EJB.8.1 Overview

For a client, an entity bean is a component that represents an object-oriented view of some entities stored in a persistent storage, such as a database, or entities that are implemented by an existing enterprise application.

A client accesses an entity bean through the entity bean's remote and home interfaces. The container provides classes that implement the entity bean's remote and home interfaces. The objects that implement the home and remote objects are remote Java objects, and are accessible from a client through the standard Java APIs for remote object invocation.

From its creation until its destruction, an entity object lives in a container. Transparently to the client, the container provides security, concurrency, transactions, persistence, and other services for the entity objects that live in the container. The container is transparent to the client ”there is no API that a client can use to manipulate the container.

Multiple clients can access an entity object concurrently. The container in which the entity bean is deployed properly synchronizes access to the entity object's state using transactions.

Each entity object has an identity which, in general, survives a crash and restart of the container in which the entity object has been created. The object identity is implemented by the container with the cooperation of the enterprise bean class.

The client view of an entity bean is location independent. A client running in the same JVM as an entity bean instance uses the same API to access the entity bean as a client running in a different JVM on the same or different machine.

A client of an entity object can be another enterprise bean deployed in the same or different container; or a client can be an arbitrary Java program, such as an application, applet, or servlet. The client view of an entity bean can also be mapped to non-Java client environments, such as CORBA clients not written in the Java programming language.

Multiple enterprise beans can be deployed in a container. For each entity bean deployed in a container, the container provides a class that implements the entity bean's home interface . The home interface allows the client to create, find, and remove entity objects within the enterprise bean's home. A client can look up the entity bean's home interface through JNDI API; it is the responsibility of the container to make the entity bean's home interface available in the JNDI API name space.

A client view of an entity bean is the same, irrespective of the implementation of the entity bean and its container. This ensures that a client application is portable across all container implementations in which the entity bean might be deployed.