Spring 整合 JPA 實戰：Hibernate + MySQL 完整配置指南

專案依賴配置

<dependencies>
  <!-- Spring 核心 -->
  <dependency><groupId>org.springframework</groupId><artifactId>spring-orm</artifactId><version>4.0.5.RELEASE</version></dependency>
  <dependency><groupId>org.springframework</groupId><artifactId>spring-context</artifactId><version>4.0.5.RELEASE</version></dependency>
  <dependency><groupId>org.springframework</groupId><artifactId>spring-test</artifactId><version>4.0.5.RELEASE</version></dependency>

  <!-- JUnit -->
  <dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.12</version></dependency>

  <!-- Hibernate 作為 JPA Provider -->
  <dependency><groupId>org.hibernate</groupId><artifactId>hibernate-core</artifactId><version>4.3.1.Final</version></dependency>
  <dependency><groupId>org.hibernate</groupId><artifactId>hibernate-entitymanager</artifactId><version>4.3.1.Final</version></dependency>

  <!-- MySQL 驅動 -->
  <dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>5.1.31</version></dependency>
</dependencies>

JPA 核心配置

persistence.xml（放置於 META-INF/）

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" xmlns="https://java.sun.com/xml/ns/persistence"
  xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="https://java.sun.com/xml/ns/persistence https://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
  <persistence-unit name="myJPA" transaction-type="RESOURCE_LOCAL">
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
    <class>com.domain.User</class>
    <class>com.domain.Driver</class>
    <class>com.domain.Car</class>
    <properties>
      <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5Dialect"/>
      <property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver"/>
      <property name="hibernate.connection.username" value="root"/>
      <property name="hibernate.connection.password" value="000"/>
      <property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/jpa?useUnicode=true&characterEncoding=UTF-8"/>
      <property name="hibernate.max_fetch_depth" value="3"/>
      <property name="hibernate.hbm2ddl.auto" value="update"/>
      <property name="hibernate.show_sql" value="true"/>
      <property name="hibernate.format_sql" value="true"/>
      <property name="javax.persistence.validation.mode" value="none"/>
    </properties>
  </persistence-unit>
</persistence>

關鍵說明：

• transaction-type="RESOURCE_LOCAL"：本地事務，非 JTA
• hbm2ddl.auto=update：自動更新表結構，開發環境適用
• 整合 Spring 後可改用 LocalContainerEntityManagerFactoryBean 替代 persistence.xml

實體類別設計

駕駛員實體（一對多關聯汽車）

@Entity
@Table(name = "driver")
public class Driver {
    @Id @GeneratedValue
    private Long id;

    @Column(name = "firstname")
    private String firstName;

    @Column(name = "lastname")
    private String lastName;

    @OneToMany(cascade = CascadeType.ALL)  // 傳播性持久化
    @JoinColumn(name = "driver_id")
    private Set<Car> cars = new HashSet<>();

    // getter/setter/toString 省略...
}

汽車實體

@Entity
@Table(name = "car")
public class Car {
    @Id @GeneratedValue
    private Long id;

    @Column(name = "name")
    private String name;
    // getter/setter/toString 省略...
}

關鍵註解：cascade=CascadeType.ALL 表示持久化 Driver 時自動級聯持久化關聯的 Car 集合。

核心操作測試

建立 EntityManagerFactory 與基本驗證

@Test
public void openTest() {
    EntityManagerFactory emf = Persistence.createEntityManagerFactory("myJPA");
    System.out.println("工廠開啟狀態：" + emf.isOpen());
}

持久化新實體（含級聯）

@Test
public void addTest() {
    EntityManagerFactory emf = Persistence.createEntityManagerFactory("myJPA");
    EntityManager em = emf.createEntityManager();
    EntityTransaction tx = em.getTransaction();
    tx.begin();

    Driver driver = new Driver();
    driver.setFirstName("Taylor");
    driver.setLastName("Swift");

    Car car1 = new Car(); car1.setName("BMW");
    Car car2 = new Car(); car2.setName("AUDI");

    driver.getCars().add(car1);
    driver.getCars().add(car2);

    em.persist(driver);  // 級聯持久化 cars

    tx.commit();
    em.close();
}

查詢與刪除操作

@Test
public void findTest() {
    EntityManagerFactory emf = Persistence.createEntityManagerFactory("myJPA");
    EntityManager em = emf.createEntityManager();
    EntityTransaction tx = em.getTransaction();
    tx.begin();

    // find：立即查詢，無結果返回 null
    Driver driver = em.find(Driver.class, 1L);

    // getReference：延遲載入（可能拋出 EntityNotFoundException）
    Car car = em.getReference(Car.class, 2L);

    driver.setFirstName("Justin");  // 髒數據自動檢測，提交時更新
    em.remove(car);  // 刪除

    tx.commit();
    em.close();
}

核心機制深度解析

自動髒數據檢測

JPA 追蹤所有由 EntityManager 載入的實體。實體狀態變更會被標記為「髒數據」，提交事務時自動執行 UPDATE。前提：實體處於「受管狀態」（關聯有效的 EntityManager）。

實體生命週期狀態

• 新建態：new 出來，未關聯 EntityManager
• 受管態：持久化後、find/getReference 載入，受 EM 管理
• 游離態：EM 關閉或 detach() 後，變更不再被追蹤
• 移除態：remove() 標記刪除，提交後從資料庫刪除

游離態重新關聯

// 合併游離實體回受管態
Driver managedDriver = em.merge(detachedDriver);

下一步預告

下篇將介紹 Spring Data JPA：以 JpaRepository 介面替代樣板代碼，實現零代碼 CRUD、分頁查詢、規範查詢等進階功能。