定义请求方法

@Multipart
@POST(RequestApi.GET_DASH_NAME)
Observable<Message> getXXX( @Part MultipartBody.Part body);

获取将要上传的文件并创建MultipartBody.Part对象

  //获取文件路径
    String path =   Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS) + File.separator+"2.jpg" ;
    Log.d(TAG, path);
  //获取路径对应的文件
    File file = new File(path);
    //得到请求体
    RequestBody fileRQ = RequestBody.create(MediaType.parse("image/jpeg"), file);
    //创建MultipartBody.Part对象
    //注意:这个file是后台定义的参数名
    MultipartBody.Part part =MultipartBody.Part.createFormData("file", file.getName(), fileRQ);

请求方法

 RetrofitClient.getApiService().getXXX(part)
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe(new Observer<Message>() {
                @Override
                public void onSubscribe(Disposable d) {
      //订阅
                    subscribe(d);

                }

                @Override
                public void onNext(Message message) {

                    mView.showLoading();
                    mView.setData(message);
                }

                @Override
                public void onError(Throwable e) {
                    Log.e(TAG,e.getMessage());

                        mView.dismissLoading();
                }

                @Override
                public void onComplete() {
                    mView.dismissLoading();
                }
            });