That is quite an old blog, it is likely that the same code will no longer work. Adding request handlers is not too complicated. Take a look at the documentation:
You can also check on github for some examples https://github.com/hgeldenhuys/Monolith-main/blob/aac484da95cfeaf9363372bc3ac77b425f9a0375/javasource/appcloudservices/actions/StartSignOnServlet.java
Hope this helps
Mendix’ DeepLink module implements custom requesthandlers and is more properly written within Java. Please check the javasource folder of that module to see how custom requesthandlers are properly implemented in Java.
I used this module as an example in the past!