Locating Enity Bean

In Jakarta EE 10, Entity Beans from J2EE (EJB 2.x) have been fully replaced by Java Persistence API (JPA), which offers a more flexible, modern, and POJO-based approach to persistence. The concept of locating an entity bean using a primary key has been modernized using JPA's `EntityManager` and its method:

<T> T find(Class<T> entityClass, Object primaryKey);

✅ How Primary Key-Based Lookup is Replicated in Jakarta EE 10 (Using JPA)
Instead of using JNDI lookups or `home.findByPrimaryKey()` as in J2EE Entity Beans, in Jakarta EE 10 you do the following:
✅ Step-by-Step Comparison

J2EE (Entity Beans)	Jakarta EE 10 (JPA)
Requires remote/local interface	POJOs annotated with @Entity
home.findByPrimaryKey(primaryKey)	entityManager.find(Entity.class, primaryKey)
Container-managed persistence and lifecycle	You manage persistence with EntityManager
EJB deployment descriptors (XML)	Uses annotations like @Entity, @Id, @GeneratedValue

✅ Example in Jakarta EE 10 (JPA-based):
Entity Class:

import jakarta.persistence.*;

@Entity
public class Customer {
    @Id
    private Long id;

    private String name;

    // getters and setters
}

import jakarta.persistence.*;
import jakarta.ejb.Stateless;

@Stateless
public class CustomerService {

    @PersistenceContext
    private EntityManager entityManager;

    public Customer findCustomer(Long id) {
        return entityManager.find(Customer.class, id);
    }
}

✅ Key Benefits Over J2EE Style

• No need for home interfaces
• No JNDI lookups
• Entity lifecycle managed via `EntityManager`
• Annotations make entity configuration simpler and type-safe
• Cleaner exception handling (e.g., `NoResultException`, `EntityNotFoundException`)

✅ Optional Enhancements
You can also use:

• entityManager.getReference() – lazy fetch proxy
• JPQL queries for more flexible lookups
• CriteriaBuilder for type-safe dynamic queries

Summary: The primary key lookup of entity beans in J2EE is now cleanly replicated and improved in Jakarta EE 10 through JPA's `EntityManager.find()`. This is more maintainable, testable, and integrates seamlessly with the CDI and EJB architecture.

In Jakarta EE 10, the term "entity bean" (from the old EJB 2.x model) is deprecated and no longer used.
Instead, we use JPA entities, which are simple POJOs (Plain Old Java Objects) annotated with `@Entity`.
🔄 Terminology Shift

Legacy Term (J2EE)	Modern Jakarta EE 10 Term
Entity Bean	JPA Entity
Home Interface	EntityManager.find()
Deployment Descriptor	Annotations (@Entity, @Id, etc.)
Container-managed Fields	POJO fields with annotations

✅ JPA Entities ≈ ERD Entities
JPA entities are aligned with ERD (Entity-Relationship Diagram) concepts:

• In ER modeling, an entity maps to a table.
• In JPA, an `@Entity` maps to a table.
• Each field in the entity corresponds to a column.
• The `@Id` field maps to the primary key.

🧠 Example Mapping
ERD Table: `Customer(id, name, email)`
JPA Entity:

@Entity
public class Customer {

    @Id
    private Long id;

    private String name;
    private String email;

    // getters/setters
}

In Jakarta EE 10, you are still modeling *entities", just with a more lightweight, modern, and decoupled architecture compared to the old EJB-based system.

For J2EE which was used during the dotcom era, the server side application would use a primary key to locate an entity bean? Has the use of entity beans in Jakarta EE 10 been deprecated. Describe the server side Java technology which is used to locate the primary key of a MySQL database table.

If the client knows the primary key of the persistent data that it needs, it can use that primary key to look up the bean.
The home object has a method findByPrimaryKey(PrimaryKey) that is used to create an instance of the bean and initialize it with the persistent data. The mechanism is described in the following series of images.

The `EJBObject` interface was part of the EJB 2.x remote invocation model, which required:

• A remote interface that extended javax.ejb.EJBObject
• Explicit use of RMI/IIOP
• Use of JNDI lookups to obtain the stub object

Example (legacy J2EE):

public interface CustomerRemote extends EJBObject {
    public String getName() throws RemoteException;
}

❌ Deprecated and Removed

• As of EJB 3.x, and continuing into Jakarta EE 10, this model has been completely replaced by a simpler POJO-based, annotation-driven model.
• `javax.ejb.EJBObject` is not used or required for any modern enterprise bean.
• Instead, remote and local interfaces are defined as plain interfaces using `@Remote` or `@Local`.

✅ Modern Jakarta EE 10 Alternative

@Remote
public interface CustomerService {
    String getName();
}

@Stateless
public class CustomerServiceBean implements CustomerService {
    public String getName() {
        return "Alice";
    }
}

• No need for EJBObject, EJBHome, or RMI stubs.
• Clients invoke methods via dependency injection or portable JNDI names.

✅ Jakarta EE 10 API Confirmation
The Jakarta EE 10 API (jakarta.ejb) does not include `EJBObject`. The Jakarta platform has officially removed legacy EJB interfaces and deployment models tied to CORBA and heavy container contracts. You can verify this directly via the Jakarta EE 10 API documentation:
jakarta.ejb package
`EJBObject` is not listed.
✅ Summary

• ✅ EJBObject was required in EJB 2.x (J2EE)
• ❌ It is not present in Jakarta EE 10
• ✅ Modern beans use annotations (`@Stateless`, `@Stateful`) and plain interfaces
• ✅ Clients interact directly with beans or through lightweight dependency injection / JNDI

The bean instance for that data now exists. If any client subsequently invokes the findByPrimaryKey() method on the home object, passing it the existing primary key, then the container simply returns the remote reference to the EJBObject. There is no lookup in the database or creation of a new instance or EJBObject. It is very efficient. The following diagram illustrates what happens:

Take a moment to test your knowledge on finding an entity bean using the primary key by clicking the Quiz link below.
Finding Entity Bean - Quiz
The next lesson introduces Bean-Managed Persistence (BMP).