How perform validation and display error message in same form in JSP?

Question

How can I display an error message in the very same JSP when a user submits a wrong input? I do not intend to throw an exception and show an error page.

Answer 1

I'm not quite sure what you mean by "display error message". If you have a standard error handling, then you can always check for options:

<%
    if(wrong option selected)
        throw new Exception("Invalid option selected");
%>

Of course, this is just the notion; preferably, you'd have your own exception class. But then again, I'm not quite sure what you're after.