Empty List when trying to upload many files in Spring with ng-file-upload

Question

I have the following controller method for uploading multiple files at once, inspired by this blog post and answers to this question as well:

@RequestMapping         


        

Answer 1

I think that in the way you sent data from front, it can not bound with java.util.List. If you create a JSON data as request and you annotated your List with @RequestBody like:

@RequestMapping(value = "/{user}/attachment", method = RequestMethod.POST)
@PreAuthorize(...)
public void upload(@PathVariable User user, 
                   @RequestBody List<MultipartFile> files) {
  // handle files
}

this should work. Some info here.

Answer 2

for multiple files. do this in your javascript

//first add files to form data
var formData = new FormData();
for (let i = 0; i < files.length; i++) {
    formData.append("images", files[i]);
}

//post files to backend e.g using angular
 $http.post('upload', formData, {
     transformRequest: angular.identity,
     headers: {'Content-Type': undefined}
 })
 .then(function(response){
      console.log("UPLOAD COMPLETE::=> ", response);
 }, function (error) {
      console.log(error);
 });

Do this in your java

//your java method signature
@PostMapping(value = "/upload", consumes = MediaType.MULTIPART_FORM_DATA_VALUE )
public Response uploadImage(RequestParam(value = "images") MultipartFile[] images){

}

Answer 3

That works for me, sending big 'email' object with multiple file attachments from UI to back-end:

Angular

sendEmailWithAttachments(taskId: string, template: string, email: any, modelConfig: any, files: any[]) {
    let formData = new FormData();
    formData.append('form', new Blob([JSON.stringify(email)], {type: 'application/json'}));
    files.forEach(file  => {
        formData.append('files', file);
    });

    return this.$http({
        method: 'POST',
        data: formData,
        url: this.baseUrl + '/' + taskId + '/email-with-attachment?template=' + template,
        headers: {
            'Content-Type': undefined
        },
        responseType: 'arraybuffer'
    });
}

Java Spring

@RequestMapping(value = "{taskId}/email-with-attachment", method = RequestMethod.POST, consumes = MULTIPART_FORM_DATA_VALUE)
public void sendEmailWithAttachment(
        @PathVariable String taskId,
        @RequestParam String template,
        @RequestParam("form") MultipartFile form,
        @RequestParam("files") List<MultipartFile> files) throws IOException {
    Map<String, String> parameters = new ObjectMapper().readValue(form.getInputStream(), HashMap.class);

    System.out.println("taskId", taskId);
    System.out.println("template", template);
    System.out.println("files", files);
    System.out.println("parameters", parameters);
}

Answer 4

The problem was that ng-file-upload by default submits array of files using names file[0], file[1] etc. It is configurable with the arrayKey value when using Upload Service. Setting it to empty string forces the files to be sent under the same file key, which is correctly resolved with Spring and the @RequestParam("file") List<MultipartFile> contains all files that has been submitted.

Upload.upload({url: url, data: {file: arrayOfFiles}, arrayKey: ''})

Answer 5

Try to use @ModelAttribute like this:

    @RequestMapping(value = "/{user}/attachment", method = RequestMethod.POST)
    @PreAuthorize(...) 
    public void upload(@PathVariable User user,@ModelAttribute("uploadFile") FileUpload uploadFile) throws IllegalStateException, IOException {

    List<MultipartFile> files = uploadFile.getFiles();
    ...

And create a class like:

     public class FileUpload {
     private List<MultipartFile> files;
     public List<MultipartFile> getFiles() {
        return files;
     }

    public void setFiles(List<MultipartFile> files) {
       this.files= files;
      }
   }