Summary (Enterprise JavaBeans)

2.4. 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 interface defines life-cycle methods for creating, finding, and destroying beans and the remote interface defines the public business methods of the bean. The bean class is where the state and behavior of the bean are implemented.

There are two basic kinds of beans: session and entity. Entity beans are persistent and represent a person, place, or thing. Session beans are extensions of the client and embody a process or a workflow that defines how other beans interact. Session beans are not persistent, receiving their state from the client, and they live only as long as the client needs them.

The EJB object and EJB home are conceptual constructs that delegate method invocations to the bean class from the client and help the container to manage the bean class. The client does not interact with the bean directly. Instead, the client software interacts with EJBObject and EJBHome stubs, which are connected to the EJB object and EJB homes respectively. The EJB object implements the remote interface and expands the bean class's functionality. The EJB home implements the home interface and works closely with the container to create, locate, and remove beans.

Beans interact with their container through the well-defined bean-container contract. This contract provides callback methods, the EJBContext, and the JNDI environment context (EJB 1.1 only). The callback methods notify the bean class that it is involved in state management event. The EJBContext and JNDI environment context provides the bean instance with information about its environment. The container-server contract is not well defined and remains proprietary at this time. Future versions of EJB may specify the container-server contract.