JPA – Successful Storage of Post Only When Input Tag Name is "file"

July 24, 2023

I’m implementing a feature to store posts using JPA. In the service class, I have the following method:

public void boardWrite(Board board, MultipartFile file) throws Exception, IOException {
    if (!file.isEmpty()) {
        String path = "E:\\image\\sell";
        UUID uuid = UUID.randomUUID();
        String filename = uuid + "_" + file.getOriginalFilename();
        File saveFile = new File(path, filename);
        file.transferTo(saveFile);
        board.setPhoto(filename);
        board.setPhoto_url("/sell/" + filename);
    }

    boardRepository.save(board);
}

Additionally, in the controller, I call it as follows:

@PostMapping("/add")
public String add(Board board, MultipartFile file) throws Exception {
    service.boardWrite(board, file);
    return "redirect:list";
}

The part of the HTML where I get the file input is as follows:

<tr>
    <td width="150" align="center">Photo Attachment</td>
    <td>
        <input type="file" name="file" class="form-control" id="inputGroupFile02">
    </td>
</tr>

When I set the name attribute of the input tag to "file", the post is successfully stored. However, if I use a different name such as "file1" or "photo", it results in a 400 error. I’m curious about the reason behind this behavior. Why does it only work when the input tag name is "file"?

>Solution :

The argument MultipartFile file is equivalent to: @RequestParam MultipartFile file

If you don’t specify a name with the @RequestParam annotation the variable name is used as default. In your case this is file.

You can use other names by either changing your variable name or adding the @RequestParam annotation with a name:
@RequestParam("photo") MultipartFile file.

If you have to support multiple names, create proxy methods:

@PostMapping(value="/add", params = "photo")
public String addPhoto(@RequestParam(value="photo", required=true) MultipartFile file){
   return addFile(file);
}

@PostMapping(value="/add", params = "file")
public String addFile(@RequestParam(value="file", required=true) MultipartFile file){
   // ...
}