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Java - EJB
What is EJB ?
EJB stands for Enterprise JavaBean and is a widely-adopted server side component architecture for J2EE. It enables rapid development of mission-critical application that are versatile, reusable and portable across middleware while protecting IT investment and preventing vendor lock-in.
What is session Facade?
Session Facade is a design pattern to access the Entity bean through local interface than accessing directly. It increases the performance over the network. In this case we call session bean which on turn call entity bean.
What is EJB role in J2EE?
EJB technology is the core of J2EE. It enables developers to write reusable and portable server-side business logic for the J2EE platform.
What is the difference between EJB and Java beans?
EJB is a specification for J2EE server, not a product; Java beans may be a graphical component in ID
What are the key features of the EJB technology?
1. EJB components are server-side components written entirely in the Java programming language
2. EJB components contain business logic only - no system-level programming & services, such as transactions, security, life-cycle, threading, persistence, etc. are automatically managed for the EJB component by the EJB server.
3. EJB architecture is inherently transactional, distributed, portable multi-tier, scalable and secure.
4. EJB components are fully portable across any EJB server and any OS.
5. EJB architecture is wire-protocol neutral--any protocol can be utilized like IIOP,JRMP, HTTP, DCOM,etc.
What are the key benefits of the EJB technology?
1. Rapid application development
2. Broad industry adoption
3. Application portability
4. Protection of IT investment
How many enterprise beans?
There are three kinds of enterprise beans:
1. session beans,
2. entity beans, and
3. message-driven beans.
What is message-driven bean?
A message-driven bean combines features of a session bean and a Java Message Service (JMS) message listener, allowing a business component to receive JMS. A message-driven bean enables asynchronous clients to access the business logic in the EJB tier.
What is Entity Bean and Session Bean ?
Entity Bean is a Java class which implements an Enterprise Bean interface and provides the implementation of the business methods. There are two types: Container Managed Persistence(CMP) and Bean-Managed Persistence(BMP).
Session Bean is used to represent a workflow on behalf of a client.
There are two types: Stateless and Stateful.
Stateless bean is the simplest bean. It doesn't maintain any conversational state with clients between method invocations.
Stateful bean maintains state between invocations.
How EJB Invocation happens?
Retrieve Home Object reference from Naming Service via JNDI. Return Home Object reference to the client. Create me a new EJB Object through Home Object interface. Create EJB Object from the Ejb Object. Return EJB Object reference to the client. Invoke business method using EJB Object reference. Delegate request to Bean (Enterprise Bean).

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