This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
I don't understand what "absolute path" you are asking about. From the code you posted, it looks like you wanted an absolute path on the server. But a FileItem object doesn't correspond to any location in the server's file system, it's just a set of bytes which was uploaded from the client system.
There's nothing stopping you from choosing a directory on the server to store the uploaded file in, and in fact that would probably be the best approach.