Gvfs obtains this information from the shared-mime-info database. The default handler is stored per-user, in the file $XDG_DATA_HOME/applications/mimeapps.list.
MIMETYPE should be a mime-type such as text/plain or application/mbox. HANDLER should be the name of an existing desktop file such as gedit.desktop.
The following options are understood:
On success 0 is returned, a non-zero failure code otherwise.
gvfs-open(1), m[blue]Shared MIME-Info specificationm