Session 是啥

4.4.7.2.1 How the Web Container Manages Session State

Application servers typically track user sessions with somecombination of cookies and/or URL rewriting to store a session ID onthe client. The session ID identifies the session, and the server isresponsible for associating each HttpServletRequest with its corresponding HttpSessionobject. The J2EE server handles the details of using cookies and URLrewriting. The section "Maintaining Client State" in The J2EE Tutorialexplains in detail how to manage Web-tier session state.