How to upload multiple files using Webflux?

I already found some solutions. Let's suppose that we send an http POST request with an parameter files which contains our files.

Note responses are arbitrary

1. RestController with RequestPart

   @PostMapping("/upload")
   public Mono<String> process(@RequestPart("files") Flux<FilePart> filePartFlux) {
       return filePartFlux.flatMap(it -> it.transferTo(Paths.get("/tmp/" + it.filename())))
           .then(Mono.just("OK"));
   }
   

2. RestController with ModelAttribute

   @PostMapping("/upload-model")
   public Mono<String> processModel(@ModelAttribute Model model) {
       model.getFiles().forEach(it -> it.transferTo(Paths.get("/tmp/" + it.filename())));
       return Mono.just("OK");
   }
   
   class Model {
       private List<FilePart> files;
       //getters and setters
   }
   

3. Functional way with HandlerFunction

   public Mono<ServerResponse> upload(ServerRequest request) {
       Mono<String> then = request.multipartData().map(it -> it.get("files"))
           .flatMapMany(Flux::fromIterable)
           .cast(FilePart.class)
           .flatMap(it -> it.transferTo(Paths.get("/tmp/" + it.filename())))
           .then(Mono.just("OK"));
   
       return ServerResponse.ok().body(then, String.class);
   }
   

the key is use toParts instead of toMultipartData, which is more simpler. Here is the example that works with RouterFunctions.

private Mono<ServerResponse> working2(final ServerRequest request) {
    final Flux<Void> voidFlux = request.body(BodyExtractors.toParts())
        .cast(FilePart.class)
        .flatMap(filePart -> {
            final String extension = FilenameUtils.getExtension(filePart.filename());
            final String baseName = FilenameUtils.getBaseName(filePart.filename());
            final String format = LocalDateTime.now().format(DateTimeFormatter.BASIC_ISO_DATE);

            final Path path = Path.of("/tmp", String.format("%s-%s.%s", baseName, format, extension));
            return filePart.transferTo(path);
        });

    return ServerResponse
        .ok()
        .contentType(APPLICATION_JSON_UTF8)
        .body(voidFlux, Void.class);
}

You can iterate hashmap with Flux and return Flux

Flux.fromIterable(hashMap.entrySet())
            .map(o -> hashmap.get(o));

and it will be send as an array with filepart