通過在表中及POJO中增加一個version字段來表示記錄的版本，來達到多用戶同時更改一條數據的沖突

數據庫腳本：

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標簽必須跟在id標簽后面-->
    <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>

測試代碼：

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();
      
        
        /**//*
         * 模擬多個session操作student數據表
         */
        
        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();
        
        //這時候，兩個版本號是相同的
        System.out.println("v1="+stu1.getVersion()+"--v2="+stu2.getVersion());
        
        Transaction tx1=session1.beginTransaction();
        stu1.setName("session1");
        tx1.commit();
        //這時候，兩個版本號是不同的，其中一個的版本號遞增了
        System.out.println("v1="+stu1.getVersion()+"--v2="+stu2.getVersion());
        
        Transaction tx2=session2.beginTransaction();
        stu2.setName("session2");
        tx2.commit();
        
        
        
    }

}

運行結果：

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，第二個“用戶”session2修改數據時候，記錄的版本號已經被session1更新過了，所以拋出了紅色的異常，我們可以在實際應用中處理這個異常，例如在處理中重新讀取數據庫中的數據，同時將目前的數據與數據庫中的數據展示出來，讓使用者有機會比較一下，或者設計程序自動讀取新的數據

注意：如果手工設置stu.setVersion()自行更新版本以跳過檢查,則這種樂觀鎖就會失效，應對方法可以將Student.java的setVersion設置成private