java - How to use interceptor to add Headers in Retrofit 2.0?

Question

Our team decide to adopt Retrofit 2.0 and I'm doing some initial research on it. I'm a newbie to this library.

I'm wondering how to use interceptor to add customized headers via Retrofits 2.0 in our Android app. There are many tutorials about using interceptor to add headers in Retrofit 1.X, but since the APIs have changed a lot in the latest version, I'm not sure how to adapt those methods in the new version. Also, Retrofit hasn't update its new documentation yet.

For example, in the following codes, how should I implement the Interceptor class to add extra headers? Besides, what exactly is the undocumented Chain object? When will the intercept() be called?

    OkHttpClient client = new OkHttpClient();
    client.interceptors().add(new Interceptor() {
        @Override
        public Response intercept(Chain chain) throws IOException {
            Response response = chain.proceed(chain.request());

            // How to add extra headers?

            return response;
        }
    });

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

Answer 1

Check this out.

public class HeaderInterceptor implements Interceptor {
    @Override
    public Response intercept(Chain chain) throws IOException {
        Request request = chain.request()
                .newBuilder()
                .addHeader("appid", "hello")
                .addHeader("deviceplatform", "android")
                .removeHeader("User-Agent")
                .addHeader("User-Agent", "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:38.0) Gecko/20100101 Firefox/38.0")
                .build();
        Response response = chain.proceed(request);
        return response;
    }
}

Kotlin

class HeaderInterceptor : Interceptor {
    override fun intercept(chain: Interceptor.Chain): Response = chain.run {
        proceed(
            request()
                .newBuilder()
                .addHeader("appid", "hello")
                .addHeader("deviceplatform", "android")
                .removeHeader("User-Agent")
                .addHeader("User-Agent", "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:38.0) Gecko/20100101 Firefox/38.0")
                .build()
        )        
    }
}