JPA - Hibernate Entity Manager

package dto;

import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;

// The Entity annotation specifies that the class is an entity and it is mapped to a database table
@Entity
public class Student {
    // The Id annotation specifies the primary key of the entity
    @Id
    // GeneratedValue annotation provides the strategy for generating primary key values
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    // Name of the student
    private String name;
    
    // Age of the student
    private int age;

    // Getters and Setters
    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    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;
    }
}

package dto;

import jakarta.persistence.*;
import java.util.List;

// Data Access Object (DAO) class for handling Student entities
public class StudentDAO {
    private EntityManagerFactory entityManagerFactory;

    // Constructor to initialize the EntityManagerFactory
    public StudentDAO() {
        entityManagerFactory = Persistence.createEntityManagerFactory("hibernateDemo");
    }

    // Method to save a Student entity to the database
    public void saveStudent(Student student) {
        EntityManager entityManager = entityManagerFactory.createEntityManager();
        EntityTransaction transaction = entityManager.getTransaction();
        transaction.begin();
        entityManager.persist(student);
        transaction.commit();
        entityManager.close();
    }

    // Method to find students by their name
    public List<Student> findStudentByName(String name) {
        EntityManager entityManager = entityManagerFactory.createEntityManager();
        try {
            TypedQuery<Student> query = entityManager.createQuery("SELECT s FROM Student s WHERE s.name = :name", Student.class);
            query.setParameter("name", name);
            return query.getResultList();
        } finally {
            entityManager.close();
        }
    }

    // Method to update a Student entity in the database
    public void updateStudent(Student student) {
        EntityManager entityManager = entityManagerFactory.createEntityManager();
        EntityTransaction transaction = entityManager.getTransaction();
        transaction.begin();
        entityManager.merge(student);
        transaction.commit();
        entityManager.close();
    }

    // Method to delete a Student entity from the database
    public void deleteStudent(Student student) {
        EntityManager entityManager = entityManagerFactory.createEntityManager();
        EntityTransaction transaction = entityManager.getTransaction();
        transaction.begin();
        // Check if the entity is managed by the EntityManager, and if not, merge it before removal
        entityManager.remove(entityManager.contains(student) ? student : entityManager.merge(student));
        transaction.commit();
        entityManager.close();
    }
}

import dto.Student;
import dto.StudentDAO;
import java.util.List;

public class MainApp {

    public static void main(String[] args) {
        // Instantiate the StudentDAO class
        StudentDAO studentDAO = new StudentDAO();

        // Create and save a new student
        Student student = new Student();
        student.setName("Mahesh");
        student.setAge(25);
        studentDAO.saveStudent(student);

        // Create and save another student
        Student student2 = new Student();
        student2.setName("Eswar");
        student2.setAge(22);
        studentDAO.saveStudent(student2);

        // Find students with the name "Eswar"
        List<Student> students = studentDAO.findStudentByName("Eswar");
        if (!students.isEmpty()) {
            System.out.println("Found Students:");
            for (Student s : students) {
                System.out.println(s.getName());
            }
        } else {
            System.out.println("No students found with the given name.");
        }
    }
}