从网络上获得一个图片，将他转变为缩略图（放大或缩小图片的宽高），然后再转换为MultipartFile对象 方便图片上传

/**
 * @author gaoyang
 * @create 2021-02-02 17:30
 */
public class ImageUtls {

    /**
     * 重新按比例设置图片的大小
     * @param scale
     * @param url
     * @return
     * @throws ImageFormatException
     * @throws IOException
     */
    public static MultipartFile resize(float scale, String url) throws ImageFormatException, IOException {
        URL targetURL = new URL(url);
        Image image = ImageIO.read(targetURL);
        int[] size = getSize(scale, image);
        return resize(size[0], size[1], url, image);
    }

    /**
     * <b>function:</b> 将Image的宽度、高度缩放到指定width、height
     *
     * @param width       缩放的宽度
     * @param height      缩放的高度
     * @param url         图片地址
     * @param targetImage 即将缩放的目标图片
     * @return 分片文件
     * @throws ImageFormatException
     * @throws IOException
     */
    public static MultipartFile resize(int width, int height, String url, Image targetImage) throws ImageFormatException, IOException {
        width = Math.max(width, 1);
        height = Math.max(height, 1);
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        image.getGraphics().drawImage(targetImage, 0, 0, width, height, null);
        ByteArrayOutputStream os = new ByteArrayOutputStream();
        ImageIO.write(image, url.substring(url.lastIndexOf(".") + 1), os);
        InputStream is = new ByteArrayInputStream(os.toByteArray());
        String[] split = url.split("/");
        String name = split[split.length - 1];
        MultipartFile multipartFile = new MockMultipartFile(name, name, "", is);
        image.flush();
        os.close();
        is.close();
        return multipartFile;
    }

    /**
     * <b>function:</b> 通过指定的比例和图片对象，返回一个放大或缩小的宽度、高度
     *
     * @param scale 缩放比例
     * @param image 图片对象
     * @return 返回宽度、高度
     * @author hoojo
     * @createDate 2012-2-7 上午10:27:59
     */
    public static int[] getSize(float scale, Image image) {
        int targetWidth = image.getWidth(null);
        int targetHeight = image.getHeight(null);
        long standardWidth = Math.round(targetWidth * scale);
        long standardHeight = Math.round(targetHeight * scale);
        return new int[]{Integer.parseInt(Long.toString(standardWidth)), Integer.parseInt(String.valueOf(standardHeight))};
    }

}