This might be a good opportunity to dispel some of the myths about cookies, and why, if used properly, they can be a good thing. Cookies are just information that is stored in your browser. That information is sent back to a web site when a page request is made. Simply put, cookies cannot interact with a user's hard disk. The JDC uses the value stored in the cookie to help with navigation through the web site.
Cookies allow a straightforward way of authenticating users only once.
Session-tracking information is used only to gather information so that it can provide members with the information they are seeking. Each time the servlet is invoked, its service method is run. This is handled by the Java Web Server. For now, assume the value returned is valid. If this is a user's first visit to the web site, that is, they have an invalid or no session, the JDC redirects the browser to the SessionServlet.