连接数据库的简易购物车

好的，以下是一个简易的购物车示例，包含连接数据库的部分：

1. 创建一个数据库表，用于存储购物车信息，例如：

CREATE TABLE `cart` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `user_id` int(11) NOT NULL,
  `product_id` int(11) NOT NULL,
  `quantity` int(11) NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `uniq_user_product` (`user_id`,`product_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

2. 创建一个购物车实体类，例如：

public class Cart {
    private int id;
    private int userId;
    private int productId;
    private int quantity;

    public Cart() {}

    public Cart(int userId, int productId, int quantity) {
        this.userId = userId;
        this.productId = productId;
        this.quantity = quantity;
    }

    //省略getter和setter方法
}

3. 创建一个购物车数据访问对象（DAO），用于实现对购物车表的增删改查操作，例如：

public class CartDao {
    private Connection conn = null;
    private PreparedStatement ps = null;
    private ResultSet rs = null;

    public CartDao() {
        conn = DBUtil.getConnection(); //获取数据库连接
    }

    //添加购物车记录
    public void addCart(Cart cart) {
        String sql = "INSERT INTO cart(user_id, product_id, quantity) VALUES(?, ?, ?)";
        try {
            ps = conn.prepareStatement(sql);
            ps.setInt(1, cart.getUserId());
            ps.setInt(2, cart.getProductId());
            ps.setInt(3, cart.getQuantity());
            ps.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            DBUtil.close(conn, ps, rs); //关闭数据库连接
        }
    }

    //更新购物车记录
    public void updateCart(Cart cart) {
        String sql = "UPDATE cart SET quantity=? WHERE user_id=? AND product_id=?";
        try {
            ps = conn.prepareStatement(sql);
            ps.setInt(1, cart.getQuantity());
            ps.setInt(2, cart.getUserId());
            ps.setInt(3, cart.getProductId());
            ps.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            DBUtil.close(conn, ps, rs); //关闭数据库连接
        }
    }

    //删除购物车记录
    public void deleteCart(int userId, int productId) {
        String sql = "DELETE FROM cart WHERE user_id=? AND product_id=?";
        try {
            ps = conn.prepareStatement(sql);
            ps.setInt(1, userId);
            ps.setInt(2, productId);
            ps.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            DBUtil.close(conn, ps, rs); //关闭数据库连接
        }
    }

    //查询购物车记录
    public Cart getCart(int userId, int productId) {
        String sql = "SELECT * FROM cart WHERE user_id=? AND product_id=?";
        Cart cart = null;
        try {
            ps = conn.prepareStatement(sql);
            ps.setInt(1, userId);
            ps.setInt(2, productId);
            rs = ps.executeQuery();
            if (rs.next()) {
                cart = new Cart();
                cart.setId(rs.getInt("id"));
                cart.setUserId(rs.getInt("user_id"));
                cart.setProductId(rs.getInt("product_id"));
                cart.setQuantity(rs.getInt("quantity"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            DBUtil.close(conn, ps, rs); //关闭数据库连接
        }
        return cart;
    }
}

4. 在Servlet中实现加入购物车的逻辑，例如：

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //获取用户ID和商品ID
    int userId = Integer.parseInt(request.getParameter("userId"));
    int productId = Integer.parseInt(request.getParameter("productId"));

    //查询购物车中是否已经存在该商品
    CartDao cartDao = new CartDao();
    Cart cart = cartDao.getCart(userId, productId);

    if (cart == null) { //购物车中不存在该商品，添加一条新记录
        cart = new Cart(userId, productId, 1);
        cartDao.addCart(cart);
    } else { //购物车中已经存在该商品，将数量加1
        cart.setQuantity(cart.getQuantity() + 1);
        cartDao.updateCart(cart);
    }

    //跳转到购物车页面
    response.sendRedirect("cart.jsp");
}

注意：以上示例代码仅供参考，实际开发中需要根据具体情况进行修改和调整。此外，为了保证安全性，需要对SQL语句进行预编译和参数化处理，防止SQL注入攻击。