Why is my tomcat valve not being invoked?

Question

I try to implement a Tomcat valve (currently using 7.0.55) that should intercept every request that reaches the Tomcat serivce, regardless of Connector and whatnot, regardless o

Answer 1

Turns out it is caused by a missing ROOT-directory in Tomcat's webapps-dir. I think that Tomcat does filter incoming requests rather rigorously at a very early point in time, even before any valves can handle and mess with the request.
And if there's no default context (i.e. no ROOT-dir) then Tomcat (thinks to) know(s) that a request to non-existing-webapp cannot succeed and thus does not even call the valve(s). With a default context Tomcat cannot know what will happen to the request and thus the valve gets its chance to intercept the request.