最近在做项目中要用到redis锁,因为项目是集群部署,所以要考虑分布式锁,查了一些资料,发现有些会产生误导,所以还是记录一下redis分布式锁的正确打开方式,话不多说,先上代码
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.data.redis.core.RedisCallback;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.stereotype.Component;
import org.springframework.util.StringUtils;
import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisCluster;
import redis.clients.jedis.JedisCommands;
import javax.annotation.Resource;
import java.util.ArrayList;
import java.util.List;
import java.util.UUID;
/**
* @author superchen
* @since 2018/5/16
**/
@Component
public class RedisDistributedLock{
@Resource
private RedisTemplate<String, Object> redisTemplate;
public static final String UNLOCK_LUA;
static {
StringBuilder sb = new StringBuilder();
sb.append("if redis.call(\"get\",KEYS[1]) == ARGV[1] ");
sb.append("then ");
sb.append(" return redis.call(\"del\",KEYS[1]) ");
sb.append("else ");
sb.append(" return 0 ");
sb.append("end ");
UNLOCK_LUA = sb.toString();
}
private final Logger logger = LoggerFactory.getLogger(RedisDistributedLock.class);
public boolean setLock(String key, long expire) {
try {
RedisCallback<String> callback = (connection) -> {
JedisCommands commands = (JedisCommands) connection.getNativeConnection();
String uuid = UUID.randomUUID().toString();
return commands.set(key, uuid, "NX", "PX", expire);
};
String result = redisTemplate.execute(callback);
return !StringUtils.isEmpty(result);
} catch (Exception e) {
logger.error("set redis occured an exception", e);
}
return false;
}
public String get(String key) {
try {
RedisCallback<String> callback = (connection) -> {
JedisCommands commands = (JedisCommands) connection.getNativeConnection();
return commands.get(key);
};
String result = redisTemplate.execute(callback);
return result;
} catch (Exception e) {
logger.error("get redis occured an exception", e);
}
return "";
}
public boolean releaseLock(String key,String requestId) {
// 释放锁的时候,有可能因为持锁之后方法执行时间大于锁的有效期,此时有可能已经被另外一个线程持有锁,所以不能直接删除
try {
List<String> keys = new ArrayList<>();
keys.add(key);
List<String> args = new ArrayList<>();
args.add(requestId);
// 使用lua脚本删除redis中匹配value的key,可以避免由于方法执行时间过长而redis锁自动过期失效的时候误删其他线程的锁
// spring自带的执行脚本方法中,集群模式直接抛出不支持执行脚本的异常,所以只能拿到原redis的connection来执行脚本
RedisCallback<Long> callback = (connection) -> {
Object nativeConnection = connection.getNativeConnection();
// 集群模式和单机模式虽然执行脚本的方法一样,但是没有共同的接口,所以只能分开执行
// 集群模式
if (nativeConnection instanceof JedisCluster) {
return (Long) ((JedisCluster) nativeConnection).eval(UNLOCK_LUA, keys, args);
}
// 单机模式
else if (nativeConnection instanceof Jedis) {
return (Long) ((Jedis) nativeConnection).eval(UNLOCK_LUA, keys, args);
}
return 0L;
};
Long result = redisTemplate.execute(callback);
return result != null && result > 0;
} catch (Exception e) {
logger.error("release lock occured an exception", e);
} finally {
// 清除掉ThreadLocal中的数据,避免内存溢出
//lockFlag.remove();
}
return false;
}
}
首先我们要通过Maven引入Jedis
开源组件,在pom.xml
文件加入下面的代码:
<dependency> <groupId>redis.clients</groupId> <artifactId>jedis</artifactId> <version>2.9.0</version> </dependency>
不管是加锁还是解锁,都要保持操作的原子性,否则就有可能产生死锁。上面的setNX方法不再赘述,不懂的童鞋可以自行百度。