How to use interceptor to add Headers in Retrofit 2.0?

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()        )            }}

Another alternative from the accepted answer

public class HeaderInterceptor implements Interceptor {    @Override    public Response intercept(Chain chain) throws IOException {        Request request = chain.request();        request = request.newBuilder()                .addHeader("headerKey0", "HeaderVal0")                .addHeader("headerKey0", "HeaderVal0--NotReplaced/NorUpdated") //new header added                .build();        //alternative        Headers moreHeaders = request.headers().newBuilder()                .add("headerKey1", "HeaderVal1")                .add("headerKey2", "HeaderVal2")                .set("headerKey2", "HeaderVal2--UpdatedHere") // existing header UPDATED if available, else added.                .add("headerKey3", "HeaderKey3")                .add("headerLine4 : headerLine4Val") //line with `:`, spaces doesn't matter.                .removeAll("headerKey3") //Oops, remove this.                .build();        request = request.newBuilder().headers(moreHeaders).build();        /* ##### List of headers ##### */        // headerKey0: HeaderVal0        // headerKey0: HeaderVal0--NotReplaced/NorUpdated        // headerKey1: HeaderVal1        // headerKey2: HeaderVal2--UpdatedHere        // headerLine4: headerLine4Val        Response response = chain.proceed(request);        return response;    }}

   public class ServiceFactory {      public static ApiClient createService(String authToken, String userName, String password) {            OkHttpClient defaultHttpClient = new OkHttpClient.Builder()                    .addInterceptor(                            chain -> {                                Request request = chain.request().newBuilder()                                        .headers(getJsonHeader(authToken))                                        .build();                                return chain.proceed(request);                            })                    .authenticator(getBasicAuthenticator(userName, password))                    .build();            return getService(defaultHttpClient);        }        private static Headers getJsonHeader(String authToken) {            Headers.Builder builder = new Headers.Builder();            builder.add("Content-Type", "application/json");            builder.add("Accept", "application/json");            if (authToken != null && !authToken.isEmpty()) {                builder.add("X-MY-Auth", authToken);            }            return builder.build();        }        private static Authenticator getBasicAuthenticator(final String userName, final String password) {            return (route, response) -> {                String credential = Credentials.basic(userName, password);                return response.request().newBuilder().header("Authorization", credential).build();            };        }          private static ApiClient getService(OkHttpClient defaultHttpClient) {            return new Retrofit.Builder()                    .baseUrl(BASE_URL)                    .addConverterFactory(GsonConverterFactory.create())                    .addCallAdapterFactory(RxJavaCallAdapterFactory.create())                    .client(defaultHttpClient)                    .build()                    .create(ApiClient.class);        }}