SocketReadWrite.java

package nio.sandbox;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Iterator;
import java.util.Set;

/**
 * Created by weinanli on 14/07/2017.
 */
public class SocketReadWrite {

    private static Selector _selector;
    private static ByteBuffer _buffer = ByteBuffer.allocateDirect(1024);

    public static void main(String[] args) throws Exception {
        _selector = Selector.open();

        ServerSocketChannel channel = ServerSocketChannel.open();

        channel.socket().bind(new InetSocketAddress(8080));

        channel.configureBlocking(false);

        channel.register(_selector, SelectionKey.OP_ACCEPT);

        while (!Thread.interrupted()) {
            _selector.select();
            Set keys = _selector.selectedKeys();
            Iterator iterator = keys.iterator();
            while (iterator.hasNext()) {
                SelectionKey key = (SelectionKey) (iterator.next());

                if (key.isAcceptable()) {
                    acceptRequestAndRegisterReadEvent(key);
                }

                if (key.isReadable()) {
                    readRequestAndEcho(key);
                    
                }
                iterator.remove();
            }
        }
    }

    private static void readRequestAndEcho(SelectionKey key) throws IOException {
        SocketChannel _channel = (SocketChannel) key.channel();
        _buffer.clear();

        int count = 0;
        while ((count = _channel.read(_buffer)) > 0) {
            _buffer.flip();

            while(_buffer.hasRemaining()) {
                _channel.write(_buffer); // echo
            }
        }

        _buffer.clear();
    }

    private static void acceptRequestAndRegisterReadEvent(SelectionKey key) {
        ServerSocketChannel channel = (ServerSocketChannel) key.channel();
        try {
            SocketChannel _channel = channel.accept();
            
            _channel.configureBlocking(false);
            _channel.register(_selector, SelectionKey.OP_READ);

            _buffer.clear();
            _buffer.put("Hi!\r\n".getBytes());
            _buffer.flip();
            _channel.write(_buffer);
            
        } catch (IOException e) {
            // nothing to do
        }
    }
}