4 配置Hibernate

Hibernate MySql连接配置

在Hibernate中，可以配置很多种数据库，例如MySql、Sql Server和Oracle，Hibernate MySql连接配置举例如下

出错“The processing instruction must begin with the name of the target”，看了几遍xml文件的内容也没发现什么特别，在网上搜了搜发现还是个通病，很多人都遇到过这种问题。其原因是

<? xml version = "1.0" encoding = "UTF-8" ?> 的问号和"xml"之间多了个空格，去掉空格后<?xml version = "1.0" encoding = "UTF-8" ?>就ok了。

hibernate.cfg.xml出错：The content of element type "property" must match "(meta,(column|formula) 恩，根据我的经验，可能是你的映射文件没有写好的原因，还有就是property标签的相对应属性值的value写的不对！！！！！

这样说吧，假如你在建立一个类，叫Student，包名字叫做com.bjsxt.hibernate.model

你就得建立一个映射文件，名字叫做Student.hbm.xml里面的内容的package属性就是com.bjsxt.hibernate.model

Hibernate 报错：this project is not a myeclipse hibernate project . assuming hibernate 3 cap

解决；

项目名上右键--〉myeclipse-->add hibernate capabilites -->next-->hibernate config file --> existing -->选择现有工程存在的hibernate配置文件--> next --> 不生成factory class --> end

添加库文件

从www.hibernate.org网站下载Hibernate发布包（如hibernate.jar），从www.mysql.com下载MySQL的JDBC驱动程序jar包，将这两个jar包放在lib目录
将以下jar包拷到lib目录中：asm.jar、cglib-2.1.3.jar、commons-collections-2.1.1.jar、commons-logging-1.0.4.jar、dom4j-1.6.1.jar、ehcache-1.1.jar、jta.jar
在工程的classpath中包含上述库文件

建立持久化类
例如Product.java：

package test;
//持久化类
public class Product
{

private int id ;
private String name ;
public Product()
{

}
public int getId()
{

return id ;

}
public void setId(int id)
{

this.id = id;

}
public String getName()
{

return name ;

}
public void setName(String name)
{

this.name = name;

}
}

编写反映持久化类与数据库表映射关系的Hibernate映射文件
例如Product.hbm.xml：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-// Hibernate /Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="test">
<class name="Product" table="product" catalog="factory">
<id name="id" column="id" type=" int ">
<generator class="native"/>
</id>
<property name="name" column="name" type="java.lang.String" length="255" unique="false"/>
</class>
</hibernate-mapping>

编写Hibernate配置文件
并在配置文件中通过mapping元素加入持久化类与数据库表映射的信息，即通过resource指定上一步建立的映射文件的位置。例如 Hibernate.cfg.xml

<?xml version="1.0" encoding="UTF-8"?>
<!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 = "connection.driver_class">com.mysql.jdbc.Driver</property>

<property name = "connection.url">jdbc:mysql://127.0.0.1:3306/factory</property>

<property name = "connection.username"></property>

<property name = "connection.password"></property>

<property name = "dialect">org.hibernate.dialect.MySQLDialect</property>

<property name = "hbm2ddl.auto">create</property>

<property name = "show_sql">true</property>

<property name = "format_sql">true</property>

<mapping resource = "Product.hbm.xml"/>

</session-factory>
</hibernate-configuration>

使用ThreadLocal控制Session
例如：

package test;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.cfg.Configuration;

public class HibernateSessionFactory {
private static Log log = LogFactory.getLog(HibernateSessionFactory.class);

// Path of configuration file
private static String CONFIG_FILE_LOCATION = "/hibernate.cfg.xml";
private static String configFile = CONFIG_FILE_LOCATION;

// Use ThreadLocal to control Session object
private static final ThreadLocal<Session> threadLocal = new ThreadLocal<Session>();
private static Configuration configuration = new Configuration();
private static org.hibernate.SessionFactory sessionFactory;

/**
* Abstraction: Obtain Session
*/
public static Session getSession() throws HibernateException {
Session session = threadLocal.get();

// Rebulid Session object if there is no session in ThreadLocal
if (session == null || !session.isOpen()) {
if (sessionFactory == null) {
rebuildSessionFactory();
}
// Obtain Session object
session = (sessionFactory != null) ? sessionFactory.openSession()
: null;
threadLocal.set(session);
}
return session;
}

/**
* Abstract: Build SessionFactory object
*/
public static void rebuildSessionFactory() {
try {
// Initial application using configuration file
configuration.configure(configFile);
// Create SessionFactory object according to the configuration
// Data model can be created in MySQL automatically after execute this method
sessionFactory = configuration.buildSessionFactory();
} catch (Exception e) {
e.printStackTrace();
}
}

/**
* Abstraction: Close Session object
*/
public static void closeSession() throws HibernateException
{
Session session = (Session) threadLocal.get();
threadLocal.set(null);
if (session != null)
{
session.close();
}
}
}

在src目录下建立 ehcache.xml文件，内容如下：

使用Session操作数据库

经过上述过程，就可完成Hibernate的配置了，接下来可以编写程序操作数据库。
具体实例：

package test;

import org.hibernate.Session;
import org.hibernate.Transaction;

import test.Product;
import test.HibernateSessionFactory;

public class Main {
public static void main(String [] args)
{
// Get session
Session session = HibernateSessionFactory.getSession();
Transaction tx = null;
try
{
// Begin transaction
tx = session.beginTransaction();

// Create a Product object and set its property
Product product = new Product();
product.setName("Apple");

// Save the object
session.save(product);
// Commin
tx.commit();
}
catch (Exception e)
{
if (tx != null)
{
tx.rollback();
}
try
{
// Spread the exception
throw e;
}
catch (Exception e2)
{
e2.printStackTrace();
}
}
finally
{
// Close the session
session.close();
}
}
}