How do you create a thumbnail image out of a JPEG in Java?

Question

Can someone please help with some code for creating a thumbnail for a JPEG in Java.

I\'m new at this, so a step by step explanation would be appreciated.

Answer 1

Simple way to create a thumbnail without stretching or a library. Works with transparency in pngs, too.

public File createThumbnail(String imageUrl, String targetPath) {
    final int imageSize = 100;
    File thumbnail = new File(targetPath);

    try {
        thumbnail.getParentFile().mkdirs();
        thumbnail.createNewFile();
        BufferedImage sourceImage = ImageIO.read(new File(imageUrl));
        float width = sourceImage.getWidth();
        float height = sourceImage.getHeight();

        BufferedImage img2;
        if (width > height) {
            float scaledWidth = (width / height) * (float) imageSize;
            float scaledHeight = imageSize;

            BufferedImage img = new BufferedImage((int) scaledWidth, (int) scaledHeight, sourceImage.getType());
            Image scaledImage = sourceImage.getScaledInstance((int) scaledWidth, (int) scaledHeight, Image.SCALE_SMOOTH);
            img.createGraphics().drawImage(scaledImage, 0, 0, null);

            int offset = (int) ((scaledWidth - scaledHeight) / 2f);
            img2 = img.getSubimage(offset, 0, imageSize, imageSize);
        }
        else if (width < height) {
            float scaledWidth = imageSize;
            float scaledHeight = (height / width) * (float) imageSize;

            BufferedImage img = new BufferedImage((int) scaledWidth, (int) scaledHeight, sourceImage.getType());
            Image scaledImage = sourceImage.getScaledInstance((int) scaledWidth, (int) scaledHeight, Image.SCALE_SMOOTH);
            img.createGraphics().drawImage(scaledImage, 0, 0, null);

            int offset = (int) ((scaledHeight - scaledWidth) / 2f);
            img2 = img.getSubimage(0, offset, imageSize, imageSize);
        }
        else {
            img2 = new BufferedImage(imageSize, imageSize, sourceImage.getType());
            Image scaledImage = sourceImage.getScaledInstance(imageSize, imageSize, Image.SCALE_SMOOTH);
            img2.createGraphics().drawImage(scaledImage, 0, 0, null);
        }
        ImageIO.write(img2, "png", thumbnail);
    }
    catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    return thumbnail;
}