Http 415 Unsupported Media type error with JSON

I am calling a REST service with a JSON request and it responds with a HTTP 415 "Unsupported Media Type" error.

The request content type is set to ("Content-Type", "application/json; charset=utf8").

It works fine if I don't include a JSON object in the request. I am using the google-gson-2.2.4 library for JSON.

I tried using a couple of different libraries but it made no difference.

Can anybody please help me to resolve this?

Here is my code:

public static void main(String[] args) throws Exception {
  JsonObject requestJson = new JsonObject();
  String url = "xxx";
  
  //method call for generating json
  requestJson = generateJSON();
  URL myurl = new URL(url);
  HttpURLConnection con = (HttpURLConnection)myurl.openConnection();
  con.setDoOutput(true);
  con.setDoInput(true);
  
  con.setRequestProperty("Content-Type", "application/json; charset=utf8");
  con.setRequestProperty("Accept", "application/json");
  con.setRequestProperty("Method", "POST");
  OutputStream os = con.getOutputStream();
  os.write(requestJson.toString().getBytes("UTF-8"));
  os.close();

  StringBuilder sb = new StringBuilder();  
  int HttpResult =con.getResponseCode();
  if(HttpResult ==HttpURLConnection.HTTP_OK){
    BufferedReader br = new BufferedReader(new InputStreamReader(con.getInputStream(),"utf-8"));  

    String line = null;
    while ((line = br.readLine()) != null) {  
      sb.append(line + "\n");  
    }
    br.close(); 
    System.out.println(""+sb.toString());  

  } else {
    System.out.println(con.getResponseCode());
    System.out.println(con.getResponseMessage());  
  }
}
public static JsonObject generateJSON () throws MalformedURLException {
  String s = "http://www.example.com";
  s.replaceAll("/", "\\/");
  JsonObject reqparam=new JsonObject();
  reqparam.addProperty("type", "arl");
  reqparam.addProperty("action", "remove");
  reqparam.addProperty("domain", "staging");
  reqparam.addProperty("objects", s);
  return reqparam;
}

The value of requestJson.toString() is :

{
  "type": "arl",
  "action": "remove",
  "domain": "staging",
  "objects": "http://www.example.com"
}

Not sure about the reason, but removing charset=utf8 from con.setRequestProperty("Content-Type", "application/json; charset=utf8") resolved the issue.