The SerlvetPathMatches class caches welcome file lookups which is great, unless you have a dynamic resource manager which can switch out the root for static files on the fly.  This causes the caching of welcome files to "bleed over" between different absolute paths. 

I would suggest a feature that causes the SerlvetPathMatches class to first capture the absolute path that the resource manager resolves to and then incorporate that into the welcome file cache.  That way if the resources are being served from /path/to/webroot1 for one thread, but being served from /path/to/webroot2 in another thread, each of those absolute paths will have their own cached welcome files.  

This ticket is created as a result of this mailing list thread:

https://groups.google.com/g/undertow-dev/c/ryDnfSVCHSY/m/l05QbUCwDQAJ