Java NIO (Non-blocking I/O) with Server-Client Example – java.nio.ByteBuffer and channels.Selector – Java NIO Vs. IO

Java NIO is my favorite topic. I have been working with NIO since last 2 years and would like to share simple Server-Client code for my readers who are free to use this code in their production environment.

Starting JDK 1.4, NIO was created to allow all Java programmers to implement very high-speed input/output without having to deal with custom native code. NIO uses java.nio.buffer library compare to simple I/O which drains and fills back buffer internally any operating system.

In this tutorial we will go over java.nio.channels and java.nio.channels.Selector libraries.

• channels represent connections to entities that are capable of performing I/O operations, such as files and sockets; defines selectors, for multiplexed, non-blocking I/O operations.
• selector may be created by invoking the open method of this class, which will use the system’s default selector provider to create a new selector.

If you have below questions then you are at right place:

• How to get started with Java NIO
• What is Java NIO and Java NIO tutorials
• Asynchronous Java NIO
• What is the exact use of java nio package
• How to implement High-Performance I/O with Java NIO

Let’s get started:

Step-1

• Create CrunchifyNIOServer.java which opens connection on port 1111
• use isAcceptable() to check if channel is ready to accept a new socket connection
  • If yes – connect it
• use isReadable() to check if channel is ready for reading
  • if yes – read from buffer and print on Eclipse console
• Once you get last company name “crunchify”
  • close connection

Step-2

• Create CrunchifyNIOClient.java which tries to connect to server on port 1111
• Create ArrayList with 5 company names
• Iterate through ArrayList and send each companyName to server
• Close connection after task finish

Take a look at this Java Code:

Server Code – CrunchifyNIOServer.java

package crunchify.com.tutorials;

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;

/**
 * @author Crunchify.com
 *
 */

public class CrunchifyNIOServer {

	@SuppressWarnings("unused")
	public static void main(String[] args) throws IOException {

		// Selector: multiplexor of SelectableChannel objects
		Selector selector = Selector.open(); // selector is open here

		// ServerSocketChannel: selectable channel for stream-oriented listening sockets
		ServerSocketChannel crunchifySocket = ServerSocketChannel.open();
		InetSocketAddress crunchifyAddr = new InetSocketAddress("localhost", 1111);

		// Binds the channel's socket to a local address and configures the socket to listen for connections
		crunchifySocket.bind(crunchifyAddr);

		// Adjusts this channel's blocking mode.
		crunchifySocket.configureBlocking(false);

		int ops = crunchifySocket.validOps();
		SelectionKey selectKy = crunchifySocket.register(selector, ops, null);

		// Infinite loop..
		// Keep server running
		while (true) {

			log("i'm a server and i'm waiting for new connection and buffer select...");
			// Selects a set of keys whose corresponding channels are ready for I/O operations
			selector.select();

			// token representing the registration of a SelectableChannel with a Selector
			Set<SelectionKey> crunchifyKeys = selector.selectedKeys();
			Iterator<SelectionKey> crunchifyIterator = crunchifyKeys.iterator();

			while (crunchifyIterator.hasNext()) {
				SelectionKey myKey = crunchifyIterator.next();

				// Tests whether this key's channel is ready to accept a new socket connection
				if (myKey.isAcceptable()) {
					SocketChannel crunchifyClient = crunchifySocket.accept();

					// Adjusts this channel's blocking mode to false
					crunchifyClient.configureBlocking(false);

					// Operation-set bit for read operations
					crunchifyClient.register(selector, SelectionKey.OP_READ);
					log("Connection Accepted: " + crunchifyClient.getLocalAddress() + "\n");

					// Tests whether this key's channel is ready for reading
				} else if (myKey.isReadable()) {
					
					SocketChannel crunchifyClient = (SocketChannel) myKey.channel();
					ByteBuffer crunchifyBuffer = ByteBuffer.allocate(256);
					crunchifyClient.read(crunchifyBuffer);
					String result = new String(crunchifyBuffer.array()).trim();

					log("Message received: " + result);

					if (result.equals("Crunchify")) {
						crunchifyClient.close();
						log("\nIt's time to close connection as we got last company name 'Crunchify'");
						log("\nServer will keep running. Try running client again to establish new connection");
					}
				}
				crunchifyIterator.remove();
			}
		}
	}

	private static void log(String str) {
		System.out.println(str);
	}
}

Client Code – CrunchifyNIOClient.java

package crunchify.com.tutorials;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SocketChannel;
import java.util.ArrayList;

/**
 * @author Crunchify.com
 *
 */

public class CrunchifyNIOClient {

	public static void main(String[] args) throws IOException, InterruptedException {

		InetSocketAddress crunchifyAddr = new InetSocketAddress("localhost", 1111);
		SocketChannel crunchifyClient = SocketChannel.open(crunchifyAddr);

		log("Connecting to Server on port 1111...");

		ArrayList<String> companyDetails = new ArrayList<String>();

		// create a ArrayList with companyName list
		companyDetails.add("Facebook");
		companyDetails.add("Twitter");
		companyDetails.add("IBM");
		companyDetails.add("Google");
		companyDetails.add("Crunchify");

		for (String companyName : companyDetails) {

			byte[] message = new String(companyName).getBytes();
			ByteBuffer buffer = ByteBuffer.wrap(message);
			crunchifyClient.write(buffer);

			log("sending: " + companyName);
			buffer.clear();

			// wait for 2 seconds before sending next message
			Thread.sleep(2000);
		}
		crunchifyClient.close();
	}

	private static void log(String str) {
		System.out.println(str);
	}
}

Result at Server Side:

i'm a server and i'm waiting for new connection and buffer select...
Connection Accepted: /127.0.0.1:1111

i'm a server and i'm waiting for new connection and buffer select...
Message received: Facebook
i'm a server and i'm waiting for new connection and buffer select...
Message received: Twitter
i'm a server and i'm waiting for new connection and buffer select...
Message received: IBM
i'm a server and i'm waiting for new connection and buffer select...
Message received: Google
i'm a server and i'm waiting for new connection and buffer select...
Message received: Crunchify

It's time to close connection as we got last company name 'Crunchify'

Server will keep running. Try running client again to establish new connection
i'm a server and i'm waiting for new connection and buffer select...

Result at Client Side:

Connecting to Server on port 1111...
sending: Facebook
sending: Twitter
sending: IBM
sending: Google
sending: Crunchify