在Spring Cloud封装的Feign中并不直接支持传文件，但可以通过引入Feign的扩展包来实现，本文就来具体说说如何实现。

服务提供方（接收文件）

服务提供方的实现比较简单，就按Spring MVC的正常实现方式即可，比如：

@EnableFeignClients
@EnableDiscoveryClient
@SpringBootApplication
public class Application {

    @RestController
    public class UploadController {

        @PostMapping(value = "/uploadFile", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
        public String handleFileUpload(@RequestPart(value = "file") MultipartFile file) {
            return file.getName();
        }

    }

    public static void main(String[] args) {
        new SpringApplicationBuilder(Application.class).web(true).run(args);
    }

}

服务消费方（发送文件）

在服务消费方由于会使用Feign客户端，所以在这里需要在引入feign对表单提交的依赖，具体如下：

<dependency>
   <groupId>io.github.openfeign.form</groupId>
   <artifactId>feign-form</artifactId>
   <version>3.0.3</version>
</dependency>
<dependency>
   <groupId>io.github.openfeign.form</groupId>
   <artifactId>feign-form-spring</artifactId>
   <version>3.0.3</version>
</dependency>
<dependency>
   <groupId>commons-fileupload</groupId>
   <artifactId>commons-fileupload</artifactId>
   <version>1.3.3</version>
</dependency>

定义文件上传方的应用主类和FeignClient，假设服务提供方的服务名为 eureka-feign-upload-server

@EnableFeignClients
@EnableDiscoveryClient
@SpringBootApplication
public class Application {

    public static void main(String[] args) {
        new SpringApplicationBuilder(Application.class).web(true).run(args);
    }

}

@FeignClient(value = "upload-server", configuration = UploadService.MultipartSupportConfig.class)
public interface UploadService {
 
    @PostMapping(value = "/uploadFile", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
    String handleFileUpload(@RequestPart(value = "file") MultipartFile file);
 
    @Configuration
    class MultipartSupportConfig {
        @Bean
        public Encoder feignFormEncoder() {
            return new SpringFormEncoder();
        }
    }
 
}

在启动了服务提供方之后，尝试在服务消费方编写测试用例来通过上面定义的Feign客户端来传文件，比如：

@Slf4j
@RunWith(SpringJUnit4ClassRunner.class)
@SpringBootTest
public class UploadTester {

    @Autowired
    private UploadService uploadService;

    @Test
    @SneakyThrows
    public void testHandleFileUpload() {

        File file = new File("upload.txt");
        DiskFileItem fileItem = (DiskFileItem) new DiskFileItemFactory().createItem("file",
                MediaType.TEXT_PLAIN_VALUE, true, file.getName());

        try (InputStream input = new FileInputStream(file); OutputStream os = fileItem.getOutputStream()) {
            IOUtils.copy(input, os);
        } catch (Exception e) {
            throw new IllegalArgumentException("Invalid file: " + e, e);
        }

        MultipartFile multi = new CommonsMultipartFile(fileItem);

        log.info(uploadService.handleFileUpload(multi));
    }

}

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