乐观锁(Optimistic Lock)之version(版本号)与timestamp(时间戳)配置解读

version(版本号)

版本号配置中须指明  optimistic-lock="version"

在测试类HibernateTest中session1会话查询修改student表后， 如果session2会话中再对student表进行修改，此时会抛出org.hibernate.StaleObjectStateException异常，意思是说第一次修改后表中version的值会由0变为1（表中version的初始值为0），当第二次尝试进行修改的时候底层会将查询时获得version(值为0)与数据库中一更新的值为1的version进行对比，发现0 < 1 便会抛出以上异常（大概是过期的类状态异常的意思）。

HibernateTest类代码如下：

package com.hibernate;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

public class HibernateTest {
	private static SessionFactory sessionFactory;
	static
	{
		try
		{
			sessionFactory = new Configuration().configure().buildSessionFactory();
		}
		catch(Exception ex)
		{
			ex.printStackTrace();
		}
	}
	public static void main(String[] args) {
		
		
		Session session = sessionFactory.openSession();
		Transaction tx  = null;
		try
		{
			tx = session.beginTransaction();
//			Student student = new Student();
//			student.setName("zhangsan");
//			student.setAge(20);
//			student.setCardId("14");
//			session.save(student);
//			tx.commit();
			
			Session session1 = sessionFactory.openSession();
			Session session2 = sessionFactory.openSession();
			
			Student student1 = (Student)session1.createQuery("from Student s where s.name = :name").setString("name", "zhangsan").uniqueResult();
			Student student2 = (Student)session2.createQuery("from Student s where s.name = :name").setString("name", "zhangsan").uniqueResult();
			
			System.out.println(student1.getVersion());
			System.out.println(student2.getVersion());
			
			Transaction tx1 = session1.beginTransaction();
			student1.setName("lisi");
			tx1.commit();
			
			System.out.println(student1.getVersion());
			System.out.println(student2.getVersion());
			
			Transaction tx2 = session2.beginTransaction();
			student2.setCardId("111");
			tx2.commit();
			
			System.out.println(student1.getVersion());
			System.out.println(student2.getVersion());
			
			
			
		}
		catch(Exception ex)
		{
			ex.printStackTrace();
			if(null != tx)
			{
				tx.rollback();
			}
		}
		finally
		{
			session.close();
		}
		
	}

}

对应的控制台的输出信息如下：

Hibernate: 
    select
        student0_.id as id0_,
        student0_.version as version0_,
        student0_.cardId as cardId0_,
        student0_.age as age0_,
        student0_.name as name0_ 
    from
        student student0_ 
    where
        student0_.name=?
Hibernate: 
    select
        student0_.id as id0_,
        student0_.version as version0_,
        student0_.cardId as cardId0_,
        student0_.age as age0_,
        student0_.name as name0_ 
    from
        student student0_ 
    where
        student0_.name=?
0
0
Hibernate: 
    update
        student 
    set
        version=?,
        cardId=?,
        age=?,
        name=? 
    where
        id=? 
        and version=?
1
0
Hibernate: 
    update
        student 
    set
        version=?,
        cardId=?,
        age=?,
        name=? 
    where
        id=? 
        and version=?
org.hibernate.StaleObjectStateException: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect): [com.hibernate.Student#ef3262e84974c56c014974c56dc60000]

timestamp(时间戳)

时间戳配置中无须指明optimistic-lock参数

对于timestamp的测试方法与version原理方法基本一样，大家可以自己尝试一下,谢谢!