HibernateTest.java
代码：
/**
*
*/
package com.b510.examplex;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
/**
*
* @author XHW
*
* @date 2011-7-15
*
*/
public class HibernateTest {
/**
* @param args
*/
public static void main(String[] args) {
new HibernateTest().getGuestbooks();
}
public void getGuestbooks(){
SessionFactory sessionFactory=HibernateSessionFactoryUtil.getSessionFactory();
Session session1=sessionFactory.getCurrentSession();
System.out.println("Session1:"+session1);
Transaction tx=session1.beginTransaction();
//Guestbook gb=(Guestbook)session1.load(Guestbook.class, 1);
Guestbook gb=(Guestbook)session1.get(Guestbook.class, 1);
System.out.println("ID : "+gb.getId()+"name: "+gb.getName());
tx.commit();
System.out.println("----------------------------------");
Session session2=sessionFactory.getCurrentSession();
System.out.println("Session2:"+session2);
System.out.println("session1是否等于session2 ？");
System.out.println(session1==session2);
session2.beginTransaction();
// gb=(Guestbook)session2.load(Guestbook.class, 1); load和get方法在这里可以随便使用，不会影响运行的结果
gb=(Guestbook)session2.get(Guestbook.class, 1);
System.out.println("ID : "+gb.getId()+"name: "+gb.getName());
session2.getTransaction().commit();
}
}
运行效果：
log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
Session1:SessionImpl(PersistenceContext[entityKeys=[],collectionKeys=[]];ActionQueue[insertions=[] updates=[] deletions=[] collectionCreations=[] collectionRemovals=[] collectionUpdates=[]])
Hibernate:
select
guestbook0_.id as id0_0_,
guestbook0_.version as version0_0_,
guestbook0_.name as name0_0_,
guestbook0_.email as email0_0_,
guestbook0_.phone as phone0_0_,
guestbook0_.title as title0_0_,
guestbook0_.content as content0_0_,
guestbook0_.created_time as created8_0_0_
from
users.guestbook guestbook0_
where
guestbook0_.id=?
ID : 1name: liuwei
----------------------------------
Session2:SessionImpl(PersistenceContext[entityKeys=[],collectionKeys=[]];ActionQueue[insertions=[] updates=[] deletions=[] collectionCreations=[] collectionRemovals=[] collectionUpdates=[]])
session1是否等于session2 ？
false
ID : 1name: liuwei
我们看到，session1和session2两个session对象是不想等的，也就是说两个session的地址不是同一个内存地址
然而我们却看到，这里却只用了一条select语句，我们明明是查询两条记录啊！这说明HIbernate的缓存是跨session的
也就是一个session对象被干掉了以后，他的缓存还是存在的，不因session被干掉二干掉。这样在我们读取相同的数据
的时候就不会再却读数据库，而是直接从缓存中读取出来。
测试代码二：
HibernateTest.java
代码；
/**
*
*/
package com.b510.examplex;
import java.util.List;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
/**
*
* @author XHW
*
* @date 2011-7-15
*
*/
public class HibernateTest {
/**
* @param args
*/
public static void main(String[] args) {
new HibernateTest().getGuestbooks();
}
public void getGuestbooks(){
SessionFactory sessionFactory=HibernateSessionFactoryUtil.getSessionFactory();
Session session1=sessionFactory.getCurrentSession();
Transaction tx=session1.beginTransaction();
Query query=session1.createQuery("from Guestbook");
List<Guestbook> list=query.list();
for(Guestbook gb:list){
System.out.println("ID : "+gb.getId()+"name: "+gb.getName());
}
tx.commit();
System.out.println("----------------------------------");
Session session2=sessionFactory.getCurrentSession();
session2.beginTransaction();
query=session2.createQuery("from Guestbook");
list=query.list();
for(Guestbook gb:list){
System.out.println("ID : "+gb.getId()+"name: "+gb.getName());
}
session2.getTransaction().commit();
}
}
运行效果：
log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
Hibernate:
select
guestbook0_.id as id0_,
guestbook0_.version as version0_,
guestbook0_.name as name0_,
guestbook0_.email as email0_,
guestbook0_.phone as phone0_,
guestbook0_.title as title0_,
guestbook0_.content as content0_,
guestbook0_.created_time as created8_0_
from
users.guestbook guestbook0_
ID : 1name: liuwei
ID : 2name: Hongtenzone@foxmail.com
ID : 3name: Hongten
ID : 4name: HOngten
ID : 5name: HOngten
ID : 6name: HOngten
ID : 7name: HOngten
----------------------------------
Hibernate:
select
guestbook0_.id as id0_,
guestbook0_.version as version0_,
guestbook0_.name as name0_,
guestbook0_.email as email0_,
guestbook0_.phone as phone0_,
guestbook0_.title as title0_,
guestbook0_.content as content0_,
guestbook0_.created_time as created8_0_
from
users.guestbook guestbook0_
ID : 1name: liuwei
ID : 2name: Hongtenzone@foxmail.com
ID : 3name: Hongten
ID : 4name: HOngten
ID : 5name: HOngten
ID : 6name: HOngten
ID : 7name: HOngten
我们看到的结果是用两条select语句，查出了相同的结果！
这个list对象有这么一个特点：他只是从数据库中读取数据，放到缓存中，但是据对不会到缓存中
去索要数据。也就是说list只是贡献缓存，不会索要缓存。
他不用二级缓存。
测试代码三：
HibernateTest.java
代码：
/**
*
*/
package com.b510.examplex;
import java.util.List;
import java.util.Iterator;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
/**
*
* @author XHW
*
* @date 2011-7-15
*
*/
public class HibernateTest {
/**
* @param args
*/
public static void main(String[] args) {
new HibernateTest().getGuestbooks();
}
public void getGuestbooks(){
SessionFactory sessionFactory=HibernateSessionFactoryUtil.getSessionFactory();
Session session1=sessionFactory.getCurrentSession();
Transaction tx=session1.beginTransaction();
Query query=session1.createQuery("from Guestbook");
List<Guestbook> list=query.list();
for(Guestbook gb:list){
System.out.println("ID : "+gb.getId()+"name: "+gb.getName());
}
tx.commit();
System.out.println("----------------------------------");
Session session2=sessionFactory.getCurrentSession();
session2.beginTransaction();
query=session2.createQuery("from Guestbook");
Iterator it=query.iterate();
while(it.hasNext()){
Guestbook gb=(Guestbook)it.next();
System.out.println("ID : "+gb.getId()+"name: "+gb.getName());
}
session2.getTransaction().commit();
}
}
运行效果：
log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
Hibernate:
select
guestbook0_.id as id0_,
guestbook0_.version as version0_,
guestbook0_.name as name0_,
guestbook0_.email as email0_,
guestbook0_.phone as phone0_,
guestbook0_.title as title0_,
guestbook0_.content as content0_,
guestbook0_.created_time as created8_0_
from
users.guestbook guestbook0_
ID : 1name: liuwei
ID : 2name: Hongtenzone@foxmail.com
ID : 3name: Hongten
ID : 4name: HOngten
ID : 5name: HOngten
ID : 6name: HOngten
ID : 7name: HOngten
----------------------------------
Hibernate:
select
guestbook0_.id as col_0_0_
from
users.guestbook guestbook0_
ID : 1name: liuwei
ID : 2name: Hongtenzone@foxmail.com
ID : 3name: Hongten
ID : 4name: HOngten
ID : 5name: HOngten
ID : 6name: HOngten
ID : 7name: HOngten
第一条selelct语句是从数据库中读出数据然后将数据放入二级缓存中，接着进入第二个会话
Iterator会向二级缓存索要查询的数据，他的方式是首先将要查的实体类的主键值获取到，
这样在底层上就要使用一条selelct id 的语句，就是我们看到的第二条selelct语句。这样就获取了
这个持久化对象的的主键值的一个集合。从 这个主键值集合中再分别读出一个主键值，将他的其他内容
读取出来。如上面显示的一样，先获取Id=1，然后获取id=1的其他数据，如name字段的值，然后再获取
id=2，再获取id=2的其他数据(name),以这种方式进行下去，直到读取完数据。还要申明的是，Iterator
都是先从二级缓存中获取数据，如果不在二级缓存中，那么要使用“n+1”方式了。
看下面的测试代码：
HibernateTest.java
代码：
/**
*
*/
package com.b510.examplex;
import java.util.List;
import java.util.Iterator;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
/**
*
* @author XHW
*
* @date 2011-7-15
*
*/
public class HibernateTest {
/**
* @param args
*/
public static void main(String[] args) {
new HibernateTest().getGuestbooks();
}
public void getGuestbooks(){
SessionFactory sessionFactory=HibernateSessionFactoryUtil.getSessionFactory();
/*
Session session1=sessionFactory.getCurrentSession();
Transaction tx=session1.beginTransaction();
Query query=session1.createQuery("from Guestbook");
List<Guestbook> list=query.list();
for(Guestbook gb:list){
System.out.println("ID : "+gb.getId()+"name: "+gb.getName());
}
tx.commit();
*/
System.out.println("----------------------------------");
Session session2=sessionFactory.getCurrentSession();
session2.beginTransaction();
Query query=session2.createQuery("from Guestbook");
Iterator it=query.iterate();
while(it.hasNext()){
Guestbook gb=(Guestbook)it.next();
System.out.println("ID : "+gb.getId()+"name: "+gb.getName());
}
session2.getTransaction().commit();
}
}
运行效果：
log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
----------------------------------
Hibernate:
select
guestbook0_.id as col_0_0_
from
users.guestbook guestbook0_ “n+1”方式中 的“1”
Hibernate:
select
guestbook0_.id as id0_0_,
guestbook0_.version as version0_0_,
guestbook0_.name as name0_0_,
guestbook0_.email as email0_0_,
guestbook0_.phone as phone0_0_,
guestbook0_.title as title0_0_,
guestbook0_.content as content0_0_,
guestbook0_.created_time as created8_0_0_
from
users.guestbook guestbook0_
where
guestbook0_.id=?
ID : 1name: liuwei
Hibernate:
select
guestbook0_.id as id0_0_,
guestbook0_.version as version0_0_,
guestbook0_.name as name0_0_,
guestbook0_.email as email0_0_,
guestbook0_.phone as phone0_0_,
guestbook0_.title as title0_0_,
guestbook0_.content as content0_0_,
guestbook0_.created_time as created8_0_0_
from
users.guestbook guestbook0_
where
guestbook0_.id=?
ID : 2name: Hongtenzone@foxmail.com
Hibernate:
select
guestbook0_.id as id0_0_,
guestbook0_.version as version0_0_,
guestbook0_.name as name0_0_,
guestbook0_.email as email0_0_,
guestbook0_.phone as phone0_0_,
guestbook0_.title as title0_0_,
guestbook0_.content as content0_0_,
guestbook0_.created_time as created8_0_0_
from
users.guestbook guestbook0_
where
guestbook0_.id=?
ID : 3name: Hongten
Hibernate:
select
guestbook0_.id as id0_0_,
guestbook0_.version as version0_0_,
guestbook0_.name as name0_0_,
guestbook0_.email as email0_0_,
guestbook0_.phone as phone0_0_,
guestbook0_.title as title0_0_,
guestbook0_.content as content0_0_,
guestbook0_.created_time as created8_0_0_
from
users.guestbook guestbook0_
where
guestbook0_.id=?
ID : 4name: HOngten
Hibernate:
select
guestbook0_.id as id0_0_,
guestbook0_.version as version0_0_,
guestbook0_.name as name0_0_,
guestbook0_.email as email0_0_,
guestbook0_.phone as phone0_0_,
guestbook0_.title as title0_0_,
guestbook0_.content as content0_0_,
guestbook0_.created_time as created8_0_0_
from
users.guestbook guestbook0_
where
guestbook0_.id=?
ID : 5name: HOngten
Hibernate:
select
guestbook0_.id as id0_0_,
guestbook0_.version as version0_0_,
guestbook0_.name as name0_0_,
guestbook0_.email as email0_0_,
guestbook0_.phone as phone0_0_,
guestbook0_.title as title0_0_,
guestbook0_.content as content0_0_,
guestbook0_.created_time as created8_0_0_
from
users.guestbook guestbook0_
where
guestbook0_.id=?
ID : 6name: HOngten
Hibernate:
select
guestbook0_.id as id0_0_,
guestbook0_.version as version0_0_,
guestbook0_.name as name0_0_,
guestbook0_.email as email0_0_,
guestbook0_.phone as phone0_0_,
guestbook0_.title as title0_0_,
guestbook0_.content as content0_0_,
guestbook0_.created_time as created8_0_0_
from
users.guestbook guestbook0_
where
guestbook0_.id=?
ID : 7name: HOngten
这就是“n+1”或者说“1+n”方式，也就是说，我们要查询的结果只有7条记录，但是，我们看到 的selelctyuj
却是8条。首先从缓存中去找，没有找到，就向数据库发出请求，查询出数据。然后执行id=2的Guestbook对象，
缓存中没有记录，有要向数据库发出请求，以这种方式进行下去。
要注意 的是：如果二级缓存中没有任何对象或者说是数据，那么这时如果我们采用Iterator方法，就会用到“n+1”
条selelct语句，这时还不如list的查询效率高。所以我们要用Iterator的时候的前提是二级缓存中要有数据，这样
的查询效率要才会高。不然会出现相反的效果。
测试代码四；
HibernateTest.java
代码：
/**
*
*/
package com.b510.examplex;
import java.util.List;
import java.util.Iterator;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
/**
*
* @author XHW
*
* @date 2011-7-15
*
*/
public class HibernateTest {
/**
* @param args
*/
public static void main(String[] args) {
new HibernateTest().getGuestbooks();
}
public void getGuestbooks(){
SessionFactory sessionFactory1=new Configuration().configure().buildSessionFactory();
Session session1=sessionFactory1.getCurrentSession();
Transaction tx1=session1.beginTransaction();
Guestbook gb=(Guestbook)session1.get(Guestbook.class, 1);
System.out.println("ID : "+gb.getId()+"name: "+gb.getName());
System.out.println(sessionFactory1);
sessionFactory1.close();
System.out.println("----------------------------------");
SessionFactory sessionFactory2=new Configuration().configure().buildSessionFactory();
Session session2=sessionFactory2.getCurrentSession();
Transaction tx2=session2.beginTransaction();
Guestbook gb2=(Guestbook)session2.get(Guestbook.class, 1);
System.out.println("ID : "+gb2.getId()+"name: "+gb2.getName());
System.out.println(sessionFactory2);
sessionFactory2.close();
}
}
运行效果：
log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
Hibernate:
select
guestbook0_.id as id0_0_,
guestbook0_.version as version0_0_,
guestbook0_.name as name0_0_,
guestbook0_.email as email0_0_,
guestbook0_.phone as phone0_0_,
guestbook0_.title as title0_0_,
guestbook0_.content as content0_0_,
guestbook0_.created_time as created8_0_0_
from
users.guestbook guestbook0_
where
guestbook0_.id=?
ID : 1name: liuwei
org.hibernate.impl.SessionFactoryImpl@1fcc0a2
----------------------------------
Hibernate:
select
guestbook0_.id as id2_0_,
guestbook0_.version as version2_0_,
guestbook0_.name as name2_0_,
guestbook0_.email as email2_0_,
guestbook0_.phone as phone2_0_,
guestbook0_.title as title2_0_,
guestbook0_.content as content2_0_,
guestbook0_.created_time as created8_2_0_
from
users.guestbook guestbook0_
where
guestbook0_.id=?
ID : 1name: liuwei
org.hibernate.impl.SessionFactoryImpl@19b46dc
Hibernate的二级缓存是跟SessionFactory相关的，所以当一个SessionFactory对象关闭后，二级缓存中的
数据就会跟着这个SessionFactory对象的关闭而随之消失，当我们启动第二个SessionFactory对象的时候，这个
这个对象的二级缓存生效。当然当这个SessionFactory对象关闭的时候，二级缓存中的数据也会消失。
因此，我们就会看到两个select语句。
所以：Hibernate的二级缓存又被叫做SessionFactory缓存