isReachable() returns false in Android

Question

I have a situation when my phone is working as a hotspot and I need to detect all devices which connected to my phone and find their MAC addresses. I wrote something like this:

public void getListOfConnectedDevice() {
    Thread thread = new Thread(new Runnable() {

        @Override
        public void run() {
            BufferedReader br = null;
            boolean isFirstLine = true;

            try {
                br = new BufferedReader(new FileReader("/proc/net/arp"));
                String line;

                while ((line = br.readLine()) != null) {
                    if (isFirstLine) {
                        isFirstLine = false;
                        continue;
                    }

                    String[] splitted = line.split(" +");

                    if (splitted != null && splitted.length >= 4) {

                        String ipAddress = splitted[0];
                        String macAddress = splitted[3];

                       boolean isReachable = InetAddress.getByName(
                                splitted[0]).isReachable(300);// this is network call so we cant do that on UI thread, so I take background thread.
                        Log.d(TAG, "ip: " + splitted[0]);
                        Log.d(TAG, "isReachable: " + isReachable);
                        if (isReachable) {
                            Log.d("Device Information", ipAddress + " : "
                                    + macAddress);
                            macAddresses.add(macAddress); //My List<String>
                        }
                    }
                }
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                try {
                    br.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    });
    thread.start();
}

But boolean isReachable = InetAddress.getByName(splitted[0]).isReachable(300); returns only false if device connected or disconnected. And I can't find any info to find solution. Or are there any other solutions? (For not rooted phones).

Answer 1

Well, i found that android keep MAC addreses of devices for about 10 min (On different devices - different time), and only way - use ADB shell command to clear that list, BUT! it works only on rooted devices.

But this code can help you (works not with all devices):

public void getListOfConnectedDevice() {
    final Thread thread = new Thread(new Runnable() {

        @Override
        public void run() {
            macAddresses.clear();
            BufferedReader br = null;
            boolean isFirstLine = true;
            try {

                br = new BufferedReader(new FileReader("/proc/net/arp"));
                String line;

                while ((line = br.readLine()) != null) {
                    if (isFirstLine) {
                        isFirstLine = false;
                        continue;
                    }

                    String[] splitted = line.split(" +");

                    if (splitted != null && splitted.length >= 4) {

                        String ipAddress = splitted[0];
                        String macAddress = splitted[3];

                        Node node = new Node(ipAddress, macAddress);
                        boolean isReachable = node.isReachable;
                        Log.d(TAG, "isReachable: " + isReachable);
                        if (isReachable) {
                            Log.d("Device Information", ipAddress + " : "
                                    + macAddress);
                            macAddresses.add(macAddress);
                        }
                    }
                }
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                try {
                    br.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    });
    thread.start();
}