Hibernate——以面向对象的思维操作关系数据库（一）

Hibernate是一个轻量级的ORM开源框架。Hibernate解脱了面对繁琐的JDBC的开发者，使得变成更加面向对象化，将之前的连接语句，增删改查等语句进行了很好的封装，使得业务逻辑等的编写更加的容易；使移植数据库也变得十分的容易，即根据不同的数据库配置configuration.cfg.xml就可以轻松改变数据库；下面以一个代码段稍作解释：

一 ：每个相对应的实体都会有相对应的映射文件，映射文件的作用主要是维护实体间的关系。

实体类User：

package com.bjpowernode.hibernate;

import java.util.Date;

public class User {

	private String id;

	private String name;

	private String password;

	private Date createTime;

	private Date expireTime;

	public String getId() {
		return id;
	}

	public void setId(String id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getPassword() {
		return password;
	}

	public void setPassword(String password) {
		this.password = password;
	}

	public Date getCreateTime() {
		return createTime;
	}

	public void setCreateTime(Date createTime) {
		this.createTime = createTime;
	}

	public Date getExpireTime() {
		return expireTime;
	}

	public void setExpireTime(Date expireTime) {
		this.expireTime = expireTime;
	}
}

映射文件：

<?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>
	<class name="com.bjpowernode.hibernate.User">
		<id name="id">
			<generator class="uuid"/>
		</id>
		<property name="name"/>
		<property name="password"/>
		<property name="createTime"/>
		<property name="expireTime"/>
	</class>
</hibernate-mapping>

将映射文件生成dll文件：

package com.bjpowernode.hibernate;

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

/**
 * 将hbm生成ddl
 * @author Administrator
 *
 */
public class ExportDB {

	public static void main(String[] args) {

		//默认读取hibernate.cfg.xml文件
		Configuration cfg = new Configuration().configure();

		SchemaExport export = new SchemaExport(cfg);
		export.create(true, true);
	}
}

二 ：在configuration.cfg.xml中配置基本信息，并将映射文件信息配置到configuration.cfg.xml中

configuration.cfg.xml配置文件：

<!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.driver_class">com.mysql.jdbc.Driver</property>
		<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/hibernate_first</property>
		<property name="hibernate.connection.username">root</property>
		<property name="hibernate.connection.password">bjpowernode</property>
		<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
		<property name="hibernate.show_sql">true</property>
		<mapping resource="com/bjpowernode/hibernate/User.hbm.xml"/>
	</session-factory>
</hibernate-configuration>

三：建立客户端类Client，添加用户数据到数据库

package com.bjpowernode.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文件
		Configuration cfg = new Configuration().configure();

		//建立SessionFactory
		SessionFactory factory = cfg.buildSessionFactory();

		//取得session
		Session session = null;
		try {
			session = factory.openSession();
			//开启事务
			session.beginTransaction();
			User user = new User();
			user.setName("张三");
			user.setPassword("123");
			user.setCreateTime(new Date());
			user.setExpireTime(new Date());

			//保存User对象
			session.save(user);

			//提交事务
			session.getTransaction().commit();
		}catch(Exception e) {
			e.printStackTrace();
			//回滚事务
			session.getTransaction().rollback();
		}finally {
			if (session != null) {
				if (session.isOpen()) {
					//关闭session
					session.close();
				}
			}
		}
	}
}

总结：上面只是一个小例子，但是从小例子中我们依稀可以感受到那种封装给我们带来的便捷了。