从数据库到jsp视图页面的用户名和密码验证

Question

如果从数据库中检索到的用户名和密码不正确，那么我会在jsp页面本身显示错误，而不是重定向到另一个页面。

现在，如果用户名和密码无效，我会显示一条来自验证servlet的消息。如何在jsp视图中使用javascript或任何其他工具在前端显示消息？

以下是我的登录表：

<form id="loginform" class="form-horizontal" name="myForm" method="POST" action="ValidateLoginServlet2.do" onSubmit="return validateLogin()">
    <input type="text" class="form-control" name="uname" placeholder="username">                                        
    <input id="login-password" type="password" class="form-control" name="pwd" placeholder="password">
    <input type="submit" value="Login" href="#" class="btn btn-success" />
</form>

和我的验证登录servlet：

protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
//        processRequest(request, response);
        PrintWriter out = response.getWriter();

        String username = request.getParameter("uname");
        String password = request.getParameter("pwd");
        System.out.println(username);
        System.out.println(password);

        try
        {
            Connection con = OracleDBConnection.getConnection();
            PreparedStatement statement = con.prepareStatement("select firstname, password from registration where firstname =? and password=?");
            statement.setString(1, username);
            statement.setString(2, password);
            ResultSet result = statement.executeQuery();
            if(result.next()){
                response.sendRedirect("LoginSuccessful.jsp");
            }else{
                out.println("username and password are incorrect");
            }
        }catch(Exception e){
            System.out.println("DB related Error");
            e.printStackTrace();
        }   
    }

Answer 1

您可以使用<span>元素来显示从servlet request获得的错误消息，下面是JSP页面：

<form id="loginform" class="form-horizontal" name="myForm" method="POST" action="ValidateLoginServlet2.do" onSubmit="return validateLogin()">
    <input type="text" class="form-control" name="uname" placeholder="username">                                        
    <input id="login-password" type="password" class="form-control" name="pwd" placeholder="password">
    <input type="submit" value="Login" href="#" class="btn btn-success" />
    <span style="color:red;">${errMsg}</span>
</form>

在servlet中，您可以在else语句中设置一个错误消息，如下所示：

if(result.next()) {
    response.sendRedirect("LoginSuccessful.jsp");
}else{
    request.setAttribute("errMsg", "username and password are incorrect");
    // The following will keep you in the login page
    RequestDispatcher rd = request.getRequestDispatcher("/login.jsp");
    rd.forward(request, response); 
}

为了防止下次在if块中成功登录时显示相同的错误，您可以像这样重置ErrMsg：

request.setAttribute("errMsg", "");

Answer 2

在验证登录servlet的else部分中，放入以下代码：

if(result.next()){
    response.sendRedirect("LoginSuccessful.jsp");
}
else{
  HttpSession session = request.getSession();
  session.setAttribute("wrong_uname_pass", "1");
  response.sendRedirect("index.jsp");
}

并将以下代码放在index.jsp的第一部分(或者在哪里是您的登录表单)

<%
if(session.getAttribute("wrong_uname_pass") != null){
%>
<script>

alert("wrong user name or password");
</script>

<%
session.removeAttribute("wrong_uname_pass");
}

%>