session监听器HttpSessionListener接口获得在线用户运行出错,帮忙看看

//hello类
package lognumber;import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;public  class hello implements HttpSessionListener {
    String name;
    public hello(String name){
        this.name=name;
    }
    public String getName() {
     return name;
 }
 public void setName(String name) {
     this.name = name;
 }
    public void sessionCreated(HttpSessionEvent se) {
        test.add(name);
    }    
    public void sessionDestroyed(HttpSessionEvent se) {
        test.delete(name);
    }
}
//test类
package lognumber;
import java.util.ArrayList;
public class test {
   static ArrayList list=new ArrayList();
    public static void add(String name){// 添加用户
        list.add(name);
    }
    public static void delete(String name){//删除用户
        list.remove(name);
    }
    public static ArrayList getName(){
        return list;
    }
    
}//Servlet1package lognumber;import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;
import lognumber.*;
public class Servlet1 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(CONTENT_TYPE);
        PrintWriter out = response.getWriter();
        request.setCharacterEncoding("gbk");
        String name = request.getParameter("name");
        hello he=new hello(name);
       ArrayList list=test.getName();
        out.println("当前在线用户");
        for (int i = 0; i < list.size(); i++) {
            out.println(list.get(i));
        }
    }
    //Process the HTTP Post request
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws
            ServletException, IOException {
        doGet(request, response);
    }    //Clean up resources
    public void destroy() {
    }
}
//XML配置
<?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>WebModule1</display-name>
  <listener>
    <listener-class>lognumber.hello</listener-class>
  </listener>
  <servlet>
    <servlet-name>servlet1</servlet-name>
    <servlet-class>lognumber.Servlet1</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>servlet1</servlet-name>
    <url-pattern>/servlet1</url-pattern>
  </servlet-mapping>
</web-app>//刚一运行就提示
严重: Error configuring application listener of class lognumber.hello
java.lang.InstantiationException: lognumber.hello
at java.lang.Class.newInstance0(Class.java:335)
at java.lang.Class.newInstance(Class.java:303)
at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:3618)
at org.apache.catalina.core.StandardContext.start(StandardContext.java:4104)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1012)
at org.apache.catalina.core.StandardHost.start(StandardHost.java:718)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1012)
at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:442)
at org.apache.catalina.core.StandardService.start(StandardService.java:450)
at org.apache.catalina.core.StandardServer.start(StandardServer.java:683)
at org.apache.catalina.startup.Catalina.start(Catalina.java:537)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:271)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:409)
2007-4-2 22:39:53 org.apache.catalina.core.StandardContext listenerStart
严重: Skipped installing application listeners due to previous error(s)
2007-4-2 22:39:53 org.apache.catalina.core.StandardContext start
严重: Error listenerStart
2007-4-2 22:39:53 org.apache.catalina.core.StandardContext start
严重: Context [/WebModule1] startup failed due to previous errors