How I can to know in JSP if one page has been called by other page

Question

Hi,
I have a JSP portlet with one form to submit some information about clients.
When the visitor click one image the form is submitted correctly and the information is stored into database.
The problem is that I can't clean the values of the strings after the insert and when I call the page again, the code insert again the last information in the form.
My JSP code is supported in the feedback code of JPDK, but I can't ask for the value of submit button because the submit is done by the click over the image, with the next code:
<img height=16 alt=Submit src="/pictures/stacksite/form_send.gif"
width=99 border=0>
I ask for one input box required, if is null run the insert code, if don't I display the form page.
How I can clean this variables or how I know if the page has been submitted immediatly before. What variable I can request in JSP to know that or what I can do?
Regards,
FABIAN

Answer 1

I'm not sure that any javascript is necessary. You just need to turn the image into a 'proper' submit button, using the <BUTTON> element. This will cause the form and all its data to be POSTED, rather than to be sent as a query in a GET request. Note that it is important that the form passes on the value of the PortletRendererUtil.PAGE_LINK parameter using a hidden field, so that the jsp remembers the portal 'context' it is running in. E.g.
<%
// Derive a portlet-specific name for the submit parameter
String submitParam = HttpPortletRendererUtil.portletParameter(request, "submit");
if (request.getParameter(submitParam) != null )
... handle the data ...
%>
<form name="contactinfo" method="POST" action="<%= HttpPortletRendererUtil.htmlFormActionLink(request,PortletRendererUtil.PAGE_LINK) %>" >
<%= HttpPortletRendererUtil.htmlFormHiddenFields(request,PortletRendererUtil.PAGE_LINK) %>
<BUTTON name="<%= submitParam %>" value="submit" type="submit"><IMG src="/pictures/stacksite/form_send.gif" alt="submit"></BUTTON>
</FORM>
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