J2EE™ Tutorial, The

Finalizing a Servlet

When a servlet container determines that a servlet should be removed from service (for example, when a container wants to reclaim memory resources, or when it is being shut down), it calls the destroy method of the Servlet interface. In this method, you release any resources the servlet is using and save any persistent state. The following destroy method releases the database object created in the init method described in Initializing a Servlet (page 222):

public void destroy() {
   bookDB = null; 
} 

All of a servlet’s service methods should be complete when a servlet is removed. The server tries to ensure this completion by calling the destroy method only after all service requests have returned or after a server-specific ...