dotCMS 1.9 (as of 188.8.131.52) comes with tooling that allows integration with JSP applications.
This example shows how to use the included JSP viewtool. JSPs can be included in any template, container or content item, which makes "wrapping" your existing JSP app in dotCMS driven templates and content straightforward.
Where the file.jsp lives on the PHYSICAL file system under the web root. The tool does a requestDispatcher.include, which means you have the actual request and response in your JSP. <%@include in your JSP will work as well.