学习hibernate笔记

浏览数：51 / 时间：2015年06月20日

       以前学习java的时候，一开始就学习了hibernate，那时候总觉得ssh非常高大上，所以就急忙看了下相关视频。不过因为实际需要不高，所以后来一直没有使用上hibernate组件。现在一年过去了，也疯狂学习了java一段时间了，做过几个不大的项目，但是总算对java有些了解。现在参加了工作，公司使用的就是ssh，所以这两天又重新开始捣鼓hibernate。这次学习直接使用editplus，直接开发。看了官网的demo，发现英语也没有想象中那么困难。哈哈，把自己的学习记录下来吧。这里主要记录三个方面：

       1.如何搭建hibernate

       2.几种常用映射关系（one - to -one，one - to - many, many - to - one, many - to - many）


搭建hibernate（直接使用文本编辑器）

第一步：这个过程也不复杂，主要是下载到hibernate相关jar包，然后将必要的jar引入到classpath中，具体什么是classpath，大家可以百度下。如果不导入到classpath中，会出现不能找到类的异常。为什么会出现这种情况呢？大家可以百度下，java 的类加载过程。

第二步：编写hibernate.cfg.xml文件。这个大家不用手写，直接去hibernate文章中copy一个即可。下面给出我的代码

<?xml version='1.0' encoding='utf-8' ?>
<!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>  
           <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>  
           <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/hibernate_demo</property>  
           <property name="hibernate.connection.username">root</property>  
           <property name="hibernate.connection.password">root</property>  
           <property name="dialect">org.hibernate.dialect.MySQLDialect</property>  
           <property name="hibernate.show_sql">true</property>  
		   <!--if the value='create, means create table, every time open hibernate, if will drop the old scheme'-->
		   <property name="hbm2ddl.auto">update</property> 
		   <mapping resource="User.xml"/> 
		   <mapping resource="Address.xml"/>  
      </session-factory>

</hibernate-configuration>
第三步：开始制作一个工具类，用来初始化hibernate组件。由于难度不高，直接给出代码，这些在文章中都已经有了，大家可以自己下载document看看。下面是代码：

import java.io.*;
import org.hibernate.*;
import org.hibernate.cfg.*;

/**
 * that is a hibernate config util
 * */
public class HibernateConfigurationUtil{
    
	private static HibernateConfigurationUtil singleton = new HibernateConfigurationUtil("hibernate.cfg.xml");
    private static SessionFactory factory;

	/**
	 * singleton pattern
	 * */
	private HibernateConfigurationUtil(String configXml){
	    init(configXml);
	}
    
	public void init(String configXml){
	     Configuration cfg = new Configuration().configure(new File("hibernate.cfg.xml"));
		 factory = cfg.buildSessionFactory();   // build the session factory
	}
    
	public static SessionFactory getSessionFactory(){
	    if(factory == null) return null;
		return factory;
	}

    /**
	 * open a new Session
	 *
	 * */
	public static Session openSession(){
	    Session session = factory.openSession();
		return session;
	}

}

注意下，这个类使用单例设计模式，因为hibernate组建在启动Configuration时，是非常耗时的，而且这个对象在启动之后不能改变，所以每个工程中，启动一次即可。

第三步：编写BaseHibernateDao，这个类注意是封装了save, delete, update, load这四个方法。

import java.io.*;
import org.hibernate.*;
import org.hibernate.cfg.*;

/**
 * that is the base hibernate dao,
 * it define a series of method to access database
 * if you want to 'delete, update a object, the object must exists in hibernate memery'
 *
 * @author luohong
 * @date 2014-08-07 
 * */
public class BaseHibernateDao{
	public BaseHibernateDao(){
	}

    /**
	 * try to save a object
	 * */
	public void save(Object object){
	    Session session = HibernateConfigurationUtil.openSession();
		// open transaction
		Transaction transaction = session.beginTransaction();
		session.save(object);
		// commint transaction
		transaction.commit();

	}

	/**
	 * try to update a object
	 * */
	public void update(Object object){
	    Session session = HibernateConfigurationUtil.openSession();
		// open transaction
		Transaction transaction = session.beginTransaction();
		session.update(object);
		// commint transaction
		transaction.commit();
	}
    
    /**
	 * try to delete a object
	 * */
	public void delete(Object object){
	    Session session = HibernateConfigurationUtil.openSession();
		// open transaction
		Transaction transaction = session.beginTransaction();
		session.delete(object);
		// commint transaction
		transaction.commit();
	}
    
	/**
	 * try to load a object from database by className and id
	 * */
	public Object load(Class<?> className, Serializable id){
		Session session = HibernateConfigurationUtil.openSession();
        // there is no need for transaction
		return session.load(className, id);
	}

}

注意：在save, update, delete方法中，只用了Transaction，要开启事务，否则数据库找不到相关记录。

第四步：到了这里之后，就非常简单了，只需要针对具体的类，扩展BaseHibernateDao即可。下面给出一个一对多的例子。模拟情景：用户（User）拥有多个住址（Address）首先给出两个类：

import java.util.*;


public class User{
	private int id;
	private String password;
	private String name;
    private Set<Address> addressSet;

	public void setAddressSet(Set<Address> addressSet){
	    this.addressSet = addressSet;
	}

	public Set<Address> getAddressSet(){
	    return addressSet;
	}

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

	public String getName(){
	    return name;
	}

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

	public int getId(){
	    return id;
	}

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

	public String getPassword(){
	    return password;
	}

	public String toString(){
	    return "id = " + id + ", name = " + name + ", password = " 
			+ password + ", addressSet = " + addressSet;
	}
}

/**
 * that is the user address
 * a user have many address, but a adress belong to a user
 * It is the classical 1 * n relationship
 * @author luohong
 * @date 2014-08-07
 * */
 public class Address {

//=====================properties=============================
	 private int id;
	 //private User belongTo;
	 private String code;
	 private String city;
	 private String street;
	 private String homeNumber;


//===================setter and getter========================
	 public void setId(int id){
	     this.id = id;
	 }

	 public int getId(){
	     return id;
	 }
/*
	 public void setBelongTo(User user){
	     this.belongTo = belongTo;
	 }

	 public User getBelongTo(){
	     return belongTo;
	 }
*/

	 public void setCode(String code){
	     this.code = code;
	 }

	 public String getCode(){
	     return code;
	 }

	 public void setCity(String city){
	     this.city = city;
	 }

	 public String getCity(){
	     return city;
	 }

	 public void setHomeNumber(String homeNumber){
	     this.homeNumber = homeNumber;
	 }

	 public String getHomeNumber(){
		 return homeNumber;
	 }

	 public String getStreet(){
	     return street;
	 }

	 public void setStreet(String street){
         this.street = street;
	 }

//========================toString================================
	 public String toString(){
	     return "id = " + id + ", city = " + city + ", street = " + street + ", homeNumber = " + homeNumber 
			 + ", code = " + code;// + ", belongTo = " + belongTo;
	 } 

     
 }

给出相关的User.xml, Address.xml；这个例子使用的是单向一对多。

<?xml version="1.0"?>  
<!DOCTYPE hibernate-mapping PUBLIC  
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"  
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">  


<hibernate-mapping>

	<class name="User" table="user">
		<id name="id">
			<generator class="increment"/>
		</id>
		 
		<property name="password"/>

		<property name="name"/>
		
		<!--one to many-->
		<set name="addressSet" cascade="all">
		    <!--define the foreight column name-->
		    <key column="user_id"/>
			<!--define the foreight table name-->
			<one-to-many class="Address"/> 
		</set>
	</class>

</hibernate-mapping>  

<?xml version="1.0"?>  
<!DOCTYPE hibernate-mapping PUBLIC  
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"  
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">  


<hibernate-mapping>

	<class name="Address" table="address">
		<id name="id">
			<generator class="increment"/>
		</id>
		<property name="code"/>

		<property name="city"/>

		<property name="street"/>
		<property name="homeNumber"/>

	</class>

</hibernate-mapping>


然后编写一个UserDao，继承BaseHibernateDao，也很简单，哈哈，一看就懂，这就是hibernate的厉害之处。

import java.util.*;
import org.hibernate.*;
/**
 * user dao extends BaseHibernateDao
 * you can add new functions to the custom dao
 * 
 * 
 * @author luohong
 * @date 2014-08-07
 * */
public class UserDao extends BaseHibernateDao{
    /**
	 * delete a user by userId
	 *
	 * */
	public void deleteById(String id){
		if (id == null) return;  // do nothing

		String hql = "delete User where id=?";
		// 1 open session
	    Session session = HibernateConfigurationUtil.openSession(); 
		// 2 create a query
		Query query = session.createQuery(hql);
		// 3 set the parameter to query
		query.setString(1, id);
		// 4 execute query
		query.executeUpdate();
	}
    
	/**
	 * find all user from database
	 * */
	public List<User> findAllUsers(){
	    String hql = "from User";
		Session session = HibernateConfigurationUtil.openSession();
		Query query = session.createQuery(hql);
		List userList = query.list();
		return (List<User>)userList;
	}
}

剩下的就是测试啦，come on...

import java.io.*;
import java.util.*;

/**
 * hibernate orm 框架demo
 * @author luohong
 * @date 2014-08-06 
 * 
 * */
public class HibernateDemo{
	public static void main(String[] args) throws Exception{
	    
		UserDao userDao = new UserDao();
        
		User user = new User();
		user.setName("luohong");
		user.setPassword("luohong");
        
		Set<Address> addressSet = new HashSet<Address>();
		for(int i=0; i<3; i++){
			Address address = new Address();
			address.setCode("111");
			address.setCity("hongkang");
			address.setStreet("universal street");
			address.setHomeNumber("a-2846");
			//address.setBelongTo(user);
			
			addressSet.add(address);
		}

		user.setAddressSet(addressSet);

		userDao.save(user);
	}
}





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标签： hibernate java 数据库 singleton hibernate java 数据库 singleton

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