java鬼混笔记：Hibernate：7、乐观锁（有代码）和悲观锁（无代码）

这次的笔记是hibernate对数据并发操作时用到的一功能 ，锁！

锁分为二种，一种是 悲观锁，一种是乐观锁。看名字就知道哪个好了。

悲观锁：

悲观锁的走的道路是：一个事务拿到一条数据后进行操作，就锁了这条数据，别的事务想拿这条数据操作是不行的，得等上一个事务搞定后，才放锁给下一个事务处理。比如基本的转账和取钱，取钱时先查询用户有多少钱可以取，select pirce from card where userid = 1,转账前也要查询有卡里有多少钱（因为转账后的钱-转账前的钱 = 要转的钱，所以要先给用户看一下转前有多少，然后看看转后数目是不是对的），因为取钱时这条数据被锁了，所以转账时，得等用户把钱取出来后（card = card-取出的钱），这时才可以转账。这种方法可以让数据一致性，但效率低，毕竟依赖数据库的锁机制，开销还是有的，所以基本没用这种锁。悲观锁代码我就不贴了，也没什么意义。

乐观锁：

乐观锁走的道路是在表里加一个字段，比如版本version（ 整数），或者时间戳 timestamp，当我们更新数据时，判断你拿出这条数据所属的版本号和时间戳是否是一致，是就更新，不是就说明这条数据被别人修改过了,抛出异常(org.hibernate.StaleObjectStateException)，你得重新获取这条数据才能重新处理。

上代码：

Version控制：

Img.java

package com.e;import java.io.Serializable;import java.util.Date;public class Img implements Serializable {/**  *   */private static final long serialVersionUID = -1133307425564153298L;private Integer id;private Integer number;private Integer vs;// 版本号public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public Integer getNumber() {return number;}public void setNumber(Integer number) {this.number = number;}public Integer getVs() {return vs;}public void setVs(Integer vs) {this.vs = vs;}}

Img.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 package="com.e"><class name="Img" table="img" lazy="false" ><id name="id" type="java.lang.Integer"><column name="id" /><generator class="identity" /></id><!-- version中name和column像平时那样使用 --><version name="vs" column="vs" type="integer"></version><property name="number" type="java.lang.Integer"></property></class></hibernate-mapping> 

Dao.java

//public void testLock() {    // 模拟两个事务同时拿到了同一条数据 后进行修改Session s1 = this.getSessionFactory().openSession();Session s2 = this.getSessionFactory().openSession();Img img1 = (Img)s1.get(Img.class, 1);Img img2 = (Img)s2.get(Img.class, 1);lock1(s1, img1);lock2(s2, img2);    }public void lock1(Session session, Img img) {Transaction tx = null;try {    tx = session.beginTransaction();    System.out.println("2017更新前版本："+img.getVs());    img.setNumber(2017);    session.update(img);    tx.commit();    System.out.println("2017更新后版本："+img.getVs());} catch (Exception e) {e.printStackTrace();if(e instanceof StaleObjectStateException) {System.out.println("..............................1");}if(tx != null){tx.rollback();}} finally {if(session != null) {session.close();}}    }public void lock2(Session session, Img img) {Transaction tx = null;try {    tx = session.beginTransaction();    System.out.println("2018更新后版本："+img.getVs());    img.setNumber(2018);    session.update(img);    tx.commit();    System.out.println("2018更新后版本："+img.getVs());} catch (Exception e) {if(e instanceof StaleObjectStateException) {System.out.println("..............................2");}e.printStackTrace();if(tx != null){tx.rollback();}} finally {if(session != null) {session.close();}}    }//

抛出异常了，但成功更新了 2017,2018在后面版本冲突了，2018捕获异常重新处理才行

//Hibernate: select img0_.id as id0_0_, img0_.vs as vs0_0_, img0_.number as number0_0_ from img img0_ where img0_.id=?Hibernate: select img0_.id as id0_0_, img0_.vs as vs0_0_, img0_.number as number0_0_ from img img0_ where img0_.id=?2017更新前版本：15Hibernate: update img set vs=?, number=? where id=? and vs=?2017更新后版本：162018更新后版本：15Hibernate: update img set vs=?, number=? where id=? and vs=?..............................2org.hibernate.StaleObjectStateException: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect): [com.e.Img#1]at org.hibernate.persister.entity.AbstractEntityPersister.check(AbstractEntityPersister.java:1950)at org.hibernate.persister.entity.AbstractEntityPersister.update(AbstractEntityPersister.java:2594)at org.hibernate.persister.entity.AbstractEntityPersister.updateOrInsert(AbstractEntityPersister.java:2494)at org.hibernate.persister.entity.AbstractEntityPersister.update(AbstractEntityPersister.java:2821)at org.hibernate.action.EntityUpdateAction.execute(EntityUpdateAction.java:113)at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:273)at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:265)at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:185)at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:321)at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:51)at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1216)at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:383)at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:133)at com.d.ImgD.lock2(ImgD.java:76)at com.d.ImgD.testLock(ImgD.java:39)at com.s.ImgS.testLock(ImgS.java:30)at com.s.ImgS$$FastClassByCGLIB$$4539feb8.invoke(<generated>)at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:698)at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96)at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:91)at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:631)at com.s.ImgS$$EnhancerByCGLIB$$dcffcc8b.testLock(<generated>)at com.c.ImgC.index(ImgC.java:22)at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)at java.lang.reflect.Method.invoke(Unknown Source)at org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:219)at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:745)at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:686)at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80)at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:925)at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:856)at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:936)at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:827)at javax.servlet.http.HttpServlet.service(HttpServlet.java:624)at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:812)at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:218)at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:956)at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:442)at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1082)at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:623)at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)at java.lang.Thread.run(Unknown Source)//

Timestamp控制：（其实一version一样，换个字段而已）

img.java ： 把private Integer vs;// 版本 换成 private Date ts;// 时间

img.hbm.xml ： 把 <version name="vs" column="vs" type="integer"></version> 换成 <timestamp name="ts" column="ts"></timestamp>

OK。。。。