引用：
悲观锁与乐观锁：
http://www.iteye.com/topic/179267
http://hi.baidu.com/ahuzl/blog/item/1340fe8307dc16b56d81194b.html
事务管理机制：
http://www.router.net.cn/Article/26494.html
http://www.iteye.com/topic/280746
悲观锁示例：
POJO 为User类
在示例中从数据库load出来，分别用两个测试方法来，在第一个方法里面设置断点，会发现直到第一个方法执行完，第二个方法才进行更新。
说明锁定的情况下其它session不能更新。
package com.bjsxt.hibernate;
import junit.framework.TestCase;
import org.hibernate.LockMode;
import org.hibernate.Session;
public class PessimisticLockingTest extends TestCase {
public void testUpdate1() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
User user = (User)session.load(User.class, "402880f6286c790b01286c7911eb0001", LockMode.UPGRADE);
System.out.println("name=" + user.getName());
System.out.println("password=" + user.getPassword());
user.setPassword("a");
session.update(user);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testUpdate2() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
User user = (User)session.load(User.class, "402880f6286c790b01286c7911eb0001", LockMode.UPGRADE);
System.out.println("name=" + user.getName());
System.out.println("password=" + user.getPassword());
user.setPassword("b");
session.update(user);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
}
乐观锁：
在User类里面增加属性version
package com.bjsxt.hibernate;
import java.util.Date;
public class User {
private String id;
private String name;
private String password;
private Date createTime;
private Date expireTime;
//采用乐观锁，进行并发控制
private int version;
public Date getCreateTime() {
return createTime;
}
public void setCreateTime(Date createTime) {
this.createTime = createTime;
}
public Date getExpireTime() {
return expireTime;
}
public void setExpireTime(Date expireTime) {
this.expireTime = expireTime;
}
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 String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public int getVersion() {
return version;
}
public void setVersion(int version) {
this.version = version;
}
}
配置文件：
<?xml version="1.0"?> <!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.bjsxt.hibernate.User" optimistic-lock="version"> <id name="id"> <generator class="uuid"/> </id> <version name="version"/> <property name="name"/> <property name="password"/> <property name="createTime"/> <property name="expireTime"/> </class> </hibernate-mapping>
一样采用两个测试方法进行测试：
package com.bjsxt.hibernate;
import java.util.Date;
import org.hibernate.LockMode;
import org.hibernate.Session;
import junit.framework.TestCase;
public class OptimisticLockingTest extends TestCase {
public void testUpdate1() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
User user = (User)session.load(User.class, "402880f6286c93c101286c93c7130001");
System.out.println("name=" + user.getName());
System.out.println("password=" + user.getPassword());
user.setPassword("a");
session.update(user);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testUpdate2() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
User user = (User)session.load(User.class, "402880f6286c93c101286c93c7130001");
System.out.println("name=" + user.getName());
System.out.println("password=" + user.getPassword());
System.out.println("version=" + user.getVersion());
user.setPassword("b");
session.update(user);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
}
可在第一个方法中设置断点，debug，而第二个方法run。看看执行的情况。
乐观锁User的表
+------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +------------+--------------+------+-----+---------+-------+ | id | varchar(255) | NO | PRI | NULL | | | version | int(11) | NO | | NULL | | | name | varchar(255) | YES | | NULL | | | password | varchar(255) | YES | | NULL | | | createTime | datetime | YES | | NULL | | | expireTime | datetime | YES | | NULL | | +------------+--------------+------+-----+---------+-------+
虽然加了version字段，但是不需要设置该属性值，如下：
package com.bjsxt.hibernate;
import java.util.Date;
import org.hibernate.Session;
public class InitData {
public static void main(String[] args) {
Session session = null;
User user = new User();
try {
session = HibernateUtils.getSession();
session.beginTransaction();
user.setName("张三");
user.setPassword("123");
user.setCreateTime(new Date());
user.setExpireTime(new Date());
session.save(user);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
}
我在测试方法一中的System.out.println("name=" + user.getName());处设置断点，然后执行debug这个方法。
执行到断点处，我们发现从数据库查询出来的version=0,这时再执行测试方法二，会发现测试方法二立刻执行，并把version变成为1,测试方法二执行完，我们再按F6下一步时，测试方法一执行到commit的时候会抛出异常：
这是因为乐观锁发现自身的version<=数据库中的version的时候更新不了。。
org.hibernate.StaleObjectStateException: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect): [com.bjsxt.hibernate.User#402880f6286c93c101286c93c7130001]