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.