Project Implementation to Update an Entity in JPA

package model;

import jakarta.persistence.*;

@Entity
@Table(name = "employees")
public class Employee {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;
    private double salary;
    private String department;

    // 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 double getSalary() {
        return salary;
    }

    public void setSalary(double salary) {
        this.salary = salary;
    }

    public String getDepartment() {
        return department;
    }

    public void setDepartment(String department) {
        this.department = department;
    }
}

package repository;

import jakarta.persistence.EntityManager;
import jakarta.persistence.EntityManagerFactory;
import jakarta.persistence.EntityTransaction;
import jakarta.persistence.Persistence;
import model.Employee;

public class EmployeeRepository {
    
    // Create an entity manager factory
    private final EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("EmployeePU");

    // Find an employee by ID
    public Employee findEmployeeById(Long id) {
        EntityManager entityManager = entityManagerFactory.createEntityManager();
        try {
            return entityManager.find(Employee.class, id);
        } finally {
            entityManager.close();
        }
    }

    // Save an employee to the database
    public void saveEmployee(Employee employee) {
        EntityManager entityManager = entityManagerFactory.createEntityManager();
        EntityTransaction transaction = entityManager.getTransaction();
        try {
            transaction.begin();
            entityManager.persist(employee);
            transaction.commit();
        } catch (Exception ex) {
            if (transaction.isActive()) {
                transaction.rollback();
            }
            ex.printStackTrace();
        } finally {
            entityManager.close();
        }
    }

    // Update an existing employee in the database
    public void updateEmployee(Employee employee) {
        EntityManager entityManager = entityManagerFactory.createEntityManager();
        EntityTransaction transaction = entityManager.getTransaction();
        try {
            transaction.begin();
            entityManager.merge(employee);
            transaction.commit();
        } catch (Exception ex) {
            if (transaction.isActive()) {
                transaction.rollback();
            }
            ex.printStackTrace();
        } finally {
            entityManager.close();
        }
    }
}

import model.Employee;
import repository.EmployeeRepository;

public class MainApplication {
    public static void main(String[] args) {
        // Creating an instance of EmployeeRepository
        EmployeeRepository employeeRepository = new EmployeeRepository();

        // Adding a new employee
        Employee newEmployee = new Employee();
        newEmployee.setName("John Doe");
        newEmployee.setSalary(5000);
        newEmployee.setDepartment("IT");

        // Persisting the new employee
        employeeRepository.saveEmployee(newEmployee);
        System.out.println("New Employee Added:");
        printEmployeeData(newEmployee);

        // Retrieving the newly added employee
        Long employeeId = newEmployee.getId();
        Employee retrievedEmployee = employeeRepository.findEmployeeById(employeeId);

        // Updating the retrieved employee
        if (retrievedEmployee != null) {
            retrievedEmployee.setSalary(6000);
            retrievedEmployee.setDepartment("Finance");
            employeeRepository.updateEmployee(retrievedEmployee);

            System.out.println("\nEmployee Data After Update:");
            // Retrieving the updated employee
            Employee updatedEmployee = employeeRepository.findEmployeeById(employeeId);
            printEmployeeData(updatedEmployee);
        }
    }

    private static void printEmployeeData(Employee employee) {
        if (employee != null) {
            System.out.println("ID: " + employee.getId());
            System.out.println("Name: " + employee.getName());
            System.out.println("Salary: " + employee.getSalary());
            System.out.println("Department: " + employee.getDepartment());
        } else {
            System.out.println("Employee not found.");
        }
    }
}