[转载]hibernate的乐观锁

http://esffor.iteye.com/blog/168243

通过在表中及POJO中增加一个version字段来表示记录的版本，来达到多用户同时更改一条数据的冲突

数据库脚本：

create table studentVersion (id varchar ( 32 ),name varchar ( 32 ),ver int );

POJO

package Version;

public class Student ... {
private String id;
private String name;
privateint version;
public String getId() ...{
return id;
}
publicvoid setId(String id) ...{
this.id = id;
}
public String getName() ...{
return name;
}
publicvoid setName(String name) ...{
this.name = name;
}
publicint getVersion() ...{
return version;
}
publicvoid setVersion(int version) ...{
this.version = version;
}


}

Student.hbm.xml

<? xml version="1.0" encoding="utf-8" ?>
<! DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
<!--
Mapping file autogenerated by MyEclipse - Hibernate Tools
-->
< hibernate-mapping >
< class name ="Version.Student" table ="studentVersion" >
< id name ="id" unsaved-value ="null" >
< generator class ="uuid.hex" ></ generator >
</ id >
<!-- version标签必须跟在id标签后面 -->
< version name ="version" column ="ver" type ="int" ></ version >
< property name ="name" type ="string" column ="name" ></ property >
</ class >

</ hibernate-mapping >

Hibernate.cfg.xml

<? xml version='1.0' encoding='UTF-8' ?>
<! DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd" >

<!-- Generated by MyEclipse Hibernate Tools. -->
< hibernate-configuration >

< session-factory >
< property name ="connection.username" > root </ property >
< property name ="connection.url" >
jdbc:mysql://localhost:3306/schoolproject?characterEncoding=gb2312 &amp; useUnicode=true
</ property >
< property name ="dialect" >
org.hibernate.dialect.MySQLDialect
</ property >
< property name ="myeclipse.connection.profile" > mysql </ property >
< property name ="connection.password" > 1234 </ property >
< property name ="connection.driver_class" >
com.mysql.jdbc.Driver
</ property >
< property name ="hibernate.dialect" >
org.hibernate.dialect.MySQLDialect
</ property >
< property name ="hibernate.show_sql" > true </ property >
< property name ="current_session_context_class" > thread </ property >
< property name ="jdbc.batch_size" > 15 </ property >
< mapping resource ="Version/Student.hbm.xml" />




</ session-factory >

</ hibernate-configuration >

测试代码：

package Version;


import java.io.File;
import java.util.Iterator;
import java.util.Set;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

public class Test ... {


publicstaticvoid main(String[] args) ...{

String filePath=System.getProperty("user.dir")+File.separator+"src/Version"+File.separator+"hibernate.cfg.xml";
File file=new File(filePath);
System.out.println(filePath);
SessionFactory sessionFactory=new Configuration().configure(file).buildSessionFactory();
Session session=sessionFactory.openSession();
Transaction t=session.beginTransaction();

Student stu=new Student();
stu.setName("tom11");
session.save(stu);
t.commit();


/**//*
* 模拟多个session操作student数据表
*/

Session session1=sessionFactory.openSession();
Session session2=sessionFactory.openSession();
Student stu1=(Student)session1.createQuery("from Student s where s.name='tom11'").uniqueResult();
Student stu2=(Student)session2.createQuery("from Student s where s.name='tom11'").uniqueResult();

//这时候，两个版本号是相同的
System.out.println("v1="+stu1.getVersion()+"--v2="+stu2.getVersion());

Transaction tx1=session1.beginTransaction();
stu1.setName("session1");
tx1.commit();
//这时候，两个版本号是不同的，其中一个的版本号递增了
System.out.println("v1="+stu1.getVersion()+"--v2="+stu2.getVersion());

Transaction tx2=session2.beginTransaction();
stu2.setName("session2");
tx2.commit();



}

}

运行结果：

Hibernate: insert into studentVersion (ver, name, id) values (?, ?, ?)
Hibernate: select student0_.id as id0_, student0_.ver as ver0_, student0_.name as name0_ from studentVersion student0_ where student0_.name='tom11'
Hibernate: select student0_.id as id0_, student0_.ver as ver0_, student0_.name as name0_ from studentVersion student0_ where student0_.name='tom11'
v1=0--v2=0
Hibernate: update studentVersion set ver=?, name=? where id=? and ver=?
v1=1--v2=0
Hibernate: update studentVersion set ver=?, name=? where id=? and ver=?
Exception in thread "main" org.hibernate.StaleObjectStateException: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect): [Version.Student#4028818316cd6b460116cd6b50830001]

可以看到，第二个“用户”session2修改数据时候，记录的版本号已经被session1更新过了，所以抛出了红色的异常，我们可以在实际应用中处理这个异常，例如在处理中重新读取数据库中的数据，同时将目前的数据与数据库中的数据展示出来，让使用者有机会比较一下，或者设计程序自动读取新的数据

注意：如果手工设置stu.setVersion()自行更新版本以跳过检查,则这种乐观锁就会失效，应对方法可以将Student.java的setVersion设置成private