How can I communicate between a JSP and an included JSP, included via the <jsp:include> syntax?

You can't really "communicate" with an included JSP, but there are a couple of other mechanisms that may help you.

Firstly, you could pass parameters to your included JSP using the <jsp:param> tags. The included JSP can then use these parameters to perform specific processing, etc.

Alternatively, you could use an instance of a JavaBean for the lifetime of that "request" (or session), and let the included JSP ask the bean for any information it requires.