Spring mvc upload multiple files at once with AJAX doesn't work

Question

I'm using Spring boot 2.0.1 and I'm trying to upload multiple files with dropzone. Everything is working perfectly when I'm using uploadMultiple: false on Dropzone.js. When I set uploadMultiple: true, My Controller stops working.

The controller class is as follow:

@PostMapping(value = "/img/upload")
public ResponseEntity<?> fileUpload(@RequestParam("file") MultipartFile[] files){

    System.out.println(files.length);
    for (MultipartFile file : files) {
        try {
            file.transferTo(new File("/opt/img/" + file.getOriginalFilename()));
            System.out.println(file.getOriginalFilename());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    return new ResponseEntity<>("File Uploaded Successfully.", HttpStatus.OK);
}

The files are no more than 1MB and my settings are

spring.servlet.multipart.max-file-size=10MB
spring.servlet.multipart.max-request-size=10MB

My request header when I upload the files:

------WebKitFormBoundaryihPcX9WHR5UA9jGD
Content-Disposition: form-data; name="file[0]"; filename="cars-02-01.png"
Content-Type: image/png


------WebKitFormBoundaryihPcX9WHR5UA9jGD
Content-Disposition: form-data; name="file[1]"; filename="Screenshot from 2018-05-03 23-31-53.jpg"
Content-Type: image/jpeg

Everything seems perfect. I still cannot find the reason for this problem?

Answer 1

It seems that I should use the MultipartHttpServletRequest instead of MultipartFile[] files. I Changed the method to:

@PostMapping(value = "/img/upload")
public ResponseEntity<?> fileUpload(MultipartHttpServletRequest request) {
    Map<String, MultipartFile> fileMap = request.getFileMap();

    for (MultipartFile file : fileMap.values()) {
        try {
            file.transferTo(new File("/opt/img/" + file.getOriginalFilename()));
            System.out.println(file.getOriginalFilename());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    return new ResponseEntity<>("File Uploaded Successfully.", HttpStatus.OK);
}