hibernate中的optimistic-lock(...

最新推荐文章于 2023-08-09 08:36:23 发布

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#hibernate #session #user #myeclipse #class #generator

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本文介绍如何在Hibernate中实现乐观锁，通过具体示例演示如何在User实体类中添加version字段并配置XML映射文件，同时提供了测试代码来展示在并发场景下如何检测版本冲突。

注意：要在user表中增加一个字段：version int
User.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">

<hibernate-mapping>
<class name="com.shiryu.otm.User" table="user" dynamic-update="true" dynamic-insert="true" optimistic-lock="version" >
    <id name="id" type="java.lang.Integer">
      <column name="id" />
      <generator class="native" />
    </id>
    
    <version name="version" column="version" type="java.lang.Integer" />

    <property name="name" type="java.lang.String">
      <column name="name" length="50" />
    </property>
    <property name="age" type="java.lang.Integer" column="age" />

    <set name="addresses" table="address" cascade="all" order-by="address desc">

      <key column="user_id"></key>
      <one-to-many class="com.shiryu.otm.Address" />
    </set>
</class>
</hibernate-mapping>

OptimisticlLockingTest.java

package com.shiryu.otm;

import java.util.List;

import org.hibernate.Criteria;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.criterion.Expression;

//乐观锁 Optimistic Lock
public class OptimisticLockingTest {
    public static void main(String[] args) {
        SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
        Session session = sessionFactory.openSession();
        Criteria criteria = session.createCriteria(User.class);
        criteria.add(Expression.eq("name", "zhaiyu"));

        List l = criteria.list();

        User user = (User) l.get(0);
        Transaction tr = session.beginTransaction();
        user.setAge(21);// 更新age字段
        tr.commit();
        session.close();
        // 每次对数据库进行更新时，数据库中version都在递增

        // 现在我们尝试在tr.commit之前，启动另外一个Session，对zhaiyu用户进行操作，模拟并发时的情景

        Session session1 = sessionFactory.openSession();
        Criteria criteria1 = session1.createCriteria(User.class);
        criteria1.add(Expression.eq("name", "zhaiyu"));

        Session session2 = sessionFactory.openSession();
        Criteria criteria2 = session2.createCriteria(User.class);
        criteria2.add(Expression.eq("name", "zhaiyu"));

        List userList1 = criteria1.list();
        List userList2 = criteria2.list();

        User user1 = (User) userList1.get(0);
        User user2 = (User) userList2.get(0);

        Transaction tr1 = session1.beginTransaction();
        Transaction tr2 = session2.beginTransaction();

        user1.setAge(26);// 更新age字段
        tr1.commit();

        user2.setAge(44);// 更新age字段
        tr2.commit();// 系统出现StaleObjectStateException异常，并指出版本检测失败
    }
}