Hibernate乐观锁实现之Version

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

POJO

?

package?Version;

public?class?Student?{
??private?String?id;
??private?String?name;
??private?int?version;
public?String?getId()?{
????return?id;
}
public?void?setId(String?id)?{
????this.id?=?id;
}
public?String?getName()?{
????return?name;
}
public?void?setName(String?name)?{
????this.name?=?name;
}
public?int?getVersion()?{
????return?version;
}
public?void?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&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?{


????public?static?void?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