tomcat报错如下：
HTTP Status 500 - /WebRoot/news.jsp (line: 9, column: 0) The value for the useBean class attribute dao.UserDAO is invalid.
type Exception report
message /WebRoot/news.jsp (line: 9, column: 0) The value for the useBean class attribute dao.UserDAO is invalid.
description The server encountered an internal error that prevented it from fulfilling this request.
news.jsp的代码为：
<%@ page language="java" import="java.util.*" pageEncoding="utf-8" session="True"%>
<%@ page import="java.sql.*" %>
<%@ page import="dao.UserDAO" %>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<jsp:useBean id="mybean" class="dao.UserDAO"></jsp:useBean>
<jsp:setProperty name="user" property="*"></jsp:setProperty>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<base href="<%=basePath%>">
<title>新闻</title>
<link href="<%=request.getContextPath()%>/WebRoot/css/news.css" type="text/css" rel="stylesheet"/>
</head>
<body>
</body>
</html>
UserDAO.java的代码为：
package dao;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Connection;
import java.sql.Statement;
import com.mysql.jdbc.PreparedStatement;
public class UserDAO {
Connection con = null;
Statement stat = null;
PreparedStatement pstat = null;
ResultSet rs = null;
public UserDAO() {}
//取得数据连接
public Connection GetConn() {
try{
Class.forName("com.mysql.jdbc.Driver").newInstance();
String url = "jdbc:mysql://localhost:3306/spassage";
con = DriverManager.getConnection(url,"root","to123day");
}catch(Exception ex){
ex.printStackTrace();
}
return con;
}
//执行数据库查询并返回查询结果
public ResultSet query(String sql){
try{
con = GetConn();
stat = con.createStatement();
rs = stat.executeQuery(sql);
}catch(Exception ex){
ex.printStackTrace();
}
return rs;
}
//关闭数据库连接
public void close(){
try{
if (rs != null)rs.close();
if (stat != null)stat.close();
if (pstat != null)pstat.close();
if (rs != null)rs.close();
}catch(Exception ex){
ex.printStackTrace();
}
}
}
D:\apache-tomcat-8.0.24\webapps\tsnews\WebRoot\WEB-INF\classes\dao目录下UserDAO.class已经存在
哪里出问题了？
找到原因了，因为com.mysql.jdbc.PreparedStatement的包没有放在WEB-INF\lib下，运行的时候没有正确导入，导致dao.UserDAO无效。