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背景

对于一些内部使用的管理系统来说，可能没有引入Redis，又想基于现有的基础设施处理并发问题，而数据库是每个应用都避不开的基础设施之一，因此分享个我曾经维护过的一个系统中，使用数据库表来实现事务锁的方式。

之前在文章Java业务功能并发问题处理中实现了使用MySQL行锁、Redis分布式锁来处理业务并发问题，这次来填坑了，如果想了解其他并发问题处理方式和区别，可以看看文章Java业务功能并发问题处理哈。

业务流程说明

方案分析

适用场景

1. 应用服务有多个实例，但是数据库是单实例；
2. 没有用上Redis的应用服务，想通过现有的基础设施解决并发数据问题

待改进措施

1. 设置超时机制：当出现锁无法及时释放时需要手动删除表数据，可以设置逻辑删除字段或者定时器删除过期数据；
2. 重试获取锁机制：设置一定的循环次数，当获取不到锁时休眠200毫秒再次获取，直到循环次数用尽后再返回失败；
3. 锁重入支持：通过增加加锁次数字段让当同一个线程可以重复获取锁

程序实现过程

框架及工具说明

• 技术框架：SpringBoot、MyBatis、Maven
• 数据库：MySQL
• 测试工具：Apifox
• 表设计及代码说明：
  1. 唯一索引：需要有一个用于判断唯一的字段，在数据库表中通过指定唯一索引来实现；
  2. 加锁的线程号：避免A线程加的锁，被B线程删除；
  3. 锁的可见性要单独事务：添加事务锁的逻辑应在我们执行业务逻辑的事务之前，且不能跟业务逻辑的事务在一块，否则在事务提交前其他线程根本看不到这个锁，也就达不到我们锁的目的了；
  4. 为了我们的锁更方便使用，也可以将加锁逻辑抽到注解中实现，注解的实现流程：
     • 在pom文件中引入spring-boot-starter-aop
     • 编写自定义注解ConcurrencyLock
     • 实现切面类（Aspect）逻辑

代码展示

为了能让大家更关注加解锁逻辑，本文只保留主要代码，参考链接处会放置码云（gitee）的源码地址(或者点击此处跳转)；
另外，本文就不展示注解方式的使用了，以免占用篇幅。

代码结构图

实体类

/*** 并发锁实体类*/
public class ConcurrencyLockBean {/*** 数据库主键*/private Long id;/*** 操作节点*/private String businessNode;/*** 订单唯一编号*/private String businessUniqueNo;/*** 线程ID*/private Long threadId;/*** 创建日期*/private Date creationDate;
}/*** 订单实体类*/
@Setter
@Getter
@ToString
public class OrderInfoBean {/*** 自增长主键*/private int id;/*** 订单号*/private String orderNo;/*** 物料数量*/private Integer itemQty;
}

ConcurrencyLockServiceImpl.java

@Slf4j
@Service
public class ConcurrencyLockServiceImpl implements ConcurrencyLockService {ConcurrencyLockMapper mapper;/*** service类注入*/@AutowiredConcurrencyLockServiceImpl(ConcurrencyLockMapper mapper) {this.mapper = mapper;}@Overridepublic Boolean tryLock(String businessNode, String businessUniqueNo) {long threadId = Thread.currentThread().getId();ConcurrencyLockBean concurrencyLock = mapper.selectConcurrencyLock(businessNode, businessUniqueNo);if (concurrencyLock != null) {log.info("{}数据正在操作中，请稍后", threadId);return false;}ConcurrencyLockBean lock = new ConcurrencyLockBean();lock.setBusinessNode(businessNode);lock.setBusinessUniqueNo(businessUniqueNo);lock.setThreadId(threadId);try {int insertCount = mapper.insertConcurrencyLock(lock);if (insertCount == 0) {log.info("{}获取锁失败，请稍后重试", threadId);return false;}} catch (Exception e) {log.info("{}获取锁异常，请稍后重试", threadId);return false;}log.info("{}完成锁表插入", threadId);return true;}@Overridepublic void unLock(String businessNode, String businessUniqueNo) {ConcurrencyLockBean lock = new ConcurrencyLockBean();long threadId = Thread.currentThread().getId();lock.setThreadId(threadId);lock.setBusinessNode(businessNode);lock.setBusinessUniqueNo(businessUniqueNo);mapper.deleteConcurrencyLock(lock);log.info("{}执行解锁完毕", threadId);}
}

ConcurrencyLockMapper.java

import org.apache.ibatis.annotations.Param;public interface ConcurrencyLockMapper {/*** 根据业务节点和唯一业务号查询锁*/ConcurrencyLockBean selectConcurrencyLock(@Param("businessNode") String businessNode, @Param("businessUniqueNo") String businessUniqueNo);/*** 插入锁*/int insertConcurrencyLock(ConcurrencyLockBean lock);/*** 删除锁*/int deleteConcurrencyLock(ConcurrencyLockBean lock);
}

ConcurrencyLockMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.runningrookie.mapper.ConcurrencyLockMapper"><select id="selectConcurrencyLock" resultType="com.runningrookie.domain.ConcurrencyLockBean">SELECTTHREAD_ID,BUSINESS_NODE,BUSINESS_UNIQUE_NO,CREATION_DATEFROM concurrency_lockWHERE BUSINESS_UNIQUE_NO = #{businessUniqueNo}AND BUSINESS_NODE = #{businessNode}</select><insert id="insertConcurrencyLock" useGeneratedKeys="true" keyProperty="id">INSERT INTO concurrency_lock (THREAD_ID,BUSINESS_NODE,BUSINESS_UNIQUE_NO,CREATION_DATE)VALUES(#{threadId}, #{businessNode}, #{businessUniqueNo}, NOW());</insert><delete id="deleteConcurrencyLock">DELETE FROM concurrency_lockWHERE THREAD_ID = #{threadId}and BUSINESS_NODE = #{businessNode}and BUSINESS_UNIQUE_NO = #{businessUniqueNo}</delete>
</mapper>

ConcurrencyLock.java注解

@Target({ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface ConcurrencyLock {String businessNode();String businessUniqueNoKey();
}

ConcurrencyLockAspect.java注解类

@Aspect
@Component
@Slf4j
public class ConcurrencyLockAspect {ConcurrencyLockService concurrencyLockService;@AutowiredConcurrencyLockAspect(ConcurrencyLockService concurrencyLockService) {this.concurrencyLockService = concurrencyLockService;}// 环绕切面@Around("@annotation(concurrencyLock)")public Object around(ProceedingJoinPoint joinPoint, ConcurrencyLock concurrencyLock) throws Throwable {long threadId = Thread.currentThread().getId();Object[] args = joinPoint.getArgs();if (args.length == 0) {return joinPoint.proceed();}// 通过反射获取值String invokeMethodName = "get" + concurrencyLock.businessUniqueNoKey().substring(0, 1).toUpperCase() + concurrencyLock.businessUniqueNoKey().substring(1);// 获取Order类的Class对象Class<?> clazz = args[0].getClass();// 获取getOrderNo方法的Method对象Method method = clazz.getMethod(invokeMethodName);// 调用getOrderNo方法并获取返回值String businessUniqueNo = method.invoke(args[0]).toString();Boolean isSuccessLock = concurrencyLockService.tryLock(concurrencyLock.businessNode(), businessUniqueNo);if (!isSuccessLock) {log.info("{}加锁失败，请稍后重试", threadId);// 生成与切点方法相同的返回对象return AjaxResult.error("加锁失败，请稍后重试");}try {log.info("{}开始执行业务逻辑", threadId);joinPoint.proceed();} finally {concurrencyLockService.unLock(concurrencyLock.businessNode(), businessUniqueNo);}return joinPoint.proceed();}
}

OrderInfoController.java

@RestController
@RequestMapping("/orderInfo")
public class OrderInfoController {OrderInfoService orderInfoService;@Autowiredprivate OrderInfoController(OrderInfoService orderInfoService) {this.orderInfoService = orderInfoService;}@PostMappingpublic AjaxResult saveOrderInfo(@RequestBody OrderInfoBean bean) {return orderInfoService.saveOrderInfo(bean);}
}

OrderServiceImpl.java

/*** 订单逻辑代码*/
@Slf4j
@Service
public class OrderInfoServiceImpl implements OrderInfoService {ConcurrencyLockService concurrencyLockService;/*** service类注入*/@AutowiredOrderInfoServiceImpl(ConcurrencyLockService concurrencyLockService) {this.concurrencyLockService = concurrencyLockService;}@Overridepublic AjaxResult saveOrderInfo(OrderInfoBean bean) {long threadId = Thread.currentThread().getId();final String businessNode = "插入";Boolean isSuccessLock = concurrencyLockService.tryLock(businessNode, bean.getOrderNo());if (!isSuccessLock) {return AjaxResult.error("加锁失败，请稍后重试");}try {log.info("{}开始执行业务逻辑", threadId);// TODO:模拟业务逻辑耗时Thread.sleep(1500);} catch (InterruptedException e) {throw new RuntimeException(e);} finally {concurrencyLockService.unLock(businessNode, bean.getOrderNo());}return AjaxResult.success();}@Override@ConcurrencyLock(businessNode = "插入", businessUniqueNoKey = "orderNo")@Transactionalpublic AjaxResult saveOrderInfoByAnnotation(OrderInfoBean bean) {// TODO:模拟业务逻辑耗时Thread.sleep(1500);return AjaxResult.success();}
}

pom.xml相关依赖

在dependencies中添加下列依赖

<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-aop</artifactId>
</dependency>
<dependency><groupId>org.mybatis.spring.boot</groupId><artifactId>mybatis-spring-boot-starter</artifactId><version>2.1.4</version>
</dependency>
<!-- Mysql驱动包 -->
<dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId>
</dependency>

事务处理表的表结构

CREATE TABLE `concurrency_lock` (`ID` int NOT NULL AUTO_INCREMENT COMMENT '主键',`THREAD_ID` int DEFAULT NULL COMMENT '线程号',`BUSINESS_NODE` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci DEFAULT NULL COMMENT '操作节点',`BUSINESS_UNIQUE_NO` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci DEFAULT NULL COMMENT '单据号',`CREATION_DATE` datetime DEFAULT NULL COMMENT '创建时间',PRIMARY KEY (`ID`),UNIQUE KEY `uni_business_no` (`BUSINESS_UNIQUE_NO`,`BUSINESS_NODE`) USING BTREE
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci;

测试输出结果

使用Apifox并发发送5次请求，可以看到实际成功获取到锁并执行的只有一个线程

17:08:00.449 [http-nio-8080-exec-1] c.r.service.impl.ConcurrencyLockServiceImpl - 40完成锁表插入
17:08:00.462 [http-nio-8080-exec-1] c.runningrookie.service.impl.OrderInfoServiceImpl - 40开始执行业务逻辑
17:08:00.573 [http-nio-8080-exec-5] c.r.service.impl.ConcurrencyLockServiceImpl - 44获取锁异常，请稍后重试
17:08:00.573 [http-nio-8080-exec-4] c.r.service.impl.ConcurrencyLockServiceImpl - 43获取锁异常，请稍后重试
17:08:00.573 [http-nio-8080-exec-3] c.r.service.impl.ConcurrencyLockServiceImpl - 42获取锁异常，请稍后重试
17:08:00.573 [http-nio-8080-exec-2] c.r.service.impl.ConcurrencyLockServiceImpl - 41获取锁异常，请稍后重试
17:08:00.574 [http-nio-8080-exec-1] c.r.service.impl.ConcurrencyLockServiceImpl - 40执行解锁完毕

参考链接

gitee代码仓库地址：数据库并发锁