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java – Android Broadcast Address

Posted by: admin June 15, 2020 Leave a comment

Questions:

I am making a Client Server application for my Android phone.

I have created a UDP Server in Python which sits and listens for connections.

I can put either the server IP address in directly like 192.169.0.100 and it sends data fine. I can also put in 192.168.0.255 and it find the server on 192.169.0.100.

Is it possible to get the broadcast address of the network my Android phone is connected to? I am only ever going to use this application on my Wifi network or other Wifi networks.

Cheers

How to&Answers:

As the broadcast IP address is the current IP address but finishing with 255, you can do something like this:

public String getLocalIpAddress() {
    try {
        for (Enumeration<NetworkInterface> en = NetworkInterface
                .getNetworkInterfaces(); en.hasMoreElements();) {
            NetworkInterface intf = en.nextElement();
            for (Enumeration<InetAddress> enumIpAddr = intf.getInetAddresses(); enumIpAddr.hasMoreElements();) {
                InetAddress inetAddress = enumIpAddr.nextElement();
                if (!inetAddress.isLoopbackAddress()) {
                    return inetAddress.getHostAddress().toString();
                }
            }
        }
    } catch (SocketException ex) {}
    return null;
}

public static String getBroadcast() throws SocketException {
    System.setProperty("java.net.preferIPv4Stack", "true");
    for (Enumeration<NetworkInterface> niEnum = NetworkInterface.getNetworkInterfaces(); niEnum.hasMoreElements();) {
        NetworkInterface ni = niEnum.nextElement();
        if (!ni.isLoopback()) {
            for (InterfaceAddress interfaceAddress : ni.getInterfaceAddresses()) {
                return interfaceAddress.getBroadcast().toString().substring(1);
            }
        }
    }
    return null;
}

Answer:

From

http://code.google.com/p/boxeeremote/source/browse/trunk/Boxee+Remote/src/com/andrewchatham/Discoverer.java?spec=svn28&r=28

private InetAddress getBroadcastAddress() throws IOException {
    WifiManager wifi = (WifiManager) getSystemService(Context.WIFI_SERVICE);
    DhcpInfo dhcp = wifi.getDhcpInfo();
    // handle null somehow

    int broadcast = (dhcp.ipAddress & dhcp.netmask) | ~dhcp.netmask;
    byte[] quads = new byte[4];
    for (int k = 0; k < 4; k++)
      quads[k] = (byte) (broadcast >> (k * 8));
    return InetAddress.getByAddress(quads);
}

This has the advantage of only looking at WIFI. I know OP said “I am only ever going to use this application on my Wifi network or other Wifi networks.” but it’s worth mentioning this in case someone else needs a non-wifi alternative.

Answer:

Here is a method that should work:

    public static String getBroadcast(){
    String found_bcast_address=null;
     System.setProperty("java.net.preferIPv4Stack", "true"); 
        try
        {
          Enumeration<NetworkInterface> niEnum = NetworkInterface.getNetworkInterfaces();
          while (niEnum.hasMoreElements())
          {
            NetworkInterface ni = niEnum.nextElement();
            if(!ni.isLoopback()){
                for (InterfaceAddress interfaceAddress : ni.getInterfaceAddresses())
                {

                  found_bcast_address = interfaceAddress.getBroadcast().toString();
                  found_bcast_address = found_bcast_address.substring(1);

                }
            }
          }
        }
        catch (SocketException e)
        {
          e.printStackTrace();
        }

        return found_bcast_address;
}

Answer:

A simpler way perhaps …

public static String getBroadcast() throws Exception {
    System.setProperty("java.net.preferIPv4Stack", "true");
    InetAddress inet = InetAddress.getLocalHost();
    NetworkInterface net = NetworkInterface.getByInetAddress(inet);
    InterfaceAddress [] interfaceAddresses = net.getInterfaceAddresses().toArray(new InterfaceAddress[0]);
    if ( interfaceAddresses.length > 0 ) {
        return interfaceAddresses[0].getBroadcast().toString().substring(1);
    } else {
        return "255.255.255";
    }
}