How to upload and download files in Spring Boot?

File upload and download in SpringBoot can be achieved by following these steps:

1. Upload files:

@RestController
public class FileUploadController {

    @PostMapping("/upload")
    public String uploadFile(@RequestParam("file") MultipartFile file) {
        try {
            // 保存文件到指定路径
            File newFile = new File("path/to/save/" + file.getOriginalFilename());
            file.transferTo(newFile);
            return "File uploaded successfully";
        } catch (IOException e) {
            return "File upload failed";
        }
    }
}

1. Download the files:

@RestController
public class FileDownloadController {

    @GetMapping("/download/{fileName}")
    public ResponseEntity<Resource> downloadFile(@PathVariable String fileName) {
        Resource resource = new FileSystemResource("path/to/save/" + fileName);
        
        HttpHeaders headers = new HttpHeaders();
        headers.add(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=" + resource.getFilename());
        
        return ResponseEntity.ok()
                .headers(headers)
                .contentLength(resource.contentLength())
                .contentType(MediaType.APPLICATION_OCTET_STREAM)
                .body(resource);
    }
}

In file upload, use the @RequestParam annotation to retrieve the uploaded file and save it to a specified path. In file download, use the @PathVariable annotation to retrieve the file name to be downloaded, then return the corresponding file resource and set the response header to prompt the browser to download the file.