Sample TCP Client

We have seen the Client Architecture. Lets explore a sample Client implementation.

We shall use Sumup Client as a reference implementation.

We will remove boiler plate code and concentrate on the important constructs. Below the code for the Client :

public static void main(String[] args) throws Throwable {
    NioSocketConnector connector = new NioSocketConnector();
    connector.setConnectTimeoutMillis(CONNECT_TIMEOUT);

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

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

    for (;;) {
        try {
            ConnectFuture future = connector.connect(new InetSocketAddress(HOSTNAME, PORT));
            future.awaitUninterruptibly();
            session = future.getSession();
            break;
        } catch (RuntimeIoException e) {
            System.err.println("Failed to connect.");
            e.printStackTrace();
            Thread.sleep(5000);
        }
    }

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

To construct a Client, we need to do following

  • Create a Connector
  • Create a Filter Chain
  • Create a IOHandler and add to Connector
  • Bind to Server

Lets examine each one in detail

Create a Connector

NioSocketConnector connector = new NioSocketConnector();

Here we have created a NIO Socket connector

Create a Filter Chain

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

We add Filters to the Filter Chain for the Connector. Here we have added a ProtocolCodec, to the filter Chain.

Create IOHandler

connector.setHandler(new ClientSessionHandler(values));

Here we create an instance of ClientSessionHandler and set it as a handler for the Connector.

Bind to Server

IoSession session;

for (;;) {
    try {
        ConnectFuture future = connector.connect(new InetSocketAddress(HOSTNAME, PORT));
        future.awaitUninterruptibly();
        session = future.getSession();
        break;
    } catch (RuntimeIoException e) {
        System.err.println("Failed to connect.");
        e.printStackTrace();
        Thread.sleep(5000);
    }
}

Here is the most important stuff. We connect to remote Server. Since, connect is an async task, we use the ConnectFuture class to know the when the connection is complete. Once the connection is complete, we get the associated IoSession. To send any message to the Server, we shall have to write to the session. All responses/messages from server shall traverse the Filter chain and finally be handled in IoHandler.