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本篇内容介绍了“如何实现Javabean与JSP的购物车功能”的有关知识，在实际案例的操作过程中，不少人都会遇到这样的困境，接下来就让小编带领大家学习一下如何处理这些情况吧！希望大家仔细阅读，能够学有所成！
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首先呢，在买了东西之后要放在购物车里，当车子里的物品有相同时就叠加，不再创建物品对象，有了物品之后肯 定要有价格，数量等等对象。这些对象我们要封装在JAVABEAN 中的！有了Javabean就需要建立SERVLET来进行与业务层连接，我们就需要有，增加购物车，删除购物车，清楚购物车等一系列的Servlet和SERVICE层连接！SERVICE层调用DAO层，这些步骤正体现出了MVC的设计模式！下面我们看具体的实现基于Javabean与JSP的购物车功能吧！
(1) 1. 代表购物车的ShoppingCart 类
public class ShoppingCart { //装载 ShoppingCartItem 的数据结构: Map, 键： 书的 id, 值: 书对应的 ShoppingCartItem private Map books = null; public ShoppingCart(){ books = new HashMap(); } public Map getBooks() { return books; } public Book getBook(String bookId){ Book book = null; ShoppingCartItem sci = this.books.get(bookId); if (sci == null) return null; return sci.getBook (); } public float getTotalPrice(){ float totalPrice = 0.0f; //对 books 中的 value 进行遍历, 取其 price 属性的和 Iterator iterator = books.values().iterator (); while(iterator.hasNext()){ ShoppingCartItem sci = iterator.next(); totalPrice += sci.getPrice(); } return totalPrice; } public int getTotalQuantity(){ int quantity = 0; //对 books 中的 value 进行遍历, 取其 quantity 属性的和 Iterator iterator = books.values().iterator(); while(iterator.hasNext()) { ShoppingCartItem sci = iterator.next(); quantity += sci.getQuantity(); } return quantity; } public boolean isExistInShoppingCart(String bookId){ return this.books.get(bookId) != null; } public ShoppingCartItem getShoppingCartItemByBookId(String bookId){ return this.books.get(bookId); } public void addNewItemToShoppingCart(ShoppingCartItem sci) { this.books.put(sci.getBook().getId(), sci); } } 2. 代表购物车中的物品
public class ShoppingCartItem { //具体指向某本书 private Book book; //当前商品在购物车中的数量 private int quantity; public ShoppingCartItem(Book book) { this.book = book; this.quantity = 1; } //当前商品的总价格 private float price; public void incrementQuantity(){ this.quantity++; } public Book getBook() { return book; } public void setBook(Book book) { this.book = book; } public int getQuantity() { return quantity; } public void setQuantity(int quantity) { this.quantity = quantity; } public float getPrice() { return this.book.getPrice() * this.quantity; } }(2)建立DAO,此时有人会问，这次DAO为什么没有购物车呢，因为购物车是没有数据的，而是里面的物品才有 数据的，当有更新购物车里面的物品时才会早DAO里面写方法！
public class BookDAO { // public void upadateBookQuantityByBookId(Connection conn, String bookId, int quantity){ String sql = "UPDATE books SET saleAmount = saleAmount + ? WHERE id = ?"; Object [] params = new Object[]{quantity, bookId}; QueryRunner queryRunner = new QueryRunner (); try { queryRunner.update(conn, sql, params); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); throw new RuntimeException (MyBookStoreConstants.UPDATE_BOOK_SALEAMOUNT_BY_BOOK_ID_EXCEPTION); } }(3) 建立业务层,涉及到添加，清空等方法！这边佟刚老师的代码都有详细的解释！
public class BookService { //根据给定的 ShoppingCart 对象, 调用 DAO 方法进行数据库更新操作 public void buyBooks(ShoppingCart sc){ //对 sc 中的 ShoppingCartItem 对象进行遍历, 调用 BookDAO.upadateBookQuantityByBookId 方法 Connection conn = null; conn = DBHelper.getConnection(); try { Iterator shoppingCartItemSet = sc.getBooks().values ().iterator(); BookDAO bookDAO = new BookDAO (); while(shoppingCartItemSet.hasNext()) { ShoppingCartItem sci = shoppingCartItemSet.next (); String bookId = sci.getBook().getId (); int quantity = sci.getQuantity (); bookDAO.upadateBookQuantityByBookId(conn, bookId, quantity); } }finally { DBHelper.releaseDBSource(null, null, conn); } } //参数 items 中的键为 书的 id 号, 值为购 物车中对应的 数量 public void updateShoppingCart(Map items, ShoppingCart sc){ Set keySet = null; keySet = items.keySet (); for(Iterator it = keySet.iterator(); it.hasNext(); ) { String bookId = it.next(); int quantity = items.get (bookId); if(quantity <= 0) { sc.getBooks().remove(bookId); }else { sc.getShoppingCartItemByBookId(bookId).setQuantity (quantity); } } } //清空购物车 public void clearShoppingCart(ShoppingCart sc) { sc.getBooks().clear(); } public void deleteShoppingCartItemById(String id, ShoppingCart sc){ //删除 sc 中的 id 元素 sc.getBooks().remove(id); } //把 id 对应的 ShoppingCartItem 对象放入购物车 ShoppingCart 对象中 public void addToShoppingCart(String id, ShoppingCart sc) { //1. 查看 sc 中有没有 id 对应的 ShoppingCartItem 对象 if(sc.isExistInShoppingCart(id)){ //1.1 有: 把该对象取出, 使其数量 + 1, 调用 sci.increseQuantity(); 方法 ShoppingCartItem scsci = sc.getShoppingCartItemByBookId(id); sci.incrementQuantity(); } //1.2 没有: 创建一个新的 ShoppingCartItem 对象, 并将其放入 sc 中, 以书的 id 作为键 else{ //1.2.1 根据 id 获取相应的 Book 对象, 调用 BookDAO 的 selectBookByBookId() 方法 Book book = null; BookDAO bookDAO = null; bookDAO = new BookDAO(); book = bookDAO.selectBookByBookId(id); ShoppingCartItem sci = null; sci = new ShoppingCartItem (book); sc.addNewItemToShoppingCart(sci); } } } (4)这段是 检查购物车是有对象的，这里单独拿出来是可以很好的在WEB开发中很好的进行重用 的。
public class MyBookStoreUtils { private MyBookStoreUtils(){} public static ShoppingCart getShppingCartForCreateOrExist(HttpServletRequest request) { ShoppingCart sc = null; //2.1 检查在 HttpSession 对象中有没有购物车对象 , 即检查 session 中是否有 MyBookStoreConstants.SHOOPING_CART_KEY 属性 // 若 已经存在, 说明购物车存在, 直接取出 HttpSession session = null; session = request.getSession(); Object obj = session.getAttribute (MyBookStoreConstants.SHOOPING_CART_KEY); if(obj != null) { sc = (ShoppingCart) obj; } //2.2 若不存在 MyBookStoreConstants.SHOOPING_CART_KEY 属性, 创建一个购物车对象, 并把该对象放入 Session 中 else{ sc = new ShoppingCart (); session.setAttribute(MyBookStoreConstants.SHOOPING_CART_KEY, sc); } return sc; } public static ShoppingCart getShppingCartForExist(HttpServletRequest request) { ShoppingCart sc = null; //2.1 检查在 HttpSession 对象中有没有购物车对象 , 即检查 session 中是否有 MyBookStoreConstants.SHOOPING_CART_KEY 属性 // 若 已经存在, 说明购物车存在, 直接取出 HttpSession session = null; session = request.getSession(); Object obj = session.getAttribute (MyBookStoreConstants.SHOOPING_CART_KEY); if(obj != null) { sc = (ShoppingCart) obj; } //2.2 若不存在 MyBookStoreConstants.SHOOPING_CART_KEY 属性, 抛出异常, 提示用户还不存在购物车. else { throw new RuntimeException (MyBookStoreConstants.NO_SHOPPING_CART_EXCETPION); } return sc; } }(5)这里是所有与购物车相关的SERVLET.
这个是更新数据的，需要在SERVICE中调用DAO的!
public class UpdateShoppingCartServlet extends HttpServlet { public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //获取表单信息 // request.getParameter(""); 方法行不通, 因为表单的 name 是随时变化的 //获取表单中的所有 name Enumeration nameEnums = request.getParameterNames(); Map items = new HashMap(); //遍历 nameEnums, 再取出对应的 Value, 封装到 items 中 try { while(nameEnums.hasMoreElements()) { String bookId = nameEnums.nextElement(); String quantity = request.getParameter (bookId); items.put(bookId, Integer.parseInt (quantity)); } } catch (NumberFormatException e) { // TODO Auto-generated catch block e.printStackTrace (); throw new RuntimeException (MyBookStoreConstants.QUANTITY_FORMAT_EXCEPTION); } //获 取购物车对象 ShoppingCart sc = null; sc = MyBookStoreUtils.getShppingCartForExist(request); //调用 Service 方法 BookService bookService = new BookService (); bookService.updateShoppingCart(items, sc); //派发页面 : showShoppingCart.jsp 页面 String forwardPage = "/WEB- INF/jsp/showShoppingCart.jsp"; request.getRequestDispatcher(forwardPage).forward (request, response); } } public class ShowShoppingCartServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //做一个转发 String forwardPage = null; forwardPage = "/WEB- INF/jsp/showShoppingCart.jsp"; RequestDispatcher dispatcher = null; dispatcher = request.getRequestDispatcher (forwardPage); dispatcher.forward(request, response); } } public class ReceiptServlet extends HttpServlet { public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //1. 获取表单信息: name 和 cardId //2. 调用 Service 方法, 更新 books 表各条 book 的 saleAmount 字段 //2.1 获取购物车 ShoppingCart sc = MyBookStoreUtils.getShppingCartForExist(request); BookService bookService = new BookService(); bookService.buyBooks (sc); //2.1 使 Session 失效 HttpSession session = null; session = request.getSession(); session.invalidate (); //3. 派发页面: receipt.jsp 页面 request.getRequestDispatcher("/WEB-INF/jsp/receipt.jsp").forward(request, response); } } 这段我先开始很纳闷老师为什么会这样写呢，其实很简单，写个专门的转发的SERVLET这样，在每次转发的时候就只连接一个servlet比连接多个更来的简洁！提高了效率！
public class ForwardServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //1. 获取 path String path = request.getParameter("path"); //2. 派 发页面 request.getRequestDispatcher(path).forward(request, response); } } public class DeleteShoppingCartItemServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //1. 获取 id 号 String id = request.getParameter("bookid"); //2. 调用 BookService 方法 deleteShoppingCartItemById：, 进行删除操作 ShoppingCart sc = MyBookStoreUtils.getShppingCartForExist(request); String bookTitle = sc.getBook(id).getTitle(); BookService bookService = new BookService (); bookService.deleteShoppingCartItemById(id, sc); //3. 派发页面 request.setAttribute(MyBookStoreConstants.DELETE_FROM_SHOPPING_CART_BOOK_TITLE, bookTitle); String forwardPage = "/WEB- INF/jsp/showShoppingCart.jsp"; //4. 判断购物车是否为空, 若为空则派发到 emptyCart.jsp 页面 if(sc.getBooks().isEmpty()) forwardPage = "/WEB- INF/jsp/emptyCart.jsp"; RequestDispatcher dispatcher = null; dispatcher = request.getRequestDispatcher (forwardPage); dispatcher.forward(request, response); } }这里是清空购物车的SERVLET.
public class ClearShoppingCartServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //1. 调用方法 BookService bookService = new BookService (); ShoppingCart sc = null; sc = MyBookStoreUtils.getShppingCartForExist (request); bookService.clearShoppingCart (sc); //2. 派发页面 String forwardPage = null; forwardPage = "/WEB- INF/jsp/emptyCart.jsp"; RequestDispatcher dispatcher = request.getRequestDispatcher(forwardPage); dispatcher.forward(request, response); } } public class AddToShoppingCartServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //1. 获取书的 id 号 String bookId = null; bookId = request.getParameter("bookId"); //2. 获取 购物车对象: 调用 getShppingCart 方法 ShoppingCart sc = null; sc = MyBookStoreUtils.getShppingCartForCreateOrExist(request); //3. 调用 Service 方法把 id 对应的 ShoppingCartItem 对象放入购物车 ShoppingCart 对象中： addToShoppingCart(id, shoppingCart); BookService bookService = null; bookService = new BookService(); bookService.addToShoppingCart(bookId, sc); //4. 派发页面 String forwardPage = "/index.jsp"; //4.1 获取书名 String bookTitle = null; //bookTitle = sc.getBooks().get(bookId).getBook().getTitle (); bookTitle = sc.getBook(bookId).getTitle(); //4.2 将书 名放入请求域中, 以让页面进行显示 request.setAttribute (MyBookStoreConstants.ADD_TO_SHOPPING_CART_BOOK_TITLE, bookTitle); RequestDispatcher dispatcher = null; dispatcher = request.getRequestDispatcher (forwardPage); dispatcher.forward(request, response); } }(6)下面是显示层，对应着其相应的SERVLET.下面的JSP页面运用到了我们前段时间学的JSTL，EL表示.
'cashier.jsp'
