文章目录
一、前言
二、synchronized关键字
数据准备
环境搭建
依赖
yml配置
启动类
mapper
实体类
controller类
service接口
serviceimpl实现接口
不加synchronized测试
加上关键字synchronized测试
扣减库存
三、ReentrantLock锁
四 总结
一、前言
本篇讲解单体应用中实现扣减库存，分别使用synchronized和ReentrantLock实现锁，不会出现扣除超卖的现象。
二、synchronized关键字
数据准备
库存表
-- test.stock definition
CREATE TABLE `stock` (
`stock_id` int NOT NULL AUTO_INCREMENT COMMENT '库存主键',
`product_id` int NOT NULL COMMENT '商品ID',
`stock_num` int DEFAULT NULL COMMENT '库存数量',
`create_time` datetime DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间',
`create_by` varchar(100) DEFAULT NULL COMMENT '创建人',
`update_time` datetime DEFAULT CURRENT_TIMESTAMP COMMENT '更新时间',
`update_by` varchar(100) DEFAULT NULL COMMENT '更新人',
PRIMARY KEY (`stock_id`),
KEY `stock_product_id_IDX` (`product_id`) USING BTREE,
CONSTRAINT `stock_FK` FOREIGN KEY (`product_id`) REFERENCES `product` (`product_id`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci COMMENT='库存表';
数据
INSERT INTO test.stock
(stock_id, product_id, stock_num, create_time, create_by, update_time, update_by)
VALUES(6, 6, 5000, '2022-09-06 15:19:18', 'elite', '2022-09-06 15:19:18', 'elite');
环境搭建
依赖
<dependencies>
<!--web-->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<!--mybtais-plus-->
<dependency>
<groupId>com.baomidou</groupId>
<artifactId>mybatis-plus-boot-starter</artifactId>
<version>3.4.1</version>
</dependency>
<dependency>
<groupId>commons-lang</groupId>
<artifactId>commons-lang</artifactId>
<version>2.6</version>
</dependency>
<!--druid数据源-->
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>druid</artifactId>
<version>1.2.8</version>
</dependency>
<dependency>
<groupId>cn.hutool</groupId>
<artifactId>hutool-all</artifactId>
<version>5.1.4</version>
</dependency>
<!--fastjson-->
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>fastjson</artifactId>
<version>1.2.76</version>
</dependency>
<!--mysql连接包-->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.27</version>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.11</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
</dependency>
</dependencies>
yml配置
server:
port: 8899
##配置应用的名字
spring:
application:
name: CurrentcyLockApplication
profiles:
active: dev
##配置数据库
datasource:
##mysql配置
type: com.alibaba.druid.pool.DruidDataSource
url: jdbc:mysql://ip:3306/test
driver-class-name: com.mysql.jdbc.Driver
username: root
password: 123456
启动类
@SpringBootApplication
public class CurrentcyLockApplication
{
public static void main( String[] args )
{
SpringApplication.run(CurrentcyLockApplication.class,args);
}
}
mapper
/**
* 库存映射类
*/
@Mapper
public interface StockMapper extends BaseMapper<Stock> {
@Select("SELECT stock_id, product_id, stock_num, create_time, create_by, update_time, update_by\n" +
"FROM test.stock where product_id = #{productId}")
Stock getStockByProductId(Integer productId);
}
实体类
@Data
@EqualsAndHashCode(callSuper = false)
@TableName("`stock`")
public class Stock {
/**
* 用户ID
*/
@TableId(value = "stock_id", type = IdType.AUTO)
private Integer stockId;
/**
* 商品ID
*/
@TableField(value = "product_id")
private Integer productId;
/**
* 库存数量
*/
@TableField(value = "stock_num")
private Integer stockNum;
//创建人
@TableField(value = "create_by")
private String createBy;
//创建时间
@JsonFormat(timezone = "GMT+8", pattern = "yyyy-MM-dd HH:mm:ss")
@DateTimeFormat(pattern = "yyyy-MM-dd HH:mm:ss")
@TableField(value = "create_time",fill = FieldFill.INSERT)
private String createTime;
//更新人
@TableField(value = "update_by")
private String updateBy;
//更新时间
@JsonFormat(timezone = "GMT+8", pattern = "yyyy-MM-dd HH:mm:ss")
@DateTimeFormat(pattern = "yyyy-MM-dd HH:mm:ss")
@TableField(value = "update_time",fill = FieldFill.INSERT_UPDATE)
private String updateTime;
}
controller类
@RestController
@RequestMapping("/stock")
public class StockController {
@Autowired
IStockService stockService;
/**
* 扣减库存
* @return
*/
@GetMapping("/deductStock/{productId}")
public String deductStock(@PathVariable("productId") Integer productId){
return stockService.deductStock(productId);
}
}
service接口
/**
* 库存处理的逻辑
*/
public interface IStockService extends IService<Stock> {
String deductStock(Integer productId);
}
serviceimpl实现接口
@Service
@Slf4j
public class IStockServiceImpl extends ServiceImpl<StockMapper, Stock> implements IStockService {
@Autowired
StockMapper stockMapper;
/**
* 扣减库存
* @return
*/
@Override
public String deductStock(Integer productId) {
log.info("扣减库存开始......");
Stock stock = stockMapper.getStockByProductId(productId);
log.info("当前库存量:" + stock.getStockNum());
//扣减库存
if (stock.getStockNum() > 0) {
//默认扣减1
stock.setStockNum(stock.getStockNum() - 1);
stockMapper.updateById(stock);
} else {
log.info("扣减库存失败,无库存可用......");
return "扣减库存失败";
}
return "ok";
}
}
不加synchronized测试
库存5000，使用jemeter发送100个线程循环50次进行扣减库存。
此时库存4863,出现了超卖的情况。
加上关键字synchronized测试
方法上加上关键字synchronized
public synchronized String deductStock(Integer productId)
synchronized 了独占的排他锁，只能一个一个线程进行执行。
三、ReentrantLock锁
private final ReentrantLock lock = new ReentrantLock();
/**
* 扣减库存
* @return
*/
@Override
public /*synchronized*/ String deductStock(Integer productId) {
log.info("扣减库存开始......");
//幂等性
//尝试获取锁：
// 成功获取则立即返回true，获取失败则立即返回false。不必一直等待锁的释放
if (lock.tryLock()) {
try {
//处理重复通知
//接口调用的幂等性：无论接口被调用多少次，以下业务执行一次
//获取库存数量
Stock stock = stockMapper.getStockByProductId(productId);
log.info("当前库存量:" + stock.getStockNum());
//扣减库存
if (stock.getStockNum() > 0) {
//默认扣减1
stock.setStockNum(stock.getStockNum() - 1);
stockMapper.updateById(stock);
} else {
log.info("扣减库存失败,无库存可用......");
return "扣减库存失败";
}
}finally {
lock.unlock();
}
}
return "ok";
ReentrantLock是可重入锁，请不到锁的情况下返回false,不必一直等待。
四 总结
本篇讲解都是JDk自身提供的工具来实现锁，对于分布式部署的服务并不适用。分布式服务需要用分布式锁来实现，如数据库来实现，或者redis来实现分布式锁。
