OpenFeign client with MultipartFile -

Question

Here is my application.

@SpringBootApplication
@EnableFeignClients
public class PostLabApplication {

    public static void main(String[] args) {
        SpringApplication.run(PostLabApplication.class, args);
    }

    @Data
    public static class Book {
        private String author;
        private String title;
    }

    @Data
    private static class Comment {
        private String id;
        private String content;
        private MultipartFile file;
    }

    @RestController
    public class MyController {

        @Autowired
        MyFeignClient myFeignClient;

        @PostMapping(value = "/books", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
        public String addBook(@RequestPart("book") Book book, @RequestPart(name = "comments") List<Comment> comments) {
            System.out.println(book);
            System.out.println(comments);
            System.out.println("addBook - Ok");
            return "addBook - Ok";
        }

        @GetMapping("/books-client")
        public String consumeAddBook() throws Exception {
            Book book = new Book();
            book.setAuthor("John");
            book.setTitle("Java");
            List<Comment> comments = new ArrayList<>();

            Comment comment = new Comment();
            comment.setId("001");
            comment.setContent("hello");

            ClassPathResource resource = new ClassPathResource("application.properties");
            InputStream inputStream = resource.getInputStream();
//            InputStreamReader streamReader = new InputStreamReader(inputStream, StandardCharsets.UTF_8);
//            BufferedReader reader = new BufferedReader(streamReader);
//            String content = "";
//            for (String line; (line = reader.readLine()) != null;) {
//                content += line;
//            }
//            System.out.println(content);
            MultipartFile multipartFile = new MockMultipartFile("application.properties", "application.properties", "text/plain", IOUtils.toByteArray(inputStream));
            comment.setFile(multipartFile);

            comments.add(comment);
            myFeignClient.addBook(book, comments);
            return "CLIENT OK";
        }

    }

    @FeignClient(name = "book", url = "http://127.0.0.1:8080")
    public interface MyFeignClient {
        @PostMapping(value = "/books", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
        String addBook(@RequestPart("book") Book book, @RequestPart(name = "comments") List<Comment> comments);
    }

    public class MyClientConfiguration {
        @Bean
        JsonFormWriter jsonFormWriter() {
            return new JsonFormWriter();
        }
    }
    @Configuration
    public class SerializationConfiguration {
        @Bean
        public ObjectMapper objectMapper() {
            return new ObjectMapper().disable(SerializationFeature.FAIL_ON_EMPTY_BEANS);
        }
    }

}

Calling "/book-client" is giving me that exception :

feign.codec.EncodeException: Unexpected IOException (of type java.io.FileNotFoundException): MultipartFile resource [application.properties] cannot be resolved to absolute file path

Yet if I uncomment the commented lines, the file content is displaying.

And if I comment the comment.setFile(multipartFile); it is working but of course with a null file : [PostLabApplication.Comment(id=001, content=hello, file=null)]

I also tried with MultipartFile multipartFile = new MockMultipartFile("application.properties", "Hello".getBytes()); but same result.

What's the problem ? What's the solution for having it working ?