Why my spring rest application receive 404

I use spring rest to send and receive json request/response, I deployed it to tomcat webapps under/orb, and send to http://localhost/orb, but got 404 979, it didn't reach it. What is wrong?

Here is my web.xml:
  <web-app>
    <servlet>
    <servlet-name>dispatcher</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
 </servlet>

   <servlet-mapping>
    <servlet-name>dispatcher</servlet-name>
    <url-pattern>/*</url-pattern>
   </servlet-mapping>
   ...
When I configure it as root context, I can receive request/response by   http://localhost/