Tomcat 8 webapp, dynamically add PostResources - servlets

Question

I have a webapp which uses a listener to dynamically add servlet instances.
Each servlet instance is defined by a user-defined configuration files, and encapsulates a distinct dataset. Each of these datasets may also include some user-defined static web files (HTML, JPG, CSS etc).
The static resources for each servlet instance are stored outside the webapp folder (to avoid deletion on redeployment), and each servlet instance has a separate folder hierarchy.
In the listener contextInitialized method, I am using
javax.servlet.ServletContext.addServlet
to add each of my servlet instances, and
javax.servlet.ServletRegistration.Dynamic.addMapping
to add the URL mapping for this servlet.
I would like to add other mappings for the static content in external folders.
In Tomcat 7, I extended org.apache.catalina.servlets.DefaultServlet
to change the relativePath to my new document root, but this class
does not work in Tomcat 8 0 - ClassNotFoundException (org.apache.naming.resources.FileDirContext).
Tomcat 8 has a new 'Resources' framework which should make this much more straightforward.
My question is - how can I add a PostResources element to my context dynamically (at web app startup, inside my listener), without editing the web.xml?
In my listener, I should be able to do something like this:
WebResourceRoot root = new StandardRoot(context);
root.createWebResourceSet(WebResourceRoot.ResourceSetType.POST,
"/my/url", "my/filesystem/path", null, "/");
but I cannot figure out how to get the required context (org.apache.catalina.Context), which is a completely different type to the similarly named javax.servlet.ServletContext provided by the ServletContextEvent in the listener contextInitialized method.
Any suggestions?
Thanks.

Answer 1

I think I have figured it out using the MBeanServer.
This seems a bit of a roundabout method though - is there no way of getting to the StandardRoot or StandardContext object from the ServletContext?
import javax.management.MBeanServer;
import javax.management.MBeanServerFactory;
import javax.management.ObjectName;
import javax.servlet.ServletContext;
import org.apache.catalina.core.StandardContext;
import org.apache.catalina.core.StandardEngine;
import org.apache.catalina.Container;
import org.apache.catalina.Server;
import org.apache.catalina.Service;
import org.apache.catalina.WebResourceRoot;
...
private void addPostResources(ServletContext servletContext)
throws Exception /* just for debugging */ {
MBeanServer mbs = MBeanServerFactory.findMBeanServer(null).get(0);
ObjectName name = new ObjectName("Catalina","type","Server");
Server server = (Server)mbs.getAttribute(name, "managedResource");
Service service = server.findService("Catalina");
StandardEngine engine = service.getContainer();
Container hostContainer = engine.findChild(engine.getDefaultHost());
StandardContext standardContext = (StandardContext)hostContainer.findChild(servletContext.getContextPath());
WebResourceRoot root = standardContext.getResources();
root.createWebResourceSet(WebResourceRoot.ResourceSetType.POST,
"/my/url", "my/filesystem/path", null, "/");
}