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。