Can I tell what the file type of a BufferedImage originally was?

In my code, I have a BufferedImage that was loaded with the ImageIO class like so:

BufferedImage image = ImageIO.read(new File (filePath);

Later on, I want to save it to a byte array, but the ImageIO.write method requires me to pick either a GIF, PNG, or JPG format to write my image as (as described in the tutorial here).

I want to pick the same file type as the original image. If the image was originally a GIF, I don't want the extra overhead of saving it as a PNG. But if the image was originally a PNG, I don't want to lose translucency and such by saving it as a JPG or GIF. Is there a way that I can determine from the BufferedImage what the original file format was?

I'm aware that I could simply parse the file path when I load the image to find the extension and just save it for later, but I'd ideally like a way to do it straight from the BufferedImage.

Solution

As other answers has also mentioned, the BufferedImage has no "format" (i.e. no file format, it does have one of several pixel formats, or pixel "layouts"). There are third party libraries that can tell you the file format of a file, but for this particular use case there is no need for that.

If you prefer using only ImageIO and not adding new dependencies to your project, you could write something like:

ImageInputStream input = ImageIO.createImageInputStream(new File(filePath));

try {
    Iterator<ImageReader> readers = ImageIO.getImageReaders(input);

    if (readers.hasNext()) {
        ImageReader reader = readers.next();

        try {
            reader.setInput(input);

            BufferedImage image = reader.read(0);  // Read the same image as ImageIO.read

            // Do stuff with image...

            // When done, either (1):
            String format = reader.getFormatName(); // Get the format name for use later
            if (!ImageIO.write(image, format, outputFileOrStream)) {
                // ...handle not written
            }
            // (case 1 done)

            // ...or (2):
            ImageWriter writer = ImageIO.getImageWriter(reader); // Get best suitable writer

            try {
                ImageOutputStream output = ImageIO.createImageOutputStream(outputFileOrStream);

                try {
                    writer.setOutput(output);
                    writer.write(image);
                }
                finally {
                    output.close();
                }
            }
            finally {
                writer.dispose();
            }
            // (case 2 done)
        }
        finally {
            reader.dispose();
        }
    }
}
finally {
    input.close();
}