100년 뒤 개발자 한승규입니다.

저번에 배웠던 CRUD를 사용해서 간단한 프로그램을 구현해보자.

package UserProgram;

import jakarta.persistence.EntityManager;
import jakarta.persistence.EntityManagerFactory;
import jakarta.persistence.Persistence;

public class EMF {

    private static EntityManagerFactory entityManagerFactory;

    public static void init(){
        entityManagerFactory = Persistence.createEntityManagerFactory("jpabegin");
    }

    public static EntityManager getEntityManager() {
        return entityManagerFactory.createEntityManager();
    }

    public static void close(){
        entityManagerFactory.close();
    }
}

어차피 EntityManagerFactory는 계속 사용을 해야하니, 초기화하고 EntityManagerFactory에서 EntityManager를 가져올 수 있는 class를 작성해준다.

당연히 간편하게 사용하기 위해 만드는 것으로 굳이 안 만들어도 되기는 한다.

그 다음에 DB에서 사용할 User 객체를 만들어준다.

저번에 사용했던 그대로 사용할 예정이다.

package UserProgram;

import jakarta.persistence.Entity;
import jakarta.persistence.Id;
import jakarta.persistence.Table;

import java.time.LocalDateTime;

@Entity
@Table(name = "user")
public class User {

    @Id
    private String email;
    private String name;
    private LocalDateTime create_date;

    protected User(){}

    public User(String email, String name, LocalDateTime create_date) {
        this.email = email;
        this.name = name;
        this.create_date = create_date;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getName() {
        return name;
    }

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

    public LocalDateTime getCreate_data() {
        return create_date;
    }

    public void setCreate_data(LocalDateTime create_data) {
        this.create_date = create_data;
    }

    @Override
    public String toString() {
        return "User{" +
                "email='" + email + '\'' +
                ", name='" + name + '\'' +
                ", create_data=" + create_date +
                '}';
    }
}

이제 본격적으로 JPA를 사용할 차례이다.

Service 하는 메서드들을 한 곳에 모아 클래스로 작성했다.

package UserProgram;

import jakarta.persistence.Entity;
import jakarta.persistence.EntityManager;
import jakarta.persistence.EntityTransaction;

public class UserService {

    public void CreateUser(User user){
        EntityManager entityManager = EMF.getEntityManager();
        EntityTransaction entityTransaction = entityManager.getTransaction();

        try{
            entityTransaction.begin();
            entityManager.persist(user);
            entityTransaction.commit();
        }catch(Exception exception){
            entityTransaction.rollback();
            throw exception;
        } finally {
            entityManager.close();
        }
    }

    public User ReadUser(String email){
        EntityManager entityManager = EMF.getEntityManager();
        try{
            User user = entityManager.find(User.class, email);
            if(user == null) throw new NullPointerException();
            else return user;
        }finally{
            entityManager.close();
        }
    }

    public void UpdateUser(String email, String name){
        EntityManager entityManager = EMF.getEntityManager();
        EntityTransaction entityTransaction = entityManager.getTransaction();

        try{
            entityTransaction.begin();
            User user = entityManager.find(User.class, email);
            if(user == null) throw new NullPointerException();
            user.setName(name);
            entityTransaction.commit();
        }catch (Exception exception){
            entityTransaction.rollback();
            throw exception;
        }finally {
            entityManager.close();
        }
    }

    public void DeleteUser(String email){
        EntityManager entityManager = EMF.getEntityManager();
        EntityTransaction entityTransaction = entityManager.getTransaction();

        try{
            entityTransaction.begin();
            User user = entityManager.find(User.class, email);
            if (user == null) throw new NullPointerException();
            entityManager.remove(user);
            entityTransaction.commit();
        }catch(Exception exception){
            entityTransaction.rollback();
            throw exception;
        }finally {
            entityManager.close();
        }
    }
}

우선 저번에 배운 CRUD를 사용하였고, 다른 점이 있다면 static으로 작성된 EntityManagerFactory를 사용하였다.

우선 예외는 대충 넘기고 나중에 추가로 작성하도록 하겠다.

package UserProgram;

import java.time.LocalDateTime;
import java.util.Scanner;

public class UserProgram {

    private static UserService userService = new UserService();

    private static String email;
    private static String name;

    public static void main(String[] args) {
        EMF.init();

        Scanner scanner = new Scanner(System.in);

        boolean flag = true;

        while(flag){
            System.out.print("1. Create, 2. Read, 3. Update, 4. Delete, 5. exit : ");
            int answer = scanner.nextInt();
            switch(answer){
                case 1:
                    CreateMethod();
                    break;
                case 2:
                    ReadMethod();
                    break;
                case 3:
                    UpdateMethod();
                    break;
                case 4:
                    DeleteMethod();
                    break;
                case 5:
                    flag = false;
                    break;
            }
        }

        EMF.close();
        scanner.close();
    }

    private static void inputEmail(){
        Scanner scanner = new Scanner(System.in);
        System.out.print("input email:");
        email = scanner.nextLine();
    }

    private static void inputName(){
        Scanner scanner = new Scanner(System.in);
        System.out.print("input name:");
        name = scanner.nextLine();
    }

    private static void CreateMethod(){
        inputEmail();
        inputName();
        User user = new User(email, name, LocalDateTime.now());
        try{
            userService.CreateUser(user);
        }catch(Exception exception){
            System.out.println("createError");
        }
    }

    private static void ReadMethod(){
        inputEmail();
        try{
            User user = userService.ReadUser(email);
            System.out.println(user);
        }catch(Exception exception){
            System.out.println("readError");
        }
    }

    private static void UpdateMethod(){
        inputEmail();
        inputName();
        try{
            userService.UpdateUser(email, name);
            System.out.println(userService.ReadUser(email));
        }catch(Exception exception){
            System.out.println("updateError");
        }
    }

    private static void DeleteMethod(){
        inputEmail();
        try{
            userService.DeleteUser(email);
        }catch(Exception exception){
            System.out.println("deleteError");
        }
    }
}

이렇게 프로그램을 작성하였다.

그러면 이렇게 프로그램이 잘 작동한다.

값을 추가하고 삭제하는 메서드들도 잘 작동이 된다.