Question

当我在eclipse中启动动态应用程序时，我的Login.html被设置为欢迎文件，并显示出来。在那里，我有一个简单的表格：

Login.html文件

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>Login</title>
</head>
<body>
    <form action="LoginServlet" method="post">
        <table>
            <tr><td align="right">Username:</td><td><input type="text" name="userName"/></td></tr>
            <tr><td align="right">Password:</td><td><input type="password" name="password"/></td></tr>
            <tr><td/><td><input type="submit" value="Submit"></td></tr>
        </table>
    </form>
    <p>
        <a href="Register.html">Register</a>
    </p>
</body>
</html>

LoginServlet的代码：

    public class LoginServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

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

        doPost(request, response);
    }

    @SuppressWarnings("unchecked")
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String userName = request.getParameter("userName");
        String password = request.getParameter("password");

        ServletContext context = getServletContext();
        Map<String, User> users = (Map<String, User>) context.getAttribute("users");

        User user = users.get(userName);
        if (user == null) {
            response.sendRedirect("./Login.html");
            return;
        }
        if (!user.getUserName().equals(userName)) {
            response.sendRedirect("./Login.html");
            return;
        }

        if (!user.getPassword().equals(password)) {
            response.sendRedirect("./Login.html");
            return;
        }

        request.getSession().setAttribute("loggedInUser", user);

        response.sendRedirect("./WebShopServlet");

    }

}

我还有一个InitListener类，我在其中创建了2个用户并将其放在上下文中：

public class InitListener implements ServletContextListener {

    public void contextDestroyed(ServletContextEvent event) {
        // TODO Auto-generated method stub

    }

    public void contextInitialized(ServletContextEvent event) {


        ServletContext context = event.getServletContext();

        Map<String, User> users = new LinkedHashMap<>();
        User user = null;
        user = new User("a", "a", Role.ADMIN);
        users.put(user.getUserName(), user);
        user = new User("b", "b", Role.USER);
        users.put(user.getUserName(), user);
        context.setAttribute("users", users);

        Products products = new Products(context.getRealPath(""));
        context.setAttribute("products", products);

    }

现在，当我在浏览器中单击以制成形式提交时出现错误。在eclipse控制台中，它说这是第34行的空指针异常，这是LoginServlet中的 User user = users.get（userName）; 。

动态应用中的Tomcat服务器空指针异常

0 个答案: