Hi Stefania,
I set on the BaseX 90 web.xml the old version of the servlet and that seemed to work. I am not sure if i will encounter other problems though. is the setting necessary in basex 9.0? or am i ok to downgraded for BaseX 90
I have no experience with WebSphere Liberty, so you may need to try if everything works as expected.
As Servlet 4.0 is used a lot in practice nowadays: Did you already try to contact the WebSphere developer team in order to find out when version 4 will be supported?
Best, Christian