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：

 

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 &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  {


    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