Add Header Parameter in Retrofit

Question

I'm trying to call an API which requires me to pass in an API key.

My Service call using HttpURLConnection is working perfectly.

url = new URL("https://developers.zomato.com/api/v2.1/search?entity_id=3&entity_type=city&q=" + params[0]);
        urlConnection = (HttpURLConnection) url.openConnection();

        urlConnection.setRequestProperty("user-key","9900a9720d31dfd5fdb4352700c");

        if (urlConnection.getResponseCode() != 200) {
            Toast.makeText(con, "url connection response not 200 | " + urlConnection.getResponseCode(), Toast.LENGTH_SHORT).show();
            Log.d("jamian", "url connection response not 200 | " + urlConnection.getResponseCode());
            throw new RuntimeException("Failed : HTTP error code : " + urlConnection.getResponseCode());
        }

However, I'm not sure how this works with RetroFit as my call in going into Failure at all times. Heres the code I'm using for the same service call

 @GET("search")
Call<String> getRestaurantsBySearch(@Query("entity_id") String entity_id, @Query("entity_type") String entity_type, @Query("q") String query,@Header("Accept") String accept, @Header("user-key") String userkey);

and I'm using this to call it

Call<String> call = endpoint.getRestaurantsBySearch("3","city","mumbai","application/json","9900a9720d31dfd5fdb4352700c");

All these calls are going into the OnFailure Method in RetroFit. If I send it without the HeaderParameters it goes into Success with a 403 because I obviously need to pass the api key somewhere but I cant figure out how.

@GET("search")
Call<String> getRestaurantsBySearch(@Query("entity_id") String entity_id, @Query("entity_type") String entity_type, @Query("q") String query);

The error I'm getting in OnFailure is

java.lang.IllegalStateException: Expected a string but was BEGIN_OBJECT at line 1 column 2 path $

Answer 1

Try this type header for Retrofit 1.9 and 2.0. For Json Content Type.

@Headers({"Accept: application/json"})
@POST("user/classes")
Call<playlist> addToPlaylist(@Body PlaylistParm parm);

You can add many more headers i.e

@Headers({
        "Accept: application/json",
        "User-Agent: Your-App-Name",
        "Cache-Control: max-age=640000"
    })

Dynamically Add to headers:

@POST("user/classes")
Call<ResponseModel> addToPlaylist(@Header("Content-Type") String content_type, @Body RequestModel req);

Call you method i.e

mAPI.addToPlayList("application/json", playListParam);

Or

Want to pass everytime then Create HttpClient object with http Interceptor:

OkHttpClient httpClient = new OkHttpClient();
        httpClient.networkInterceptors().add(new Interceptor() {
            @Override
            public com.squareup.okhttp.Response intercept(Chain chain) throws IOException {
                Request.Builder requestBuilder = chain.request().newBuilder();
                requestBuilder.header("Content-Type", "application/json");
                return chain.proceed(requestBuilder.build());
            }
        });

Then add to retrofit object

Retrofit retrofit = new Retrofit.Builder().baseUrl(BASE_URL).client(httpClient).build();

UPDATE if you are using Kotlin remove the { } else it will not work