How to handle file uploads in a Java Spring Boot application?
Spring Boot simplifies file uploading by configuring the multipart attribute to limit the file size and enable functions. It uses @RequestParam to receive files and combines with MultipartFile to implement uploading. It needs to verify the type, purify the file name, store it in a safe path, and configure static resources to access uploaded files.
Handling file uploads in a Spring Boot application is straightforward with built-in support for multipart requests. Here's how to do it step by step.
Enable Multipart File Uploads
SprinBoot enables multipart configuration by default, but you can customize it in application.properties or application.yml :
#application.properties spring.servlet.multipart.max-file-size=10MB spring.servlet.multipart.max-request-size=10MB spring.servlet.multipart.enabled=true
This limits file size and ensures the feature is active.
Create a Controller to Handle Uploads
Use @RequestParam to bind the uploaded file in your controller:
@RestController
public class FileUploadController {
<pre class='brush:php;toolbar:false;'>@PostMapping("/upload")
public ResponseEntity<String> uploadFile(@RequestParam("file") MultipartFile file) {
if (file.isEmpty()) {
return ResponseEntity.badRequest().body("Please select a file to upload.");
}
try {
// Save the file (example: to local filesystem)
String uploadDir = "uploads/";
Path path = Paths.get(uploadDir file.getOriginalFilename());
Files.write(path, file.getBytes());
return ResponseEntity.ok("File uploaded successfully: " file.getOriginalFilename());
} catch (IOException e) {
return ResponseEntity.status(500).body("Failed to upload file: " e.getMessage());
}
} }
Save Files Securely
When saving files, consider these best practices:
- Validate file type using file.getContentType() or file extension checks
- Sanitize filenames to prevent directory traversal (eg, reject names with
..) - Store files outside the web root or use a secure location
- Limit allowed file types and sizes
Handle Multiple Files
To accept multiple files, change the parameter to an array:
@PostMapping("/upload-multiple")
public ResponseEntity<String> uploadFiles(@RequestParam("files") MultipartFile[] files) {
Arrays.stream(files).forEach(this::saveFile);
return ResponseEntity.ok("Files uploaded successfully.");
}
You can also serve uploaded files by mapping a static directory:
@Configuration
public class WebConfig implements WebMvcConfigurer {
@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
registry.addResourceHandler("/files/**")
.addResourceLocations("file:uploads/");
}
}
Then users can access uploaded files via /files/filename.jpg .
Basically that's all you need—Spring Boot handles the heavy lifting, and you focus on storage, validation, and security.
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