GWT - Load a configuration item from context.xml

I have a GWT RPC application deployed to Tomcat 8, and I want the server code to load some configuration data (hostname and port to another service). Otherwise the service works fine. I have read multiple suggestions but I cant get it to work.

A snippet from my Tomcat context.xml (I'm aware that context.xml requires me to restart tomcat when changed - that is OK).

<Context reloadable="true">

  <Parameter name="config_hostname" value="192.168.2.199" override="false"/>
  <Parameter name="config_port" value="8888" override="false"/>

In my service implementation I have a setup() method. In that I try to access the config by:

String hostname = getServletConfig().getInitParameter("config_hostname");
String port = getServletConfig().getInitParameter("config_port");

however that doesnt work. Can anyone put me on the right track?