private static Collection<Node> getNodeMatching(Node body, String regexp) {
   final Collection<Node> nodes = new ArrayList<>();
   if (body.getNodeName().matches(regexp)) nodes.add(body);
   if (body.getChildNodes().getLength() == 0) return nodes;
   NodeList returnList = body.getChildNodes();
   for (int k = 0; k < returnList.getLength(); k++) {
     final Node node = returnList.item(k);
     nodes.addAll(getNodeMatching(node, regexp));
   }
   return nodes;
 }
 /**
  * Discover WS device on the local network with specified filter
  *
  * @param regexpProtocol url protocol matching regexp like "^http$", might be empty ""
  * @param regexpPath url path matching regexp like "onvif", might be empty ""
  * @return list of unique device urls filtered
  */
 public static Collection<URL> discoverWsDevicesAsUrls(String regexpProtocol, String regexpPath) {
   final Collection<URL> urls =
       new TreeSet<>(
           new Comparator<URL>() {
             public int compare(URL o1, URL o2) {
               return o1.toString().compareTo(o2.toString());
             }
           });
   for (String key : discoverWsDevices()) {
     try {
       final URL url = new URL(key);
       boolean ok = true;
       if (regexpProtocol.length() > 0 && !url.getProtocol().matches(regexpProtocol)) ok = false;
       if (regexpPath.length() > 0 && !url.getPath().matches(regexpPath)) ok = false;
       if (ok) urls.add(url);
     } catch (MalformedURLException e) {
       e.printStackTrace();
     }
   }
   return urls;
 }
 /**
  * Discover WS device on the local network
  *
  * @return list of unique devices access strings which might be URLs in most cases
  */
 public static Collection<String> discoverWsDevices() {
   final Collection<String> addresses = new ConcurrentSkipListSet<>();
   final CountDownLatch serverStarted = new CountDownLatch(1);
   final CountDownLatch serverFinished = new CountDownLatch(1);
   final Collection<InetAddress> addressList = new ArrayList<>();
   try {
     final Enumeration<NetworkInterface> interfaces = NetworkInterface.getNetworkInterfaces();
     if (interfaces != null) {
       while (interfaces.hasMoreElements()) {
         NetworkInterface anInterface = interfaces.nextElement();
         if (!anInterface.isLoopback()) {
           final List<InterfaceAddress> interfaceAddresses = anInterface.getInterfaceAddresses();
           for (InterfaceAddress address : interfaceAddresses) {
             addressList.add(address.getAddress());
           }
         }
       }
     }
   } catch (SocketException e) {
     e.printStackTrace();
   }
   ExecutorService executorService = Executors.newCachedThreadPool();
   for (final InetAddress address : addressList) {
     Runnable runnable =
         new Runnable() {
           public void run() {
             try {
               final String uuid = UUID.randomUUID().toString();
               final String probe =
                   WS_DISCOVERY_PROBE_MESSAGE.replaceAll(
                       "<wsa:MessageID>urn:uuid:.*</wsa:MessageID>",
                       "<wsa:MessageID>urn:uuid:" + uuid + "</wsa:MessageID>");
               final int port = random.nextInt(20000) + 40000;
               @SuppressWarnings("SocketOpenedButNotSafelyClosed")
               final DatagramSocket server = new DatagramSocket(port, address);
               new Thread() {
                 public void run() {
                   try {
                     final DatagramPacket packet = new DatagramPacket(new byte[4096], 4096);
                     server.setSoTimeout(WS_DISCOVERY_TIMEOUT);
                     long timerStarted = System.currentTimeMillis();
                     while (System.currentTimeMillis() - timerStarted < (WS_DISCOVERY_TIMEOUT)) {
                       serverStarted.countDown();
                       server.receive(packet);
                       final Collection<String> collection =
                           parseSoapResponseForUrls(
                               Arrays.copyOf(packet.getData(), packet.getLength()));
                       for (String key : collection) {
                         addresses.add(key);
                       }
                     }
                   } catch (SocketTimeoutException ignored) {
                   } catch (Exception e) {
                     e.printStackTrace();
                   } finally {
                     serverFinished.countDown();
                     server.close();
                   }
                 }
               }.start();
               try {
                 serverStarted.await(1000, TimeUnit.MILLISECONDS);
               } catch (InterruptedException e) {
                 e.printStackTrace();
               }
               if (address instanceof Inet4Address) {
                 server.send(
                     new DatagramPacket(
                         probe.getBytes(),
                         probe.length(),
                         InetAddress.getByName(WS_DISCOVERY_ADDRESS_IPv4),
                         WS_DISCOVERY_PORT));
               } else {
                 server.send(
                     new DatagramPacket(
                         probe.getBytes(),
                         probe.length(),
                         InetAddress.getByName(WS_DISCOVERY_ADDRESS_IPv6),
                         WS_DISCOVERY_PORT));
               }
             } catch (Exception e) {
               e.printStackTrace();
             }
             try {
               serverFinished.await((WS_DISCOVERY_TIMEOUT), TimeUnit.MILLISECONDS);
             } catch (InterruptedException e) {
               e.printStackTrace();
             }
           }
         };
     executorService.submit(runnable);
   }
   try {
     executorService.shutdown();
     executorService.awaitTermination(WS_DISCOVERY_TIMEOUT + 2000, TimeUnit.MILLISECONDS);
   } catch (InterruptedException ignored) {
   }
   return addresses;
 }