Java/ImageIO获取图像尺寸而不读取整个文件？

Question

有没有办法在不读取整个文件的情况下获取图像的尺寸？

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();
        }
    }
} 

感谢sfussenegger提出的建议

Answer 2

使用ImageReader.getHeight(int)和ImageReader.getWidth(int)通常只读取图像标题(我正在查看JDK6源代码).所以ImageReader很可能是最好的选择.