先运行一个java写的局域网聊天，效果图如下

后使用c#图形修改如下：

c#代码：

servlet服务端

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Windows.Forms;
using System.Net;
using System.Net.Sockets;
using System.Threading;
using System.IO;
using System.Text;
using System.Text.RegularExpressions;

namespace Server
{
	public partial class MainForm : Form
	{
		private TcpListener listener;
		
		private Dictionary<String,TcpClient> socketList;
		private bool tag = true;
		private StringBuilder charList;
		
		public MainForm()
		{
			InitializeComponent();
			Control.CheckForIllegalCrossThreadCalls = false;
		}
		
		void Bu_StartClick(object sender, EventArgs e)
		{
			cb_chatList.Items.Clear();
			selectChat.Text="";
			int port = 8888;
			//创建服务端，并且启动
			try{
				listener = new TcpListener(IPAddress.Parse(ipAddress()),port);
				listener.Start();	
				
				bu_Start.Enabled = false;
				bu_stop.Enabled = true;
			}catch(Exception ex)
			{
				MessageBox.Show("服务器启动失败， 原因："+ex.Message);
				bu_Start.Enabled = true;
				bu_stop.Enabled = false;
				return;
			}
			selectChat.Text = "服务器启动成功，访问IP："+ipAddress()+"  端口号："+port;
			
			//记录住连接的客户端
			socketList = new Dictionary<String,TcpClient>();
			charList = new StringBuilder();
			
			//使用多线程，用于多个客户端接入
			Thread th = new Thread(new ThreadStart(executeTask));
			th.Start();
		}
		public void executeTask()
		{
			while(tag)
			{
				//等待用户连接
				TcpClient client = null;
				try{
					client = listener.AcceptTcpClient();
				}catch(Exception)
				{
				}
				Thread th = new Thread(executeRead);
				th.Start((Object)client);
			}
		}
		public void executeRead(Object pamars)
		{
			//永久监听读取客户端
			TcpClient client = pamars as TcpClient;
			while(tag)
			{
				NetworkStream ns = client.GetStream();
				StreamReader sr = new StreamReader(ns);
				String msg = String.Empty;
				String people = String.Empty;
				try {
					msg = sr.ReadLine();
					if(msg.IndexOf("<clientName>")!=-1)
					{
						msg = Regex.Split(msg,"=")[1];
				        cb_chatList.Items.Add(msg);       		
			        	charList.Append(msg).Append("<@>");
						socketList.Add(msg,client);
						msg = "<br>欢迎【"+msg+"】光临<br>";
					}
					selectChat.AppendText(msg.Replace("<br>","\r\n"));
					sendMsg(String.Empty,msg);
				} catch (Exception) {
					//MessageBox.Show(ex.Message.ToString());
					break;
				}
			}
		}
		public void sendMsg(String target,String msg)
		{
			if(String.Empty!=target)
			{
				TcpClient client = socketList[target];
				StreamWriter sw = new StreamWriter(client.GetStream());
				sw.WriteLine(msg);
				sw.Flush();	
			}else{
				Dictionary<String,TcpClient>.KeyCollection keyColl = socketList.Keys;
				foreach (String name in keyColl) 
				{
					StreamWriter sw = new StreamWriter(socketList[name].GetStream());
					sw.WriteLine(msg+"<@=@>"+charList.ToString());
					sw.Flush();				
				}
			}
		}
		/*根据计算名获取IP地址*/
		public String ipAddress()
		{
			IPAddress[] address = Dns.GetHostAddresses(Dns.GetHostName());
			return address[2].ToString();
		}
		
		void ServerFromFormClosing(object sender, FormClosingEventArgs e)
		{
			e.Cancel = false;
			if(tag)
				tag = false;
			if(listener!=null)
				listener.Stop();
		}
		
		void Bu_stopClick(object sender, EventArgs e)
		{
			bu_Start.Enabled = true;
			bu_stop.Enabled = false;
			if(tag)
				tag = false;
			if(listener!=null)
				listener.Stop();
		}
	}
}

using System;
using System.Drawing;
using System.Windows.Forms;
using System.Threading;
using System.Net;
using System.Net.Sockets;
using System.IO;
using System.Text;
using System.Text.RegularExpressions;

namespace Client
{
	public partial class MainForm : Form
	{
		private System.Windows.Forms.Timer closeWindowTimer;
		
		private StreamReader sr;
		private StreamWriter sw;
		private TcpClient tc;
		private ClientLong cl;
		private bool tag = true;
			
		public MainForm(TcpClient tcp,ClientLong clo)
		{
			cl = clo;
			tc = tcp;
			InitializeComponent();
			Control.CheckForIllegalCrossThreadCalls = false;
			bu_simple.Hide();
		}
		void ClientFromLoad(object sender, EventArgs e)
		{
			PiayCheckedChanged();
		}
		
	   /*事件方法*/
       public  void PiayCheckedChanged()
       {
            closeWindowTimer = new System.Windows.Forms.Timer();
            closeWindowTimer.Interval = 1000;
            closeWindowTimer.Tick += new EventHandler(theout);
            closeWindowTimer.Start();
        }
        
        /*执行的事件*/
        public void theout(object source, EventArgs  e)
        {
        	//这里单独开一个线程用来显示信息
        	try{
	        	Thread t1 = new Thread(new ThreadStart(readMsg));
	        	t1.Start();
        	}catch(Exception)
        	{
        	}
        }
        void readMsg()
        {
        	if(tag && tc!=null){
	        	sr = new StreamReader(tc.GetStream());
	        	String msg = sr.ReadLine();
	        	String[] address =  Regex.Split(msg,"<@=@>");
	        	chatText.AppendText(address[0].Replace("<br>","\r\n"));
	        	address = Regex.Split(address[1],"<@>");
	        	cb_chatList.Items.Clear();
	        	foreach (String s in address)
	        	{
	        		if(!String.IsNullOrEmpty(s) && s != cl.clientName)
		        		cb_chatList.Items.Add(s);       		
	        	}
        	}
        }
		void Button1Click(object sender, EventArgs e)
		{
			if(String.IsNullOrEmpty(textBox2.Text)){
				MessageBox.Show("请输入消息");return;
			}
			sw = new StreamWriter(tc.GetStream());
			sw.WriteLine("<br>"+cl.clientName+"　　"+DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss")+"<br>　"+textBox2.Text);
			textBox2.Text = "";
			sw.Flush();
		}
		void Bu_exitClick(object sender, EventArgs e)
		{
			MainFormFormClosing(null,null);
		}
		void Button2Click(object sender, EventArgs e)
		{
			chatText.Text = "";	
		}
		void MainFormFormClosing(object sender, FormClosingEventArgs e)
		{
			closeWindowTimer.Stop();
			cl.Close();
			tag = false;
			if(sr!=null)
				sr.Close();
			if(sw!=null)
				sw.Close();
		}
		void Bu_simpleClick(object sender, EventArgs e)
		{
			String selected = cb_chatList.Text;
			if(selected==null)
			{
				MessageBox.Show("请选择单聊对象");
				return;
			}
		}
	}
}

补充：

1：上传下载文件、聊天表情、私聊、踢人.......都是可以扩展的功能。

只是目前还有可执行的思路，希望有相同爱好者多多提出宝贵意见。我会继续关注。