Java 读取/缩小图片：javax.imageio.IIOException: Unsupported Image Type

用Java来对图片进行操作：放大/缩小，resize，文件压缩

正常情况下，使用

BufferedImage image = ImageIO.read(new File("d:/test.jpg"));

或者直接使用第三方组件：net.coobird.thumbnailator

net.coobird.thumbnailator.Thumbnails
  .of(new File("d:/test.jpg"))
  .size(100,100)//比如原来像素是300x300,现在转成100x100
  .toFile(new File("d:/test_100x100.jpg"));
//实际底层也是ImageIO.read(new File("d:/test.jpg"));

有时候遇到图片读取就GG了

javax.imageio.IIOException: Unsupported Image Type
	at com.sun.imageio.plugins.jpeg.JPEGImageReader.readInternal(JPEGImageReader.java:1079)
	at com.sun.imageio.plugins.jpeg.JPEGImageReader.read(JPEGImageReader.java:1050)
	at javax.imageio.ImageIO.read(ImageIO.java:1448)
	at javax.imageio.ImageIO.read(ImageIO.java:1308)

在stackoverflow上找到了解决方案：

/**
* @author: https://www.cnblogs.com/tomcatandjerry/
* @date 2020-2-26
*/
private static BufferedImage readImageWithNoError(File imageFile) {
        try {
            return ImageIO.read(imageFile);
        } catch (Exception e) {
            try {
                //Find a suitable ImageReader
                Iterator readers = ImageIO.getImageReadersByFormatName("JPEG");
                ImageReader reader = null;
                while (readers.hasNext()) {
                    reader = (ImageReader) readers.next();
                    if (reader.canReadRaster()) {
                        break;
                    }
                }
                //Stream the image file (the original CMYK image)
                ImageInputStream input;
                input = ImageIO.createImageInputStream(imageFile);
                if (input == null) {
                    logger.error("ImageIO.createImageInputStream return null");
                    return null;
                }
                reader.setInput(input);
                //Read the image raster
                Raster raster = reader.readRaster(0, null);
                //Create a new RGB image
                BufferedImage bi = new BufferedImage(raster.getWidth(), raster.getHeight(), BufferedImage.TYPE_4BYTE_ABGR);
                //Fill the new image with the old raster
                bi.getRaster().setRect(raster);
                BufferedImage greyImage = makeGrey(bi);
                return greyImage;
            } catch (Exception e1) {
                logger.error("readImageWithNoError: error", e1);
                return null;
            }
        }
    }

    //对图片做灰化处理
	public static BufferedImage makeGrey(BufferedImage img) {
        //更换图片图层： https://www.cnblogs.com/tomcatandjerry/
        BufferedImage bufferedImage = new BufferedImage(img.getWidth(), img.getHeight(), BufferedImage.TYPE_3BYTE_BGR);
        bufferedImage.getGraphics().drawImage(img, 0, 0, img.getWidth(), img.getHeight(), null);
        bufferedImage = new ColorConvertOp(ColorSpace.getInstance(ColorSpace.CS_sRGB), null).filter(img, bufferedImage);
        return bufferedImage;
    }

这样就可以正常操作图片了。

>! 注意：如果是ImageIO.read()出错的文件，转换后，如果按jpg/或者其他方式生成图片，大小跟源文件不同的。如果需要按文件大小来缩放，需要生成一个临时的jpg文件File，用这个File来计算源文件的大小

Java 读取/缩小图片：javax.imageio.IIOException: Unsupported Image Type

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