Spring Boot Rest Api - Multiple @RequestPart not working with Feign client

Question

I have a Spring Boot 2.4.3 with

@RestController
public class DemoFeignController {
    @PutMapping(value = "/document", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
    public String upload(@RequestPart("file") MultipartFile multipartFile,
                         @RequestPart("config") String config) {
        System.out.println(multipartFile.getSize());
        System.out.println("config:" + config);
        return "upload";
    }
    @PutMapping(value = "/document2", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
    public String upload2(@RequestPart("file") MultipartFile multipartFile,
                         @RequestPart("config") DocumentConfiguration documentConfiguration) {
        System.out.println(multipartFile.getSize());
        System.out.println("config2:" + documentConfiguration);
        return "upload2";
    }
}

I also have

@Component
public class DemoFeignServiceAdapter extends WebMvcConfigurerAdapter {
    @Autowired
    DemoFeignServiceInterceptor filetnetServiceInterceptor;
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(filetnetServiceInterceptor);
    }
}

and

@Component
public class DemoFeignServiceInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("Pre Handle http request");
        request.getParts().stream()
                .forEach(part -> {
                    System.out.println(part.getName());
                });
        return true;
    }
}

and eventually

@Data public class DocumentConfiguration { private String name; private String type; }

If I call those 2 endpoints with Postman, it's working.

With

Calling /upload and /upload2, I can see in the logs

Pre Handle http request
file
config
1161530
config:{"name": "my-document", "type": "pdf"}
Pre Handle http request
file
config
1161530
config2:DocumentConfiguration(name=my-document, type=pdf)

config2:DocumentConfiguration(name=my-document, type=pdf)

Now with Feign client

@FeignClient(name = "demo-service", url = "http://localhost:8090")
public interface DemoFeignProxy {
    @PutMapping(value = "/document", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
    String upload(@RequestPart("file") MultipartFile multipartFile,
                         @RequestPart("config") String config);
    @PutMapping(value = "/document2", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
    String upload2(@RequestPart("file") MultipartFile multipartFile,
                          @RequestPart("config") DocumentConfiguration documentConfiguration);
}

and

@SpringBootTest
class DemoFeignApplicationTests {
    @Autowired
    DemoFeignProxy demoFeignProxy;
    @Test
    void upload() {
        byte[] file = "Hello world".getBytes(StandardCharsets.UTF_8);
        MultipartFile multipartFile = new MockMultipartFile("file", "temp", "text/plain", file);
        System.out.println(demoFeignProxy.upload(multipartFile, "my-config"));
    }
    @Test
    void upload2() {
        byte[] file = "Hello world".getBytes(StandardCharsets.UTF_8);
        MultipartFile multipartFile = new MockMultipartFile("file", "temp", "text/plain", file);
        DocumentConfiguration documentConfiguration = new DocumentConfiguration();
        documentConfiguration.setName("my-config");
        documentConfiguration.setType("pdf");
        System.out.println(demoFeignProxy.upload2(multipartFile, documentConfiguration));
    }
}

For upload, it's working.

Pre Handle http request
file
config
11
config:my-config

But for upload2, it's not working

Pre Handle http request
file
name
type
2021-03-02 13:39:05.850  WARN 20836 --- [nio-8090-exec-2] .w.s.m.s.DefaultHandlerExceptionResolver : 
Resolved [org.springframework.web.multipart.support.MissingServletRequestPartException: Required request part 'config' is not present]

I don't understand why I have name and type instead of config.

Because it's fine with Postman, I suppose the problem is coming from the Feign client. But I don't know what I'm missing.

Edit:

Calling http://127.0.0.1:8090/swagger-ui/index.html I also have an exception

javax.servlet.ServletException: org.apache.tomcat.util.http.fileupload.impl.InvalidContentTypeException: the request doesn't contain a multipart/form-data or multipart/mixed stream, content type header is null