[FIXED] MultipartFile with additional properties from Angular to Spring Boot

Issue

I have the following spring-boot function that works and is able to read MultipartFiles that is sent from Angular front-end code.

@PostMapping(value = "/upload")
@Operation(summary = "Upload Files")
public ResponseEntity<Map<String, List<String>>> uploadFiles(@RequestParam("files") MultipartFile[] files) {

    List<String> exceptions = new ArrayList<>();
    List<String> fileNames = new ArrayList<>();
    
    for (MultipartFile file : files) {
        try {
            Path fileStorage = get(DIRECTORY, fileName).toAbsolutePath().normalize();
            copy(file.getInputStream(), fileStorage, true);
            fileNames.add(fileName);
        } catch (Exception e) {
            exceptions.add(e.getClass().getName() + ": " + e.getMessage());
        }
    }

    Map<String, List<String>> map = new HashMap<>();
    map.put("data", fileNames);
    map.put("errors", exceptions);
    return ResponseEntity.ok().body(map);

}

My problem is, I have a couple of properties (checksum and author) that I need to get on each file. This is the sample of the file object that gets added as FormData.

How will I be able to get them in my backend code?

Here's the Request Payload

Here's the Request Header coming from Angular

Solution

I found this article that helped me fix my problem: https://blogs.perficient.com/2020/07/27/requestbody-and-multipart-on-spring-boot/

@PostMapping(value = "/upload", consumes = { MediaType.APPLICATION_JSON, MediaType.MULTIPART_FORM_DATA })
@Operation(summary = "Upload Files")
public ResponseEntity<Map<String, List<String>>> uploadFiles(@RequestPart("files") MultipartFile[] files,
        @RequestPart("fileUploadMetadataList") String inputFileUploadMetadataList) {

    ObjectMapper mapper = new ObjectMapper();
    CollectionType listType = mapper.getTypeFactory().constructCollectionType(ArrayList.class,
            FileUploadMetadataEntity.class);
    try {
        List<FileUploadMetadata> fileUploadMetadataList = mapper.readValue(inputFileUploadMetadataList, listType);
        /*** fileUploadMetadataList => CONTAINS EXACTLY WHAT I NEEDED ***/
    
    } catch (JsonMappingException jsonMappingError) {
        jsonMappingError.printStackTrace();
    } catch (JsonProcessingException jsonProcessingError) {
        jsonProcessingError.printStackTrace();
    }

    // ... some other statements

}

And in Angular, this is what I needed to do:

// ... some other statements

const formData = new FormData();
const fileUploadMetaDataList: FileUploadMetadata[] = [];

for (const file of this.files) {
  const fileUploadMetadata: FileUploadMetadata = {
    fileName: file.name,
    checksum: file.checksum,
    author: file.author,
    fileSize: file.size,
    lastModifiedDate: file.lastModifiedDate,
    uploadDate: new Date(),
  };
  formData.append('files', file);
  fileUploadMetaDataList.push(fileUploadMetadata);
}

formData.append(
  'fileUploadMetadataList',
  JSON.stringify(fileUploadMetaDataList)
);

// ... some other statements

Answered By - ericute
Answer Checked By - Terry (JavaFixing Volunteer)