实例讲解JSPModel2体系结构（中）
点击次数：38 次 发布日期：2008-11-26 17:04:30 作者：源代码网
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实例讲解JSP Model2体系结构（中） 探索ＭＶＣ设计模式 （作者：周斌编译 ） 理解“音乐无国界” “音乐无国界”的主界面是JSP页 Eshop.jsp(见代码清单1)。你会注意到，这个页面几乎只作为专门的用户界面，不承担任何处理任务――是一个最理想的JSP方案。另外，请注意另一个JSP页Cart.jsp（见代码清单2）被Eshop.jsp通过指令<jsp:include page="Cart.jsp" flush="true" />包含于其中。 代码清单 1:EShop.jsp <%@ page session="true" %> <html> <head> <title>Music Without Borders</title> </head> <body bgcolor="#33CCFF"> <font face="Times New Roman,Times" size="+3"> Music Without Borders </font> <hr><p> <center> <form name="shoppingForm" action="/examples/servlet/ShoppingServlet" method="POST"> <b>CD:</b> <select name=CD> <option>Yuan | The Guo Brothers | China | $14.95</option> <option>Drums of Passion | Babatunde Olatunji | Nigeria | $16.95</option> <option>Kaira | Tounami Diabate| Mali | $16.95</option> <option>The Lion is Loose | Eliades Ochoa | Cuba | $13.95</option> <option>Dance the Devil Away | Outback | Australia | $14.95</option> <option>Record of Changes | Samulnori | Korea | $12.95</option> <option>Djelika | Tounami Diabate | Mali | $14.95</option> <option>Rapture | Nusrat Fateh Ali Khan | Pakistan | $12.95</option> <option>Cesaria Evora | Cesaria Evora | Cape Verde | $16.95</option> <option>Ibuki | Kodo | Japan | $13.95</option> </select> <b>Quantity: </b><input type="text" name="qty" SIZE="3" value=1> <input type="hidden" name="action" value="ADD"> <input type="submit" name="Submit" value="Add to Cart"> </form> </center> <p> <jsp:include page="Cart.jsp" flush="true" /> </body> </html> 代码清单 2:Cart.jsp <%@ page session="true" import="java.util.*, shopping.CD" %> <% Vector buylist = (Vector) session.getValue("shopping.shoppingcart"); if (buylist != null && (buylist.size() > 0)) { %> <center> <table border="0" cellpadding="0" width="100%" bgcolor="#FFFFFF"> <tr> <td><b>ALBUM</b></td> <td><b>ARTIST</b></td> <td><b>COUNTRY</b></td> <td><b>PRICE</b></td> <td><b>QUANTITY</b></td> <td></td> </tr> <% for (int index=0; index < buylist.size();index++) { CD anOrder = (CD) buylist.elementAt(index); %> <tr> <td><b><%= anOrder.getAlbum() %></b></td> <td><b><%= anOrder.getArtist() %></b></td> <td><b><%= anOrder.getCountry() %></b></td> <td><b><%= anOrder.getPrice() %></b></td> <td><b><%= anOrder.getQuantity() %></b></td> <td> <form name="deleteForm" action="/examples/servlet/ShoppingServlet" method="POST"> <input type="submit" value="Delete"> <input type="hidden" name= "delindex" value="<%= index %>"> <input type="hidden" name="action" value="DELETE"> </form> </td> </tr> <% } %> </table> <p> <form name="checkoutForm" action="/examples/servlet/ShoppingServlet" method="POST"> <input type="hidden" name="action" value="CHECKOUT"> <input type="submit" name="Checkout" value="Checkout"> </form> </center> <% } %> 这里，Cart.jsp操纵着基于会话的购物车的表达，在MVC体系中，购物车就充当Model的角色。 观察Cart.jsp开头处的脚本片段： <% Vector buylist = (Vector) session.getValue("shopping.shoppingcart"); if (buylist != null && (buylist.size() > 0)) { %> 这段脚本主要是从会话中取出购物车。如果购物车是空的或尚未创建，则它什么都不显示；因此，当用户第一次访问这个应用程序时，呈现给他的视图如图3所示： [myimg]upload/68-3.png[/myimg] 图3：音乐无国界，主视图 图中按钮文字：放入购物车 如果购物车不为空，则选中的物品被依次从购物车中取出，如下面的脚本片段所示： <% for (int index=0; index < buylist.size(); index++) { CD anOrder = (CD) buylist.elementAt(index); %> 描述物品的变量一旦被创建，就会被用JSP表达式直接嵌入静态HTML模板中去。图4显示了当用户向购物车中放入一些物品后的视图。 [myimg]upload/68-4.png[/myimg] 图4：音乐无国界，购物车视图 图中文字：Music Without Borders：音乐无国界；Quantity：数量；ALBUM：唱片；ARTIST：演唱者；COUNTRY：国家；PRICE：价格；Delete：删除；Checkout：结帐。 这里需要注意的重要一点是，在Eshop.jsp和Cart.jsp中实现的对所有动作的处理都由一个servlet――ShoppingServlet.java控制，如代码清单3所示： 代码清单3:ShoppingServlet.java import java.util.*; import java.io.*; import javax.servlet.*; import javax.servlet.http.*; import shopping.CD; public class ShoppingServlet extends HttpServlet { public void init(ServletConfig conf) throws ServletException { super.init(conf); } public void doPost (HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { HttpSession session = req.getSession(false); if (session == null) { res.sendRedirect("http://localhost:8080/error.html"); } Vector buylist= (Vector)session.getValue("shopping.shoppingcart"); String action = req.getParameter("action"); if (!action.equals("CHECKOUT")) { if (action.equals("DELETE")) { String del = req.getParameter("delindex"); int d = (new Integer(del)).intValue(); buylist.removeElementAt(d); } else if (action.equals("ADD")) { //以前是否购买了同样的cd? boolean match=false; CD aCD = getCD(req); if (buylist==null) { //将第一张CD放入购物车 buylist = new Vector(); //第一份定单 buylist.addElement(aCD); } else { // 不是第一次购买 for (int i=0; i< buylist.size(); i++) { CD cd = (CD) buylist.elementAt(i); if (cd.getAlbum().equals(aCD.getAlbum())) { cd.setQuantity(cd.getQuantity()+aCD.getQuantity()); buylist.setElementAt(cd,i); match = true; } //if name matches结束 } // for循环结束 if (!match) buylist.addElement(aCD); } } session.putValue("shopping.shoppingcart", buylist); String url="/jsp/shopping/EShop.jsp"; ServletContext sc = getServletContext(); RequestDispatcher rd = sc.getRequestDispatcher(url); rd.forward(req, res); } else if (action.equals("CHECKOUT")) { float total =0; for (int i=0; i< buylist.size();i++) { CD anOrder = (CD) buylist.elementAt(i); float price= anOrder.getPrice(); int qty = anOrder.getQuantity(); total += (price * qty); } total += 0.005; String amount = new Float(total).toString(); int n = amount.indexOf("."); amount = amount.substring(0,n+3); req.setAttribute("amount",amount); String url="/jsp/shopping/Checkout.jsp"; ServletContext sc = getServletContext(); RequestDispatcher rd = sc.getRequestDispatcher(url); rd.forward(req,res); } } private CD getCD(HttpServletRequest req) { //想象一下如果这些都在一个脚本片段中会有多么难看 String myCd = req.getParameter("CD"); String qty = req.getParameter("qty"); StringTokenizer t = new StringTokenizer(myCd,"|"); String album= t.nextToken(); String artist = t.nextToken(); String country = t.nextToken(); String price = t.nextToken(); price = price.replace("$"," ").trim(); CD cd = new CD(); cd.setAlbum(album); cd.setArtist(artist); cd.setCountry(country); cd.setPrice((new Float(price)).floatValue()); cd.setQuantity((new Integer(qty)).intValue()); return cd; } } 源代码网供稿. |
