Java/ImageIO getting image dimensions without reading the entire file?

问题

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;

回答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

回答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.

回答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).

来源：https://stackoverflow.com/questions/1559253/java-imageio-getting-image-dimensions-without-reading-the-entire-file