使用commons-imaging 获取图片的尺寸

   implementation ('org.apache.commons:commons-imaging:1.0.0-alpha5')

//1、通过MultipartFile file 获取ImageInfo
 ImageInfo imageInfo = Imaging.getImageInfo(file.getBytes());
 
 //2、获取DPI
 BigDecimal widthDpiBD = new BigDecimal(imageInfo.getPhysicalWidthDpi());
 if(widthDpiBD.compareTo(BigDecimal.ZERO) < 0){
      throw new BusinessException("图片DPI不存在！");
   }
   
  BigDecimal widthBD = new BigDecimal(imageInfo.getWidth());
  //3、获取英寸
  BigDecimal widthInches = widthBD.divide(widthDpiBD, 2, RoundingMode.HALF_UP);
  BigDecimal heightDpiBD = new BigDecimal(imageInfo.getPhysicalHeightDpi());
  if(heightDpiBD.compareTo(BigDecimal.ZERO) < 0){
        throw new BusinessException("图片DPI不存在！");
   }
   BigDecimal heightBD = new BigDecimal(imageInfo.getHeight());
   BigDecimal heightInches = heightBD.divide(heightDpiBD, 2, RoundingMode.HALF_UP);
   // 4、将物理尺寸转换为毫米
   double widthMm = widthInches.multiply(new BigDecimal("25.4")).setScale(0, RoundingMode.HALF_UP).doubleValue();
   double heightMm = heightInches.multiply(new BigDecimal("25.4")).setScale(0, RoundingMode.HALF_UP).doubleValue();