hibernate 实例

学ehcache中涉及hibernate，做一个小例子入门，记下以备后查。

 1. 创建hibernate.cfg.xml，为hibernate主配置文件, 通过修改其中的session-factory中的配置，可以实现后台DB的切换。

<!DOCTYPE hibernate-configuration PUBLIC 
   "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <property name="hibernate.connection.url">jdbc:mysql://localhost/hibernate_first</property>
        <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="hibernate.connection.username">root</property>
        <property name="hibernate.connection.password">beauty</property>
        <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
        <property name="hibernate.show_sql">true</property>
        <mapping resource="com/bjsxt/hibernate/User.hbm.xml"/>
    </session-factory>
</hibernate-configuration>

2. 定义实体类User

package com.bjsxt.hibernate;

import java.util.Date;

public class User {

        private String id;
        private String name;
        private String password;
        private Date createTime;
        private Date expireTime;
    　　 省略getter/setter...        
}

3.  创建实体类映射文件User.hbm.xml(此文件可以任意命名，标准为类名.hbm.xml)，位置通常与实体类放在一个package中

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.bjsxt.hibernate">
    <class name="User" table="t_user" >
        <id name="id" column="userid"><generator class="uuid"></generator></id>
        <property name="name"></property>
        <property name="password"/>
        <property name="createTime"/>
        <property name="expireTime"/>
    </class>
</hibernate-mapping>

4.  编写hbm2ddl工具，从实体类直接生成数据库表. 注意, 表是自动导的，hibernate_first数据库是要自己手动建的

package com.bjsxt.hibernate;

import org.hibernate.cfg.Configuration;
import org.hibernate.tool.hbm2ddl.SchemaExport;

/*将Class.hbm.xml转换为DDL文件,这个类可以反复使用的^@@^  */
public class ExportDB {
    /**     * @param args     */
    public static void main(String[] args) {//读取hibernate.cfg.xml配置文件
        Configuration cfg= new Configuration().configure();        
        SchemaExport export = new SchemaExport(cfg);
        export.create(true,true);        
    }
}

5. 运行ExportDB ，先爽一爽

mysql> describe t_user;
+------------+--------------+------+-----+---------+-------+
| Field      | Type         | Null | Key | Default | Extra |
+------------+--------------+------+-----+---------+-------+
| userid     | varchar(255) | NO   | PRI | NULL    |       |
| name       | varchar(255) | YES  |     | NULL    |       |
| password   | varchar(255) | YES  |     | NULL    |       |
| createTime | datetime     | YES  |     | NULL    |       |
| expireTime | datetime     | YES  |     | NULL    |       |
+------------+--------------+------+-----+---------+-------+
5 rows in set (0.36 sec)

6. 写client类，以操作对象的方法操作数据库中的数据

package com.bjsxt.hibernate;
import java.util.Date;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class Client {
    public static void main(String[] args) {
        //读取hibernate.cfg.xml配置文件
        Configuration cfg= new Configuration().configure();
        //一个DB对应一个sessionFactory
        SessionFactory factory = cfg.buildSessionFactory();
        Session session = null;
        User user =null;
        try{
        session=factory.openSession();
        session.beginTransaction();
        user= new User();
        user.setName("lisi");
        user.setPassword("1223");
        user.setCreateTime(new Date());
        user.setExpireTime(new Date());
        session.save(user);
        user.setName("wangwu");
        session.getTransaction().commit();
        }
        catch (Exception e)
        {e.printStackTrace();
        session.getTransaction().rollback();}
        finally
        {
            HibernateUtils.closeSession(session);
        }
        
        user.setName("ac");
        try{
            session = HibernateUtils.getSession();
            session.beginTransaction();
            session.update(user);
            session.getTransaction().commit();
        }
        catch(Exception e)
        {e.printStackTrace();
        session.getTransaction().rollback();
        }
        finally
        {
            HibernateUtils.closeSession(session);
        }  
    }
}

 7. 书写测试用例，从DB中取数据

package com.bjsxt.hibernate;

import java.util.Iterator;
import java.util.List;
import org.hibernate.Query;
import org.hibernate.Session;
import junit.framework.TestCase;

public class QueryTest extends TestCase {
    public void testQuery()
    {
        Session session=null;        
        try{
         session= HibernateUtils.getSession();
        session.beginTransaction();
        
        Query query = session.createQuery("from User");
        query.setFirstResult(0);
        query.setMaxResults(2);
        List userList = query.list();
        
        for (Iterator iter = userList.iterator();iter.hasNext();)
        {
            User user = (User)iter.next();
            System.out.println(user.getId()+"---"+ user.getName());
        }
        session.getTransaction().commit();
        }
        catch(Exception e)
        {
            e.printStackTrace();
            session.getTransaction().rollback();
        }
        finally
        {
            HibernateUtils.closeSession(session);
        }
    }}

运行结果如下：

Hibernate: select user0_.userid as userid0_, user0_.name as name0_, user0_.password as password0_, user0_.createTime as createTime0_, user0_.expireTime as expireTime0_ from t_user user0_ limit ?
402880e43b5ba096013b5ba097a30001---second
402880e43b5ba0ab013b5ba0ac070001---second

hibernate较好的实现了对底层jdbc的封装，代码中看不到jdbc的迹象，极大的简化了DAO层开发。

但它对sql的掌握力较差，不能操作底层sql算是不足之处。