Java连接数据库 #06# SQL与代码分离（精化版本）

索引

• DAO层依赖关系草图
• 应用示例

接Java连接数据库#05#，对代码进行改进。

DAO层依赖关系草图

应用示例（只需3步！）

1、首先定义接口类：

package org.sample.shop.common.dao;

import org.sample.shop.common.entity.Cart;
import org.sample.shop.common.entity.Order;

import java.util.List;

public interface CartDAO {

    int addItem(Long uid, Long itemId);

    int removeItem(Long id);

    int removeAll(Long uid); // 清空购物车

    List<Cart> listByUid(Long uid);

    Order getPreOrder(Long uid);
}

2、然后书写相应的SQL以及返回类型（id的默认格式是“文件名_方法名”）：

<sql id="cart_addItem">
    INSERT INTO cart(user_id, item_id)
    VALUES (?, ?)
</sql>
<sql id="cart_removeAll">
    DELETE FROM cart WHERE user_id=?
</sql>
<sql id="cart_removeItem">
    DELETE FROM cart WHERE id=?
</sql>
<sql id="cart_getByUid" type="org.sample.shop.common.entity.Cart">
    SELECT id, user_id AS userId, item_id AS itemId FROM cart WHERE user_id=?
</sql>
<sql id="cart_getPreOrder" type="org.sample.shop.common.entity.OrderDetail">
    SELECT cart.id, item_id AS itemId, item.user_id AS userId, price
    FROM cart
    LEFT JOIN item ON cart.item_id = item.id
    WHERE cart.user_id=?
</sql>
<sql id="cart_getSum" type="java.lang.Number">
    SELECT SUM(price) AS sum
    FROM cart
    LEFT JOIN item ON cart.item_id = item.id
    WHERE cart.user_id=?
</sql>

3、最后，通过QueryRunnerProxy执行SQL并拿到所需对象。

package org.sample.shop.common.dao.impl;

import org.sample.shop.common.dao.CartDAO;
import org.sample.shop.common.db.QueryRunnerProxy;
import org.sample.shop.common.entity.Cart;
import org.sample.shop.common.entity.Order;
import org.sample.shop.common.entity.OrderDetail;

import java.util.List;
import java.util.Map;

public class CartDAOImpl implements CartDAO {

    @Override
    public int addItem(Long uid, Long itemId) {
        return QueryRunnerProxy.update("cart_addItem", uid, itemId);
    }

    @Override
    public int removeItem(Long id) {
        return QueryRunnerProxy.update("cart_removeItem", id);
    }

    @Override
    public int removeAll(Long uid) {
        return QueryRunnerProxy.update("cart_removeAll", uid);
    }

    @Override
    public List<Cart> listByUid(Long uid) {
        return QueryRunnerProxy.query("cart_getByUid", uid);
    }

    @Override
    public Order getPreOrder(Long uid) {
        Order order = new Order();
        order.setUserId(uid); // 设置买家id
        // 1. 查总价
        List<Map> mapList = QueryRunnerProxy.query("cart_getSum", uid);
        Double total = Double.parseDouble(mapList.get(0).get("sum").toString());
        order.setTotal(total);
        // 2. 查对应的物品清单
        List<OrderDetail> details = QueryRunnerProxy.query("cart_getPreOrder", uid);
        order.setDetails(details);
        return order;
    }
}

具体实现代码参考github：https://github.com/xkfx/simple-shop

不过还有一些线程安全方面的隐患待解决。。。。。。。。。。。。。