How to Serialize ImageIcon Object?

Question

I am trying to build a client-server Program in which the server sends the image to client and client displays the received image in JFrame. I am converting Image on the server-side to ImageIcon object and sending it to the client via ObjecOutputStream. But it fails and gives me failed to load image contents error on server-side, it happens while the ObjectOutputStream.writeObject() method is called.

Server-side code

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

public class ImageServer{

  private static ServerSocket serverSocket;
  private static final int PORT = 1234;

  public static void main(String[] args){

       System.out.println("Opening port…\n");
       try{
         serverSocket = new ServerSocket(PORT);
       }
       catch(IOException ioEx){
         System.out.println("Unable to attach to port!");
         System.exit(1);
       }
       while(true){
             try{
               Socket connection = serverSocket.accept();

               ObjectOutputStream outStream =new ObjectOutputStream(
                                              connection.getOutputStream());
               ImageIcon icon=new ImageIcon("//Give image path//");
               System.out.println(icon.getImageLoadStatus());// To check if image is loded correctly or not.

               outStream.writeObject(icon);

               outStream.flush();
             }
            catch(IOException ioEx){
                ioEx.printStackTrace();
            }
      }
 }
}

Just give the path for an image file, for testing purposes.

Client-side code

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

public class ImageClient extends JFrame{
    private InetAddress host;
    private final int PORT = 1234;
    private ImageIcon image;

    public static void main(String[] args){

         ImageClient pictureFrame = new ImageClient();
         pictureFrame.setSize(340,315);
         pictureFrame.setVisible(true);
         pictureFrame.setDefaultCloseOperation(EXIT_ON_CLOSE);  
    }

   public ImageClient(){
        try{
           host = InetAddress.getLocalHost();
        }
        catch(UnknownHostException uhEx){

            System.out.println("Host ID not found!");
            System.exit(1);
        }

        try{
            Socket connection = new Socket(host,PORT);

            ObjectInputStream inStream =new ObjectInputStream(
                                           connection.getInputStream());

            image = (ImageIcon)inStream.readObject();

            connection.close();
        }
        catch(IOException ioEx){
              ioEx.printStackTrace();
        }
        catch(ClassNotFoundException cnfEx){
              cnfEx.printStackTrace();
        }

        repaint();
  }

  public void paint(Graphics g){
       image.paintIcon(this,g,0,0);
   }
}

Error generated on Server-side

java.io.IOException: failed to load image contents
     at javax.swing.ImageIcon.writeObject(Unknown Source)
     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
     at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
     at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
     at java.lang.reflect.Method.invoke(Unknown Source)
     at java.io.ObjectStreamClass.invokeWriteObject(Unknown Source)
     at java.io.ObjectOutputStream.writeSerialData(Unknown Source)
     at java.io.ObjectOutputStream.writeOrdinaryObject(Unknown Source)
     at java.io.ObjectOutputStream.writeObject0(Unknown Source)
     at java.io.ObjectOutputStream.writeObject(Unknown Source)
     at ImageServer.main(ImageServer.java:27)

This is a code excerpt from the following book: http://www.springer.com/us/book/9781447152538

Answer 1

Okay, so I created an project using Netbeans. I placed a image (named 29bd6417998561.5635a605ad357.png in the package named images.

I created the Server class...

import java.io.IOException;
import java.io.ObjectOutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;

public class Server {

    private static final int PORT = 9999;

    public static void main(String[] args) {

        System.out.println("Opening port…\n");
        try (ServerSocket serverSocket = new ServerSocket(PORT)) {
            while (true) {
                ;
                try {
                    System.out.println("Waiting for connection");
                    Socket connection = serverSocket.accept();

                    System.out.println("Read image...");
                    ImageIcon icon = new ImageIcon(ImageIO.read(Server.class.getResource("/images/29bd6417998561.5635a605ad357.png")));

                    System.out.println("Read image...");
                    try (ObjectOutputStream outStream = new ObjectOutputStream(connection.getOutputStream())) {
                        System.out.println("Write image");
                        outStream.writeObject(icon);
                    }
                } catch (IOException ioEx) {
                    ioEx.printStackTrace();
                }
            }
        } catch (IOException ioEx) {
            System.out.println("Unable to attach to port!");
            System.exit(1);
        }
    }
}

and created the Client class...

import java.io.IOException;
import java.io.ObjectInputStream;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;

public class Client {

    private InetAddress host;
    private final int PORT = 9999;
    private ImageIcon image;
    private JLabel label;

    public static void main(String[] args) {

        Client pictureFrame = new Client();
    }

    public Client() {
        try {
            host = InetAddress.getLocalHost();
        } catch (UnknownHostException uhEx) {

            System.out.println("Host ID not found!");
            System.exit(1);
        }

        JFrame frame = new JFrame();
        label = new JLabel();
        frame.add(label);

        System.out.println("Connect to server");
        try (Socket connection = new Socket(host, PORT)) {
            try (ObjectInputStream inStream = new ObjectInputStream(connection.getInputStream())) {
                System.out.println("Read image");
                image = (ImageIcon) inStream.readObject();
                label.setIcon(image);
                System.out.println("All done");
            } catch (ClassNotFoundException ex) {
                ex.printStackTrace();
            }
        } catch (IOException ex) {
            ex.printStackTrace();
        }

        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
}

I started the Server and ran the Client and it worked fine...

Disclaimer...

Undoubtedly, others will point out the inherent issues with this code, but that's not the point of the example.

Firstly, you should never be performing blocking or long running operations from within the Event Dispatching Thread (like connecting to a server and/or reading an image from it). You should also not be modifying the UI from outside the context of the Event Dispatching Thread (kind of safe here as the frame's not realised on the screen, but still not a great example).

In both cases, something like a SwingWorker would help solve those issues.

Take a look at Work Threads and SwingWorker for more details