📄 672175.xml
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<?xml version='1.0' encoding='GB2312'?>
<?xml-stylesheet type='text/xsl' href='../csdn.xsl'?>
<Topic>
<Issue>
<PostUserNickName>灵子</PostUserNickName>
<rank>二级(初级)</rank>
<ranknum>user2</ranknum>
<credit>97</credit>
<TopicId>672175</TopicId>
<TopicName>把连接数据库的语句封装到access_dbconnect.class中</TopicName>
<PostUserId>159900</PostUserId>
<PostUserName>lingzi</PostUserName>
<RoomName>JSP</RoomName>
<ReplyNum>20</ReplyNum>
<PostDateTime>2002-4-24 11:44:35</PostDateTime>
<Point>50</Point>
<ReadNum>0</ReadNum>
<RoomId>28</RoomId>
<EndState>2</EndState>
<Content>把连接数据库的语句封装到access_dbconnect.class中
jsp调用beans的语法如下：
<%@ page language="java" import="java.sql.*" %>
<%@ page contentType="text/html;charset=gb2312"%>
<html>
<head>
	<title>查询</title>
</head>
<body>
<JSP:useBean id="view" scope="page" class="access.access_dbconnect"/>
<%
  ResultSet rs;//到本行为止调试是正确的
  rs=view.executeQuery("select * from user_info");//到本行调试就出错了。
  while(rs.next())
      {
%>
姓名：<%=rs.getString("name")%>
</p>
<% } %>
<hr>
</body>
</html>
但是提示出现了下列错误：
javax.servlet.ServletException: Compilation error occured: 
 Found 1 errors in JSP file:
C:\\Program Files\\Allaire\\JRun\\servers\\default\\default-app\\view.jsp:12: Error: "view" is either a misplaced package name or a non-existent entity.
为什么说id="view"出错呢？</Content>
</Issue>
<Replys>
<Reply>
<PostUserNickName></PostUserNickName>
<rank>一星(中级)</rank>
<ranknum>star1</ranknum>
<credit>100</credit>
<ReplyID>4415341</ReplyID>
<TopicID>672175</TopicID>
<PostUserId>228290</PostUserId>
<PostUserName>dylanwolf</PostUserName>
<Point>0</Point>
<Content><JSP:useBean  改成 <jsp:useBean
试试</Content>
<PostDateTime>2002-4-24 11:53:20</PostDateTime>
</Reply>
<Reply>
<PostUserNickName>卧龙</PostUserNickName>
<rank>四级(中级)</rank>
<ranknum>user4</ranknum>
<credit>100</credit>
<ReplyID>4415382</ReplyID>
<TopicID>672175</TopicID>
<PostUserId>223374</PostUserId>
<PostUserName>wjfxiao</PostUserName>
<Point>0</Point>
<Content>class路径正确吗？</Content>
<PostDateTime>2002-4-24 11:54:55</PostDateTime>
</Reply>
<Reply>
<PostUserNickName>见到PLMM就脸红</PostUserNickName>
<rank>五级(中级)</rank>
<ranknum>user5</ranknum>
<credit>100</credit>
<ReplyID>4416209</ReplyID>
<TopicID>672175</TopicID>
<PostUserId>150822</PostUserId>
<PostUserName>waterdragonfly</PostUserName>
<Point>0</Point>
<Content>似乎是路径的问题，
你的BEAN所在的目录正确吗？</Content>
<PostDateTime>2002-4-24 12:37:59</PostDateTime>
</Reply>
<Reply>
<PostUserNickName>见到PLMM就脸红</PostUserNickName>
<rank>五级(中级)</rank>
<ranknum>user5</ranknum>
<credit>100</credit>
<ReplyID>4416234</ReplyID>
<TopicID>672175</TopicID>
<PostUserId>150822</PostUserId>
<PostUserName>waterdragonfly</PostUserName>
<Point>0</Point>
<Content>似乎是路径的问题，
你的BEAN所在的目录正确吗？</Content>
<PostDateTime>2002-4-24 12:39:21</PostDateTime>
</Reply>
<Reply>
<PostUserNickName>灵子</PostUserNickName>
<rank>二级(初级)</rank>
<ranknum>user2</ranknum>
<credit>97</credit>
<ReplyID>4416887</ReplyID>
<TopicID>672175</TopicID>
<PostUserId>159900</PostUserId>
<PostUserName>lingzi</PostUserName>
<Point>0</Point>
<Content>如果是路径的问题那单独调试这一行ResultSet rs;也应该错的。
但是如果单独调试以下却是正确的。
<%@ page language="java" import="java.sql.*" %>
<%@ page contentType="text/html;charset=gb2312"%>
<html>
<head>
    <title>查询</title>
</head>
<body>
<JSP:useBean id="view" scope="page" class="access.access_dbconnect"/>
<%
  ResultSet rs;//到本行为止调试是正确的
  %>
</Content>
<PostDateTime>2002-4-24 13:13:33</PostDateTime>
</Reply>
<Reply>
<PostUserNickName>卧龙</PostUserNickName>
<rank>四级(中级)</rank>
<ranknum>user4</ranknum>
<credit>100</credit>
<ReplyID>4417159</ReplyID>
<TopicID>672175</TopicID>
<PostUserId>223374</PostUserId>
<PostUserName>wjfxiao</PostUserName>
<Point>0</Point>
<Content>access.access_dbconnect的路径正确吗？
ResultSet rs;//到本行为止调试是正确的
只能说明出错肯定在access.access_dbconnect上
</Content>
<PostDateTime>2002-4-24 13:27:22</PostDateTime>
</Reply>
<Reply>
<PostUserNickName>灵子</PostUserNickName>
<rank>二级(初级)</rank>
<ranknum>user2</ranknum>
<credit>97</credit>
<ReplyID>4417728</ReplyID>
<TopicID>672175</TopicID>
<PostUserId>159900</PostUserId>
<PostUserName>lingzi</PostUserName>
<Point>0</Point>
<Content>我的view.jsp是放在根目录下的。我的access_dbconnect.class是放在相对于根目录的WEB-INF\classes下的。
把连接数据库的语句封装到access_dbconnect.class中
jsp调用beans的语法如下：
<%@ page language="java" import="java.sql.*" %>
<%@ page contentType="text/html;charset=gb2312"%>
<html>
<head>
	<title>查询</title>
</head>
<body>
<jsp:useBean id="view" scope="page" class="access.access_dbconnect"/>
<%
  ResultSet rs;
  rs=view.executeQuery("select * from user_info");
  String name;
  while(rs.next())
      {
       name=rs.getString("name");
      }
%>
</body>
</html>
但是提示出现了下列错误：
/view.jsp:
null
java.lang.NullPointerException
	at jrun__view2ejsp9._jspService(jrun__view2ejsp9.java:56)
	at allaire.jrun.jsp.HttpJSPServlet.service(HttpJSPServlet.java:40)
	at allaire.jrun.servlet.JRunSE.service(JRunSE.java:1013)
	at allaire.jrun.servlet.JRunSE.runServlet(JRunSE.java:925)
	at allaire.jrun.servlet.JRunNamedDispatcher.forward(JRunNamedDispatcher.java:34)
	at allaire.jrun.jsp.JSPServlet.service(JSPServlet.java:175)
	at allaire.jrun.servlet.JRunSE.service(JRunSE.java:1013)
	at allaire.jrun.servlet.JRunSE.runServlet(JRunSE.java:925)
	at allaire.jrun.servlet.JRunRequestDispatcher.forward(JRunRequestDispatcher.java:88)
	at allaire.jrun.servlet.JRunSE.service(JRunSE.java:1131)
	at allaire.jrun.servlet.JvmContext.dispatch(JvmContext.java:330)
	at allaire.jrun.http.WebEndpoint.run(WebEndpoint.java:107)
	at allaire.jrun.ThreadPool.run(ThreadPool.java:272)
	at allaire.jrun.WorkerThread.run(WorkerThread.java:75)
如果把
 while(rs.next())
      {
       name=rs.getString("name");
      }
这几行注释了，程序运行的时候不出现错误。但是这几行这么错了？？？
</Content>
<PostDateTime>2002-4-24 13:53:48</PostDateTime>
</Reply>
<Reply>
<PostUserNickName>卧龙</PostUserNickName>
<rank>四级(中级)</rank>
<ranknum>user4</ranknum>
<credit>100</credit>
<ReplyID>4417980</ReplyID>
<TopicID>672175</TopicID>
<PostUserId>223374</PostUserId>
<PostUserName>wjfxiao</PostUserName>
<Point>0</Point>
<Content>这几行没错，程序报了空指针异常，可能是
rs是null
rs=view.executeQuery("select * from user_info");
这句执行了吗？</Content>
<PostDateTime>2002-4-24 14:05:59</PostDateTime>
</Reply>
<Reply>
<PostUserNickName>灵子</PostUserNickName>
<rank>二级(初级)</rank>
<ranknum>user2</ranknum>
<credit>97</credit>
<ReplyID>4418550</ReplyID>
<TopicID>672175</TopicID>
<PostUserId>159900</PostUserId>
<PostUserName>lingzi</PostUserName>
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