I am writing a server application that should forward a file and upload it to another server.

front-end ---> forwarder ---> backend

The forwarder received the file from the frontend successfully. But when I try to forward it, I get an error:

@Autowired
private BackendFeignClient backend;

public ResponseEntity<FileMetadataOutDTO> forward(FileMetadataInDTO fileMetadataInDTO, MultipartFile file, String jwtToken)
{
    return backend.save(fileMetadataInDTO, file, jwtToken);
}

The feign client looks like this:

@FeignClient(
        name = "file-upload-client", url = "${manager.root.uri}", configuration = BackendFeignClient.MultipartSupportConfig.class)
public interface BackendFeignClient
{
    @PostMapping(value = "/upload", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
    public ResponseEntity<FileMetadataOutDTO> save(
            @RequestPart("fileMetadataInDTO") FileMetadataInDTO fileMetadataInDTO,
            @RequestPart("file") MultipartFile file,
            @RequestHeader(HttpHeaders.AUTHORIZATION) String jwtToken);

    public class MultipartSupportConfig {
        @Autowired
        private ObjectFactory<HttpMessageConverters> messageConverters;

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

The backend, just like the forwarder, accepts the file and metadata like this:

@PostMapping(consumes = "multipart/form-data")
public FileMetadataOutDTO save(
        @Valid @RequestPart(value = "fileMetadataInDTO") FileMetadataInDTO fileMetadataInDTO,
        @RequestPart(value = "file", required = true) MultipartFile file)
{
    return fileService.save(calibrationCertificateInDTO, file);
}

Unfortunately, I get this error:

Converted error json {
  "type" : "about:blank",
  "title" : "Bad Request",
  "status" : 400,
  "detail" : "Required part 'fileMetadataInDTO' is not present.",
  "instance" : "/api/v1/upload"
}

I tried adding MediaType.APPLICATION_JSON_VALUE , but then the body could not be encoded.

consumes = { MediaType.APPLICATION_JSON_VALUE, MediaType.MULTIPART_FORM_DATA_VALUE }

I also added those dependencies:

<dependency>
    <groupId>io.github.openfeign.form</groupId>
    <artifactId>feign-form</artifactId>
    <version>3.8.0</version>
</dependency>
<dependency>
    <groupId>io.github.openfeign.form</groupId>
    <artifactId>feign-form-spring</artifactId>
    <version>3.8.0</version>
</dependency>

But it didn’t help.