Problems developing module that uploads text files for parsing later

I am developing a module which supports upload of a text file which should be parsed later. I am trying to retrieve an uploaded file in my controller, but although it does recognize multipart form data submission, the file is not available.

In my JSP I have a form field:

<form method="post" enctype="multipart/form-data">
Select file to upload:
<input type="file" name="my_file"/><br/><br/>
<input type="submit" value="Upload File" name="uploadButton" />

I am trying to access the file in the controller like this:

boolean isMultipart = ServletFileUpload.isMultipartContent(request);//this gives TRUE

DiskFileItemFactory factory = new DiskFileItemFactory();
factory.setRepository(new File("/tmp"));
ServletFileUpload upload = new ServletFileUpload(factory);
List<FileItem> items = upload.parseRequest(request);

isMultipart is “TRUE” so it does recognize a file is submitted, but the size of items is 0.

Please see and this example in OpenMRS codebase (in the example UploadForm has the MultipartFile field):