update number set x=x-1 where x > 0

/**
 * 獲取庫存回調(diào)
 * @author yuhao.wang
 */
public interface IStockCallback {

 /**
  * 獲取庫存
  * @return
  */
 int getStock();
}

/**
 * 扣庫存
 *
 * @author yuhao.wang
 */
@Service
public class StockService {
    Logger logger = LoggerFactory.getLogger(StockService.class);

    /**
     * 不限庫存
     */
    public static final long UNINITIALIZED_STOCK = -3L;

    /**
     * Redis 客戶端
     */
    @Autowired
    private RedisTemplate<String, Object> redisTemplate;

    /**
     * 執(zhí)行扣庫存的腳本
     */
    public static final String STOCK_LUA;

    static {
        /**
         *
         * @desc 扣減庫存Lua腳本
         * 庫存（stock）-1：表示不限庫存
         * 庫存（stock）0：表示沒有庫存
         * 庫存（stock）大于0：表示剩余庫存
         *
         * @params 庫存key
         * @return
         *   -3:庫存未初始化
         *   -2:庫存不足
         *   -1:不限庫存
         *   大于等于0:剩余庫存（扣減之后剩余的庫存）
         *      redis緩存的庫存(value)是-1表示不限庫存，直接返回1
         */
        StringBuilder sb = new StringBuilder();
        sb.append("if (redis.call('exists', KEYS[1]) == 1) then");
        sb.append("    local stock = tonumber(redis.call('get', KEYS[1]));");
        sb.append("    local num = tonumber(ARGV[1]);");
        sb.append("    if (stock == -1) then");
        sb.append("        return -1;");
        sb.append("    end;");
        sb.append("    if (stock >= num) then");
        sb.append("        return redis.call('incrby', KEYS[1], 0 - num);");
        sb.append("    end;");
        sb.append("    return -2;");
        sb.append("end;");
        sb.append("return -3;");
        STOCK_LUA = sb.toString();
    }

    /**
     * @param key           庫存key
     * @param expire        庫存有效時間,單位秒
     * @param num           扣減數(shù)量
     * @param stockCallback 初始化庫存回調(diào)函數(shù)
     * @return -2:庫存不足; -1:不限庫存; 大于等于0:扣減庫存之后的剩余庫存
     */
    public long stock(String key, long expire, int num, IStockCallback stockCallback) {
        long stock = stock(key, num);
        // 初始化庫存
        if (stock == UNINITIALIZED_STOCK) {
            RedisLock redisLock = new RedisLock(redisTemplate, key);
            try {
                // 獲取鎖
                if (redisLock.tryLock()) {
                    // 雙重驗(yàn)證，避免并發(fā)時重復(fù)回源到數(shù)據(jù)庫
                    stock = stock(key, num);
                    if (stock == UNINITIALIZED_STOCK) {
                        // 獲取初始化庫存
                        final int initStock = stockCallback.getStock();
                        // 將庫存設(shè)置到redis
                        redisTemplate.opsForValue().set(key, initStock, expire, TimeUnit.SECONDS);
                        // 調(diào)一次扣庫存的操作
                        stock = stock(key, num);
                    }
                }
            } catch (Exception e) {
                logger.error(e.getMessage(), e);
            } finally {
                redisLock.unlock();
            }

        }
        return stock;
    }

    /**
     * 加庫存(還原庫存)
     *
     * @param key    庫存key
     * @param num    庫存數(shù)量
     * @return
     */
    public long addStock(String key, int num) {

        return addStock(key, null, num);
    }

    /**
     * 加庫存
     *
     * @param key    庫存key
     * @param expire 過期時間（秒）
     * @param num    庫存數(shù)量
     * @return
     */
    public long addStock(String key, Long expire, int num) {
        boolean hasKey = redisTemplate.hasKey(key);
        // 判斷key是否存在，存在就直接更新
        if (hasKey) {
            return redisTemplate.opsForValue().increment(key, num);
        }

        Assert.notNull(expire,"初始化庫存失敗，庫存過期時間不能為null");
        RedisLock redisLock = new RedisLock(redisTemplate, key);
        try {
            if (redisLock.tryLock()) {
                // 獲取到鎖后再次判斷一下是否有key
                hasKey = redisTemplate.hasKey(key);
                if (!hasKey) {
                    // 初始化庫存
                    redisTemplate.opsForValue().set(key, num, expire, TimeUnit.SECONDS);
                }
            }
        } catch (Exception e) {
            logger.error(e.getMessage(), e);
        } finally {
            redisLock.unlock();
        }

        return num;
    }

    /**
     * 獲取庫存
     *
     * @param key 庫存key
     * @return -1:不限庫存; 大于等于0:剩余庫存
     */
    public int getStock(String key) {
        Integer stock = (Integer) redisTemplate.opsForValue().get(key);
        return stock == null ? -1 : stock;
    }

    /**
     * 扣庫存
     *
     * @param key 庫存key
     * @param num 扣減庫存數(shù)量
     * @return 扣減之后剩余的庫存【-3:庫存未初始化; -2:庫存不足; -1:不限庫存; 大于等于0:扣減庫存之后的剩余庫存】
     */
    private Long stock(String key, int num) {
        // 腳本里的KEYS參數(shù)
        List<String> keys = new ArrayList<>();
        keys.add(key);
        // 腳本里的ARGV參數(shù)
        List<String> args = new ArrayList<>();
        args.add(Integer.toString(num));

        long result = redisTemplate.execute(new RedisCallback<Long>() {
            @Override
            public Long doInRedis(RedisConnection connection) throws DataAccessException {
                Object nativeConnection = connection.getNativeConnection();
                // 集群模式和單機(jī)模式雖然執(zhí)行腳本的方法一樣，但是沒有共同的接口，所以只能分開執(zhí)行
                // 集群模式
                if (nativeConnection instanceof JedisCluster) {
                    return (Long) ((JedisCluster) nativeConnection).eval(STOCK_LUA, keys, args);
                }

                // 單機(jī)模式
                else if (nativeConnection instanceof Jedis) {
                    return (Long) ((Jedis) nativeConnection).eval(STOCK_LUA, keys, args);
                }
                return UNINITIALIZED_STOCK;
            }
        });
        return result;
    }
}

/**
 * @author yuhao.wang
 */
@RestController
public class StockController {

    @Autowired
    private StockService stockService;

    @RequestMapping(value = "stock", produces = MediaType.APPLICATION_JSON_UTF8_VALUE)
    public Object stock() {
        // 商品ID
        long commodityId = 1;
        // 庫存ID
        String redisKey = "redis_key:stock:" + commodityId;
        long stock = stockService.stock(redisKey, 60 * 60, 2, () -> initStock(commodityId));
        return stock >= 0;
    }

    /**
     * 獲取初始的庫存
     *
     * @return
     */
    private int initStock(long commodityId) {
        // TODO 這里做一些初始化庫存的操作
        return 1000;
    }

    @RequestMapping(value = "getStock", produces = MediaType.APPLICATION_JSON_UTF8_VALUE)
    public Object getStock() {
        // 商品ID
        long commodityId = 1;
        // 庫存ID
        String redisKey = "redis_key:stock:" + commodityId;

        return stockService.getStock(redisKey);
    }

    @RequestMapping(value = "addStock", produces = MediaType.APPLICATION_JSON_UTF8_VALUE)
    public Object addStock() {
        // 商品ID
        long commodityId = 2;
        // 庫存ID
        String redisKey = "redis_key:stock:" + commodityId;

        return stockService.addStock(redisKey, 2);
    }
}