Hibernate 实现原理

整体流程
1：通过configuration来读cfg.xml文件
2：得到SessionFactory 工厂
3：通过SessionFactory 工厂来创建Session实例
4：通过Session打开事务
5：通过session的api操作数据库
6：事务提交
7：关闭连接

为什么要用：
1. 对JDBC访问数据库的代码做了封装，大大简化了数据访问层繁琐的重复性代码。  
2. Hibernate是一个基于JDBC的主流持久化框架，是一个优秀的ORM实现。他很大程度的简化DAO层的编码工作。  
3. hibernate使用Java反射机制，而不是字节码增强程序来实现透明性。  
4. hibernate的性能非常好，因为它是个轻量级框架。映射的灵活性很出色。它支持各种关系数据库，从一对一到多对多的各种复杂关系。



两种取得session方法：
openSession和getCurrentSession区别 
openSession：永远创建新的session 需手动close，事务提交不会自动close
getCurrentSession：事务没提交之前。在上下文找，有可能返回旧的session，事务提交了，会得到新的session。事务提交，session自动close
上下文，在配置文件指定：
   <property name="current_session_context_class">thread</property>
    jta | thread | managed | custom.Class 
     thread常用—》必须指明current_session_context_class，否则抛异常

a.sessionFactory.openSession();

sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
       Session session = sessionFactory.openSession();   //创建新的session对象
       session.beginTransaction();
       session.save(t);
       session.getTransaction().commit();
      session.close() ;                               //关闭session对象

     

b.sessionFactory.getCurrentSession();

 sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
       Session session = sessionFactory.getCurrentSession();   //获取当前"上下文"中的session对象
       session.beginTransaction();
       session.save(t);
       Session session2 = sessionFactory.getCurrentSession();
	   System.out.println(session == session2);  //true
       session.getTransaction().commit();            //事务提交自动关闭该session
       System.out.println(session == session2);  //false                               

一、没有通过applicationContext.xml配置文件加载hibernate.cfg.xml,而是通过
自定义的类HibernateUtil.java创建sessionFactory对象

1.TeamDaoHibernate
package com.org.momo.dao.hibernateTemplate;

import java.util.List;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;

import com.org.momo.bean.PageInfo;
import com.org.momo.bean.Team;
import com.org.momo.dao.TeamDao;
import com.org.momo.util.HibernateUtil;

public class TeamDaoHibernate implements TeamDao {
	private SessionFactory sessionFactory;
	
	public TeamDaoHibernatenotused() {
		sessionFactory = HibernateUtil.getSessionFactory();
	}

	public void insert(Team team) throws Exception {
		Session session = sessionFactory.openSession();
		
		Transaction transaction = session.beginTransaction();
		session.save(team);
		transaction.commit();
		
		session.close() ;
	}

	public void deleteById(Integer id) throws Exception {
		Session session = sessionFactory.openSession();
		Transaction transaction = session.beginTransaction();
		
		String hql = "delete from Team where id=?";
		Query query = session.createQuery(hql);
		query.setInteger(0, id);
		query.executeUpdate();
		
		transaction.commit();
		session.close();
	}

	public void update(Team team) throws Exception {
		Session session = sessionFactory.openSession();
		Transaction transaction = session.beginTransaction();
		
		session.merge(team);
		
		transaction.commit();
		session.close();
	}

	public List<Team> findAll() throws Exception {
		List<Team> teams = null;
		
		Session session = sessionFactory.openSession();
		
		Query query = session.createQuery("from Team");
		teams = query.list();
		
		session.close();
		
		return teams;
	}

	public Team findById(Integer id) throws Exception {
		Team team = null;
		
		Session session = sessionFactory.openSession();
		Query query = session.createQuery("from Team where id=?");
		query.setInteger(0, id);
		team = (Team)query.uniqueResult();
		session.close();
		
		return team;
	}

	public List<Team> findAllPage(PageInfo pageInfo) throws Exception {
		List<Team> teams = null;
		
		Session session = sessionFactory.openSession();
		
		Query queryTotal = session.createQuery("select count(id) from Team");
		int rowCount = ((Long)queryTotal.uniqueResult()).intValue() ;  //先转换为Long 在转换为int
		int pageTotal = rowCount/pageInfo.getPageRows();
		if(rowCount%pageInfo.getPageRows() > 0) {
			pageTotal++;
		}
		pageInfo.setPageTotal(pageTotal);
		
		Query query = session.createQuery("from Team");
		query.setFirstResult(pageInfo.getPageRows()*(pageInfo.getCurrentPage()-1));
		query.setMaxResults(pageInfo.getPageRows());
		teams = query.list();
		
		session.close();
		
		return teams;
	}

}

2.HibernateUtil.java

    package com.org.momo.util;

import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;


public class HibernateUtil {
	  private static final SessionFactory sessionFactory;
      static{
    	  try{
    		  //初始化hibernate.cfg.xml配置，建立数据库连接
    		  sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
    	  }catch(Exception e){
    		  e.printStackTrace() ;
    		  throw new ExceptionInInitializerError(e) ;
    	  }
      }
      
      public static SessionFactory getSessionFactory(){
    	  return sessionFactory ;
      }
}

二、通过配置Spring的applicationContext.xml文件加载，spring对Hibernate的支持（HibernateTemplate）

1.applicationContext.xml

   <?xml version="1.0" encoding="UTF-8"?>
<beans
xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">

	<bean id="teamService" class="com.org.momo.service.impl.TeamServiceImpl">
		<property name="teamDao" ref="teamDao"></property>
	</bean>
	<bean id="adminService" class="com.org.momo.service.impl.AdminServiceImpl">
		<property name="adminDao" ref="adminDao"></property>
	</bean>
    <bean id="logService" class="com.org.momo.service.impl.LogServiceImpl">
        <property name="logDao" ref="logDao"></property>
    </bean>
    <bean id="studentService" class="com.org.momo.service.impl.StudentServiceImpl">
        <property name="studentDao" ref="studentDao"></property>
    </bean>
    
    <bean id="sessionFactory" class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean">
		<property name="configLocation" value="classpath:hibernate.cfg.xml"/>
	</bean>
	<bean id="hibernateTemplate" class="org.springframework.orm.hibernate3.HibernateTemplate">
		<property name="sessionFactory" ref="sessionFactory"/>
	</bean>
    
    
    <bean id="teamDao" class="com.org.momo.dao.hibernateTemplate.TeamDaoHibernateTemplate">
		<property name="hibernateTemplate" ref="hibernateTemplate"/>
	</bean>
    <bean id="adminDao" class="com.org.momo.dao.hibernateTemplate.AdminDaoHibernateTemplate">
        <property name="hibernateTemplate" ref="hibernateTemplate"/>
    </bean>
    <bean id="logDao" class="com.org.momo.dao.hibernateTemplate.LogDaoHibernateTemplate">
        <property name="hibernateTemplate" ref="hibernateTemplate"/>
    </bean>
    <bean id="studentDao" class="com.org.momo.dao.hibernateTemplate.StudentDaoHibernateTemplate">
        <property name="hibernateTemplate" ref="hibernateTemplate"/>
    </bean>
    

    <bean class="org.springframework.context.annotation.CommonAnnotationBeanPostProcessor">
    </bean>
</beans>

2.HibernateTemplate

  package com.org.momo.dao.hibernateTemplate;

import java.sql.SQLException;
import java.util.List;

import org.hibernate.HibernateException;
import org.hibernate.Query;
import org.hibernate.Session;
import org.springframework.orm.hibernate3.HibernateCallback;
import org.springframework.orm.hibernate3.support.HibernateDaoSupport;

import com.org.momo.bean.PageInfo;
import com.org.momo.bean.Team;
import com.org.momo.dao.TeamDao;

public class TeamDaoHibernateTemplate extends HibernateDaoSupport implements TeamDao {

	public void deleteById(Integer id) throws Exception {
        Team team = this.getHibernateTemplate().load(Team.class, id) ;
		this.getHibernateTemplate().delete(team) ;
	}

	public List<Team> findAll() throws Exception {
		return this.getHibernateTemplate().loadAll(Team.class);
	}

	public Team findById(Integer id) throws Exception {
		List<Team> teams = this.getHibernateTemplate().find("from Team where id=?",id) ;
		if(!teams.isEmpty()){
			return teams.get(0) ;
		}else{
		return null;
		}
	}

	public void insert(Team team) throws Exception {
		this.getHibernateTemplate().save(team) ;
	}

	public void update(Team team) throws Exception {
		this.getHibernateTemplate().update(team);
	}

	public List<Team> findAllPage(final PageInfo pageInfo) throws Exception {
		List<Team> teams = null;
		
		int rowTotal = ((Long)this.getHibernateTemplate().find("select count(id) from Team").get(0)).intValue();
		int pageTotal = rowTotal/pageInfo.getPageRows();
		if(rowTotal%pageInfo.getPageRows() > 0) {
			pageTotal++;
		}
		pageInfo.setPageTotal(pageTotal);
		
		teams = this.getHibernateTemplate().executeFind(new HibernateCallback(){
			public Object doInHibernate(Session session)
					throws HibernateException, SQLException {
				Query query = session.createQuery("from Team");
				query.setFirstResult(pageInfo.getPageRows()*(pageInfo.getCurrentPage()-1));
				query.setMaxResults(pageInfo.getPageRows());
				return query.list();
			}
			
		});
		
		return teams;
	}

}