- Objects provide encapsulation/re-usability at the class level.
- A component can be comprised of multiple objects
- Component = logical groups of classes = distributed objects = business objects
- A component can be developed to address a specific enterprise applications.
- Hence, components can provide significant encapsulation/re-usability in the partitioned enterprise problems.
- Component model = components + their environments + contracts for interaction
- EJB is a server side component model. Used to create application server side components
- Most sophisticated application server = CTM = Transaction Processing Monitors + Object Request Brokers = J2EE Servers
- EJB components: entity, session, message-driven
- Entity beans = real world objects = business objects = data objects = customers = products = may be contained as records in the database = persistent
- Multiple clients can access entity beans concurrently
- Session beans = processes + tasks. Example: the act of reserving a ticket = to control work flow = to handle a series of tasks carried out by the entity beans = can also access/(help to access) data = do not represent data = transient = after the task is done – no need to maintain states = do not need to support concurrent access
- Message-driven beans = stateless beans = no component interface = respond to client requests = clients place requests through JMS = support concurrent client access = can be used to perform tasks and manage interactions among beans = asynchronous = request and response two separate processes, RMI = synchronous
From: http://sitestree.com/?p=4958
Categories:Java Short Notes
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Post Data:2012-11-26 13:23:36
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