Paul Mutton, who graduated at the University of Kent at Canterbury in 2001 with first class honours in Computer Science (BSc Hons), created a very small standalone web server written in Java (less than 4 KByte). A more advanced version has less than 10 KByte and is called Jibble Web Server.
The softwares are OSI Certified Open Source Software, available under the GNU General Public License (GPL). Commercial licences are also available.
Other useful Java projects from Paul Mutton are :