做秒杀，先把功能做出来再进行优化，因此本节主要实现下单的一个基本流程。

1. 表设计

商品表：

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CREATE TABLE `goods`(
	`id` BIGINT(20) NOT NULL AUTO_INCREMENT COMMENT '商品ID',
	`goods_name` VARCHAR(16) DEFAULT NULL COMMENT '商品名称',
	`goods_title` VARCHAR(64) DEFAULT NULL COMMENT '商品标题',
	`goods_img` VARCHAR(64) DEFAULT NULL COMMENT '商品图片',
	`goods_detail` LONGTEXT COMMENT '商品的详情介绍',
	`goods_price` DECIMAL(10,2) DEFAULT '0.00' COMMENT '商品单价',
	`goods_stock` INT(11) DEFAULT '0' COMMENT '商品库存，-1表示没有限制',
	PRIMARY KEY (`id`)
);

秒杀商品表：

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CREATE TABLE `miaosha_goods`(
	`id` BIGINT(20) NOT NULL AUTO_INCREMENT COMMENT '秒杀商品ID',
	`goods_id` BIGINT(16) DEFAULT NULL COMMENT '商品id',
	`miaosha_price` DECIMAL(10,2) DEFAULT '0.00' COMMENT '秒杀价',
	`stock_count` INT(11) DEFAULT '0' COMMENT '库存数量',
	`start_date` datetime DEFAULT NULL COMMENT '秒杀开始时间',
	`end_date` datetime DEFAULT NULL COMMENT '秒杀结束时间',
	PRIMARY KEY (`id`)
);

订单信息表：

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CREATE TABLE `order_info`(
	`id` BIGINT(20) NOT NULL AUTO_INCREMENT COMMENT 'order ID',
	`user_id` BIGINT(20) DEFAULT NULL COMMENT '用户id',
	`goods_id` BIGINT(20) DEFAULT NULL COMMENT '商品id',
	`delivery_addr_id` BIGINT(20) DEFAULT NULL COMMENT '收货地址',
	`goods_name` VARCHAR(16) DEFAULT NULL COMMENT '商品名称',
	`goods_count` INT(11) DEFAULT '0' COMMENT '商品数量',
	`goods_price` DECIMAL(10,2) DEFAULT '0.00' COMMENT '商品单价',
	`order_channel` TINYINT(4) DEFAULT '0' COMMENT '1pc,2android,3ios',
	`status` TINYINT(4) DEFAULT '0' COMMENT '0新建未支付，2已支付，3已发货4，已收货，5已完成',
	`create_date` datetime DEFAULT NULL COMMENT '订单创建时间',
	`pay_date` datetime DEFAULT NULL COMMENT '支付时间',
	PRIMARY KEY (`id`)
);

秒杀订单表：

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CREATE TABLE `miaosha_order`(
	`id` BIGINT(20) NOT NULL AUTO_INCREMENT COMMENT '秒杀 order ID',
	`user_id` BIGINT(20) DEFAULT NULL COMMENT '用户id',
	`order_id` BIGINT(20) DEFAULT NULL COMMENT '订单id',
	`goods_id` BIGINT(20) DEFAULT NULL COMMENT '商品id',
	PRIMARY KEY (`id`)
);

2. 商品列表页展示

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@Mapper
public interface GoodsDao {

    @Select("select g.*,mg.stock_count,mg.start_date,mg.end_date,mg.miaosha_price from miaosha_goods mg left join goods g on mg.goods_id = g.id")
    List<GoodsVo> getGoodsVoList();
}

注意要创建一个vo对象来承载goods和miaosha_goods两个对象。

另外注意，之前的yml中对于mybatis的配置，忘记了配置驼峰写法：

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configuration:
    map-underscore-to-camel-case: true

jsp就不贴在这了。

3. 商品详情页面

接收前端传来的goods_id，因为要处理显示秒杀活动还剩多少秒，所以进行了相应的判断，以及秒杀的状态。

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@RequestMapping("/to_detail/{goodsId}")
public String toList(@PathVariable("goodsId") long goodsId,Model model, MiaoshaUser user){
    if(user == null)
        return "login";
    model.addAttribute("user",user);

    GoodsVo goodsVo = goodsService.getGoodsVoByGoodsId(goodsId);
    model.addAttribute("goods",goodsVo);
    long startAt = goodsVo.getStartDate().getTime();
    long endAt = goodsVo.getEndDate().getTime();
    long now = System.currentTimeMillis();
    int miaoshaStatus = 0;//秒杀活动的状态，0-秒杀前；1-正在秒杀；2-秒杀结束
    int remainSeconds = 0;//秒杀活动还剩多少秒
    if(now < startAt){
        miaoshaStatus = Constants.MiaoshaStatus.BEFORE_START;
        remainSeconds = (int)(startAt-now)/1000;
    }else if (now > endAt){
        miaoshaStatus = Constants.MiaoshaStatus.AFTER_MIAOSHA;
        remainSeconds = -1;
    }else {
        miaoshaStatus = Constants.MiaoshaStatus.ON_MIAOSHA;
        remainSeconds = 0;
    }

    model.addAttribute("miaoshaStatus",miaoshaStatus);
    model.addAttribute("remainSeconds",remainSeconds);
    return "goods_detail";
}

对于前端，只需要拿到这个remainSeconds就可以了，可以对应显示秒杀还剩多久、秒杀是否结束等。

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function countDown(){
	var remainSeconds = $("#remainSeconds").val();
	var timeout;
	if(remainSeconds > 0){//秒杀还没开始，倒计时
		$("#buyButton").attr("disabled", true);
		timeout = setTimeout(function(){
			$("#countDown").text(remainSeconds - 1);
			$("#remainSeconds").val(remainSeconds - 1);
			countDown();
		},1000);
	}else if(remainSeconds == 0){//秒杀进行中
		$("#buyButton").attr("disabled", false);
		if(timeout){
			clearTimeout(timeout);
		}
		$("#miaoshaTip").html("秒杀进行中");
	}else{//秒杀已经结束
		$("#buyButton").attr("disabled", true);
		$("#miaoshaTip").html("秒杀已经结束");
	}
}

4. 秒杀功能实现

判断库存
   |
根据userId和goodsId判断是否已经抢过了
   |
减库存，下订单，并且写入秒杀订单(同一事务中完成)

判断库存：

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//判断库存
GoodsVo goodsVo = goodsService.getGoodsVoByGoodsId(goodsId);
if(goodsVo.getStockCount() <= 0){
    model.addAttribute("errmsg", CodeMsg.MIAO_SHA_OVER.getMsg());
    return "miaosha_fail";
}

判断是否已经抢过了：

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//判断是否已经秒杀到了
MiaoshaOrder miaoshaOrder = orderService.getMiaoshaOrderByUserIdGoodsId(user.getId(),goodsId);
if(miaoshaOrder != null){
    model.addAttribute("errmsg", CodeMsg.REPEATE_MIAOSHA.getMsg());
    return "miaosha_fail";
}

减库存，下订单，并且写入秒杀订单(同一事务中完成)：

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//减库存、下订单、写入秒杀订单,需要在一个事务中执行
OrderInfo orderInfo = miaoshaService.miaosha(user,goodsVo);

在MiaoshaService中写：

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@Transactional
public OrderInfo miaosha(MiaoshaUser user, GoodsVo goods) {
    //减库存、下订单、写入秒杀订单
    boolean success =goodsService.reduceStock(goods);
    if(success){
        return orderService.createOrder(user,goods);
    }else{
        return null;
    }
}

对于减库存：

这里只需要减miaosha_goods表里的库存即可。因为秒杀的数据是先从goods表里得到的，所以goods表里的库存此段已经减掉了。

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@Update("update miaosha_goods set stock_count = stock_count-1 where goods_id=#{goodsId}")
int reduceStock(MiaoshaGoods g);
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public boolean reduceStock(GoodsVo goods) {
    MiaoshaGoods g = new MiaoshaGoods();
    g.setGoodsId(goods.getId());
    int ret = goodsDao.reduceStock(g);
    return ret > 0;
}

对于创建订单：先是普通的order_info表插入，还有一个是miaosha_order表插入，那么就要在一个事务中执行。

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@Transactional
public OrderInfo createOrder(MiaoshaUser user, GoodsVo goods) {
    OrderInfo orderInfo = new OrderInfo();
    orderInfo.setCreateDate(new Date());
    orderInfo.setDeliveryAddrId(0L);
    orderInfo.setGoodsCount(1);
    orderInfo.setGoodsId(goods.getId());
    orderInfo.setGoodsName(goods.getGoodsName());
    orderInfo.setGoodsPrice(goods.getMiaoshaPrice());
    orderInfo.setOrderChannel(1);
    orderInfo.setStatus(Constants.OrderStatus.NOT_PAID.getStatus());//新建未支付
    orderInfo.setUserId(user.getId());

    orderDao.insert(orderInfo);

    MiaoshaOrder miaoshaOrder = new MiaoshaOrder();
    miaoshaOrder.setGoodsId(goods.getId());
    miaoshaOrder.setOrderId(orderInfo.getId());
    miaoshaOrder.setUserId(user.getId());

    orderDao.insertMiaoshaOrder(miaoshaOrder);

    return orderInfo;
}

对于，orderDao.insert(orderInfo)的具体实现：

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@Insert("insert into order_info(user_id,goods_id,goods_name,goods_price,goods_count,order_channel,status,create_date) " +
            "values(#{userId},#{goodsId},#{goodsName},#{goodsPrice},#{goodsCount},#{orderChannel},#{status},#{" +
            "createDate})")
@SelectKey(keyColumn = "id",keyProperty = "id",resultType = long.class,before = false,statement = "select last_insert_id()")
long insert(OrderInfo orderInfo);

对于orderDao.insertMiaoshaOrder(miaoshaOrder)的具体实现：

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@Insert("insert into miaosha_order(user_id,goods_id,order_id)values(#{userId},#{goodsId},#{orderId})")
int insertMiaoshaOrder(MiaoshaOrder miaoshaOrder);

下单成功的话，就跳到订单详情页面：

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return "order_detail";

否则跳到错误提示页面：

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return "miaosha_fail";