聊天程序
........\DisplayServlet.java
........\MainServlet.java
........\MessageServlet.java
........\TopServlet.java
........\UserList.java
........\UserServlet.java
........\example_3_sg
........\............\DisplayServlet.class
........\............\MainServlet.class
........\............\MessageServlet.class
........\............\TopServlet.class
........\............\UserList.class
........\............\UserServlet.class
........\web.txt