Exception in thread "HouseKeeper" java.lang.NullPointerException

Exception in thread "HouseKeeper" java.lang.NullPointerException2011-04-26 08:52虽然这个错误不影响项目，但是项目中的 class 类一改动 就无法自动启动起来了。因为这个错误导致的。很是麻烦！

解决方法：（次方法也是来源于网络中，我只是再次分享。或者把零散的整合在一起说了）

package cn.com.***.***.servlet;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.logicalcobwebs.proxool.ProxoolFacade;

/**
 * Servlet implementation class HouseKeeperServlet
 */
public class HouseKeeperServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    public void destroy() {
          //此处添加处理 
          ProxoolFacade.shutdown();
    }

    /**
     * @see HttpServlet#HttpServlet()
     */
    public HouseKeeperServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
         doGet(request, response);
    }

}

import org.logicalcobwebs.proxool.ProxoolFacade;
/*
 * 此类用来处理 在class类进行修改的时候 保存了之后服务自动重新启动 报：
 *  Exception in thread "HouseKeeper" java.lang.NullPointerException
 *  错误原因为：
 *  This is because Proxool is not being shutdown properly. 
 *  If the JVM stops then Proxool recognises that and shuts down gracefully, 
 *  but if you redeploy Proxool into some environments (for example, a servlet container) 
 *  then Proxool needs to be explicitly told so by calling ProxoolFacade.shutdown(). 
 *  If you have a servlet container then you could put it in the servlet's destroy() method. 
 *  Alternatively, use the ServletConfigurator to both configure and shutdown Proxool 
 */

<!-- for resolving HouseKeeper bug-->
  <servlet> 
    <servlet-name>loadServlet</servlet-name> 
    <servlet-class>cn.com.xxx.xxx.HouseKeeperServlet</servlet-class> 
    <load-on-startup>1</load-on-startup> 
  </servlet>