Using if-else in JSP

It’s almost always advisable to not use scriptlets in your JSP. They’re considered bad form. Instead, try using JSTL (JSP Standard Tag Library) combined with EL (Expression Language) to run the conditional logic you’re trying to do. As an added benefit, JSTL also includes other important features like looping.

Instead of:

<%String user=request.getParameter("user"); %>
<%if(user == null || user.length() == 0){
    out.print("I see! You don't have a name.. well.. Hello no name");   
}
else {%>
    <%@ include file="response.jsp" %>
<% } %>

Use:

<c:choose>
    <c:when test="${empty user}">
        I see!  You don't have a name.. well.. Hello no name
    </c:when>
    <c:otherwise>
        <%@ include file="response.jsp" %>
    </c:otherwise>
</c:choose>

Also, unless you plan on using response.jsp somewhere else in your code, it might be easier to just include the html in your otherwise statement:

<c:otherwise>
    <h1>Hello</h1>
    ${user}
</c:otherwise>

Also of note. To use the core tag, you must import it as follows:

 <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>

You want to make it so the user will receive a message when the user submits a username. The easiest way to do this is to not print a message at all when the “user” param is null. You can do some validation to give an error message when the user submits null. This is a more standard approach to your problem. To accomplish this:

In scriptlet:

<% String user = request.getParameter("user");
   if( user != null && user.length() > 0 ) {
       <%@ include file="response.jsp" %>
   }
%>

In jstl:

<c:if test="${not empty user}">
    <%@ include file="response.jsp" %>
</c:if>