代码清单4-5 listItem()函数

原版代码：

    public boolean listItem(
            Jedis conn, String itemId, String sellerId, double price) {

        String inventory = "inventory:" + sellerId;
        String item = itemId + '.' + sellerId;
        long end = System.currentTimeMillis() + 5000;

        while (System.currentTimeMillis() < end) {
            conn.watch(inventory);
            if (!conn.sismember(inventory, itemId)){
                conn.unwatch();
                return false;
            }
            Transaction trans = conn.multi();
            trans.zadd("market:", price, item);
            trans.srem(inventory, itemId);
            List<Object> results = trans.exec();
            // null response indicates that the transaction was aborted due to
            // the watched key changing.
            if (results == null){
                continue;
            }
            return true;
        }
        return false;
    }

在实际项目运行的改进代码

public boolean listItem(Jedis conn, String itemId, String sellerId, double price) {
        //1.执行初始化操作：拼接字符串得到key值
        String  inventory=new StringBuffer().append("inventory:").append(sellerId).toString();
        String  item=new StringBuffer().append(itemId).append(".").append(sellerId).toString();   
        long end = System.currentTimeMillis() + 5000;
        while (System.currentTimeMillis() < end) {
            //2.对卖家包裹进行监视
            conn.watch(inventory);
            //3.验证卖家想要销售的商品是否存在与卖家的包裹当中
            if (!conn.sismember(inventory, itemId)){
                conn.unwatch();
                return false;
            }
            //商品存在于卖家的包裹之中，开启事物
            Transaction trans = conn.multi();
            //在商品添加到买卖市场中
            trans.zadd("market:", price, item);
            //移除卖家包裹中的商品
            trans.srem(inventory, itemId);
            //提交事物
            List<Object> results = trans.exec();
            // null response indicates that the transaction was aborted due to
            // the watched key changing.
            //判断事物是否成功执行
            if (results == null){
                //事物执行失败，继续执行事物
                continue;
            }
            //事物执行成功，返回
            return true;
        }
        conn.close();
        //超时
        return false;
    }