Skip to main content
Advertisement

3.6 Handling File Uploads (MultipartFile)

Learn how to handle image or document uploads in web applications using the MultipartFile interface and its related configurations.

1. How File Uploads Work (multipart/form-data)​

Files are large binary data, not simple text. Therefore, they cannot be efficiently sent using application/json. For this purpose, HTTP uses a special encoding called multipart/form-data. In Spring, we receive this data using the MultipartFile interface.

2. File Upload Implementation Example​

Controller Implementation​

@RestController
@Slf4j
public class FileUploadController {

    @PostMapping("/api/upload")
    public String uploadFile(@RequestParam("file") MultipartFile file) throws IOException {
        if (file.isEmpty()) {
            return "File is empty.";
        }

        log.info("Filename: {}", file.getOriginalFilename());
        log.info("File Size: {} bytes", file.getSize());
        log.info("Content Type: {}", file.getContentType());

        // Example: Saving to a local directory
        String fullPath = "/uploads/" + file.getOriginalFilename();
        file.transferTo(new File(fullPath));

        return "Upload Success: " + fullPath;
    }
}

3. Upload Capacity Configuration (application.yml)​

Spring Boot has small default limits for file uploads. To allow large files, add the following to your application.yml:

spring:
  servlet:
    multipart:
      max-file-size: 10MB      # Max size for a single file
      max-request-size: 50MB   # Max total size for a single HTTP request

4. Practical Considerations​

  1. Duplicate Filenames: Using the original filename directly can lead to overwriting existing files. It is safer to generate unique filenames using tools like UUID.
  2. Security: If an uploaded file is an executable script (.php, .sh, etc.), the server could be compromised. Always validate file extensions and perform security checks.
  3. Storage Choice: While saving to a local directory is fine initially, scaling a service usually requires switching to dedicated cloud storage like ** AWS S3**.
Advertisement
Advertisement