Spring MVC file upload controller - I'd like the controller to be called as soon as the upload starts

Question

Using a naked servlet\'s doPost, when a file upload starts, doPost is immediately called. I can then stream the files from the request object using the commons FileItemIterator.

Answer 1

You want streaming file uploads however when using Spring’s multipart (file upload) support it uses the classic approach. This basically means that all multipart parts of a request are parsed before the request is actually handed down to the controller. This is needed because a MultipartFile can be used as method argument and for this to work it needs to be available to the controller.

If you want to handle streaming file uploads you will have to disable Spring's multipart support and do the parsing yourself in the controller, the same way you would do in a servlet.

@Controller
public class FileUploadController {

    @RequestMapping("/upload")
    public void upload(HttpServletRequest request) {
        boolean isMultipart = ServletFileUpload.isMultipartContent(request);
        if (!isMultipart) {
            // Inform user about invalid request
        }

        // Create a new file upload handler
        ServletFileUpload upload = new ServletFileUpload();

        // Parse the request
        FileItemIterator iter = upload.getItemIterator(request);
        while (iter.hasNext()) {
            FileItemStream item = iter.next();
            String name = item.getFieldName();
            InputStream stream = item.openStream();
            if (item.isFormField()) {
                System.out.println("Form field " + name + " with value "+ Streams.asString(stream) + " detected.");
            } else {
                System.out.println("File field " + name + " with file name " + item.getName() + " detected.");
            // Process the input stream
            ...
            }
        }
    }
}

See also how to upload a file using commons file upload streaming api and Apache commons fileupload "Streaming API"