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Enterprise JavaBeans:
- Server-side, modular, and reusable components that comprise specific units of functionality
- EJBs are found through Java Naming and Directory Interface (JNDI)
- Has certain restrictions
- Communicates via RMI over IIOP (Remote Method Invocation over Internet Inter-ORB Protocol)

3 types of EJBs:
- Session
- Entity
- Message-Driven

Entity Bean:
- Persistent until explicity deleted
- Identified by a primary key
- Can either be BMP (Bean Managed Persistence - programmer writes the persistence mechanism) or CMP (Container Managed Persistence - app server handles the persistence)
- Typically persisted by a database

Session Bean:
- Can be either stateful or stateless
- Does not have a primary key

Stateless Session Bean:
- Can be pooled

Stateful Session Bean:
- Maintains state information
- Generally used to maintain session when HttpSession is not available

EJB Interfaces:
- Remote - interface used by client outside the JVM of the EJB (uses RMI)
- RemoteHome - creates/gets the remote interface
- Local - interface used by client within the same JVM as the EJB (doesn't use RMI)
- LocalHome - creates/gets the home interface

Usage:
- Most common EJB is stateless session bean
- Stateful session bean and entity beans are rarely used

Tutorials:
EJBTut
Sun EJB Tutorial
Getting started with EJB

Articles:
Stateful Session EJBs: Beasts of Burden
EJB 2.0 - Remote/Local

FAQ:
jGuru

Portals:
Sun EJB
EJBean

Links:
Google
EJB Links

Books:
Mastering EJB 2
EJB Design Patterns

Tools:
XDoclet

Posted: 2003-06-25 21:29:07


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