Title: 2.3 - Sample TCP Client 
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# 2.3 - Sample TCP Client

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

We shall use [Sumup Client](http://mina.apache.org/mina-project/xref/org/apache/mina/example/sumup/Client.html) as a reference implementation.

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

	:::java
	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

	:::java
	NioSocketConnector connector = new NioSocketConnector();

Here we have created a NIO Socket connector

## Create a Filter Chain

	:::java
	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

	:::java
	connector.setHandler(new ClientSessionHandler(values));

Here we create an instance of [ClientSessionHandler](http://mina.apache.org/mina-project/xref/org/apache/mina/example/sumup/ClientSessionHandler.html) and set it as a handler for the Connector.

## Bind to Server

	:::java
	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](http://mina.apache.org/mina-project/xref/org/apache/mina/core/future/ConnectFuture.html) class to know the when the connection is complete.
Once the connection is complete, we get the associated [IoSession](http://mina.apache.org/mina-project/xref/org/apache/mina/core/session/IoSession.html). 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.