Hibernate_并发（悲观锁&乐观锁）_Demo

来源：互联网发布：在淘宝点击卖家没反应编辑：程序博客网时间：2024/05/21 17:50

package org.zttc.itat.test;import org.hibernate.LockOptions;import org.hibernate.Session;import org.junit.Test;import org.zttc.itat.model2.Student;import org.zttc.itat.util.HibernateUtil;public class TestLock {@Test<pre name="code" class="java"><?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping package="org.com.test.model">    <class name="Student" table="t_student">    <!-- <cache usage="read-only"/> -->        <id name="id">            <!-- <generator class="assigned"/> --><!-- 这个需要开发人员自己定义id -->            <generator class="native"/><!-- 会自动生成一个字符串，此时主键必须为字符串 -->        </id>        <version name="version"/>        <property name="name"/>        <property name="sex"/>      <many-to-one name="classroom" column="c_id" fetch="select"/> <!-- fetch="join" -->    </class></hibernate-mapping>

package org.com.test.model;//@Cache(usage=CacheConcurrencyStrategy.READ_ONLY)public class Student {private int id;private String name;private String sex;private Classroom classroom;private int version;public int getVersion() {return version;}public void setVersion(int version) {this.version = version;}public Student() {}public Student(String name, String sex, Classroom classroom) {this.name = name;this.sex = sex;this.classroom = classroom;}public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getSex() {return sex;}public void setSex(String sex) {this.sex = sex;}public Classroom getClassroom() {return classroom;}public void setClassroom(Classroom classroom) {this.classroom = classroom;}}

package org.com.test.test;import org.com.test.model.Student;import org.com.test.util.HibernateUtil;import org.hibernate.Session;import org.junit.Test;public class TestLock {@Testpublic void testUpdate01() {Session session = null;try {session = HibernateUtil.getSession();session.beginTransaction();//只要使用这种方式来load就会为其增加锁//Student stu = (Student)session.load(Student.class,1,LockOptions.UPGRADE);Student stu = (Student)session.load(Student.class, 1);stu.setName("张三");session.getTransaction().commit();} catch (Exception e) {e.printStackTrace();} finally {HibernateUtil.closeSession(session);}}@Testpublic void testUpdate02() {Session session = null;try {session = HibernateUtil.getSession();session.beginTransaction();//Student stu = (Student)session.load(Student.class,1,LockOptions.UPGRADE);Student stu = (Student)session.load(Student.class, 1);stu.setSex("女");session.getTransaction().commit();} catch (Exception e) {e.printStackTrace();} finally {HibernateUtil.closeSession(session);}}}

一般并发会导致更新丢失，有两种解决方案可以解决并发的问题
1、悲观锁
悲观锁是Hibernate基于数据库的机制来实现的，hibernate是基于同步的机制实现的，当只要读取了这个对象，这个对象就会被加锁
只有在第一个对象读取完成之后第二个对象才能读取。这样将会大大的影响效率
2、乐观锁
乐观锁是在数据库中增加一个version的字段来实现的，每一次修改都会让这个字段的数字加1，在读取的时候根据version这个版本数据来读取
这样如果并发修改就会抛出异常

0 0