此为即时通讯系统文档，详细介绍如何用Java做一个简单的即时通讯,该项目的主要功能为聊天,包括群聊和私聊,即对所有人聊天和对单人聊天.-This is the Im system documentation, details on how to use Java to do a simple instant messaging, the main function of the project s chat, including group chat and private chat, that