Converting x-www-form-urlencoded to json

In my app I have controller which perform several operation on request received as JSON, but sometimes I receive request as x-www-form-urlencoded. I would like to convert it to JSON at begining of controller action.

For example I would like to convert:

%7B%0A++%22action%22=%22new_pet%22%2C&%22content%22=%7B&%220%22=%7B&%22name%22=%22Amigo%22%2C&%22sex%22=%22male%22%2C&%22owner%22=%227449903%22%2C&%22type%22=%22dog%22&%7D%0A++%7D%2C%0A++%22controller%22=%22animal%22

to:

{
  "action": "new_pet",
  "content": {
    "0": {
      "name": "Amigo",
      "sex": "male",
      "owner": "7449903",
      "type": "dog"
    }
  },
  "controller": "animal"
}