I added a servlet filter by calling ServletContext.addFilter(name, filterInstance)

the init method of filterInstance (the instance I created and registered) is called, but its destroy method is not called throughout the life of the webapp, even after undeploy.

I would expect the init/destroy methods to be symmetric; if one is called, the other should be called too, to release any resources and clean things up.

For the container-managed filter instance (see AS7-5802), init and destroyed are correctly called.