首先，本文不是介绍或讲解，而是实例。
知道点进来的最想要什么，我也不写废话，直接贴代码！

需要添加的依赖

    implementation 'io.reactivex.rxjava2:rxjava:2.2.4'
    implementation 'io.reactivex.rxjava2:rxandroid:2.1.0'
    implementation 'com.squareup.okhttp3:okhttp:3.1.2'
    implementation 'com.squareup.retrofit2:retrofit:2.5.0'
    implementation 'com.squareup.retrofit2:converter-gson:2.5.0'
    implementation 'com.squareup.retrofit2:adapter-rxjava2:2.5.0'
    implementation 'com.squareup.okhttp3:logging-interceptor:3.12.1'

这段才是本体

public class ServiceFactory {
    static final String TAG = "ServiceFactory";
    public static String baseUrl;
    private Retrofit retrofit;

    private static volatile ServiceFactory mInstance;

    public static ServiceFactory getInstance() {
        if(null == mInstance){
            synchronized (ServiceFactory.class) {
                if(null == mInstance) mInstance = new ServiceFactory();
            }
        }
        return mInstance;
    }

    private ServiceFactory(){
        retrofit = new Retrofit.Builder()
                .client(createHttpClient())
                .baseUrl(baseUrl)
                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .addConverterFactory(GsonConverterFactory.create())
                .build();
    }

    public <T> T create(Class<T> reqInterface) {
        return retrofit.create(reqInterface);
    }

    private OkHttpClient createHttpClient() {
        return new OkHttpClient.Builder()
                .connectTimeout(60, TimeUnit.SECONDS)
                .writeTimeout(60, TimeUnit.SECONDS)
                .readTimeout(60, TimeUnit.SECONDS)
                .addInterceptor(createLoggingInterceptor())
                .addInterceptor(createParamInterceptor())
                .build();
    }

    //创建日志拦截器
    private Interceptor createLoggingInterceptor() {
        HttpLoggingInterceptor interceptor = new HttpLoggingInterceptor(message -> {
            try {
                String text = URLDecoder.decode(message, "utf-8");
                Log.d(TAG, text);
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
                Log.e(TAG, message);
            }
        });
        interceptor.setLevel(HttpLoggingInterceptor.Level.BODY);
        return interceptor;
    }

    //创建公共参数拦截器。
    private Interceptor createParamInterceptor() {
        return chain -> {
            Request request = chain.request();
            HttpUrl url = request.url(); //原url

            StringBuilder urlBuilder = new StringBuilder(url.toString());
            if(url.toString().contains("?")) urlBuilder.append("&");
            else urlBuilder.append("?");

            StringBuilder paramBuilder = new StringBuilder()
                    .append("&param1=").append(param1)
                    .append("&param2=").append(param1);
            Log.d(TAG, "public parameter : " + paramBuilder.toString());

            //url拼接公共参数后重新构建请求
            Request newReq = request.newBuilder().url(urlBuilder.append(paramBuilder).toString()).build();
            return chain.proceed(newReq);
        };
    }
}

定义一个接口

public interface CommonRequest {

    @GET("......")
    Observable<Login> doLogin(@QueryMap Map<String, String> map);
    //这个返回的Login对应到json映射的实体类。
}

用起来！

HashMap<String, String> map = new HashMap<>();
        map.put("userName", userName);
        map.put("passWord", passWord);
        ServiceFactory.getInstance().create(CommonRequest.class)
                .doLogin(map)
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(new Observer<Login>() {
                    @Override
                    public void onSubscribe(Disposable d) {
                        
                    }

                    @Override
                    public void onNext(Login login) {
                        //这个返回的bean对应到json映射的实体类。
                    }

                    @Override
                    public void onError(Throwable e) {

                    }

                    @Override
                    public void onComplete() {

                    }
                });

以上

转载请注明出处，@via 小风风吖-详细的Retrofit2 + RxJava2封装 蟹蟹。