Java Socket connection without ServerSocket listening

Question

This is the code where I connected two Socket without any ServerSocket :

package primary;

import java.awt.FlowLayout;
import java.io.EOFException;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.concurrent.*;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;

public class Client extends JFrame implements Runnable {
    private final String myName;
    private ServerSocket listener;
    private Socket connection1;
    private Socket connection2;
    private ObjectOutputStream output1;
    private ObjectOutputStream output2;
    private ObjectInputStream input1;
    private ObjectInputStream input2;
    private Object receiveObject;
    private Object1 sendObject1;
    private Object2 sendObject2;
    private final int[] myLocalPort;
    private final int[] connectionPort;
    private ExecutorService service;
    private Future<Boolean> future1;
    private Future<Boolean> future2;

    public Client(final String myName, int[] myLocalPort, int[] connectionPort) {
        super(myName);
        this.myName = myName;
        this.myLocalPort = myLocalPort;
        this.connectionPort = connectionPort;
        sendObject1 = new Object1("string1", "string2", myName);
        sendObject2 = new Object2("string1", 2.5, 2, true, myName);
        initComponents();
    }
    public void exe() {
        ExecutorService eService = Executors.newCachedThreadPool();
        eService.execute(this);
    }

    @Override
    public void run() {
        try {
                displayMessage("Attempting connection\n");
                try {
                    connection1  = new Socket(InetAddress.getByName("localhost"), connectionPort[0],
                            InetAddress.getByName("localhost"), myLocalPort[0]);
                    displayMessage(myName + " connection1\n");
                } catch (Exception e) {
                    displayMessage("failed1\n");
                    System.err.println("1" + myName + e.getMessage() + "\n");
                }
                try {
                    connection2  = new Socket(InetAddress.getByName("localhost"), connectionPort[1],
                            InetAddress.getByName("localhost"), myLocalPort[1]);
                    displayMessage(myName + " connection2\n");
                } catch (Exception e) {
                    displayMessage("failed2\n");
                    System.err.println("2" + myName + e.getMessage() + "\n");
                }
            displayMessage("Connected to: " + connection1.getInetAddress().getHostName() + "\n\tport: "
                    + connection1.getPort() + "\n\tlocal port: " + connection1.getLocalPort() + "\n"
                    + connection2.getInetAddress().getHostName() + "\n\tport: " + connection2.getPort()
                    + "\n\tlocal port: " + connection2.getLocalPort() + "\n\n");
            output1 = new ObjectOutputStream(connection1.getOutputStream());
            output1.flush();
            output2 = new ObjectOutputStream(connection2.getOutputStream());
            output2.flush();
            input1 = new ObjectInputStream(connection1.getInputStream());
            input2 = new ObjectInputStream(connection2.getInputStream());
            displayMessage("Got I/O stream\n");
            setTextFieldEditable(true);
            service = Executors.newFixedThreadPool(2);
            future1 = service.submit(
                    new Callable<Boolean>() {

                @Override
                public Boolean call() throws Exception {
                    try {
                        processConnection(input1);
                        displayMessage("input1 finished");
                    } catch (IOException e) {
                        displayMessage("blah");
                    }
                    return true;
                }
            });
            future2 = service.submit(
                    new Callable<Boolean>() {

                @Override
                public Boolean call() throws Exception {
                    try {
                        processConnection(input2);
                        displayMessage("input2 finished");
                    } catch (IOException e) {
                        displayMessage("foo");
                    }
                    return true;
                }
            });
        } catch (UnknownHostException e) {
            displayMessage("UnknownHostException\n");
            e.printStackTrace();
        } catch (EOFException e) {
            displayMessage("EOFException\n");
            e.printStackTrace();
        } catch (IOException e) {
            displayMessage("IOException\n");
            e.printStackTrace();
        } catch(NullPointerException e) {
            System.err.println("asdf " + e.getMessage());
        } finally {
            try {
                displayMessage("i'm here\n");
                if((future1 != null && future1.get()) && (future2 != null && future2.get())) {
                    displayMessage(future1.get() + " " + future2.get() + "\n");
                    displayMessage("Closing Connection\n");
                    setTextFieldEditable(false);
                    if(!connection1.isClosed()) {
                        output1.close();
                        input1.close();
                        connection1.close();
                    }
                    if(!connection2.isClosed()) {
                        output2.close();
                        input2.close();
                        connection2.close();
                    }
                    displayMessage("connection closed\n");
                }
            } catch (IOException e) {
                displayMessage("IOException on closing");
            } catch (InterruptedException e) {
                displayMessage("InterruptedException on closing");
            } catch (ExecutionException e) {
                displayMessage("ExecutionException on closing");
            }
        }
    }//method run ends
    private void processConnection(ObjectInputStream input) throws IOException {
        String message = "";
        do {
            try {
                receiveObject = input.readObject();
                if(receiveObject instanceof String) {
                    message = (String) receiveObject;
                    displayMessage(message + "\n");
                } else if (receiveObject instanceof Object1) {
                    Object1 receiveObject1 = (Object1) receiveObject;
                    displayMessage(receiveObject1.getString1() + " " + receiveObject1.getString2()
                            + " " + receiveObject1.toString() + "\n");
                } else if (receiveObject instanceof Object2) {
                    Object2 receiveObject2 = (Object2) receiveObject;
                    displayMessage(receiveObject2.getString1() + " " + receiveObject2.getD()
                            + " " + receiveObject2.getI() + " " + receiveObject2.toString() + "\n");
                }
            } catch (ClassNotFoundException e) {
                displayMessage("Unknown object type received.\n");
            }
            displayMessage(Boolean.toString(message.equals("terminate\n")));
        } while(!message.equals("terminate"));
        displayMessage("finished\n");
        input = null;
    }

    private void initComponents() {

        dataField = new javax.swing.JTextField();
        sendButton1 = new javax.swing.JButton();
        sendButton2 = new javax.swing.JButton();
        jScrollPane1 = new javax.swing.JScrollPane();
        resultArea = new javax.swing.JTextArea();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setLayout(new FlowLayout());
        dataField.setEditable(false);
        dataField.setColumns(20);
        dataField.addActionListener(new java.awt.event.ActionListener() {
            @Override
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                dataFieldActionPerformed(evt);
            }
        });

        sendButton1.setText("Send Object 1");
        sendButton1.addActionListener(new java.awt.event.ActionListener() {
            @Override
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                sendButton1ActionPerformed(evt);
            }
        });

        sendButton2.setText("Send Object 2");
        sendButton2.addActionListener(new java.awt.event.ActionListener() {
            @Override
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                sendButton2ActionPerformed(evt);
            }
        });

        resultArea.setColumns(25);
        resultArea.setRows(15);
        resultArea.setEditable(false);
        resultArea.setRows(5);
        jScrollPane1.setViewportView(resultArea);

        add(dataField);
        add(sendButton1);
        add(sendButton2);
        add(jScrollPane1);
        pack();
    }
    private void dataFieldActionPerformed(java.awt.event.ActionEvent evt) {                                          
        // TODO add your handling code here:
        sendData(evt.getActionCommand());
        dataField.setText("");
    }                                         

    private void sendButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                            
        // TODO add your handling code here:
        sendData(sendObject1);
    }                                           

    private void sendButton2ActionPerformed(java.awt.event.ActionEvent evt) {                                            
        // TODO add your handling code here:
        sendData(sendObject2);
    }                                  

    private void displayMessage(final String messageToDisplay) {
        SwingUtilities.invokeLater(
                new Runnable() {
            @Override
                    public void run() {
                        resultArea.append(messageToDisplay);
                    }
                });
    }
    private void setTextFieldEditable(final boolean editable) {
        SwingUtilities.invokeLater(
                new Runnable() {

            @Override
            public void run() {
                dataField.setEditable(editable);
            }
        });
    }
    private void sendData(final Object object) {
        try {
            output1.writeObject(object);
            output1.flush();
            output2.writeObject(object);
            output2.flush();
            displayMessage(myName + ": " + object.toString() + "\n");
        } catch (IOException e) {
            displayMessage("Error writing object\n");
        }
    }

    private javax.swing.JTextField dataField;
    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JTextArea resultArea;
    private javax.swing.JButton sendButton1;
    private javax.swing.JButton sendButton2;
}

And the main:

    package primary;

import javax.swing.SwingUtilities;


public class Main {
    private static Object locker;

    public static void main(String[] args) {
        locker = new Object();
        final int[][] a = new int[6][];
        final int[][] b = new int[6][];
        final int[][] c;
        a[0] = new int[] {12340, 12341};
        a[1] = new int[] {12342, 12344};
        a[2] = new int[] {12342, 12343};
        a[3] = new int[] {12340, 12345};
        a[4] = new int[] {12344, 12345};
        a[5] = new int[] {12341, 12343};

        b[0] = new int[] {22340, 22341};
        b[1] = new int[] {22342, 22344};
        b[2] = new int[] {22342, 22343};
        b[3] = new int[] {22340, 22345};
        b[4] = new int[] {22344, 22345};
        b[5] = new int[] {22341, 22343};

        c = a;
        SwingUtilities.invokeLater(
                new Runnable() {

            @Override
            public void run() {
                Client client1 = new Client("client1", c[0], c[1]);
                client1.exe();
                client1.setLocation(0, 0);
                client1.setVisible(true);
            }
        });
        SwingUtilities.invokeLater(
                new Runnable() {

            @Override
            public void run() {
                Client client2 = new Client("client2", c[2], c[3]);
                client2.exe();
                client2.setLocation(0, 200);
                client2.setVisible(true);
            }
        });
        SwingUtilities.invokeLater(
                new Runnable() {

            @Override
            public void run() {
                Client client3 = new Client("client3", c[4], c[5]);
                client3.exe();
                client3.setLocation(0, 400);
                client3.setVisible(true);

            }
        });
    }
}

Here Object1 and Object2 are just two Serializable Objects. All the sockets connect perfectly, it seems. If I exit the system without calling the close() methods for the sockets and their input, output streams and re-run, it works fine still. But if I exit system after making sure that the close() methods are called, and I re-run again, I get this: 1client2Address already in use: connect

1client3Address already in use: connect

2client3Address already in use: connect

asdf null
1client1Connection refused: connect

2client2Connection refused: connect

asdf null
2client1Connection refused: connect

asdf null

I re-run again and again, I keep getting this, unless, I wait a certain amount of time and re-run again, it works just fine as the first time. Why something like this happening? why it's taking so much time if I close the socket and not when not closing them? Are they really closing or just merely connecting the existing connection when I do not close the sockets? But when using ServerSocket it doesn't seem to happen in cases when I close. What is actually going on?

Another question, ServerSocket supposedly hands out its end of Socket connection to a localport other than on which it is listening. If it is true, why do I get the listening localport when I call Socket.getLocalPort(), for all the socket it accepted?

Answer 1

Don't use the 3rd and 4th parameters when creating the Socket . There is no genuine need to specify the local address, short of a VPN, and no genuine need to specify a local port at all other than as a figment of your netadmin's imagination.

ServerSocket supposedly hands out its end of Socket connection to a localport other than on which it is listening.

No it doesn't. All the accepted sockets use the same local port as the listening port.