案例：实现在购物车中添加商品和删除购物车中指定商品的功能

一、向购物车中添加商品

1.1.创建AddCartServlet

public class AddCartServlet extends HttpServlet {
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		doPost(request, response);
	}
	@SuppressWarnings("unchecked")
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		// 1.得到商品id
		String id = request.getParameter("id");
		// 2.调用service层方法，根据id查找商品
		ProductService service = new ProductService();
		try {
			Product p = service.findProductById(id);
			//3.将商品添加到购物车
			//3.1获得session对象
			HttpSession session = request.getSession();
			//3.2从session中获取购物车对象
			Map cart = (Map)session.getAttribute("cart");
			//3.3如果购物车为null,说明没有商品存储在购物车中，创建出购物车
			if (cart == null) {
				cart = new HashMap();
			}
			//3.4向购物车中添加商品
			Integer count = cart.put(p, 1);//returns: the previous value associated with key, or null if there was no mapping for key.
			//3.5如果商品数量不为空，则商品数量+1，否则添加新的商品信息
			if (count != null) {
				cart.put(p, count + 1);
			}			
			session.setAttribute("cart", cart);
			response.sendRedirect(request.getContextPath() + "/client/cart.jsp");
			return;
		} catch (FindProductByIdException e) {
			e.printStackTrace();
		}
	}
}

1.2.编写购物车页面cart.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<%@taglib prefix="p" uri="http://www.itcast.cn/tag"%>








	
	
	
	

		

			

				

					

						首页
						    >    购物车
					
					

						

							

								
								

									

										

											
										
									
									

										

											

												

													
序号
													
商品名称
													
价格
													
       数量
													
库存
													
小计
													
取消
												
											
											
											 
											
												

													

														
${vs.count}
														
${entry.key.name }
														
${entry.key.price }
														

														    
															
															 
															
															
															
														
														
${entry.key.pnum}
														
${entry.key.price*entry.value}
														

														    
															X
														
													
												
												
											

											

												

													

														合计：  ${total}元
													
												
											
											

											    
												
													
												
												    
                                                 
												
													
												
											
										
									
								
							
						
					
				
			
		
	
	

二、删除购物车中指定商品

创建ChangeCartServlet

/**
 * 购物车内容变更
 * @author admin
 *
 */
public class ChangeCartServlet extends HttpServlet {
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		doPost(request, response);
	}
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		// 1.得到商品id
		String id = request.getParameter("id");
		// 2.得到要修改的数量
		int count = Integer.parseInt(request.getParameter("count"));
		// 3.从session中获取购物车.
		HttpSession session = request.getSession();
		Map cart = (Map) session.getAttribute("cart");
		Product p = new Product();
		p.setId(id);
		if (count != 0) {
			cart.put(p, count);
		} else {
			cart.remove(p);
		}
		response.sendRedirect(request.getContextPath() + "/client/cart.jsp");
		return;
	}
}