displaying error message in login page after login failure

jsp, servlets

Solution

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

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

It would be better if you go for JSTL:

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

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

Problem

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> ``` 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); } ``` 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

Original source