一种基于redis的分布式锁的实现（当前项目中在使用）

主要思想是利用redis执行命令时的单线程特性。

/**
 * 分布式锁
 */
@Component
public class DistributedLock {

    public static final Logger logger = LoggerFactory.getLogger(DistributedLock.class);
    /**
     * 加锁默认超时时间
     */
    private static final long DEFAULT_TIMEOUT_SECOND = 5;
    /**
     * 获取所等待的时间
     */
    private static final long DEFAULT_WAITE_TIMEOUT_SECOND = 5;
    /**
     * 加锁循环等待时间
     */
    private static final long LOOP_WAIT_TIME_MILLISECOND = 30;
    @Autowired
    @Qualifier("redisCacheService")
    private BaseCacheService cacheService;

    /**
     * 有超时等待的加锁
     *
     * @param timeoutSecond      如果为null,使用默认超时时间
     * @param waiteTimeoutSecond 若果为null,使用默认超时时间
     * @return 加锁的值（超时时间：-1表示获取失败，超时）
     */
    public long lock(String key, Long timeoutSecond, Long waiteTimeoutSecond) {

        logger.info("Thread：" + Thread.currentThread().getName() + " start lock");
        long beganTime = System.currentTimeMillis() / 1000;
        //如果参数错误
        if (timeoutSecond != null && timeoutSecond <= 0) {
            timeoutSecond = DEFAULT_TIMEOUT_SECOND;
        }
        timeoutSecond = timeoutSecond == null ? DEFAULT_TIMEOUT_SECOND : timeoutSecond;
        if (waiteTimeoutSecond != null && waiteTimeoutSecond <= 0) {
            waiteTimeoutSecond = DEFAULT_WAITE_TIMEOUT_SECOND;
        }
        waiteTimeoutSecond =
                waiteTimeoutSecond == null ? DEFAULT_WAITE_TIMEOUT_SECOND : waiteTimeoutSecond;
        while (true) {
            //等待超时判断
            long endTime = System.currentTimeMillis() / 1000;
            if ((endTime - beganTime) >= waiteTimeoutSecond) {
                return -1l;
            }
            //超时时间点
            long timeoutTimeMilli = cacheService.getCurrentTimeMilliForCache() + timeoutSecond * 1000;

            //如果设置成功
            if (cacheService.setIfAbsent(key, timeoutTimeMilli)) {
                logger.info("Thread：" + Thread.currentThread().getName() + " lock success");
                return timeoutTimeMilli;
            }

            //如果已经超时
            Long value = cacheService.getVal(key, Long.class);
            if (value != null && value.longValue() < cacheService.getCurrentTimeMilliForCache()) {

                //设置新的超时时间
                Long oldValue = cacheService.getAndSet(key, timeoutTimeMilli);

                //多个线程同时getset，只有第一个才可以获取到锁
                if (value.equals(oldValue)) {
                    logger.info("Thread：" + Thread.currentThread().getName() + " lock success");
                    return timeoutTimeMilli;
                }
            }

            //延迟一定毫秒，防止请求太频繁
            try {
                Thread.sleep(LOOP_WAIT_TIME_MILLISECOND);
            } catch (InterruptedException e) {
                logger.error("DistributedLock lock sleep error", e);
            }
        }
    }

    /**
     * 无超时等待的加锁
     *
     * @param timeoutSecond 如果为null,使用默认超时时间
     * @return 加锁的值（超时时间）
     */
    public long lock(String key, Long timeoutSecond) {

        logger.info("Thread：" + Thread.currentThread().getName() + " start lock");

        //如果参数错误
        if (timeoutSecond != null && timeoutSecond <= 0) {
            timeoutSecond = DEFAULT_TIMEOUT_SECOND;
        }
        timeoutSecond = timeoutSecond == null ? DEFAULT_TIMEOUT_SECOND : timeoutSecond;
        while (true) {
            //超时时间点
            long timeoutTimeMilli = cacheService.getCurrentTimeMilliForCache() + timeoutSecond * 1000;

            //如果设置成功
            // 若在redis中、没有相应的key值，那么可以认为，当前线程即或得该锁。
            if (cacheService.setIfAbsent(key, timeoutTimeMilli)) {
                logger.info("Thread：" + Thread.currentThread().getName() + " lock success");
                return timeoutTimeMilli;
            }

            //如果已经超时
            // 此时该key在redis已存在，获取该key的值
            Long value = cacheService.getVal(key, Long.class);
            if (value != null && value.longValue() < cacheService.getCurrentTimeMilliForCache()) {

                //设置新的超时时间
                // 如果此时获取到的oldValue，与前面获取的value相同，则说明该线程可以获得锁
                // 获得锁后，set进新值。
                Long oldValue = cacheService.getAndSet(key, timeoutTimeMilli);

                //多个线程同时getset，只有第一个才可以获取到锁
                if (value.equals(oldValue)) {
                    logger.info("Thread：" + Thread.currentThread().getName() + " lock success");
                    return timeoutTimeMilli;
                }
            }

            //延迟一定毫秒，防止请求太频繁
            try {
                Thread.sleep(LOOP_WAIT_TIME_MILLISECOND);
            } catch (InterruptedException e) {
                logger.error("DistributedLock lock sleep error", e);
            }
        }
    }

    /**
     * 释放锁
     */
    public void unLock(String key, long lockValue) {

        logger.info("Thread：" + Thread.currentThread().getName() + " start unlock");
        Long value = cacheService.getVal(key, Long.class);
        if (value != null && value.equals(lockValue)) {//如果是本线程加锁
            cacheService.deleteVal(key);
            logger.info("Thread：" + Thread.currentThread().getName() + " unlock success");
        }
    }
}