Message box in my JSP.

Hi,
I made a form and i need to have a message box that inform the user if one or more field are empty.
I tried with the following:
<%
if (".....one field is null.....")
{
this.showMessageDialog(null,"You need to enter a value...");
}
else
{
%>
<%@ include file="Response.jsp" %>
<%
}
%>
But it does'nt work. Do i have to insert the showMessageDialog inside my bean with the parent.showMesageDialog()?
I know that i can do it with javascript but i prefer java.
Is it possible??
Thank you very much
Jeff

JSP is *server side*. All JSP code is run on the server, and then sent back to the client. So even if you got it to work, where would it show up?

Please use Javascript for the validation since it runs on the Client side.
Remember JSP code runs at the web server...and not at the client!!!