參考：Redis實(shí)現(xiàn)分布式鎖的7種方案 - 知乎

1、 準(zhǔn)備數(shù)據(jù)庫表，如下SQL表示庫存表，有主鍵ID和庫存數(shù)量字段

CREATE TABLE `t_stock` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `quantity` bigint(20) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin;

初始數(shù)據(jù)id? ? ? ? ? ?quantity

? ? ? ? ? ? ? 1111? ? ? ?9

2、pom.xml文件

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.6.4</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.hmblogs</groupId>
    <artifactId>hmblogs</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>hmblogs</name>
    <description>hmblogs</description>
    <properties>
        <java.version>8</java.version>
        <druid.version>1.2.8</druid.version>
        <log4jdbc.version>1.16</log4jdbc.version>
    </properties>
    <dependencies>
        <!-- druid數(shù)據(jù)源驅(qū)動(dòng) -->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid-spring-boot-starter</artifactId>
            <version>${druid.version}</version>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

        <!-- mybatis -->
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.5.3.1</version>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>

        <!--Mysql依賴包-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>

        <!--lombok插件-->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>

        <!--監(jiān)控sql日志-->
        <dependency>
            <groupId>org.bgee.log4jdbc-log4j2</groupId>
            <artifactId>log4jdbc-log4j2-jdbc4.1</artifactId>
            <version>${log4jdbc.version}</version>
        </dependency>

        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.9</version>
        </dependency>

        <dependency>
            <groupId>redis.clients</groupId>
            <artifactId>jedis</artifactId>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

3、應(yīng)用配置文件

server:
  port: 8081
  servlet.context-path: /

#配置數(shù)據(jù)源
spring:
  datasource:
    druid:
      db-type: com.alibaba.druid.pool.DruidDataSource
      driverClassName: net.sf.log4jdbc.sql.jdbcapi.DriverSpy
      url: jdbc:log4jdbc:mysql://${DB_HOST:localhost}:${DB_PORT:3306}/${DB_NAME:eladmin}?serverTimezone=Asia/Shanghai&characterEncoding=utf8&useSSL=false
      username: ${DB_USER:root}
      password: ${DB_PWD:123456}

4、StockMapper.xml如下

<?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.hmblogs.backend.dao.StockMapper">
    <resultMap id="BaseResultMap" type="com.hmblogs.backend.entity.Stock">
        <id column="id" property="id"/>
        <result column="quantity" property="quantity"/>
    </resultMap>

    <sql id="BaseResultMap">
        id, quantity
    </sql>

    <select id="findAll" resultMap="BaseResultMap">
        select
        <include refid="BaseResultMap"/>
        from t_stock

    </select>

    <select id="findById" resultMap="BaseResultMap"  parameterType="com.hmblogs.backend.entity.Stock">
        select
        <include refid="BaseResultMap"/>
        from t_stock
        where id=#{id}
    </select>

    <update id="updateStockById" parameterType="com.hmblogs.backend.entity.Stock">
        update t_stock set quantity=quantity-1 where id=#{id}
    </update>
</mapper>

5、BackendApplication

package com.hmblogs.backend;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class BackendApplication {

    public static void main(String[] args) {
        SpringApplication.run(BackendApplication.class, args);
    }

}

6、Stock.java如下

package com.hmblogs.backend.entity;


import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.Data;

@Data
@TableName("t_stock")
public class Stock {

    @TableId(value="id", type = IdType.AUTO)
    private Integer id;

    private Integer quantity;

}

7、StockMapper

package com.hmblogs.backend.dao;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.hmblogs.backend.entity.Stock;
import org.apache.ibatis.annotations.Mapper;

import java.util.List;

@Mapper
public interface StockMapper extends BaseMapper<Stock> {
    List<Stock> findAll();

    Stock findById(Stock stock);

    Integer updateStockById(Stock stock);
}

8、OrderController

package com.hmblogs.backend.controller;

import com.hmblogs.backend.dao.StockMapper;
import com.hmblogs.backend.entity.Stock;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.util.StringUtils;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import redis.clients.jedis.Jedis;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.TimeUnit;
import java.util.stream.IntStream;

@RestController
@Slf4j
public class OrderController {

    @Autowired
    private StockMapper stockMapper;

    //總庫存
    private long nKuCuen = 0;
    //商品key名字
    private String shangpingKey = "computer_key";
    //獲取鎖的超時(shí)時(shí)間 秒
    private int timeout = 30 * 1000;

    @GetMapping("/qiangdan")
    public List<String> qiangdan() {

        //搶到商品的用戶
        List<String> shopUsers = new ArrayList<>();

        //構(gòu)造很多用戶
        List<String> users = new ArrayList<>();
        IntStream.range(0, 10000).parallel().forEach(b -> {
            users.add("神牛-" + b);
        });

        //初始化庫存
        nKuCuen = 10;

        //模擬開搶
        users.parallelStream().forEach(b -> {
            String shopUser = qiang(b);
            if (!StringUtils.isEmpty(shopUser)) {
                shopUsers.add(shopUser);
            }
        });

        return shopUsers;
    }

    /**
     * 模擬搶單動(dòng)作
     *
     * @param b
     * @return
     */
    private String qiang(String b) {
        //用戶開搶時(shí)間
        long startTime = System.currentTimeMillis();

        //未搶到的情況下，30秒內(nèi)繼續(xù)獲取鎖
        while ((startTime + timeout) >= System.currentTimeMillis()) {
            //商品是否剩余
            if (nKuCuen <= 0) {
                break;
            }
            Jedis jedisCom = new Jedis("localhost",6379);
            jedisCom.auth("heming");
            if (jedisCom.setnx(shangpingKey, b)==1) {
                //用戶b拿到鎖
                log.info("用戶{}拿到鎖...", b);
                try {
                    //商品是否剩余
                    if (nKuCuen <= 0) {
                        break;
                    }

                    //模擬生成訂單耗時(shí)操作，方便查看：神牛-50 多次獲取鎖記錄
                    try {
                        TimeUnit.SECONDS.sleep(1);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }

                    //搶購成功，商品遞減，記錄用戶
                    nKuCuen -= 1;
                    int id = 1111;
                    Stock stock = new Stock();
                    stock.setId(id);
                    Stock stockDo = stockMapper.findById(stock);
                    Integer quantity = stockDo.getQuantity();
                    if(quantity!=null && quantity>0){
                        stockMapper.updateStockById(stock);
                        log.info("update success.");
                    }else{
                        log.info("no update.");
                    }

                    //搶單成功跳出
                    log.info("用戶{}搶單成功跳出...所剩庫存：{}", b, nKuCuen);

                    return b + "搶單成功，所剩庫存：" + nKuCuen;
                } finally {
                    log.info("用戶{}釋放鎖...", b);
                    //釋放鎖
                    jedisCom.del(shangpingKey, b);
                }
            }
        }
        return "";
    }

}

9、驗(yàn)證

瀏覽器訪問http://localhost:8081/qiangdan

查看Idea的console內(nèi)容，

?將console內(nèi)容拿到notepad++里面搜索

但是，搜索"update success."內(nèi)容，預(yù)期是9次，實(shí)際也是9次，符合我的需要，沒有讓庫存變成負(fù)數(shù)，

?查看數(shù)據(jù)庫表的庫存，id為1111的記錄的quantity為0，不是1，也不是負(fù)數(shù)

10、繼續(xù)第二種緯度的驗(yàn)證?

StockController的代碼如下：

package com.hmblogs.backend.controller;

import com.hmblogs.backend.dao.StockMapper;
import com.hmblogs.backend.entity.Stock;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import redis.clients.jedis.Jedis;
import java.util.Date;

@RestController
@Slf4j
public class StockController {

    @Autowired
    private StockMapper stockMapper;

    /**
     * redis test
     * @return
     */
    @GetMapping(value = "/reduceStock")
    public void redisTestLock(){
        log.info("reduceStock");
        int id = 1111;
        String key = "reduceStock"+id;
        String time = new Date().getTime()+"";
        Jedis jedisCom = new Jedis("localhost",6379);
        jedisCom.auth("heming");
        if (jedisCom.setnx(key, time)==1) {
            log.info("{}生成鎖...", time);
            try{
                Stock stock = new Stock();
                stock.setId(id);
                Stock stockDo = stockMapper.findById(stock);
                Integer quantity = stockDo.getQuantity();
                if(quantity!=null && quantity>0){
                    stockMapper.updateStockById(stock);
                    log.info("update success.");
                }else{
                    log.info("no update.");
                }
            } finally {
                log.info("{}釋放鎖...", time);
                //釋放鎖
                jedisCom.del(key, time);
            }
        }
    }
}

將庫存改為10，驗(yàn)證，通過壓測驗(yàn)證有沒有保證鎖應(yīng)該有的作用，控制查庫存和當(dāng)不小于0的時(shí)候減少庫存這2個(gè)邏輯的原子性，預(yù)期做到，實(shí)際做到了。利用APIPost工具做壓測，如下圖所示

查看server的控制臺

?

?然后把這些內(nèi)容復(fù)制到notepad++里面搜索，

搜索reduceStock，有100個(gè)結(jié)果

搜索"生成鎖..."和"釋放鎖..."，都有14次結(jié)果，說明jedisCom.setnx(key, time)==1成立的次數(shù)有14次。

?搜索"update success."，有10次結(jié)果，說明減少庫存減少了10次，

此時(shí)查看數(shù)據(jù)庫表的庫存，發(fā)現(xiàn)為0

?搜索"no update."，發(fā)現(xiàn)有4個(gè)結(jié)果，說明有4次獲得鎖了，但是庫存已經(jīng)是0了，不能再減庫存了，庫存不能為負(fù)的。

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