Apache Mina

public class ClientActivity extends Activity {

    private static final String HOSTNAME = "192.168.2.145";
    private static final int PORT = 9123;
    private static final long CONNECT_TIMEOUT = 30 * 1000L; // 30 seconds
    private IoSession session;
    private NioSocketConnector connector;
    private ConnectFuture future;

    // Set this to false to use object serialization instead of custom codec.
    private static final boolean USE_CUSTOM_CODEC = true;

    public class ClientSessionHandler extends IoHandlerAdapter {
        private final Logger LOGGER = LoggerFactory.getLogger(ClientSessionHandler.class);
        private boolean finished;

        public ClientSessionHandler() {
        }

        public boolean isFinished() {
            return finished;
        }

        public void sessionOpened(IoSession s) {
            session = s;
        }

        public void messageReceived(IoSession session, Object message) {
            // server only sends ResultMessage. otherwise, we will have to identify
            // its type using instanceof operator.
            ResultMessage rm = (ResultMessage) message;

            if (rm.isOk()) {
                EditText et = (EditText)findViewById(R.id.messageBoard);
                et.append(rm.getValue());
            } else {
                // seever returned error code because of overflow, etc.
                Log.d("***************************", "Server error, disconnecting...");
                session.close(true);
                finished = true;
            }
        }

        public void exceptionCaught(IoSession session, Throwable cause) {
            session.close(true);
        }
    }

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

    public void connectToServerButtonClicked(View v){
        connector = new NioSocketConnector();
        connector.setConnectTimeoutMillis(CONNECT_TIMEOUT);

        if (USE_CUSTOM_CODEC) {
            connector.getFilterChain().addLast("codec", new ProtocolCodecFilter(new MessageProtocolCodecFactory(false)));
        } else {
            connector.getFilterChain().addLast("codec", new ProtocolCodecFilter(new ObjectSerializationCodecFactory()));
        }

        connector.getFilterChain().addLast("logger", new LoggingFilter());
        connector.setHandler(new ClientSessionHandler());

        for (; ; ) {
            try {
                future = connector.connect(new InetSocketAddress(HOSTNAME, PORT));
                future.awaitUninterruptibly();
                session = future.getSession();
                break;
            } catch (RuntimeIoException e) {
                Log.d("***************************", "Failed to connect.");
                e.printStackTrace();
                try {
                    Thread.sleep(5000);
                } catch (InterruptedException e1) {
                    e1.printStackTrace();
                }
            }
        }

        // wait until the summation is done
        session.getCloseFuture().awaitUninterruptibly();
        connector.dispose();
    }

    public void sendMessageButtonClicked(View v){

        if (session == null){
            Log.d("***************************", "Session is null");
            return;
        }

        AddMessage am = new AddMessage();
        am.setSequence(1); // copy sequence
        EditText et = (EditText)findViewById(R.id.message);
        am.setValue(et.getText().toString());
        session.write(am);
    }
}