由于自己也是在网上几经一番折腾才找到部分博客并加以修改实现; 话不多说直接上代码;

1.1 文件上传之服务端代码(在此处以服务端内部上传OSS为例)

     @PostMapping(value = "upload")
    public BaseResult<String> test(MultipartFile file) {
        String downloadUrl = fileService.upload(file);
        Preconditions.checkArgument(StringUtils.isNotEmpty(downloadUrl), UPLOAD_FILE_ERROR);
        return BaseResult.generateSuccessRestlt(downloadUrl);
    }
  
      @Override
    public String upload(MultipartFile file) {
        String filename = file.getOriginalFilename();
        try (InputStream inputStream = file.getInputStream()) {
            PutObjectRequest putObjectRequest = new PutObjectRequest(fileConfig.getBucketName(),
                filename, inputStream);
            ossClient.putObject(putObjectRequest);
        } catch (IOException e) {
            log.error("filename:[{}],获取文件输入流错误!", filename, e);
            return null;
        } catch (OSSException | ClientException e) {
            log.info("上传文件失败filename:[{}]", filename, e);
            return null;
        }
        return filename;
    }

1.2 文件下载之服务端代码

      @GetMapping(value = "download")
    public void down(@RequestParam(value = "filename") String filename,
        HttpServletResponse response) {
        fileService.download(filename, response);
    }

      @Override
    public void download(String filepath, HttpServletResponse response) {
        response
            .setContentType("application/x-download;charset=" + Charsets.UTF_8.displayName());
        response.addHeader("Content-Disposition",
            "attachment;filename=" + this.reWriteChinese(filepath));
        // ossObject包含文件所在的存储空间名称、文件名称、文件元信息以及一个输入流。
        OSSObject ossObject;
        try {
            ossObject = ossClient.getObject(fileConfig.getBucketName(), filepath);
        } catch (OSSException | ClientException e) {
            log.error("获取OSS文件连接异常,filePath:[{}]", filepath, e);
            return;
        }

        try (OutputStream outputStream = response.getOutputStream();
            InputStream inputStream = ossObject.getObjectContent()) {
            IOUtils.copy(inputStream, outputStream);
            outputStream.flush();
        } catch (IOException e) {
            log.error("下载文件异常 filepath:[{}]", filepath, e);
        }
    }

1.3 文件上传和下载FeignClient调用方代码

  /*
 * Copyright (c) 2020 daguimu.geek@gmail.com
 * All rights reserved.
 *
 */
package com.dagm.api.feignclient;

import feign.Response;
import feign.codec.Encoder;
import feign.form.spring.SpringFormEncoder;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.context.annotation.Bean;
import org.springframework.http.MediaType;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RequestPart;
import org.springframework.web.multipart.MultipartFile;

/**
 * @author Guimu
 * @date 2020/01/08
 */
@FeignClient(value = "file-service", configuration = FileFeign.MultipartSupportConfig.class)
public interface FileFeign {

    /**
     * 调用feign 对文件进行上传
     *
     * @param file 待上传的文件
     * @return com.dagm.shorter.res.BaseResult<java.lang.String>
     * @author Guimu
     * @date 2020/1/8
     */
    @PostMapping(value = "/inner/upload", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
    BaseResult<String> upload(@RequestPart("file") MultipartFile file);

    /**
     * 文件下载
     *
     * @return feign.Response
     * @author Guimu
     * @date 2020/1/8
     */
    @GetMapping(value = "/inner/download")
    Response download(@RequestParam("filename") String filename);

    class MultipartSupportConfig {

        @Bean
        public Encoder feignFormEncoder() {
            return new SpringFormEncoder();
        }
    }
}

1.4 tip:

1. 文件的上传下载服务端代码, 和一般的上传下载一样：
   OpenFeign 文件上传需要配置Encoder, 我这里用的是feign-form; 也可以选择其他的;
   feign-form 版本对应 3.5版本之后的对应OpenFeign 10.* , 3.5版本之前的对应OpenFeign9.*

1.5 相关的pom 依赖

     <dependency>
      <groupId>io.github.openfeign.form</groupId>
      <artifactId>feign-form</artifactId>
      <version>3.4.1</version>
    </dependency>
    <dependency>
      <groupId>io.github.openfeign.form</groupId>
      <artifactId>feign-form-spring</artifactId>
      <version>3.4.1</version>
    </dependency>

1.6 附加一个调用方使用OpenFeign 上传文件和下载并返回给调用方客户端的demo

   
   @PostMapping(value = "upload")
   public BaseResult<String> test(MultipartFile file) {
       return fileFeign.upload(file);
   }

   @GetMapping(value = "download")
   public void download(@RequestParam(value = "filename") String filename,
       HttpServletResponse httpServletResponse) {
       httpServletResponse
           .setContentType("application/x-download;charset=" + Charsets.UTF_8.displayName());
       httpServletResponse.addHeader("Content-Disposition",
           "attachment;filename=" + this.reWriteChinese(filename));
       Response response = fileFeign.download(filename);
       Response.Body body = response.body();
       try (OutputStream outputStream = httpServletResponse.getOutputStream();
           InputStream inputStream = body.asInputStream()) {
           IOUtils.copy(inputStream, outputStream);
           outputStream.flush();
       } catch (IOException e) {
           log.error("下载文件异常 filepath:[{}]", filename, e);
       }
   }