Server.java

import java.io.*;
import java.net.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Server extends JFrame
{
    private JTextField userText; // input text
    private JTextArea chatWindow;
    private ObjectOutputStream output;
    private ObjectInputStream input;
    private ServerSocket server;
    private Socket connection;


    // constructor
    public Server()
    {
      super("Spivotron's IM");
      userText = new JTextField();
      userText.setEditable(false);
      userText.addActionListener(
        new ActionListener(){
          public void actionPerformed(ActionEvent event){
                sendMessage(event.getActionCommand());
                userText.setText(""); // reset userText to blank string
          }
        }
      );
      add(userText, BorderLayout.NORTH);
      chatWindow = new JTextArea();
      add(new JScrollPane(chatWindow));
      setSize(300, 150);
      setVisible(true);
    }
    // set up and run the server
    public void startRunning()
    {
      try{
        server = new ServerSocket(6789, 100); // port number and maximum number of people that can connect
        while(true){
          try{
            // connect and have a connection
            waitForConnection();
            setupStreams();
            whileChatting();
          }catch(EOFException eofException){ // program ends and connection stops
            showMessage("\n Server ended the connection!");
          }finally{
            closeCrap();
          }
        }
      }catch(IOException ioException){
        ioException.printStackTrace();
      }
    }
    // wait for connection, then display connetion information
    private void waitForConnection() throws IOException{
      showMessage("Waiting for someone to connect...\n");
      connection = server.accept(); // creates a Socket when the users connect
      showMessage(" Now connected to "+connection.getInetAddress().getHostName());
    }
    // get stream to send and receive data
    private void setupStreams() throws IOException
    {
      output  = new ObjectOutputStream(connection.getOutputStream());
      output.flush(); // cleans out leftover data
      input   = new ObjectInputStream(connection.getInputStream());
      showMessage("\n Streams are not setup! \n");
    }
    // during the chat conversation
    private void whileChatting() throws IOException{
      String message = "You are now connected!";
      sendMessage(message);
      ableToType(true);
      do {
        // have a conversation
        try{
          message = (String) input.readObject(); // view sent data as object
          showMessage("\n"+message);

        }catch(ClassNotFoundException classNotFoundException){
          showMessage("\n Unknown data type");
        }
      } while (!message.equals("CLIENT - END"));
    }

    // close streams and sockets
    private void closeCrap(){
      showMessage("\nClosing connection...\n");
      ableToType(false);
      try{
        output.close();
        input.close();
        connection.close();

      }catch(IOException ioException){
        ioException.printStackTrace();
      }
    }
    // send a message to a client
    private void sendMessage(String message)
    {
      try{
        output.writeObject("SERVER - " + message);
        output.flush();
        showMessage("\nSERVER - "+message);

      }catch(IOException ioException){
        chatWindow.append("\n ERROR. CANNOT SEND MESSAGE");
      }
    }

    // updates chatWindow
    private void showMessage(final String text)
    {
      SwingUtilities.invokeLater(
        new Runnable(){
          public void run(){
            chatWindow.append(text);
          }
        }
      );
    }
    // let the user type stuff into their box
    private void ableToType(final boolean tof){
      SwingUtilities.invokeLater(
        new Runnable(){
          public void run(){
            userText.setEditable(tof);
          }
        }
      );
    }
}