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&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
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