java局域网聊天室 基于java编写局域网多人聊天室

public class User{
 /**
  * 用户信息类
  * 用于记录用户个人信息:姓名以及IP
  */
 private String name;
 private String ip;

 public User(String name, String ip) {
  this.name = name;
  this.ip = ip;
 }
 public String getName() {
  return name;
 }
 public void setName(String name) {
  this.name = name;
 }
 public String getIp() {
  return ip;
 }
 public void setIp(String ip) {
  this.ip = ip;
 }
}

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.GridLayout;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.BindException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import java.util.StringTokenizer;

import javax.swing.DefaultListModel;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JSplitPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.border.TitledBorder;

public class Server_more {

 private JFrame frame;
 private JTextArea contentArea; //文本域
 private JTextField txt_message; //用于显示文本信息
 private JTextField txt_max;  //设置最大连接人数
 private JTextField txt_port; //设置端口号
 private JButton btn_start;  //开始按钮
 private JButton btn_stop;  //断开按钮
 private JButton btn_send;  //发送按钮
 private JPanel northPanel;  //北方面板
 private JPanel southPanel;  //南方面板
 private JScrollPane rightPanel; //左边滚动条
 private JScrollPane leftPanel; //右边滚动条
 private JSplitPane centerSplit; //分割线
 private JList userList;   //列表组件
 private DefaultListModel listModel;

 private ServerSocket serverSocket;
 private ServerThread serverThread;
 private ArrayList<ClientThread> clients;

 private boolean isStart = false;

 // 主方法,程序执行入口
 public static void main(String[] args) {
  new Server_more();
 }

 // 执行消息发送
 public void send() {
  if (!isStart) {
   JOptionPane.showMessageDialog(frame, "服务器还未启动,不能发送消息！", "错误",
     JOptionPane.ERROR_MESSAGE);
   return;
  }
  if (clients.size() == 0) {
   JOptionPane.showMessageDialog(frame, "没有用户在线,不能发送消息！", "错误",
     JOptionPane.ERROR_MESSAGE);
   return;
  }
  String message = txt_message.getText().trim();
  if (message == null || message.equals("")) {
   JOptionPane.showMessageDialog(frame, "消息不能为空！", "错误",
     JOptionPane.ERROR_MESSAGE);
   return;
  }
  sendServerMessage(message);// 群发服务器消息
  contentArea.append("服务器：" + txt_message.getText() + "\r\n");
  txt_message.setText(null);
 }

 // 构造放法
 public Server_more() {
  frame = new JFrame("服务器");
  // 更改JFrame的图标：
  //frame.setIconImage(Toolkit.getDefaultToolkit().createImage(Client.class.getResource("qq.png")));
  //frame.setIconImage(Toolkit.getDefaultToolkit().createImage(Server.class.getResource("qq.png")));
  contentArea = new JTextArea();
  contentArea.setEditable(false);
  contentArea.setForeground(Color.blue);
  txt_message = new JTextField();
  txt_max = new JTextField("30");
  txt_port = new JTextField("6666");
  btn_start = new JButton("启动");
  btn_stop = new JButton("停止");
  btn_send = new JButton("发送");
  btn_stop.setEnabled(false);
  listModel = new DefaultListModel();
  userList = new JList(listModel);

  southPanel = new JPanel(new BorderLayout());
  southPanel.setBorder(new TitledBorder("写消息"));
  southPanel.add(txt_message, "Center");
  southPanel.add(btn_send, "East");
  leftPanel = new JScrollPane(userList);
  leftPanel.setBorder(new TitledBorder("在线用户"));

  rightPanel = new JScrollPane(contentArea);
  rightPanel.setBorder(new TitledBorder("消息显示区"));

  centerSplit = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT, leftPanel,
    rightPanel);
  centerSplit.setDividerLocation(100);
  northPanel = new JPanel();
  northPanel.setLayout(new GridLayout(1, 6));
  northPanel.add(new JLabel("人数上限"));
  northPanel.add(txt_max);
  northPanel.add(new JLabel("端口"));
  northPanel.add(txt_port);
  northPanel.add(btn_start);
  northPanel.add(btn_stop);
  northPanel.setBorder(new TitledBorder("配置信息"));

  frame.setLayout(new BorderLayout());
  frame.add(northPanel, "North");
  frame.add(centerSplit, "Center");
  frame.add(southPanel, "South");
  frame.setSize(600, 400);
  //frame.setSize(Toolkit.getDefaultToolkit().getScreenSize());//设置全屏
  int screen_width = Toolkit.getDefaultToolkit().getScreenSize().width;
  int screen_height = Toolkit.getDefaultToolkit().getScreenSize().height;
  frame.setLocation((screen_width - frame.getWidth()) / 2,
    (screen_height - frame.getHeight()) / 2);
  frame.setVisible(true);

  // 关闭窗口时事件
  frame.addWindowListener(new WindowAdapter() {
   public void windowClosing(WindowEvent e) {
    if (isStart) {
     closeServer();// 关闭服务器
    }
    System.exit(0);// 退出程序
   }
  });

  // 文本框按回车键时事件
  txt_message.addActionListener(new ActionListener() {
   public void actionPerformed(ActionEvent e) {
    send();
   }
  });

  // 单击发送按钮时事件
  btn_send.addActionListener(new ActionListener() {
   public void actionPerformed(ActionEvent arg0) {
    send();
   }
  });

  // 单击启动服务器按钮时事件
  btn_start.addActionListener(new ActionListener() {
   public void actionPerformed(ActionEvent e) {
    if (isStart) {
     JOptionPane.showMessageDialog(frame, "服务器已处于启动状态，不要重复启动！",
       "错误", JOptionPane.ERROR_MESSAGE);
     return;
    }
    int max;
    int port;
    try {
     try {
      max = Integer.parseInt(txt_max.getText());
     } catch (Exception e1) {
      throw new Exception("人数上限为正整数！");
     }
     if (max <= 0) {
      throw new Exception("人数上限为正整数！");
     }
     try {
      port = Integer.parseInt(txt_port.getText());
     } catch (Exception e1) {
      throw new Exception("端口号为正整数！");
     }
     if (port <= 0) {
      throw new Exception("端口号 为正整数！");
     }
     serverStart(max, port);
     contentArea.append("服务器已成功启动!人数上限：" + max + ",端口：" + port
       + "\r\n");
     JOptionPane.showMessageDialog(frame, "服务器成功启动!");
     btn_start.setEnabled(false);
     txt_max.setEnabled(false);
     txt_port.setEnabled(false);
     btn_stop.setEnabled(true);
    } catch (Exception exc) {
     JOptionPane.showMessageDialog(frame, exc.getMessage(),
       "错误", JOptionPane.ERROR_MESSAGE);
    }
   }
  });

  // 单击停止服务器按钮时事件
  btn_stop.addActionListener(new ActionListener() {
   public void actionPerformed(ActionEvent e) {
    if (!isStart) {
     JOptionPane.showMessageDialog(frame, "服务器还未启动，无需停止！", "错误",
       JOptionPane.ERROR_MESSAGE);
     return;
    }
    try {
     closeServer();
     btn_start.setEnabled(true);
     txt_max.setEnabled(true);
     txt_port.setEnabled(true);
     btn_stop.setEnabled(false);
     contentArea.append("服务器成功停止!\r\n");
     JOptionPane.showMessageDialog(frame, "服务器成功停止！");
    } catch (Exception exc) {
     JOptionPane.showMessageDialog(frame, "停止服务器发生异常！", "错误",
       JOptionPane.ERROR_MESSAGE);
    }
   }
  });
 }

 // 启动服务器
 public void serverStart(int max, int port) throws java.net.BindException {
  try {
   clients = new ArrayList<ClientThread>();
   serverSocket = new ServerSocket(port);
   serverThread = new ServerThread(serverSocket, max);
   serverThread.start();
   isStart = true;
  } catch (BindException e) {
   isStart = false;
   throw new BindException("端口号已被占用，请换一个！");
  } catch (Exception e1) {
   e1.printStackTrace();
   isStart = false;
   throw new BindException("启动服务器异常！");
  }
 }

 // 关闭服务器
 @SuppressWarnings("deprecation")
 public void closeServer() {
  try {
   if (serverThread != null)
    serverThread.stop();// 停止服务器线程

   for (int i = clients.size() - 1; i >= 0; i--) {
    // 给所有在线用户发送关闭命令
    clients.get(i).getWriter().println("CLOSE");
    clients.get(i).getWriter().flush();
    // 释放资源
    clients.get(i).stop();// 停止此条为客户端服务的线程
    clients.get(i).reader.close();
    clients.get(i).writer.close();
    clients.get(i).socket.close();
    clients.remove(i);
   }
   if (serverSocket != null) {
    serverSocket.close();// 关闭服务器端连接
   }
   listModel.removeAllElements();// 清空用户列表
   isStart = false;
  } catch (IOException e) {
   e.printStackTrace();
   isStart = true;
  }
 }

 // 群发服务器消息
 public void sendServerMessage(String message) {
  for (int i = clients.size() - 1; i >= 0; i--) {
   clients.get(i).getWriter().println("服务器：" + message + "(多人发送)");
   clients.get(i).getWriter().flush();
  }
 }

 // 服务器线程
 class ServerThread extends Thread {
  private ServerSocket serverSocket;
  private int max;// 人数上限

  // 服务器线程的构造方法
  public ServerThread(ServerSocket serverSocket, int max) {
   this.serverSocket = serverSocket;
   this.max = max;
  }

  public void run() {
   while (true) {// 不停的等待客户端的链接
    try {
     Socket socket = serverSocket.accept();
     if (clients.size() == max) {// 如果已达人数上限
      BufferedReader r = new BufferedReader(
        new InputStreamReader(socket.getInputStream()));
      PrintWriter w = new PrintWriter(socket
        .getOutputStream());
      // 接收客户端的基本用户信息
      String inf = r.readLine();
      StringTokenizer st = new StringTokenizer(inf, "@");
      User user = new User(st.nextToken(), st.nextToken());
      // 反馈连接成功信息
      w.println("MAX@服务器：对不起，" + user.getName()
        + user.getIp() + "，服务器在线人数已达上限，请稍后尝试连接！");
      w.flush();
      // 释放资源
      r.close();
      w.close();
      socket.close();
      continue;
     }
     ClientThread client = new ClientThread(socket);
     client.start();// 开启对此客户端服务的线程
     clients.add(client);
     listModel.addElement(client.getUser().getName());// 更新在线列表
     contentArea.append(client.getUser().getName()
       + client.getUser().getIp() + "上线!\r\n");
    } catch (IOException e) {
     e.printStackTrace();
    }
   }
  }
 }

 // 为一个客户端服务的线程
 class ClientThread extends Thread {
  private Socket socket;
  private BufferedReader reader;
  private PrintWriter writer;
  private User user;

  public BufferedReader getReader() {
   return reader;
  }

  public PrintWriter getWriter() {
   return writer;
  }

  public User getUser() {
   return user;
  }

  // 客户端线程的构造方法
  public ClientThread(Socket socket) {
   try {
    this.socket = socket;
    reader = new BufferedReader(new InputStreamReader(socket
      .getInputStream()));
    writer = new PrintWriter(socket.getOutputStream());
    // 接收客户端的基本用户信息
    String inf = reader.readLine();
    StringTokenizer st = new StringTokenizer(inf, "@");
    user = new User(st.nextToken(), st.nextToken());
    // 反馈连接成功信息
    writer.println(user.getName() + user.getIp() + "与服务器连接成功!");
    writer.flush();
    // 反馈当前在线用户信息
    if (clients.size() > 0) {
     String temp = "";
     for (int i = clients.size() - 1; i >= 0; i--) {
      temp += (clients.get(i).getUser().getName() + "/" + clients
        .get(i).getUser().getIp())
        + "@";
     }
     writer.println("USERLIST@" + clients.size() + "@" + temp);
     writer.flush();
    }
    // 向所有在线用户发送该用户上线命令
    for (int i = clients.size() - 1; i >= 0; i--) {
     clients.get(i).getWriter().println(
       "ADD@" + user.getName() + user.getIp());
     clients.get(i).getWriter().flush();
    }
   } catch (IOException e) {
    e.printStackTrace();
   }
  }

  @SuppressWarnings("deprecation")
  public void run() {// 不断接收客户端的消息，进行处理。
   String message = null;
   while (true) {
    try {
     message = reader.readLine();// 接收客户端消息
     if (message.equals("CLOSE"))// 下线命令
     {
      contentArea.append(this.getUser().getName()
        + this.getUser().getIp() + "下线!\r\n");
      // 断开连接释放资源
      reader.close();
      writer.close();
      socket.close();

      // 向所有在线用户发送该用户的下线命令
      for (int i = clients.size() - 1; i >= 0; i--) {
       clients.get(i).getWriter().println(
         "DELETE@" + user.getName());
       clients.get(i).getWriter().flush();
      }

      listModel.removeElement(user.getName());// 更新在线列表

      // 删除此条客户端服务线程
      for (int i = clients.size() - 1; i >= 0; i--) {
       if (clients.get(i).getUser() == user) {
        ClientThread temp = clients.get(i);
        clients.remove(i);// 删除此用户的服务线程
        temp.stop();// 停止这条服务线程
        return;
       }
      }
     } else {
      dispatcherMessage(message);// 转发消息
     }
    } catch (IOException e) {
     e.printStackTrace();
    }
   }
  }

  // 转发消息
  public void dispatcherMessage(String message) {
   StringTokenizer stringTokenizer = new StringTokenizer(message, "@");
   String source = stringTokenizer.nextToken();
   String owner = stringTokenizer.nextToken();
   String content = stringTokenizer.nextToken();
   message = source + "：" + content;
   contentArea.append(message + "\r\n");
   if (owner.equals("ALL")) {// 群发
    for (int i = clients.size() - 1; i >= 0; i--) {
     clients.get(i).getWriter().println(message + "(多人发送)");
     clients.get(i).getWriter().flush();
    }
   }
  }
 }
}

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.GridLayout;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.util.HashMap;
import java.util.Map;
import java.util.StringTokenizer;

import javax.swing.DefaultListModel;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JSplitPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.border.TitledBorder;

public class Client_more{

 private JFrame frame;
 private JList userList;
 private JTextArea textArea;
 private JTextField textField;
 private JTextField txt_port;
 private JTextField txt_hostIp;
 private JTextField txt_name;
 private JButton btn_start;
 private JButton btn_stop;
 private JButton btn_send;
 private JPanel northPanel;
 private JPanel southPanel;
 private JScrollPane rightScroll;
 private JScrollPane leftScroll;
 private JSplitPane centerSplit;

 private DefaultListModel listModel;
 private boolean isConnected = false;

 private Socket socket;
 private PrintWriter writer;
 private BufferedReader reader;
 private MessageThread messageThread;// 负责接收消息的线程
 private Map<String, User> onLineUsers = new HashMap<String, User>();// 所有在线用户

 // 主方法,程序入口
 public static void main(String[] args) {
  new Client_more();
 }

 // 执行发送
 public void send() {
  if (!isConnected) {
   JOptionPane.showMessageDialog(frame, "还没有连接服务器，无法发送消息！", "错误",
     JOptionPane.ERROR_MESSAGE);
   return;
  }
  String message = textField.getText().trim();
  if (message == null || message.equals("")) {
   JOptionPane.showMessageDialog(frame, "消息不能为空！", "错误",
     JOptionPane.ERROR_MESSAGE);
   return;
  }
  sendMessage(frame.getTitle() + "@" + "ALL" + "@" + message);
  textField.setText(null);
 }

 // 构造方法
 public Client_more() {
  textArea = new JTextArea();
  textArea.setEditable(false);
  textArea.setForeground(Color.blue);
  textField = new JTextField();
  txt_port = new JTextField("6666");
  txt_hostIp = new JTextField("127.0.0.1");
  txt_name = new JTextField("吴承潜");
  btn_start = new JButton("连接");
  btn_stop = new JButton("断开");
  btn_send = new JButton("发送");
  listModel = new DefaultListModel();
  userList = new JList(listModel);

  northPanel = new JPanel();
  northPanel.setLayout(new GridLayout(1, 7));
  northPanel.add(new JLabel("端口"));
  northPanel.add(txt_port);
  northPanel.add(new JLabel("服务器IP"));
  northPanel.add(txt_hostIp);
  northPanel.add(new JLabel("姓名"));
  northPanel.add(txt_name);
  northPanel.add(btn_start);
  northPanel.add(btn_stop);
  northPanel.setBorder(new TitledBorder("连接信息"));

  rightScroll = new JScrollPane(textArea);
  rightScroll.setBorder(new TitledBorder("消息显示区"));
  leftScroll = new JScrollPane(userList);
  leftScroll.setBorder(new TitledBorder("在线用户"));
  southPanel = new JPanel(new BorderLayout());
  southPanel.add(textField, "Center");
  southPanel.add(btn_send, "East");
  southPanel.setBorder(new TitledBorder("写消息"));

  centerSplit = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT, leftScroll,
    rightScroll);
  centerSplit.setDividerLocation(100);

  frame = new JFrame("客户机");
  // 更改JFrame的图标：
 // frame.setIconImage(Toolkit.getDefaultToolkit().createImage(Client.class.getResource("qq.png")));
  frame.setLayout(new BorderLayout());
  frame.add(northPanel, "North");
  frame.add(centerSplit, "Center");
  frame.add(southPanel, "South");
  frame.setSize(600, 400);
  int screen_width = Toolkit.getDefaultToolkit().getScreenSize().width;
  int screen_height = Toolkit.getDefaultToolkit().getScreenSize().height;
  frame.setLocation((screen_width - frame.getWidth()) / 2,
    (screen_height - frame.getHeight()) / 2);
  frame.setVisible(true);

  // 写消息的文本框中按回车键时事件
  textField.addActionListener(new ActionListener() {
   public void actionPerformed(ActionEvent arg0) {
    send();
   }
  });

  // 单击发送按钮时事件
  btn_send.addActionListener(new ActionListener() {
   public void actionPerformed(ActionEvent e) {
    send();
   }
  });

  // 单击连接按钮时事件
  btn_start.addActionListener(new ActionListener() {
   public void actionPerformed(ActionEvent e) {
    int port;
    if (isConnected) {
     JOptionPane.showMessageDialog(frame, "已处于连接上状态，不要重复连接!",
       "错误", JOptionPane.ERROR_MESSAGE);
     return;
    }
    try {
     try {
      port = Integer.parseInt(txt_port.getText().trim());
     } catch (NumberFormatException e2) {
      throw new Exception("端口号不符合要求!端口为整数!");
     }
     String hostIp = txt_hostIp.getText().trim();
     String name = txt_name.getText().trim();
     if (name.equals("") || hostIp.equals("")) {
      throw new Exception("姓名、服务器IP不能为空!");
     }
     boolean flag = connectServer(port, hostIp, name);
     if (flag == false) {
      throw new Exception("与服务器连接失败!");
     }
     frame.setTitle(name);
     JOptionPane.showMessageDialog(frame, "成功连接!");
    } catch (Exception exc) {
     JOptionPane.showMessageDialog(frame, exc.getMessage(),
       "错误", JOptionPane.ERROR_MESSAGE);
    }
   }
  });

  // 单击断开按钮时事件
  btn_stop.addActionListener(new ActionListener() {
   public void actionPerformed(ActionEvent e) {
    if (!isConnected) {
     JOptionPane.showMessageDialog(frame, "已处于断开状态，不要重复断开!",
       "错误", JOptionPane.ERROR_MESSAGE);
     return;
    }
    try {
     boolean flag = closeConnection();// 断开连接
     if (flag == false) {
      throw new Exception("断开连接发生异常！");
     }
     JOptionPane.showMessageDialog(frame, "成功断开!");
    } catch (Exception exc) {
     JOptionPane.showMessageDialog(frame, exc.getMessage(),
       "错误", JOptionPane.ERROR_MESSAGE);
    }
   }
  });

  // 关闭窗口时事件
  frame.addWindowListener(new WindowAdapter() {
   public void windowClosing(WindowEvent e) {
    if (isConnected) {
     closeConnection();// 关闭连接
    }
    System.exit(0);// 退出程序
   }
  });
 }

 /**
  * 连接服务器
  * 
  * @param port
  * @param hostIp
  * @param name
  */
 public boolean connectServer(int port, String hostIp, String name) {
  // 连接服务器
  try {
   socket = new Socket(hostIp, port);// 根据端口号和服务器ip建立连接
   writer = new PrintWriter(socket.getOutputStream());
   reader = new BufferedReader(new InputStreamReader(socket
     .getInputStream()));
   // 发送客户端用户基本信息(用户名和ip地址)
   sendMessage(name + "@" + socket.getLocalAddress().toString());
   // 开启接收消息的线程
   messageThread = new MessageThread(reader, textArea);
   messageThread.start();
   isConnected = true;// 已经连接上了
   return true;
  } catch (Exception e) {
   textArea.append("与端口号为：" + port + " IP地址为：" + hostIp
     + " 的服务器连接失败!" + "\r\n");
   isConnected = false;// 未连接上
   return false;
  }
 }

 /**
  * 发送消息
  * 
  * @param message
  */
 public void sendMessage(String message) {
  writer.println(message);
  writer.flush();
 }

 /**
  * 客户端主动关闭连接
  */
 @SuppressWarnings("deprecation")
 public synchronized boolean closeConnection() {
  try {
   sendMessage("CLOSE");// 发送断开连接命令给服务器
   messageThread.stop();// 停止接受消息线程
   // 释放资源
   if (reader != null) {
    reader.close();
   }
   if (writer != null) {
    writer.close();
   }
   if (socket != null) {
    socket.close();
   }
   isConnected = false;
   return true;
  } catch (IOException e1) {
   e1.printStackTrace();
   isConnected = true;
   return false;
  }
 }

 // 不断接收消息的线程
 class MessageThread extends Thread {
  private BufferedReader reader;
  private JTextArea textArea;

  // 接收消息线程的构造方法
  public MessageThread(BufferedReader reader, JTextArea textArea) {
   this.reader = reader;
   this.textArea = textArea;
  }

  // 被动的关闭连接
  public synchronized void closeCon() throws Exception {
   // 清空用户列表
   listModel.removeAllElements();
   // 被动的关闭连接释放资源
   if (reader != null) {
    reader.close();
   }
   if (writer != null) {
    writer.close();
   }
   if (socket != null) {
    socket.close();
   }
   isConnected = false;// 修改状态为断开
  }

  public void run() {
   String message = "";
   while (true) {
    try {
     message = reader.readLine();
     StringTokenizer stringTokenizer = new StringTokenizer(
       message, "/@");
     String command = stringTokenizer.nextToken();// 命令
     if (command.equals("CLOSE"))// 服务器已关闭命令
     {
      textArea.append("服务器已关闭!\r\n");
      closeCon();// 被动的关闭连接
      return;// 结束线程
     } else if (command.equals("ADD")) {// 有用户上线更新在线列表
      String username = "";
      String userIp = "";
      if ((username = stringTokenizer.nextToken()) != null
        && (userIp = stringTokenizer.nextToken()) != null) {
       User user = new User(username, userIp);
       onLineUsers.put(username, user);
       listModel.addElement(username);
      }
     } else if (command.equals("DELETE")) {// 有用户下线更新在线列表
      String username = stringTokenizer.nextToken();
      User user = (User) onLineUsers.get(username);
      onLineUsers.remove(user);
      listModel.removeElement(username);
     } else if (command.equals("USERLIST")) {// 加载在线用户列表
      int size = Integer
        .parseInt(stringTokenizer.nextToken());
      String username = null;
      String userIp = null;
      for (int i = 0; i < size; i++) {
       username = stringTokenizer.nextToken();
       userIp = stringTokenizer.nextToken();
       User user = new User(username, userIp);
       onLineUsers.put(username, user);
       listModel.addElement(username);
      }
     } else if (command.equals("MAX")) {// 人数已达上限
      textArea.append(stringTokenizer.nextToken()
        + stringTokenizer.nextToken() + "\r\n");
      closeCon();// 被动的关闭连接
      JOptionPane.showMessageDialog(frame, "服务器缓冲区已满！", "错误",
        JOptionPane.ERROR_MESSAGE);
      return;// 结束线程
     } else {// 普通消息
      textArea.append(message + "\r\n");
     }
    } catch (IOException e) {
     e.printStackTrace();
    } catch (Exception e) {
     e.printStackTrace();
    }
   }
  }
 }
}