{
       "ADDTNLINFO":
        {
                "Tag":
                  {
                    "name": "a",
                    "value": "10"
                  },
                "Tag":
                  {
                    "name": "a b",
                    "value": "20"
                  },
                "Tag":
                 {
                    "name": "a b c",
                    "value": "30"
                 }
         }
 }

import com.google.gson.Gson;
List<Dto> beans = service.something();
Gson gson = new Gson();
// convert your list to json
String jsonCartList = gson.toJson(beans);