EJB Fundamentals
An
enterprise bean is a software component with the following attributes:
- distributed: runs on multiple computers.
- server side: runs on the server. This gives it ample computing power, and centralized support (versus a heavy client, which requires distributed support).
- multitier: it is part of an entire framework with divisions of labor. Presentation is handled on one tier, business logic on another tier, and data on yet another tier.
- The client deals with a single interface for simplicity, but the enterprise bean can be composed of multiple classes.
- The interface and the bean itself must be compliant with the EJB specification.
- Beans can be called by the client, or they can be called by each other.
- For example, consider an airline reservation service. It may have a bean to check seat availability, another bean to actually reserve seats, a third bean to process payment information, and a fourth bean to update frequent flier data.