JPG Thumbnails

Question

Hi!
I've searched the net for information on how to read the thumbnail
image that many JPG files have embedded into them. No success until
now. Can somebody help me with a piece of java code (not using any kind
of external library, only JSDK classes, please) I can use in my
application, please ? I'm looking at the javax.imageio.ImageReader API
but I don't know where to start.
Thanks in advance

Answer 1

import java.awt.*;
import java.awt.geom.*;
import java.awt.image.*;
import java.io.*;
import java.net.*;
import java.util.*;
import javax.imageio.*;
import javax.imageio.metadata.*;
import javax.imageio.stream.*;
import javax.swing.*;
import java.util.List;
public class ThumsUp {
    public static void main(String[] args) throws IOException {
        String suffix = "jpeg";
        write(suffix);
        read(suffix);
    public static void write(String suffix) throws IOException {
        File file = new File("test." + suffix);
        URL url = new URL("http://weblogs.java.net/jag/Image52-large.jpeg");
        BufferedImage image = ImageIO.read(url);
        GraphicsConfiguration gc = getDefaultConfiguration();
        BufferedImage thumb0 = resizeImage(image, 100,50, gc);
        BufferedImage thumb1 = resizeImage(image, 200,100, gc);
        BufferedImage thumb2 = resizeImage(image, 75,75, gc);
        List thumbs = Arrays.asList(new Object[]{thumb0, thumb1, thumb2});
        IIOImage iioImage = new IIOImage(image, thumbs, (IIOMetadata)null);
        Iterator writers = ImageIO.getImageWritersBySuffix(suffix);
        if (!writers.hasNext())
            throw new IOException("no writers for "+suffix);
        ImageWriter writer = (ImageWriter) writers.next();
        ImageOutputStream out = ImageIO.createImageOutputStream(file);
        writer.setOutput(out);
        writer.write(iioImage);
        writer.dispose();
    public static void read(String suffix) throws IOException {
        File file = new File("test." + suffix);
        Iterator readers = ImageIO.getImageReadersBySuffix(suffix);
        if (!readers.hasNext())
            throw new IOException("no readers for " + suffix);
        ImageReader reader = (ImageReader) readers.next();
        ImageInputStream in = ImageIO.createImageInputStream(file);
        reader.setInput(in);
        System.out.println("supports thumbs = " + reader.readerSupportsThumbnails());
        System.out.println("has thumbnails = " + reader.hasThumbnails(0));
        int numThumbs = reader.getNumThumbnails(0);
        System.out.println("numthumbs = " + numThumbs);
        BufferedImage[] thumbs = new BufferedImage[numThumbs];
        for(int i=0; i<thumbs.length; ++i)
            thumbs[i] = reader.readThumbnail(0, i);
        BufferedImage original = reader.read(0);
        JFrame f = new JFrame("X");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Container cp = f.getContentPane();
        cp.setLayout(new FlowLayout());
        JLabel imLabel = new JLabel(new ImageIcon(original));
        imLabel.setBorder(BorderFactory.createTitledBorder("original image"));
        cp.add(imLabel);
        for(int i=0; i<thumbs.length; ++i) {
            JLabel label = new JLabel(new ImageIcon(thumbs));
label.setBorder(BorderFactory.createTitledBorder("thumb #"+i));
cp.add(label);
f.pack();
f.setVisible(true);
public static BufferedImage resizeImage(BufferedImage image, int maxW, int maxH, GraphicsConfiguration gc) {
int w = image.getWidth(), h = image.getHeight();
double ratio = Math.min(maxW / (double) w, maxH / (double) h);
int newW = (int)(w*ratio), newH = (int)(h*ratio);
BufferedImage result = gc.createCompatibleImage(newW, newH, image.getColorModel().getTransparency());
Graphics2D g = result.createGraphics();
g.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BICUBIC);
g.drawRenderedImage(image, AffineTransform.getScaleInstance(ratio, ratio));
g.dispose();
return result;
public static GraphicsConfiguration getDefaultConfiguration() {
GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
GraphicsDevice gd = ge.getDefaultScreenDevice();
return gd.getDefaultConfiguration();