Question

I am doing some server side form validation and in the case that one or more of the fields is incorrectly filled out, an array gets populated with all of the error messages. On the client side, I have a scriplet that checks for the existence of any error messages and if there are any, it displays them. When the page comes from the servlet it knows if it has failed or not because on a successful submission, it would not reload the form jsp page at all.

This is how I am displaying the error:

<%if(request.getSession().getAttribute("errors") != null){ %>
<jsp:include page="error.jsp"></jsp:include>
<br>
<% } %>

And the error.jsp page is:

<%@ page import="java.util.ArrayList" %>

<h3>Oops...We Have a Problem</h3>
Please review and fix the following errors.
<br>
<%
ArrayList errMessages = (ArrayList)request.getSession().getAttribute("errors");
for(int i=0; i<errMessages.size(); i++){
out.println(errMessages.get(i));
%>
<br>

This all works fine, but I am following the MVC/Model 2 Paradigm approach in where I keep the code confined to servlets and the html (display objects) confined to jsp pages. Obviously, this small example breaks the rules.

Is there a way to “pre-build” the jsp page on the servlet so it knows to display the error.jsp and I can do the whole array abstraction on the server? In this example it only seems like a tiny bit of code in the jsp that can’t hurt, but in other examples I can see this code becoming a much larger section of the page and that is what I would like to avoid.

Answer 1

Just use taglibs instead of scriptlets to control the flow in JSP. JSTL is a standard JSP taglib and it offers flow control tags.

<c:if test="${not empty errors}">
    <jsp:include page="error.jsp" />
</c:if>

and

<c:forEach items="${errors}" var="error">
    <c:out value="${error}" /><br/>
</c:forEach>

See also:

• How to avoid Java code in JSP files?