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
1<jsp:include flush="true" page="Cart.jsp"></jsp:include>
包含于其中。
代码清单 1:EShop.jsp
1@ page session="true"
1<html>
2<head>
3<title>Music Without Borders</title>
4</head>
5<body bgcolor="#33CCFF">
6<font face="Times New Roman,Times" size="+3">
7
8Music Without Borders
9
10</font>
11<hr/><p>
12<center>
13<form action="/examples/servlet/ShoppingServlet" method="POST" name="shoppingForm">
14<b>CD:</b>
15<select name="CD">
16<option>Yuan | The Guo Brothers | China | $14.95</option>
17<option>Drums of Passion | Babatunde Olatunji | Nigeria | $16.95</option>
18<option>Kaira | Tounami Diabate| Mali | $16.95</option>
19<option>The Lion is Loose | Eliades Ochoa | Cuba | $13.95</option>
20<option>Dance the Devil Away | Outback | Australia | $14.95</option>
21<option>Record of Changes | Samulnori | Korea | $12.95</option>
22<option>Djelika | Tounami Diabate | Mali | $14.95</option>
23<option>Rapture | Nusrat Fateh Ali Khan | Pakistan | $12.95</option>
24<option>Cesaria Evora | Cesaria Evora | Cape Verde | $16.95</option>
25<option>Ibuki | Kodo | Japan | $13.95</option>
26</select>
27<b>Quantity: </b><input name="qty" size="3" type="text" value="1"/>
28<input name="action" type="hidden" value="ADD"/>
29<input name="Submit" type="submit" value="Add to Cart"/>
30</form>
31</center>
32<p>
33<jsp:include flush="true" page="Cart.jsp"></jsp:include>
34</p></p></body>
35</html>
代码清单 2:Cart.jsp
1@ page session="true" import="java.util.*, shopping.CD"
1
2
3Vector buylist = (Vector) session.getValue("shopping.shoppingcart");
4
5if (buylist != null && (buylist.size() > 0)) {
6
1<center>
2<table bgcolor="#FFFFFF" border="0" cellpadding="0" width="100%">
3<tr>
4<td><b>ALBUM</b></td>
5<td><b>ARTIST</b></td>
6<td><b>COUNTRY</b></td>
7<td><b>PRICE</b></td>
8<td><b>QUANTITY</b></td>
9<td></td>
10</tr>
11
for (int index=0; index < buylist.size();index++) {
CD anOrder = (CD) buylist.elementAt(index);
1
2<tr>
3<td><b>```
4= anOrder.getAlbum()
5```</b></td>
6<td><b>```
7= anOrder.getArtist()
8```</b></td>
9<td><b>```
10= anOrder.getCountry()
11```</b></td>
12<td><b>```
13= anOrder.getPrice()
14```</b></td>
15<td><b>```
16= anOrder.getQuantity()
17```</b></td>
18<td>
19<form action="/examples/servlet/ShoppingServlet" method="POST" name="deleteForm">
20<input type="submit" value="Delete"/>
21<input name="delindex" type="hidden" value="```
22= index
23```"/>
24<input name="action" type="hidden" value="DELETE"/>
25</form>
26</td>
27</tr>
28
}
1
2</table>
3<p>
4<form action="/examples/servlet/ShoppingServlet" method="POST" name="checkoutForm">
5<input name="action" type="hidden" value="CHECKOUT"/>
6<input name="Checkout" type="submit" value="Checkout"/>
7</form>
8</p></center>
1 }
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：
1
2
3Vector buylist = (Vector) session.getValue("shopping.shoppingcart");
4
5if (buylist != null && (buylist.size() > 0)) {
6
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：
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：
1
2
3for (int index=0; index < buylist.size(); index++) {
4
5CD anOrder = (CD) buylist.elementAt(index);
6
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。
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;
}
}