Example of a Nonblokcing Socket-Server with java.nio

java-nio-nonblocking-socket.java

package de.mazdermind;

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;

public class Main {

	public static void main(String[] args) throws IOException {
		String bind = "0.0.0.0";
		int port = 9999;

		System.out.println(String.format("Starting Server on %s:%d", bind, port));

		Selector selector = Selector.open();
		ServerSocketChannel serverSocket = ServerSocketChannel.open();
		serverSocket.bind(new InetSocketAddress(bind, port));
		serverSocket.configureBlocking(false);
		serverSocket.register(selector, SelectionKey.OP_ACCEPT);

		//noinspection InfiniteLoopStatement
		while (true) {
			selector.select();

			Set<SelectionKey> selectedKeys = selector.selectedKeys();
			Iterator<SelectionKey> iter = selectedKeys.iterator();
			while (iter.hasNext()) {
				SelectionKey key = iter.next();

				if (key.isAcceptable()) {
					SocketChannel client = serverSocket.accept();
					System.out.println(String.format("Incoming Connection from %s", client.getRemoteAddress()));
					client.configureBlocking(false);
					client.register(selector, SelectionKey.OP_READ);
				}

				if (key.isReadable()) {
					SocketChannel client = (SocketChannel) key.channel();
					read(client);
				}

				iter.remove();
			}
		}

	}

	private static void read(SocketChannel client) throws IOException {
		ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
		int numBytesRead = client.read(byteBuffer);
		System.out.println(String.format("read %d bytes to buffer", numBytesRead));
	}
}

Follow-Up reading Line-by-Line: https://gist.github.com/MaZderMind/0be1dea275ea25b39dc753583d742851