Question

I want to transmit a serialized object over a socket channel.
I want make “Hi friend” string as serialized object and then write this object in socket channel while in the other end i want to read the same object and retrieve the data.

All these things I want to do using Java SocketChannel. How to do this?
I have tried like below, but did not get any data in the recipient side.

private static void writeObject(Object obj, SelectionKey selectionKey) {
    ObjectOutputStream oos;
    try {
        SocketChannel channel = (SocketChannel) selectionKey.channel();
        oos = new ObjectOutputStream(Channels.newOutputStream(channel));

        oos.writeObject(obj);
    } catch (IOException ex) {
        ex.printStackTrace();
    }
}

private static Object readObject(SelectionKey selectionKey) {
    ObjectInputStream ois;
    Object obj = new Object();
    SocketChannel channel = (SocketChannel) selectionKey.channel();
    try {
        ois = new ObjectInputStream(Channels.newInputStream(channel));
        obj = ois.readObject();
    } catch (Exception ex) {
        ex.printStackTrace();
    }
    return obj;
}

Answer 1

Your SocketChannel handling seems to be incomplete, see this complete example for SocketChannels transferring a byte:

/*
 * Writer
 */
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.net.InetSocketAddress;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;

public class Sender {
    public static void main(String[] args) throws IOException {
        System.out.println("Sender Start");

        ServerSocketChannel ssChannel = ServerSocketChannel.open();
        ssChannel.configureBlocking(true);
        int port = 12345;
        ssChannel.socket().bind(new InetSocketAddress(port));

        String obj ="testtext";
        while (true) {
            SocketChannel sChannel = ssChannel.accept();

            ObjectOutputStream  oos = new 
                      ObjectOutputStream(sChannel.socket().getOutputStream());
            oos.writeObject(obj);
            oos.close();

            System.out.println("Connection ended");
        }
    }
}

And the Reader

/*
 * Reader
 */
import java.io.IOException;
import java.io.ObjectInputStream;
import java.net.InetSocketAddress;
import java.nio.channels.SocketChannel;

public class Receiver {
    public static void main(String[] args) 
    throws IOException, ClassNotFoundException {
        System.out.println("Receiver Start");

        SocketChannel sChannel = SocketChannel.open();
        sChannel.configureBlocking(true);
        if (sChannel.connect(new InetSocketAddress("localhost", 12345))) {

            ObjectInputStream ois = 
                     new ObjectInputStream(sChannel.socket().getInputStream());

            String s = (String)ois.readObject();
            System.out.println("String is: '" + s + "'");
        }

        System.out.println("End Receiver");
    }
}

When you first start the Server, then the Receiver, you’ll get the following output:

Server’s console

Sender Start
Connection ended

Receiver’s console

Receiver Start
String is: 'testtext'
End Receiver

This is not the best solution, but follows your use of Java’s ServerSocketChannel