Prepare the incoming request, checking to see the request is sending
        JSON content in the request body. If so, the content is decoded and
        assigned to the json_arguments attribute.

def prepare(self):
        """Prepare the incoming request, checking to see the request is sending
        JSON content in the request body. If so, the content is decoded and
        assigned to the json_arguments attribute.

        """
        super(RequestHandler, self).prepare()
        if self.request.headers.get('content-type', '').startswith(self.JSON):
            self.request.body = escape.json_decode(self.request.body)