如何在joomla版本3.x中获取发布数据

Try to get data with 1POST` in joomla :

header('content-type: application/json; charset=utf-8');
header('enctype="multipart/form-data" method="post"');
header('HTTP/1.1 200 OK');
$jinput = JFactory::getApplication()->input;
$catid =  $jinput->post->getint('catid', 0);

but it always return 0 also when i try :

$catid = $jinput->getint('catid',0);

it works to receive with GET But not works with POST

How to fix it to works out with POST ?