Java Spring with Angular 16 uploading multiple files with JSON attached

I have an Java application running Spring and on it I have an endpoint to receive multiple files but, every time I hit it I get "415 Status".

This is my endpoint:

@PostMapping(value = "/upload", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
public List<Media> uploadMediaToS3(@RequestPart("files") Set<MultipartFile> files,
                                   @RequestPart("mediaUploads") Set<MediaUploadDTO> mediaUploadDTOs,
                                   @RequestParam("profileId") UUID profileId) throws IOException, FindMeDataNotFoundException {
    logger.info("WORKED! " + profileId.toString());
    return new ArrayList<>();
}

And this is how I'm building the request on my Angular application: PS: postMedia is an array of { fileData: fileToSend, base64: event.target!.result!.toString() }.

    let formDataWithFiles = new FormData();
    let filesRaw = [] as Array<File>;
    let filesInfo = [] as Array<Media>;
    this.postMedias.forEach(postMedia => {
      filesRaw.push(new File([postMedia.base64], postMedia.fileData.fileName));
      filesInfo.push(postMedia.fileData);
    });
    formDataWithFiles.append('files', new Blob(filesRaw));
    formDataWithFiles.append('mediaUploads', JSON.stringify(filesInfo));
    console.log(formDataWithFiles);
    this.postService.uploadMedias(formDataWithFiles, this.profileId);

The service call is:

  uploadMedias(files: FormData, profileId: string) {
return firstValueFrom(this.appService.POST<Media>(`medias/upload?profileId=${profileId}`, files)).then(savedMedia => {
  return savedMedia;
}, error => {
  throw error;
});

} My files are being upload to my Angular application by an Input type file and are being save onto a variable by using this code:

if (file.target.files[0]['size'] / 1e+6 == this.maxMediaSize) {
  this.openSnackBar(this.translateService.instant('CUSTOM-FILE-INPUT.MAX-SIZE-ERROR') + `${this.maxMediaSize}Mb`, 2500);
} else {
  let reader = new FileReader();
  reader.readAsDataURL(file.target.files[0]);
  let fileToSend: Media = {} as Media;
  fileToSend.mediaExtension = file.target.files[0].type.substring(file.target.files[0].type.indexOf('/') + 1).toUpperCase();
  fileToSend.mediaPrivacy = 'PUBLIC';
  fileToSend.mediaPrice = 0.0
  fileToSend.whenToDelete = new Date().getTime();
  fileToSend.fileName = file.target.files[0].name;
  fileToSend.mediaType = 'PROFILE_AVATAR_MEDIA';

  reader.onload = (event) => {
    this.formFiles.push({ fileData: fileToSend, base64: event.target!.result!.toString() });
  };
 }

I tried using Postman to test this endpoint but, getting nowhere either:

I have another endpoint that saves a single file and it works perfectly:

@PostMapping(value = "/update-avatar", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
public Media uploadAvatarToS3(@RequestPart("avatar") MultipartFile avatar,
                              @RequestPart("mediaUpload") MediaUploadDTO mediaUploadDTO,
                              @RequestParam("profileId") UUID profileId) throws IOException, FindMeDataNotFoundException {
    return mediaService.uploadAvatar(avatar, profileId, mediaUploadDTO);
}

My application.properties has the "multipart" properties in it:

spring.servlet.multipart.enabled=true
spring.servlet.multipart.location=${java.io.tmpdir}
spring.servlet.multipart.max-file-size=100MB
spring.servlet.multipart.max-request-size=100MB

My Spring version is 3.3.3 with Java 17

If anyone has any idea on what I could try, it'd help a lot! Thanks in advance!

Got it working by making some changes: On my Back end, I had to change the Set<MultipartFile> medias to MultipartFile[] medias, then it was able to give me more than just a 415 code. After that, I changed the front-end to this:

          this.postMedias.forEach(postMedia => {
            formDataWithFiles.append('medias', new File([base64ToFile(postMedia.base64)], postMedia.fileData.fileName));
            filesInfo.push(postMedia.fileData);
          });
          formDataWithFiles.append('mediaUploads', new Blob([JSON.stringify(filesInfo)], { type: 'application/json' }));
          this.postService.uploadMedias(formDataWithFiles, this.cookieService.get('ProfileId'), result.id).then(result => {
            this.loadPosts();
          });

I forgot to actually parse the Base64 to file using base64ToFile, after that it worked perfectly.