I'm having some difficulty understanding what you're trying to do. Is your XSLT replacing the JSP, or to be used in conjunction with it?
If you're using a Java-based XSLT processor such as Saxon or Xalan, then they have mechanisms to call out to Java classes, but the details depend on the product. Generally, however, I would suggest passing information to the stylesheet in a parameter rather than getting it by calling Java extension functions.
Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference