import java.awt.*;
import java.awt.image.*;
import java.io.*;
import java.util.*;
import javax.imageio.*;
import javax.imageio.stream.*;
 
public class ImageKit {
    static {
        ImageIO.setUseCache(false);
    }
 
    //Tested buffering. Reads 1000bytes/call for jpeg (200 for png, 100 for gif)
    public static BufferedImage read(InputStream in) throws IOException {
        BufferedImage image = ImageIO.read(in);
        if (image == null)
            throw new IOException("Read fails");
       return image;
    }
 
    public static BufferedImage read(byte[] bytes) {
         try {
             return read(new ByteArrayInputStream(bytes));
         } catch(IOException e) {
             throw new RuntimeException(e);
         }
    }
 
    //quality means jpeg output, if quality is < 0 ==> use default quality
    public static void write(BufferedImage image, float quality, OutputStream out) throws IOException {
        Iterator writers = ImageIO.getImageWritersBySuffix("jpeg");
        if (!writers.hasNext())
            throw new IllegalStateException("No writers found");
        ImageWriter writer = (ImageWriter) writers.next();
        ImageOutputStream ios = ImageIO.createImageOutputStream(out);
        writer.setOutput(ios);
        ImageWriteParam param = writer.getDefaultWriteParam();
        if (quality >= 0) {
            param.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
            param.setCompressionQuality(quality);
        }
        writer.write(null, new IIOImage(image, null, null), param);
        ios.close();
        writer.dispose();
    }
 
    public static byte[] toByteArray(BufferedImage image, float quality) {
        try {
            ByteArrayOutputStream out = new ByteArrayOutputStream(50000);
            write(image, quality, out);
            return out.toByteArray();
        } catch(IOException e) {
            throw new RuntimeException(e);
        }
    }
 
    public static BufferedImage compress(BufferedImage image, float quality) {
        return read(toByteArray(image, quality));
    }
 
    public static void flush(BufferedImage image) {
        try {
            if (image != null)
                image.flush();
        } catch (NullPointerException e) {
            //bug in sun's code
        }
 
    }
}

import java.awt.*;
import java.awt.image.*;
import java.io.*;
import java.net.*;
import java.text.*;
import javax.imageio.*;
import javax.swing.*;
import javax.swing.event.*;
 
public class CompressedView extends JComponent {
    private BufferedImage originalImage, compressedImage;
    private float quality=0.1f;
    private int compressedSize;
 
    public float getQuality() {
        return quality;
    }
 
    public int getCompressedSize() {
        return compressedSize;
    }
 
    public void setQuality(float quality) {
        this.quality = quality;
        calculateCompressedImage();
    }
 
    private void calculateCompressedImage() {
        compressedImage = null;
        if (originalImage == null) {
            compressedSize = 0;
        } else {
            byte[] buff = ImageKit.toByteArray(originalImage, quality);
            compressedImage = ImageKit.read(buff);
            compressedSize = buff.length;
        }
        repaint();
    }
 
    public void setImage(BufferedImage image) {
        originalImage = image;
        calculateCompressedImage();
    }
 
    public int getImageWidth() {
        return (originalImage == null) ? 0 : originalImage.getWidth();
    }
 
    public int getImageHeight() {
        return (originalImage == null) ? 0 : originalImage.getHeight();
    }
 
    public Dimension getPreferredSize() {
        return new Dimension(getImageWidth()*2, getImageHeight());
    }
 
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        if (originalImage == null)
            return;
        g.drawImage(originalImage, 0, 0, null);
        g.drawImage(compressedImage, originalImage.getWidth(), 0, null);
    }
 
    public static void main(String[] args) throws IOException {
        URL url = new URL("http://today.java.net/jag/bio/JagHeadshot-small.jpg");
        BufferedImage image = ImageIO.read(url);
        final CompressedView view = new CompressedView();
        view.setImage(image);
        final JLabel percent = new JLabel();
        final JLabel size = new JLabel();
        JSlider slider = new JSlider();
        slider.addChangeListener(new ChangeListener(){
            NumberFormat format = NumberFormat.getIntegerInstance();
 
            public void stateChanged(ChangeEvent e) {
                JSlider sl = (JSlider) e.getSource();
                percent.setText(sl.getValue() + "%");
                if (!sl.getValueIsAdjusting()) {
                    view.setQuality(sl.getValue()/100f);
                    size.setText(format.format(view.getCompressedSize()) + " bytes");
                }
            }
        });
        slider.setValue((int)(100* view.getQuality()));
        JToolBar tb = new JToolBar();
        tb.add(percent);
        tb.add(slider);
        tb.add(size);
        JFrame f = new JFrame("CompressedView");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Container cp = f.getContentPane();
        cp.add(tb, BorderLayout.NORTH);
        cp.add(view);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }
}