并发自定义主键生成策略
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本人邮箱: kco1989@qq.com
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github: https://github.com/kco1989/kco
代码已经全部托管[github]((https://github.com/kco1989/kco/tree/master/primaryKeyBuild)有需要的同学自行下载
前言
在项目开发中,我遇到一个需求.就是要生成自定义的主键.
主键的格式为:前缀 + 当天日期 + 自增长序列号
自增长序列号: 这个序列号是每天从0或1开始自增长的
在了解完需要之后,我做了简单的分析之后就马上进入编码模式,这里我使用的是mysql数据,全部代码已经上传到github,有需要的同学自行下载
目录结构(项目管理工具用的maven)
- src
- main
- java
- com.kco.bean.SequenceNumberBean
- com.kco.dao.SequenceNumberDao
- com.kco.Enum.SequenceNumberEnum
- com.kco.service.SequenceNumberService
- com.kco.service.SequenceNumberServiceImpl
- resources
- META-INF/mybatis/mapper/SequenceNumberDao.xml
- META-INF/mybatis/sql-map-config.xml
- META-INF/spring/spring-base-jdbc.xml
- log4j.properties
- java
- test
- java
- com.kco.TestSequenceNumberService
- java
- main
- pom.xml
编码
1, 首先创建一个maven工程,配置一下jar依赖 pom.xml
<?xml version="1.0" encoding="UTF-8"?><project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.kco</groupId> <artifactId>mytestcode</artifactId> <version>1.0-SNAPSHOT</version> <dependencies> <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-lang3</artifactId> <version>3.3.2</version> </dependency> <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-io</artifactId> <version>1.3.2</version> </dependency> <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-collections4</artifactId> <version>4.1</version> </dependency> <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-dbcp2</artifactId> <version>2.0.1</version> </dependency> <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-pool2</artifactId> <version>2.3</version> </dependency> <!-- test --> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.10</version> <scope>test</scope> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-test</artifactId> <scope>test</scope> <version>4.2.3.RELEASE</version> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.12</version> <scope>runtime</scope> </dependency> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.2.7</version> </dependency> <!-- spring --> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-context</artifactId> <version>4.2.3.RELEASE</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-context-support</artifactId> <version>4.2.3.RELEASE</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-tx</artifactId> <version>4.2.3.RELEASE</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-jdbc</artifactId> <version>4.2.3.RELEASE</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-beans</artifactId> <version>4.2.3.RELEASE</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-aop</artifactId> <version>4.2.3.RELEASE</version> </dependency> <!-- aop --> <dependency> <groupId>org.aspectj</groupId> <artifactId>aspectjrt</artifactId> <version>1.8.8</version> </dependency> <dependency> <groupId>org.aspectj</groupId> <artifactId>aspectjtools</artifactId> <version>1.8.8</version> </dependency> <dependency> <groupId>org.aspectj</groupId> <artifactId>aspectjweaver</artifactId> <version>1.8.8</version> </dependency> <!--spring mybatis 整合--> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis-spring</artifactId> <version>1.2.2</version> </dependency> <dependency> <groupId>log4j</groupId> <artifactId>log4j</artifactId> <version>1.2.17</version> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-log4j12</artifactId> <version>1.7.13</version> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-api</artifactId> <version>1.7.13</version> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>jcl-over-slf4j</artifactId> <scope>runtime</scope> <version>1.7.13</version> </dependency> </dependencies> <build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <version>3.5.1</version> <configuration> <source>1.8</source> <target>1.8</target> <encoding>UTF-8</encoding> </configuration> </plugin> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-resources-plugin</artifactId> <version>2.6</version> <configuration> <nonFilteredFileExtensions> <nonFilteredFileExtension>tbl</nonFilteredFileExtension> </nonFilteredFileExtensions> </configuration> </plugin> </plugins> </build></project>2., 初始化数据库
CREATE TABLE PUB_SEQUENCE_NUMBER( prefix VARCHAR(10) NOT NULL PRIMARY KEY COMMENT '前缀(主键)', NAME VARCHAR(30) NOT NULL COMMENT '描述', toda y char(8) NOT NULL COMMENT '当天日期', minNum INTEGER NOT NULL DEFAULT 0 COMMENT '序列号最小号码', currentNum INTEGER NOT NULL DEFAULT 0 COMMENT '当前序列号', numLength INTEGER NOT NULL DEFAULT 8 COMMENT '序列号长度');3, 整合spring和mybatis,创建线程池和事务切面等 spring-base-jdbc.xml
<?xml version="1.0" encoding="UTF-8"?><beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xmlns:tx="http://www.springframework.org/schema/tx" xmlns:aop="http://www.springframework.org/schema/aop" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd"> <context:annotation-config/> <context:component-scan base-package="com.kco" /> <!-- 配置config的数据库 --> <bean id="dataSource" class="org.apache.commons.dbcp2.BasicDataSource"> <property name="driverClassName" value="com.mysql.jdbc.Driver"/> <property name="url" value="jdbc:mysql:///test?useUnicode=yes&characterEncoding=utf8&allowMultiQueries=true"/> <property name="username" value="root"/> <property name="password" value="123456"/> <property name="minIdle" value="10"/> <property name="maxIdle" value="10"/> <property name="maxWaitMillis" value="-1"/> <property name="maxTotal" value="10"/> </bean> <!-- spring和MyBatis完美整合--> <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean" > <property name="dataSource" ref="dataSource" /> <property name="configLocation" value="classpath:META-INF/mybatis/sql-map-config.xml" /> <property name="mapperLocations" value="classpath*:META-INF/mybatis/mapper/*Dao.xml" /> </bean> <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer" id="mapperScannerConfigurer"> <property name="annotationClass" value="org.springframework.stereotype.Repository"/> <property name="basePackage" value="com.kco.dao"/> </bean> <bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager"> <property name="dataSource" ref="dataSource" /> </bean> <tx:advice id="txAdvice"> <tx:attributes> <tx:method name="*" propagation="REQUIRED" rollback-for="java.lang.Throwable"/> </tx:attributes> </tx:advice> <aop:config> <aop:advisor advice-ref="txAdvice" pointcut="execution(* *..*ServiceImpl*.*(..))"/> </aop:config></beans>4, 配置mybatis sql-map-config.xml
<?xml version="1.0" encoding="UTF-8" ?><configuration><properties> <property name="dialect" value="mysql"/> <property name="pageSqlId" value=".*Page$"/></properties><settings> <setting name="cacheEnabled" value="false"/> <setting name="lazyLoadingEnabled" value="false"/></settings></configuration>5, 因为要生成自定义主键一般在开发阶段就已经能确定,所以我这里使用了一个枚举类来管理所有的自定义主键 com.kco.Enum.SequenceNumberEnum
package com.kco.Enum;import com.kco.bean.SequenceNumberBean;/** * com.kco.Enum * Created by swlv on 2016/10/25. */public enum SequenceNumberEnum { GD(new SequenceNumberBean("GD","工单主键生成策略", 1, 1, 8)); private SequenceNumberBean sequenceNumberBean; SequenceNumberEnum(SequenceNumberBean sequenceNumberBean){ this.sequenceNumberBean = sequenceNumberBean; } public SequenceNumberBean getSequenceNumberBean() { return sequenceNumberBean; }}6, 数据库PUB_SEQUENCE_NUMBER对应的bean类 com.kco.bean.SequenceNumberBean
package com.kco.bean;/** * 主键生成策略的bean * com.kco.bean * Created by swlv on 2016/10/25. */public class SequenceNumberBean { private String prefix; private String name; private String today; private int minNum; private int currentNum; private int numLength; public String getPrefix() { return prefix; } public void setPrefix(String prefix) { this.prefix = prefix; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getToday() { return today; } public void setToday(String today) { this.today = today; } public int getMinNum() { return minNum; } public void setMinNum(int minNum) { this.minNum = minNum; } public int getCurrentNum() { return currentNum; } public void setCurrentNum(int currentNum) { this.currentNum = currentNum; } public int getNumLength() { return numLength; } public void setNumLength(int numLength) { this.numLength = numLength; } public SequenceNumberBean() { } public SequenceNumberBean(String prefix, String name, int minNum, int currentNum, int numLength) { this.prefix = prefix; this.name = name; this.minNum = minNum; this.currentNum = currentNum; this.numLength = numLength; } @Override public String toString() { return "SequenceNumberBean{" + "prefix='" + prefix + '\'' + ", name='" + name + '\'' + ", today='" + today + '\'' + ", minNum=" + minNum + ", currentNum=" + currentNum + ", numLength=" + numLength + '}'; }}7, 服务层的接口类以及实现 com.kco.service.SequenceNumberService
package com.kco.service;import com.kco.Enum.SequenceNumberEnum;/** * com.kco.service * Created by swlv on 2016/10/25. */public interface SequenceNumberService { /** * 生成一个主键 * @param sequenceNumberEnum 主键生成类型 * @return 返回一个生成的主键 */ String newSequenceNumber(SequenceNumberEnum sequenceNumberEnum);}com.kco.service.SequenceNumberServiceImpl
package com.kco.service;import com.kco.Enum.SequenceNumberEnum;import com.kco.bean.SequenceNumberBean;import com.kco.dao.SequenceNumberDao;import org.springframework.stereotype.Service;import javax.annotation.Resource;/** * com.kco.service * Created by swlv on 2016/10/25. */@Servicepublic class SequenceNumberServiceImpl implements SequenceNumberService{ @Resource private SequenceNumberDao sequenceNumberDao; @Override public synchronized String newSequenceNumber(SequenceNumberEnum sequenceNumberEnum) { if (sequenceNumberEnum == null){ return null; } try { SequenceNumberBean sequenceNumberBean = sequenceNumberDao.newSequenceNumber(sequenceNumberEnum.getSequenceNumberBean().getPrefix()); Thread.sleep(100); if (sequenceNumberBean == null){ sequenceNumberBean = sequenceNumberEnum.getSequenceNumberBean(); sequenceNumberBean.setToday(sequenceNumberDao.getToday()); } Thread.sleep(100); sequenceNumberDao.updateSequenceNumber(sequenceNumberBean); Thread.sleep(100); return String.format("%s%6s%08d", sequenceNumberBean.getPrefix(), sequenceNumberBean.getToday(), sequenceNumberBean.getCurrentNum()); } catch (InterruptedException e) { e.printStackTrace(); return ""; } }}8, 数据库dao层接口 com.kco.dao.SequenceNumberDao
package com.kco.dao;import com.kco.bean.SequenceNumberBean;import org.apache.ibatis.annotations.Param;import org.springframework.stereotype.Repository;/** * com.kco.dao * Created by swlv on 2016/10/25. */@Repositorypublic interface SequenceNumberDao { /** * 根据前缀生成一个序列号信息 * @param prefix 前缀 * @return 新的序列号信息 */ SequenceNumberBean newSequenceNumber(@Param("prefix") String prefix); /** * 将生成的序列号信息更新到数据库中 * @param sequenceNumberBean 需要更新信息 */ void updateSequenceNumber(@Param("bean") SequenceNumberBean sequenceNumberBean); /** * 获取数据库当天日期 * @return */ String getToday();}9., dao层mybatis的实现 SequenceNumberDao.xml
<?xml version="1.0" encoding="UTF-8"?><mapper namespace="com.kco.dao.SequenceNumberDao"> <resultMap id="sequenceNumberResultMap" type="com.kco.bean.SequenceNumberBean"> <id property="prefix" column="prefix"/> <result property="name" column="name"/> <result property="today" column="today"/> <result property="minNum" column="minNum"/> <result property="currentNum" column="currentNum"/> <result property="numLength" column="numLength"/> </resultMap> <select id="newSequenceNumber" resultMap="sequenceNumberResultMap"> SELECT prefix,name,today,minNum,currentNum + 1 as currentNum,numLength FROM PUB_SEQUENCE_NUMBER WHERE prefix = #{prefix} AND today = DATE_FORMAT(CURRENT_DATE(),'%Y%m%d') </select> <update id="updateSequenceNumber" parameterType="com.kco.bean.SequenceNumberBean"> REPLACE INTO PUB_SEQUENCE_NUMBER(prefix,name,today,minNum,currentNum,numLength) VALUES(#{bean.prefix}, #{bean.name}, DATE_FORMAT(CURRENT_DATE(),'%Y%m%d'), #{bean.minNum}, #{bean.currentNum},#{bean.numLength}) </update> <select id="getToday" resultType="string"> SELECT DATE_FORMAT(CURRENT_DATE(),'%Y%m%d') </select></mapper>10, 编写测试代码(模拟并发测试) com.kco.TestSequenceNumberService
package com.kco;import com.kco.Enum.SequenceNumberEnum;import com.kco.service.SequenceNumberService;import org.apache.commons.collections4.CollectionUtils;import org.springframework.context.ApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;import java.util.ArrayList;import java.util.Collections;import java.util.List;import java.util.Queue;import java.util.concurrent.ArrayBlockingQueue;/** * com.cmbchina.base.service * Created by swlv on 2016/10/25. */public class TestSequenceNumberService { public static void main(String[] args) throws InterruptedException { ApplicationContext applicationContext = new ClassPathXmlApplicationContext("META-INF/spring/spring-base-jdbc.xml"); SequenceNumberService sequenceNumberService = applicationContext.getBean(SequenceNumberService.class); Queue<String> queue = new ArrayBlockingQueue<String>(200); List<Thread> list = new ArrayList<>(); for (int i = 0;i < 200; i ++){ list.add(new Thread(()->{ String key = sequenceNumberService.newSequenceNumber(SequenceNumberEnum.GD); queue.add(key); })); } for (Thread thread : list){ thread.start(); } while (queue.size() != 200); System.out.println(queue); }}11, 至此整个项目就已经搭建完成
细节解析
在
com.kco.service.SequenceNumberServiceImpl#newSequenceNumber的实现中在更新当天日期字符串时,使用的是sequenceNumberBean.setToday(sequenceNumberDao.getToday());这是因为服务器的时间跟数据库的时间有可能不一致,这里以数据库的时间为准
测试
1, 查询数据库的数据 SELECT count(1) FROM PUB_SEQUENCE_NUMBER
结果:
2, 清空数据后,再运行com.kco.TestSequenceNumberService#main
3, 然后查一下数据库 SELECT * FROM PUB_SEQUENCE_NUMBER
问题出现了,明明我是启动了200个线程在跑,怎么才生成176个主键,检查代码也没有问题啊,
newSequenceNumber也加了关键字synchronized.先把这个问题放一下,来回忆一下
synchronized的用法,
synchronized是在线程池在访问共同变量时使其加锁,达到互斥的效果
共同变量?共同变量?咦,好像有什么不对劲的地方.newSequenceNumber使用的都是局部变量,没有共同变量啊!不对?是有共同变量,那个共同变量就是数据库的记录
除此之外使用synchronized还有一个问题,这个项目是web项目的一部分,一般在部署web项目都是有几个单边,即在不同的PC部署几个一模一样的代码,再通过集群访问的方式随机访问其中一台.那么这几个应用其实就是多进程程序,都不再一个JVM中执行,加synchronized来保证互斥,是不够的.
4, 既然知道是数据库同步出现了问题,那么怎么保证数据库同步呢?
上网搜索一下,发现数据库有悲观锁和乐观锁
解决方法就是在Dao层的实现
<select id="newSequenceNumber" resultMap="sequenceNumberResultMap"> SELECT prefix,name,today,minNum,currentNum + 1 as currentNum,numLength FROM PUB_SEQUENCE_NUMBER WHERE prefix = #{prefix} AND today = DATE_FORMAT(CURRENT_DATE(),'%Y%m%d') </select>改为
<select id="newSequenceNumber" resultMap="sequenceNumberResultMap"> SELECT prefix,name,today,minNum,currentNum + 1 as currentNum,numLength FROM PUB_SEQUENCE_NUMBER WHERE prefix = #{prefix} AND today = DATE_FORMAT(CURRENT_DATE(),'%Y%m%d') for UPDATE </select>5, 然后再重新查一下数据库 SELECT * FROM PUB_SEQUENCE_NUMBER
发现问题解决了,这里是用到了数据库锁表的机制来实现同步.
以后有机会再学一下数据库同步,
悲观锁和乐观锁.因为这个我还不太熟悉,这里就不卖弄了.
6., 修改一下 com.kco.Enum.SequenceNumberEnum 再增加一个自定义主键GDD(new SequenceNumberBean("GDD","工单主键生成策略", 1, 1, 8))
7., 清空数据,然后运行com.kco.TestSequenceNumberService#main
8, 修改com.kco.TestSequenceNumberService2#main
将String key = sequenceNumberService.newSequenceNumber(SequenceNumberEnum.GD);改为String key = sequenceNumberService.newSequenceNumber(SequenceNumberEnum.GDD);再次运行com.kco.TestSequenceNumberService#main, 这是用来模拟两个程序同时访问数据的情况
9, 查询数据 SELECT * FROM PUB_SEQUENCE_NUMBER
数据正常
10., 清空数据,连续运行两次com.kco.TestSequenceNumberService2#main模拟多进程对生成同一个自定义主键
11, 查询结果 SELECT * FROM PUB_SEQUENCE_NUMBER
至此, 全部搞定
遗留问题
- 数据库
悲观锁和乐观锁具体是怎么样的.有什么区别? for update锁表对性能有没有什么影响,除了性能,还有其他隐藏的隐患?
这几个问题就留给读者(还有我自己)自行查资料研究了
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