Enterprise JavaBeans (EJB): Creating Beans and Session/Entity Types

What is a JavaBean?

A JavaBean is a reusable, plain Java class following simple conventions so that tools, frameworks, and IDEs can inspect and manipulate it automatically.

JavaBean Conventions

1. Class must have a public no-argument constructor
2. Properties are private, accessed via public getter/setter methods
3. The class should be Serializable

import java.io.Serializable;

public class Student implements Serializable {
    private String name;
    private int age;

    public Student() { } // no-arg constructor

    public String getName() { return name; }
    public void setName(String name) { this.name = name; }

    public int getAge() { return age; }
    public void setAge(int age) { this.age = age; }
}

JavaBean Properties

Enterprise JavaBeans (EJB)

EJB is a server-side component architecture for building scalable, transactional, and secure distributed business applications. EJB components run inside an EJB container (part of a Java EE / Jakarta EE application server), which supplies transaction management, security, concurrency, and remote access — so the developer focuses on business logic only.

Types of Enterprise Beans

Creating a Stateless Session Bean

import javax.ejb.Stateless;

@Stateless
public class CalculatorBean implements CalculatorRemote {
    public int add(int a, int b) {
        return a + b;
    }
}

// Remote business interface
public interface CalculatorRemote {
    int add(int a, int b);
}

Creating a Stateful Session Bean

import javax.ejb.Stateful;
import java.util.ArrayList;
import java.util.List;

@Stateful
public class ShoppingCartBean implements ShoppingCartRemote {
    private List<String> items = new ArrayList<>();

    public void addItem(String item) {
        items.add(item);           // remembered for this client's session
    }

    public List<String> getItems() {
        return items;
    }
}

Entity Beans

An Entity Bean represents persistent business data stored in a database — each instance typically maps to one row of a table. Modern Java EE replaces the old EJB 2.x Entity Bean model with JPA (@Entity), but the concept is the same:

import javax.persistence.Entity;
import javax.persistence.Id;

@Entity
public class Employee {
    @Id
    private int empId;
    private String name;
    private double salary;

    // getters and setters
}

Session Bean vs Entity Bean

Key Takeaway: A JavaBean is just a class with a no-arg constructor and getters/setters. Enterprise JavaBeans extend that idea into server-managed components — Stateless beans for reusable logic, Stateful beans for per-client conversations, and Entity beans (now largely JPA @Entity) for persistent data.