Como remeter um arquivo .json via POST?

import java.io.BufferedReader;

import java.io.File; import java.io.FileInputStream; import java.io.IOException; import java.io.InputStreamReader; import java.io.OutputStream; import java.io.OutputStreamWriter; import java.io.PrintWriter; import java.net.HttpURLConnection; import java.net.URL; import java.net.URLConnection; import java.util.ArrayList; import java.util.List;

public class MultipartUtility { private final String boundary; private static final String LINE_FEED = "\r\n"; private HttpURLConnection httpConn; private String charset; private OutputStream outputStream; private PrintWriter writer;

public MultipartUtility(String requestURL, String charset)
        throws IOException {
    this.charset = charset;

    // creates a unique boundary based on time stamp
    boundary = "===" + System.currentTimeMillis() + "===";

    URL url = new URL(requestURL);
    httpConn = (HttpURLConnection) url.openConnection();
    httpConn.setUseCaches(false);
    httpConn.setDoOutput(true); // indicates POST method
    httpConn.setDoInput(true);
    httpConn.setRequestProperty("User-Agent", "CodeJava Agent");
    httpConn.setRequestProperty("Test", "Bonjour");
    outputStream = httpConn.getOutputStream();
    writer = new PrintWriter(new OutputStreamWriter(outputStream, charset),
            true);
}


public void addFormField(String name, String value) {
    writer.append("--" + boundary).append(LINE_FEED);
    writer.append("Content-Disposition: form-data; name=\"" + name + "\"")
            .append(LINE_FEED);
    writer.append("Content-Type: text/plain; charset=" + charset).append(
            LINE_FEED);
    writer.append(LINE_FEED);
    writer.append(value).append(LINE_FEED);
    writer.flush();
}


public void addFilePart(String fieldName, File uploadFile)
        throws IOException {
    String fileName = uploadFile.getName();
    writer.append("--" + boundary).append(LINE_FEED);
    writer.append(
            "Content-Disposition: form-data; name=\"" + fieldName
                    + "\"; filename=\"" + fileName + "\"")
            .append(LINE_FEED);
    writer.append(
            "Content-Type: "
                    + URLConnection.guessContentTypeFromName(fileName))
            .append(LINE_FEED);
    writer.append("Content-Transfer-Encoding: binary").append(LINE_FEED);
    writer.append(LINE_FEED);
    writer.flush();

    FileInputStream inputStream = new FileInputStream(uploadFile);
    byte[] buffer = new byte[4096];
    int bytesRead = -1;
    while ((bytesRead = inputStream.read(buffer)) != -1) {
        outputStream.write(buffer, 0, bytesRead);
    }
    outputStream.flush();
    inputStream.close();

    writer.append(LINE_FEED);
    writer.flush();    
}


public void addHeaderField(String name, String value) {
    writer.append(name + ": " + value).append(LINE_FEED);
    writer.flush();
}

public List<String> finish() throws IOException {
    List<String> response = new ArrayList<String>();

    writer.append(LINE_FEED).flush();
    writer.append("--" + boundary + "--").append(LINE_FEED);
    writer.close();

    // checks server's status code first
    int status = httpConn.getResponseCode();
    if (status == HttpURLConnection.HTTP_OK) {
        BufferedReader reader = new BufferedReader(new InputStreamR

* Classe de postagem do arquivo

import java.io.File; import java.io.IOException; import java.util.List;

public class MultipartFileUploader {

 public static void main(String[] args) {
        String charset = "UTF-8";
        File uploadFile1 = new File("C:/Users/u6016951/eclipse-workspace/JSON/answer.json");

        String requestURL = "https://api.codenation.dev/v1/challenge/dev-ps/submit-solution?token=e41c43500cc81ba8247b2cd63aff0754f8c4a6c5";

        try {
            MultipartUtility multipart = new MultipartUtility(requestURL, charset);

            multipart.addHeaderField("Content-Type", "multipart/form-data");

            multipart.addFilePart("answer", uploadFile1);

            List<String> response = multipart.finish();

            System.out.println("SERVER REPLIED:");

            for (String line : response) {
                System.out.println(line);
            }
        } catch (IOException ex) {
            System.err.println("Teste: "+ex);
        }
    }

}