What is the difference between JavaBean and EJB?
A Java Bean is a software component written in the Java programming language
that conforms to the JavaBeans component specification. The JavaBeans APIs became
part of the “core” Java APIs as of the 1.1 release of the JDK.
The JavaBeans specification defines a Java-based software component model that
adds a number of features to the Java programming language. Some of these
features include:
.introspection
.customization
.events
.properties
.persistence
Enterprise JavaBeans (EJBs) are Java-based software components that are built
to comply with Java’s EJB specification and run inside of an EJB container
supplied by a J2EE provider. An EJB container provides distributed application
functionality such as transaction support, persistence and lifecycle management
for the EJBs.
What is abstract schema?
Abstract schema is part of an entity bean’s deployment descriptor which defines
the bean’s persistent fields and their relationship. Abstract schema is
specified for entity beans with container managed persistence. We specify the
name of the Abstract schema name in the deployment descriptor. The queries written in EJB QL for the finder methods references
this name. The information provided in this Abstract Schema is used by the
container for persistence management and relationship management.
What is local interface. How values
will be passed?
An EJB can use local client view only if it is really guaranteed that other
enterprise beans or clients will only address the bean within a single JVM.
With local client view, you can do pass-by-reference, which means your bean, as
well as the client, will work directly with one copy of the data. Any changes
made by the bean will be seen by the client and vice versa. Pass-by-reference
eliminates time/system expenses for copying data variables, which provides a
performance advantage.
What is Message Driven Bean?
An MDB is essentially a message consumer that can listen to a message
destination or a message endpoint and gets activated when a message arrives. By
design, MDBs are anonymous in nature and hence cannot be directly invoked by a
client. The only way to invoke an MDB is to send a message to the destination
or endpoint to which it is listening. As MDBs are stateless in nature and are
not related to any specific client, they can be pooled for concurrent
processing of messages.
What are the call back methods
in Entity bean?
Callback methods allows the container to notify the
bean of events in its life cycle. The callback methods are defined in the javax.ejb.EntityBean interface.
What are the services provided by container?
Container services are totally depends upon the “vendor implementation”. But
more or less most of the vendors suppots the basic
services like,
LifeCycle Management - It is Automatic.
Session Management - it is used by Developer coded callback methods…
Transaction Management - it is used by configuring deployment descriptor (DD) .
Security management - it is used by configuring deployment descriptor (DD) .
The other services, if any will be in advanced versions, and depends on Vendor
specific.
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