In Servlet the "request.getParts().stream()..." adds a "empty" Part object

Question

In my JSP I have a form where the user can upload a file.

<form method="post" action="linkToAction" role="form" enctype="multipart/form-data">
  <input name="files" type="file" class="form-control-file" multiple="true" >
</form>

Reading this answer, in my servlet I get the files uploaded:

List<Part> fileParts = request.getParts().stream().filter(part -> "files".equals(part.getName())).collect(Collectors.toList());

If the user doesn't upload anything, I would expect that the List<Part> fileParts would be empty! However, it is not as the above statement adds in the list fileParts, an empty Part. If the user uploads 1 file, the above statement adds again 1 valid Part object.

One quick solution that I thought, is to check the length of the filename:

for (Part filePart : fileParts) {
        String fileName = Paths.get(filePart.getSubmittedFileName()).getFileName().toString(); /
         if (fileName.length() != 0) {
                   //do my job here
         }
}

However, why is this happening?

Vishwa Ratna · Answer 1 · 2019-12-18T11:36:49.653

1

you can check the empty condition in stream itself.

List<Part> fileParts = request.getParts().stream()
                                         .filter(part -> "files".equals(part.getName()) && Objects.nonNull(part.getName()))
                                         .collect(Collectors.toList());

edited Dec 18 '19 at 11:36

answered Dec 18 '19 at 11:29

Vishwa Ratna

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score 1 · Accepted Answer · edited Dec 19 '19 at 07:18

1

You need to check if Part#getSize() is bigger than 0.

List<Part> nonEmptyFileParts = request.getParts().stream()
    .filter(part -> "files".equals(part.getName()) && part.getSize() > 0)
    .collect(Collectors.toList());

The referenced answer has in the meanwhile been updated, thanks.

edited Dec 19 '19 at 07:18

yaylitzis

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answered Dec 18 '19 at 16:12

BalusC

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do you know why this would happen? I ran into something similar. But in my case I receive the filename in part, but part.getSize() is zero. – Mudasir Ali Jun 30 '20 at 08:54
@MudasirAli: Most probably bug in specific browser related to autofill or unselecting files. – BalusC Jun 30 '20 at 08:59

In Servlet the "request.getParts().stream()..." adds a "empty" Part object

2 Answers2