How get multiple images with springboot?-CodePudding

Goodmorning everyone, I am creating a web application for my degree and I have been running into a problem for several days related to the loading and retrive of images from the database. I can upload the photos without major problems, I still leave the controller code:

    @PostMapping()
public AckDto handleImagePost(@RequestParam ("file") MultipartFile file, @RequestParam Long userId, @RequestParam Long contestId) throws ServiceException, IOException {

    PhotoDto photoDto = new PhotoDto();
    photoDto.setTitle("Test Image");
    photoDto.setDescription("Test description");
    photoDto.setImage(file.getBytes());
    return photoService.saveImagineFile(photoDto, userId, contestId);

}

While for the get of the photos I can only take one photo with the following method:

        @GetMapping(value = "/image", produces = MediaType.IMAGE_PNG_VALUE)
public Resource downloadImage(@RequestParam Long contestId) throws ServiceException, IOException {
    Photo photo = photoService.findByContest_Id(contestId);

    byte[] image = photoService.findByContest_Id(contestId).getImage();;


    return new ByteArrayResource(image);
}

while if I try to take more photos with the following code obviously changing the Service and Repository:

    @GetMapping(value = "/image", produces = MediaType.IMAGE_PNG_VALUE)
public List<Resource> downloadImage(@RequestParam Long contestId) throws ServiceException, IOException {

    List<Photo> photo = photoService.findByContest_Id(contestId);
    List<Resource> results = new ArrayList<>();

    for(Photo p : photo){
        results.add(new ByteArrayResource(p.getImage()));
    }

    return results;
}

it returns me the following errors:

org.springframework.http.converter.HttpMessageNotWritableException: No converter for [class java.util.ArrayList] with preset Content-Type 'null'

I also tried to return a PhotoDto list but it doesn't change anything, Some idea?

If you need any other class, ask and it will be given to you.

CodePudding user response：

Not sure if the following works for you, but you can zip all images and then retrieve them in a unique file.

The code example (taken from the reference below):

@GetMapping(value = "/zip-download", produces="application/zip")
public void zipDownload(@RequestParam List<String> name, HttpServletResponse response) throws IOException {
    ZipOutputStream zipOut = new ZipOutputStream(response.getOutputStream());
    for (String fileName : name) {
        FileSystemResource resource = new FileSystemResource(fileBasePath   fileName);
        ZipEntry zipEntry = new ZipEntry(resource.getFilename());
        zipEntry.setSize(resource.contentLength());
        zipOut.putNextEntry(zipEntry);
        StreamUtils.copy(resource.getInputStream(), zipOut);
        zipOut.closeEntry();
    }
    zipOut.finish();
    zipOut.close();
    response.setStatus(HttpServletResponse.SC_OK);
    response.addHeader(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\""   zipFileName   "\"");
}

Reference: https://www.devglan.com/spring-boot/spring-boot-file-upload-download

CodePudding user response：

Rather than returning a List, return a ResponseEntity<List>. It MIGHT work.

Problem is that whatever way you're going about it, it's unlikely the frontend will be able to pull out your images.

UUEncoding them manually and putting them in the HTTP headers is probably your best bet. That way the frontend can iterate over the headers containing the images and get them one by one in a format it should be able to decode.