Spring Boot使用Jedis实现分布式锁

Spring Boot使用Jedis实现分布式锁

在单机应用中通过使用synchronized关键字、JUC的Lock来实现线程安全是没问题的，但在分布式环境中就有可能出现问题，因为这些同步机制、锁是不能跨机器的，所以这里介绍的分布式锁就很有必要。

首先创建两个Spring Boot项目。

pom.xml（两个项目都一样）:

<?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>2.3.5.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.kaven</groupId>
    <artifactId>distributelock</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>distributelock</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <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>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>redis.clients</groupId>
            <artifactId>jedis</artifactId>
            <version>3.3.0</version>
            <type>jar</type>
            <scope>compile</scope>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

Jedis组件（两个项目都一样）：

package com.kaven.distributelock.component;
import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Component;
import redis.clients.jedis.Jedis;
@Component
public class JedisComponent { 
    @Bean
    public Jedis jedis(){ 
        return new Jedis("localhost",6379);
    }
}

项目一接口：

package com.kaven.distributelock.controller;
import com.kaven.distributelock.lock.JedisLock;
import org.springframework.web.bind.annotation.PutMapping;
import org.springframework.web.bind.annotation.RestController;
import redis.clients.jedis.Jedis;
import javax.annotation.Resource;
import java.util.UUID;
import java.util.concurrent.atomic.AtomicInteger;
@RestController
public class NumberController { 
    private AtomicInteger count = new AtomicInteger(0);
    @Resource
    private Jedis jedis;
    @PutMapping("/number")
    public synchronized void subNumber() throws InterruptedException { 
        Integer number = Integer.parseInt(jedis.get("number"));
        Thread.sleep(400);
        number-=1;
        jedis.set("number" , number.toString());
        count.addAndGet(1);
        System.out.println(count.get());
    }
}

项目二接口：

package com.kaven.distributelock.controller;
import org.springframework.web.bind.annotation.PutMapping;
import org.springframework.web.bind.annotation.RestController;
import redis.clients.jedis.Jedis;
import javax.annotation.Resource;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Lock;
@RestController
public class NumberController { 
    private AtomicInteger count = new AtomicInteger(0);
    @Resource
    private Jedis jedis;
    @PutMapping("/number")
    public synchronized void subNumber() throws InterruptedException { 
        Integer number = Integer.parseInt(jedis.get("number"));
        Thread.sleep(1000);
        number-=1;
        jedis.set("number" , number.toString());
        count.addAndGet(1);
        System.out.println(count.get());
    }
}

启动类（两个项目都一样）：

package com.kaven.distributelock;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class DistributeLockApplication { 
    public static void main(String[] args) { 
        SpringApplication.run(DistributeLockApplication.class, args);
    }
}

项目一运行在8080端口，项目二运行在8081端口。

测试：




从上面几张图可以得知，项目一接口会将number减100次，而项目二接口会将number减50次，并且都执行成功了，理想情况下redis里面的number应该为0，但实际情况却为86，如下图所示，所以synchronized关键字在分布式环境下是不能保障数据同步的（只能单机应用场景的锁，是不能保障分布式环境下数据同步）。

接下来使用Jedis实现分布式锁（两个项目都一样）：

package com.kaven.distributelock.lock;
import redis.clients.jedis.Jedis;
import redis.clients.jedis.params.SetParams;
import java.util.Collections;
public class JedisLock { 
    private static final String LOCK_SUCCESS = "OK";
    private static final Long RELEASE_SUCCESS = 1L;
    /** * 尝试获取分布式锁 * @param jedis Redis客户端 * @param lockKey 锁 * @param requestId 请求标识 * @param millisecondsToExpire 超期时间 * @return 是否获取成功 */
    public static boolean tryGetDistributedLock(Jedis jedis, String lockKey, String requestId, long millisecondsToExpire) { 
        String result = jedis.set(lockKey,requestId, SetParams.setParams().nx().px(millisecondsToExpire));
        if (LOCK_SUCCESS.equals(result)) { 
            return true;
        }
        return false;
    }
    /** * 释放分布式锁 * @param jedis Redis客户端 * @param lockKey 锁 * @param requestId 请求标识 * @return 是否释放成功 */
    public static boolean releaseDistributedLock(Jedis jedis, String lockKey, String requestId) { 
        String script = "if redis.call('get', KEYS[1]) == ARGV[1] then return redis.call('del', KEYS[1]) else return 0 end";
        Object result = jedis.eval(script, Collections.singletonList(lockKey), Collections.singletonList(requestId));
        if (RELEASE_SUCCESS.equals(result)) { 
            return true;
        }
        return false;
    }
}

项目一接口：

package com.kaven.distributelock.controller;
import com.kaven.distributelock.lock.JedisLock;
import org.springframework.web.bind.annotation.PutMapping;
import org.springframework.web.bind.annotation.RestController;
import redis.clients.jedis.Jedis;
import javax.annotation.Resource;
import java.util.UUID;
import java.util.concurrent.atomic.AtomicInteger;
@RestController
public class NumberController { 
    private AtomicInteger count = new AtomicInteger(0);
    @Resource
    private Jedis jedis;
    @PutMapping("/number")
    public void subNumber() throws InterruptedException { 
        String requestId = UUID.randomUUID().toString();
        String LOCKKEY = "LOCKKEY";
        if(JedisLock.tryGetDistributedLock(jedis , LOCKKEY , requestId , 3000)){ 
            Integer number = Integer.parseInt(jedis.get("number"));
            Thread.sleep(400);
            number-=1;
            jedis.set("number" , number.toString());
            count.addAndGet(1);
            System.out.println(count.get());
            JedisLock.releaseDistributedLock(jedis , LOCKKEY , requestId);
        }
    }
}

项目二接口：

package com.kaven.distributelock.controller;
import com.kaven.distributelock.lock.JedisLock;
import org.springframework.web.bind.annotation.PutMapping;
import org.springframework.web.bind.annotation.RestController;
import redis.clients.jedis.Jedis;
import javax.annotation.Resource;
import java.util.UUID;
import java.util.concurrent.atomic.AtomicInteger;
@RestController
public class NumberController { 
    private AtomicInteger count = new AtomicInteger(0);
    @Resource
    private Jedis jedis;
    @PutMapping("/number")
    public void subNumber() throws InterruptedException { 
        String requestId = UUID.randomUUID().toString();
        String LOCKKEY = "LOCKKEY";
        if(JedisLock.tryGetDistributedLock(jedis , LOCKKEY , requestId , 3000)){ 
            Integer number = Integer.parseInt(jedis.get("number"));
            Thread.sleep(1000);
            number-=1;
            jedis.set("number" , number.toString());
            count.addAndGet(1);
            System.out.println(count.get());
            JedisLock.releaseDistributedLock(jedis , LOCKKEY , requestId);
        }
    }
}

将redis里面的number变量设置成3000（字符串），因为没有获取到锁的话，代码就直接跑完了，所以这里让测试次数多一些，项目一接口请求2000次，项目二接口请求1000次（因为获取到锁只是少部分）。


同时点击测试。

结果如下：

项目一接口获取到锁34次。

项目二接口获取到锁218次。

结果很显然是正确的（34+218=3000-2748）。

Spring Boot使用Jedis实现分布式锁就介绍到这里。

写博客是博主记录自己的学习过程，如果有错误，请指正，谢谢！