Retrofit

import com.google.common.base.MoreObjects;
import com.google.inject.AbstractModule;
import com.google.inject.Guice;
import com.google.inject.Injector;
import com.google.inject.Provides;
import okhttp3.ConnectionPool;
import okhttp3.OkHttpClient;
import retrofit2.*;
import retrofit2.http.GET;
import retrofit2.http.Headers;
import retrofit2.http.Path;

import javax.inject.Inject;
import java.io.IOException;
import java.util.List;
import java.util.concurrent.TimeUnit;

class Post {

    private final long userId;
    private final long id;
    private final String title;
    private final String body;

    public Post(long userId, long id, String title, String body) {
        this.userId = userId;
        this.id = id;
        this.title = title;
        this.body = body;
    }

    @Override
    public String toString() {
        return MoreObjects.toStringHelper(Post.class)
                .add("userId", userId)
                .add("id", id)
                .add("title", title)
                .add("body", body)
                .toString();
    }

}

interface PostClient {

    @Headers({
            "Accept: application/json"
    })
    @GET("posts/{id}")
    Call<Post> findPostById(@Path("id") long id);

    @Headers({
            "Accept: application/json"
    })
    @GET("posts")
    Call<List<Post>> findAllPosts();

}

class App {

    private final Retrofit retrofit;

    @Inject
    public App(Retrofit retrofit) {
        this.retrofit = retrofit;
    }

    public void test() {
        PostClient postClient = retrofit.create(PostClient.class);

        // sync
        try {
            Response<Post> response = postClient.findPostById(12).execute();
            System.out.println(response.body());
            System.out.println("-------------------");
        } catch (IOException e) {
            System.out.println("Error. :(");
            System.out.println("-------------------");
        }

        // async
        postClient.findAllPosts().enqueue(new Callback<List<Post>>() {
            @Override
            public void onResponse(Call<List<Post>> call, Response<List<Post>> response) {
                System.out.println(response.body().get(0));
                System.out.println("-------------------");
            }

            @Override
            public void onFailure(Call<List<Post>> call, Throwable throwable) {
                System.out.println("Error. :(");
                System.out.println("-------------------");
            }
        });
    }

}

class AppModule extends AbstractModule {

    @Override
    protected void configure() {
    }

    @Provides
    public Retrofit provideRetrofit() {
        ConnectionPool connectionPool = new ConnectionPool(5, 60, TimeUnit.SECONDS);

        OkHttpClient httpClient = new OkHttpClient.Builder()
                .connectTimeout(100, TimeUnit.MILLISECONDS)
                .readTimeout(500, TimeUnit.MILLISECONDS)
                .connectionPool(connectionPool)
                .build();

        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl("http://jsonplaceholder.typicode.com/")
                .client(httpClient)
                .addConverterFactory(GsonConverterFactory.create())
                .build();

        return retrofit;
    }

}

public class Application {

    public static void main(String[] args) throws IOException {
        Injector injector = Guice.createInjector(new AppModule());
        App app = injector.getInstance(App.class);
        app.test();
    }

}