I need to convert file in base64.
At the moment it saves the files well but not in base 64

My code in Controller is:

```
@PostMapping("/upload")
public ResponseEntity <Response> uploadFiles(@RequestParam("files") 
 List <MultipartFile> files) throws Exception { 

    fileServiceAPI.save(files);
    return ResponseEntity.status(HttpStatus.OK)
            .body(new Response("The files were successfully uploaded to the server"));

}

```

My code in service:

```
private final Path rootFolder = 
Paths.get("upload");

@Override
public void save(MultipartFile file) throws Exception {
    Files.copy(file.getInputStream(), this.rootFolder.resolve(file.getOriginalFilename()));
}

@Override
public void save(List<MultipartFile> files) throws Exception {

    for(MultipartFile file: files){

        this.save(file);
    }
}

```