Redis实现库存扣减的解决方案防止商品超卖

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

public interface IStockCallback {

 
 int getStock();
}

@Service
public class StockService {
    Logger logger = LoggerFactory.getLogger(StockService.class);

    
    public static final long UNINITIALIZED_STOCK = -3L;

    
    @Autowired
    private RedisTemplate<String, Object> redisTemplate;

    
    public static final String STOCK_LUA;

    static {
        
        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();
    }

    
    public long stock(String key, long expire, int num, IStockCallback stockCallback) {
        long stock = stock(key, num);
        // 初始化库存
        if (stock == UNINITIALIZED_STOCK) {
            RedisLock redisLock = new RedisLock(redisTemplate, key);
            try {
                // 获取锁
                if (redisLock.tryLock()) {
                    // 双重验证，避免并发时重复回源到数据库
                    stock = stock(key, num);
                    if (stock == UNINITIALIZED_STOCK) {
                        // 获取初始化库存
                        final int initStock = stockCallback.getStock();
                        // 将库存设置到redis
                        redisTemplate.opsForValue().set(key, initStock, expire, TimeUnit.SECONDS);
                        // 调一次扣库存的操作
                        stock = stock(key, num);
                    }
                }
            } catch (Exception e) {
                logger.error(e.getMessage(), e);
            } finally {
                redisLock.unlock();
            }

        }
        return stock;
    }

    
    public long addStock(String key, int num) {

        return addStock(key, null, num);
    }

    
    public long addStock(String key, Long expire, int num) {
        boolean hasKey = redisTemplate.hasKey(key);
        // 判断key是否存在，存在就直接更新
        if (hasKey) {
            return redisTemplate.opsForValue().increment(key, num);
        }

        Assert.notNull(expire,"初始化库存失败，库存过期时间不能为null");
        RedisLock redisLock = new RedisLock(redisTemplate, key);
        try {
            if (redisLock.tryLock()) {
                // 获取到锁后再次判断一下是否有key
                hasKey = redisTemplate.hasKey(key);
                if (!hasKey) {
                    // 初始化库存
                    redisTemplate.opsForValue().set(key, num, expire, TimeUnit.SECONDS);
                }
            }
        } catch (Exception e) {
            logger.error(e.getMessage(), e);
        } finally {
            redisLock.unlock();
        }

        return num;
    }

    
    public int getStock(String key) {
        Integer stock = (Integer) redisTemplate.opsForValue().get(key);
        return stock == null ? -1 : stock;
    }

    
    private Long stock(String key, int num) {
        // 脚本里的KEYS参数
        List<String> keys = new ArrayList<>();
        keys.add(key);
        // 脚本里的ARGV参数
        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();
                // 集群模式和单机模式虽然执行脚本的方法一样，但是没有共同的接口，所以只能分开执行
                // 集群模式
                if (nativeConnection instanceof JedisCluster) {
                    return (Long) ((JedisCluster) nativeConnection).eval(STOCK_LUA, keys, args);
                }

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

@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;
        // 库存ID
        String redisKey = "redis_key:stock:" + commodityId;
        long stock = stockService.stock(redisKey, 60 * 60, 2, () -> initStock(commodityId));
        return stock >= 0;
    }

    
    private int initStock(long commodityId) {
        // TODO 这里做一些初始化库存的操作
        return 1000;
    }

    @RequestMapping(value = "getStock", produces = MediaType.APPLICATION_jsON_UTF8_VALUE)
    public Object getStock() {
        // 商品ID
        long commodityId = 1;
        // 库存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;
        // 库存ID
        String redisKey = "redis_key:stock:" + commodityId;

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