您好我正在尝试在jsp页面中显示数据库的内容。我希望数据的连接和处理在java文件中，并且只有数据的显示将包含在jsp页面中。< / p>
我正在使用tomcat服务器。我的WEB-INF / lib文件夹中有ojdbc6.jar和jstl-1.2.jar。
请告知我缺少的东西。 任何想法将不胜感激。 谢谢。
这是java文件的内容。
public class DBConn extends HttpServlet {
public void getData(HttpServletRequest request,
HttpServletResponse response) throws IOException,
ServletException {
Connection connection = null;
List dataList = new ArrayList();
try {
// Load the JDBC driver
String driverName = "oracle.jdbc.driver.OracleDriver";
Class.forName(driverName);
// Create a connection to the database
String serverName = "localhost";
String portNumber = "1521";
String sid = "xe";
String url =
"jdbc:oracle:thin:@" + serverName + ":" + portNumber + ":" +
sid;
String username = "hr";
String password = "hr";
connection = DriverManager.getConnection(url, username, password);
Statement stmt = connection.createStatement();
ResultSet rset = stmt.executeQuery("select * from employees");
while (rset.next()) {
dataList.add(rset.getInt("employee_id"));
dataList.add(rset.getString("first_name"));
}
stmt.close();
} catch (ClassNotFoundException e) {
// Could not find the database driver
} catch (SQLException e) {
// Could not connect to the database
}
request.setAttribute("data", dataList);
String strViewPage = "index.jsp";
RequestDispatcher dispatcher =
request.getRequestDispatcher(strViewPage);
if (dispatcher != null) {
dispatcher.forward(request, response);
}
}
}
这是jsp文件的内容。
<%@page import="java.util.List"%>
<%@page import="java.util.Iterator"%>
<%@page language="java" import="java.util.*" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>JSP Page</title>
</head>
<body>
<h1>Hello World!</h1>
<table border="1" width="303">
<tr>
<td width="119"><b>Employee ID</b></td>
<td width="168"><b>First Name</b></td>
</tr>
<%Iterator itr;%>
<% List data = (List) request.getAttribute("data");
for (itr = data.iterator(); itr.hasNext();) {
%>
<tr>
<td width="119"><%=itr.next()%></td>
<td width="168"><%=itr.next()%></td>
</tr>
<%}%>
</table>
</body>
</html>
<?xml version="1.0" encoding="UTF-8"?>
<web-app
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
version="3.0">
<!-- Config here. No taglibs! -->
<!--
To change this template, choose Tools | Templates
and open the template in the editor.
-->
<!--web.xml code -->
<servlet>
<servlet-name>DBConn</servlet-name>
<servlet-class>DBConn</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>DBConn</servlet-name>
<url-pattern>/DBConn</url-pattern>
</servlet-mapping>
</web-app>
org.apache.jasper.JasperException: An exception occurred processing JSP page /index.jsp at line 26
23: </tr>
24: <%Iterator itr;%>
25: <% List data = (List) request.getAttribute("data");
26: for (itr = data.iterator(); itr.hasNext();) {
27: %>
28: <tr>
29: <td width="119"><%=itr.next()%></td>
Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:568)
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:722)
org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
root cause
java.lang.NullPointerException
org.apache.jsp.index_jsp._jspService(index_jsp.java:88)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
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:722)
org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
答案 0 :(得分：1)
您必须从网络浏览器（客户端）doGet或http://localhost:8084/DBConn请求 servlet 的http://localhost:8084/webapp_context/DBConn服务方法。
创建POJO，
public class Employee{
private Integer id;
private String name;
//public constructors and
//setter/getter
}
并更改您的servlet代码，
public class DBConn extends HttpServlet{
@Override
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws IOException, ServletException {
Connection connection = null;
Statement stmt=null;
ResultSet rset=null;
List<Employee> dataList = new ArrayList<Employee>();
try {
// Load the JDBC driver
String driverName = "oracle.jdbc.driver.OracleDriver";
Class.forName(driverName);
// Create a connection to the database
String serverName = "localhost";
String portNumber = "1521";
String sid = "xe";
String url = "jdbc:oracle:thin:@" + serverName + ":" + portNumber + ":" + sid;
String username = "hr";
String password = "hr";
connection = DriverManager.getConnection(url, username, password);
stmt = connection.createStatement();
rset = stmt.executeQuery("select * from employees");
while (rset.next()) {
dataList.add(new Employee(rset.getInt("employee_id"),
rset.getString("first_name"));
}
} catch (ClassNotFoundException e) {
// Could not find the database driver
} catch (SQLException e) {
// Could not connect to the database
} finally{
if(rs!=null){
try{
rs.close();
}catch(Exception ex) { /* */ }
}
if(stmt!=null){
try{
stmt.close();
}catch(Exception ex) { /* */ }
}
if(connection !=null){
try{
connection.close();
}catch(Exception ex) { /* */ }
}
}
request.setAttribute("data", dataList);
String strViewPage = "index.jsp";
RequestDispatcher dispatcher = request.getRequestDispatcher(strViewPage);
if (dispatcher != null) {
dispatcher.forward(request, response);
}
}
}
和index.jsp中的标记，
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<c:forEach var="employee" items="${data}">
<br/> ${employee.id} ${employee.name}
</c:forEach>
注意：永远不要在默认包中创建类型（类）。您必须必须为POJO和Servlet子类指定包名。