Component Types -- Entity Beans

• Most complex component type in the EJB model.

• Represent business objects and an in-memory view of persistent data (data in a database).

• Can be shared by multiple users simultaneously.

• Inherently transactional and can survive server crashes.

• Persistent and represent the data even as it changes over time - periodic synchronization.

Two types of Entity Beans:

Bean-Managed Persistence:

• Entity beans are responsible for making all necessary calls to synchronize data.

• Container will notify the bean when to synchronize - normally occurs when a new transaction is started and after the transaction commits. This is achieved by calls to ejbLoad and ejbStore.

Container-Managed Persistence:

• Containers are responsible for making all necessary calls to synchronize data - provides tools for generating necessary code, scripts or SQL statements.

• The Bean Developer specifies container-managed persistent fields and relationship fields in the deployment descriptor.

• The tools that the container provides for deploying a bean are not defined by EJB specification - can be different for different vendors.

Synchronous Interaction Between Session and Entity Beans