Upload files ：

	@PostMapping(value = "/upload")
    public Mono<String> requestBodyFlux(@RequestPart("filePart") FilePart filePart) throws IOException {
    
        System.out.println(filePart.filename());
        Path tempFile = Files.createTempFile("tmp", filePart.filename());
        //NOTE  Method 1 
        AsynchronousFileChannel channel =
                AsynchronousFileChannel.open(tempFile, StandardOpenOption.WRITE);
        DataBufferUtils.write(filePart.content(), channel, 0)
        .subscribe();
        //NOTE  Method 2 
// filePart.transferTo(tempFile.toFile());
        System.out.println(tempFile.toString());
        return Mono.just(filePart.filename());
    }

File download ：

    @GetMapping("/download")
    public Mono<Void> downloadByWriteWith(ServerHttpResponse response) throws IOException {
    
        ZeroCopyHttpOutputMessage zeroCopyResponse = (ZeroCopyHttpOutputMessage) response;
        response.getHeaders().set(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=cert.crt");
        response.getHeaders().setContentType(MediaType.APPLICATION_OCTET_STREAM);
        Resource resource = new ClassPathResource("cert.crt");
        File file = resource.getFile();
        return zeroCopyResponse.writeWith(file, 0, file.length());
    }