Hibernate入门笔记

相关基础概念请从其它教材简单了解，这里仅记录下第一个Hibernate程序的实现步骤。

环境说明：

java开发工具：eclipse MARS.2 Release(4.5.2)

hibernate版本:hibernate-release-4.3.6.Final

Web 容器：Tomcat v8.0

数据库：MySQL 5.6.19-enterprise-commercial-advanced

jdbc驱动：mysql-connector-java-commercial-5.1.30-bin.jar

1.下载hibernate。

2.下载jdbc驱动文件。

3.在eclipse中新建web project,命名为firsthibernate。

4.拷贝hibernate/lib/required文件夹下的所有jar文件、以及jdbc驱动文件（此文件另外下载）到项目的WEB-INF/lib文件夹下，拷贝hibernate/project/etc下的hibernate.cfg.xml文件到项目的src目录下。

5.新建实体类Cat，Hibernate中配置实体类有两种方法：XML文件配置和@注解配置，本例采用@注解配置，相关注解代表的含义在代码中都有注明如下：

package com.levice.firsthibernate.bean;

import java.util.Date;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;

@Entity                              //注解Entity表示该类能被Hibernate持久化
@Table(name = "tb_cat")              //指定该Entity对应的数据表名
public class Cat {

    @Id                              //指定该列为主键。主键类型最好不要使用int等原始类型
    @GeneratedValue(strategy = GenerationType.AUTO) //主键类型auto表示该主键为自增长型
    private Integer id;
    
    @Column(name = "name")           //指定该属性对应的数据库表的列为name，列名与属性名一样时这句注解可省略
    private String name;
    
    @Column(name = "description")
    private String description;
    
    @ManyToOne                       //指定实体类之间的关系，本例表示多对一关系
    @JoinColumn(name = "mother_id")
    private Cat mother;
    
    @Temporal(TemporalType.TIMESTAMP)//日期类型（DATE，TIME或TIMESTEMP）
    @Column(name = "birthday")
    private Date birthday;
    
    
    //getters and setters
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getDescription() {
        return description;
    }
    public void setDescription(String description) {
        this.description = description;
    }
    public Cat getMother() {
        return mother;
    }
    public void setMother(Cat mother) {
        this.mother = mother;
    }
    public Date getBirthday() {
        return birthday;
    }
    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }    
}

6.修改配置文件hibernate.cfg.xml,内容及注释如下：

<!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
    <session-factory>
        <!-- 配置JDBC -->
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="connection.url">jdbc:mysql://localhost:3306/hibernate</property>
        <property name="connection.username">root</property>
        <property name="connection.password">123456</property>
        
        <!-- 指定使用MySQL数据库格式的SQL语句 -->
        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
        
        <!-- 指定在控制台打印生成的SQL语句 -->
        <property name="show_sql">true</property>
        
        <!-- 指定Hibernate启动时自动创建表结构 -->
        <property name="hbm2ddl.auto">create</property>
        
        <!-- 加上这一句以防止未知错误 -->
        <property name="current_session_context_class">thread</property>
        
        <!-- 指定Cat类为Hibernate实体类 -->
        <mapping class="com.levice.firsthibernate.bean.Cat"/>
    </session-factory>
</hibernate-configuration>

7.初始化数据库，在MySQL中创建数据库hibernate，SQL代码如下：

create database hibernate;

8.配置HibernateUtil,就是修改HibernateUtil.java文件，这个文件在下载的hibernate文件中有，但我Copy过来的时候，一直没调试成功，于是采用了一个版本比较老的HibernateUtil。这个文件的作用是获取SessionFactory从而获取Session，不同版本的hiberate中获取SessionFactory的方法都不同，这里可以新建一个HibernateUtil.java文件，然后把下面的代码copy进去。

package com.levice.firsthibernate.util;

import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;

@SuppressWarnings("deprecation")
public class HibernateUtil {

    private static final SessionFactory sessionFactory;
    static{
        try{
            sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
        }catch(Throwable ex){
            System.err.println("Initial SessionFactory creation failed.");
            throw new ExceptionInInitializerError(ex);
        }
    }
    
    public static SessionFactory getSessionFactory(){
        return sessionFactory;
    }
}

9.执行Hibernate程序，创建一个包含主函数main的类CatTest,代码及注释如下：

package com.levice.firsthibernate.test;

import java.awt.Font;
import java.util.Date;
import java.util.List;
import javax.swing.JOptionPane;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.levice.firsthibernate.bean.Cat;
import com.levice.firsthibernate.util.HibernateUtil;

public class CatTest {

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        /*初始化几只Cat的信息*/
        Cat mother = new Cat();
        mother.setName("Mother White");
        mother.setDescription("This is mother cat");
        mother.setBirthday(new Date());

        Cat kitty = new Cat();
        kitty.setMother(mother);
        kitty.setName("Kitty");
        kitty.setDescription("This is Kitty");
        kitty.setBirthday(new Date());

        Cat tom = new Cat();
        tom.setMother(mother);
        tom.setName("Tom");
        tom.setDescription("This is Tom");
        tom.setBirthday(new Date());

        @SuppressWarnings("static-access")
        Session session = new HibernateUtil().getSessionFactory().openSession(); //获取session并open，开启一个Hibernate会话
        Transaction trans = session.beginTransaction(); //开启一个事务

        session.persist(mother); //将mother保存到数据库
        session.persist(kitty);
        session.persist(tom);

        @SuppressWarnings("all")
        List<Cat> catList = session.createQuery(" from Cat ").list(); //查询数据库中所有的猫
        StringBuffer result = new StringBuffer();
        result.append("all cats: 

");
        for (Cat cc : catList) {
            result.append("name:" + cc.getName() + "
");
            result.append("mother:" + (cc.getMother() == null ? "null" : cc.getMother().getName()) + "
");
            result.append("description:" + cc.getDescription() + "

");
        }

        trans.commit(); //提交事务
        session.close(); //关闭Hibernate会话

        //用Swing显示查询结果
        JOptionPane.getRootFrame().setFont(new Font("Arial", Font.BOLD, 14));
        JOptionPane.showMessageDialog(null, result.toString());

    }

}

10.运行CatTest，可以看到如下输出：

控制台输出的SQL语句如下：

Hibernate: alter table tb_cat drop foreign key FK_dix3h50rxo8ahrcu5roir75n1
Hibernate: drop table if exists tb_cat
Hibernate: create table tb_cat (id integer not null auto_increment, birthday datetime, description varchar(255), name varchar(255), mother_id integer, primary key (id))
Hibernate: alter table tb_cat add constraint FK_dix3h50rxo8ahrcu5roir75n1 foreign key (mother_id) references tb_cat (id)
Hibernate: insert into tb_cat (birthday, description, mother_id, name) values (?, ?, ?, ?)
Hibernate: insert into tb_cat (birthday, description, mother_id, name) values (?, ?, ?, ?)
Hibernate: insert into tb_cat (birthday, description, mother_id, name) values (?, ?, ?, ?)
Hibernate: select cat0_.id as id1_0_, cat0_.birthday as birthday2_0_, cat0_.description as descript3_0_, cat0_.mother_id as mother_i5_0_, cat0_.name as name4_0_ from tb_cat cat0_