Multipart Request using spring RestTemplate

RestTemplate-Multipart.java

  protected ResponseEntity<Resource<List<Attachment>>> patchMultipartApiV1_Treatments_TID(final String aTID,
                                                                                            final Treatment aTreatment,
                                                                                            final boolean keepLock,
                                                                                            final MultipartFile... aMultipartFiles) throws IOException {

        final MultiValueMap<String, Object> theMultipartRequest = new LinkedMultiValueMap<>();

        // creating an HttpEntity for the JSON part:
        final HttpHeaders theJsonHeader = new HttpHeaders();
        theJsonHeader.setContentType(MediaType.APPLICATION_JSON);
        theMultipartRequest.add("treatment", new HttpEntity<>(aTreatment, theJsonHeader));

        // creating an HttpEntity for the file part:
        if (aMultipartFiles != null) {
            for (final MultipartFile theMultipartFile : aMultipartFiles) {
                final HttpHeaders theFileHeader = new HttpHeaders();
                if (StringUtils.hasText(theMultipartFile.getContentType())) {
                    theFileHeader.add(HttpHeaders.CONTENT_TYPE, theMultipartFile.getContentType());
                } else {
                    theFileHeader.setContentType(MediaType.APPLICATION_OCTET_STREAM);
                }
                theFileHeader.add(HttpHeaders.CONTENT_DISPOSITION, String.format("form-data; name=\"file\"; filename=\"%s\"", theMultipartFile.getName()));
                theMultipartRequest.add("file", new HttpEntity<>(theMultipartFile.getBytes(), theFileHeader));
            }
        }

        final HttpHeaders theMultipartHeaders = headers();
        theMultipartHeaders.set(properties.getSecurity().getApiKeyName(), properties.getSecurity().getApiKey());
        theMultipartHeaders.set(HttpHeaders.ACCEPT, MediaType.APPLICATION_JSON_UTF8_VALUE);
        theMultipartHeaders.set(HttpHeaders.CONTENT_TYPE, MediaType.MULTIPART_FORM_DATA_VALUE);

        final HttpEntity<MultiValueMap<String, Object>> theHttpEntity = new HttpEntity<>(theMultipartRequest, theMultipartHeaders);

        final String theUrlTemplate = AbstractV1Endpoint.API_V1 + (keepLock ? TreatmentsEndpoint.PATCH_TREATMENTS_TID + "?keepLock=true" : TreatmentsEndpoint.PATCH_TREATMENTS_TID);

        final ParameterizedTypeReference<Resource<List<Attachment>>> aTypeReference = new ParameterizedTypeReference<Resource<List<Attachment>>>() {};

        return testRestTemplate().exchange(theUrlTemplate, HttpMethod.PATCH, theHttpEntity, aTypeReference, aTID);
    }

What format will do

What format will do

It's String.format

THANK YOU SOOOOOO MUCH. I was searching the whole internet for a working solution for my problem and you just gave it to me :)

Thanks a lot - solved a few things on my end.
If anybody stumbles upon this to send data from an InputStream, use

theMultipartRequest.add("file", new HttpEntity<>(new InputStreamResource(INPUTSTREAM), theFileHeader));

Thanks @stefan-huettemann

The secret sauce for me was...
theFileHeader.add(HttpHeaders.CONTENT_DISPOSITION, String.format("form-data; name=\"file\"; filename=\"%s\"", theMultipartFile.getName()));