return a Channel for the resource. If the resource can be made locally available, a FileChannel is returned.
return the file for the WebFileObject.
return the fileObject size in bytes. This may contact the server to get the size, and this caches the size.
returns true is the file is locally available, meaning clients can call getFile() and the readable File reference will be available in interactive time. For FileObjects from HttpFileSystem, a HEAD request is made to ensure that the local file is as new as the website one (when offline=false).