I use ServletContextListener to start/stop of one internal working thread.

In contextInitialized(ServletContextEvent event) the Thread object will be 
created and started, than registred as an attribute:

ServletContext context = event.getServletContext();
MailerThread mailerThread = new MailerThread(...);
context.setAttribute("de.mints.interrisk.mail.thread", mailerThread) 

In contextDestroyed(ServletContextEvent event) the thread must be interrupted:

ServletContext context = event.getServletContext();
Thread thread = (Thread)context.getAttribute("de.mints.interrisk.mail.thread");
thread.interrupt();

Under Tomcat 5.5.4 it works fine, but under 5.5.7 thread == null. It seems the 
context's attributes go lost.