面试中又被问到Redis如何实现抢购，赶快代码实现一波吧！

Log log = LogFactory.getLog(getClass());

    @Autowired  
    private RedisTemplate<String, Object> redisTemplate;  

    @Test
    public void testSys() throws Exception{
        log.info("开始");

         MsService service = new MsService();

         for (int i = 0; i < 10; i++) {
             ThreadB threadA = new ThreadB(service, redisTemplate, "MSKEY");
             threadA.start();
             log.info("*******************结束");
         }

    }

private MsService service;
    private RedisTemplate<String,Object> redisTemplate;
    private String key;

    public ThreadB(MsService service,RedisTemplate<String,Object> redisTemplate,String key) {
        this.service = service;
        this.redisTemplate=redisTemplate;
        this.key=key;
    }

    @Override
    public void run() {
        try {
            service.seckill(redisTemplate, key);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

Log log = LogFactory.getLog(getClass());

     /***
     * 抢购代码
     * @param redisTemplate
     * @param key pronum 首先用客户端设置数量
     * @return
     * @throws InterruptedException 
     */
    public boolean seckill(RedisTemplate<String,Object> redisTemplate, String key) throws Exception {
        RedisLock lock = new RedisLock(redisTemplate, key, 10000, 20000);
        try {
            if (lock.lock()) {
                // 需要加锁的代码
                String pronum=lock.get("pronum");
                //修改库存
                if(Integer.parseInt(pronum)-1>=0) {
                    lock.set("pronum",String.valueOf(Integer.parseInt(pronum)-1));
                    log.info("库存数量:"+pronum+"     成功!!!"+Thread.currentThread().getName());
                }else {
                    log.info("已经被抢光了，请参与下轮抢购");
                }
                log.info("++++++++++++++++++++++++++++++++++++++参加了抢购");
                return true;
            } 


        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            // 为了让分布式锁的算法更稳键些，持有锁的客户端在解锁之前应该再检查一次自己的锁是否已经超时，再去做DEL操作，因为可能客户端因为某个耗时的操作而挂起，
            // 操作完的时候锁因为超时已经被别人获得，这时就不必解锁了。 ————这里没有做
            lock.unlock();
        }
        return false;
    }

public class RedisLock {

    private static Logger logger = LoggerFactory.getLogger(RedisLock.class);

    private RedisTemplate<String,Object> redisTemplate;

    private static final int DEFAULT_ACQUIRY_RESOLUTION_MILLIS = 100;

    /**
     * Lock key path.
     */
    private String lockKey;

    /**
     * 锁超时时间，防止线程在入锁以后，无限的执行等待
     */
    private int expireMsecs = 60 * 1000;

    /**
     * 锁等待时间，防止线程饥饿
     */
    private int timeoutMsecs = 10 * 1000;

    private volatile boolean locked = false;

    /**
     * Detailed constructor with default acquire timeout 10000 msecs and lock
     * expiration of 60000 msecs.
     *
     * @param lockKey
     *            lock key (ex. account:1, ...)
     */
    public RedisLock(RedisTemplate<String,Object> redisTemplate, String lockKey) {
        this.redisTemplate = redisTemplate;
        this.lockKey = lockKey + "_lock";
    }

    /**
     * Detailed constructor with default lock expiration of 60000 msecs.
     *
     */
    public RedisLock(RedisTemplate<String,Object> redisTemplate, String lockKey, int timeoutMsecs) {
        this(redisTemplate, lockKey);
        this.timeoutMsecs = timeoutMsecs;
    }

    /**
     * Detailed constructor.
     *
     */
    public RedisLock(RedisTemplate<String,Object> redisTemplate, String lockKey, int timeoutMsecs, int expireMsecs) {
        this(redisTemplate, lockKey, timeoutMsecs);
        this.expireMsecs = expireMsecs;
    }

    /**
     * @return lock key
     */
    public String getLockKey() {
        return lockKey;
    }

    public String get(final String key) {
        Object obj = null;
        try {
            obj = redisTemplate.execute(new RedisCallback<Object>() {
                @Override
                public Object doInRedis(RedisConnection connection) throws DataAccessException {
                    StringRedisSerializer serializer = new StringRedisSerializer();
                    byte[] data = connection.get(serializer.serialize(key));
                    connection.close();
                    if (data == null) {
                        return null;
                    }
                    return serializer.deserialize(data);
                }
            });
        } catch (Exception e) {
            logger.error("get redis error, key : {}", key);
        }
        return obj != null ? obj.toString() : null;
    }


    public String set(final String key,final String value) {
        Object obj = null;
        try {
            obj = redisTemplate.execute(new RedisCallback<Object>() {
                @Override
                public Object doInRedis(RedisConnection connection) throws DataAccessException {
                    StringRedisSerializer serializer = new StringRedisSerializer();
                    connection.set(serializer.serialize(key), serializer.serialize(value));
                    return serializer;
                }
            });
        } catch (Exception e) {
            logger.error("get redis error, key : {}", key);
        }
        return obj != null ? obj.toString() : null;
    }

    public boolean setNX(final String key, final String value) {
        Object obj = null;
        try {
            obj = redisTemplate.execute(new RedisCallback<Object>() {
                @Override
                public Object doInRedis(RedisConnection connection) throws DataAccessException {
                    StringRedisSerializer serializer = new StringRedisSerializer();
                    Boolean success = connection.setNX(serializer.serialize(key), serializer.serialize(value));
                    connection.close();
                    return success;
                }
            });
        } catch (Exception e) {
            logger.error("setNX redis error, key : {}", key);
        }
        return obj != null ? (Boolean) obj : false;
    }

    private String getSet(final String key, final String value) {
        Object obj = null;
        try {
            obj = redisTemplate.execute(new RedisCallback<Object>() {
                @Override
                public Object doInRedis(RedisConnection connection) throws DataAccessException {
                    StringRedisSerializer serializer = new StringRedisSerializer();
                    byte[] ret = connection.getSet(serializer.serialize(key), serializer.serialize(value));
                    connection.close();
                    return serializer.deserialize(ret);
                }
            });
        } catch (Exception e) {
            logger.error("setNX redis error, key : {}", key);
        }
        return obj != null ? (String) obj : null;
    }

    /**
     * 获得 lock. 实现思路: 主要是使用了redis 的setnx命令,缓存了锁. reids缓存的key是锁的key,所有的共享,
     * value是锁的到期时间(注意:这里把过期时间放在value了,没有时间上设置其超时时间) 执行过程:
     * 1.通过setnx尝试设置某个key的值,成功(当前没有这个锁)则返回,成功获得锁
     * 2.锁已经存在则获取锁的到期时间,和当前时间比较,超时的话,则设置新的值
     *
     * @return true if lock is acquired, false acquire timeouted
     * @throws InterruptedException
     *             in case of thread interruption
     */
    public synchronized boolean lock() throws InterruptedException {
        int timeout = timeoutMsecs;
        while (timeout >= 0) {
            long expires = System.currentTimeMillis() + expireMsecs + 1;
            String expiresStr = String.valueOf(expires); // 锁到期时间
            if (this.setNX(lockKey, expiresStr)) {
                // lock acquired
                locked = true;
                return true;
            }

            String currentValueStr = this.get(lockKey); // redis里的时间
            if (currentValueStr != null && Long.parseLong(currentValueStr) < System.currentTimeMillis()) {
                // 判断是否为空，不为空的情况下，如果被其他线程设置了值，则第二个条件判断是过不去的
                // lock is expired

                String oldValueStr = this.getSet(lockKey, expiresStr);
                // 获取上一个锁到期时间，并设置现在的锁到期时间，
                // 只有一个线程才能获取上一个线上的设置时间，因为jedis.getSet是同步的
                if (oldValueStr != null && oldValueStr.equals(currentValueStr)) {
                    // 防止误删（覆盖，因为key是相同的）了他人的锁——这里达不到效果，这里值会被覆盖，但是因为什么相差了很少的时间，所以可以接受

                    // [分布式的情况下]:如过这个时候，多个线程恰好都到了这里，但是只有一个线程的设置值和当前值相同，他才有权利获取锁
                    // lock acquired
                    locked = true;
                    return true;
                }
            }
            timeout -= DEFAULT_ACQUIRY_RESOLUTION_MILLIS;

            /*
             * 延迟100 毫秒, 这里使用随机时间可能会好一点,可以防止饥饿进程的出现,即,当同时到达多个进程,
             * 只会有一个进程获得锁,其他的都用同样的频率进行尝试,后面有来了一些进行,也以同样的频率申请锁,这将可能导致前面来的锁得不到满足.
             * 使用随机的等待时间可以一定程度上保证公平性
             */
            Thread.sleep(DEFAULT_ACQUIRY_RESOLUTION_MILLIS);

        }
        return false;
    }

    /**
     * Acqurired lock release.
     */
    public synchronized void unlock() {
        if (locked) {
            redisTemplate.delete(lockKey);
            locked = false;
        }
    }

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