web.xml中必须要添上:<web-app>    <display-name>Tomcat Examples</display-name>
    <description>
      Tomcat Example servlets and JSP pages.
    </description>    <servlet-mapping>
        <servlet-name>invoker</servlet-name>
        <url-pattern>/servlet/*</url-pattern>
    </servlet-mapping>
</web-app>