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]