interface.java

package com.example.hanlufeng.retrofitdemo;

import okhttp3.ResponseBody;
import retrofit2.Call;
import retrofit2.http.GET;
import retrofit2.http.Url;

interface ApiEndpoints {
    @GET
    Call<ResponseBody> rxGetImageCall(@Url String imageUrl);
}

mainactivity.java

package com.example.hanlufeng.retrofitdemo;


import android.app.Activity;
import android.os.Bundle;
import android.util.Log;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

import java.io.IOException;
import java.util.concurrent.TimeUnit;

import okhttp3.OkHttpClient;
import okhttp3.ResponseBody;
import retrofit2.Call;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.adapter.rxjava.RxJavaCallAdapterFactory;

public class MainActivity extends Activity {

    OkHttpClient client;
    Retrofit retrofit;
    ApiEndpoints apiService;
    final String url = "http://javascript.info/tutorial/hello-world";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //HttpLoggingInterceptor logging = new HttpLoggingInterceptor();
        // set your desired log level
        //logging.setLevel(HttpLoggingInterceptor.Level.BODY);
        Gson gson = new GsonBuilder()
                .setLenient()
                .create();

        this.client = new OkHttpClient.Builder()
                //.addInterceptor(logging)
                .connectTimeout(25, TimeUnit.SECONDS)
                .readTimeout(25, TimeUnit.SECONDS)
                .build();

        // retrofit with custom client
        this.retrofit = new Retrofit.Builder()
                .baseUrl("https://api.github.com/")
                //.addConverterFactory(GsonConverterFactory.create(gson))
                .addCallAdapterFactory(RxJavaCallAdapterFactory.create())
                .client(client)
                .build();
        this.apiService = retrofit.create(ApiEndpoints.class);

        Thread mThread = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    Call<ResponseBody> downCall = downloadImageCall(url);
                    Response<ResponseBody> response = downCall.execute();

                    String value = String.format("body: %1$s --- successful: %2$s --- message: %3$s --- raw: %4$s", response.body().string(),
                            response.isSuccessful(), response.message(), response.raw().toString()
                            );

                    Log.i("Separate", "*********************************************************************");
                    Log.i("VALUE", value);

                } catch (IOException e1) {
                    e1.printStackTrace();
                }
            }
        });

        mThread.start();
    }

    public Call<ResponseBody> downloadImageCall(String uri) {
        return apiService.rxGetImageCall(uri);
    }
}