MQTT - how connect using environment specific URL

 In my tests, I use project properties like host, port to connect to the app uder test.. 

Now is problem to do the same with MQTT.. I have on each environment differend port and host name.. 

HOW I can use per environment other connection?

IOW: how I can use project properties? in connection URL definition? this is impossible.

When the URL is in string.. without port number.. all works.. 

WHY???? common????? I can not set the port number? why???