How do you formally disconect a client from a server?

[Eric Larsen]

Hey, everybody. I'm writing a chat server and client, and I've noticed that whenever I just shut down the client, the server throws an error, but no functionality is affected. In fact, if it weren't for the fact that I have the CLI for the server open whenever I'm running it, I wouldn't have noticed this at all. Is this even worth the time to fix? If so, how would I do that? I'm using plain Sockets, by the way.

Client source code:

package com.teslarobotics.net;

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

public class SimpleChatClient {

	JTextField outgoing;
	JTextArea incoming;
	JScrollPane scroller;
	PrintWriter writer;
	BufferedReader reader;
	Socket socket;
	JTextField nameField;
	SendAction action;

	public static void main(String[] args) {

		SimpleChatClient client = new SimpleChatClient();

		client.go();

	}

	public void go () {

		JFrame frame = new JFrame("Eric's Simple Chat Client");
		JPanel mainPanel = new JPanel();
		incoming = new JTextArea(15, 50);
		incoming.setLineWrap(true);
		incoming.setWrapStyleWord(true);
		incoming.setEditable(false);
		outgoing = new JTextField(20);
		JLabel screenName = new JLabel("Screen name: ");
		nameField = new JTextField(10);

		scroller = new JScrollPane(incoming);
		scroller.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
		scroller.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);

		JButton sendButton = new JButton("Send");
		sendButton.addActionListener(action = new SendAction());
		outgoing.getInputMap().put(KeyStroke.getKeyStroke("ENTER"), "Enter");
		outgoing.getActionMap().put("Enter", action);

		mainPanel.add(screenName);
		mainPanel.add(nameField);
		mainPanel.add(scroller);
		mainPanel.add(outgoing);
		mainPanel.add(sendButton);

		setUpNetworking();

		Thread readerThread = new Thread(new IncomingReader());
		readerThread.start();

		frame.getContentPane().add(BorderLayout.CENTER, mainPanel);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setSize(600,340);
		frame.setVisible(true);

	}

	public void setUpNetworking () {

		try {

			socket = new Socket("127.0.0.1", 5000);
			writer = new PrintWriter(socket.getOutputStream());
			reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
			System.out.println("Connected to server.");

		} catch (Exception ex) {

			System.out.println("Failed to connect.");
			ex.printStackTrace();

		}

	}

//	public class SendButtonListener implements ActionListener {
//
//		public void actionPerformed (ActionEvent ev) {
//
//			if (nameField.getText().trim().isEmpty()) {
//
//				nameField.setText("Anonymous");
//
//			}
//
//			try {
//
//				writer.println(nameField.getText().trim() + ": " + outgoing.getText());
//				writer.flush();
//
//			} catch (Exception ex) {
//
//				System.out.println("Failed to send.");
//				ex.printStackTrace();
//
//			}
//
//			outgoing.setText("");
//			outgoing.requestFocus();
//
//		}
//
//	}

	public class IncomingReader implements Runnable {

		public void run () {

			String message;

			try {

				while((message = reader.readLine()) != null) {

					System.out.println("recieved: " + message);

					incoming.append(message + "\n");

					JScrollBar bar = scroller.getVerticalScrollBar();

					bar.setValue(bar.getMaximum());

				}

			} catch (Exception ex) {

				ex.printStackTrace();

			}

		}

	}

	public class SendAction extends AbstractAction {

		public void actionPerformed (ActionEvent ev) {

			if (nameField.getText().trim().isEmpty()) {

				nameField.setText("Anonymous");

			}

			if (!(outgoing.getText().trim().isEmpty())) {

				try {

					writer.println(nameField.getText().trim() + ": " + outgoing.getText());
					writer.flush();

				} catch (Exception ex) {

					System.out.println("Failed to send.");
					ex.printStackTrace();

				}

			}

			outgoing.setText("");
			outgoing.requestFocus();

		}

	}

}

The server source code:

package com.teslarobotics.net;

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

public class SimpleChatServer {

	ArrayList<PrintWriter> clientOutputStreams;

	public static void main(String[] args) {

		SimpleChatServer server = new SimpleChatServer();
		server.go();

	}

	public void go () {

		clientOutputStreams = new ArrayList<PrintWriter>();

		try {

			ServerSocket serverSocket = new ServerSocket(5000);

			while(true) {

				Socket socket = serverSocket.accept();

				PrintWriter writer = new PrintWriter(socket.getOutputStream());

				clientOutputStreams.add(writer);

				Thread thread = new Thread(new ClientHandler(socket));

				thread.start();

				System.out.println("Client connected");

			}

		} catch (Exception ex) {

			ex.printStackTrace();

		}

	}

	public class ClientHandler implements Runnable {

		BufferedReader reader;

		Socket sock;

		public ClientHandler (Socket clientSocket) {

			try{ 

				sock = clientSocket;

				reader = new BufferedReader(new InputStreamReader(sock.getInputStream()));

			} catch (Exception ex) {

				ex.printStackTrace();

			}

		}

		public void run () {

			String message;

			try{ 

				while((message = reader.readLine()) != null) {

					System.out.println("recieved: " + message);

					broadcast(message);

				}

			} catch (Exception ex) {

				ex.printStackTrace();

			}

		}

	}

	public void broadcast (String message) {

		Iterator<PrintWriter> it = clientOutputStreams.iterator();

		while(it.hasNext()) {

			try {

				PrintWriter writer = it.next();

				writer.println(message);

				writer.flush();

			} catch (Exception ex) {

				ex.printStackTrace();

			}

		}

	}

}

[William Brogden]

Is this even worth the time to fix? If so, how would I do that?

Good practice would be to catch the exception, log the fact that the client disconnected and clean up any resources in use.

Bill