How to convert schema.ResourceData to go map or json in resourceXXXCreate?

Hi,
i am writing a customized terraform provider, in resourceXXXCreate, I need to covert the input schema.ResourceData to a go map or json to import the object data, is there any function in https://godoc.org/github.com/hashicorp/terraform/helper/schema I can use?
thanks

Start with the helper/schema.ResourceData API and the resourceXXXCreate entry point named in the question. Check the SDK documentation and existing provider examples for supported ways to access the input, then confirm whether a map or JSON conversion is available. Done means providing a documented, working conversion path or clearly recording that the SDK does not support one.

Written by the indexing model from the issue text.