数据库表没有显示在jsp webapp表上 [英] database table not showing up on jsp webapp table
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问题描述
我正在尝试将表格内容从ms访问表导入到jsp网页表中，但是我在第31行仍然收到错误，虽然我的代码很好，有人可以详细说明我的错误吗？
继承人jsp代码：
I am trying to import table contents from a ms access table to a jsp web page table , however I keep getting an error on line 31 although my code is fine, can someone elaborate me on whats wrong here?
heres the jsp code :
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<%@page language="java" import="java.io.*, java.util.*,java.sql.*"%>
<jsp:useBean id="data" scope="page" class="HW.search"/>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Web Tech Homework</title>
</head>
<body>
<table border="1">
<tr>
<th></th>
<th>CarID</th>
<th>FirmName</th>
<th>CarModel</th>
<th>CarType</th>
<th>ProductYear</th>
<th>Km</th>
<th>Color</th>
<th>EngineType</th>
<th>Price</th>
<th>ExtraInformation</th>
</tr>
<%
int counter = 0;
ResultSet rs = data.getCarTable();
while (rs.next()) { // row by row
//database colums name
counter++;
int t1 = rs.getInt("CarID"); // 1st col
String t2 = rs.getString("FirmName");// 1st col
String t3 = rs.getString("CarModel");// 1st col
String t4 = rs.getString("CarType");// 1st col
String t5 = rs.getString("ProductYear");// 1st col
String t6 = rs.getString("Km");// 1st col
String t7 = rs.getString("Color");// 1st col
String t8 = rs.getString("EngineType");// 1st col
String t9 = rs.getString("Price");// 1st col
String t10 = rs.getString("ExtraInfomation");// 1st col
%>
<tr>
<td><input type="radio" name="<%=counter%>"/></td>
<td><%=t1%></td>
<td><%=t2%></td>
<td><%=t3%></td>
<td><%=t4%></td>
<td><%=t5%></td>
<td><%=t6%></td>
<td><%=t7%></td>
<td><%=t8%></td>
<td><%=t9%></td>
<td><%=t10%></td>
</tr>
<% } //close while loop here %>
</table>
<%
rs.close();
%>
</body>
</html>
用于建立访问连接的我的Java类：
My Java Class For Establishing Access Connection :
package HW;
import java.sql.*;
public class database {
static Connection con = null;
public database() {
makeConnection();
}
public void makeConnection() {
String driver = "sun.jdbc.odbc.JdbcOdbcDriver";
String url = "jdbc:odbc:DB";
try {
//Class.forName(driver);
con = DriverManager.getConnection(url);
} catch (Exception err) {
System.out.println(err);
}
}
}
我的Java类获取表内容：
My Java Class For Getting Table Contents :
package HW;
import java.sql.*;
public class search {
public search() {
new database();
}
public ResultSet getCarTable() {
ResultSet rs = null;
try {
Statement stmt = database.con.createStatement();
rs = stmt.executeQuery("SELECT * FROM CAR");
} catch (Exception err) {
err.printStackTrace();
}
return rs;
}
}
浏览器错误：
ERROR BY THE BROWSER :
HTTP Status 500 - java.lang.NullPointerException
type Exception report
message java.lang.NullPointerException
description The server encountered an internal error that prevented it from fulfilling this request.
exception
org.apache.jasper.JasperException: java.lang.NullPointerException
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:549)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:470)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
root cause
java.lang.NullPointerException
HW.search.getCarTable(search.java:16)
org.apache.jsp.index_jsp._jspService(index_jsp.java:101)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
note The full stack trace of the root cause is available in the Apache Tomcat/7.0.53 logs.
Apache Tomcat/7.0.53
推荐答案
连接对象变为空。
Connection object getting null.
Statement stmt = database.con.createStatement();
检查makeConnection（）方法是否可以实际上返回一个对象。
Check makeConnection() method whether it actually return an object or else.
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