Try to implement TCP / IP + NIO with JAVA

This article uses Java 10.0.1 installed on WIN10.

at first

Last time I made a BIO transfer path, today I will continue to implement NIO.

About NIO

What is NIO

Simply put, it doesn't block I / O requests. You can improve existing I / O processing (BIO).

Bad points of BIO

First, for the request from the client side, two parts, a connection request and an I / O request, are included. Connection requests are always made, but I / O requests are made from time to time. Therefore, the method of preparing one processing thread regardless of one request regardless of whether or not there is I / O processing such as BIO wastes the performance of the server.

Good points of NIO

NIO has only one processing thread for every request from the client side. If there is an I / O request, ask another thread for I / O processing.


*** SocketChannel *** and *** ServerSocketChannel *** are provided from the Java language, so this time I will try to implement TCP / IP + NIO using these. (Official API is here: SocketChannel, [ServerSocketChannel](https://docs Server side files

** Contents of **

public class ChannelServer {

    public static void main(String[] args) throws IOException {
        // I/Prepare a thread pool to process O requests
        ThreadPoolExecutor executor = new ThreadPoolExecutor(3, 10, 1000, TimeUnit.MILLISECONDS, 
                new ArrayBlockingQueue<Runnable>(100));

        ServerSocketChannel serverSocketChannel =;
        serverSocketChannel.bind(new InetSocketAddress(1234));

        while (true) {
            SocketChannel socketChannel = serverSocketChannel.accept();

            if (socketChannel != null) {
                //Commit the request to the thread pool
                executor.submit(new ChannelServerThread(socketChannel));

** Contents of **

*** Thread to process request ***

public class ChannelServerThread implements Runnable {

    private SocketChannel socketChannel;
    private String remoteName;

    public ChannelServerThread(SocketChannel socketChannel) throws IOException {
        this.socketChannel = socketChannel;
        this.remoteName = socketChannel.getRemoteAddress().toString();
        System.out.println("client:" + remoteName + " access successfully!");

    // I/Handle O request
    public void run() {
        ByteBuffer buffer = ByteBuffer.allocate(1024);
        ByteBuffer sizeBuffer = ByteBuffer.allocate(4);
        StringBuilder sb = new StringBuilder();
        byte b[];
        //Read data and length from socketChannel and output to standard output
        while(true) {
            try {
                int read =;
                if (read != -1) {
                    int size = sizeBuffer.getInt();
                    int readCount = 0;
                    b = new byte[1024];
                    while (readCount < size) {
                        read =;
                        if (read != -1) {
                            readCount += read;
                            int index = 0 ;
                            while(buffer.hasRemaining()) {
                                b[index++] = buffer.get();
                                if (index >= b.length) {
                                    index = 0;
                                    sb.append(new String(b,"UTF-8"));
                            if (index > 0) {
                                sb.append(new String(b,"UTF-8"));
                    System.out.println(remoteName +  ":" + sb.toString());
            } catch (Exception e) {
                System.out.println(remoteName + "access colsed");
                try {
                } catch (IOException ex) {

** Client-side files **

*** Creates a socketChannel and accesses the specified server and port ***

public class ChannelClient {

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

        SocketChannel socketChannel =;
        socketChannel.connect(new InetSocketAddress(1234));
        while (true) {
            Scanner sc = new Scanner(;
            String next =;
            sendMessage(socketChannel, next);

    //Prepare a container for Channel to IPO
    public static void sendMessage(SocketChannel socketChannel, String mes) throws IOException {
        if (mes == null || mes.isEmpty()) {
        byte[] bytes = mes.getBytes("UTF-8");
        int size = bytes.length;
        ByteBuffer buffer = ByteBuffer.allocate(size);
        ByteBuffer sizeBuffer = ByteBuffer.allocate(4);


        ByteBuffer dest[] = {sizeBuffer,buffer};
        while (sizeBuffer.hasRemaining() || buffer.hasRemaining()) {

Result authentication

*** Starting the server and waiting for a connection: ***


PS C:\Users\ma\Documents\work\socket\nio_tcp> java ChannelServer

*** Launch clients 1 and 2 respectively and enter something: ***

** Client 1 **

PS C:\Users\ma\Documents\work\socket\nio_tcp> java ChannelClient
Exception in thread "main"
PS C:\Users\ma\Documents\work\socket\nio_tcp>

** Client 2 **

java ChannelClient
Exception in thread "main"
PS C:\Users\ma\Documents\work\socket\nio_tcp>


PS C:\Users\ma\Documents\work\socket\nio_tcp> java ChannelServer
client:/ access successfully!
client:/ access successfully!
/ colsed
/ colsed


This time, I made a TCP / IP + NIO transfer path using Java's SocketChannel and ServerSocketChannel libraries. We were also able to authenticate that one server can handle multiple requests at the same time.

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