OkHttp Interceptors

Interceptors and authenticators are one of them.

Why To Choose?

How Interceptors Works

Add Headers Using Interceptors

Add the Authorization in the header field is the common example while sending the HTTP request.
If we need the header field with the value in each and every request then we can use the interceptor to add this information.

This way, you need not to add the @Header in every end point declaration. There are two ways to add the headers. We can override the existing key with the same key or we can add them just without checking them.

Below is the code snippet we can add with overriding header:
OkHttpClient.Builder httpClient = new OkHttpClient.Builder(); httpClient.addInterceptor(new Interceptor()
{
@Override public Response intercept(Interceptor.Chain chain) throws IOException {
Request original = chain.request(); // Request customization: add request headers
Request.Builder requestBuilder = original.newBuilder() .header("Authorization", "auth-value"); // <-- this is the important line Request request = requestBuilder.build();
return chain.proceed(request);
}
});
OkHttpClient client = httpClient.build();

Blow is the code snippet we can add when we have multiple headers with the same key. The method we need to use is .addHeader.

OkHttpClient.Builder httpClient = new OkHttpClient.Builder(); httpClient.addInterceptor(new Interceptor() {
@Override
public Response intercept(Interceptor.Chain chain) throws IOException { Request original = chain.request(); // Request customization: add request headers
Request.Builder requestBuilder = original.newBuilder() .addHeader("Cache-Control", "no-cache")
.addHeader("Cache-Control", "no-store");
Request request = requestBuilder.build(); return chain.proceed(request); } });
OkHttpClient client = httpClient.build();


Error Handling

Interceptors provide another feature i.e error handling globally. In every request’s response, we need to handle the error codes. If we use an interceptor then we can have a single place where we can handle major errors.

Advantage of this approach is every request made deals the error in the same way.

OkHttpClient okHttpClient = new OkHttpClient.Builder() .addInterceptor(new Interceptor() {
@Override public okhttp3.Response intercept(Chain chain) throws IOException
{
Request request = chain.request();
okhttp3.Response response = chain.proceed(request); // todo deal with the issues the way you need to
if (response.code() == 500)
{
startActivity( new Intent( ErrorHandlingActivity.this, ServerIsBrokenActivity.class ) );
return response;
}
if (response.code() == 401)
{
//Required logic
return response;
}
if (response.code() == 403)
{
//Required logic
return response;
}
return response;
}
}) .build();
Retrofit.Builder builder = new Retrofit.Builder() .baseUrl("https://10.0.2.2:3000/") .client(okHttpClient) .addConverterFactory(GsonConverterFactory.create()); Retrofit retrofit = builder.build();

Conclusion

OkHttp Interceptors provide great methods to handle the app data globally, to log the request and response and also to add the authentication headers. Also we can refresh the token when it will be unauthorised.