The book demonstrates integration of JasperReports into JSP/Web applications, but it does not touch Flex at all, because it is a totally different topic. I guess you can follow either of the following two ways to use JasperReports in Flex applications:
1. Embed Flex within a
JSP page. This way you can also include your Jasper report into the JSP page.
2. Do the real work. Transform/Embed the html (and corresponding images) from JasperReports into your MXML.