POST request with curl command for android using a JSON file

Question

I want to send a POST request with the below curl command:

curl -d @request.json --header "Content-Type: application/json" https://www.googleapis.com/qpxExpress/v1/trips/search?key=my_API_key

I have created a JSON file with name request.json using the below code:

public void CreateJSONFile(View view) throws IOException, JSONException {
 JSONObject request_hdr = new JSONObject();
 JSONObject request = new JSONObject();
 JSONArray slice = new JSONArray();
 JSONObject data = new JSONObject();

 request.put("solutions", 20);
 request.put("refundable", "false");

 JSONObject addl_info = new JSONObject();
 addl_info.put("adultCount",Num_Adult);
 addl_info.put("infantInLapCount",Num_Infant);
 addl_info.put("infantInSeatCount", 0);
 addl_info.put("childCount",0);
 addl_info.put("seniorCount", 0);
 request.put("passengers",addl_info);

 data.put("origin",Origin);
 data.put("destination",Destination);
 data.put("date", Start_Date);
 slice.put(data);
 request.put("slice",slice);

 request_hdr.put("request",request);

 text = request_hdr.toString();

 FileOutputStream fileOutputStream = openFileOutput("request.json", MODE_PRIVATE);
 fileOutputStream.write(text.getBytes());
 fileOutputStream.close();
}

Now how do I trigger the POST request with the curl command using the JSON file created. I have found couple of examples which uses Name-Value Pairs or JSON Objects. How do I use a JSON file instead of that. Please help me out.

Thanks in advance!