Java How to connect from Android emulator to application on localhost?

To connect from an Android emulator to an application on localhost, you will need to use the IP address "10.0.2.2" as the hostname in your Android app's code. This IP address is a special alias to your host loopback interface (localhost or 127.0.0.1) from the emulator, and it allows you to access the host machine from the emulator.

Here is an example of how you can use the 10.0.2.2 IP address to connect to a local server in an Android app:

URL url = new URL("http://10.0.2.2:8080/path/to/resource");
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("GET");
connection.setConnectTimeout(5000);
connection.setReadTimeout(5000);
connection.connect();

// read the response and do something with it

This code creates a new URL object with the "http://10.0.2.2:8080/path/to/resource" URL, and then opens a connection to the server using the HttpURLConnection class. It sets the request method to "GET" and sets timeouts for the connection and read operations. Finally, it calls the connect method to establish the connection.

You can then read the response from the server using the InputStream and BufferedReader classes, or use a library such as Retrofit to simplify the process.

Make sure that the server is running on your host machine and listening on the correct port (e.g. 8080 in the example above). You may also need to configure the firewall or network settings on your host machine to allow incoming connections from the emulator.