Retrofit and OkHttp power network operations in Android apps. Master API definitions, custom interceptors, and token-based authentication.
Defining Retrofit API Interface
Create type-safe API endpoints:
interface ApiService {
@GET("users/{id}")
suspend fun getUser(@Path("id") userId: String): User
@POST("posts")
suspend fun createPost(@Body post: PostRequest): PostResponse
@GET("posts")
suspend fun listPosts(
@Query("page") page: Int = 1,
@Query("limit") limit: Int = 20
): List<Post>
}
Setting Up Retrofit with OkHttp
Configure HTTP client with interceptors:
val httpClient = OkHttpClient.Builder()
.addInterceptor(LoggingInterceptor())
.addNetworkInterceptor(StethoInterceptor())
.connectTimeout(30, TimeUnit.SECONDS)
.readTimeout(30, TimeUnit.SECONDS)
.writeTimeout(30, TimeUnit.SECONDS)
.build()
val retrofit = Retrofit.Builder()
.baseUrl("https://api.example.com/")
.client(httpClient)
.addConverterFactory(GsonConverterFactory.create())
.addCallAdapterFactory(RxJava3CallAdapterFactory.create())
.build()
val apiService = retrofit.create(ApiService::class.java)
Adding Authentication Interceptor
Automatically attach tokens to requests:
class AuthInterceptor(private val tokenProvider: TokenProvider) : Interceptor {
override fun intercept(chain: Interceptor.Chain): Response {
val originalRequest = chain.request()
val token = tokenProvider.getAuthToken()
val authenticatedRequest = originalRequest.newBuilder()
.header("Authorization", "Bearer $token")
.build()
return chain.proceed(authenticatedRequest)
}
}
// Add to OkHttpClient
httpClient.addInterceptor(AuthInterceptor(tokenProvider))
Error Handling and Retry Logic
Implement robust error handling:
class ErrorInterceptor : Interceptor {
override fun intercept(chain: Interceptor.Chain): Response {
var response = chain.proceed(chain.request())
if (response.code == 401) {
// Token expired, refresh and retry
refreshToken()
response = chain.proceed(chain.request())
}
return response
}
}
// Use with coroutines
viewModelScope.launch {
try {
val user = apiService.getUser("123")
updateUI(user)
} catch (e: HttpException) {
showError("HTTP Error: ${e.code()}")
} catch (e: IOException) {
showError("Network Error")
}
}
Retrofit simplifies API integration. Combine it with proper interceptor setup for production-ready networking.
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