Android : Android WebView extract JSON

Due to some circumstances, JSON is being retrieved using a Webview. What's the best way to extract the JSON? As far as I know, has to be via Javascript. What exactly to call in the Javacript: document.GetElementsByTagName('body')? Is there any other better way? Because looks like the JSON is automatically encapsulated in some HTML by Webview.

For now, it won't be possible to retrieve JSON via HttpClient, which would be the best option.

Thanks!