Question

当我在Tomcat Web服务器上运行此程序，并尝试使用正确或错误的凭据过帐FORM时，将导致HTTP / 500错误。

servlet代码：

/*
 * Written by Leonardo van de Weteringh
 */
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 java.io.IOException;

@WebServlet("/check")
public class check extends HttpServlet {

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        final String Username = "Noord";
        final String Password = "Korea";

        String formUsername = request.getParameter("username");
        String formPassword = request.getParameter("password");

        if (formUsername.equals(Username) && formPassword.equals(Password)) {
            response.sendRedirect("/internet/ok.html");
        } else {
            RequestDispatcher view = request.getRequestDispatcher("/internet/fail.html");
            view.forward(request, response);
        }
    }
}

这是登录页面代码：

<!DOCTYPE html>
<html lang="en">
<head>
<title>Koryo Airlines DPRK</title>
<link rel="stylesheet" type="text/css" href="../../scripts/css/login.css">
<link rel="shortcut icon" type="image/png" href="../../content/images/favicon.png"/>
<meta name="viewport" content="width=device-width, initial-scale=1">
</head>
<body>
<div class=navbar>
<ul class=horinav>
  <li class=horinav><a href="../../.">Home</a></li>
  <li class=horinav><a href="../../news/news.html">News</a></li>
  <li class=horinav><a href="../../contact/contact.html">Contact</a></li>
  <li class=horinav><a href="../../about/about.html">About</a></li>
  <li class=horinav>
  <div class=dropdown>
    <button class="dropbtn">More...</button>
  <div class="dropdown-content">
    <a href="../../about/flyingkoryo.html">Flying Koryo</a>
    <a href="../../about/aboutkoryo.html">About Koryo</a>
    <a href="../../about/bagage.html">Bagage</a>
    <a href="../../about/checkin.html">Check-In Procedure</a>
    <a href="../../websites/koreatoday.html">Korea Today</a>
    <a href="../../websites/friendsofkorea.html">More Websites...</a>
  </div>  
  <li class=horinav style="float:right"><a href="../register/register.html">Register</a></li>
  <li class=horinav style="float:right"><a class="active" href="#">Login</a></li>
</ul>
</div>
<div class="row">
<div class="column">
<center><img src="../content/images/banner.jpg" alt="" height="200" width="50%"></center>
</div>
</div>

<h1> Koryo Airlines Login Portal</h1>

<form action="/check" method="post">
  <div class="imgcontainer">
    <img src="../../content/images/login.jpg" alt="Avatar" class="avatar">
  </div>
<center>
  <div class="container">
    <label for="username"><b>Username</b></label>
    <input type="text" name="username" placeholder="Gebruikersnaam" maxlength="20" required>
<br>
    <label for="password"><b>Password</b></label>
    <input type="password" name="password" placeholder="Wachtwoord" maxlength="20" required>

    <button type="submit">Login</button>

    <label>
      <input type="checkbox" checked="checked" name="remember"> Remember me
    </label>
  </div>
</center>
  <div class="container" style="background-color:#f1f1f1">
    <button onclick="window.location.href='../../index.html'" type="button" class="cancelbtn">Cancel</button>
    <span class="psw">Forgot <a href="./forgotpsw.html">password?</a></span>
  </div>

</form>

</body>
</html>

我得到的错误：

 java.lang.NullPointerException check.doPost(check.java:21)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
 org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)

有人可以帮我吗。这是Servlet需要做的：

接受来自表单的输入并将其过帐。
要使用硬编码的username检查（验证）输入，然后 password，看是否有匹配项。
重定向到页面ok.html或fail.html

Answer 1

也许您的变量（formUsername或formPassword）为空值，所以您的程序给出了一个空指针。

您应该检查是否可以从请求中获取名称和密码。

Answer 2

感谢prasad_的最后评论，将POST更改为GET，以检查给定的变量。它们似乎在HTML表单中不匹配。我更改了

<input type="text" name="username" placeholder="Gebruikersnaam" maxlength="20" required>

到

<input type="text" name="Username" placeholder="Gebruikersnaam" maxlength="20" required>

和

<input type="password" name="password" placeholder="Wachtwoord" maxlength="20" required>

到

<input type="password" name="Password" placeholder="Wachtwoord" maxlength="20" required>

所有其他更改均保持不变，并且再次起作用。输入“确定”后的凭据将重定向到ok.html

Answer 3

我意识到您的servlet代码没有覆盖默认的doPost方法。您通常应该有这样的东西

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
                   throws ServletException, IOException

还有我可以说的另一件事，就是检查您是否要添加javax.servlet.api-3.0.1.jar（可能是最新版本）

Java Servlet使用状态代码HTTP / 500运行

3 个答案: