为什么我的servlet配置正确，但是就是提示404找不到我配置的servlet

这个servlet案例是我写的一个例子，有一个jsp页面负责提交一个简单的订单，运行没问题，但是已提交订单到servlet就提示 （jdStudy为项目名）

HTTP Status 404 - /jdStudy/post

--------------------------------------------------------------------------------

type Status report

message /jdStudy/post

description The requested resource (/jdStudy/post) is not available.


以下是web.xml的配置
<servlet>
<servlet-name>ShoppingCart</servlet-name>
<servlet-class>com.jiandong1.ShoppingCart</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>ShoppingCart</servlet-name>
<url-pattern>/ShoppingCart</url-pattern>
</servlet-mapping>
映射的servlet类为：
package com.jiandong1;

省略导包内容

public class ShoppingCart extends HttpServlet {

@Override
public void init(ServletConfig config) throws ServletException {
super.init(config);
}

@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
//取得Session对象，如果不存在Session对象则为此次会话创建该对象
HttpSession session = req.getSession(true);
Integer itemCount = (Integer)session.getAttribute("itemCount");
//如果session是新的
if (itemCount == null) {
itemCount = new Integer(0);
PrintWriter out = resp.getWriter();
resp.setContentType("text/html");
//接收传来的参数
String[] itemSelected;
String itemName;
itemSelected = req.getParameterValues("item");
if (itemSelected != null) {
for (int i = 0; i < itemSelected.length; i++) {
itemName = itemSelected[i];
itemCount = new Integer(itemCount.intValue() + 1);//+1将1转换为字符串对象
//购买的条目
session.setAttribute("item" + itemCount, itemName);
//总条目数
session.setAttribute("itemCount", itemCount);
}
}
out.print("<html>");
out.print("<title>");
out.print("选项列表");
out.print("</title>");
out.print("<body><h4>Session 列表：</h4><hr><br><br>");
for (int i = 0; i <= itemCount.intValue(); i++) {
out.print((String)session.getAttribute("item" + i) + "<hr>");
}
out.print("</body>");
out.print("</html>");
out.close();
}
}

@Override
public void destroy() {
super.destroy();
}

}