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

public class TCPServer1 {

    private static int idConn; //id da coneccao
    public ArrayList<UserThread> al; // an ArrayList to keep the list of the Client
    private SimpleDateFormat sdf;// to System.out.println time
    private int porto;//porto tcp para comunicar
    private boolean isOn;// switch on/off para o servidor
    private boolean isFirst; //para saber qual servidor tcp esta up


    TCPServer1(int porto){
        this.porto = porto;
        al = new ArrayList<UserThread>();
        isFirst = true;
        start();
    }



    private void start(){
        isOn = true;
        try{
            UDPServer udpServer = new UDPServer(7000);
            ServerSocket serverSocket = new ServerSocket(porto);
            while(isOn){
                System.out.println("TCP Waiting on port "+porto+"...");
                Socket socket = serverSocket.accept(); //aceita a coneccao
                if(!isOn)
                    break;
                UserThread ut = new UserThread(socket);
                al.add(ut);
                ut.start();
            }
            //fecha a coneccao
            try{
                serverSocket.close();
                for (int i=0;i<al.size() ;i++ ) {
                    UserThread ut = al.get(i);
                    try{
                        ut.in.close();
                        ut.out.close();
                        ut.socket.close();
                    }
                    catch(IOException e){e.printStackTrace();}
                }
            }catch(Exception ex){ex.printStackTrace();}
        }catch(IOException e){e.printStackTrace();}

    }

    synchronized void remove(int id){
        for (int i=0;i<al.size() ;i++ ) {
            UserThread ut = al.get(i);
            if(ut.id == id){
                al.remove(i);
                return;
            }

        }
    }



    private synchronized void sendToAll(String msg){
        System.out.println(msg);
        for (int i = al.size();--i >=0 ; ) {
            UserThread ut = al.get(i);
            if(!ut.writeMsg(msg)){
                al.remove(i);
                System.out.println("Removed " + ut.username);
            }

        }
    }

    public static void main(String[] args) {
        //default -> 2000, pode ser especificado outro via terminal
        int porto = 2000;
        switch(args.length) {
            case 1:
            try {
                porto = Integer.parseInt(args[0]);
            }
            catch(Exception e) {
                System.out.println("Invalid port number.");
                return;
            }
            case 0:
            break;
            default:
            System.out.println("Using default port");
            return;

        }

        TCPServer1 server = new TCPServer1(porto);


    }


    class UserThread extends Thread {

        Socket socket;
        ObjectInputStream in;
        ObjectOutputStream out;
        // my unique id (easier for deconnection)
        int id;
        // the Username of the Client
        String username;
        // the only type of message a will receive
        Message cm;
        // the date I connect
        String date;

        // Constructore
        UserThread(Socket socket) {
            // a unique id
            id = ++idConn;
            this.socket = socket;

            try
            {
                out = new ObjectOutputStream(socket.getOutputStream());
                in  = new ObjectInputStream(socket.getInputStream());
                // read the username
                username = (String) in.readObject();
                System.out.println(username + " just connected.");
            }
            catch (IOException e) {
                System.out.println("Exception creating new Input/output Streams: " + e);
                return;
            }
            // have to catch ClassNotFoundException
            // but I read a String, I am sure it will work
            catch (ClassNotFoundException e) {
            }

        }

        // what will run forever
        public void run() {
            // to loop until LOGOUT
            boolean isOn = true;
            while(isOn) {
                // read a String (which is an object)
                try {
                    cm = (Message) in.readObject();
                }
                catch (IOException e) {
                    System.out.println(username + " Exception reading Streams: " + e);
                    break;
                }
                catch(ClassNotFoundException e2) {
                    break;
                }
                // the messaage part of the Message
                String message = cm.getMessage();

                // Switch on the type of message receive
                switch(cm.getType()) {

                    case Message.msg:
                    sendToAll(username + ": " + message);
                    break;
                    case Message.logout:
                    System.out.println(username + " disconnected with a LOGOUT message.");
                    isOn = false;
                    break;
                    case Message.users:
                    writeMsg("List of the users connected at " + sdf.format(new Date()) + "n");
                    // scan al the users connected
                    for(int i = 0; i < al.size(); ++i) {
                        UserThread ct = al.get(i);
                        writeMsg((i+1) + ") " + ct.username + " since " + ct.date);
                    }
                    break;
                }
            }
            // remove myself from the arrayList containing the list of the
            // connected Clients
            remove(id);
            close();
        }

        // try to close everything
        private void close() {
            // try to close the connection
            try {
                if(out != null) out.close();
            }
            catch(Exception e) {}
            try {
                if(in != null) in.close();
            }
            catch(Exception e) {};
            try {
                if(socket != null) socket.close();
            }
            catch (Exception e) {}
        }

        /*
         * Write a String to the Client output stream
         */
        private boolean writeMsg(String msg) {
            // if Client is still connected send the message to it
            if(!socket.isConnected()) {
                close();
                return false;
            }
            // write the message to the stream
            try {
                out.writeObject(msg);
            }
            // if an error occurs, do not abort just inform the user
            catch(IOException e) {
                System.out.println("Error sending message to " + username);
                System.out.println(e.toString());
            }
            return true;
        }
    }

}

Hope to get some help from you, I've searched similar problems but the solutions to these problems don't seem to help much.