Compare between EJB3.0 and EJB2.0

Configuration & Performance improvements in EJB3.0 over EJB2.0

1. EJB2.0 uses XMLDescriptor files to define bean configuration and dependencies and performs JNDI lookups for object references which is slow on performance.
EJB3.0 uses POJOs with newly introduced metadata annotation instead of JNDI lookups and XMLDeployment Descriptor files.This architecture results in better performance.

2. In EJB2.0 one has to write Home and Remote Interfaces and also implement standard interfaces like javax.ejb.SessionBean which requires the implementation of container callback methods like ejbPassivate, ejbActivate, ejbLoad, ejbStore etc.
EJB3.0 is a simple POJO and doesn't need to implement Home or Remote Interfaces and other standard interfaces like javax.ejb.SessionBean. So no need to implement container callback methods like ejbPassivate, ejbActivate, ejbLoad, ejbStore etc. This results in a simplified configuration and better performance.

Flexibility & Portability improvements in EJB3.0 over EJB2.0

1. EJB2.0 objects are heavyweight.
EJB 3.0 entities do not need to implement the interfaces explained above, so they are lightweight and easy to convert from a DAO to Entity bean or vice versa.

2. In EJB2.0 EJB-QL is not very flexible and has limitations.
EJB3.0 uses a refined EJB-QL which allows multiple levels of joins and hence database queries written are very flexible

3. EJB2.0 uses entity beans to access the database.
EJB3.0 supports Java Persistence API for all its data needs which is more generalized and eliminates portability issues.

4. EJB2.0 needs a EJB Container to run.
EJB3.0 does not need to implement standard interfaces and hence can be loaded and run in independent JVM without the need of an EJB container.

5. EJB2.0 has limitations in terms of its pluggability with third party persistence providers.
EJB3.0 can be used with pluggable third party persistence providers.

6. In EJB2.0 security is provided through the use of Deployment descriptors.
In EJB3.0 Security can be provided through annotations which simplifies the configuration and setup tasks and also reduces performance overheads.