Get referer url

[Gnu Ubuntu]

Hi,
In my app I'm redirected to an external url, and after I need to return to
my app. I'm looking for a way to store the referer url before exiting my app
to return to.
For now, I'm using :
String referer = request.getHeader("referer");
But it's not safe to referer to this browser information.

Do you know an other way to get previous url please?

Thanks in advance.