基于redis实现分布式锁

1、适用于单节点的分布式锁
2、多节点的分布式锁可使用redlock等框架实现

分布式锁需要解决如下几个问题
问题1：获取锁的唯一性（多个线程不能同时获取一个锁）
问题2：锁要有过期时间（一个线程获取锁后宕机，导致其它线程都获取不到锁）
问题3：释放锁时，只能释放自己（本线程）创建的锁

获取锁

key: 锁名，业务唯一
value: 使用线程id + 时间戳
1、redis的SETNX是key不存在时，才能set成功【问题1】
2、锁需要添加过期时间，并且获取锁和设置过期时间要保证原子性，这里使用Lua脚本（Lua脚本在redis执行是原子性的）执行【问题2】

代码实现

	/* 获取锁保证原子性*/private static final String SET_KEY_LUA = "if redis.call('setnx',KEYS[1],ARGV[1]) == 1 then" +" return redis.call('expire',KEYS[1],ARGV[2]) else return 0 end";/* 获取锁* @param expire 锁过期时间，单位秒* @return*/public Boolean lock(Integer expire) {if (expire == null || expire <= 0) {expire = DEFAULT_EXPIRE;}RedisScript<Long> redisScript = new DefaultRedisScript(SET_KEY_LUA, Long.class);Long result = (Long) redisTemplate.execute(redisScript, Arrays.asList(key), value, String.valueOf(expire));return SUCCESS.equals(result);}

解锁

解锁时检查value值是否和当前线程的value一致，一致才能解锁【问题3】

代码实现

	/* 释放锁保证原子性*/private static final String DELETE_LUA = "if redis.call('get',KEYS[1]) == ARGV[1] then" +"    return redis.call('del', KEYS[1])" +"    else" +"    return 0" +"    end";/* 解锁*/public void unlock() {RedisScript<Long> redisScript = new DefaultRedisScript(DELETE_LUA, Long.class);redisTemplate.execute(redisScript, Arrays.asList(key), value);}

完整代码

Lock.java

import lombok.Data;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.script.DefaultRedisScript;
import org.springframework.data.redis.core.script.RedisScript;import java.util.Arrays;/* 锁*/
@Data
public class Lock {private String key;private String value;private RedisTemplate redisTemplate;/* 获取锁保证原子性*/private static final String SET_KEY_LUA = "if redis.call('setnx',KEYS[1],ARGV[1]) == 1 then" +" return redis.call('expire',KEYS[1],ARGV[2]) else return 0 end";/* 释放锁保证原子性*/private static final String DELETE_LUA = "if redis.call('get',KEYS[1]) == ARGV[1] then" +"    return redis.call('del', KEYS[1])" +"    else" +"    return 0" +"    end";private static final Long SUCCESS = 1L;// 默认过期时间5分钟private static final Integer DEFAULT_EXPIRE = 5 * 60;public Lock(String key, RedisTemplate redisTemplate) {this.key = key;this.value = Thread.currentThread().getName() + "-" + System.currentTimeMillis();this.redisTemplate = redisTemplate;}/* 获取锁，默认60秒过期* @return*/public Boolean lock() {return this.lock(DEFAULT_EXPIRE);}/* 获取锁* @param expire 锁过期时间，单位秒* @return*/public Boolean lock(Integer expire) {if (expire == null || expire <= 0) {expire = DEFAULT_EXPIRE;}RedisScript<Long> redisScript = new DefaultRedisScript(SET_KEY_LUA, Long.class);Long result = (Long) redisTemplate.execute(redisScript, Arrays.asList(key), value, String.valueOf(expire));return SUCCESS.equals(result);}/* 解锁*/public void unlock() {RedisScript<Long> redisScript = new DefaultRedisScript(DELETE_LUA, Long.class);redisTemplate.execute(redisScript, Arrays.asList(key), value);}
}

LockService.java

import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.stereotype.Service;@Service
@Slf4j
public class LockServiceImpl implements LockService {@Autowiredprivate RedisTemplate redisTemplate;@Overridepublic Lock getLock(String key) {return new Lock(key,  redisTemplate);}
}

使用

		String key = "xxx";Integer expire = 5;Lock lock = lockService.getLock(key);if (!lock.lock(expire)) {log.warn("未获取到分布式锁, key: {}", key);return null;}log.info("获取到分布式锁, key: {}", key);try {... ...} finally {lock.unlock();log.info("分布式锁已释放, key: {}", key);}