Android : Recive JSON object in a PHP from a Android

Sorry to bother you guys but I have a problem.

Is my fist time developing a php with JSON and also working with a online DB from a Android Device, my problem is that I don't know why my php returns null a like I haven't send him any variables at all.

My php code is:

<?php

 $data = file_get_contents('php://input');
 $json = json_decode($data, true);

 var_dump($json);

?>

The question is: Which is the way to collect the JSON data that the Android Device has send to my php?

If some one asks that is the way I send the data from my Android Device to the php:

In my android app I send the JSON object this way:

    HttpResponse response =null;
    DefaultHttpClient httpClient = new DefaultHttpClient();

    HttpConnectionParams.setSoTimeout(httpClient.getParams(), 5000);
         HttpConnectionParams.setConnectionTimeout(httpClient.getParams(),3000);

    HttpPost request = new HttpPost(url);

    StringEntity se = new StringEntity(json.toString());
    se.setContentEncoding(new BasicHeader(HTTP.CONTENT_TYPE,
            "application/json"));
    try{
     response = httpClient.execute(request);
    }catch(SocketException sE)
    {
        throw sE;
    }

Thank you very much and sorry for my bad writing skills