Enterprise JavaBeans, Fourth Edition

Summary

This chapter covered a lot of ground describing the basic architecture of an EJB system. At this point, you should understand that beans are business object components. The home interfaces define life-cycle methods for creating, finding, and destroying beans, and the remote and local interfaces define the public business methods of the bean. Message-driven beans do not have component interfaces. The bean class is where the state and behavior of the bean are implemented.

There are three basic kinds of beans: entity, session, and message-driven. Entity beans are persistent and represent a person, place, or thing. Session beans are extensions of the client and embody a process or a taskflow that defines how other beans interact. Session beans are not persistent: they receive their state from the client, and they live only as long as the client needs them. Message-driven beans are integration points that allow other applications to interact with EJB applications using JMS or, in EJB 2.1, some other J2eeCA 1.5-compliant resource. Message-driven beans, like stateless session beans, are not persistent and do not maintain conversational state.

The EJB object and EJB home are conceptual constructs that delegate method invocations to session and entity beans from the client and help the container to manage the enterprise bean at runtime. The clients of entity and session beans do not interact with the instances of the bean class directly. Instead, the client software interacts with ...