项目启动时 Exception in thread "HouseKeeper" java.lang.NullPointerException

首先查看是否是端口冲突引起，在日志信息该错误位置往上找，如果再无错误信息，而只有该错误，则原因可能如下：

原因：

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

中文翻译如下：

解决方法：

package com.zang.util;

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;

/*
 * 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
 */
public class HouseKeeperServlet extends HttpServlet {
     private static final long serialVersionUID = 4829418704873725291L;

     public void destroy() {
      //此处添加处理
      ProxoolFacade.shutdown(0);
     }

     public void doPost(HttpServletRequest request, HttpServletResponse response)
       throws ServletException, IOException {
      doGet(request, response);
     }

     public void doGet(HttpServletRequest request, HttpServletResponse response)
       throws ServletException, IOException {

     }
}

在web.xml中加入

    <servlet>
        <servlet-name>loadServlet</servlet-name>
                <servlet-class>com.zang.util.HouseKeeperServlet</servlet-class>
           <load-on-startup>1</load-on-startup>
    </servlet>