Retrieves the absolute file path to the named resource. This can be used, for example, to
locate configuration or authority files. The resource should be declared in the
<externalResourceDependencies> section of the descriptor.
This only works if the resource is a local file. If the resource is not a local file (for
example, it could be an http
URL, then an exception will be thrown.
URL decoding will be done on the file path, so it is safe to use this method for file paths
that contain spaces.
For backwards compatibility, if the key is not declared as a resource dependency, it is looked
up directly in the
#getDataPath() and the class path. However, this usage is
deprecated and support may be dropped in future versions. ALL external resource dependencies
should be declared in the descriptor.