Retrofit Java 11 Http Client adapter

An adapter between Retrofit and asynchronous non-blocking Java 11 Http Client.

With Retrofit by default OkHttp client is used under the hood as an HTTP client library which is a great library, but it has one major flaw - under the hood OkHttp uses blocking IO even for async calls (Dispatcher creates a worker thread per each network call). It's acceptable for Android applications where a number of background threads usually is not too big, but for Java web server applications a thread per each network call sometimes is a major no-go.

The adapter solves the problem by bringing to Retrofit support of fully asynchronous non-blocking Java 11 Http Client. With the adapter, Http Client seamlessly integrates into Retrofit architecture - Retrofit features like converter or call adapter factories (like Retrofit Project Reactor for example) tend to work out of the box.

Download

Gradle

repositories {
    maven {
        url  "https://dl.bintray.com/ankburov/maven"
    }
}

dependencies {
    compile "io.ankburov:retrofit-http-client-adapter:<version>"
}

Usage

Declare a Retrofit interface:

public interface GitHubService {
    
    // synchronous call
    @GET("users/{user}/repos")
    Call<List<Repo>> listRepos(@Path("user") String user);
    
    // asynchronous call
    CompletableFuture<List<Repo>> listReposAsync(@Path("user") String user);
}

Create an instance of Retrofit interface

HttpClient httpClient = HttpClient.newHttpClient();

HttpClientRetrofitCallFactory callFactory = HttpClientRetrofitCallFactory.builder(httpClient)
        .build();

Retrofit retrofit = new Retrofit.Builder()
        .baseUrl("https://api.github.com/")
        .callFactory(callFactory)
        .build();

GitHubService service = retrofit.create(GitHubService.class);

Interceptors

Java 11 HTTP Client currently lacks the support of interceptors concept - code that wraps around an HTTP call. The library adds the feature for all (sync and asyc) requests. To use it, implement io.ankburov.retrofit.httpclient.Interceptor interface and register the instance to the call factory:

public class CallMetricsInterceptor implements Interceptor {

    private final MeterRegistry meterRegistry;
    
    @Override
    public Request onRequest(@NotNull Request request) {
        return request.newBuilder()
                .tag(Timer.Sample.class, Timer.start(meterRegistry))
                .build();
    }
    
    @Override
    public Response onResult(@NotNull Request request, @Nullable Response response, @Nullable Throwable throwable) {
        request.tag(Timer.Sample.class)
                .stop(Timer.builder("call_duration")
                .description("Call duration")
                .tag("method", request.method())
                .tag("path", request.url().encodedPath())
                .publishPercentileHistogram(false)
                .publishPercentiles(0.8, 0.9, 0.95)
                .register(meterRegistry));
        return response;
    }
}

callFactory.addInterceptor(new CallMetricsInterceptor())