How to post JSON to PHP with curl
Jordans analysis of why the $_POST-array isn't populated is correct. However, you can use
$data = file_get_contents("php://input");to just retrieve the http body and handle it yourself. See PHP input/output streams.
From a protocol perspective this is actually more correct, since you're not really processing http multipart form data anyway. Also, use application/json as content-type when posting your request.
I believe you are getting an empty array because PHP is expecting the posted data to be in a Querystring format (key=value&key1=value1).
Try changing your curl request to:
curl -i -X POST -d 'json={"screencast":{"subject":"tools"}}' \ http://localhost:3570/index.php/trainingServer/screencast.jsonand see if that helps any.