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Hibernate入门 - Transaction

�� — Fri, 29 Jul 2005 02:46:00 GMT

Hibernate是对JDBC的轻量��对象��装�Q?/SPAN>Hibernate本��n是不具备Transaction处理功能的，Hibernate�?/SPAN>Transaction实际上是底层�?/SPAN>JDBC Transaction的封装，或者是JTA Transaction的封装，下面我们详细的分析：

Hibernate可以配置�?/SPAN>JDBCTransaction或者是JTATransaction�Q�这取决于你�?/SPAN>hibernate.properties中的配置:

#hibernate.transaction.factory_class net.sf.hibernate.transaction.JTATransactionFactory

#hibernate.transaction.factory_class net.sf.hibernate.transaction.JDBCTransactionFactory

如果你什么都不配�|�，默认情况下��?/SPAN>JDBCTransaction�Q�如果你配置为：

hibernate.transaction.factory_class net.sf.hibernate.transaction.JTATransactionFactory

��?/SPAN>JTATransaction不管你准备让Hibernate使用JDBCTransaction�Q�还�?/SPAN>JTATransaction�Q�我的忠告就是什么都不配�Q�将让它保持默认状态，如下�Q?/SPAN>

#hibernate.transaction.factory_class net.sf.hibernate.transaction.JTATransactionFactory

#hibernate.transaction.factory_class net.sf.hibernate.transaction.JDBCTransactionFactory

在下面的分析中我会给出原因�?/SPAN>

一�?/SPAN>JDBC Transaction

看看使用JDBC Transaction的时候我们的代码例子�Q?/SPAN>

Session session = sf.openSession();

Transaction tx = session.beginTransactioin();

...

session.flush();

tx.commit();

session.close();

�q�是默认的情况，当你在代码中使用Hibernate�?/SPAN>Transaction的时候实际上��是JDBCTransaction。那�?/SPAN>JDBCTransaction�I�竟是什么东西呢�Q�来看看源代码就清楚了：

Hibernate2.0.3源代码中的类

net.sf.hibernate.transaction.JDBCTransaction:

public void begin() throws HibernateException {

...

if (toggleAutoCommit) session.connection().setAutoCommit(false);

...

}

�q�是启动Transaction的方法，看到connection().setAutoCommit(false) 了吗�Q�是不是很熟悉？再来�?/SPAN>

public void commit() throws HibernateException {

...

try {

if ( session.getFlushMode()!=FlushMode.NEVER ) session.flush();

try {

session.connection().commit();

committed = true;

}

...

toggleAutoCommit();

}

�q�是提交�Ҏ��Q�看�?/SPAN>connection().commit() 了吗�Q�下面就不用我多说了�Q�这个类代码非常��单易懂，通过阅读使我们明�?/SPAN>Hibernate�?/SPAN>Transaction都在�q�了些什么？我现在把�?/SPAN>Hibernate写的例子��译�?/SPAN>JDBC�Q�大家就一目了然了�Q?/SPAN>

Connection conn = ...; <--- session = sf.openSession();

conn.setAutoCommit(false); <--- tx = session.beginTransactioin();

... <--- ...

conn.commit(); <--- tx.commit(); (对应左边的两�?/SPAN>)

conn.setAutoCommit(true);

conn.close(); <--- session.close();

看明白了吧，Hibernate�?/SPAN>JDBCTransaction�Ҏ��是conn.commit而已�Q�根本毫无神�U�可�a��Q�只不过�?/SPAN>Hibernate中，Session打开的时候，��׃��自动conn.setAutoCommit(false)�Q�不像一般的JDBC�Q�默认都�?/SPAN>true�Q�所以你最后不�?/SPAN>commit也没有关�p�，�׃��Hibernate已经�?/SPAN>AutoCommit�l�关掉了�Q�所以用Hibernate的时候，你在�E�序中不�?/SPAN>Transaction的话�Q�数据库�Ҏ��没有反应�?/SPAN>

二�?/SPAN>JTATransaction

如果你在EJB中��?/SPAN>Hibernate�Q�或者准备用JTA来管理跨Session的长事务�Q�那么就需要��?/SPAN>JTATransaction�Q�先看一个例子：

javax.transaction.UserTransaction tx = new InitialContext().lookup("javax.transaction.UserTransaction");

Session s1 = sf.openSession();

...

s1.flush();

s1.close();

...

Session s2 = sf.openSession();

...

s2.flush();

s2.close();

tx.commit();

�q�是标准的��?/SPAN>JTA的代码片断，Transaction是跨Session的，它的生命周期�?/SPAN>Session要长。如果你�?/SPAN>EJB中��?/SPAN>Hibernate�Q�那么是最��单不�q�的了，你什�?/SPAN>Transaction代码�l�统都不要写了，直接�?/SPAN>EJB的部�|�描�q�符上配�|�某某方法是否��用事务就可以了�?/SPAN>

现在我们来分析一�?/SPAN>JTATransaction的源代码

net.sf.hibernate.transaction.JTATransaction:

public void begin(InitialContext context, ...

...

ut = (UserTransaction) context.lookup(utName);

...

看清楚了吗？和我上面写的代码 tx = new Initial

Context?().lookup("javax.transaction.UserTransaction");

是不是完全一��P��

public void commit() ...

...

if (newTransaction) ut.commit();

...

JTATransaction的控制稍微复杂，不过仍然可以很清楚的看出�?/SPAN>Hibernate是如何封�?/SPAN>JTA�?/SPAN>Transaction代码的�?/SPAN>

但是你现在是否看��C��什么问题？仔细想一下，Hibernate Transaction是从Session中获得的�Q?/SPAN>tx = session.beginTransaction()�Q�最后要先提�?/SPAN>tx�Q�然后再session.close�Q�这完全�W�合JDBC�?/SPAN>Transaction的操作顺序，但是�q�个��序是和JTA�?/SPAN>Transactioin操作��序��d��矛盾的！�Q�！

JTA是先启动Transaction�Q�然后启�?/SPAN>Session�Q�关�?/SPAN>Session�Q�最后提�?/SPAN>Transaction�Q�因此当你��?/SPAN>JTA�?/SPAN>Transaction的时候，那么��千万不要��?/SPAN>Hibernate�?/SPAN>Transaction�Q�而是应该像我上面�?/SPAN>JTA的代码片断那样��用才行�?/SPAN>

�ȝ��Q?/SPAN>

1、在JDBC上��?/SPAN>Hibernate 必须写上Hibernate Transaction代码�Q�否则数据库没有反应。此�?/SPAN>Hibernate�?/SPAN>Transaction��是Connection.commit而已

2、在JTA上��?/SPAN>Hibernate �?/SPAN>JTA�?/SPAN>Transaction代码�Q�不要写Hibernate�?/SPAN>Transaction代码�Q�否则程序会报错

3、在EJB上��?/SPAN>Hibernate 什�?/SPAN>Transactioin代码都不要写�Q�在EJB的部�|�描�q�符里面配置

|---CMT(Container Managed Transaction)

|---BMT(Bean Managed Transaction)

|----JDBC Transaction

|----JTA Transaction

提问�Q?/SPAN>

javax.transaction.UserTransaction tx = new InitialContext().lookup("javax.transaction.UserTransaction");

Session s1 = sf.openSession();

...

s1.flush();

s1.close();

...

Session s2 = sf.openSession();

...

s2.flush();

s2.close();

tx.commit();

s1不关闭，使用s2�q�行操作的代码中使用s1可不可以�Q�我觉得�q�样更加节约资源�Q�不需要反复的�q�接、关闭）�?/SPAN>sf.opengSession()�Ӟ��q�没�?/SPAN>setAutoCommit(false)�Q�我想问的是�Q�如果不�~�写��M��事务代码�Q�如�Q?/SPAN>

Session s = sf.openSession();

......

s.close();

数据库会不会有反应（此时应该是默�?/SPAN>AutoCommit�?/SPAN>true�Q��?/SPAN>

不会有反应。在sf.openSession()

创徏Session实例的时候，��已�l�调用了conn.setAutoCommit(false)了�?/SPAN>

另外�Q�我想问一下：


      1. s.flush()是不是必��ȝ�� 
      2. s.close()是不是一定要关闭

回答�Q?/SPAN>

s.flush不是必须的，s.close()会调用一��?/SPAN>s.flush()

s.close()正常情况下应该关闭，除非你是�?/SPAN>ThreadLocal��理Session�?/SPAN>

s1不关闭，使用s2�q�行操作的代码中使用s1可不可以�Q�我觉得�q�样更加节约资源�Q�不需要反复的�q�接、关闭）

在这个例子中看不出来JTA的作用�?/SPAN>

假设

Class A {


  find() {
    Session s1 = sf.openSession(); 
    ... 
    s1.flush(); 
    s1.close(); 
  }

}

Class B {


  find() {
    Session s2 = sf.openSession(); 
    ... 
    s2.flush(); 
    s2.close(); 
  }
}
Main {
 
  tx = ...;
  A.find();
  B.find();
  tx.commit();
}
看明白了吗？JTA�?/SPAN>Transaction���理是跨�c�调用的�?/SPAN>


������ 2005-07-29 10:46 发表评论



�W�一个Hibernate例子
������ — Fri, 29 Jul 2005 02:07:00 GMT
�q�是一个简单的例子
1. 在mySQL中徏立一张USER表�?/P>
CREATE TABLE USER ( 
    user_id CHAR(32) NOT NULL PRIMARY KEY, 
    name VARCHAR(16) NOT NULL, 
    sex CHAR(1), 
    age INT 
);
2. 建立一个pojo
package com.xy;
public class User { 
    private String id; 
    private String name; 
    private char sex; 
    private int age; 
    public int getAge() { 
        return age; 
    } 
    public String getId() { 
        return id; 
    } 
    public String getName() { 
        return name; 
    } 
    public char getSex() { 
        return sex; 
    } 
    public void setAge(int i) { 
        age = i; 
    } 
    public void setId(String string) { 
        id = string; 
    } 
    public void setName(String string) { 
        name = string; 
    } 
    public void setSex(char c) { 
        sex = c; 
    } 
}
3. hibernate.cfg.xml文�g
 
    PUBLIC "-//Hibernate/Hibernate Configuration DTD//EN" 
    " 

 
     
         
        true 
         
        net.sf.hibernate.dialect.MySQLDialect 
         
        com.mysql.jdbc.Driver 
         
        jdbc:mysql://localhost/jiejie 
         
        root 
         
         
         
         
     
 
4. User.hbm.xml
 
    PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN" 
    " 

 
     
         
             
             
         
         
             
         
         
         
     

5. ���试文�g
package com.xy;
import java.util.List;
import java.util.ListIterator;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import net.sf.hibernate.*;
import net.sf.hibernate.cfg.*;
public class HibernateTest {
 private static Log log = LogFactory.getLog(HibernateTest.class); 
 public void find() {
  SessionFactory sessionFactory;
  try {
   sessionFactory = new Configuration().configure()
     .buildSessionFactory();
   Session session = sessionFactory.openSession();
   List users = session.find("from User");
   session.close();
   sessionFactory.close();
   for (ListIterator iterator = users.listIterator(); iterator
     .hasNext();) {
    User user = (User) iterator.next();
    System.out.println(user.getName() + "\n\tAge: " + user.getAge()
      + "\n\tSex: " + user.getSex());
   }
  } catch (HibernateException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
 }
 public void insert() {
  SessionFactory sessionFactory;
  try {
   sessionFactory = new Configuration().configure()
     .buildSessionFactory();
   User user = new User();
   user.setName("caterpillar");
   user.setSex('M');
   user.setAge(23);
   Session session = sessionFactory.openSession();
   Transaction tx = session.beginTransaction();
   session.save(user);
   tx.commit();
   session.close();
   sessionFactory.close();
   System.out.println("插入数据OK!请在MySQL查看�l�果�Q?);
  } catch (HibernateException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
 }
 public static void main(String[] args) throws HibernateException {
  new HibernateTest().find();
  new HibernateTest().insert();
 }
}

6. 文�g�l�构和所用到的jar�?BR>

 
7. 操作�l�果

log4j:WARN No appenders could be found for logger (net.sf.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
Hibernate: select user0_.user_id as user_id, user0_.name as name, user0_.sex as sex, user0_.age as age from USER user0_
caterpillar
 Age: 28
 Sex: M
caterpillar
 Age: 28
 Sex: M
caterpillar
 Age: 28
 Sex: M
caterpillar
 Age: 23
 Sex: M
qqqqq
 Age: 20
 Sex: M
www
 Age: 21
 Sex: M
yyy
 Age: 20
 Sex: M
yyy
 Age: 20
 Sex: M
yyy
 Age: 20
 Sex: M
yyy
 Age: 20
 Sex: M
Hibernate: insert into USER (name, sex, age, user_id) values (?, ?, ?, ?)
插入数据OK!请在MySQL查看�l�果�Q?BR>


������ 2005-07-29 10:07 发表评论