HttpsURLConnection POST method failing. I don't know if I have the correct writer and/or outputstream writer. For multipart/form-data

Question

I am using multipart/form-data to send a POST request. I used a file that has the data stored as a csv.The file is person,positon,id. I am concerned that the error could be not having the correct writer like Dataoutput stream vs outputstream. The way I have the carriage returns and line feeds setup or any of my connection settings are off. The URL is correct but the last parameter asks for a file name and I put that in content-dispostion. I can't get rid of this error with all the changes I make. I just want to know if anything on this is incorrect. I get back a 500 error but that leads to the received this error:

org.springframework.web.multipart.MultipartException: Could not parse multipart servlet request; nested exception is java.io.IOException: org.apache.tomcat.util.http.fileupload.impl.IOFileUploadException: Processing of multipart/form-data request failed. Stream ended unexpectedly

Any advice or changes would be appreciated.

public static String postFile(String url) throws IOException {

      String boundary = "xxxxxxxxxxxxxxxxxxxxxxxxx";

      String charset = "UTF-8";

      String CRLF = "\r\n";

      int boundaryLength = 181;     

      try {

          BufferedReader in = null;

          File userss = new File("bytesExampleCSV.csv");

          URL obj = new URL(url);

          HttpsURLConnection conn = (HttpsURLConnection) obj.openConnection();

          conn.setRequestMethod("POST");

          conn.setDoOutput(true);

          conn.setDoInput(true);

          conn.setUseCaches(false);

          conn.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary);

          conn.setRequestProperty("User-Agent",

                    "Mozilla/5.0 (Linux; Android 6.0; Nexus 5 Build/MRA58N) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/90.0.4430.93 Mobile Safari/537.36");


          conn.setRequestProperty("Connection", "keep-alive");

          conn.setRequestProperty("Content-Length", String.valueOf((userss.length()) + boundaryLength));

          conn.connect();

          OutputStream output = conn.getOutputStream();

          PrintWriter writer = new PrintWriter(new OutputStreamWriter(output, charset), true);

          try {

               writer.append("--").append(boundary).append(CRLF);

               writer.append("Content-Disposition: form-data; name=\"bytesExampleCSV.csv\"; filename=\""

                         + userss.getName() + "\"").append(CRLF);

               writer.append("Content-Type: text/plain; charset=" + charset).append(CRLF);

               writer.append(CRLF).flush();

               Files.copy(userss, output);

               output.flush();

               // writer.append(CRLF);

               writer.append("--" + boundary + "--").append(CRLF).flush();

               writer.close();

               conn.disconnect();

               System.out.println(output);

          } catch (Exception e) {

               e.printStackTrace();

          }