用Java写个分布式锁

以下是一个简单的Java分布式锁实现：

import redis.clients.jedis.Jedis;

public class DistributedLock {

    private Jedis jedis;
    private String lockKey;
    private int expireTime;
    private boolean locked = false;

    public DistributedLock(Jedis jedis, String lockKey, int expireTime) {
        this.jedis = jedis;
        this.lockKey = lockKey;
        this.expireTime = expireTime;
    }

    public boolean lock() {
        long nowTime = System.currentTimeMillis();
        long lockExpireTime = nowTime + expireTime + 1;
        String result = jedis.set(lockKey, String.valueOf(lockExpireTime), "NX", "PX", expireTime);
        if ("OK".equals(result)) {
            locked = true;
            return true;
        } else {
            String lockTimeStr = jedis.get(lockKey);
            if (lockTimeStr != null && Long.parseLong(lockTimeStr) >= nowTime) {
                return false;
            } else {
                String oldLockTimeStr = jedis.getSet(lockKey, String.valueOf(lockExpireTime));
                if (oldLockTimeStr == null || oldLockTimeStr.equals(lockTimeStr)) {
                    locked = true;
                    return true;
                } else {
                    return false;
                }
            }
        }
    }

    public boolean unlock() {
        if (locked) {
            jedis.del(lockKey);
            locked = false;
            return true;
        }
        return false;
    }
}

该实现使用Redis作为分布式锁存储介质，利用Redis的SET命令的NX（不存在则设置）选项来实现锁的获取，利用GETSET命令来实现锁的释放。其中，expireTime表示锁的过期时间，单位为毫秒。如果获取锁成功，则返回true，否则返回false。释放锁时，如果当前线程持有锁，则释放锁并返回true，否则返回false。