Java/ImageIO 在不读取整个文件的情况下获取图像尺寸？

Question

Is there a way to get the dimensions of an image without reading the entire file?

URL url=new URL(<BIG_IMAGE_URL>);
BufferedImage img=ImageIO.read(url);
System.out.println(img.getWidth()+" "+img.getHeight());
img=null;

Answer 1

try(ImageInputStream in = ImageIO.createImageInputStream(resourceFile)){
    final Iterator<ImageReader> readers = ImageIO.getImageReaders(in);
    if (readers.hasNext()) {
        ImageReader reader = readers.next();
        try {
            reader.setInput(in);
            return new Dimension(reader.getWidth(0), reader.getHeight(0));
        } finally {
            reader.dispose();
        }
    }
} 

Thanks to sfussenegger for the suggestion

Answer 2

Using ImageReader.getHeight(int) and ImageReader.getWidth(int) normally only reads the image header (I'm looking at JDK6 sources). So ImageReader is most likely the best choice.

Answer 3

You'll have to look into ImageReader.getImageMetadata() . Unfortunately, The Java Image API is not at all easy to use.

You can find descriptions of the metadata formats in the package documentation of javax.imageio.metadata .

There are third party libraries that are easier to use, such as MediaUtil (last updated 3 years ago, but it worked well for me).