Can you try replacing localhost with “127.0.0.1” in your code?
Also, keep in mind localhost/chattest/index.cfm is NOT the same as localhost:8888/chattest/index.cfm (first is port 80, second is port 8888) and that’s probably why you’re getting the “Deze site is niet bereikbaar” message. Sounds like using localhost/chattest/index.cfm (or 127.0.0.1/chattest/index.cfm) is what you should be doing, and using port 8888 to connect to ws in your code (something like ws://127.0.0.1:8888/ws/echo, i think).
If you can provide us your code and web.xml file, we can help debug more.