boot入门思想 spring_SpringBoot入门建站全系列（二十一）Mybatis使用乐观锁与悲观锁...

SpringBoot入门建站全系列（二十一）Mybatis使用乐观锁与悲观锁

一、概述

之前有两篇《SpringBoot入门建站全系列（三）Mybatis操作数据库》和《SpringBoot入门建站全系列（四）Mybatis使用进阶篇:动态SQL与分页》介绍了Springboot如何结合Mybatis进行数据库访问操作。这一篇介绍下springboot环境下Mybatis如何进行乐观锁、悲观锁的使用。

悲观锁和乐观锁的概念：

悲观锁：就是独占锁，不管读写都上锁了。传统的关系型数据库里边就用到了很多这种锁机制，比如行锁，表锁等，读锁，写锁等，都是在做操作之前先上锁。Java中synchronized和ReentrantLock等独占锁就是悲观锁思想的实现。
乐观锁：不上锁，读取的时候带版本号，写入的时候带着这个版本号，如果不一致就失败，乐观锁适用于多读的应用类型，因为写多的时候会经常失败。

代码可以在Springboot组件化构建https://www.pomit.cn/java/spring/springboot.html中的MybatisLock组件中查看，并下载。

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二、配置

本文假设你已经引入spring-boot-starter-web。已经是个SpringBoot项目了,如果不会搭建，可以打开这篇文章看一看《SpringBoot入门建站全系列（一）项目建立》。

2.1 Maven依赖

需要引入spring-boot-starter-data-jpa，这里要访问数据库，所以要依赖数据库相关jar包。

<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>org.mybatis.spring.boot</groupId><artifactId>mybatis-spring-boot-starter</artifactId></dependency><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId></dependency><dependency><groupId>org.apache.commons</groupId><artifactId>commons-dbcp2</artifactId></dependency>

2.2 配置文件

在application.properties 中需要添加下面的配置：

spring.datasource.type=org.apache.commons.dbcp2.BasicDataSource
spring.datasource.dbcp2.max-wait-millis=60000
spring.datasource.dbcp2.min-idle=20
spring.datasource.dbcp2.initial-size=2
spring.datasource.dbcp2.validation-query=SELECT 1
spring.datasource.dbcp2.connection-properties=characterEncoding=utf8
spring.datasource.dbcp2.validation-query=SELECT 1
spring.datasource.dbcp2.test-while-idle=true
spring.datasource.dbcp2.test-on-borrow=true
spring.datasource.dbcp2.test-on-return=falsespring.datasource.driverClassName = com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql://127.0.0.1:3306/boot?useUnicode=true&characterEncoding=utf8&serverTimezone=UTC
spring.datasource.username=cff
spring.datasource.password=123456mybatis.configuration.log-impl=org.apache.ibatis.logging.stdout.StdOutImpl

这里面，包含了数据库连接信息、数据源的连接池配置信息、mybatis配置信息。

spring.datasource.dbcp2是配置dbcp2的连接池信息；
spring.datasource.type指明数据源的类型；
最上面的http://spring.datasource.xxx指明数据库连接池信息；
mybatis.configuration.log-impl指明mybatis的日志打印方式

三、悲观锁

悲观锁在数据库的访问中使用，表现为：前一次请求没执行完，后面一个请求就一直在等待。

3.1 Dao层

数据库要实现悲观锁，就是将sql语句带上for update即可。 for update 是行锁

所在mybatis的查询sql加上for update，就实现了对当前记录的锁定，就实现了悲观锁。

UserInfoDao :

package com.cff.springbootwork.mybatislock.dao;import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.Update;import cn.pomit.springwork.mybatislock.domain.UserInfo;@Mapper
public interface UserInfoDao {@Select({"<script>","SELECT ","user_name as userName,passwd,name,mobile,valid, user_type as userType, version as version","FROM user_info_test","WHERE user_name = #{userName,jdbcType=VARCHAR} for update","</script>"})UserInfo findByUserNameForUpdate(@Param("userName") String userName);@Update({"<script>"," update user_info_test set"," name = #{name, jdbcType=VARCHAR}, mobile = #{mobile, jdbcType=VARCHAR},version=version+1 "," where user_name=#{userName}","</script>"})int update(UserInfo userInfo);@Insert({"<script>","INSERT INTO user_info_test","( user_name,","name ,","mobile,","passwd,","version",") "," values ","( #{userName},","#{name},","#{mobile},","#{passwd},","#{version}"," ) ","</script>"})int save(UserInfo entity);
}

这里，findByUserNameForUpdate的sql中加上了for update。update就是普通的更新而已。

3.2 Service层

更新数据库前，先调用findByUserNameForUpdate方法，使上面的配置的悲观锁锁定表记录，然后再更新。

UserInfoService ：

package com.cff.springbootwork.mybatislock.service;import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import org.springframework.util.StringUtils;import cn.pomit.springwork.mybatislock.domain.UserInfo;
import cn.pomit.springwork.mybatislock.mapper.UserInfoDao;@Service
public class UserInfoService {@AutowiredUserInfoDao userInfoDao;public void save(UserInfo entity) {entity.setVersion(0);userInfoDao.save(entity);}@Transactionalpublic UserInfo getUserInfoByUserNamePessimistic(String userName) {return userInfoDao.findByUserNameForUpdate(userName);}@Transactionalpublic void updateWithTimePessimistic(UserInfo entity, int time) throws InterruptedException {      UserInfo userInfo = userInfoDao.findByUserNameForUpdate(entity.getUserName());if (userInfo == null)return;if (!StringUtils.isEmpty(entity.getMobile())) {userInfo.setMobile(entity.getMobile());}if (!StringUtils.isEmpty(entity.getName())) {userInfo.setName(entity.getName());}Thread.sleep(time * 1000L);userInfoDao.update(userInfo);}@Transactionalpublic void updatePessimistic(UserInfo entity) {UserInfo userInfo = userInfoDao.findByUserNameForUpdate(entity.getUserName());if (userInfo == null)return;if (!StringUtils.isEmpty(entity.getMobile())) {userInfo.setMobile(entity.getMobile());}if (!StringUtils.isEmpty(entity.getName())) {userInfo.setName(entity.getName());}userInfoDao.update(userInfo);}}

测试中，我们在update方法中sleep几秒，其他线程的update将一直等待。

3.3 测试Web层

可以先调用/update/{time}接口，延迟执行，然后马上调用/update接口，会发现，/update接口一直在等待/update/{time}接口执行完成。

MybatisPessLockRest :

package com.cff.springbootwork.mybatislock.web;import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;import cn.pomit.springwork.mybatislock.domain.UserInfo;
import cn.pomit.springwork.mybatislock.service.UserInfoService;/*** 测试悲观锁* * @author fufei**/
@RestController
@RequestMapping("/mybatispesslock")
public class MybatisPessLockRest {@AutowiredUserInfoService userInfoService;@RequestMapping(value = "/detail/{name}", method = { RequestMethod.GET })public UserInfo detail(@PathVariable("name") String name) {return userInfoService.getUserInfoByUserNamePessimistic(name);}@RequestMapping(value = "/save")public String save(@RequestBody UserInfo userInfo) throws InterruptedException {userInfoService.save(userInfo);return "0000";}@RequestMapping(value = "/update/{time}")public String update(@RequestBody UserInfo userInfo, @PathVariable("time") int time) throws InterruptedException {userInfoService.updateWithTimePessimistic(userInfo, time);return "0000";}@RequestMapping(value = "/update")public String update(@RequestBody UserInfo userInfo) throws InterruptedException {userInfoService.updatePessimistic(userInfo);return "0000";}
}

四、乐观锁

数据库访问dao层还是3.1那个UserInfoDao。

4.1 Dao层

UserInfoDao更新时，需要携带version字段进行更新：and version = #{version}。如果version不一致，是不会更新成功的，这时候，我们的select查询是不能带锁的。

UserInfoDao :

package com.cff.springbootwork.mybatislock.dao;import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.Update;import cn.pomit.springwork.mybatislock.domain.UserInfo;@Mapper
public interface UserInfoDao {@Select({"<script>","SELECT ","user_name as userName,passwd,name,mobile,valid, user_type as userType, version as version","FROM user_info_test","WHERE user_name = #{userName,jdbcType=VARCHAR}","</script>"})UserInfo findByUserName(@Param("userName") String userName);@Update({"<script>"," update user_info_test set"," name = #{name, jdbcType=VARCHAR}, mobile = #{mobile, jdbcType=VARCHAR},version=version+1 "," where user_name=#{userName} and version = #{version}","</script>"})int updateWithVersion(UserInfo userInfo);@Insert({"<script>","INSERT INTO user_info_test","( user_name,","name ,","mobile,","passwd,","version",") "," values ","( #{userName},","#{name},","#{mobile},","#{passwd},","#{version}"," ) ","</script>"})int save(UserInfo entity);
}

4.2 Service层

service层我们做一下简单的调整。更新数据库前，先调用findByUserName方法，查询出当前的版本号，然后再更新。

UserInfoService ：

package com.cff.springbootwork.mybatislock.service;import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import org.springframework.util.StringUtils;import cn.pomit.springwork.mybatislock.domain.UserInfo;
import cn.pomit.springwork.mybatislock.mapper.UserInfoDao;@Service
public class UserInfoService {@AutowiredUserInfoDao userInfoDao;public UserInfo getUserInfoByUserName(String userName){return userInfoDao.findByUserName(userName);}public void save(UserInfo entity) {entity.setVersion(0);userInfoDao.save(entity);}@Transactionalpublic void updateWithTimeOptimistic(UserInfo entity, int time) throws Exception {      UserInfo userInfo = userInfoDao.findByUserName(entity.getUserName());if (userInfo == null)return;if (!StringUtils.isEmpty(entity.getMobile())) {userInfo.setMobile(entity.getMobile());}if (!StringUtils.isEmpty(entity.getName())) {userInfo.setName(entity.getName());}Thread.sleep(time * 1000L);int ret = userInfoDao.updateWithVersion(userInfo);if(ret < 1)throw new Exception("乐观锁导致保存失败");}@Transactionalpublic void updateOptimistic(UserInfo entity) throws Exception {UserInfo userInfo = userInfoDao.findByUserName(entity.getUserName());if (userInfo == null)return;if (!StringUtils.isEmpty(entity.getMobile())) {userInfo.setMobile(entity.getMobile());}if (!StringUtils.isEmpty(entity.getName())) {userInfo.setName(entity.getName());}int ret = userInfoDao.updateWithVersion(userInfo);if(ret < 1)throw new Exception("乐观锁导致保存失败");}}

4.2 测试Web层

可以先调用/update/{time}接口，延迟执行，然后马上调用/update接口，会发现，/update接口不会等待/update/{time}接口执行完成，读取完版本号能够成功更新数据，但是/update/{time}接口等待足够时间以后，更新的时候会失败，因为它的版本和数据库的已经不一致了。

注意： 这里更新失败不会抛异常，但是返回值会是0，即更新不成功，需要自行判断。jpa的乐观锁可以抛出异常，手动catch到再自行处理。

MybatisOptiLockRest ：

package com.cff.springbootwork.mybatislock.web;import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;import cn.pomit.springwork.mybatislock.domain.UserInfo;
import cn.pomit.springwork.mybatislock.service.UserInfoService;/*** 测试乐观锁* @author fufei**/
@RestController
@RequestMapping("/mybatislock")
public class MybatisOptiLockRest {@AutowiredUserInfoService userInfoService;@RequestMapping(value = "/detail/{name}", method = { RequestMethod.GET })public UserInfo detail(@PathVariable("name") String name) {return userInfoService.getUserInfoByUserName(name);}@RequestMapping(value = "/save")public String save(@RequestBody UserInfo userInfo) throws InterruptedException {userInfoService.save(userInfo);return "0000";}@RequestMapping(value = "/update/{time}")public String update(@RequestBody UserInfo userInfo, @PathVariable("time") int time) throws Exception {userInfoService.updateWithTimeOptimistic(userInfo, time);return "0000";}@RequestMapping(value = "/update")public String update(@RequestBody UserInfo userInfo) throws Exception {userInfoService.updateOptimistic(userInfo);return "0000";}
}