YourNote 602: Enterprise JavaBeans (EJB) - zhamri/CSC584-Enterprise_Programming GitHub Wiki

1. What is EJB?

Enterprise JavaBeans (EJB) is a server-side Java technology used to build enterprise applications.

EJB provides built-in services such as:

  • Transaction management
  • Security
  • Dependency Injection
  • Concurrency management
  • Scheduling
  • Messaging
  • Remote access
  • Distributed computing

EJB runs inside an EJB Container provided by a Jakarta EE Application Server.

Examples:

  • WildFly
  • GlassFish
  • Payara Server
  • JBoss EAP
  • TomEE

2. Why was EJB created?

Before EJB, developers had to manually handle:

  • Database transactions
  • Security
  • Object lifecycle
  • Resource pooling
  • Thread management

Example without EJB:

public void transferMoney() {

    Connection conn = null;

    try {
        conn = dataSource.getConnection();
        conn.setAutoCommit(false);

        withdraw();
        deposit();

        conn.commit();

    } catch (Exception e) {

        conn.rollback();

    }
}

EJB automates many of these tasks.

3. EJB Architecture

Client
   |
   v
EJB Container
   |
   v
Enterprise Bean
   |
   v
Database

The EJB Container provides:

  • Transactions
  • Security
  • Dependency Injection
  • Lifecycle Management
  • Thread Management
  • Connection Pooling

4. Types of EJB

There are three main types of Session Beans.

4.1 Stateless Session Bean

Most commonly used EJB.

import jakarta.ejb.Stateless;

@Stateless
public class StudentService {

    public String hello() {
        return "Hello Student";
    }

}

Characteristics

  • Does not store client state
  • Reusable
  • High performance
  • Thread-safe

Examples

  • Login service
  • Student service
  • Product service
  • Customer service

4.2 Stateful Session Bean

Stores data for a specific client.

import jakarta.ejb.Stateful;

@Stateful
public class ShoppingCart {

    private int totalItems = 0;

    public void addItem() {
        totalItems++;
    }

    public int getTotalItems() {
        return totalItems;
    }

}

Characteristics

  • Maintains state
  • One bean instance per client
  • More memory usage

Examples

  • Shopping cart
  • Online reservation
  • Multi-step form

4.3 Singleton Session Bean

Only one instance exists in the application.

import jakarta.ejb.Singleton;

@Singleton
public class SystemConfiguration {

    private String version = "1.0";

    public String getVersion() {
        return version;
    }

}

Characteristics

  • Single instance
  • Shared by all users
  • Suitable for global data

Examples

  • Application settings
  • Cache management
  • System configuration

5. Dependency Injection

EJB supports Dependency Injection using @EJB.

Without Dependency Injection

StudentService service = new StudentService();

With Dependency Injection

@EJB
private StudentService service;

Benefits:

  • Loose coupling
  • Easier maintenance
  • Easier testing

6. Transactions

One of the most important EJB features.

Example:

@Stateless
public class BankService {

    public void transferMoney() {

        withdraw();

        deposit();

    }

}

If one operation fails:

Withdraw Success
Deposit Failed

Result:
Rollback Everything

Transaction management is handled automatically.

7. Transaction Attributes

EJB supports several transaction behaviors.

@TransactionAttribute(
    TransactionAttributeType.REQUIRED
)
Attribute Description
REQUIRED Join existing transaction or create new
REQUIRES_NEW Always create new transaction
MANDATORY Transaction must already exist
SUPPORTS Use transaction if available
NOT_SUPPORTED Execute without transaction
NEVER Transaction not allowed

8. Security

EJB supports declarative security.

@RolesAllowed("ADMIN")
public void deleteStudent() {

}

Only users with the ADMIN role can execute the method.

Common Security Annotations

@RolesAllowed

@PermitAll

@DenyAll

9. Local EJB

Used within the same application.

Interface

import jakarta.ejb.Local;

@Local
public interface StudentServiceLocal {

    String getStudentName();

}

Implementation

@Stateless
public class StudentService implements StudentServiceLocal {

    public String getStudentName() {
        return "Ali";
    }

}

Advantages

  • Faster
  • Same JVM
  • Lower overhead

10. Remote EJB

Used across servers or applications.

Interface

import jakarta.ejb.Remote;

@Remote
public interface StudentServiceRemote {

    String getStudentName();

}

Implementation

@Stateless
public class StudentService implements StudentServiceRemote {

    public String getStudentName() {
        return "Ali";
    }

}

Advantages

  • Distributed computing
  • Enterprise integration

Disadvantages

  • Network overhead

11. Asynchronous EJB

Execute methods in the background.

import jakarta.ejb.Asynchronous;

@Asynchronous
public void sendEmail() {

    System.out.println("Sending email");

}

Examples

  • Email sending
  • Report generation
  • Background processing

12. Timer Service

EJB provides scheduling support.

import jakarta.ejb.Schedule;

@Schedule(hour="0", minute="0")
public void backupDatabase() {

}

Runs every day at midnight.

Examples

  • Database backup
  • Daily reports
  • Data synchronization

13. Message-Driven Bean (MDB)

Used for asynchronous messaging.

import jakarta.ejb.MessageDriven;

@MessageDriven
public class OrderProcessor {

}

Architecture:

Producer
   |
Queue
   |
MDB
   |
Database

Common Message Brokers

  • ActiveMQ
  • RabbitMQ
  • IBM MQ

Use Cases

  • Order processing
  • Notification systems
  • Event-driven systems

14. EJB Lifecycle

Stateless Bean Lifecycle

Create
  |
Ready
  |
Destroy

Stateful Bean Lifecycle

Create
  |
Ready
  |
Passivate
  |
Activate
  |
Destroy

Definitions

State Description
Create Bean created
Ready Bean active
Passivate Bean temporarily stored
Activate Bean restored
Destroy Bean removed

15. Common EJB Annotations

Annotation Purpose
@Stateless Stateless Bean
@Stateful Stateful Bean
@Singleton Singleton Bean
@EJB Dependency Injection
@Local Local Interface
@Remote Remote Interface
@Asynchronous Background Execution
@Schedule Scheduler
@MessageDriven Message Bean
@RolesAllowed Security
@TransactionAttribute Transaction Management

16. EJB Advantages

  • Simplifies enterprise development
  • Automatic transaction management
  • Built-in security
  • Built-in scheduling
  • Dependency Injection
  • Distributed application support
  • Scalable architecture

17. EJB Disadvantages

  • Requires application server
  • More complex than Spring Boot
  • Higher memory consumption
  • Slower startup time
  • Less popular for new projects

18. EJB vs Spring Boot

Feature EJB Spring Boot
Container Application Server Embedded Server
Deployment WAR / EAR Executable JAR
Learning Curve Higher Easier
Startup Time Slower Faster
Microservices Limited Excellent
Cloud Support Moderate Excellent
Popularity Today Lower Very High

19. Typical Enterprise Application Using EJB

Web Application
       |
       v
EJB Layer
       |
       v
JPA Layer
       |
       v
Database

Example:

StudentController
        |
StudentEJB
        |
StudentRepository
        |
PostgreSQL

Summary

EJB is a Jakarta EE technology for building enterprise applications.

Core concepts to master:

  • Stateless Session Bean
  • Stateful Session Bean
  • Singleton Session Bean
  • Dependency Injection
  • Transaction Management
  • Security
  • Local and Remote EJB
  • Message-Driven Bean
  • Timer Service
  • EJB Lifecycle

Although Spring Boot is more popular for new projects today, understanding EJB is important because many enterprise systems in banks, insurance companies, government agencies, and large organizations still use EJB-based architectures.