openfire，如何配置使支持群聊的离线信息 - openfire报错

With MUC, this is completely dependent on the setup of the room itself. If the room is marked as persistent, then all messages sent to that room are stored and available later. When a user joins the room, those messages are either flooded to the user or the user can request them as defined by the spec. You can mark a room persistent when creating the room or, at least in openfire, there is a parameter to make all rooms persistent and you can create some additional defaults for how messages are handled.

不是太明白，能否说的更直接些，是否需要改写什么接口