设计原理：

服务器端接受客户端的连接请求，同时启动一个线程处理这个连接，线程不停的读取客户端输入，然后把输入加入队列中，等候处理。在线程启动的同时将线程加入队列中，以便在需要的时候定位和取出。

｛源码｝

import java.io.*;

import java.net.*;

import java.util.*;

import java.lang.*;

public class Server extends ServerSocket

{

private static ArrayList User_List = new ArrayList();

private static ArrayList Threader = new ArrayList();

private static LinkedList Message_Array = new LinkedList();

private static int Thread_Counter = 0;

private static boolean isClear = true;

protected static final int SERVER_PORT = 10000;

protected FileOutputStream LOG_FILE = new FileOutputStream("d:/connect.log", true);

public Server() throws FileNotFoundException, IOException

{

super(SERVER_PORT);

new Broadcast();

//append connection log

Calendar now = Calendar.getInstance();

String str = "[" + now.getTime().toString() + "] Accepted a connection\015\012";

byte[] tmp = str.getBytes();

LOG_FILE.write(tmp);

try

{

while (true)

{

Socket socket = accept();

new CreateServerThread(socket);

}

}

finally

{

close();

}

}

public static void main(String[] args) throws IOException

{

new Server();

}

//--- Broadcast

class Broadcast extends Thread

{

public Broadcast()

{

start();

}

public void run()

{

while (true)

{

if (!isClear)

{

String tmp = (String)Message_Array.getFirst();

for (int i = 0; i < Threader.size(); i++)

{

CreateServerThread client = (CreateServerThread)Threader.get(i);

client.sendMessage(tmp);

}

Message_Array.removeFirst();

isClear = Message_Array.size() > 0 ? false : true;

}

}

}

}

//--- CreateServerThread

class CreateServerThread extends Thread

{

private Socket client;

private BufferedReader in;

private PrintWriter out;

private String Username;

public CreateServerThread(Socket s) throws IOException

{

client = s;

in = new BufferedReader(new InputStreamReader(client.getInputStream()));

out = new PrintWriter(client.getOutputStream(), true);

out.println("--- Welcome to this chatroom ---");

out.println("Input your nickname:");

start();

}

public void sendMessage(String msg)

{

out.println(msg);

}

public void run()

{

try

{

int flag = 0;

Thread_Counter++;

String line = in.readLine();

while (!line.equals("bye"))

{

if (line.equals("l"))

{

out.println(listOnlineUsers());

line = in.readLine();

continue;

}

if (flag++ == 0)

{

Username = line;

User_List.add(Username);

out.println(listOnlineUsers());

Threader.add(this);

pushMessage("[< " + Username + " come on in >]");

}

else

{

pushMessage("" + line);

}

line = in.readLine();

}

out.println("--- See you, bye! ---");

client.close();

}

catch (IOException e)

{}

finally

{

try

{

client.close();

}

catch (IOException e)

{}

Thread_Counter--;

Threader.remove(this);

User_List.remove(Username);

pushMessage("[< " + Username + " left>]");

}

}

private String listOnlineUsers()

{

String s ="-+- Online list -+-\015\012";

for (int i = 0; i < User_List.size(); i++)

{

s += "[" + User_List.get(i) + "]\015\012";

}

s += "-+---------------------+-";

return s;

}

private void pushMessage(String msg)

{

Message_Array.addLast(msg);

isClear = false;

}

}

}

这就是程序运行后，多用户登陆并且输入信息后的屏幕。实现了信息的实时广播。用户输入"l"就可以列出在线人员表。