java - How to get IP address and names of all devices in local network on Android

Question

I want to see all the connected devices on my network with java, but I can't get it working. I have attached some screenshots below of how I want it to be output. I would like to have the name (for example "TP Link Router" or "Nexus 5X") and the IP address.

I have searched a lot on google and stackoverflow, but nothing seemed to work for me. Even GitHub has no effective code. I tried searching for UPnP, Local Area Network, subnets, etc, but found nothing.

InetAddress localhost = InetAddress.getLocalHost();
byte[] ip = localhost.getAddress();
for (int i = 1; i <= 254; i++) {
    ip[3] = (byte)i;
    InetAddress address = InetAddress.getByAddress(ip);
    if (address.isReachable(1000)) {
        System.out.println(address + address.getHostAddress() + address.getAddress() + address.getHostName() + address.getCanonicalHostName());
    }
}

I did in fact find a duplicate (sort of) question, but it hasn't been answered for over a year. Source

Answer 1

The main problem is that you're grabbing the wrong IP address. InetAddress.getLocalHost() is returning 127.0.0.1 and that's just your device.

Use the Wifi IP address in instead:

ConnectivityManager cm = (ConnectivityManager)context.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo activeNetwork = cm.getActiveNetworkInfo();
WifiManager wm = (WifiManager)context.getSystemService(Context.WIFI_SERVICE);

WifiInfo connectionInfo = wm.getConnectionInfo();
int ipAddress = connectionInfo.getIpAddress();
String ipString = Formatter.formatIpAddress(ipAddress);

Here is a quick and dirty AsyncTask that does that:

static class NetworkSniffTask extends AsyncTask<Void, Void, Void> {

  private static final String TAG = Constants.TAG + "nstask";

  private WeakReference<Context> mContextRef;

  public NetworkSniffTask(Context context) {
    mContextRef = new WeakReference<Context>(context);
  }

  @Override
  protected Void doInBackground(Void... voids) {
    Log.d(TAG, "Let's sniff the network");

    try {
      Context context = mContextRef.get();

      if (context != null) {

        ConnectivityManager cm = (ConnectivityManager)context.getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo activeNetwork = cm.getActiveNetworkInfo();
        WifiManager wm = (WifiManager)context.getSystemService(Context.WIFI_SERVICE);

        WifiInfo connectionInfo = wm.getConnectionInfo();
        int ipAddress = connectionInfo.getIpAddress();
        String ipString = Formatter.formatIpAddress(ipAddress);


        Log.d(TAG, "activeNetwork: " + String.valueOf(activeNetwork));
        Log.d(TAG, "ipString: " + String.valueOf(ipString));

        String prefix = ipString.substring(0, ipString.lastIndexOf(".") + 1);
        Log.d(TAG, "prefix: " + prefix);

        for (int i = 0; i < 255; i++) {
          String testIp = prefix + String.valueOf(i);

          InetAddress address = InetAddress.getByName(testIp);
          boolean reachable = address.isReachable(1000);
          String hostName = address.getCanonicalHostName();

          if (reachable)
            Log.i(TAG, "Host: " + String.valueOf(hostName) + "(" + String.valueOf(testIp) + ") is reachable!");
        }
      }
    } catch (Throwable t) {
      Log.e(TAG, "Well that's not good.", t);
    }

  return null;
}

Here are the permissions:

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

Not all routers allow this, so to get the names in a other way is to send the mac adress to an api and get the brand name back in return.

String macAdress = "5caafd1b0019";
String dataUrl = "http://api.macvendors.com/" + macAdress;
HttpURLConnection connection = null;
try {
    URL url = new URL(dataUrl);
    connection = (HttpURLConnection) url.openConnection();
    connection.setRequestMethod("POST");
    connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
    connection.setDoInput(true);
    connection.setDoOutput(true);
    DataOutputStream wr = new DataOutputStream(connection.getOutputStream());
    wr.flush();
    wr.close();
    InputStream is = connection.getInputStream();
    BufferedReader rd = new BufferedReader(new InputStreamReader(is));
    StringBuffer response = new StringBuffer();
    String line;
    while ((line = rd.readLine()) != null) {response.append(line);response.append('
');}
    rd.close();
    String responseStr = response.toString();
    Log.d("Server response", responseStr);
} catch (Exception e) {e.printStackTrace();} finally {if (connection != null) {connection.disconnect();}}