GWT Project web xml configuration for export button

In my GWT project, I have a ReportClient.java class and PushButton("Export"), when click the button, the actionlistner part have the code com.google.gwt.user.client.Window.open(GWT.getModuleName()+"","","");

and I have a ExcelServlet.java class it is a servlet class

now I need how to configure in web xml for servlet and mapping for ExcelServlet.java class??

(shows in image detail)

I already having in the web xml is

  <servlet>
    <servlet-name>IVClientServlet</servlet-name>
    <servlet-class>cti.gwtdemo.server.IVClientServiceImpl</servlet-class>

    <init-param>
        <param-name>intelview_hostname</param-name>
        <param-value>localhost</param-value>
    </init-param>
    <init-param>
        <param-name>intelview_port</param-name>
        <param-value>5050</param-value>
    </init-param>
</servlet>
<servlet-mapping>
    <servlet-name>IVClientServlet</servlet-name>
    <url-pattern>/http://ift.tt/2pfPrNs;
</servlet-mapping>

now my question is how do I configure for pushbutton, Please Help me

Thanks in advance Ramananenter image description here