Adding header to all request with Retrofit 2

java

network-operations

interceptors

header-management

byAlex Kataev·Sep 4, 2024

To add headers universally, we apply interceptors in Retrofit 2. Start by implementing an Interceptor and tagging it onto your OkHttpClient:

public class UniversalHeaderInterceptor implements Interceptor {
  @Override
  public Response intercept(Chain chain) throws IOException {
    // Passenger "Header" has boarded the train.
    Request request = chain.request().newBuilder()
        .addHeader("Header-Name", "Value")
        .build();
    // Next stop: the Internet! Let's go.
    return chain.proceed(request);
  }
}

OkHttpClient client = new OkHttpClient.Builder()
    .addInterceptor(new UniversalHeaderInterceptor())
    .build();

Follow this by instantiating your Retrofit using this client. This ensures that your header tags along for the ride in every request.

Swifter Header Manipulation

Retrofit 2, a power-tool for network operations, simplifies header management when used in conjunction with OkHttp interceptors. Retrofit 2 delegates networking tasks to OkHttp, allowing you to employ interceptors and shape requests effortlessly.

Action time with Interceptors

Would you use a sledgehammer to crack a nut? Similarly, Interceptors are powerhouses best suited to tasks such as:

Authenticating: Handle headers for OAuth tokens.
Flexing formats: Use the Accept header to express your desired data format.

Interceptor's superpowers

Like a multi-tool Swiss army knife, the intercept() method in an Interceptor is malleable to solve various tasks:

Common parameters: APIs keys or session data can be promptly added to every request.
Retry failed requests: Retry logic can be easily implemented.
Log: Vital information can be logged for debugging.

On-demand headers

In a dynamic landscape, endpoints might ask for different headers. Retrofit 2 translucently handles it via @Header and @Headers:

@Header: Give it to a service method parameter to assign a header dynamically.
@Headers: Decipher it as a guard stationed above the method declaration, adding static headers to every request.

Irreplaceable toolbox

A GsonConverterFactory for JSON parsing, and API base URL via .baseUrl() are some commonplace tools in our Retrofit garage. Add a HttpLoggingInterceptor for a more detailed log, but restrict its use to debug builds to maintain security.

Interceptors: Regular Joe or Sherlock Holmes?

OkHttpClient differentiates between the casual Joe (Application Interceptors) and sleuth Sherlock (Network Interceptors):

Joe: Inspects every request and response, without caring if the response is cached.
Sherlock: Only knocks when the response is fresh from the network, hence, suitable for monitoring and logging.

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