Hibernate 零配置開發：用 JPA 註解替代 hbm.xml 映射文件

Hibernate 註解映射實戰：從逆向工程到零 XML 配置

JPA 規範推薦使用註解將映射元數據與實體類內聚，避免維護雙份文件（Java 類 + .hbm.xml）。本文演示在 Eclipse 中利用 Hibernate Tools 逆向工程，從數據庫表自動生成帶註解的實體類，並完成配置與測試全流程。

一、準備工作：數據庫表結構

以 MySQL 表 commodity 為例：

CREATE TABLE commodity (
  Id INT PRIMARY KEY AUTO_INCREMENT,
  name VARCHAR(100),
  price DOUBLE,
  unit VARCHAR(50),
  category VARCHAR(100),
  description VARCHAR(1000),
  seller INT
);

二、Hibernate 核心配置 (hibernate.cfg.xml)

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
  "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
  "https://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
  <session-factory>
    <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
    <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
    <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/zzh</property>
    <property name="hibernate.connection.username">root</property>
    <property name="hibernate.connection.password">root</property>
    <property name="show_sql">true</property>
    <property name="hbm2ddl.auto">update</property>
    <!-- 註解實體類掃描 -->
    <mapping class="com.zzh.Commodity"/>
  </session-factory>
</hibernate-configuration>

關鍵點：<mapping class="..."/> 用於註解實體；若用 .hbm.xml 則用 resource 屬性。

三、逆向工程生成註解實體類

1. 創建 hibernate.reveng.xml 指定目標表：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-reverse-engineering PUBLIC
  "-//Hibernate/Hibernate Reverse Engineering DTD 3.0//EN"
  "https://hibernate.sourceforge.net/hibernate-reverse-engineering-3.0.dtd">
<hibernate-reverse-engineering>
  <table-filter match-catalog="zzh" match-name="commodity"/>
</hibernate-reverse-engineering>

2. Eclipse 中配置 Hibernate Code Generation Configuration：

• 選中 Domain code (Java) 與 Generate EJB 3 annotations
• 取消勾選 Generate .hbm.xml files
• 執行生成

四、生成的實體類 Commodity.java 解析

package com.zzh;

import javax.persistence.*;

@Entity
@Table(name = "commodity", catalog = "zzh")
public class Commodity implements java.io.Serializable {

    private Integer id;
    private String name;
    private Double price;
    private String unit;
    private String category;
    private String description;
    private Integer seller;

    // 無參構造器（Hibernate 必須）
    public Commodity() {}

    // 全參構造器
    public Commodity(String name, Double price, String unit,
                     String category, String description, Integer seller) {
        this.name = name; this.price = price; this.unit = unit;
        this.category = category; this.description = description; this.seller = seller;
    }

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "Id", unique = true, nullable = false)
    public Integer getId() { return id; }
    public void setId(Integer id) { this.id = id; }

    @Column(name = "name", length = 100)
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }

    @Column(name = "price", precision = 11)
    public Double getPrice() { return price; }
    public void setPrice(Double price) { this.price = price; }

    @Column(name = "unit", length = 50)
    public String getUnit() { return unit; }
    public void setUnit(String unit) { this.unit = unit; }

    @Column(name = "category", length = 100)
    public String getCategory() { return category; }
    public void setCategory(String category) { this.category = category; }

    @Column(name = "description", length = 1000)
    public String getDescription() { return description; }
    public void setDescription(String description) { this.description = description; }

    @Column(name = "seller")
    public Integer getSeller() { return seller; }
    public void setSeller(Integer seller) { this.seller = seller; }
}

核心註解說明

五、SessionFactory 工具類 (HibernateUtil)

package com.zzh.utl;
import org.hibernate.*;
import org.hibernate.boot.registry.*;
import org.hibernate.cfg.Configuration;

public class HibernateUtil {
    private static final SessionFactory sessionFactory;

    static {
        Configuration config = new Configuration().configure(); // 讀取 hibernate.cfg.xml
        StandardServiceRegistryBuilder builder = new StandardServiceRegistryBuilder()
                .applySettings(config.getProperties());
        StandardServiceRegistry registry = builder.build();
        sessionFactory = config.buildSessionFactory(registry);
    }

    public static SessionFactory getSessionFactory() { return sessionFactory; }
    public static Session openSession() { return sessionFactory.openSession(); }
    public static void closeSession(Session s) { if (s != null) s.close(); }
}

六、JUnit 測試驗證

package anno;
import org.hibernate.Query;
import org.hibernate.Session;
import org.junit.*;
import com.zzh.Commodity;
import com.zzh.utl.HibernateUtil;
import java.util.List;

public class ZhuShiTest {
    private Session session;

    @Before
    public void setUp() { session = HibernateUtil.openSession(); }

    @After
    public void tearDown() { HibernateUtil.closeSession(session); }

    @Test
    public void testQueryAll() {
        String hql = "FROM Commodity";
        Query query = session.createQuery(hql);
        List<Commodity> list = query.list();
        for (Commodity c : list) {
            System.out.println("name: " + c.getName());
        }
        Assert.assertTrue(list.size() > 0);
    }
}

七、避坑指南：.hbm.xml 時代的包名陷阱

早期使用 .hbm.xml 時，<class name="Commodity"> 缺少包名會導致 MappingException: entity not found。修正為 <class name="com.zzh.Commodity"> 即可解決。註解方式將類名與包名綁定在 Java 代碼中，從根本消除此類配置錯誤。

八、總結與展望

• 註解映射實現「零配置」：無 .hbm.xml，映射信息與代碼同步維護。
• 逆向工程一鍵生成，開發效率大幅提升。
• 後續將講解關聯映射註解（@OneToMany、@ManyToMany、雙向關聯等）。

參考教材：《Struts2+Spring3+Hibernate框架技術精講與整合案例》