Session Timeouts | Java Servlets Tutorial pdf

Session Timeouts

In the HTTP protocol, there is no explicit termination signal when a client is no longer active. This means that the only mechanism that can be used to indicate when a client is no longer active is a timeout period.
The default timeout period for sessions is defined by the servlet container and can be obtained via the getMaxInactiveInterval method of the HttpSession interface. 

This timeout can be changed by the Developer using the setMaxInactiveInterval method of the HttpSession interface. The timeout periods used by these methods are defined in seconds. By definition, if the timeout period for a session is set to -1, the session will never expire. The session invalidation will not take effect until all servlets using that session have exited the service method. Once the session invalidation is initiated, a new request must not be able to see that session.