Android scan for server socket

Question

Below is my code for my main activity, the program run with no error but i cannot get the IP Address of a server which is run by an arduino with WiFi shield. i want to update the ListView when he sees a server and want to display its IP Address.

public class MainActivity extends Activity {

ArrayList<PostList> server;
ArrayAdapter<PostList> adapter;
ListView server_list;

Socket socket = null;
int port = 50000;
int timeout = 1000;
final ExecutorService es = Executors.newFixedThreadPool(20);

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    Button scan = (Button)findViewById(R.id.scan);  
    server_list = (ListView)findViewById(R.id.serverlist);
    server = new ArrayList<PostList>();

    scan.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View arg0) {
            // TODO Auto-generated method stub
             String iIPv4 = "192.168.254.0";
                iIPv4 = iIPv4.substring(0, iIPv4.lastIndexOf("."));
                iIPv4 += ".";

                for (int i = 1; i < 255; i++) {
                    findSocket(es, iIPv4 + i, port, timeout);
                }
                adapter = new PostAdapter(MainActivity.this, server);
                server_list.setAdapter(adapter);



        }
    });
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

public static Future<Boolean> findSocket(final ExecutorService es,
        final String ip, final int port, final int timeout) {
    return es.submit(new Callable<Boolean>() {
        @Override
        public Boolean call() {
            try {
                Socket socket = new Socket();
                socket.connect(new InetSocketAddress(ip, port), timeout);
                socket.close(); 
                ArrayList<PostList> server = new ArrayList<PostList>();
                server.add(new PostList(ip));

                return true;
            } catch (Exception ex) {
                return false;
            }
        }
    });
   }

   } 

Answer 1

got an answer, but another problem is that it runs too slow to scan the ip address;

 public class MainActivity extends Activity {

private Button connectPhones;
private boolean connected = false;
private String serverIP = "192.168.254.";


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    connectPhones = (Button) findViewById(R.id.scan);
    connectPhones.setOnClickListener(connectListener);

}

private OnClickListener connectListener = new OnClickListener() {

    @Override
    public void onClick(View v) {

        if (!connected) {
                Thread cThread = new Thread(new ClientThread());
                cThread.start();
        }
    }
};

public class ClientThread implements Runnable {

    public void run() {

        for (int i = 0; i < 255; i++){
            String ipadd = serverIP + i;

        try {
            Log.d("ClientActivity", "C: Connecting...");
            Socket socket = new Socket(ipadd, 50000);
            connected = true;
            if (connected) {
                try {
                    Log.d("ClientActivity", "C: Sending command.");
                    PrintWriter out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(socket
                                .getOutputStream())), true);
                        out.println("Hey Server im " + ipadd);
                        Log.d("ClientActivity", "C: Sent.");
                } catch (Exception e) {
                    Log.e("ClientActivity", "S: Error", e);
                }
            }
            socket.close();
            Log.d("ClientActivity", "C: Closed.");
        } catch (Exception e) {
            Log.e("ClientActivity", "C: Error", e);
            connected = false;
        }
        }

    }
}


}