This week's book giveaway is in the OCAJP forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide 1Z0-808 and have Jeanne Boyarsky & Scott Selikoff on-line! See this thread for details.
The HttpClient library can help greatly in implementing file upload over HTTP, and the FileUpload library can handle the server part (assuming that the server is a servlet engine). See http://faq.javaranch.com/java/FileUpload for detail.