How to parse this JSON response with GSON after a

问题:

I'm trying to parse a JSON response using GSON after a Retrofit GET request. I don't need all the keys and values so I only @Expose the ones that I need and instructed the parser to do so. The request fires OK and the response come clean, but looking into logcat I found this error which evidently points me that POJO model is bad formatted or implemented:

04-09 12:16:01.679 5604-5604/? V/Retrofit error﹕ retrofit.converter.ConversionException: com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_ARRAY but was BEGIN_OBJECT at line 1 column 2 path $

This is the JSON response (which returns ok after GET request):

{
   objects: [
   {
     rating: 0.97,
     name: "High Line",
     ranking: 0,
     url: "http://www.thehighline.org",
     price: null,
     phone: "2125006035",
     last_sync: 1428328869,
     photos: [
    "https://irs3.4sqi.net/img/general/original/11402168_2zKtnTfWXPJJJAaX7N6g1EMPTR7ahNqSAOsMotN-jNU.jpg"
     ],
     local_id: 13778,
     likes: 0,
     city_id: 2621,
     address: "btwn Gansevoort & W 34th St",
     resource_uri: "/api/v1/venues/40f1d480f964a5206a0a1fe3/",
     id: "40f1d480f964a5206a0a1fe3",
     categories: [
     {
       name: "Park",
       parent: {
            local_id: 7,
            name_id: "sights",
            name: "Landmarks",
           id: "4d4b7105d754a06377d81259"
       },
       local_id: 494,
       name_id: "park",
       category_id: 7,
       id: "4bf58dd8d48988d163941735"
    }
   ],
   location: {
      lat: 40.7470618874989,
      lng: -74.0051937103271
   }
  },
  {
    rating: 0.97,
    name: "Central Park",
    ranking: 0,
    url: "http://www.centralparknyc.org",
    price: null,
    phone: "2123106600",
    last_sync: 1428521923,
    photos: [
  "https://irs2.4sqi.net/img/general/original/655018_Zp3vA90Sy4IIDApvfAo5KnDItoV0uEDZeST7bWT-qzk.jpg"
    ],
    local_id: 13826,
    likes: 0,
    city_id: 2621,
    address: "59th St to 110th St",
    resource_uri: "/api/v1/venues/412d2800f964a520df0c1fe3/",
    id: "412d2800f964a520df0c1fe3",
    categories: [
    {
       name: "Park",
       parent: {
          local_id: 7,
          name_id: "sights",
          name: "Landmarks",
          id: "4d4b7105d754a06377d81259"
       },
       local_id: 494,
       name_id: "park",
       category_id: 7,
       id: "4bf58dd8d48988d163941735"
     }
    ],
    location: {
      lat: 40.7888599444948,
      lng: -73.9611625671387
    }
   }
 ],
  meta: {
    total_count: 1344,
    next: "/api/v1/venues/?city_id=2621&category=topPicks&offset=2&limit=2&format=json",
    limit: 2,
    offset: 0
    }
}

This is the main activity call to the Retrofit service:

   Map<String, String> params = new HashMap<String, String>();
    params.put("city_id", "2621");
    params.put("offset", "0");
    params.put("limit", "2"); 
    params.put("category", "topPicks");
    params.put("format", "json");


    ApiClient.getApiClient().listVenues(params, new Callback<List<ApiResponse>>() {

        @Override
        public void success(List<ApiResponse> venues, Response response) {

            //consumir venues
            Log.v("RETROFIT SUCCESS", response.getBody().toString());

            mAdapter = new MainCustomAdapter(venues);
            mRecyclerView.setAdapter(mAdapter);

        }

        @Override
        public void failure(RetrofitError retrofitError) {

            if (retrofitError.getResponse() != null) {
                Log.v("Retrofit error", retrofitError.getCause().toString());
            }
            //manejar el fallo


        }
    });

This is the Api client:

public class ApiClient {
private static ApiVenuesInterface apiVenues;

public static ApiVenuesInterface getApiClient() {

   Gson gson = new GsonBuilder().excludeFieldsWithoutExposeAnnotation().create();

    if (apiVenues == null) {
        RestAdapter restAdapter = new RestAdapter.Builder()

                .setEndpoint("http://endpoint.com")
                .setConverter(new GsonConverter(gson))
                .setLogLevel(RestAdapter.LogLevel.FULL).setLog(new AndroidLog("RETROFIT"))
                .build();

        apiVenues = restAdapter.create(ApiVenuesInterface.class);
    }

    return apiVenues;
}

 public interface ApiVenuesInterface {
     //llamada asíncrona al querystring de venues
     @GET("/api/v1/venues")
     void listVenues(@QueryMap Map<String, String> params, Callback<List<ApiResponse>> callback);
}}

And finally this my POJO model (which I believe is the place where the main problem is):

    public class ApiResponse {
    private List<Object> objects = new ArrayList<Object>();

}
class Object {

    @Expose
    private String name;
    @Expose
    private List<String> photos = new ArrayList<String>();
    @Expose
    private String address;
    @Expose
    private List<Category> categories = new ArrayList<Category>();

    /**
     *
     * @return
     * The name
     */
    public String getName() {
        return name;
    }


    /**
     *
     * @return
     * The photos
     */
    public List<String> getPhotos() {
        return photos;
    }

    /**
     *
     * @return
     * The address
     */
    public String getAddress() {
        return address;
    }

    /**
     *
     * @return
     * The categories
     */
    public List<Category> getCategories() {
        return categories;
    }

    class Category {
        @Expose
        private String name;

        /**
         *
         * @return
         * The name
         */
        public String getName() {
            return name;
        }

    }}

So, how did I must to model my POJO to parse the data I need? Thanks in advance.

IMPORTANT EDIT: This question is valid for Retrofit 1.x. Be aware that Retrofit 2.x is a little bit different than this because it uses annotations and Call methods.

回答1:

As per earlier comment:

Based on a quick look, your Callback return type isn't of type List<ApiResponse>, but rather just ApiResponse. If you change the following, things should start working:

public interface ApiVenuesInterface {
     //llamada asíncrona al querystring de venues
     @GET("/api/v1/venues")
     void listVenues(@QueryMap Map<String, String> params, Callback<ApiResponse> callback);
}

At the moment, you're telling Gson to convert the response into a list of ApiResponse objects, but in reality it's just a single ApiResponse wrapping a list/array of items. You modelled the POJOs correctly, but not so much the retrofit callback.

---

[edit] answering your follow up question: you can access the wrapped objects by simply adding a getter to your ApiResponse class:

public List<Object> getObjects() {
    return objects;
}

A small tip: it would be good to come up with a different name for your Object class, since its name is identical to the 'mother' of all objects in Java: java.lang.Object. This is bound to lead to confusion and very prone to importing/referencing errors. Try to come up with something a little more descriptive, for example Venue (as it appears that's what you're dealing with, although I may be mistaken).

---

[edit2] Gson produces an ApiResponse object, which wraps around a List<Object>. Iterating over that list can be done like any other Java iteration; i.e. using the enhanced for-loop:

for (Object object : getObjects()) {
    // get the name for this object
    String name = object.getName();
    // get the address for this object
    String address = object.getAddress();
    // get all the photo urls for this object
    List<String> photos = object.getPhotos();
    // etc...
}

The reason you're seeing i.e. myjavapackage.Object@3c4a86e1 is because Java doesn't know how to represent your objects as a string for printing. You can change this representation by overriding the following method in your Object class:

@Override public String toString() {
    // return a string representation for this object; i.e. its name:
    return name;
}

I'd still recommend to rename your Object class to something more sensible to avoid confusing it with the built-in java.lang.Object.

回答2:

Try to remove this part from json string

{ objects:

and last curly bracket.