Minecraft plugin programming file describe?

I'm currently programming a plugin where the name and location should be written to a file. The name of the player should be in a StringList, which for example means "OfflinePlayers". Now the coordinates of the player are to be stored in a subcategory of the player name. So something like this:
Offline Player:

-[Player]

coordinates:

X, Y, Z

How can I do that? And how can I read out the coordinates at the end when the player rejoins?

Config.set ("OfflinePlayers." + player.getName () + ". Coordinates.x", location.getX ());

int x = config.getInt ("OfflinePlayers." + player.getName () + ". Coordinates.x");

Would not a double at coordinates be better?

Yes're right