Java get image extension/type using BufferedImage from URL

Use ImageReader.getFormatName()

You can get the image readers for a file using ImageIO.getImageReaders(Object input).

I haven’t tested it myself, but you can try this:

ImageInputStream iis = ImageIO.createImageInputStream(file);

Iterator<ImageReader> imageReaders = ImageIO.getImageReaders(iis);

while (imageReaders.hasNext()) {
    ImageReader reader = (ImageReader) imageReaders.next();
    System.out.printf("formatName: %s%n", reader.getFormatName());
}