Overview Of Enterprise Java Bean (EJB). COSC 513 Presentation Mei Li March 17, 2001. What is EJB ?. Widely adopted N-tier sever side component architecture for J2EE. Allows developers to quickly create scalable, versatile, reusable and portable applications.
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COSC 513 Presentation
March 17, 2001
Business Logic Layer
EJB Server & Container
(1) Create me a new EJB object (2) Create EJB object
(3) Return EJB object reference (4) Invoke business method
(5) Delegate request to bean
represent a business process, e.g. Billing credit card, trading stocks.
is associated with one client and the life of the session bean is the life of the customer.
do not survive from the server crashes
representation of persistent data
can be shared by multiple clients
can read from DB and save back to DB
has much longer life and can survive from server crashesSession Beans vs. Entity Beans
When a client needs to use a bean that has been passivated, an activation process occurred.
The state of the bean is swapped in from the persistent storage
If too many beans are instantiated, EJB container can passivate some of them
the state of the bean is saved in a persistent store or file and swapped outActivation vs. Passivation
no internal state
can be pooled to service multiple client
need not to handle activation and passivation
possess internal state
need to hand activation and passivation
examples: shopping cartStateless vs. Stateful
EJB container is responsible for saving and retrieving bean’s state
Independent of data source
Easy to develop
Entity bean is responsible for saving bean’s state.
Less adaptive than container managed entity bean
persistence need to be hard coded into the beanContainer Managed Persistent vs. Bean Managed Persistent