How to create MultipartFile with Spring 6.x.x without using MockMultipartFile

Up until Spring 5.x I was creating the multipart files that way (using now deprecated CommonsMultipartFile):

OutputStream outputStream;
final DiskFileItem diskFileItem = new DiskFileItem("file", mimeType, false, fileName, fileSize, repo));
try (InputStream inputStream = new FileInputStream(actualFile)) {
    outputStream = diskFileItem.getOutputStream();
    IOUtils.copy(inputStream, outputStream);
    return new CommonsMultipartFile(diskFileItem);
} catch (Exception e) {
    throw new GoogleConversionFailedException("Cannot build MultipartFile", e);
}

How to achieve the same result (create MultipartFile out of java.io.File) on Spring 6 without using MockMultipartFile (documentation states that it's supposed to be used for testing i really want to avoid that route)?

You could always just implement the interface which is straight-forward in your case:

public class FileMultipartFile implements MultipartFile{
    private Path path;
    public FileMultipartFile(Path path){
        this.path=path;
    }
    @Override 
    public String getName(){
        return path.getFileName().toString();
    }
    @Override 
    public String getOriginalFilename() {
        return getName();
    }
    @Override
    public String getContentType() {
        try{
             //not ideal as mentioned in the comments of https://stackoverflow.com/a/8973468/10871900 
             return Files.probeContentType(path); 
        }catch(IOException e){
             return null;
        }
    }
    @Override
    public long getSize() {
        return Files.size(path);
    }
    @Override
    public boolean isEmpty() {
        return getSize()==0;
    }
    @Override 
    public byte[] getBytes() throws IOException {
        return Files.readAllBytes(path);
    }
    @Override 
    public InputStream getInputStream() throws IOException {
         return Files.newInputStream(path);
    }
    @Override 
    public void transferTo(File dest) throws IOException, IllegalStateException {
        transferTo(dest.toPath());
    }
    @Override 
    public void transferTo(Path dest) throws IOException, IllegalStateException {
        Files.copy(path, dest);
    }
}

You can create instances using new FileMultipartFile(yourFile.toPath());

In case you want to use a custom name, mime type or similar, you can add additional fields.