HttpServletSession

HttpServletSession is an interface in Java's Servlet API that represents a user's session on a web server. It allows a web application to maintain state information about a particular client across multiple requests. When a user first visits a web application, a new session is typically created for them. This session is identified by a unique session ID, which is then sent back to the client, usually as a cookie.

Subsequent requests from the same client will carry this session ID, allowing the server to retrieve the associated session object and access any data stored within it. Data can be added to a session using the putValue(String name, Object value) method and retrieved using the getValue(String name) method. Sessions can also store objects associated with a specific name, effectively creating key-value pairs.

Sessions have a limited lifespan, defined by an inactivity timeout. If a client does not make a request for a certain period, the session is invalidated on the server to conserve resources. Developers can explicitly invalidate a session using the invalidate() method, for example, when a user logs out. The HttpServletSession interface provides methods for managing session attributes, checking if a session is new, and retrieving the session ID. It is a fundamental component for building stateful web applications in Java.