoryService.query(userId);
		List<Map<String,Object>> proList = new ArrayList<Map<String,Object>>();
		for(ProductCategory p : list){
			Map<String,Object> m = new HashMap<String,Object>();
			m.put("classId", p.getId());
			m.put("className", p.getCategoryName());
			m.put("classSort", p.getOrderby());
			proList.add(m);
		}
		
		JSONArray json = new JSONArray();  
	      json.addAll(proList);  
		
		modelAndView.addObject("json",json.toJSONString());
		System.out.println(json.toJSONString());
		return modelAndView;
	}