Wie kann ich Formular-Daten als JSON-format

Posting argument Daten aus meinem Formular funktioniert perfekt, aber ich post müssen die gleichen Informationen mithilfe von JSON. Wie kann das getan werden.
Meine form sieht wie folgt aus.

<form enctype="multipart/form-data" method="post" action="http://myrestfulservice.com/">
    <input type="text" name="name">
    <input type="text" name="email">
    <textarea name="about" rows="3"></textarea>
    <input name="file" type="file">
</form>

Und mein JSON-string sieht wie folgt aus.

{
"name":"Josh U",
"email":"[email protected]",
"about":"Get rich programming or die tryna be something else",
"file":"@/home/josh/image.png"
}

Ich habe versucht mit JSON-string, aber ich bekomme die folgende

Exception in thread "main" java.lang.RuntimeException: Failed : HTTP error code : 500
at com.ijoshluisaac.restful.client.RESTFulClientPostUsingJavaHTTPClientLibrary.main(RESTFulClientPostUsingJavaHTTPClientLibrary.java:35)

Meine JAVA-codes sieht wie folgt aus

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

  public class RESTFulClientPostUsingJavaHTTPClientLibrary {

//JSON content to post
private static final String JSON_OBJECT = "{\"name\":\"Josh U\",\"email\":\"[email protected]\",\"about\":\"Get rich programming or die tryna be something else\",\"file\":\"/home/josh/image.png\"}";

//Web services URLs
private static final String URL_SR = "http://myrestfulservice.com/";

public static void main(String[] args) {

    try {
        URL url = new URL(URL_SR);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setDoOutput(true);
        conn.setRequestMethod("POST");
        conn.setRequestProperty("Content-Type", "application/json");


        OutputStream os = conn.getOutputStream();
        os.write(JSON_OBJECT.getBytes());
        os.flush();

        if (conn.getResponseCode() != HttpURLConnection.HTTP_CREATED) {
            throw new RuntimeException("Failed : HTTP error code : "
                    + conn.getResponseCode());
        }

        BufferedReader br = new BufferedReader(new InputStreamReader(
                (conn.getInputStream())));

        String output;
        System.out.println("Successfully Executed RESTFul POST .... \n");
        while ((output = br.readLine()) != null) {
            System.out.println(output);
        }

        conn.disconnect();

    } catch (MalformedURLException e) {

        e.printStackTrace();

    } catch (IOException e) {

        e.printStackTrace();

    }

}

}