EJB3.0- Converting MDB stateless bean to stateful bean

You can't use injection of Stateful Session Beans (SFSB) into a multi-threaded component that may be shared by multiple concurrent clients like a Servlet or a Controller. Perform a JNDI lookup instead and put the bean into the HttpSession.

See also

• Stateless and Stateful Enterprise Java Beans
• New Stateful session bean instance without calling lookup

the usage of these type of ejbs are usually in service layer as service classes.

EJB3 stateless and stateful bean are actually POJO (with some annotations) and they don't have any big difference with normal classes.

but in term of usage, they have some abilities that you can't find in normal classes like:

• they can be called remotely (e.g. RMI protocol).
• they can use application server context resources like DB Connection and Transactions.

stateless or stateful: - if a task or process can be done in a single step (by a single method call) stateless is the right option like a authentication process - if a task needs a series of method calls (more than one) and you need to keep previous results to use them in next call, then go for stateful. like a shipping process (select items, add/remove and then do the transaction)

http session or stateful?

ejbs can be served in application server and they may have different type of clients like a normal swing application or ..., so you can't relay on http session in these cases.

if your appserver and webserver are different (distributed) its not good idea keep data in http session and pass/getback it to/from app server (network overhead).