HTTP Status 500 - --------------------------------------------------------------------------------type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception org.apache.jasper.JasperException
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:358)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:301)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:248)
javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
root cause java.lang.NullPointerException
org.apache.jsp.jx.chklogin_jsp._jspService(chklogin_jsp.java:66)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:133)
javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:311)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:301)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:248)
javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
note The full stack trace of the root cause is available in the Tomcat logs.
--------------------------------------------------------------------------------Apache Tomcat/5.0.12
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:358)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:301)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:248)
javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
root cause java.lang.NullPointerException
org.apache.jsp.jx.chklogin_jsp._jspService(chklogin_jsp.java:66)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:133)
javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:311)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:301)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:248)
javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
note The full stack trace of the root cause is available in the Tomcat logs.
--------------------------------------------------------------------------------Apache Tomcat/5.0.12
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- description The server encountered an internal error () that prevented it from fulfilling this reque
空指针异常
如果某个用户在输入数据时并没有提供表单域"username"的值,或通过某种途径绕过表单直接输入时,此时request.getParameter("username")的值为空(不是空字符串,是空对象null。),out对象的println方法是无法直接对空对象操作,因此代码段1所在的JSP页面将会抛出"java.lang.NullPointerException"异常。
<%@ page language="java" import="java.sql.*" errorPage=""%>
<html>
<head>
<title>建信用户登录</title>
<script language="javascript">
<!--
function isValid(){
if(loginform.username.value==""){
window.alert("您必须完成帐号的输入");
document.loginform.elements(0).focus();
return false;
}if(loginform.password.value==""){
window.alert("您必须完成密码的输入");
document.loginform.elements(1).focus();
return false;
}
loginform.submit();
}
-->
</script>
<body bgcolor="#6685c5">
<%
String Login_message=(String)session.getAttribute("Login_message");
if(Login_message==null)
Login_message="";
else
out.println(Login_message);
%>
<form action="chklogin.jsp" method="post" onSubmit="return isValid()" name="loginform">
<table width="400" border="0" align="center" cellpadding="0" cellspacing="1" bgcolor="#6685c5">
<tr>
<td bgcolor="#ffffff"><table width="400" border="0" align="center" cellpadding="0" cellspacing="0">
<tr><td colspan="3"><img src="image/jx.jpg" width="515" height="309"></td>
</tr>
<tr>
<td height="35" colspan="3"><div align="center">用户:<input type="text" name="username" size=16 maxlength=16>
密码:<input type="password" name="password" size=16 maxlength=20>
</div></td>
</tr>
<tr>
<td width="239" height="37"><div align="center"> </div></td>
<td width="21"> </td>
<td width="140"><input type="submit" name="submit" value="登陆">
<input name="reset" type="reset" value="取消"></td>
</tr>
</table></td>
</tr>
</table>
</form>
</body>
</html>
这个是登录界面,,应该没有错,可以正确运行下面这段是连接数据库操作的,,总是出现问题,请各位大虾帮帮忙。。
<%@ page contentType="text/html;charset=gb2312"%>
<%@ page language="java" import="java.sql.*" errorPage="" %>
<jsp:useBean id="JX" scope="page" class="JX_Bean.Conn_JX_Bean"/>
<%
String username,password;
request.setCharacterEncoding("GB2312");
username=request.getParameter("username");
password=request.getParameter("password");
String sql="select * from user";
JX.OpenConn();
ResultSet rs=JX.executeQuery(sql);
if(rs.next()){
rs.close();
%>
<script language="javascript">
window.alert("登录成功");
</script>
<%
}
else{
rs.close();
String msg="用户名或口令错误";
session.setAttribute("Login_message",msg);
}
%>求助高手