CCNAIVE

redis-lock

2023/9/8

# redis-lock

# 使用互斥锁-解决redis缓存击穿问题

# 1 controller

/**
 * @author lcc
 * @date 2023/09/08
 */
@RestController
@RequestMapping("/city")
public class CityController {

   private final CityService cityService;

   @Autowired
   public CityController(CityService cityService) {
      this.cityService = cityService;
   }

   @GetMapping("/{id}")
   public Object getCity(@PathVariable("id") String cityCode) {
      return cityService.getByCode(cityCode);
   }
}

# 2 service

package com.example.redis.service.impl;

import com.alibaba.fastjson.JSONObject;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.example.redis.constants.RedisConstants;
import com.example.redis.domain.City;
import com.example.redis.mapper.CityMapper;
import com.example.redis.service.CityService;
import org.apache.commons.lang.BooleanUtils;
import org.apache.commons.lang.StringUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.stereotype.Service;


import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.TimeUnit;

/**
 * @author lcc
 * @date 2023/09/08
 */
@Service
@Slf4j
public class CityServiceImpl extends ServiceImpl<CityMapper, City> implements CityService {

    private StringRedisTemplate stringRedisTemplate;
    private CityMapper cityMapper;

    @Autowired
    public CityServiceImpl(StringRedisTemplate stringRedisTemplate,
                           CityMapper cityMapper){
        this.stringRedisTemplate = stringRedisTemplate;
        this.cityMapper = cityMapper;
    }

    @Override
    public City getByCode(String cityCode) {
        String key = RedisConstants.CACHE_CITY_KEY+cityCode;
        return queryCityWithMutex(key, cityCode);
    }

    /**
     * 通过互斥锁机制查询城市信息
     * @param key
     */
    private City queryCityWithMutex(String key, String cityCode) {
        City city = null;
        // 1.查询缓存
        String cityJson = stringRedisTemplate.opsForValue().get(key);
        // 2.判断缓存是否有数据
        if (StringUtils.isNotBlank(cityJson)) {
            // 3.有,则返回
            city = JSONObject.parseObject(cityJson, City.class);
            return city;
        }
        // 4.无,则获取互斥锁
        String lockKey = RedisConstants.LOCK_CITY_KEY + cityCode;
        Boolean isLock = tryLock(lockKey);
        // 5.判断获取锁是否成功
        try {
            if (!isLock) {
                // 6.获取失败, 休眠并重试
                Thread.sleep(100);
                return queryCityWithMutex(key, cityCode);
            }
            // 7.获取成功, 查询数据库
            city = baseMapper.selectById(cityCode);
            // 8.判断数据库是否有数据
            if (city == null) {
                // 9.无,则将空数据写入redis
                stringRedisTemplate.opsForValue().set(key, "", RedisConstants.CACHE_NULL_TTL, TimeUnit.MINUTES);
                return null;
            }
            // 10.有,则将数据写入redis
            stringRedisTemplate.opsForValue().set(key, JSONObject.toJSONString(city), RedisConstants.CACHE_CITY_TTL, TimeUnit.MINUTES);
        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            // 11.释放锁
            unLock(lockKey);
        }
        // 12.返回数据
        return city;
    }

    /**
     * 获取互斥锁
     * @return
     */
    private Boolean tryLock(String key) {
        //如果key不存在则进行存储，当存在时，则代表当前互斥锁被其他线程获取了
        Boolean flag = stringRedisTemplate.opsForValue().setIfAbsent(key, "1", 10, TimeUnit.SECONDS);
        return BooleanUtils.isTrue(flag);
    }

    /**
     * 释放锁
     * @param key
     */
    private void unLock(String key) {
        stringRedisTemplate.delete(key);
    }

}

# 3 entity

package com.example.redis.domain;

import lombok.Data;

@Data
public class City {
    private Integer id;

    private String name;
}

# 4 mapper

package com.example.redis.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.example.redis.domain.City;
import org.apache.ibatis.annotations.Mapper;

@Mapper
public interface CityMapper extends BaseMapper<City> {

}

# 5 依赖

<?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>2.7.6</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>redis</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>redis</name>
    <description>redis</description>
    <properties>
        <java.version>8</java.version>
    </properties>
    <dependencies>

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


        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.5.0</version>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.27</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-beans</artifactId>
        </dependency>
        <!-- mybatis-plus -->
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.4.1</version>
        </dependency>

        <!-- lettuce pool 缓存连接池-->
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-pool2</artifactId>
        </dependency>
        <dependency>
            <groupId>commons-lang</groupId>
            <artifactId>commons-lang</artifactId>
            <version>2.6</version>
        </dependency>
        <!--处理JSON格式-->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.3</version>
        </dependency>
        <!--hutool-->
        <dependency>
            <groupId>cn.hutool</groupId>
            <artifactId>hutool-all</artifactId>
            <version>5.7.17</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.16.20</version>
        </dependency>
    </dependencies>

</project>

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