Why I can't Connect My node.js Server from My Android Java Project? [duplicate]

The localhost refers to the device on which the code is running, in this case the emulator.

If you want to refer to the computer which is running the Android simulator, use the IP address 10.0.2.2 instead.

You can read more from here.

Use 10.0.2.2 for default AVD and 10.0.3.2 for genymotion.

I used 10.0.2.2 successfully on my home machine, but at work, it did not work. After hours of fooling around, I created a new emulator instance using the Android Virtual Device (AVD) manager, and finally the 10.0.2.2 worked.

I don't know what was wrong with the other emulator instance (the platform was the same), but if you find 10.0.2.2 does not work, try creating a new emulator instance.

Try http://10.0.2.2:8080/ where 8080 is your port number. It worked perfectly. If you just try 10.0.2.2 it won't work. You need to add port number to it. Also if Microsoft IIS has been installed try turning off that feature from control panel (if using any windows os) and then try as given above.

You can actually use localhost:8000 to connect to your machine's localhost by running below command each time when you run your emulator (tested on Mac only):

adb reverse tcp:8000 tcp:8000

Just put it to Android Studio terminal.

It basically sets up a reverse proxy in which a http server running on your phone accepts connections on a port and wires them to your computer or vice versa.