登录失败后在登录页面中显示错误消息 [英] displaying error message in login page after login failure

问题描述

这是login.jsp中的部分代码

here is some part of code from login.jsp

login.jsp

         <h2 class="swd-postheader">Login</h2>
              <form method="post" action="Login.select">
                 <p><input id="username" name= "username" type="text" placeholder="Username" style="margin:10px" autofocus required></p>
                 <p> <input id="password" name="password" type="password" placeholder="Password" style="margin:10px" required></p>
                 <p><input class="swd-button" type="submit" value="Sign In">
                    <a href="register.html"><button class="swd-button" type="button">New User</button></a>
                 </p>
              </form>
              <h2><%=request.getAttribute("errorMessage") %></h2>
           </div>
        </div>

如果用户不存在，则在servlet代码中

我正在使用带有错误msg的requestdispatcher

in the servlet code if the user does't exist i'm using requestdispatcher with error msg

servlet

if(res.next())
        {
                if ((thisname.equals(res.getString("username"))) && (thispwd.equals(res.getString("password"))))
                {
                    session.setAttribute("username", request.getParameter("username"));
                    response.sendRedirect("login-success.html");
                }
                else{
                    session.invalidate();
                    request.setAttribute("errorMessage", "Invalid user or password");
                    RequestDispatcher rd = request.getRequestDispatcher("/login.jsp");
                    rd.forward(request, response);          
                }

但是事情是<h2><%=request.getAttribute("errorMessage") %></h2>运行，只要打开登录jsp就会在没有失败的情况下在页面上返回null.仅当失败发生时，它显示无效的用户或密码".所以我想检查request.getAttribute ("errorMessage")为null.是它不然后调用<h2><%=request.getAttribute("errorMessage") %></h2>.我该怎么做?还是有更好的方法

but thing is <h2><%=request.getAttribute("errorMessage") %></h2> runs whenever login jsp is opened which returns null on the page when there is no failure.only when the failure occurs it displays "invalid user or password" .so i want to check if request.getAttribute("errorMessage") is null . is its not then invoke <h2><%=request.getAttribute("errorMessage") %></h2>. how do i do it? or is there a better way

推荐答案

由于您已经在jsp中使用了scriptlet，因此可以使用:

Since you are already using scriptlet in your jsp, you can use:

<%
    if(null!=request.getAttribute("errorMessage"))
    {
        out.println(request.getAttribute("errorMessage"));
    }
%>

如果您选择JSTL，那会更好:

It would be better if you go for JSTL:

<c:if test="${not empty errorMessage}">
   <c:out value="${errorMessage}"/>
</c:if>

要了解有关$ {}的更多信息(表达语言，它是与 JSTL )，

To learn more about those ${} things (the Expression Language, which is a separate subject from JSTL), check here.

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