JPA의 첨삭 수정

JPA에 대한 도구 클래스 JPAUtil

만들기

증가:persist

변경:merge

삭제:remove

id에 따라 조회

조회 실체의 캐시 문제

지연 로드가 있는 쿼리

JPA에 대한 도구 클래스 JPAUtil 작성

Entity Manager Factory는 하나의 라인 안전 대상(즉 여러 라인이 같은 Entity Manager Factory 대상에 접근하면 라인 안전 문제가 없을 것이다)이고 Entity Manager Factory의 창설은 자원을 매우 낭비하기 때문에 JPA프로그래밍을 할 때 우리는 Entity Manager Factory의 창설을 최적화할 수 있다. 한 공정에 Entity Manager Factory만 존재하면 된다.

package com.wuxudong.utils;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

public class JPAUtils {

    private static EntityManagerFactory factory;

    static {
        factory= Persistence.createEntityManagerFactory("myJPA");
    }

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

증가:persist

// 
    @Test
    public void testPersist(){
        // 
        Customer customer=new Customer();
        customer.setCustName(" ");
        customer.setCustLevel("VIP");
        customer.setCustAddress(" ");

        EntityManager em=null;
        EntityTransaction entityTransaction=null;
        try{
            em=JPAUtils.getEntityManager();
            entityTransaction=em.getTransaction();
            entityTransaction.begin();
            em.persist(customer);
            entityTransaction.commit();
        }catch (Exception e){
            entityTransaction.rollback();
            e.printStackTrace();
        }finally {
            em.close();

        }
    }

변경:merge

 @Test
    public void mergeTest(){

        EntityManager em=null;
        EntityTransaction entityTransaction=null;
        try {
            em=JPAUtils.getEntityManager();
            entityTransaction=em.getTransaction();
            entityTransaction.begin();
            Customer customer= em.find(Customer.class,1l);
            customer.setCustName("ahfaa");
            em.clear();// customer 
            em.merge(customer);
            entityTransaction.commit();

        }catch (Exception e){
            entityTransaction.rollback();
            e.printStackTrace();
        }finally {
            em.close();
        }


    }

삭제:remove

 // 
    @Test
    public void deleteTest(){
        EntityManager em=null;
        EntityTransaction entityTransaction=null;

        try {
            em=JPAUtils.getEntityManager();
            entityTransaction=em.getTransaction();
            entityTransaction.begin();
            Customer customer = em.find(Customer.class,2l);
            em.remove(customer);
            entityTransaction.commit();
        }catch (Exception e){
            entityTransaction.rollback();
            e.printStackTrace();
        }finally {
            em.close();
        }
    }

id 기반 검색

 // ： id 
    @Test
    public void testFindById(){
        EntityManager em=null;
        EntityTransaction entityTransaction=null;

        try {
            em=JPAUtils.getEntityManager();
            entityTransaction=em.getTransaction();
            entityTransaction.begin();
            Customer customer=em.find(Customer.class,1L);
            System.out.println(customer);
            entityTransaction.commit();
        }catch (Exception e){
            entityTransaction.rollback();
            e.printStackTrace();
        }finally {
            em.close();
        }
    }

조회 실체의 캐시 문제

Entity Manager에 캐시가 있습니다.

    // 
    @Test
    public void testGetOne(){
        // 
        EntityManager em=null;
        EntityTransaction entityTransaction=null;

        try {
            // 
            em=JPAUtils.getEntityManager();
            entityTransaction=em.getTransaction();
            entityTransaction.begin();
            Customer c1=em.find(Customer.class,1l);
            Customer c2=em.find(Customer.class,1l);
            System.out.println(c1==c2);//true,EntityManager 
            entityTransaction.commit();

        }catch (Exception e){
            entityTransaction.rollback();
            e.printStackTrace();
        }finally {
            em.close();
        }

    }

지연 로드가 있는 질의

 @Test
    public void testLoadOne(){
        // 
        EntityManager em=null;
        EntityTransaction entityTransaction=null;
        try {
            em=JPAUtils.getEntityManager();
            entityTransaction=em.getTransaction();
            entityTransaction.begin();

            Customer c1=em.getReference(Customer.class,1l);
            entityTransaction.commit();
            System.out.println(c1);
        }catch (Exception e){
           entityTransaction.rollback();
            e.printStackTrace();
        }finally {
            em.close();
        }

    }