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本篇内容主要讲解“如何用redis来实现分布式锁”，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习“如何用redis来实现分布式锁”吧!
boot_redis01
boot_redis02
<?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>2.4.4</version> <relativePath/> <!-- lookup parent from repository --> </parent> <groupId>com.lau</groupId> <artifactId>boot_redis01</artifactId> <version>0.0.1-SNAPSHOT</version> <name>boot_redis01</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-web</artifactId> </dependency> <!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-actuator --> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-actuator</artifactId> </dependency> <!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-data-redis --> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-redis</artifactId> </dependency> <!-- https://mvnrepository.com/artifact/org.apache.commons/commons-pool2 --> <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-pool2</artifactId> </dependency> <!-- https://mvnrepository.com/artifact/redis.clients/jedis --> <dependency> <groupId>redis.clients</groupId> <artifactId>jedis</artifactId> <version>3.1.0</version> </dependency> <!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-aop --> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-aop</artifactId> </dependency> <!-- https://mvnrepository.com/artifact/org.redisson/redisson --> <dependency> <groupId>org.redisson</groupId> <artifactId>redisson</artifactId> <version>3.13.4</version> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-devtools</artifactId> <scope>runtime</scope> <optional>true</optional> </dependency> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <optional>true</optional> </dependency> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> </dependency> </dependencies> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins> </build> </project>
server.port=1111 spring.redis.database=0 spring.redis.host=localhost spring.redis.port=6379 #连接池最大连接数（使用负值表示没有限制）默认8 spring.redis.lettuce.pool.max-active=8 #连接池最大阻塞等待时间（使用负值表示没有限制）默认-1 spring.redis.lettuce.pool.max-wait=-1 #连接池中的最大空闲连接默认8 spring.redis.lettuce.pool.max-idle=8 #连接池中的最小空闲连接默认0 spring.redis.lettuce.pool.min-idle=0 ?
package com.lau.boot_redis01;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration;
@SpringBootApplication(exclude= {DataSourceAutoConfiguration.class})
public class BootRedis01Application {
public static void main(String[] args) {
SpringApplication.run(BootRedis01Application.class, args);
}
}package com.lau.boot_redis01.config;
import org.redisson.Redisson;
import org.redisson.config.Config;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.serializer.GenericJackson2JsonRedisSerializer;
import org.springframework.data.redis.serializer.StringRedisSerializer;
import java.io.Serializable;
@Configuration
public class RedisConfig {
@Value("${spring.redis.host}")
private String redisHost;
/**
*保证不是序列化后的乱码配置
*/
@Bean
public RedisTemplate<String, Serializable>redisTemplate(LettuceConnectionFactory connectionFactory){
RedisTemplate<String,Serializable> redisTemplate =new RedisTemplate<>();
redisTemplate.setKeySerializer(new StringRedisSerializer());
redisTemplate.setValueSerializer(new GenericJackson2JsonRedisSerializer());
redisTemplate.setConnectionFactory(connectionFactory);
return redisTemplate;
}
@Bean
public Redisson redisson(){
Config config = new Config();
config.useSingleServer().setAddress("redis://"+redisHost+":6379").setDatabase(0);
return (Redisson) Redisson.create(config);
}
}package com.lau.boot_redis01.controller;
import com.lau.boot_redis01.util.RedisUtil;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.GetMapping;
import redis.clients.jedis.Jedis;
import java.util.Collections;
import java.util.List;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
@RestController
public class GoodController {
@Autowired
private StringRedisTemplate stringRedisTemplate;
@Value("${server.port}")
private String serverPort;
private static final String REDIS_LOCK = "atguigulock";
@GetMapping("/buy_goods")
public String buy_Goods() throws Exception {
String value = UUID.randomUUID().toString() + Thread.currentThread().getName();
try{
//1、key加过期时间是因为如果redis客户端宕机了会造成死锁，其它客户端永远获取不到锁
//2、这里将setnx与锁过期两条命令合二为一，是为了解决命令分开执行引发的原子性问题：
//setnx 中间会被其它redis客户端命令加塞 2、expire
//3①、为了避免线程执行业务时间大于锁过期时间导致窜行操作，再释放锁时应判断是否是自己加的锁；
//还有另外一种解决方案：锁续期——额外开启一个守护线程定时给当前key加超时时间（如5s到期，每2.5s ttl判断一次，并加2.5s超时时间，不断续期，线程将使用主动删除key命令的方式释放锁；另，当此redis客户端命令宕机后，此守护线程会自动随之消亡，不会再主动续期——此机制使得其它redis客户端可以获得锁，不会发生死锁或长期等待）
Boolean flag = stringRedisTemplate.opsForValue().setIfAbsent(REDIS_LOCK, value, 10L, TimeUnit.SECONDS);//setnx
if(!flag){
return "获取锁失败！";
}
String result = stringRedisTemplate.opsForValue().get("goods:001");
int goodsNumber = result == null ? 0 : Integer.parseInt(result);
if (goodsNumber > 0){
int realNumber = goodsNumber - 1;
stringRedisTemplate.opsForValue().set("goods:001",realNumber + "");
System.out.println("你已经成功秒杀商品，此时还剩余：" + realNumber + "件"+"\t 服务器端口: "+serverPort);
return "你已经成功秒杀商品，此时还剩余：" + realNumber + "件"+"\t 服务器端口: "+serverPort;
}
System.out.println("商品已经售罄/活动结束/调用超时，欢迎下次光临"+"\t 服务器端口: "+serverPort);
return "商品已经售罄/活动结束/调用超时，欢迎下次光临"+"\t 服务器端口: "+serverPort;
}
finally {
// if(stringRedisTemplate.opsForValue().get(REDIS_LOCK).equals(value)){
// stringRedisTemplate.delete(REDIS_LOCK);
// }
//3②这里也存在命令的原子问题：获取当前key经相等判断后与删除对应key是两个不同命令，中间会被加塞
//解决方法1：redis事务
// stringRedisTemplate.watch(REDIS_LOCK);
// while(true){
// if(stringRedisTemplate.opsForValue().get(REDIS_LOCK).equalsIgnoreCase(value)){
// stringRedisTemplate.setEnableTransactionSupport(true);
// stringRedisTemplate.multi();
// stringRedisTemplate.delete(REDIS_LOCK);
//
// List<Object> list = stringRedisTemplate.exec();
//
// if(list == null){
// continue;
// }
// }
//
// stringRedisTemplate.unwatch();
// break;
// }
//解决方法2：lua脚本——原子操作
Jedis jedis = RedisUtil.getJedis();
String script = "if redis.call('get', KEYS[1]) == ARGV[1]"+"then "
+"return redis.call('del', KEYS[1])"+"else "+ " return 0 " + "end";
try{
Object result = jedis.eval(script, Collections.singletonList(REDIS_LOCK), Collections.singletonList(value));
if ("1".equals(result.toString())){
System.out.println("------del REDIS_LOCK_KEY success");
}
else {
System.out.println("------del REDIS_LOCK_KEY error");
}
}finally {
if (null != jedis){
jedis.close();
}
}
}
}
}问题：没有加锁，并发下数字不对，会出现超卖现象
① synchronized 不见不散
② ReentrantLock 过时不候
在单机环境下，可以使用synchronized或Lock来实现。 但是在分布式系统中，因为竞争的线程可能不在同一个节点上(同一个jvm中），所以需要一个让所有进程都能访问到的锁来实现，比如redis或者zookeeper来构建; 不同进程jvm层面的锁就不管用了，那么可以利用第三方的一个组件，来获取锁，未获取到锁，则阻塞当前想要运行的线程
注：分布式部署后，单机锁还是出现超卖现象，需要分布式锁
启动两个微服务1111和2222，访问使用：http://localhost/buy_goods(即通过nginx轮询方式访问1111和2222两个微服务)
nginx.conf配置
#user nobody;
worker_processes 1;
#error_log logs/error.log;
#error_log logs/error.log notice;
#error_log logs/error.log info;
#pid logs/nginx.pid;
events {
worker_connections 1024;
}
http {
include mime.types;
default_type application/octet-stream;
#log_format main '$remote_addr - $remote_user [$time_local] "$request" '
# '$status $body_bytes_sent "$http_referer" '
# '"$http_user_agent" "$http_x_forwarded_for"';
#access_log logs/access.log main;
sendfile on;
#tcp_nopush on;
#keepalive_timeout 0;
keepalive_timeout 65;
#gzip on;
upstream mynginx{#反向代理的服务器列表，权重相同，即负载均衡使用轮训策略
server localhost:1111 weight=1;
server localhost:2222 weight=1;
}
server {
listen 80;
server_name localhost;
#charset koi8-r;
#access_log logs/host.access.log main;
location / {
#root html;
#index index.html index.htm;
proxy_pass http://mynginx;#配置反向代理
index index.html index.htm;
}
#error_page 404 /404.html;
# redirect server error pages to the static page /50x.html
#
error_page 500 502 503 504 /50x.html;
location = /50x.html {
root html;
}
# proxy the PHP scripts to Apache listening on 127.0.0.1:80
#
#location ~ \.php$ {
# proxy_pass http://127.0.0.1;
#}
# pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
#
#location ~ \.php$ {
# root html;
# fastcgi_pass 127.0.0.1:9000;
# fastcgi_index index.php;
# fastcgi_param SCRIPT_FILENAME /scripts$fastcgi_script_name;
# include fastcgi_params;
#}
# deny access to .htaccess files, if Apache's document root
# concurs with nginx's one
#
#location ~ /\.ht {
# deny all;
#}
}
# another virtual host using mix of IP-, name-, and port-based configuration
#
#server {
# listen 8000;
# listen somename:8080;
# server_name somename alias another.alias;
# location / {
# root html;
# index index.html index.htm;
# }
#}
# HTTPS server
#
#server {
# listen 443 ssl;
# server_name localhost;
# ssl_certificate cert.pem;
# ssl_certificate_key cert.key;
# ssl_session_cache shared:SSL:1m;
# ssl_session_timeout 5m;
# ssl_ciphers HIGH:!aNULL:!MD5;
# ssl_prefer_server_ciphers on;
# location / {
# root html;
# index index.html index.htm;
# }
#}
}① 出异常的话，可能无法释放锁， 必须要在代码层面finally释放锁
② 加锁解锁，lock/unlock必须同时出现并保证调用
① 部署了微服务jar包的机器挂了，代码层面根本没有走到finally这块， 没办法保证解锁，这个key没有被删除，需要加入一个过期时间限定key
② 需要对lockKey有过期时间的设定
① 设置key+过期时间分开了，必须要合并成一行具备原子性
① 设置锁失效时间不合理
① 用redis自身的事务
i 未使用watch前：
ii使用watch后：
② 用Lua脚本
Redis可以通过eval命令保证代码执行的原子性
java配置类：
package com.lau.boot_redis01.util;
import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPool;
import redis.clients.jedis.JedisPoolConfig;
public class RedisUtil {
private static JedisPool jedisPool;
static {
JedisPoolConfig jedisPoolConfig = new JedisPoolConfig();
jedisPoolConfig.setMaxTotal(20);
jedisPoolConfig.setMaxIdle(10);
jedisPool = new JedisPool(jedisPoolConfig,"127.0.0.1",6379,100000);
}
public static Jedis getJedis() throws Exception{
if (null!=jedisPool){
return jedisPool.getResource();
}
throw new Exception("Jedispool is not ok");
}
}Jedis jedis = RedisUtil.getJedis();
String script = "if redis.call('get', KEYS[1]) == ARGV[1]"+"then "
+"return redis.call('del', KEYS[1])"+"else "+ " return 0 " + "end";
try{
Object result = jedis.eval(script, Collections.singletonList(REDIS_LOCK), Collections.singletonList(value));
if ("1".equals(result.toString())){
System.out.println("------del REDIS_LOCK_KEY success");
}
else {
System.out.println("------del REDIS_LOCK_KEY error");
}
}finally {
if (null != jedis){
jedis.close();
}
}① Redis分布式锁如何续期? 确保redisLock过期时间大于业务执行时间的问题（锁续期）
② redis单点故障——redis异步复制造成的锁丢失， 比如:主节点没来的及把刚刚set进来这条数据给从节点，就挂了。(zk/cp、redis/ap)（redis集群）
确保redisLock过期时间大于业务执行时间的问题；redis集群环境下，我们自己写的也不OK, 直接上RedLock之Redisson落地实现
1、RedisConfig.java
@Bean
public Redisson redisson(){
Config config = new Config();
config.useSingleServer().setAddress("redis://"+redisHost+":6379").setDatabase(0);
return (Redisson) Redisson.create(config);
}2、控制器类：
package com.lau.boot_redis01.controller;
import com.lau.boot_redis01.util.RedisUtil;
import lombok.val;
import org.redisson.Redisson;
import org.redisson.RedissonLock;
import org.redisson.api.RLock;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import redis.clients.jedis.Jedis;
import java.util.Collections;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
@RestController
public class GoodController_Redisson {
@Autowired
private StringRedisTemplate stringRedisTemplate;
@Value("${server.port}")
private String serverPort;
private static final String REDIS_LOCK = "atguigulock";
@Autowired
private Redisson redisson;
@GetMapping("/buy_goods2")
public String buy_Goods() throws Exception {
String value = UUID.randomUUID().toString() + Thread.currentThread().getName();
RLock lock = redisson.getLock(REDIS_LOCK);
try{
lock.lock();
String result = stringRedisTemplate.opsForValue().get("goods:001");
int goodsNumber = result == null ? 0 : Integer.parseInt(result);
if (goodsNumber > 0){
int realNumber = goodsNumber - 1;
stringRedisTemplate.opsForValue().set("goods:001",realNumber + "");
System.out.println("你已经成功秒杀商品，此时还剩余：" + realNumber + "件"+"\t 服务器端口: "+serverPort);
return "你已经成功秒杀商品，此时还剩余：" + realNumber + "件"+"\t 服务器端口: "+serverPort;
}
System.out.println("商品已经售罄/活动结束/调用超时，欢迎下次光临"+"\t 服务器端口: "+serverPort);
return "商品已经售罄/活动结束/调用超时，欢迎下次光临"+"\t 服务器端口: "+serverPort;
}
finally {
//IllegalMonitorStateException:attempt unlock lock,not locked by current thread by node_id
if(lock.isLocked() && lock.isHeldByCurrentThread()){
lock.unlock();
}
}
}
}注：在并发多的时候就可能会遇到这种错误，可能会被重新抢占
到此，相信大家对“如何用redis来实现分布式锁”有了更深的了解，不妨来实际操作一番吧！这里是亿速云网站，更多相关内容可以进入相关频道进行查询，关注我们，继续学习！
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