Flutter/dart – Connection failed

I created the simplest GET (spring boot backend) imaginable:
[…]

@GetMapping("basic")
@ResponseBody
public void basic2() {
    System.out.println("basic get invoked");
}

[…] I’m trying to create a flutter mobile app client for this.
I can invoke it via curl and I try to invoke it like this:

Future<void> _fetchData(String email) async {
   http.Response response = await 
   http.get(Uri.parse("http://localhost:8080/basic"));
   print(response.statusCode);
}

Internet access is enabled in android manifest.
I always get the same issue.
‘Unhandled Exception: Connection failed’

Do you have any idea why am I getting this?

Tried with/without port. With/with http protocol. I see in the documentation this is the way, but it doesn’t want to work really.