用javabean连接sql server 2000数据库报错，实在找不出原因啊，高分救答

javabean的源文件voteconn.java如下：
packagevote1;
importjava.sql.*;
publicclassvoteconn
{

publicstaticfinalStringsDBDriver="com.microsoft.jdbc.sqlserver.SQLServerDriver";
publicstaticfinalStringsConnStr="jdbc:microsoft:sqlserver://localhost:1433;DatabaseName=school";
publicstaticfinalStringuser="sa";
publicstaticfinalStringpassword="123456";
Connectionconnect=null;
ResultSetrs=null;
publicvoteconn()
{
try
{
Class.forName(sDBDriver);
}
catch(java.lang.ClassNotFoundExceptione)
{
System.err.println(e.getMessage());
}
}
publicResultSetexecuteQuery(Stringsql)
{
try
{
connect=DriverManager.getConnection(sConnStr,user,password);
Statementstmt=connect.createStatement();
rs=stmt.executeQuery(sql);
System.out.println("连接数据库成功");
returnrs;
}
catch(SQLExceptionex)
{
System.err.println(ex.getMessage());
System.out.println("发生异常啦");
returnnull;
}
}
publicintexecuteUpdate(Stringsql)
{
intresult=0;
try
{
connect=DriverManager.getConnection(sConnStr);
Statementstmt=connect.createStatement();
result=stmt.executeUpdate(sql);
returnresult;
}
catch(SQLExceptionex)
{
System.err.println(ex.getMessage());
returnresult;
}
}
}
将以上的源码编译成功后，把voteconn.class放到Tomcat5.5\webapps\ROOT\WEB-INF\classes\vote1\voteconn.class目录，而我的jsp文件是放在Tomcat5.5\webapps\ROOT\vote1\index.jsp目录的

index.jsp如下：
<%@pagecontentType="text/html;charset=gb2312"language="java"import="java.sql.*"errorPage=""%>
<jsp:useBeanid="ConnDbBean"scope="page"class="vote.voteconn"/>
<html>
<head>
<metahttp-equiv="Content-Type"content="text/html;charset=gb2312">
<title>网上调查表</title>
<styletype="text/css">

</style>
</head>

<body>
<divalign="center">
<p><spanclass="style1">请您投票</span>：</p>
<%ResultSetrs=ConnDbBean.executeQuery("select*fromvote1");%>
<tablewidth="150"border="1">
<formaction="vote.jsp">
<%
while(rs.next()){%>
<tr>
<td><inputtype="radio"name="type"value=<%=rs.getString("id")%>><%=rs.getString("note")%></td>
</tr>
<%}
rs.close();
%>
<tralign="center"><td><inputtype="submit"value="投票"></td></tr>
</form>
<tr><td><ahref="details.jsp">查看投票</a></td></tr>
</table>
</div>
</body>
</html>

在浏览器中执行jsp文件后报错，错误如下：
HTTPStatus500-

--------------------------------------------------------------------------------

typeExceptionreport

message

descriptionTheserverencounteredaninternalerror()thatpreventeditfromfulfillingthisrequest.

exception

org.apache.jasper.JasperException
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:510)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:393)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

rootcause

java.lang.NullPointerException
org.apache.jsp.vote1.index_jsp._jspService(org.apache.jsp.vote1.index_jsp:78)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:332)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

noteThefullstacktraceoftherootcauseisavailableintheApacheTomcat/5.5.15logs.

--------------------------------------------------------------------------------

ApacheTomcat/5.5.15

实在搞不懂是什么原因，而我用一另外一段代码却可以正然访问数据库，
并有返回值，代码Test1.java如下：
//JavaDocument
importjava.sql.*;
publicclassTest1
{
publicstaticfinalStringsDBDriver="com.microsoft.jdbc.sqlserver.SQLServerDriver";
publicstaticfinalStringurl="jdbc:microsoft:sqlserver://localhost:1433;DatabaseName=school";
publicstaticfinalStringuser="sa";
publicstaticfinalStringpassword="123456";
publicstaticvoidmain(String[]args)
{
StringqueryString="SELECT*FROMvote1";//SQL语句
Connectionconn=null;
Statementst=null;
ResultSetrs=null;
try
{
Class.forName(sDBDriver);
conn=DriverManager.getConnection(url,user,password);
st=conn.createStatement();
rs=st.executeQuery(queryString);
while(rs.next())
{
System.out.println("ID："+rs.getString("id")+"company:"+rs.getString("note")+"vote:"+rs.getString("c_num"));
}
rs.close();
st.close();
conn.close();
}
catch(Throwablet)
{
t.printStackTrace(System.out);
}
}
}

既然是这样，那么我的数据库的设置方面都应该没有错的吧，那代码又错在哪里呢，我反复看过了，
实在不知道呀，怎么返回经常为空呢，

14 个解决方案

#1

那就是有的时候数据库连不上，把数据库重新装一下，必须打上补丁
在javabean中加一个main看是不是好了，好了以后再放连JSP文件

14 个解决方案

#1

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