This all depends on where the other portlet resides.
Two portlets in a common war file can share information through the PortletSession's APPLICATION_SCOPE. Portlets packaged in different war files cannot.
CBT Tutorial on How to Use the PortletSession's APPLICATION Scope A single portlet can have several
JSP pages associated with it. So, a portlet can get fed input from one JSP, and display results generated by a different JSP. This might accomplish your request a bit better. For more advanced, wizard like applications, you can always use the
JSF Portlet or the
Struts Portlet. I have some tutorials on how to create those in my signature links.
For portlets in separate war files, you can always write data to a database table in one, and have the other portlet read from that database table and generate the results.
JDBC is available in all portlets. IBM has something called a PortletService that helps facilitate this process.
All of this though is a way of saying that really, it's not inherently possible to have one portlet display the results of the other portlet. Portlets are intended to be independed of each other. What if the user removed that second portlet from their page? You'd have one portlet taking in data, but no portlet to display the data. Does that make sense? Probably not.
Being a portlet developer requires a bit of a mind shift away from
Servlets and JSPs. Start trying to think like a portlet developer, and you'll run into less of these issues.
Best of luck!
-Cameron McKenzie