perchč non usi i mapping di web.xml?
codice:
  <servlet>
    <servlet-name>DownloadServlet</servlet-name>
    <jsp-file>/download.jsp</jsp-file>
  </servlet>
  <servlet-mapping>
    <servlet-name>DownloadServlet</servlet-name>
    <url-pattern>/download</url-pattern>
  </servlet-mapping>