How to Upload Multipart Files in Spring Boot as Part of a JSON Request Body

How can I upload multipart files in Spring Boot while including them in a JSON request body?

@RestController
public class FileUploadController {
    @PostMapping("/upload")
    public ResponseEntity<String> uploadFile(@RequestParam("file") MultipartFile file, 
                                             @RequestBody YourJsonRequestBody jsonRequest) {
        // process the file and jsonRequest
        return ResponseEntity.ok("File uploaded successfully!");
    }
}

Uploading multipart files as part of a JSON request body in Spring Boot requires a combination of file parameters and JSON deserialization. This can be broken down into capturing the file through a dedicated endpoint that allows multipart requests and extracting the JSON body separately.

@Data
public class YourJsonRequestBody {
    private String field1;
    private String field2;
    // additional fields
}

@RestController
public class FileUploadController {
    @PostMapping("/upload")
    public ResponseEntity<String> uploadFile(@RequestParam("file") MultipartFile file, 
                                             @RequestBody YourJsonRequestBody jsonRequest) {
        // Use file and jsonRequest for your logic
        return ResponseEntity.ok("File uploaded successfully!");
    }
}

Causes

• Understanding Multipart Requests in Spring Boot
• Deserializing JSON with File Uploads
• Configuration of Multipart File Handling in Spring Boot

Solutions

• Use the `@RequestParam` annotation for the file upload
• Parse the JSON using a custom request body class
• Configure your Spring Boot application to accept multipart file uploads

Mistake: Not using `@RequestParam` for the multipart file.

Solution: Ensure that the file is accepted as a parameter using `@RequestParam` in your controller method.

Mistake: Incorrectly configuring multipart settings in `application.properties`.

Solution: Set properties such as `spring.http.multipart.enabled=true` and configure max file size appropriately.