Building uPortal 4.0.0 from source, I have been trying to convert a portlet that used to work with uPortal 3.2 to now work with 4.0.0. The portlet, written using the spring portlet mvc framework, has a HTML form that includes two fields: one is a textarea and one is a file. The form attribute enctype is set to multipart/form-data. I have confirmed that the portletMultipartResolver is also set in the spring config file and uses the commons fileupload library. I should also mention that the portlet, before submission is validated by an implementation of the spring's Validator interface.
It looks like when the form is submitted, all request parameters are empty and return null. I have confirmed this by looking at the request parameters map and the size is always 0. If I remove the "enctype" element, all parameters are there but of course, file upload won't work.
This configuration works fine under uPortal 3.2. I have not yet tried to see if 4.0.1 has fixed the issue.