how to make httpPost call with json encoded body?

i am using following code to make an httpPost call but it is returning me 400 bad request when i try to give following parameters in "simple rest client" in chrome extension it works fine any one guide me what mistake am i doing here?

Simple rest Client I entered the following:

URL: http://jon2012.com/api/register Method: POST Headers: No headers, as they are not required Data: { "email": "test@example.com", "first_name":"Name" }

Android Code:

HttpClient client = new DefaultHttpClient();
        HttpConnectionParams.setConnectionTimeout(client.getParams(), 10000); //Timeout Limit
        HttpResponse response;
        JSONObject json = new JSONObject();
        try{
            HttpPost post = new HttpPost(url);
            json.put("email", email);
            json.put("first_name", name);
            StringEntity se = new StringEntity( "JSON: " + json.toString());  
            se.setContentEncoding(new BasicHeader(HTTP.CONTENT_TYPE, "application/json"));
            post.setEntity(se);
            response = client.execute(post);
            /*Checking response */
            /*if(response!=null){
                InputStream in = response.getEntity().getContent(); //Get the data in the entity
*/
            int statusCode = response.getStatusLine().getStatusCode();

        }
        catch(Exception e){
            e.printStackTrace();
           // createDialog("Error", "Cannot Estabilish Connection");
        }

any help would be appriciated