Retrofit gson with dynamic keys

Question

I've managed to get it to work without a dynamic key. By following this tutorial with this json:

Currently, I'm using Retrofit and trying to get a response with dynamic keys. However, the response body is always null:

This is the response format:

{
    "dynamic1": {
        "cityID": "id1",
        "priceRange": 15
    },
    "dynamic2": {
        "cityID": "id2",
        "priceRange": 15
    }
}

In APIUtils.java

    public static CityService getCitiesService() {
        return RetrofitClient.getClient(BASE_URL).create(CityService.class);
    }

In CityService.java

public interface CityService {

    @GET("/SAGetStrollAwayCity")
    Call<CityResponse> getCities();

    @GET("/SAGetStrollAwayCity")
    Call<CityResponse> getCities(@Query("tagged") String tags);
}

In CityResponse.java:

public class CityResponse {
    /*@SerializedName("results")
    @Expose*/ // is this the correct way?
    private Map<String, CityDetails> city = new HashMap<>();

    public Map<String, CityDetails> getCity() {
        return city;
    }

    public void setCity(Map<String, CityDetails> elemDetails) {
        this.city = elemDetails;
    }

}

In CityDetails.java

public class CityDetails {

    @SerializedName("cityID")
    @Expose
    private String cityID;
    @SerializedName("priceRange")
    @Expose
    private Integer priceRange;

    public String getCityID() {
        return cityID;
    }

    public void setCityID(String cityID) {
        this.cityID = cityID;
    }

    public Integer getPriceRange() {
        return priceRange;
    }

    public void setPriceRange(Integer priceRange) {
        this.priceRange = priceRange;
    }

}

In HomeFragment.java

public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_home, null);
        // 2nd api call
        mServiceCity = ApiUtils.getCitiesService();
        loadCities();

        return rootView;
}

public void loadCities() {
    mServiceCity.getCities().enqueue(new Callback<CityResponse>() {
        @Override
        public void onResponse(Call<CityResponse> call, Response<CityResponse> response) {
         // !!! WHY IS THE RESPONSE BODY EMPTY???
            if(response.isSuccessful()) {

//                    adapter.updateCities(response.body().getCity());

                Log.d("MainActivity", "posts loaded from API"+ response.body().getCity());
            }else {
                int statusCode  = response.code();
                // handle request errors depending on status code
            }
        }

        @Override
        public void onFailure(Call<CityResponse> call, Throwable t) {
            //showErrorMessage();
            Log.d("MainActivity", "error loading from API");

        }
    });
}

Hi this is the response: { "dynamic1": { "cityID": "id1", "priceRange": 15 }, "dynamic2": { "cityID": "id2", "priceRange": 15 } } — user1872384, Nov 14 '18 at 09:03
Okay, you mean to say this is not coming, it's always coming empty right? — Ümañg ßürmån, Nov 14 '18 at 09:03
Your CityResponse model is wrong as there is no @SerializedName(), how will it know from which key it needs to parse..!! — Prashanth Verma, Nov 14 '18 at 09:06
@Ümañgßürmån updated the questions with breakpoint at the response — user1872384, Nov 14 '18 at 09:09
@PrashanthVerma, I see... However, the keys are dynamic for keys "dynamic1" and "dynamic2". How can I go about it? In iOS it's much easier using NSDictionary with keys and values — user1872384, Nov 14 '18 at 09:10
In this line: `private Map city = new HashMap<>();` change `city` to `cityID` and try. — Ümañg ßürmån, Nov 14 '18 at 09:15
refer option 3 from this answer https://stackoverflow.com/a/51799218/4762767 — Akshay Katariya, Nov 14 '18 at 09:21
https://stackoverflow.com/questions/33758601/parse-dynamic-key-json-string-using-retrofit, I am not sure this is the right answer but go through it. — Prabha Karan, Nov 14 '18 at 09:31
@PrashanthVerma that's how the response is... and I'm just consuming it... — user1872384, Nov 14 '18 at 09:34
@Ümañgßürmån it just change the variable name... don't think changing city to cityID will do anything — user1872384, Nov 14 '18 at 09:34
hmm..there are only fixed set of keys will come? or like any key can come, i mean are the keys not predictable..? — Prashanth Verma, Nov 14 '18 at 09:39
@PrabhaKaran, that's what I'm referring to... I'm changing "public class ResultInside" in the answer to "public class CityResponse". What's wrong here? — user1872384, Nov 14 '18 at 09:42
@Ümañgßürmån, I've tried your suggestion to change it... However, just by looking at it, my gut feeling is telling me that. And apparently that's the result when I debug it after changing. Please do not feel offended. Thanks for your help. — user1872384, Nov 14 '18 at 09:52

score 6 · Accepted Answer · answered Nov 14 '18 at 10:46

Personally I'd drop the CityResponse model and just work with Map<String, CityDetails>.

The retrofit interface can then be:

public interface CityService {

  @GET("/SAGetStrollAwayCity")
  Call<Map<String, CityDetails>> getCities();

  @GET("/SAGetStrollAwayCity")
  Call<Map<String, CityDetails>> getCities(@Query("tagged") String tags);
}

In your scenario, the response body is empty because CityResponse would map to a json like:

{
  "city": {
    "dynamic1": {
      "cityID": "id1",
      "priceRange": 15
    },
    "dynamic2": {
      "cityID": "id2",
      "priceRange": 15
    }
  }
}

However, you don't have a root element called city. The json itself can already be mapped to a java Map.

Hope this helps.

:D That's fine, no worries! Glad it helped! Buy the beer to someone else in more need than me :D — Fred, Nov 14 '18 at 11:03
Thank's a lot...didn't knew we can actually parse json with map — Mehdi.ncb, Mar 18 '22 at 09:45

Retrofit gson with dynamic keys

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