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Java supports two component models: JavaBeans
for client-side processing, and Enterprise JavaBeans (EJB) which
executes on the server.
JavaBeans
A JavaBean is a reusable software component that adheres
to the JavaBeans specification from Sun Microsystems, Inc.
The JavaBeans specification defines interfaces and packaging
details implemented by a set of Java classes to become a JavaBean.
You can then construct applications by piecing together JavaBeans
programmatically or by using a visual programming tool such
as Oracle9i
JDeveloper.
Enterprise JavaBeans
(EJB) technology is a specification framework for developing and
deploying Java components. You can build distributed object oriented
business applications in Java using this standard server-side architecture.
The framework provides a complete deployment environment and a set
of services for developing and executing distributed applications.
This enables you to focus on the application logic instead of the
application framework required when building server applications.
An EJB represents a business object or service, such as a purchase
requisition, in a Java application. You code the business logic
in reusable Java software components that reside in an application
or data server and can be accessed by the clients.
Demonstration
This sample (EJB
with Bean Managed Persistence) component based
applications illustrate EJB features such as :
- Use of EJBs (both session & entity) in an application
scenario.
- Use of BMP entity beans.
- EJB component location and instantiation.
- An EJB calling another EJB.
- Calling methods on an EJB component from a client application.
- A Servlet client that accesses EJB deployed to Oracle9iAS
in the J2EE framework.
In this example, we will be creating EAR (Enterprise ARchive)
file that will be deployed to Oracle9iAS.
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