php json decode返回带有小写字段名称的数组

Question

I have a json string with following format

{"id":"38","orderId":"105","fileBackupDescription":"backup"}

after decoding the result array is of format

array
(
    [id] => 38
    [orderid] => 105
    [filebackupdescription] => backup
)

I am using it in a controller in zf2

$this->params = \Zend\Json\Json::decode($this->request->getContent(), \Zend\Json\Json::TYPE_ARRAY);