myeclipse 6.01+jsp+tomcat6.0+servlt中jsp跳转调用servlet空指针错误，不知道哪里错误，求助阿！！！

在309行加入断点，在myeclipse以debug方式启动tomcat，调试一下

<%@ page contentType="text/html; charset=gb2312"  errorPage="" %>
<%@ page import="java.io.*, java.util.*,java.lang.*,java.sql.*,foundation.da.*,
                     foundation.util.TranCode,
                     foundation.util.Debug,
                     dev.comm.WarehouseInfoBean" %>
<% request.setCharacterEncoding("GBK");
  WarehouseInfoBean bean=(WarehouseInfoBean)request.getAttribute("CommonBean");//创建Bean对象
  String pages="",rowCounts="",pageNums="";
   if(bean!=null){
     String Msg=bean.getErrorMsg("提示信息");
     if(Msg!=null){
       String javascript="<script language='JavaScript' type='text/javascript'>  alert('提示信息："+Msg+"')  </script>";
     out.print(javascript) ;
      request.removeAttribute("提示信息");
     }
     pages=bean.getPageCounts(); //满足条件的总页数
    rowCounts = bean.getRowCounts();//满足条件的总记录数
    pageNums = bean.getPageNum();//当前页页码
  }%>
<jsp:useBean id="CommonBean" scope="request" class="dev.comm.WarehouseInfoBean"/>
<jsp:setProperty name="CommonBean" property="*" />
<%if (CommonBean.isSubmit(request)){
System.out.println("================in Warehouselist is submit");
CommonBean.tranCode();
%>
<jsp:forward page="/CommonForm"/>
<%}%>
<html>
<head>
<title>设备管理系统</title>
<script language="JavaScript" src="javascripts/telecompublic.js" type="text/javascript"></script>
<script language="JavaScript" src="javascripts/content.js" type="text/javascript"></script>
<link rel="stylesheet" href="index.css" />
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<meta http-equiv= "Refresh "   content= "1 "   url= "" />
<style type="text/css">#Layer1 {
position:absolute;
width:930px;
height:330px;
z-index:1;
left: 10px;
top: 215px;
}
#Layer2 {
position:absolute;
width:971px;
height:45px;
z-index:1;
top: 170px;
left: -5px;
}
body {
background-image: url(images/bg-2.jpg);
}
</style>
<script language="JavaScript">
  var lineValue="";
  var oldObj = null;
   function switchItem1(KEY){
    if(oldObj != null){
      oldObj.className = "noClick"
    }
    newObj = event.srcElement.parentElement;
    newObj.className = "clicked"
    oldObj = newObj
    lineValue=KEY;
    var len = document.form1.elements.length;
    for(i=0;i<len;i++){
      if((document.form1.elements[i].type=="checkbox")&&(document.form1.elements[i].value==KEY)){
        if(document.form1.elements[i].checked == false){
          document.form1.elements[i].checked = true;
        }else{
          document.form1.elements[i].checked = false;
        }
      }
    }
    window.location="./CommonForm?beanName=dev.comm.WarehouseInfoBean&jspURL=DetailWareInfoPage.jsp&t_Ckbh="+KEY+"&detailFlag=true";
  }
  function orderInfos(KEY){
    document.form1.orderField.value=KEY;
    if(document.form1.orderType.value==null||document.form1.orderType.value==""||document.form1.orderType.value=="DESC"){
      document.form1.orderType.value="ASC";
    }else{
      document.form1.orderType.value="DESC";
    }
    document.form1.PubSubmit.name="bfmd_page";
    document.form1.PubSubmit.click();
  }
  function goPreviousPage(){
    var tempPageNum = document.form1.pageNum.value;
    var maxPage = document.form1.pageCounts.value;
    if(tempPageNum>1){
      document.form1.pageNum.value=tempPageNum-1;
      document.form1.PubSubmit.name="bfmd_page";
      document.form1.PubSubmit.click();
    }
  }
  function goNextPage(){
    var tempPageNum = document.form1.pageNum.value;
    var maxPage = document.form1.pageCounts.value;
    if((tempPageNum-0)<(maxPage-0)){
      document.form1.pageNum.value=tempPageNum-(-1);
      document.form1.PubSubmit.name="bfmd_page";
      document.form1.PubSubmit.click();
    }
  }
  function loadSearch(){
    document.form1.PubSubmit.name="bfmd_search";
    document.form1.PubSubmit.click();
  }
  function checkData(){
    alert('is submit');
  }
  function initLineValue(KEY){
    if (lineValue==null||lineValue==""){
      lineValue=KEY;
    }
  }
</script>   <%
/**
* 用于点击菜单项时清空会话中的条件字符串数据
*/
String setFlag = request.getParameter("setFlag");
if(setFlag!=null&&(setFlag.equals("T"))){
request.getSession().removeAttribute("whereSQL");
//request.getSession().removeAttribute("defCondition");
request.setAttribute("setFlag","F");
}%>
</head>

<body leftmargin="0" topmargin="images/0.jpg" MS_POSITIONING="GridLayout"><table width="100%" border="0" align="center" cellpadding="0" cellspacing="0"><TBODY>
<tr>
<td height="20" background="images/top_2.jpg"><table width="100%" height="100%" border="0" cellpadding="0" cellspacing="0">
<tr>
<td width="7%"><img src="images/top_1.jpg" width="70" height="20"></td>
<td width="79%"> </td>
<td width="14%"><img src="images/top_3.jpg" width="68" height="20"></td>
</tr>
</table>
</td>
</tr>
<tr>
<td height="79" background="images/bg-3.jpg"><table width="100%" height="79" border="0" cellpadding="0" cellspacing="0">
<tr><td><div align="center"><img src="images/top_left1.jpg" width="386" height="89" align="absmiddle" /></div></td><td align="right" valign="middle"><img src="images/top_6.jpg" width="207" height="89" /></td>
</tr>
</table>
</td>
</tr>
<tr>
<td height="30" bgcolor="#e3ebf5"><table width="100%" height="100%" border="0" cellpadding="0" cellspacing="0" bgcolor="#00CCFF">
<tr>
<td width="4%" align="center"><img src="iamges/0.jpg" width="17" height="16" /></td>
<td width="32%" height="25" align="center"><div align="left" class="STYLE1">
<font color=blue size=3 face="隶书">
<% Timestamp   time   =   new   Timestamp(System.currentTimeMillis());
out.println(time.toString());
%></font></div></td>
<td width="41%" align="center" class="f12"><div align="center"><marquee direction="left" class="STYLE1" ><font color=blue size=3 face="隶书">您好！欢迎使用设备管理信息系统 </font></marquee></div></td>
<td width="10%" align="left"><div align="center" class="STYLE1">
<div align="right"><a href="login0.jsp"><font color=blue size=3 face="隶书">退出系统</font></a></div>
</div></td>
<td width="1%" align="left"> </td>
<td width="12%" align="left"><div align="center" class="STYLE1"><font color=blue size=3 face="隶书"><a href="index.jsp">首页</a></font></div></td>
</tr>
</table></td>
</tr></TBODY>
</table>
<div id="Layer2">
  <div align="center" class="STYLE1">
    <td width="2" height="2" colspan="1" rowspan="1" align="center" valign="baseline" nowrap="nowrap" bgcolor="#0099FF" scope="col">
    <table width="200" border="0">
        <tr>
          <td><a href="systemManagement.jsp" target="_top" onclick="MM_nbGroup('down','group1','xtgl','',1)" onmouseover="MM_nbGroup('over','xtgl','','',1)" onmouseout="MM_nbGroup('out')"><img src="images/xtgl.jpg" alt="用户和权限修改" name="xtgl" width="140" height="25" border="0" id="xtgl" /></a></td>
          <td>  </td>
          <td><a href="caigoumanagement.jsp" target="_top" onclick="MM_nbGroup('down','group1','cggl','',1)" onmouseover="MM_nbGroup('over','cggl','','',1)" onmouseout="MM_nbGroup('out')"><img src="images/cggl.jpg" alt="设备的采购信息情况" name="cggl" width="140" height="25" border="0" id="cggl"  /></a></td>
          <td>  </td>
          <td><a href="taizhangmanagement.jsp" target="_top" onclick="MM_nbGroup('down','group1','sbtzgl','',1)" onmouseover="MM_nbGroup('over','sbtzgl','','',1)" onmouseout="MM_nbGroup('out')"><img src="images/sbtzgl.jpg" alt="设备的明细台帐详情" name="sbtzgl" width="140" height="25" border="0" id="sbtzgl"/></a></td>
          <td>  </td>
          <td><a href="shebeiyunxing.jsp" target="_top" onclick="MM_nbGroup('down','group1','sbyxgl','',1)" onmouseover="MM_nbGroup('over','sbyxgl','','',1)" onmouseout="MM_nbGroup('out')"><img src="images/sbyxgl.jpg" alt="现在运行设备的详细情况" name="sbyxgl" width="140" height="25" border="0" id="sbyxgl"  /></a></td>
          <td>  </td>
          <td><a href="shebeiweihu.jsp" target="_top" onclick="MM_nbGroup('down','group1','sbwhgl','',1)" onmouseover="MM_nbGroup('over','sbwhgl','','',1)" onmouseout="MM_nbGroup('out')"><img src="images/sbwhgl.jpg" alt="设备维护情况" name="sbwhgl" width="140" height="25" border="0" id="sbwhgl"  /></a></td>
          <td>  </td>
          <td><a href="ListWarehouseInfoPage.jsp" target="_top" onclick="MM_nbGroup('down','group1','ckgl','',1)" onmouseover="MM_nbGroup('over','ckgl','','',1)" onmouseout="MM_nbGroup('out')"><img src="images/ckgl.jpg" alt="仓库的详细情况" name="ckgl" width="140" height="25" border="0" id="ckgl" /></a></td>
        </tr>
    </table>
    </td>
</div>
</div>
<div id="Layer1">
<form name="form1" method="post" action="./ListWarehouseInfoPage.jsp" onSubmit="return checkData()">
    <input type="hidden" name="orderField" value="CommonBean.getOrderField()">
    <input type="hidden" name="orderType" value="CommonBean.getOrderType()">
    <input type="hidden" name="pageNum" value="pageNums">
    <input type="hidden" name="pageCounts" value="pages">
    <input type="hidden" name="rowCounts" value="rowCounts">
<center>
  <tr>
    <td colspan="7"><font color="blue" size="5" face="隶书">仓库信息维护</font></td>
  </tr>
  </center>
<tr><td>&nbsp</td></tr>
  <tr><td colspan="7">&nbsp</td></tr>
<table width="700" border="1" align="center" class="STYLE1">
  <tr>
    <th width="5%">选择</th>
    <th style="cursor:hand" title="单击这里，按仓库编号排序" onClick="orderInfos('t_Ckbh')">仓库编号</th>
    <th style="cursor:hand" title="单击这里，按设备类别排序" onClick="orderInfos('t_Rkcplb')">入库产品类别</th>
    <th style="cursor:hand" title="单击这里，按设备名称排序" onClick="orderInfos('t_Rkcpmc')">入库产品名称</th>
    <th style="cursor:hand" title="单击这里，按入库日期排序" onClick="orderInfos('t_Rkrq')">入库日期</th>
    <th style="cursor:hand" title="单击这里，按现有数量排序" onClick="orderInfos('t_Xysl')">现有数量</th>
    </tr>
  <% DbResultSet dbrs = bean.getDbrs();
     int i=1;
     String tmpState="",stateName="",firstRowKey="";    if(dbrs!=null&&dbrs.size()>0){
       while(dbrs.next()){
        tmpState = dbrs.getString(19);
        if(tmpState!=null && tmpState.equals("T")){
          stateName="正常";
        }else{
          stateName="缺货";
        }
        if(i==1){
          firstRowKey = dbrs.getString(1);
  %>
        <script language="JavaScript">
            initLineValue("<%=firstRowKey%>");
        </script>
        <tr class="clicked" id="<%=dbrs.getString(1)%>" onClick="switchItem1(id);" onMouseOver="this.className='clicked'" onMouseOut="this.className='noClick'">
          <td nowrap  height="16" align="center"><input type="checkbox" name="checkbox<%=i+1%>" value="<%=firstRowKey%>"></td>
          <td><%=dbrs.getString(6)%></td>
          <td><%=dbrs.getString(11)%></td>
          <td><%=dbrs.getString(10)%></td>
          <td><%=dbrs.getString(16)%></td>
        </tr>
  <%}
      else{%>
        <tr class="noClick" id="<%=dbrs.getString(1)%>" onClick="switchItem1(id);" onMouseOver="this.className='clicked'" onMouseOut="this.className='noClick'">
          <td nowrap  height="16" align="center"><input type="checkbox" name="checkbox<%=i+1%>" value="<%=firstRowKey%>"></td>
          <td><%=dbrs.getString(6)%></td>
          <td><%=dbrs.getString(11)%></td>
          <td><%=dbrs.getString(10)%></td>
          <td><%=dbrs.getString(16)%></td>
         </tr>
  <%}
        i++;
    }
   }%>
</table>

Jsp中servlet的空指针异常2008-11-16 15:30Jsp中servlet的空指针异常该异常对于初学者来说经常遇到，当一个对象的地址为空，用该对象调用方法时候会产生空指针异常；例如：<%           Object str1 = request.getSession().getAttribute("name");           if (str1 != null) {//一定要判断该对象是不是为空，空指针异常往往在这里出现              //当一个对象是空时候如果调用该对象的方法则报空指针异常；              out.println(str1.toString());           } else {           }       %>
当一个对象调用其方法，返回另一个对象的属性值的时候，诺另一个对象地址为空时候，则会产生空指针异常，该异常很难被察觉，故程序员在编程过程中一定要仔细，下面的是一个很典型的例子：
       <%           try{//空指针异常捕获，当第一次访问没有cookie，这个时候会报异常所以这里要捕获异常           //等cookie生成之后就没有异常了。           Cookie cookies[] = request.getCookies();//注意空指针异常，           //当服务端没有设置cookie对象时候则报空指异常              if (cookies[0] != null) {                  if (cookies[0].getValue().equals("jiangnan")) {                     response.sendRedirect("welcome.jsp");                  }              } else {              }           }catch(NullPointerException e){                      }
       %>

调试易

myeclipse 6.01+jsp+tomcat6.0+servlt中jsp跳转调用servlet空指针错误，不知道哪里错误，求助阿！！！

解决方案 »