Thanks.
I am sorry , I was not present my problem clearly,
I want get the URL before any user accessing it.
I set the servle as load-on-startup servlet by definded below in
web.xml

<servlet>
       <display-name>MySer</display-name>
       <servlet-name>MySer</servlet-name>
       <servlet-class>com.santa.servlet.MyServlet</servlet-class>
       <load-on-startup>30</load-on-
startup>
<<---------------------------------------- init the servlet when
server start
   </servlet>
  <servlet-mapping>
       <servlet-name>MyServlet</servlet-name>
       <url-pattern>/service/MySer</url-pattern>
   </servlet-mapping>
so ,I want get the url-pattern in the method

@Override
    public void init(ServletConfig arg0) throws ServletException {
        System.out.println("*****************************");
               // I want get the url-pattern here
        System.out.println("*****************************");
        super.init(arg0);
    }

Thank you very much for your reply.