org.apache.catalina.core.ApplicationDispatcher invoke
SEVERE: Servlet.service() for servlet UserController threw exception
java.lang.NullPointerException
at com.nic.sample.dao.UserDAO.getAllUsers(UserDAO.java:69)
at com.nic.sample.controller.UserController.doGet(UserController.java:44)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:646)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:436)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:374)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:302)
at org.apache.jasper.runtime.PageContextImpl.doForward(PageContextImpl.java:709)
at org.apache.jasper.runtime.PageContextImpl.forward(PageContextImpl.java:680)
at org.apache.jsp.index_jsp._jspService(index_jsp.java:64)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:388)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:861)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:606)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
at java.lang.Thread.run(Thread.java:662)
当我运行我的应用程序时出现上述错误，我正在使用 dao 从数据库中获取数据到 jsp，我不知道为什么会出现此错误。需要帮忙。我的jsp和DAO代码如下
我的 jsp 文件 listuser.jsp
<%@ page language="java" contentType="text/html; charset=EUC-KR" pageEncoding="EUC-KR"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt"%>
<%@page errorPage="error.jsp" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=EUC-KR">
<title>Show All Users</title>
</head>
<body>
<table border=1>
<thead>
<tr>
<th>User Id</th>
<th>First Name</th>
<th>Last Name</th>
<th>DOB</th>
<th>Email</th>
<th colspan=2>Action</th>
</tr>
</thead>
<tbody>
<c:forEach items="${users}" var="user">
<tr>
<td><c:out value="${user.userid}" /></td>
<td><c:out value="${user.firstName}" /></td>
<td><c:out value="${user.lastName}" /></td>
<td><fmt:formatDate pattern="yyyy-MMM-dd" value="${user.dob}" /></td>
<td><c:out value="${user.email}" /></td>
<td><a href="UserController?action=edit&userId=<c:out value="${user.userId}"/>">Update</a></td>
<td><a href="UserController?action=delete&userId=<c:out value="${user.userId}"/>">Delete</a></td>
</tr>
</c:forEach>
</tbody>
</table>
<p><a href="UserController?action=insert">Add User</a></p>
我的 UserDAO.java
package com.nic.sample.dao;
public class UserDAO {
private Connection connection;
public UserDAO() {
connection = DbUtil.getConnection();
}
public void addUser(User user) {
try {
PreparedStatement preparedStatement = connection.prepareStatement("insert into users(firstname,lastname,dob,email) values (?, ?, ?, ? )");
// Parameters start with 1
preparedStatement.setString(1, user.getFirstName());
preparedStatement.setString(2, user.getLastName());
preparedStatement.setDate(3, new java.sql.Date(user.getDob().getTime()));
preparedStatement.setString(4, user.getEmail());
preparedStatement.executeUpdate();
} catch (SQLException e) {
e.printStackTrace();
}
}
public void deleteUser(int userId) {
try {
PreparedStatement preparedStatement = connection.prepareStatement("delete from users where userId=?");
// Parameters start with 1
preparedStatement.setInt(1, userId);
preparedStatement.executeUpdate();
} catch (SQLException e) {
e.printStackTrace();
}
}
public void updateUser(User user) {
try {
PreparedStatement preparedStatement = connection
.prepareStatement("update users set firstname=?, lastname=?, dob=?, email=?" +
"where userid=?");
// Parameters start with 1
preparedStatement.setString(1, user.getFirstName());
preparedStatement.setString(2, user.getLastName());
preparedStatement.setDate(3, new java.sql.Date(user.getDob().getTime()));
preparedStatement.setString(4, user.getEmail());
preparedStatement.setInt(5, user.getUserid());
preparedStatement.executeUpdate();
} catch (SQLException e) {
e.printStackTrace();
}
}
public List<User> getAllUsers() {
List<User> users = new ArrayList<User>();
try {
Statement statement = connection.createStatement();
ResultSet rs = statement.executeQuery("select * from users");
while (rs.next()) {
User user = new User();
user.setUserid(rs.getInt("userid"));
user.setFirstName(rs.getString("firstName"));
user.setLastName(rs.getString("lastName"));
user.setDob(rs.getDate("dob"));
user.setEmail(rs.getString("email"));
users.add(user);
}
} catch (SQLException e) {
e.printStackTrace();
}
return users;
}
public User getUserById(int userId) {
User user = new User();
try {
PreparedStatement preparedStatement = connection.
prepareStatement("select * from users where userid=?");
preparedStatement.setInt(1, userId);
ResultSet rs = preparedStatement.executeQuery();
if (rs.next()) {
user.setUserid(rs.getInt("userid"));
user.setFirstName(rs.getString("firstName"));
user.setLastName(rs.getString("lastName"));
user.setDob(rs.getDate("dob"));
user.setEmail(rs.getString("email"));
}
} catch (SQLException e) {
e.printStackTrace();
}
return user;
}
}
请任何人帮助我，我真的被困在这里......