What is Local client view?
The local client view specification is only available in EJB 2.0. Unlike the
remote client view, the local client view of a bean is location dependent.
Local client view access to an enterprise bean requires both the local client
and the enterprise bean that provides the local client view to be in the same
JVM. The local client view therefore does not provide the location transparency
provided by the remote client view. Local interfaces and local home interfaces
provide support for lightweight access from enterprise bean that are local
clients. Session and entity beans can be tightly couple with their clients,
allowing access without the overhead typically associated with remote method
calls.
What is EJB client JAR file?
An EJB client JAR file is an optional JAR file that can contain all the class
files that a client program needs to use the client view of the enterprise
beans that are contained in the EJB JAR file. If you decide not to create a
client JAR file for an EJB module, all of the client interface classes will be
in the EJB JAR file.
What is EJB container?
An EJB container is a run-time environment that manages one or more enterprise
beans. The EJB container manages the life cycles of enterprise bean objects,
coordinates distributed transactions, and implements object security.
Generally, each EJB container is provided by an EJB server and contains a set
of enterprise beans that run on the server.
What is Deployment descriptor?
A deployment descriptor is an XML file packaged with the enterprise beans in an
EJB JAR file or an EAR file. It contains metadata describing the contents and
structure of the enterprise beans, and runtime transaction and security
information for the EJB container.
What is EJB server?
An EJB server is a high-level process or application that provides a run-time
environment to support the execution of server applications that use enterprise
beans. An EJB server provides a JNDI-accessible naming service, manages and
coordinates the allocation of resources to client applications, provides access
to system resources, and provides a transaction service. An EJB server could be
provided by, for example, a database or application server.
What is EJB architecture(components)?
Enterprise beans-An enterprise bean is a non-visual component of a distributed,
transaction-oriented enterprise application. Enterprise beans are typically
deployed in EJB containers and run on EJB servers.
There are three types of enterprise beans: session beans, entity beans, and message-driven
beans.
Session beans: Session beans are non-persistent enterprise beans. They can be stateful or stateless. A stateful
session bean acts on behalf of a single client and maintains client-specific
session information (called conversational state) across multiple method calls
and transactions. It exists for the duration of a single client/server session.
A stateless session bean, by comparison, does not maintain any conversational
state. Stateless session beans are pooled by their container to handle multiple
requests from multiple clients.
Entity beans: Entity beans are enterprise beans that contain persistent data
and that can be saved in various persistent data stores. Each entity bean
carries its own identity. Entity beans that manage their own persistence are
called bean-managed persistence (BMP) entity beans. Entity beans that delegate
their persistence to their EJB container are called container-managed
persistence (CMP) entity beans.
Message-driven beans: Message-driven beans are enterprise beans that receive
and process JMS messages. Unlike session or entity beans, message-driven beans
have no interfaces. They can be accessed only through messaging and they do not
maintain any conversational state. Message-driven beans allow asynchronous
communication between the queue and the listener, and provide separation
between message processing and business logic.
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