this.field.addActionListener(new ActionListener() { 
  
 			public void actionPerformed(ActionEvent e) { 
 				Socket socket = ClientFrame.this.client.getSocket(); 
 				if (socket != null && !socket.isClosed()) { 
 					try { 
 						//显示到本地消息框 
 						ClientFrame.this.updateMessageFrame( 
 								ClientFrame.this.client.getIdentityId(), 
 								ClientFrame.this.client.getServerTime(), 
 								ClientFrame.this.field.getText()); 
  
 						//发送给服务器，要求服务器转发这条信息 
 						ClientFrame.this.client.execute(new Command( 
 								CommandEnum.NORMAL_MESSAGE, 
 								ClientFrame.this.client.getIdentityId()) 
 								.setParameter(CommandParameter.CONTENT, //CommandParameter.CONTENT是一个标识，用来存取消息的内容 
 										ClientFrame.this.field.getText()));//取出输入框的内容 
 					} catch (IOException e1) { 
 						e1.printStackTrace(); 
 					} 
 				} 
 			} 
 		}); 
 

    //为每个客户端开启一个线程监听
    class CommandListenner implements Runnable {
        Socket socket = null;

        public CommandListenner(Socket s) {
            this.socket = s;
        }

        public void run() {
            while (Server.this.isServerStart() && this.socket != null
                    && !this.socket.isClosed()) {
                Command cmd = null;
                try {
                    cmd = Server.getRemoteCommand(this.socket);
                    Server.this.commandHandler.execute(cmd, this.socket);
                } catch (IOException e) {

                    e.printStackTrace();
                    return;
                } catch (ClassNotFoundException e) {

                    e.printStackTrace();
                    return;
                } catch (Exception e) {
                    if (this.socket == null || this.socket.isClosed()) {
                        Server.this.disconnectClientSocket(socket);
                    } else {
                        e.printStackTrace();
                    }
                }
            }
            if (this.socket != null || !this.socket.isBound()) {
                Server.this.disconnectClientSocket(socket);
            }
        }
    }

/**
    * 发送消息
    * from (消息发送者名称)
    * socket (接收者的)
    * date (时间)
    * content (消息内容)
    */
    private boolean sendMessage(String from, Socket socket, long date,
            String content) {

        if (socket != null && socket.isConnected()) {

            // 问题所在区，如果将其注释掉，下面的语句将会导致循环发送数据
            // 测试:
            System.out.println("发送给" + socket);
            return server.execute(new Command(CommandEnum.NORMAL_MESSAGE, from)
                    .setParameter(CommandParameter.CONTENT, content)
                    .setParameter(CommandParameter.IDENTITY_ID, from)
                    .setParameter(CommandParameter.TIME, date), socket);

        } else {
            // 存入数据库
            return true;
        }
    }

    /**
     * 发送命令
     * 
     * @throws IOException
     */
    public boolean execute(Command cmd) throws IOException {
        System.out.println("*");
        ObjectOutputStream oos = null;
        if (this.socket != null && !this.socket.isClosed() && cmd != null) {
            oos = new ObjectOutputStream(this.socket.getOutputStream());
            oos.writeObject(cmd);
            oos.flush();
            if (cmd.getCmd() == CommandEnum.CLIENT_CLOSE) {
                this.isConnection = false;
            }
            return true;
        }

        return false;
    }