Thread: Problems with sockets on simple server and client programs.

I set up a simple text message server and client using sockets. When I am have both programs running and connected then close the client without inputting "TERMINATE" I can't connect another client. This is the error stack I'm getting when I close the client.

java.net.BindException: Address already in use: JVM_Bind
at java.net.DualStackPlainSocketImpl.bind0(Native Method)
at java.net.DualStackPlainSocketImpl.socketBind(Unkno wn Source)
at java.net.AbstractPlainSocketImpl.bind(Unknown Source)
at java.net.PlainSocketImpl.bind(Unknown Source)
at java.net.ServerSocket.bind(Unknown Source)
at java.net.ServerSocket.<init>(Unknown Source)
at java.net.ServerSocket.<init>(Unknown Source)


I get this error when I have my server and client programs open. I then close the client window, and this error is when a new ServerSocket is created when the runServer() is called in the closeConnection() method is called. When this happens my connection still has a Socket value. How can I properly handle a client termination so another client can connect.

Another question dealing with threading. At this point I cannot connect more than one client at a time. I know I need to create a thread that handles connecting clients, so I can have multiple clients communicating with each other. I am not sure how to implement this.


Here is my server class.

public class Server extends JFrame {
 
	private JTextField enterField;
	private JTextArea displayArea;
	private ObjectOutputStream output;
	private ObjectInputStream input;
	private ServerSocket server;
	private Socket connection;
	private int counter = 1;
 
	public Server() {
		super ("Server");
		enterField = new JTextField();
		enterField.setEditable(true);
		enterField.addActionListener(new ActionListener() {
 
			@Override
			public void actionPerformed(ActionEvent event) {
				sendData(event.getActionCommand());
				enterField.setText("");
 
			}
		});
 
		add(enterField, BorderLayout.NORTH);
		displayArea = new JTextArea();
		add (new JScrollPane(displayArea));
		setSize(300,150);
		setLocation(500,500);
		setVisible(true);
	}
 
 
 
	public void runServer() {
		try {
			server = new ServerSocket(50499, 100);
			if(!server.isClosed()){
			displayMessage("\n Listening on Port: " + server.getLocalPort() + "\n");
 
			}
			while (true) {
				try {
					waitForCommunication();
					getStreams();
					processConnection();
				} catch (EOFException eofException) {
					displayMessage("\n Server terminated connection ");
				} finally {
					closeConnection();
					++counter;
				}
			}
		} catch (IOException ioException) {
			ioException.printStackTrace();
		}
	}
 
	private void closeConnection() {
		displayMessage("\nTerminating connection\n");
		setTextFieldEditable(false);
		try {
			output.close();
			input.close();
			connection.close();
		} catch (IOException ioException) {
			ioException.printStackTrace();
		}
		runServer();
 
	}
 
	private void displayMessage(final String string) {
		SwingUtilities.invokeLater(new Runnable(){
 
			@Override
			public void run() {
				displayArea.append(string);
			}
 
		});
 
	}
 
	private void processConnection() throws IOException {
		String message = "Connection Sucessful";
		sendData(message);
 
		setTextFieldEditable(true);
 
		do {
			try {
				message = (String) input.readObject();
				displayMessage("\n" + message);
			} catch (ClassNotFoundException classNotFoundException) {
				displayMessage("\nUnknown object type recieved");
			}
		} while (!message.endsWith(">>> TERMINATE"));
	}
 
	private void setTextFieldEditable(final boolean editable) {
		SwingUtilities.invokeLater(new Runnable(){
 
			@Override
			public void run() {
				enterField.setEditable(editable);
 
			}
 
		});
 
	}
 
	private void getStreams() throws IOException {
		output = new ObjectOutputStream(connection.getOutputStream());
		output.flush();
 
		input = new ObjectInputStream(connection.getInputStream());
 
		displayMessage("\nGOt I/O stream \n");
 
	}
 
	private void waitForCommunication() throws IOException {
		displayMessage("Waiting for cennection \n");
		connection = (server.accept());
		displayMessage("Connection" + counter + " received from: "
				+ connection.getInetAddress().getHostName());
	}
 
	private void sendData(String message) {
		try {
			output.writeObject("SERVER>>> " + message);
			output.flush();
			displayMessage("\nSERVER>>> " + message);
		} catch (IOException ioException){
			displayArea.append("\nError Writing Object");
		}
	}
}

This exception is thrown, when you try to bind a ServerSocket to a port, on which another application (perhaps, another ServerSocket is bonded). Here, when you close connection, your server continue to work. Hence, if you try opening another ServerSocket at the same port, you get an exception. I suggest you to close client connection at the processConnection() method (i.e., at the end of the processing). The server should be alive all the time.