购物系统,用户可以购买喜欢的商品

package www.stx.servlet; import www.stx.biz.IGoodsBiz; import www.stx.biz.ippl.GoodsBizImpl; import www.stx.pojo.Goods; import www.stx.pojo.OrderItem; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; import java.util.ArrayList; import java.util.List; //购买商品 @WebServlet("/add.do") public class AddServlet extends HttpServlet { private IGoodsBiz GoodsBiz = new GoodsBizImpl(); int j=1010; int i=0; @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doPost(req, resp); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { /** * 1.获取前端传来的信息 * 2.插入商品id，用户id 到 购物车表里 * * */ //购物车在哪里? List<OrderItem> car = (List<OrderItem>) req.getSession().getAttribute("car"); if (car == null) { // 如果购物车为空，则进行初始化 car = new ArrayList<>(); req.getSession().setAttribute("car", car); } //是哪件商品?需要用户带一个商品的id String submitId = req.getParameter("submitId"); //购物车中已经有了，数量+1 boolean f = true; try { // 可能抛出空指针异常的代码 for (OrderItem item : car) { // item就是订单项,订单项中有一个与他对应的商品 if (item.getGoods().getId().equals(Integer.parseInt(submitId))) { //数量+1 item.setQuantity(item.getQuantity() + 1); //价格需要重新计算 item.setTotal(item.getQuantity() * item.getGoods().getPrice()); f = false; break; } } //购物车中没有，添加购物车 if (f) { //生成了订单项 OrderItem item = new OrderItem(); //根据商品的id去数据库查出这件商品 Goods one = GoodsBiz.one(Integer.parseInt(submitId)); item.setId(i++); item.setOrderId(j++); item.setGoods(one); item.setQuantity(1); item.setTotal(one.getPrice()); //添加订单项到购物车 car.add(item); } req.getSession().setAttribute("total", car.stream() .mapToDouble(OrderItem::getTotal) .sum()); } catch (NullPointerException e) { e.printStackTrace(); // 处理空指针异常 } finally { //返回首页 resp.sendRedirect("index.do"); } } }