public void linkUserToChannel(String username, long channelId){
		if(!users.containsKey(username))
			System.out.println("User Service Error - User : " + username + " doesn't exist. Can't join channel : " +channelId);
		else if(ctrl.getChannel(channelId) == null)
			System.out.println("User Service Error - Channel : " + channelId + " doesn't exist. User : "+ username + "couldn'tt join this channel.");
		else if(ctrl.getChannel(channelId) instanceof Channel && !isUserLinkedToChannel(username,channelId)){
			getUser(username).addChannel(channelId);
			((Channel)ctrl.getChannel(channelId)).addUser(username);
			ctrl.sendJoinned(username,channelId);
			System.out.println("User Service - User : " + username + " joinned channel : " + channelId + ".");
		}	
	}