我用JSP＆amp;创建一个项目Servlet（和实体bean），我正在尝试创建一个用户注册为客户的表单，然后重定向到预订页面。
我想保留刚刚注册的客户的ID并将其填入禁用的文本字段，然后在下一页上创建预订。但每当我尝试通过jsp加载客户类时，整个应用程序都会因NullPointerException而崩溃。
当程序到达jsp-tags以获取我的客户时，程序似乎崩溃了，因为它确实将c.cPnr打印到控制台以及JSP文件中的测试。
<%@ page import = "g24.isp.ejb.Customer" %>
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Welcome to Ski Village!</title>
<link rel="stylesheet" href="new/css/normalize.css">
<link rel="stylesheet" href="new/css/stylesheet.css">
<link href='https://fonts.googleapis.com/css?family=Fjalla+One|Poppins:400,500,600' rel='stylesheet' type='text/css'>
<script src="javascript/script.js" type="text/javascript"></script>
</head>
<body>
<% System.out.println("test"); %>
<% Customer c = (Customer) session.getAttribute("customer"); %>
<div id="container">
<!-- HEADER + MENU -->
<header>
<div class="logo"><!-- Ski Village Logo --></div>
<div class="menu">
<ul>
<li> <a href="index.html"> Home </a></li>
<li class="left-menu"> <a href="about.html"> About </a></li>
<li class="right-menu"> <a href="booking.html" id="selected"> Book </a></li>
<li> <a href="index.html" > Test</a></li>
</ul>
</div>
</header>
<!-- PAGE CONTENT -->
<div id="wrapper">
<div class="center-form">
<form action="/HotelClient/HotelServlet" name="resForm" method="post">
<input type="text" name="cPnr" value="<%= c.getcPnr() %>" >
<input type="number" name="week" min="1" max="52" placeholder="Select week" >
<select name="cno">
<option value="1">Adventure Cabin
</option>
<option value="2">Cozy Cabin
</option>
<option value="3">Snowy Cabin
</option>
<option value="4">Hacker Cabin
</option>
</select>
<input type="submit" name="checkres" value="Check availability">
<input type="submit" name="submitresform" value="Create reservation" type="hidden">
<input name="operation" value="bajskorv" type="hidden">
</form>
</div>
<!-- FOOTER + SOCIAL ICONS -->
<footer>
<a href="http://facebook.com/"><img src="img/facebook-logo.png" class="social-icon" alt="facebook logo"></a>
<a href="http://instagram.com/"><img src="img/instagram-logo.png" class="social-icon" alt="instagram logo"></a>
<a href="http://twitter.com/"><img src="img/twitter-logo.png" class="social-icon" alt="twitter logo"></a>
<p>© 2016 | Ski Village</p>
</footer>
</div>
</div>
</body>
</html>
Servlet代码：
package g24.isp.servlets;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;
import javax.ejb.EJB;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import g24.isp.ejb.Cabin;
import g24.isp.ejb.Customer;
import g24.isp.ejb.Hotel;
import g24.isp.ejb.Reservation;
import g24.isp.facade.Facade;
import g24.isp.facade.FacadeLocal;
import g24.isp.ejb.MethodClass;
/**
* Servlet implementation class HotelServlet
*/
@WebServlet("/HotelServlet")
public class HotelServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
@EJB
private FacadeLocal facade;
/**
* @see HttpServlet#HttpServlet()
*/
public HotelServlet() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
* response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// TODO Auto-generated method stub
PrintWriter out = response.getWriter();
out.println("MainServlet-doGet");
out.close();
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
* response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// TODO Auto-generated method stub
String url = "did not get an url";
// Get hidden field
String operation = request.getParameter("operation");
MethodClass mc = new MethodClass();
if (operation.equals("createcustomer")) {
String cPnr = request.getParameter("txtcPnr");
String cAddress = request.getParameter("txtcAddress");
String cPhone = request.getParameter("txtcPhone");
String cName = request.getParameter("txtcName");
if (facade.findByCpnr(cPnr) == null) {
Customer customer = new Customer();
customer.setcPnr(cPnr);
customer.setcAddress(cAddress);
customer.setcPhone(cPhone);
customer.setcName(cName);
facade.createCustomer(customer);
url = "/new/reservation.jsp";
} else {
url = "new/newcust.jsp";
}
}
else if (operation.equals("createreservation")) {
String cpnr = request.getParameter("txtcPnr");
int week = mc.ParseStringToInt(request.getParameter("week"));
int cno = mc.ParseStringToInt(request.getParameter("cno"));
Customer cs = facade.findByCpnr(cpnr);
Cabin cb = facade.findByCabinNo(cno);
if (cb != null && cs != null) {
Reservation res = new Reservation();
res.setCabin(cb);
res.setCustomer(cs);
res.setrDate(week);
facade.createReservation(res);
url = "/Index.jsp";
} else {
System.out.println("Did not enter if statement");
url = "/Index.jsp";
}
}
else if (operation.equals("newcustomer")) {
url = "/new/newcust.jsp";
}
else if (operation.equals("setcustomer")) {
System.out.println("Servlet - Create reservation");
String cpnr = request.getParameter("txtcPnr");
System.out.println(cpnr);
url = "/new/reservation.jsp";
Customer customer = facade.findByCpnr(cpnr);
if (customer != null) {
System.out.println(customer.getcName());
session.setAttribute("customer", customer);
url = "/reservation.jsp";
}
else {
System.out.println("Customer value is null");
}
}
System.out.println(url);
RequestDispatcher dispatcher = getServletContext().getRequestDispatcher(url);
dispatcher.forward(request, response);
}
}
答案 0 :(得分：0)
可能是它没有设置会话属性，当c.getcPnr()执行时，它会抛出NullPointerException。你能检查一下属性是否在session中设置了吗？您可以尝试在jsp中打印出'c'。
答案 1 :(得分：0)
我解决了这个问题 - 我试图通过访问facade.findBycPnr（）方法找到客户。
解决方案是在创建客户时使用session.setAttribute（customer，cust）。