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-----急急急！基础问题,各位应该可以解答!------

saper 2001-12-15 09:05:47

在windows2000下安装了jdk1.3.1,tomcat3.2.3,设置如下：

-------------------------
path=%SystemRoot%\system32;%SystemRoot%;%SystemRoot%\System32\Wbem;d:\jdk1.3.1\bin;

java_home=d:\jdk1.3.1

tomcat_home=d:\tomcat3.2.3

classpath=.;d:\jdk1.3.1\lib\dt.jar;d:\jdk1.3.1\lib\tools.jar;d:\tomcat3.2.3\servlet.jar;d:\tomcat3.2.3\webserver.jar;
--------------------------
test.jsp 放在 d:\tomcat3.2.3\webapps\ROOT\jsp\ 下（jsp 目录为自己新建）

<HTML>
<head>
<meta http-equiv="Content-Type" conntent="text/html; charset=gb2312">
</head>
<BODY>
<%@ page language="java" import="java.sql.*" %>
<jsp:useBean id="sql_bean" scope="page" class="test.faq" />
<%
ResultSet rs=sql_bean.executeQuery("select * from forum_user");
while(rs.next()){
out.println("<li>"+rs.getString(1)+"</li>");
}
rs.close();
%>
</BODY>
</HTML>

-----------------------------
javabean: faq.java编译后放在d:\tomcat3.2.3\webapps\WEB_INF\classes\test 下面

package test;

import java.io.*;
import java.sql.*;

public class faq {
String sDBDriver="oracle.jdbc.driver.OracleDriver";
String sConnStr="jdbc:oracle:thin:ex_user/ex_user@192.168.0.1:1521:oradb";
Connection conn=null ;
ResultSet rs=null;
public faq(){
try{
Class.forName(sDBDriver);
}
catch(java.lang.ClassNotFoundException e){
System.err.println("faq():"+e.getMessage());
}
}
public ResultSet executeQuery(String sql){
rs=null;
try{
conn=DriverManager.getConnection(sConnStr);
Statement stmt=conn.createStatement();
rs=stmt.executeQuery(sql);
}
catch(SQLException ex){
System.err.println("aq.executeQuery:"+ex.getMessage());
}
return rs;
}
}

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

运行 http://localhost:8081/jsp/test.jsp 出现以下错误：

javax.servlet.ServletException
......以下省略（太多了）

Root cause:
java.lang.NullPointerException
..........

------------------------------------
注：以上程序在JDeveloper中可以调试通过的

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saper 2001-12-17

我解决了,原来是在Tomcat下找不到oracle dirver ,我设置了oracle dirver类路径后就好了,

谢谢各位了!

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saper 2001-12-17

To vdragon(紫龙):

应该不是你说的问题,我在JDeveloper中调试可以通过啊!

有如下错误:

Error: 500
Location: /jsp-test/jsp/faq-test.jsp
Internal Servlet Error:

javax.servlet.ServletException
at org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:459)
at jsp_0002dtest.jsp._0002fjsp_0002dtest_0002fjsp_0002ffaq_0002dtest_0002ejspfaq_0002dtest_jsp_1._jspService(_0002fjsp_0002dtest_0002fjsp_0002ffaq_0002dtest_0002ejspfaq_0002dtest_jsp_1.java:105)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:119)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.jasper.servlet.JspServlet$JspCountedServlet.service(JspServlet.java:130)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.jasper.servlet.JspServlet$JspServletWrapper.service(JspServlet.java:282)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:429)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:500)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.tomcat.core.ServletWrapper.doService(ServletWrapper.java:405)
at org.apache.tomcat.core.Handler.service(Handler.java:287)
at org.apache.tomcat.core.ServletWrapper.service(ServletWrapper.java:372)
at org.apache.tomcat.core.ContextManager.internalService(ContextManager.java:812)
at org.apache.tomcat.core.ContextManager.service(ContextManager.java:758)
at org.apache.tomcat.service.http.HttpConnectionHandler.processConnection(HttpConnectionHandler.java:213)
at org.apache.tomcat.service.TcpWorkerThread.runIt(PoolTcpEndpoint.java:416)
at org.apache.tomcat.util.ThreadPool$ControlRunnable.run(ThreadPool.java:501)
at java.lang.Thread.run(Thread.java:484)

Root cause:
java.lang.NullPointerException
at jsp_0002dtest.jsp._0002fjsp_0002dtest_0002fjsp_0002ffaq_0002dtest_0002ejspfaq_0002dtest_jsp_1._jspService(_0002fjsp_0002dtest_0002fjsp_0002ffaq_0002dtest_0002ejspfaq_0002dtest_jsp_1.java:93)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:119)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.jasper.servlet.JspServlet$JspCountedServlet.service(JspServlet.java:130)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.jasper.servlet.JspServlet$JspServletWrapper.service(JspServlet.java:282)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:429)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:500)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.tomcat.core.ServletWrapper.doService(ServletWrapper.java:405)
at org.apache.tomcat.core.Handler.service(Handler.java:287)
at org.apache.tomcat.core.ServletWrapper.service(ServletWrapper.java:372)
at org.apache.tomcat.core.ContextManager.internalService(ContextManager.java:812)
at org.apache.tomcat.core.ContextManager.service(ContextManager.java:758)
at org.apache.tomcat.service.http.HttpConnectionHandler.processConnection(HttpConnectionHandler.java:213)
at org.apache.tomcat.service.TcpWorkerThread.runIt(PoolTcpEndpoint.java:416)
at org.apache.tomcat.util.ThreadPool$ControlRunnable.run(ThreadPool.java:501)
at java.lang.Thread.run(Thread.java:484)

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yuanzi 2001-12-17

这不就是为空的错误吗？你这样catch一下看结果怎样？
try{
while(rs.next()){
out.println("<li>"+rs.getString(1)+"</li>");
}
}catch(Exceptione e){
out.println("saper错误一"+e.toString());
}
这样你看看！把那两行注释掉，不能说明 ResultSet rs=sql_bean.executeQuery("select * from forum_user");这一行返回的值是什么，如果是null，那么while(rs.next()){
out.println("<li>"+rs.getString(1)+"</li>");就会报空异常了。

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vdragon 2001-12-17

难道是rs.getString(1)抛出了Exception？
是不是第一列的类型不是String，然后是null，在toString()的时候出现异常

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saper 2001-12-17

各位帮一下忙啊!

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saper 2001-12-17

我换了tomcat4.0 出现下面错识:java.lang.NullPointerException.......

******但是在JDeveloper下调试可以通过啊!******

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tehcon 2001-12-17

应该是rs==null;
你的推断有问题，ResultSet rs=sql_bean.executeQuery("select * from forum_user");执行不报错并不能说明数据库连接没问题，因为你在bean中把exception都catch了，如果出错，返回的就是null，不然你可以注释掉while(rs.next()){
out.println("<li>"+rs.getString(1)+"</li>");
}
然后把rs打印出来看看

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saper 2001-12-16

To bookbobby: 大哥你的方法好像不灵啊! 再帮我想想!

To yuanzi(远子):"select * from forum_user " 返回不为空,数据库连接没问题的,
只是要原程序中把 while(rs.next()){
out.println("<li>"+rs.getString(1)+"</li>");
}
这两行注释掉就没问题的,可见"ResultSet rs=sql_bean.executeQuery("select * from forum_user");"这句没问题(就说明数据连接没问题),再帮我想想!

谢谢两位!

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yuanzi 2001-12-15

这与.java文件好象没有关系吧~！
建议：
1。select * from forum_user 返回的结果是什么，是不是为空?
2. 将while(rs.next()){
out.println("<li>"+rs.getString(1)+"</li>");
}
这个放到try{}catch(Exception e){}里面调试，如果还不行，在对上一句进行类试处理。
3.检查是否能正确连到数据库。
4.祝你好运！

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