hibernate 乐观所使用

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);

1 实体类

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;
	}
}

2 实体配置文件  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" optimistic-lock="version"  >
    <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>

3  hbernate.cfg.xml 主配置文件

<?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.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>

4 hibernage 的测试代码

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