Session tracking is a mechanism that servlets use to maintain state about a series requests from the same user across some period of time. The methods used for session tracking are:
a) User Authentication - occurs when a web server restricts access to some of its resources to only those clients that log in using a recognized username and password
b) Hidden form fields - fields are added to an HTML form that are not displayed in the client's browser. When the form containing the fields is submitted, the fields are sent back to the server
c) URL rewriting - every URL that the user clicks on is dynamically modified or rewritten to include extra information. The extra information can be in the form of extra path information, added parameters or some custom, server-specific URL change.
d) Cookies - a bit of information that is sent by a web server to a browser and which can later be read back from that browser.
e) Http Session- places a limit on the number of sessions that can exist in memory. This limit is set in the session.maxresidents property

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