Give details about Enterprise JavaBean?  

Enterprise JavaBeans (EJB) is an architecture for setting up program components, written in the Java programming language, that run in the server parts of a computer network that uses the client/server model. Enterprise JavaBeans is built on the JavaBeans technology for distributing program components (which are called Beans, using the coffee metaphor) to clients in a network. Enterprise JavaBeans offers enterprises the advantage of being able to control change at the server rather than having to update each individual computer with a client whenever a new program component is changed or added. EJB components have the advantage of being reusable in multiple applications. To deploy an EJB Bean or component, it must be part of a specific application, which is called a container.

Originated by Sun Microsystems, Enterprise JavaBeans is roughly equivalent to Microsoft's Component Object Model/Distributed Component Object Model architecture, but, like all Java-based architectures, programs can be deployed across all major operating systems, not just Windows. EJB's program components are generally known as servlets (little server programs). The application or container that runs the servlets is sometimes called an application server. A typical use of servlets is to replace Web programs that use the common gateway interface (CGI) and a Practical Extraction and Reporting Language script. Another general use is provide an interface between Web users and a legacy application mainframe application and its database.

In Enterprise JavaBeans, there are two types of beans: session beans and entity beans. An entity bean is described as one that, unlike a session bean, has persistence and can retain its original behavior or state.

Answered by Nishu%27s at 6:37 PM on December 21, 2008

Enterprise JavaBeans (EJB) is a managed, server-side component architecture for modular construction of enterprise applications.

The EJB specification is one of several Java APIs in the Java Platform, Enterprise Edition. EJB is a server-side model that encapsulates the business logic of an application. The EJB specification was originally developed in 1997 by IBM and later adopted by Sun Microsystems (EJB 1.0 and 1.1) and enhanced under the Java Community Process as JSR 19 (EJB 2.0), JSR 153 (EJB 2.1) and JSR 220 (EJB 3.0).

The EJB specification intends to provide a standard way to implement the back-end 'business' code typically found in enterprise applications (as opposed to 'front-end' user-interface code). Such code was frequently found to reproduce the same types of problems, and it was found that solutions to these problems are often repeatedly re-implemented by programmers. Enterprise JavaBeans were intended to handle such common concerns as persistence, transactional integrity, and security in a standard way, leaving programmers free to concentrate on the particular problem at hand.

Accordingly, the EJB specification details how an application server provides:
Persistence via the Java Persistence API (JPA)
Transaction processing
Concurrency control
Events using Java Message Service
Java Naming and directory services (JNDI)
Security ( Java Cryptography Extension (JCE) and JAAS )
Deployment of software components in an application server
Remote procedure calls using RMI-IIOP.
Exposing business methods as Web Services.

Additionally, the Enterprise JavaBean specification defines the roles played by the EJB container and the EJBs as well as how to deploy the EJBs in a container.

Answered by Alok Gupta at 10:10 AM on December 17, 2008