Application.java

@SpringBootApplication
@EnableConfigurationProperties({ApplicationProperties.class})
public class Application {
  // ...
}

application.properties

spring:
  servlet:
        multipart:
            # Enable multipart uploads
            enabled: true
            # Threshold after which files are written to disk.
            file-size-threshold: 2KB
            # Max file size
            max-file-size: 15MB
            # Max request size
            max-request-size: 20MB
application:
    file:
        ## File Storage Properties
        # All files uploaded will be stored in this directory
        upload-dir: /home/[user]/files

ApplicationProperties.java

@ConfigurationProperties(prefix = "application", ignoreUnknownFields = false)
public class ApplicationProperties {

    public File file;

    public File getFile() {
        return file;
    }

    public void setFile(File file) {
        this.file = file;
    }

    public static class File {
        public String uploadDir;

        public String getUploadDir() {
            return uploadDir;
        }

        public void setUploadDir(String uploadDir) {
            this.uploadDir = uploadDir;
        }
    }
}

FileNotFoundException.java

@ResponseStatus(HttpStatus.NOT_FOUND)
public class FileNotFoundException extends RuntimeException {
    public FileNotFoundException(String message) {
        super(message);
    }

    public FileNotFoundException(String message, Throwable cause) {
        super(message, cause);
    }
}

FileResource.java

@RestController
@RequestMapping("/api/files")
public class FileResource {

    private static final Logger logger = LoggerFactory.getLogger(FileResource.class);

    private final FileStorageService fileStorageService;

    public FileResource(FileStorageService fileStorageService) {
        this.fileStorageService = fileStorageService;
    }

    @PostMapping("/uploadFile")
    public ResponseEntity<UploadFileResponse> uploadFile(@RequestParam("file") MultipartFile file) {

        UploadFileResponse resp = saveFile(file);

        return ResponseEntity.created(URI.create( resp.getFileDownloadUri() ))
            .body(resp);

    }

    private UploadFileResponse saveFile(@RequestParam("file") MultipartFile file) {
        String fileName = fileStorageService.storeFile(file);

        String fileDownloadUri = ServletUriComponentsBuilder.fromCurrentContextPath()
            .path("/downloadFile/")
            .path(fileName)
            .toUriString();

        return new UploadFileResponse(fileName, fileDownloadUri,
            file.getContentType(), file.getSize());
    }

    @PostMapping("/uploadMultipleFiles")
    public ResponseEntity<List<UploadFileResponse>> uploadMultipleFiles(@RequestParam("files") MultipartFile[] files) {

        List<UploadFileResponse> resp = Arrays.stream(files)
            .map(this::saveFile)
            .collect(Collectors.toList());

        String fileDownloadUri = ServletUriComponentsBuilder.fromCurrentContextPath()
            .path("/downloadFile/")
            .toUriString();

        return ResponseEntity.created(URI.create( fileDownloadUri ))
            .body(resp);
    }

    @GetMapping("/downloadFile/{fileName:.+}")
    public ResponseEntity<Resource> downloadFile(@PathVariable String fileName, HttpServletRequest request) {
        // Load file as Resource
        Resource resource = fileStorageService.loadFileAsResource(fileName);

        // Try to determine file's content type
        String contentType = null;
        try {
            contentType = request.getServletContext().getMimeType(resource.getFile().getAbsolutePath());
        } catch (IOException ex) {
            logger.info("Could not determine file type.");
        }

        // Fallback to the default content type if type could not be determined
        if(contentType == null) {
            contentType = "application/octet-stream";
        }

        return ResponseEntity.ok()
            .contentType(MediaType.parseMediaType(contentType))
            .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + resource.getFilename() + "\"")
            .body(resource);
    }
    
    @DeleteMapping("/{fileName:.+}")
    public ResponseEntity<Boolean> deleteFile(@PathVariable String fileName, HttpServletRequest request) {

        try {
            boolean resp = fileStorageService.deleteFile(fileName);
            return ResponseEntity.ok()
                .body(resp);
        } catch (IOException e) {
            throw new InternalServerErrorException("");
        }
    }
}

FileStorageException.java

public class FileStorageException extends RuntimeException {
    public FileStorageException(String message) {
        super(message);
    }

    public FileStorageException(String message, Throwable cause) {
        super(message, cause);
    }
}

FileStorageService.java

@Service
public class FileStorageService implements FileStorageService {

    private final Path fileStorageLocation;

    @Autowired
    public FileStorageServiceImpl(ApplicationProperties applicationProperties) {
        this.fileStorageLocation = Paths.get(applicationProperties.getFile().getUploadDir())
            .toAbsolutePath().normalize();

        try {
            Files.createDirectories(this.fileStorageLocation);
        } catch (Exception ex) {
            throw new FileStorageException("Could not create the directory where the uploaded files will be stored.", ex);
        }
    }

    public String storeFile(MultipartFile file) {
        // Normalize file name
        String fileName = StringUtils.cleanPath(Objects.requireNonNull(file.getOriginalFilename()));

        try {
            // Check if the file's name contains invalid characters
            if(fileName.contains("..")) {
                throw new FileStorageException("Sorry! Filename contains invalid path sequence " + fileName);
            }

            // Copy file to the target location (Replacing existing file with the same name)
            Path targetLocation = this.fileStorageLocation.resolve(fileName);
            Files.copy(file.getInputStream(), targetLocation, StandardCopyOption.REPLACE_EXISTING);

            return fileName;
        } catch (IOException ex) {
            throw new FileStorageException("Could not store file " + fileName + ". Please try again!", ex);
        }
    }

    public Resource loadFileAsResource(String fileName) {
        try {
            Path filePath = this.fileStorageLocation.resolve(fileName).normalize();
            Resource resource = new UrlResource(filePath.toUri());
            if(resource.exists()) {
                return resource;
            } else {
                throw new FileNotFoundException("File not found " + fileName);
            }
        } catch (MalformedURLException ex) {
            throw new FileNotFoundException("File not found " + fileName, ex);
        }
    }
    
    @Override
    public boolean deleteFile(String fileName) throws IOException {
        Resource resource = loadFileAsResource(fileName);
        return resource.getFile().delete();
    }
}

UploadFileResponse.java

public class UploadFileResponse {

    private String fileName;
    private String fileDownloadUri;
    private String fileType;
    private long size;

    public UploadFileResponse(String fileName, String fileDownloadUri, String fileType, long size) {
        this.fileName = fileName;
        this.fileDownloadUri = fileDownloadUri;
        this.fileType = fileType;
        this.size = size;
    }

    public String getFileName() {
        return fileName;
    }

    public void setFileName(String fileName) {
        this.fileName = fileName;
    }

    public String getFileDownloadUri() {
        return fileDownloadUri;
    }

    public void setFileDownloadUri(String fileDownloadUri) {
        this.fileDownloadUri = fileDownloadUri;
    }

    public String getFileType() {
        return fileType;
    }

    public void setFileType(String fileType) {
        this.fileType = fileType;
    }

    public long getSize() {
        return size;
    }

    public void setSize(long size) {
        this.size = size;
    }
}