AWS S3 File uploading in Java - Why directly upload InputStream consume more memory than write it to temporary file, then upload?

I want to upload a file to S3 bucket using Streaming API of commons-fileupload library. This code is for parsing the request

FileItemIterator iterStream = upload.getItemIterator(request);
while (iterStream.hasNext()) {
    FileItemStream item = iterStream.next();
    String name = item.getFieldName();
    InputStream stream = item.openStream();
    if (!item.isFormField()) {
        // Process the InputStream stream (*)
    } else {
        String formFieldValue = Streams.asString(stream);
    }
}

This one is for initializing S3 client and transfer manager

s3Client = AmazonS3ClientBuilder.standard()
                .withRegion(Regions.DEFAULT_REGION)
                .withCredentials(new ProfileCredentialsProvider())
                .build();
transferManager = TransferManagerBuilder.standard()
                .withS3Client(s3Client)
                .build();

I used a 100MB file to test. At the beginning, my springboot app started with about 95MB ram usage. When using that stream(*) to upload to s3 bucket, using

        Upload upload = transferManager.upload(bucketName, key, inputStream, metadata );

is significantly more memory consumption (from 90MB->370MB) than copy stream (*) to OutputStream, then upload a file created from that outputStream (from 90MB-> 100MB)

try (
      OutputStream out = new FileOutputStream(fileName);
) {
      IOUtils.copy(inputStream, out);
}
PutObjectRequest request = new PutObjectRequest(
                existingBucketName, fileName, new File(fileName));
Upload upload = transferManager.upload(request);

I wonder why is that. What happened to the inputStream that make it consume more memory to directly upload? Thank you very much