What is an Enterprise Java Bean (EJB) and benefits of EJB

byAsif Raza •April 16, 2012

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What is Enterprise Java Beans ( EJB ):

EJB is written in Java programming language and it is a server-side component that encapsulates the business logic of a java application from customers. Business logic code is managed in EJB that fulfills the purpose of the java applications. For example, in an eCommerce web application, the enterprise java beans might implement the business logic in methods called checkAvailableItem and order product.

Benefits of Enterprise Java Beans EJB

EJB technology enables rapid and simplified the process of distributed, transactional, secure, and portable java desktop applications development and Java ee web applications development because

EJB container provides System level services to enterprise java beans.

EJB developers just focus on business logic and on solving business problems.

Because business logic lies in EJB, so Front end developer can focus on the presentation of the client interface.

The client developer does not have to code the routines that implement business rules or access databases. As a result, client-side has less codes which are particularly important for clients that run on small devices.

Java Beans are portable components that enable the java application assembler to build new applications from existing java beans.

EJB is a standard API due to which applications built on EJB can run on any complaint Java EE web application server.

Types of Enterprise Java Beans:

There are two main types of EJBs
1- Session Beans
2- Message Driven Beans

1- Session Beans

A session bean encapsulates business logic that can be invoked programmatically by a client over local, remote, or web service client views. A session bean is not persistent, which means its data is not saved to a database. EJB Session Beans has three types which are

Stateful Session Bean

In a stateful session bean, the state of an object consists of the values of its instance variables. In a stateful session bean, the instance variables represent the state of a unique client/bean session.

Stateless Session Bean

In EJB stateless session bean conversational state is not maintained with the client. When a client invokes the methods of a stateless bean, the bean’s instance variables may contain a state specific to that client but only for the duration of the invocation.

Single-tone Session Bean

A singleton session bean is instantiated once per application and exists for the whole lifecycle of the java application. A single enterprise bean instance is shared across all the applications clients and it is concurrently accessed by clients

2- Message Driven Bean (MDB)

Message Driven Beans ( MDBs ) also known as Message Beans. Message Driven Beans are business objects whose execution is triggered by messages instead of by method calls.

A message-driven bean receives messages from a queue or topic, so you must have knowledge of JMS API.

Message Driven Bean Example

To create the message-driven bean, you need to declare @MessageDriven annotation and implement the MessageListener interface.

In eclipse ide, create EJB Project then create a class as given below:

File: MyListener.java

package com.javatpoint;
import javax.ejb.MessageDriven;
import javax.jms.*;
@MessageDriven(mappedName="myTopic")
public class MyListener implements MessageListener{
@Override
public void onMessage(Message msg) {
TextMessage m=(TextMessage)msg;
try{
System.out.println("message received: "+m.getText());
}catch(Exception e){System.out.println(e);}
}
}

Export the EJB project and deploy the application.

In the glassfish server, click on applications -> deploy -> select MDB jar file by Choose File -> OK.

Now send the message using JMS that is covered in the previous page.

When to Use Enterprise Java Beans EJB

EJB can be used in any java application which is simple or complicated. Java applications can be developed without EJB. Now answer to the question " when to use EJB" is that EJB should be used if your application has any of the following requirements.

For Scalable Java Applications: The application must be scalable. To accommodate a growing number of users, you may need to distribute an application’s components across multiple machines. Not only can the enterprise beans of an application run on different machines, but also their location will remain transparent to the clients.

For Transactional java applications: In-application transactions must ensure data integrity. Enterprise java beans support transactions, the mechanisms that manage the concurrent access of shared objects.

Java Application with different Clients like Desktop, Web, Mobile, etc: The java application will have a variety of clients. With only a few lines of code, remote EJB clients can easily locate enterprise java beans. These clients can be thin, various, and numerous.

Find the below slides to learn more about Enterprise Java Beans.

EJB3 Basics from Emprovise