Top Most What's difference between Servlet/JSP session and EJB session

From a logical point of view, a Servlet/JSP session is similar to an EJB session. Using a session, in fact, a client can connect to a server and maintain his state.

But, is important to understand, that the session is maintained in different ways and, in theory, for different scopes.

A session in a Servlet, is maintained by the Servlet Container through the HttpSession object, that is acquired through the request object. You cannot really instantiate a new HttpSession object, and it doesn't contains any business logic, but is more of a place where to store objects.

A session in EJB is maintained using the SessionBeans. You design beans that can contain business logic, and that can be used by the clients. You have two different session beans: Stateful and Stateless. The first one is somehow connected with a single client. It maintains the state for that client, can be used only by that client and when the client "dies" then the session bean is "lost".

A Stateless Session Bean doesn't maintain any state and there is no guarantee that the same client will use the same stateless bean, even for two calls one after the other. The lifecycle of a Stateless Session EJB is slightly different from the one of a Stateful Session EJB. Is EJB 

Container's responsability to take care of knowing exactly how to track each session and redirect the request from a client to the correct instance of a Session Bean. The way this is done is vendor dependant, and is part of the contract.

Container View Point :
1. Servlet Container

• A HttpServlet.service() represents a client thread.
• A logical session is maintaied per such different client threads.The container manages the association rather then the Servlet.Hence Servlet from the pool of servlet instances are reusable for different threads and can be swaped in between client threads.This is why Servlet Instance variable are not thread-safe.

2. EJB Container : Stateful Session Bean.

• The Stateful Session Bean LOGICALLY is a "client thread with State".This thread can be Activated/Passivated as per the situation.But during this 
• activation/passivation essentially the state is saved plus anything else instructed by the bean developer in respective methods.
• In other words the state mangement control is available to 
• Bean developer also.This is what missing in servlet.In other words for Stateful Session Bean instance variable are thread safe.

Designers Perspective :


1. Servlet
Helps the session management but the servlet developer needs to invoke SessionManagement API to read/write.Right candidate for UserInfo,AuthInfo etc.

2.SFB
A well designed component for the stateful processes.
An object state is automaticaly managed by container.Thread-saftey is guranteed.Developer need not to bother.Right candidate for Order/Shopping Process.
Performance wise it is a FEELING that SFB are slower then simple http sessions.Hence needs to be used with care.