培训老师给小弟我们做的一个聊天小程序，大家看看好不

import java.util.*;
import java.net.*;
import java.io.*;

public class Server{
    public static final int port=10000;
    public static final Vector users=new Vector();
    public static void main(String args[]){
        ServerSocket server=null;
        try{
            server=new ServerSocket(port);
            System.out.println("Server start up on port :"+port);
            while(true){
                Socket s=server.accept();
                User user=new User(s);
                user.start();
            }
            

        }catch(Exception e){
            e.printStackTrace();
        }finally{

            if(server!=null&&!server.isClosed()){
                try{server.close();}catch(Exception e){}
            }    
        }
    }

}

class User extends Thread{
    private Socket s;
    private String userName;
    private InetAddress ip;
    public User(Socket s){
        this.s=s;
    }
    public void run(){
        try{
            InputStream input=s.getInputStream();
            OutputStream output=s.getOutputStream();
            BufferedReader buf=new 
                BufferedReader(new 
                InputStreamReader(input));
            PrintWriter pw=new 
            PrintWriter(new OutputStreamWriter(output),true);
            
            pw.println("welcome u ,enter your name :");
            userName=buf.readLine();
            Server.users.add(this);
            sendAll(userName+" has join us ");;
            long t=0;
            while(true){
                String line=buf.readLine();
                long s=System.currentTimeMillis();
                if((s-t)/1000<3){
                    pw.println("flush denied ");
                    continue;
                }
                t=s;

    
                if(line==null||line.trim().length()==0){
                pw.println("flush denied ");
                continue;
                }
                if(line.equals("bye")){
                    sendAll(userName+" leave us ");
                    Server.users.remove(this);    
                    break;
            
                }

                sendAll(userName+" said :"+line);
            }        
        }catch(Exception e){
            //e.printStackTrace();
        }finally{
            if(s!=null)try{s.close();}catch(Exception e){}
        }
    }
    public  synchronized void sendMessage(String message){
        try{
            PrintWriter pw=new 
            PrintWriter(new OutputStreamWriter(
            s.getOutputStream()));
            pw.println(message);
            pw.flush();
        }catch(Exception e){}
    }
    public void sendAll(String message){
        Iterator it=Server.users.iterator();
        while(it.hasNext()){
            User user=(User)it.next();
            user.sendMessage(message);
        }
    }
}