Android Emulator 에서 Localhost 접근을 하고 싶다면...

ADB Reverse Socket (Android only)

This solution works for me (tested with a MacBook):

1. Connect Android mobile device with USB cable to laptop
2. Enable USB Debugging on mobile device
3. On laptop, run adb reverse tcp:4000 tcp:4000
   • Use your custom port number instead of 4000
4. Now, on the mobile device, you can navigate to http://localhost:4000/, and it will actually connect to the laptop, not the mobile device

See instructions here.