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Java NIO (Non-blocking I/O) with Server-Client Example

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
Java NIO Tutorial
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);

}