public class RetrofitManager {
    private static RetrofitManager retrofitManager;
    private Retrofit retrofit;

    private RetrofitManager() {}

	// 使用单例模式封装
    public static RetrofitManager getInstance() {
        if (retrofitManager == null) {
            synchronized (RetrofitManager.class) {
                if (retrofitManager == null) {
                    retrofitManager = new RetrofitManager();
                }
            }
        }
        return retrofitManager;
    }

    public Retrofit getRetrofit() {
        if (retrofit == null) {
        	// 添加日志拦截器
            HttpLoggingInterceptor httpLoggingInterceptor = new HttpLoggingInterceptor();
            // 拦截等级为body(可以打印出完整的网络请求)
            httpLoggingInterceptor.level(HttpLoggingInterceptor.Level.BODY);
			// 使用OkHttpClient
            OkHttpClient okHttpClient = new OkHttpClient.Builder()
                    .addInterceptor(httpLoggingInterceptor)
                    .connectTimeout(1, TimeUnit.MINUTES)
                    .readTimeout(1,TimeUnit.MINUTES)
                    .build();

			// 创建出Retrofit
            retrofit = new Retrofit.Builder()
             		// 使用Gson转换工厂
                    .addConverterFactory(GsonConverterFactory.create())
					.addCallAdapterFactory(RxJava2CallAdapterFactory.create())
					// 基础Url
                    .baseUrl("http://172.81.227.127:8088/")
                    .client(okHttpClient)
                    .build();
        }
        return retrofit;
    }
}

使用Body级别的日志拦截器效果图，可以清晰看出请求方式、接口地址、入参、返回数据等

@Multipart
@POST("fileUpload")
Observable<String> upload(@Part List<MultipartBody.Part> parts);

// 实例化api接口
Api api = RetrofitManager.getInstance().getRetrofit().create(Api.class);

File file = new File("/sdcard/DCIM/Camera/IMG_20191121_010329.jpg");
RequestBody body = RequestBody.create(MediaType.parse("multipart/form-data"), file);

MultipartBody multipartBody = new MultipartBody.Builder()
                .addFormDataPart("file", "IMG.jpg", body)
                .setType(MultipartBody.FORM)
                .build();

api.upload(parts)
                .observeOn(AndroidSchedulers.mainThread())
                .subscribeOn(Schedulers.io())
                .subscribe(new Observer<String>() {
                    @Override
                    public void onNext(String s) {
                        Log.i("--",s); // 请求结果
                    }
                    @Override
                    public void onError(Throwable e) {

                    }
                    @Override
                    public void onComplete() {

                    }
                });

@Multipart
@POST("fileUploadMore")
Observable<String> uploadMore(@PartMap Map<String, List<MultipartBody.Part>> multiMap);

// 实例化api接口
Api api = RetrofitManager.getInstance().getRetrofit().create(Api.class);

File file = new File("/sdcard/DCIM/Camera/IMG_20191121_010329.jpg");
RequestBody body = RequestBody.create(MediaType.parse("multipart/form-data"), file);

MultipartBody multipartBody1 = new MultipartBody.Builder()
                .addFormDataPart("file", "sss1.jpg", body)
                .setType(MultipartBody.FORM)
                .build();
MultipartBody multipartBody2 = new MultipartBody.Builder()
                .addFormDataPart("file", "sss2.jpg", body)
                .setType(MultipartBody.FORM)
                .build();
MultipartBody multipartBody3 = new MultipartBody.Builder()
                .addFormDataPart("file", "sss3.jpg", body)
                .setType(MultipartBody.FORM)
                .build();
MultipartBody multipartBody4 = new MultipartBody.Builder()
                .addFormDataPart("file", "sss4.jpg", body)
                .setType(MultipartBody.FORM)
                .build();

// 把所有文件放入map集合中
Map<String, List<MultipartBody.Part>> parts = new HashMap<>();
parts.put("f1",multipartBody1.parts());
parts.put("f2",multipartBody2.parts());
parts.put("f3",multipartBody3.parts());
parts.put("f4",multipartBody4.parts());

api.uploadMore(parts)
                .observeOn(AndroidSchedulers.mainThread())
                .subscribeOn(Schedulers.io())
                .subscribe(new Observer<String>() {
                    @Override
                    public void onNext(String s) {
                        Log.i("--",s); // 请求结果
                    }
                    @Override
                    public void onError(Throwable e) {

                    }
                    @Override
                    public void onComplete() {

                    }
                });