It's impossible to get the last modification time, because browser sends file as byte array. File upload request contains no information about modification time.
Thanks for your quick answer, Andrei. I just thought that if tag rich:fileUpload has parameter fileUploadListener presenting an action listener method that will be notified after file uploaded. And also there is a parameter immediateUpload. If we put it to "false" then uploading is divided into two phases. After first phase the file is added to a list and we see it's name in local file system. So I thought that maybe there is some fileAddToListListener parameter that presents an action listener method in order to work with files list after adding but before upload.