Spring Boot使用Jedis实现分布式锁

港控/mmm° 2022-11-22 00:08 250阅读 0赞

## 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/> 
        </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：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3OTYwNjAz_size_16_color_FFFFFF_t_70]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3OTYwNjAz_size_16_color_FFFFFF_t_70 1]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3OTYwNjAz_size_16_color_FFFFFF_t_70 2]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3OTYwNjAz_size_16_color_FFFFFF_t_70 3]  
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）。

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3OTYwNjAz_size_16_color_FFFFFF_t_70 4]  
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）。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3OTYwNjAz_size_16_color_FFFFFF_t_70 5]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3OTYwNjAz_size_16_color_FFFFFF_t_70 6]  
同时点击测试。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3OTYwNjAz_size_16_color_FFFFFF_t_70 7]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3OTYwNjAz_size_16_color_FFFFFF_t_70 8]

结果如下：

项目一接口获取到锁`34`次。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3OTYwNjAz_size_16_color_FFFFFF_t_70 9]  
项目二接口获取到锁`218`次。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3OTYwNjAz_size_16_color_FFFFFF_t_70 10]

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3OTYwNjAz_size_16_color_FFFFFF_t_70 11]

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！

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