Host-Server~

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

public class Server extends JFrame{

	private JTextField userText;
	private JTextArea chatWindow;
	private JButton send;
	private ObjectOutputStream output; //stream that flows from my computer to friends computer
	private ObjectInputStream input;
	private ServerSocket server; 
	private Socket connection;  //socket= connection between two computers
	
	//constructor
	public Server(){
		super("Grrreat Instant Messenger");
		userText = new JTextField();
		send = new JButton("Send");		
		send.addActionListener(
				new ActionListener(){
					public void actionPerformed(ActionEvent ae){
						sendMessage(userText.getText());
					}
				}
				);
		userText.setEditable(false); //doesn't allow user to click in
		userText.addActionListener(
				new ActionListener(){
					public void actionPerformed(ActionEvent e){
						sendMessage(e.getActionCommand());
						userText.setText(""); //after send text, text area clears
					}					
				}
				);
		add(userText, BorderLayout.NORTH);
		add(send, BorderLayout.SOUTH);
		chatWindow = new JTextArea();
		add(new JScrollPane(chatWindow));
		setSize(500, 250);
		setVisible(true);
	}
	
	//set up and run the server
	public void startRunning(){
		try{
			server = new ServerSocket(6789, 100); //6789 is the port number(where do you want to connect), 100 is backlog(# people can wait to talk to you)
			while(true){
				try{
					//connect/have convo w/ someone else
					waitForConnection();
					setupStreams();
					whileChatting();
				}catch(EOFException eofException){ //end of connection or end of stream
					showMessage("\n Server ended the connection.");
				}finally{
					closeUneeded();
				}
			}
		}catch(IOException ioException){
			ioException.printStackTrace();
		}
	}
	//wait for connection, then display connection information
	private void waitForConnection() throws IOException{
		showMessage("Waiting for someone to connect. \n");
		connection = server.accept(); //blocks a connection until it's made
		showMessage("Connected to " + connection.getInetAddress().getHostName()); //returns your address once connected & host ip adress
	}
	
	//get stream to send and receive data/messages
	
	private void setupStreams()throws IOException{
		output = new ObjectOutputStream(connection.getOutputStream());
		output.flush(); //send leftover data/bytes to the other person
		input = new ObjectInputStream(connection.getInputStream());
		showMessage("\n Streams are now connected \n");
	}
	
	//during the chat conversation
	
	private void whileChatting() throws IOException{
		String message =  "You are now connected.";
		sendMessage(message);
		ableToType(true); //will allow user to type in text box
		do{
			//have a conversation
			try{
				message = (String) input.readObject(); //reads whatever user sends and stores it in message var
				showMessage("\n " + message);
			}catch(ClassNotFoundException classNotFoundException){
				showMessage("\n Error, user did not send");
			}
		}while(!message.equals("Client - END")); //if user types END program will stop
	}
	
	//close streams and sockets after done chatting
	
	private void closeUneeded() throws IOException{
		showMessage("\n Closing connections \n");
		ableToType(false);
		try{
			output.close();
			input.close();
			connection.close(); //if these aren't closed, it will waste memory
		}catch(IOException ioException){
			ioException.printStackTrace(); //printStackTrace shows the error message
		}
	}
	
	//send a message to client(comp connected to server)
	private void sendMessage(String message){
		try{
			output.writeObject("Server - " + message); //writeObject is a java method that sends message to output stream
			output.flush(); //in case any bytes are left over, flush them out
			showMessage("\nServer- " + message); //will show previous messages in Text Field
		}catch(IOException ioException){
			chatWindow.append("\n ERRROR: CAN'T SEND MESSAGE"); //append adds to chatWindow
		}
	}
	
	//updates chatWindow the only part of the GUI that is updated
	private void showMessage(final String text){ //everything that shows up in chatWindow will be a stream
		SwingUtilities.invokeLater( //updates text in chat window
				new Runnable(){ //creates a thread to update the GUI
					public void run(){
						chatWindow.append(text);
					}
				}			
			);
	}
	
	//let user type into their box
	
	private void ableToType(final boolean trueOrFalse){
		SwingUtilities.invokeLater(
				new Runnable(){
					public void run(){
						userText.setEditable(trueOrFalse);
					}
				}
			);
	}
	
}