HibernateTest.java
代码:
1 /**
2 *
3 */
4 package com.b510.examplex;
5
6 import org.hibernate.Session;
7
8
9 /**
10 *
11 * @author XHW
12 *
13 * @date 2011-7-15
14 *
15 */
16 public class HibernateTest {
17
18 /**
19 * @param args
20 */
21 public static void main(String[] args) {
22 new HibernateTest().getGuestbooks();
23 }
24
25 public void getGuestbooks(){
26 Session session=HibernateSessionFactoryUtil.getSessionFactory().openSession();
27 session.beginTransaction();
28
29 Guestbook gb=(Guestbook)session.get(Guestbook.class, 2);
30 Guestbook gb2=(Guestbook)session.get(Guestbook.class, 2);
31
32 System.out.println(gb==gb2);
33 session.getTransaction().commit();
34 }
35
36 }
运行效果:
我们会看到,这里只用了一条select语句。但是我们读的是两条记录啊!
为什么会出现这种情况呢?
这是因为 Hibernate使用了一级缓存,一级缓存又叫Session缓存
在一个会话的生命期里面,他所用到的数据会使用缓冲的,第一次读的是编号为2的数据记录
第一次读的时候,内存中什么都没有,这时候就要用一条select语句从数据库中读出一条记录,同时把这些数据放到session的缓存
里面,接下来又要读同样的数据,这时候他就不会再向数据库读取数据,而是向缓存中读取数据。
得到这个对象,把这个对象返回,所以我们看到一条select语句
Sysout(true);即:gb=gb2
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=?
true
但是,如果我们在session对象结束的时候再来sysout(gb=gb2),
会出现什么样的结果呢?
我们看看下面的运行效果就会看到,这时候会看到两条select语句,
一个session对象结束后,这是缓存中的数据会清空。
所以我们看到两条select语句。
代码:
1 /**
2 *
3 */
4 package com.b510.examplex;
5
6 import org.hibernate.Session;
7
8
9 /**
10 *
11 * @author XHW
12 *
13 * @date 2011-7-15
14 *
15 */
16 public class HibernateTest {
17
18 /**
19 * @param args
20 */
21 public static void main(String[] args) {
22 new HibernateTest().getGuestbooks();
23 }
24
25 public void getGuestbooks(){
26 Session session=HibernateSessionFactoryUtil.getSessionFactory().openSession();
27 session.beginTransaction();
28
29 Guestbook gb=(Guestbook)session.get(Guestbook.class, 2);
30 session.getTransaction().commit();
31
32 session=HibernateSessionFactoryUtil.getSessionFactory().openSession();
33 session.beginTransaction();
34
35 Guestbook gb2=(Guestbook)session.get(Guestbook.class, 2);
36 session.getTransaction().commit();
37
38 System.out.println(gb==gb2);
39 }
40
41 }
运行效果:
我们看到,我们要跟新两条记录,但是这里只是执行了一条update语句。
这是Hibernate利用缓存,用一个update就可以了。
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=?
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=?
false
HibernateTest.java
1 /**
2 *
3 */
4 package com.b510.examplex;
5
6 import org.hibernate.Session;
7
8
9 /**
10 *
11 * @author XHW
12 *
13 * @date 2011-7-15
14 *
15 */
16 public class HibernateTest {
17
18 /**
19 * @param args
20 */
21 public static void main(String[] args) {
22 new HibernateTest().getGuestbooks();
23 }
24
25 public void getGuestbooks(){
26 Session session=HibernateSessionFactoryUtil.getSessionFactory().openSession();
27 session.beginTransaction();
28
29 Guestbook gb=(Guestbook)session.get(Guestbook.class, 2);
30 Guestbook gb2=(Guestbook)session.get(Guestbook.class, 2);
31
32 gb.setName("Hongtenzone@foxmail.com");
33 gb2.setEmail("Helloworld@sina.com");
34 session.getTransaction().commit();
35
36 }
37
38 }
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=?
Hibernate:
update
users.guestbook
set
version=?,
name=?,
email=?,
phone=?,
title=?,
content=?,
created_time=?
where
id=?
and version=?
HibernateTest.java
代码:
1 /**
2 *
3 */
4 package com.b510.examplex;
5
6 import org.hibernate.Session;
7
8
9 /**
10 *
11 * @author XHW
12 *
13 * @date 2011-7-15
14 *
15 */
16 public class HibernateTest {
17
18 /**
19 * @param args
20 */
21 public static void main(String[] args) {
22 new HibernateTest().getGuestbooks();
23 }
24
25 public void getGuestbooks(){
26 Session session=HibernateSessionFactoryUtil.getSessionFactory().openSession();
27 session.beginTransaction();
28
29 Guestbook gb=(Guestbook)session.get(Guestbook.class, 2);
30 //移除gb的缓存
31 session.evict(gb);
32 Guestbook gb2=(Guestbook)session.get(Guestbook.class, 2);
33
34 System.out.println(gb==gb2);
35 session.getTransaction().commit();
36
37 }
38
39 }
运行效果:
首先查出gb对象的数据,放入缓存中,当执行session.evict(gb);语句时,就会把
缓存中的数据移除掉。
这次要查gb2对象的数据,就得从新生成一条select语句。
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=?
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=?
false
测试二:
HIbernateTest.java
代码:
1 /**
2 *
3 */
4 package com.b510.examplex;
5
6 import org.hibernate.Session;
7
8
9 /**
10 *
11 * @author XHW
12 *
13 * @date 2011-7-15
14 *
15 */
16 public class HibernateTest {
17
18 /**
19 * @param args
20 */
21 public static void main(String[] args) {
22 new HibernateTest().getGuestbooks();
23 }
24
25 public void getGuestbooks(){
26 Session session=HibernateSessionFactoryUtil.getSessionFactory().openSession();
27 session.beginTransaction();
28
29 Guestbook gb=(Guestbook)session.get(Guestbook.class, 2);
30 Guestbook gb2=(Guestbook)session.get(Guestbook.class, 3);
31 //清楚缓存,把缓存中的所有东西都给干掉,不留下任何东西
32 session.clear();
33 Guestbook gb3=(Guestbook)session.get(Guestbook.class, 2);
34 Guestbook gb4=(Guestbook)session.get(Guestbook.class, 3);
35
36 System.out.println(gb==gb3);
37 System.out.println(gb2==gb4);
38 session.getTransaction().commit();
39
40 }
41
42 }
运行效果:
我们看到session.clear();的执行效果果然是“心狠手辣”,不让敌人有丝毫反抗的有生力量……
这个方法会让缓存中的所有东西清除的干干净净。通通的,大大的,全部干掉的……
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=?
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=?
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=?
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=?
false
false
测试三:
HibernateTest.java
代码:
1 /**
2 *
3 */
4 package com.b510.examplex;
5
6 import org.hibernate.Session;
7
8
9 /**
10 *
11 * @author XHW
12 *
13 * @date 2011-7-15
14 *
15 */
16 public class HibernateTest {
17
18 /**
19 * @param args
20 */
21 public static void main(String[] args) {
22 new HibernateTest().test();
23 }
24
25 public void test(){
26 Session session=HibernateSessionFactoryUtil.getSessionFactory().openSession();
27 session.beginTransaction();
28
29 Guestbook gb=(Guestbook)session.get(Guestbook.class, 2);
30 Guestbook gb2=(Guestbook)session.get(Guestbook.class, 3);
31 //移除干净缓存中的数据
32 session.clear();
33
34 //判断gb2对象的是否在缓存中
35 System.out.println(session.contains(gb2));
36
37 //session.flush(); session刷新
38
39 //session.close(); session关闭
40
41 说明一下,在session执行下面的commit()方法后,会自动调用
42
43 flush()方法和close()方法。这两步是隐含在里面,所以不用显示出来
44
45 都是可以的。
46 session.getTransaction().commit();
47
48 }
49
50 }
运行效果:
session.contains(gb2);返回的是一个boolean值,判断缓存中是否缓存在gb2对象。
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=?
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=?
false