I know it is easy to call the function to include the java script in jsp
But to your main question: you can't call instance methods of beans using the JSTL and EL in scriptless JSP pages. All you can do is to get and set properties of the beans.
This is intentional. The whole purpose of the JSTL and EL is to help herd developers to move processing out of the pages and into servlet controllers where it belongs. Any bean processing that is more involved than accessing the properties should be done before the request is forwarded from the controller to the page.
If you absolutely need to do something on the page than can't be done with JSTL/EL, you can write custom actions or EL function to extend the ability of the pages.