模拟购物车问题

在下写了个简单的购物车，运行后添加商品但是没有显示商品，不知为何？
程序如下：
package ex3_4;import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;public class ShoppingCartViewerHidden extends HttpServlet {
    private static final String CONTENT_TYPE = "text/html; charset=GBK";    //Initialize global variables
    public void init() throws ServletException {
    }    //Process the HTTP Get request
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws
            ServletException, IOException {
        response.setContentType("text/html;charset=GBK");
        response.setCharacterEncoding("GBK");
        PrintWriter out = response.getWriter();
        out.println("<html>");
        out.println("<head><title>当前购物车中的商品</title></head>");
        out.println("</body>");
        request.setCharacterEncoding("GBK");//处理中文
        //item参数中存储有购物车中的商品
        String[] items=request.getParameterValues("item");
        //打印输出购物车中的商品
        out.println("当前,你的购物车中有这些商品:<br>");
        if (items==null) {
            out.println("<b>商品为空!</b>");
        }else{
                out.println("<ul>");
                for (int i = 0; i < items.length; i++) {
                out.println("<li>");
                out.print(items[i]);
                }
            out.println("</ul>");
         }
        //询问用户是否继续添加商品
        //将商品作为表单隐藏域传递
        out.println("<form action=\"/sessiontrack/shoppingcartviewerhidden\"method=post>");
        if(items!=null){
            for (int i = 0; i < items.length; i++) {
                out.println("<input type=hidden name=item value=\""+items[i]+"\">");
            }
        }
        int i=new Random().nextInt(100);
        out.println("<input type=hidden name=item value=\"商品");
        out.print(String.valueOf(i));
        out.println("\">");
        out.println("您愿意<br>");
        out.print("<input type=submit value=\"添加商品\">");
        out.println("</form>");
        out.println("</body></html>");
    }    //Process the HTTP Post request
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws
            ServletException, IOException {
        doGet(request, response);
    }
}XML:
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd" version="2.4">
  <display-name>Sessiontrack</display-name>
  <servlet>
    <servlet-name>shoppingcartviewerhidden</servlet-name>
    <servlet-class>ex3_4.ShoppingCartViewerHidden</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>shoppingcartviewerhidden</servlet-name>
    <url-pattern>/shoppingcartviewerhidden</url-pattern>
  </servlet-mapping>
</web-app>