OkHttpClient client = new OkHttpClient();
JSONObject json=new JSONObject();
JSONObject dataJson=new JSONObject();
dataJson.put("body","You got a message");
 dataJson.put("title","You got a message");
 json.put("notification",dataJson);
 json.put("to",regToken);
RequestBody body = RequestBody.create(JSON, json.toString());
 Request request = new Request.Builder()
 .header("Authorization","key=" + "dd") 
.url("https://fcm.googleapis.com/fcm/send") 
  .post(body)
 .build(); 
Response response = client.newCall(request).execute();
  String finalResponse = response.body().string();