* @return VFSFile from the relPath and context.
*/
private static VFSFile getRootFile(ServletContext context, String relPath) {
String rootKey = context.getContextPath()+relPath;
if (mappedServlets.containsKey(rootKey)) return mappedServlets.get(rootKey).getRoot();
ServletVFS vfs = new ServletVFS(context, relPath);
mappedServlets.put(rootKey,vfs);
return vfs.getRoot();
}