// это бин
@Stateless
public class ExampleBean {

    public Integer add(Integer x, Integer y) {
        return  x + y;
    }

}

// это сервлет его использующий
@WebServlet(name = "beanclient", urlPatterns = {"/client"})
public class ClientBean extends HttpServlet {
    private Logger log = Logger.getLogger(ClientBean.class);

    @EJB
    private ExampleBean exampleBean;

    @Override
    protected void doGet(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse) throws ServletException, IOException {
        log.debug("doPost call");

        Integer x = Integer.parseInt((String) httpServletRequest.getParameter("addX"));
        Integer y = Integer.parseInt((String) httpServletRequest.getParameter("addY"));


        Integer sum = exampleBean == null ? -1000 : exampleBean.add(x, y);

        if (sum != -1000)
            httpServletResponse.getWriter().println("X + Y = " + sum);
        else
            httpServletResponse.getWriter().println("Error!!!");
    }
}