Question

//Here is the code to request the server send the public key to client

package gameserver;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Scanner;
import java.net.Socket;
import java.io.*;
import javax.swing.JFrame;
import java.awt.*;
import javax.swing.*;

public class GameClient  extends JFrame implements ActionListener {

    private JButton b1 = new JButton("press");

    public GameClient () {
       GridLayout layout = new GridLayout(3, 0, 0, 0);
       setLayout(layout);
       setSize(320,150);

       add(b1);
       b1.addActionListener(this);

    }

    public static void main(String args[]) {
      java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                 GameClient frame = new GameClient();
                 frame.setVisible(true);
            }
      });
    }  

   public void actionPerformed(ActionEvent ae) {
       if (ae.getSource() == b1) {
            Socket socket = null;
            ObjectInputStream in = null;
            ObjectOutputStream out = null;

            Scanner console = new Scanner(System.in);

            try {
                socket = new Socket("127.0.0.1", 12346);
                in = new ObjectInputStream(socket.getInputStream());
                out = new ObjectOutputStream(socket.getOutputStream());
                Object result;
                result = in.readObject();

                System.out.println(result);
            } catch (IOException ioe) {
                ioe.printStackTrace();
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                try {
                    if (in != null) {
                        in.close();
                    } 
                    if (out != null) {
                        out.close();
                    }
                    if (socket != null) {
                        socket.close();
                    }
                } catch (IOException ioe) {
                    ioe.printStackTrace();
                }
            }           
       }

   } 
}

//server code, to send the public key to client when client connect

package gameserver;

import java.io.*;
import java.net.*;
import java.security.*; 
import javax.crypto.*; 

public class GameServer {
    public static void main(String arg[]) {
        try {
            ServerSocket ss = new ServerSocket(12346);

                        while(true) {
            Socket s = ss.accept();
            ClientHandler ch = new ClientHandler(s);
                        ch.start();

                        }
        }
        catch(IOException ioe) {
            ioe.printStackTrace();
        }
    }
}

class ClientHandler extends Thread  {

    Socket socket;
    KeyPair keyPair = null;

    public ClientHandler(Socket socket)  {
        this.socket = socket;

    }

    public KeyPair genKeyPair () {

        try {
            KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA"); 
            keyGen.initialize(1024); 
            keyPair = keyGen.generateKeyPair(); 
            //PrivateKey privateKey = keyPair.getPrivate();
            //PublicKey publicKey = keyPair.getPublic();

        } catch (NoSuchAlgorithmException e) {
            System.out.println(e.getMessage());
        }   
        return keyPair;
    }

    public void run() {
        try {             

            ObjectInputStream Ois = new ObjectInputStream(socket.getInputStream());               
            ObjectOutputStream Oos = new ObjectOutputStream(socket.getOutputStream());

            keyPair = genKeyPair ();
            PublicKey publicKey = keyPair.getPublic();
            Oos.writeObject(publicKey);

            socket.close();
        } catch(IOException ioe) {
            ioe.printStackTrace();
        }
    }

}

the problem is that, when i press the button, the client seems don’t connect to server, and receive nothing, any ideas ? thanks

Answer 1

Your code is blocked at this line:

 ObjectInputStream Ois = new ObjectInputStream(socket.getInputStream());

From the documention

Creates an ObjectInputStream that reads from the specified
InputStream. A serialization stream header is read from the stream and
verified. This constructor will block until the corresponding
ObjectOutputStream has written and flushed the header.

If a security manager is installed, this constructor will check for
the “enableSubclassImplementation” SerializablePermission when invoked
directly or indirectly by the constructor of a subclass which
overrides the ObjectInputStream.readFields or
ObjectInputStream.readUnshared methods.

Fix:

Change your

ObjectInputStream Ois = new ObjectInputStream(socket.getInputStream());               
ObjectOutputStream Oos = new ObjectOutputStream(socket.getOutputStream());

to

ObjectOutputStream Oos = new ObjectOutputStream(socket.getOutputStream());
ObjectInputStream Ois = new ObjectInputStream(socket.getInputStream());