Null pointer Exception on JSON Array using Retrofit

Question

I get this error java.lang.NullPointerException: Attempt to invoke interface method 'java.lang.Object java.util.List.get(int) on a null object reference' when I try to get the values from the list or return it's size and I can't find what it wrong. First of all, I am using the API from food2fork so I can get some recipes based on user's input(ingredients).

This is my interface.

     public interface ApiService {
    @GET("/search")
    Call<List<Recipe>> getRecipes(@Query("api") String api_key, @Query ("q")      StringBuilder st);

}

The objects' class Recipe

public class Recipe {


    @SerializedName("publisher")
    private String publisher; //to onoma tou ekdoth
    @SerializedName("f2f_url")
    private String f2f_url; //to url tis suntaghs sto site food2fork
    @SerializedName("title")
    private String title; //titlos tis suntaghs
    @SerializedName("source_url")
    private String source_url; //to url ths suntaghs se html
    @SerializedName("recipe_id")
    private int recipe_id; //to id ths suntaghs
    @SerializedName("image_url")
    private String image_url; //to url ths eikonas se jpg
    @SerializedName("social_rank")
    private double social_rank;
    @SerializedName("publisher_url")
    private String publisher_url; //to vasiko url tou ekdoth

    public String getPublisher() {
            return publisher;
    }

    public String getF2f_url() {
            return f2f_url;
    }

    public String getSource_url() {
            return source_url;
    }

    public String getTitle() {
            return title;
    }

    public int getRecipe_id() {
            return recipe_id;
    }

    public double getSocial_rank() {
            return social_rank;
    }

    public String getImage_url() {
            return image_url;
    }

    public String getPublisher_url() {
            return publisher_url;
    }

public void setPublisher(String publisher) {
    this.publisher = publisher;
}

public void setF2f_url(String f2f_url) {
    this.f2f_url = f2f_url;
}

public void setTitle(String title) {
    this.title = title;
}

public void setSource_url(String source_url) {
    this.source_url = source_url;
}

public void setRecipe_id(int recipe_id) {
    this.recipe_id = recipe_id;
}

public void setImage_url(String image_url) {
    this.image_url = image_url;
}

public void setSocial_rank(double social_rank) {
    this.social_rank = social_rank;
}

public void setPublisher_url(String publisher_url) {
    this.publisher_url = publisher_url;
}

    public Recipe(String publisher, String f2f_url, String title, String source_url, int recipe_id, String image_url, double social_rank, String publisher_url) {
            this.publisher = publisher;
            this.f2f_url = f2f_url;
            this.title = title;
            this.source_url = source_url;
            this.recipe_id = recipe_id;
            this.image_url = image_url;
            this.social_rank = social_rank;
            this.publisher_url = publisher_url;
    }

}

My main class

public class ResponseMain extends AppCompatActivity {

RecyclerView recyclerView;
public static String getApiKey() {
    return API_KEY;
}

//to key API ths selidas pou mas epistrefei to json antikeimeno
private final static String API_KEY = "fe7a73e01ac9abc09db51ebf67019f94";
StringBuilder words;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    Log.d("TAG", "MPIKA");
    setContentView(R.layout.activity_response);


    if (API_KEY.isEmpty()) {
        Toast.makeText(getApplicationContext(), "Please obtain your API key from food2fork.com first!", Toast.LENGTH_LONG);
        return;
    }
     recyclerView = (RecyclerView) findViewById(R.id.recipes_recycler_view);
    recyclerView.setLayoutManager(new LinearLayoutManager(this));


    words = addingItems_activity.getWords();
    getRetrofitArray();
}
public void getRetrofitArray() {

    Retrofit retrofit = new Retrofit.Builder()
            .baseUrl(BASE_URL)
            .addConverterFactory(GsonConverterFactory.create())
            .build();

    ApiService apiService = retrofit.create(ApiService.class);
    Call<List<Recipe>> call = apiService.getRecipes(API_KEY, words);

    call.enqueue(new Callback<List<Recipe>>() {
        @Override
        public void onResponse(Call<List<Recipe>> call, Response <List<Recipe>> response) {
            try {
                Log.d("Here comes the null exception","get title" + response.body().get(0).getTitle());
                List<Recipe> recipes = response.body();
                recyclerView.setAdapter(new Recipe_Adapter(recipes, R.layout.list_item_recipe, getApplicationContext()));
           }
            } catch (Exception e) {
                Log.d("onResponse", "There is an error", e);
                e.printStackTrace();


            }
        }

        @Override
        public void onFailure(Call <List<Recipe>> call,Throwable t) {
            Log.d("onFailure", t.toString());
        }
    });

}

} Also the words get added from another activity like this if

(itemList.size() == 1) {

                    words.append(itemList.get(0));
                }else{
                    for (int i = 0; i < (itemList.size() - 1); i++) {
                        words.append(itemList.get(i) + "%2C");

//the %2C is to show that they are separated ingredients, I found out that that's the symbol it is using to translate the comma }

                    words.append((itemList.get(itemList.size() - 1)));

                }

Answer 1

When you define return type as Call<List<Recipe>> for the method getRecipes() in ApiService interface, Retrofit expects a response from server of type JSONArray which should exactly look like -

[
  {
    "publisher": "Allrecipes.com",
    ...
  },
    ...
]

But the response is coming from the server is following -

{
  "count": 1,
  "recipes": [
    {
      "publisher": "Allrecipes.com"
      ...
    },
      ...
  ]
}

So you either need to unwrap the response writing your custom deserializer or you need to Wrap your List in to wrapper class.

Your wrapper class can be like -

public class Recipes{
        private List<Recipe> recipes;
        private int count;
        public List<Recipe> getRecipes() {
            return recipes;
        }

        public void setRecipes(List<Recipe> recipes) {
            this.recipes = recipes;
        }
    }

and hence your ApiService interface method should return Call<Recipes>

Answer 2

So I solved it by changing the first query tag and of course the class that was used as stated by the commenters. I had the @QUERY api instead of key. That's how I changed my interface:

public interface ApiService {
    @GET("api/search/")
    Call<RootObject> getMyJSON(@Query("key") String api_key, @Query("q") StringBuilder st);

}

Also, I changed the base url of my Rest Class because I put the keywords on the interface

public class RestClient {

//gia na ginei h epikoinwnia me to API prepei na xrhsimopoihsw ton retrofit builder kai na prosdiorisw
//to url tou service
public static final String BASE_URL = "http://food2fork.com/";
private ApiService apiService;
        //"?key=";
        //+  addingItems_activity.getApiKey() + "&q=" + addingItems_activity.getWords();
private static Retrofit retrofit = null;

private static Retrofit getRetrofitInstance() {

    return new Retrofit.Builder()
                .baseUrl(BASE_URL)
                .addConverterFactory(GsonConverterFactory.create())
                .build();


  }

public static ApiService getApiService()
{
    return getRetrofitInstance().create(ApiService.class);
}
}

The rest of the solution was stated by first answer. Thank you a lot!