Well the problem is that there is no way to know on the server-side that the browser has been closed. The only way to work around that is to set an appropriate timeout after which you close the session.
Also you might want to read the following
thread which discusses the same issues.
http://www.javaranch.com/ubb/Forum50/HTML/000219.html HIH
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Valentin Crettaz
Sun Certified Programmer for
Java 2 Platform
[This message has been edited by Valentin Crettaz (edited November 22, 2001).]