Simple chat server/client example

ChatClient.java

import java.io.IOException;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.Scanner;

public class ChatClient implements Runnable {

  // why is the ChatClient Multi-threaded?

	private Socket link;
	private PrintWriter outputStream;
	private Scanner inputStream;
	private int port = 7777;
	private String nick;

	public ChatClient() throws IOException {
		initialize();
	}

	private void initialize() throws IOException {
		// get server address
		Scanner keyboard = new Scanner(System.in);
		System.out.println("What is the chat server's ip address?");
		String str = keyboard.next();

		// get user nick
		System.out.println("What is your nick?");
		nick = keyboard.next();

		// connect to server
		InetAddress host = null;
		try {
			host = InetAddress.getByName(str);
		} catch (UnknownHostException e1) {
			System.out.println("Host not found");
		}
		System.out
				.println("You are now connected to: " + host.getHostAddress());

		link = null;
		try {
			link = new Socket(host, port);
			link.setReuseAddress(true);
		} catch (IOException e) {
			e.printStackTrace();
			System.out.println("not found");
		}
		inputStream = new Scanner(link.getInputStream());
		outputStream = new PrintWriter(link.getOutputStream());

		// start new thread to listen from server
		// one runnable, two threads... in which cases is this legal?
		Thread t = new Thread(this);
		t.start();

		// continuously listen your user input
		while (keyboard.hasNextLine()) {
			String msg = keyboard.nextLine();
			outputStream.println(nick + " says: " + msg);
			outputStream.flush();
		}
	}

	public static void main(String[] args) throws Exception {
		new ChatClient();
	}

	@Override
	public void run() {
		while (true) {
			if (inputStream.hasNextLine())
				System.out.println(inputStream.nextLine());
		}
	}
}

ChatClientHandler.java

import java.io.IOException;
import java.net.Socket;
import java.util.Scanner;

public class ChatClientHandler implements Runnable {

  // runnable for each client thread
	
	private Socket client;
	private ChatServer server;
	private Scanner inputStream;
	
	public ChatClientHandler(Socket client, ChatServer server) {
		this.client = client;
		this.server = server;
	}
		
	@Override
	public void run() {
		try {
			inputStream = new Scanner(client.getInputStream());
			while(true)
			{
				if(!inputStream.hasNext())
					return;
				String chatLine = inputStream.nextLine();
				System.out.println(client.getRemoteSocketAddress() + " said: " + chatLine);
				server.sendChatMessageToAll(chatLine);
			}
		} catch (IOException e) {
			e.printStackTrace();
		} 
	}

}

ChatServer.java

import java.io.IOException;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import java.util.Iterator;

public class ChatServer {

  // Toy ChatServer to illustrate multi-threading
	
	private final int port = 7777;
	private ServerSocket serverSocket;
	private ArrayList<Socket> clientList;	

	public ChatServer() {
		try {
			serverSocket = new ServerSocket(port);
			serverSocket.setReuseAddress(true);
		} catch (IOException e)
		{
			System.out.println(e.getStackTrace());
		}
		clientList = new ArrayList<Socket>();
	}

	public void startServer() throws IOException {
		System.out.println("Accepting clients...");
		while(true)
		{
			// wait for a client
			Socket client = serverSocket.accept();
			clientList.add(client);
			System.out.println("New client accepted..." + client.getRemoteSocketAddress());
			System.out.println("Total users: " + clientList.size());
			ChatClientHandler handler = new ChatClientHandler(client,this);
			Thread t = new Thread(handler);
			t.start();
		}
	}
	
	public synchronized void sendChatMessageToAll(String msg) throws IOException {
		for(Iterator<Socket> it=clientList.iterator(); it.hasNext();)
		{
			Socket client = it.next();
			if( !client.isClosed() )
			{
				PrintWriter pw = new PrintWriter(client.getOutputStream());
				pw.println(msg);
				pw.flush();
				//System.out.println("Sent to: " + client.getRemoteSocketAddress());
			}
		}
	}

	/**
	 * @param args
	 * @throws IOException 
	 */
	public static void main(String[] args) throws IOException {
		new ChatServer().startServer();
	}

}

PrintInetAddress.java

import java.net.InetAddress;
import java.net.UnknownHostException;

public class PrintInetAddress {

  public static void main(String[] args) throws UnknownHostException {
		
		System.out.println(InetAddress.getLocalHost().getHostAddress());
		System.out.println(InetAddress.getLocalHost().getHostName());
				
	}
}