Can't get selected option in controller - spring

Question

I have a form to list up buckets in select options, it uploads file to bucket after select bucket and file, but I can't get selected bucket in my controller, The folder alwsy return empty string, though mutipartFile is no problem, I really want to know why!
I googled for all this week but no result what I need!
I am very new in thymeleaf even in spring framework:(
Pls help me to solve this simple problem to you:)
part of html file as below:
<form role="form" enctype="multipart/form-data" action="#" th:object="${folder}" th:action="#{'/drill/skin/upload'}" method="POST">
<div class="form-group">
<label class="form-control-static">Select Bucket</label>
<select class="form-control" th:field="${folder}">
<option th:each="bucket : ${buckets}" th:value="${bucket.name}" th:text="${bucket.name}">bucket</option>
</select>
</div>
<label class="form-control-static" for="inputSuccess">Select Upload File</label>
<div class="form-group">
<input type="file" class="form-control" name="uploadFile"/>
</div>
<div class="form-group">
<button class="btn btn-primary center-block" type="submit">Upload</button>
</div>
</form>
controller as below:
#RequestMapping(value="/", method=RequestMethod.GET)
public String provideUploadInfo(Model model) {
List<Bucket> buckets = s3Service.listBuckets();
model.addAttribute("buckets", buckets);
model.addAttribute("folder", "com.smartstudy");
return "index";
}
#RequestMapping(value="/upload", method=RequestMethod.POST)
public String handleFileUpload(
#ModelAttribute("folder") String folder,
#RequestParam("uploadFile") MultipartFile uploadFile, Model model) {
log.info("Bucket: " + folder + ", uploadFile: " + uploadFile.getOriginalFilename());
if (!uploadFile.isEmpty() && !folder.isEmpty()) {
return s3Service.upload(uploadFile, folder);
}
return "index";
}

Answer 1

There are couple of issues in your code.
Ideally, the whole form should be encapsulated in one form-backing object. In your case, create a Java object that wraps the folder and the file together.
class BucketFileForm{
private MultipartFile uploadFile;
private String folder;
public String getFolder() {
return folder;
}
public void setFolder(String folder) {
this.folder = folder;
}
public MultipartFile getUploadFile() {
return uploadFile;
}
public void setUploadFile(MultipartFile uploadFile) {
this.uploadFile = uploadFile;
}
}
Make this object available in the model so that you can access it in the view
#RequestMapping(value="/", method=RequestMethod.GET)
public String provideUploadInfo(Model model) {
List<Bucket> buckets = s3Service.listBuckets();
model.addAttribute("buckets", buckets);
//replace this
//model.addAttribute("folder", "com.smartstudy");
//with
BucketFileForm bucketFileForm = new BucketFileForm();
bucketFileForm.setFolder("com.smartstudy");
model.addAttribute("bucketFileForm", bucketFileForm);
return "index";
}
Now, use this form-backing object in the form
<form role="form" enctype="multipart/form-data" action="#" th:object="${bucketFileForm}" th:action="#{'/drill/skin/upload'}" method="POST">
<div class="form-group">
<label class="form-control-static">Select Bucket</label>
<select class="form-control" th:field="*{folder}">
<option th:each="bucket : ${buckets}" th:value="${bucket.name}" th:text="${bucket.name}">bucket</option>
</select>
</div>
<label class="form-control-static" for="inputSuccess">Select Upload File</label>
<div class="form-group">
<input type="file" th:field="*{uploadFile}" class="form-control" name="uploadFile"/>
</div>
<div class="form-group">
<button class="btn btn-primary center-block" type="submit">Upload</button>
</div>
</form>
Then modify your POST endpoint to accomodate these changes.
#RequestMapping(value="/upload", method=RequestMethod.POST)
public String handleFileUpload(#ModelAttribute("bucketFileForm") final BucketFileForm form, final BindingResult bindingResult, Model model) {
log.info("Bucket: " + form.getFolder() + ", uploadFile: " + form.getUploadFile().getOriginalFilename());
if (!form.getUploadFile().isEmpty() && !form.getFolder().isEmpty()) {
return s3Service.upload(uploadFile, folder);
}
return "index";
}