• Session tracking in Servlets is done by using Interface HttpSession. It helps to identify a client throughout many page requests or visiting a website and to store details about that client.
• Whenever a request arrives, it checks for the preexisting session object, to fetch details of the client from there, else, if its first request from a new client, its simple creates a session object for that client. These session objects are simple java objects.
• HttpSession contains various methods to handle session object. HttpSession object lives in the server, and it automatically associated with the requester by internal mechanism like cookies or URL-rewriting. 
• Whenever an application invokes or removes an object from a session, the session checks whether the object implemented the interface HttpSessionBindingListener or not. If yes, the servlet informs the object that it has been bounded to the session, if not, notifies unbound from the session. This alert goes after the binding methods complete.

•  HTTP stands for HyperText Transfer Protocol, whereas, HTTPS is HyperText Transfer Protocol Secure.
• HTTP transmits everything as plan text, while HTTPS provides encrypted communication, so that only the recipient can decrypt and read the information.  Basically, HTTPS is a combination of HTTP and SSL (Secure Sockets Layer). This SSL is that protocol which encrypts the data.
• HTTP is fast and cheap, where HTTPS is slow and expensive.
• As, HTTPS is safe it’s widely used during payment transactions or any sensitive transactions over the internet. On the other hand, HTTP is used most of the sites over the net, even this blogspot sites also use HTTP.

• HTTP is a stateless protocol. That means, It doesn’t contain any information regarding the client.
• It works as a request-response protocol in the client-side computing model.
• As it’s an Application Layer Protocol within the Framework Internet Protocol Suite, needs a Transfer Layer Protocol (usually Transmission Control Protocol) for data transmission.  
• It carries request from Client-side (web browser) to the web server, known as HTTP Request. And again the response from the web-server to the browser, known as HTTP Response.

·        Then comes the Request Header, which contains information regarding the 
client environment like, Accept-Charset, Accept-Encoding, Authorization,etc.

• In J2EE Architecture, a web container(also known as servlet container or servlet engine), is used to manage the components like servlets, JSP.
• It provides a runtime environment to the components of J2EE.
• When ever web server receive a request it forward it to web container which deals with it by instantiating, initializing and invoking Servlets and JSP pages. So,basically it controls the whole life cycle of servlet and JSP. 
• It is a part of the web server.
• Example: Apache Tomcat.

• Server loads the servlet class.
• Creates an instance for the servlet class.
• Server initializes the instance by calling init() method.