JAVA - Get black background when uploading PNG image

Question

I am having issue when I save a png file with Google's Thumbnailator uploaded by user. It loses its transparency . Here is my coding:

@RequestMapping(method = RequestMethod.POST, path = "/upload")
@ResponseBody
public String upload(@RequestPart("file") MultipartFile picture) {
    String originalFileName = picture.getOriginalFilename();
    String suffix = 
         originalFileName.substring(originalFileName.lastIndexOf("."));
    String pictureName = UUID.randomUUID().toString() + suffix;
    String fileSavePath = gunsProperties.getFileUploadPath();
    Thumbnails.of(picture.getInputStream()).outputFormat("png")
        .scale(1f).outputQuality(0.15f)
        .toFile(new File(fileSavePath + pictureName));

    return pictureName;
}

it puts a black background. Any other way to save it as png with transparent? Thanks!

Answer 1

What writing it to the file directly instead of using the thumbnail thing? Since your scale is 1.0 anyway, you could just write it to disk directly:

picture.transferTo(new File(fileSamePath + pictureName));

OR

FileOutputStream fos = new FileOutputStream(new File(fileSamePath + pictureName));
fos.write(picture.getBytes());
fos.close();

OR try specifying the image format:

Thumbnails.of(picture.getInputStream()).imageType(BufferedImage.TYPE_INT_ARGB).outputFormat("png").scale(1f).outputQuality(0.15f).toFile(new File(fileSavePath + pictureName));

That'll make it 24-bit with transparency instead of 8-bit (if it is).