Checking servlet session attribute value in jsp file

Question

I have a no framework java application. It consists of jsp files for view and servlets for the business logic. I must set the user session is the servlet with a firstName parameter. In the jsp file, I need to check if my firstName parameter has a value or not. If the firstName parameter is set, I need to display some html in the jsp file. If it is not set, I need to display different html in the jsp file.

Servlet.java:

HttpSession session = request.getSession();
session.setAttribute("firstName", customer.getFristName());
String url = "/index.jsp";
RequestDispatcher dispatcher = getServletContext().getRequestDispatcher(url);
dispatcher.forward(request, response);

header.jsp:

// Between the <p> tags bellow I need to put some HTML with the following rules
// If firstName exist: Hello ${firstName} <a href="logout.jsp">Log out</a>
// Else: <a href="login.jsp">Login</a> or <a href="register.jsp">Register</a>

<p class="credentials" id="cr"></p>

What would be the best way to do this?

Update:

Here is a great tutorial I found on JSTL, in case anyone needs it: http://www.tutorialspoint.com/jsp/jsp_standard_tag_library.htm

Answer 1

<% if (session.getAttribute("firstName") == null) { %>
    <p> some content </p>
<% } else {%>
    <p> other content </p>
<% } %>

Answer 2

I think best way to do it is use of jstl tags. Because for simple jsp application it might good idea to add all java code to html but more heavier application it is best practice to use minimum java code on html.(seperate view layer from logic) (read this for more https://stackoverflow.com/a/3180202/2940265)
For your expectation you can easily use code like bellow

<c:if test="${not empty firstName}">
    <%--If you want to print content from session--%>
    <p>${firstName}</p>

    <%--If you want to include html--%>
<%@include file="/your/path/to/include/file.jsp" %>

    <%--include only get wrong if you give the incorrect file path --%>
</c:if>
<c:if test="${empty firstName}">
    <p>Jaathi mcn Jaathi</p>
</c:if>

If you didn't included jstl correctly you will unable to get expected output. refer this for such incident https://menukablog.wordpress.com/2016/05/10/add-jstl-tab-library-to-you-project-correctly/

Answer 3

In the servlet you can write as follows

        HttpSession session = request.getSession(true);
        session.setAttribute("firstName", customer.getFristName())
        response.sendRedirect("index.jsp");

The request.getSession(true) returns a new session if it doesn't exist any session otherwise it will return the current session. And, in the index.jsp page you can do as follows :

<%
if(session.getAttribute("firstName")==null) {
%>
<jsp:include page="firstPage.html"></jsp:include>
<%
} else {
%>
<jsp:include page="secondPage.html"></jsp:include>
<%
}%>

Here, if the firstName is null then firstPage.html will be included in the page otherwise secondPage.html.