Hibernate并发控制乐观锁实现-Version

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：

createtablestudentVersion(idvarchar(32),namevarchar(32),verint);

POJO

packageVersion;

publicclassStudent{
privateStringid;
privateStringname;
privateintversion;
publicStringgetId(){
returnid;
}
publicvoidsetId(Stringid){
this.id=id;
}
publicStringgetName(){
returnname;
}
publicvoidsetName(Stringname){
this.name=name;
}
publicintgetVersion(){
returnversion;
}
publicvoidsetVersion(intversion){
this.version=version;
}


}

Student.hbm.xml

<?xmlversion="1.0"encoding="utf-8"?>
<!DOCTYPEhibernate-mappingPUBLIC"-//Hibernate/HibernateMappingDTD3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!--
MappingfileautogeneratedbyMyEclipse-HibernateTools
-->
<hibernate-mapping>
<classname="Version.Student"table="studentVersion">
<idname="id"unsaved-value="null">
<generatorclass="uuid.hex"></generator>
</id>
<!--version标签必须跟在id标签后面-->
<versionname="version"column="ver"type="int"></version>
<propertyname="name"type="string"column="name"></property>
</class>

</hibernate-mapping>

Hibernate.cfg.xml

<?xmlversion='1.0'encoding='UTF-8'?>
<!DOCTYPEhibernate-configurationPUBLIC
"-//Hibernate/HibernateConfigurationDTD3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<!--GeneratedbyMyEclipseHibernateTools.-->
<hibernate-configuration>

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




</session-factory>

</hibernate-configuration>

测试代码：

packageVersion;


importjava.io.File;
importjava.util.Iterator;
importjava.util.Set;

importorg.hibernate.Session;
importorg.hibernate.SessionFactory;
importorg.hibernate.Transaction;
importorg.hibernate.cfg.Configuration;

publicclassTest{


publicstaticvoidmain(String[]args){

StringfilePath=System.getProperty("user.dir")+File.separator+"src/Version"+File.separator+"hibernate.cfg.xml";
Filefile=newFile(filePath);
System.out.println(filePath);
SessionFactorysessionFactory=newConfiguration().configure(file).buildSessionFactory();
Sessionsession=sessionFactory.openSession();
Transactiont=session.beginTransaction();

Studentstu=newStudent();
stu.setName("tom11");
session.save(stu);
t.commit();


/*
*模拟多个session操作student数据表
*/

Sessionsession1=sessionFactory.openSession();
Sessionsession2=sessionFactory.openSession();
Studentstu1=(Student)session1.createQuery("fromStudentswheres.name='tom11'").uniqueResult();
Studentstu2=(Student)session2.createQuery("fromStudentswheres.name='tom11'").uniqueResult();

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

Transactiontx1=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());

Transactiontx2=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