Question
Answer and Explanation
To use a Kotlin API interceptor when making a call, you'll typically be working with a library like OkHttp, which is a popular choice for handling HTTP requests in Android and Kotlin applications. Here’s a breakdown of how you can create and utilize an interceptor:
1. Understand Interceptors:
Interceptors are powerful tools that can monitor, modify, or short-circuit network requests. They are part of OkHttp's architecture and allow you to add common functionality to your API calls such as logging, adding headers, or handling authentication.
2. Creating a Kotlin Interceptor:
You’ll create a class that implements the okhttp3.Interceptor interface. This interface has a single method, intercept(chain: Interceptor.Chain), which gives you access to the request and the ability to proceed with or modify it.
Here’s an example of a simple logging interceptor:
import okhttp3.Interceptor
import okhttp3.Response
import okhttp3.logging.HttpLoggingInterceptor
class LoggingInterceptor : Interceptor {
override fun intercept(chain: Interceptor.Chain): Response {
val request = chain.request()
val t1 = System.nanoTime()
println("Sending request ${request.url} on ${chain.connection()}")
val response = chain.proceed(request)
val t2 = System.nanoTime()
println("Received response for ${response.request.url} in ${(t2 - t1) / 1e6}ms")
return response
}
}
3. Implementing Header Interceptor:
Here’s an example of how you can create an interceptor to add an authentication header to your request. Assuming you have an API token:
import okhttp3.Interceptor
import okhttp3.Response
class AuthInterceptor(private val apiToken: String) : Interceptor {
override fun intercept(chain: Interceptor.Chain): Response {
val newRequest = chain.request().newBuilder()
.addHeader("Authorization", "Bearer $apiToken")
.build()
return chain.proceed(newRequest)
}
}
4. Adding Interceptor to OkHttpClient:
You must add the interceptor to an OkHttpClient instance. This client is used to make network requests. Typically, you will do this when setting up the client (e.g. using Retrofit):
import okhttp3.OkHttpClient
val okHttpClient = OkHttpClient.Builder()
.addInterceptor(LoggingInterceptor())
.addInterceptor(AuthInterceptor("YOUR_API_TOKEN"))
.build()
5. Using the OkHttpClient with Retrofit:
If you're using Retrofit, the configured OkHttpClient should be provided during the Retrofit builder configuration:
import retrofit2.Retrofit
import retrofit2.converter.gson.GsonConverterFactory
val retrofit = Retrofit.Builder()
.baseUrl("YOUR_BASE_URL")
.client(okHttpClient)
.addConverterFactory(GsonConverterFactory.create())
.build()
Important Considerations:
Order Matters: Interceptors are applied in the order you add them. Logging interceptors should typically be added first for accurate logging of requests and responses.
Error Handling: Consider adding error handling within the interceptor. For example, you might want to retry failed requests or modify error responses.
Performance: Avoid doing heavy work in interceptors, as they are executed on the request/response pathway.
In conclusion, Kotlin API interceptors provide a flexible and powerful way to handle various aspects of your network calls. They can be easily integrated into your OkHttp client, allowing you to tailor your HTTP requests and responses as needed.