分布式锁实现 java

### Java 中实现分布式锁的最佳实践

#### 使用 ZooKeeper 实现分布式锁

ZooKeeper 是一种高效的协调服务，能够提供强一致性保障。其临时顺序节点特性非常适合用于构建分布式锁机制。

import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.ZooKeeper;

public class ZKLock {
    private final String lockPathPrefix = "/lock_";
    
    public void acquireLock(ZooKeeper zk, String path) throws Exception {
        // 创建临时顺序节点
        String createdNode = zk.create(lockPathPrefix, new byte[0], Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
        
        List<String> childrenNodes = zk.getChildren(path, false);
        Collections.sort(childrenNodes);

        if (createdNode.equals(path + "/" + childrenNodes.get(0))) {
            System.out.println("成功获取到锁");
        } else {
            Watcher watcher = event -> {
                try {
                    if(event.getType() == Event.EventType.NodeDeleted){
                        acquireLock(zk, path);  
                    }
                } catch(Exception e) {
                    throw new RuntimeException(e.getMessage());
                }
            };
            
            Stat stat = zk.exists(createdNode.substring(0, createdNode.lastIndexOf("_")), watcher);
            while(stat != null){
                Thread.sleep(100L);
                stat = zk.exists(createdNode.substring(0, createdNode.lastIndexOf("_")), watcher);
            }
        }
    }

    public void releaseLock(ZooKeeper zk, String lockPath) throws Exception {
        zk.delete(lockPath, -1);
        System.out.println("释放锁：" + lockPath);
    }
}

此代码展示了基于 ZooKeeper 的分布式锁基本框架[^1]。

#### 使用 Redis 实现分布式锁

Redis 提供了原子命令 `SET` 和 `DEL` 来支持简单的分布式锁功能。为了提高可靠性，建议采用 Redlock 算法来增强安全性。

import redis.clients.jedis.Jedis;

public class RedisDistributedLock {

    private static final long DEFAULT_EXPIRE_TIME_MS = 30 * 1000; // 默认过期时间设为30秒
    
    /**
     * 尝试加锁
     */
    public boolean tryAcquire(String key, String value, int expireTimeMs) {
        Jedis jedis = null;
        try {
            jedis = getJedis();
            String result = jedis.set(key, value, "NX", "PX", expireTimeMs);
            return "OK".equals(result);
        } finally {
            close(jedis);
        }
    }

    /**
     * 解锁
     */
    public void unlock(String key, String value) {
        Jedis jedis = null;
        try {
            jedis = getJedis();
            String luaScript =
              "if redis.call('get', KEYS[1]) == ARGV[1] then "
             +"return redis.call('del', KEYS[1]) "
             +"else return 0 end";

            Object evalResult = jedis.eval(luaScript, Arrays.asList(key), Arrays.asList(value));
            if ("0".equals(evalResult.toString())) {
                throw new IllegalMonitorStateException("您试图解锁不属于您的锁！");
            }
        } finally {
            close(jedis);
        }
    }
}

上述代码实现了利用 Lua 脚本安全地解除 Redis 锁的方法[^2]。