Talk about uploading files using slack API with Apache HttpPost

The stackoverflow article I found while trying to upload a file with the Slack API was a bit indigestive, so I'll write it down. How to upload a file using Apache HttpPost Even if you write it as above, it will be 200 OK, but "no file data" Therefore, the file upload has not been successful. I had read this article in advance, so POST multipart / form-data with HttpURLConnection I wondered if I should use InputStream, and when I checked the argument of the method in the official document, it was still there. MultipartEntityBuilder

The token used for the API has been pre-injected.

public String post(File file) {
		CloseableHttpClient client = HttpClientBuilder.create()
		        .build();
		HttpEntity requestEntity=null;
		try {
			requestEntity = MultipartEntityBuilder.create()
					.addTextBody("token", token)
					.addTextBody("filetype", "jpg")
.addBinaryBody("file", new FileInputStream(file),ContentType.IMAGE_JPEG,"graph")
			        .build();
		} catch (FileNotFoundException e1) {
			e1.printStackTrace();
		}
		HttpPost post = new HttpPost(URL);
		String result = null;
		try {
			post.setEntity(requestEntity);
			HttpResponse response = client.execute(post);
			logger.info("Status: {}", response.getStatusLine());
			result = collectResponse(response);
	
		} catch (IOException e) {
			logger.error("While posting", e);
		}
		return result;
	}

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.5</version>
</dependency>
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpmime</artifactId>
    <version>4.3.1</version>
</dependency>

Reference link: https://github.com/salahsheikh/jpushbullet/blob/master/src/main/java/com/github/silk8192/jpushbullet/PushbulletClient.java