How do I socket an Android program to a localhost server?

Question

I have server and client code that works perfectly as a Java application. The server is run on my local machine and listens on port 4444. Any Java application can connect easily, but when I move my code over to Android, I keep getting an IOException no matter what I try. I read that you have to change "localhost" to "10.0.2.2", but I'm still getting an IOException. I tried my IP address from whatsmyip.org but it still gives me an IOException. Here's my android code...

package test.myPackage;

import java.io.IOException;
import java.net.Socket;
import java.net.UnknownHostException;

import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;

public class TestProjectActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        TextView tv = new TextView(this);
        tv.setText("Hello, Android");
        setContentView(tv);

    Socket s = null;
    try {
        s = new Socket("10.0.2.2", 4444);
        tv.setText("socket: CONNECTED!");
    } catch (UnknownHostException e) {
        tv.setText("socket: unknown host");
    } catch (IOException e) {
        tv.setText("socket: IO Exception");
    }
}

}

What is your IP on your local network? Are you on linux or windows? On windows open a command window and type ipconfig in it. Just put your IPV4 in your code. On linux the open a terminal and execute ifconfig. Obviously your ISP has blocked the access to your machine from outside. Your public IP is not what you want. — Jermin Bazazian
– Jermin Bazazian, Commented Apr 26, 2012 at 15:51

Chris Stratton · Accepted Answer · 2012-04-26 17:56:20Z

2

First make sure your app has internet permission.

The only time you can use the 10.0.2.2 alias is if your app is running on an emulator and wants to contact something running on the hosting machine. This does not work with actual android devices.

For an actual android device, you would either have to put the device on the same wifi network as the PC hosting the server, find a way to abuse a tethering solution to get them on the same network over the USB cable, or move your server to a machine externally accessible from the Internet at large in order to be able to reach it from the device's mobile network connection.

And EvilDuck definitely has a point about abusing the UI thread.

answered Apr 26, 2012 at 17:56

Chris Stratton

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1 Comment

user1080952 Over a year ago

The problem was my app did not have internet permission. I added <uses-permission android:name="android.permission.INTERNET"></uses-permission> to the manifest and now it works. Thanks!

Tamir Abutbul · Accepted Answer · 2023-04-08 18:28:36Z

0

As I understand you are running Android client on a device in the same network as your server? Then you must use your servers internal IP. Localhost here will search servers on a device obviously.

whatsmyip.org will give you your external IP.

Make sure device is indeed on the same network, make sure you're using correct internal IP, make sure your server doesn't have any firewall blocking this port for LAN.

And for stop doing network activity on UI thread ffs!!!

edited Apr 8, 2023 at 18:28

Tamir Abutbul

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answered Apr 26, 2012 at 15:42

EvilDuck

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