This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
Whenever the servlet container determines that a servlet should be unloaded, perhaps to reclaim some resources or because it is being shutdown, the server calls the servlets's destroy method after allowing all of the servlet's service() threads to complete ( or a server-defined time-limit) The servlet is then eligible for a GC. The servlet container is not required to keep a servlet loaded for any specific amount of time.