import com.google.gson.Gson;

        //string转bean
        Gson gson = new Gson();
        UserPage userPage = gson.fromJson(str, UserPage.class);
        List<UserVo> data =http://www.mamicode.com/ userPage.getData();
        //加字段
        userPage.setRecordsFiltered(data.size());
        userPage.setRecordsTotal(data.size());
        //bean转string
        String json = gson.toJson(userPage);