MultipartFile with SpringBoot

This article explains two use cases of multipart files in Spring Boot.

How to receive a Multipart file in the SpringBoot application?

Suppose we have an endpoint /uploadFile that receives a file and other parameters as form data in the request body and saves it.

@PostMapping(value = "/uploadFile", consumes = MediaType.MULTIPART_FORM_DATA_VALUE, produces = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<String> uploadFile(@RequestPart(value = "file") MultipartFile file) {
  service.uploadFile(file);
  return new ResponseEntity<>("success", HttpStatus.OK);
}

• PostMapping annotation is used to represent that uploadFile handles HTTP POST requests for the given URI.
• consumes = MediaType.MULTIPART_FORM_DATA_VALUE shows that this request accepts multipart media as input data.
• RequestPart annotation is used to associate a part of a request named file with a method argument file .
• service.uploadFile is a service class method that does further processing, and it is explained below.

Now, we will write a service class method that processes the request input and saves the file.

public void uploadFile(MultipartFile file) throws UserException {
  try {
    if(file.isEmpty()) {
      throw new UserException("Empty file");
    }
    Path destination = Paths.get("rootDir").resolve(file.getOriginalFilename()).normalize().toAbsolutePath();
    Files.copy(file.getInputStream(), destiation);
  } catch(IOException e) {
    throw new UserException("Store exception");
  }
}

• file.isEmpty() is a check to validate the input data.
• Next, we create a file with the same input name in the directory named rootDir .
• The final step is to copy the content of the input file to a newly created file.

How to send a Multipart file using RestTemplate in SpringBoot?

The second use-case of multipart files is to send a file from a spring-boot server to a different server.

Here we are using RestTemplate to communicate with the second server.

public void shareFile(MultipartFile file) {
  HttpHeaders headers = new HttpHeaders();
  headers.setContentType(MediaType.MULTIPART_FORM_DATA);
  
  MultiValueMap<String, Object> body = new LinkedMultiValueMap<>();
  body.add("file_name", "testFile");
  body.add("file", file.getResource());
  
  HttpEntity<MultiValueMap<String, Object>> request = new HttpEntity<>(body, httpHeaders);
  
  RestTemplate restTemplate = new RestTemplate();
  ResponseEntity<String> response = restTemplate.postForEntity("<url-of-the-second-server>", request, String.class);
}

• headers.setContentType(MediaType.MULTIPART_FORM_DATA is used to specify the content type header for the request.
• MultiValueMap represents our request body which contains file_name and file .
• Next, we create a request object HttpEntity and pass it inside postForEntity method of RestTemplate .

References

[1] https://spring.io/guides/gs/uploading-files/
[2] https://www.baeldung.com/spring-rest-template-multipart-upload