很恼火，getInitParameter 总取不到值,该如何处理

package com.nong;import java.io.*;import java.sql.*;import javax.servlet.*;import javax.servlet.http.*;public class CreateDBServlet extends HttpServlet{    private String url;    private String user;    private String password;    String driverClass;    String s1;    public void init() throws ServletException    {                 s1=this.getInitParameter("servletParam");               }        public void doGet(HttpServletRequest req,HttpServletResponse res) throws ServletException,IOException    {                             res.setContentType("text/html");           PrintWriter out = res.getWriter();                    String s2 = getServletContext().getInitParameter("webParam");            out.println("s1"+s1);            out.println("<br>");          out.println("s2"+s2);           out.flush();           out.close();            }        public void doPost(HttpServletRequest req,HttpServletResponse res) throws ServletException,IOException    {        this.doGet(req,res);            }    }

<?xml version="1.0" encoding="UTF-8"?>  <web-app id="WebApp_ID" version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">  <context-param>  <param-name>webParam</param-name>  <param-value>aaa</param-value>  </context-param>  <servlet>  <servlet-name>test</servlet-name>  <servlet-class>Test</servlet-class>  </servlet>  <init-param>  <param-name>servletParam</param-name>   <param-value>bbb</param-value>  </init-param>   <servlet-mapping>  <servlet-name>test</servlet-name>   <url-pattern>/test</url-pattern>  </servlet-mapping>    <servlet>        <servlet-name>my</servlet-name>        <servlet-class>com.nong.CreateDBServlet</servlet-class>    </servlet>    <servlet-mapping>        <servlet-name>my</servlet-name>        <url-pattern>/my</url-pattern>    </servlet-mapping></web-app>