NiO example

NIO(Non Blocking IO)

Synchronous nonblocking , The server implementation mode is that one thread can handle multiple requests ( Connect ), All connection requests sent by the client are registered with the multiplexer selector On , The multiplexer polls the connection to have IO The request is processed ,JDK1.4 Start introducing .

Compared with tradition BIO The most intuitive understanding is not to block , Let's just make it simple NIO Take a look at

package com.tuling.nio;

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

public class NioServer {

    //  Save the client connection 
    static List<SocketChannel> channelList = new ArrayList<>();

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

        //  establish NIO ServerSocketChannel, And BIO Of serverSocket similar 
        ServerSocketChannel serverSocket = ServerSocketChannel.open();
        serverSocket.socket().bind(new InetSocketAddress(9000));
        //  Set up ServerSocketChannel Non blocking 
        serverSocket.configureBlocking(false);
        System.out.println(" Service started successfully ");

        while (true) {
            //  Non-blocking mode accept Method will not block , Otherwise, it will block 
            // NIO The non blocking of is implemented internally by the operating system , The underlying call linux Kernel accept function 
            SocketChannel socketChannel = serverSocket.accept();
            if (socketChannel != null) { //  If there is a client connecting 
                System.out.println(" Successful connection ");
                //  Set up SocketChannel Non blocking 
                socketChannel.configureBlocking(false);
                //  Save the client connection in List in 
                channelList.add(socketChannel);
            }
            //  Traverse the connection to read data 
            Iterator<SocketChannel> iterator = channelList.iterator();
            while (iterator.hasNext()) {
                SocketChannel sc = iterator.next();
                ByteBuffer byteBuffer = ByteBuffer.allocate(128);
                //  Non-blocking mode read Method will not block , Otherwise, it will block 
                int len = sc.read(byteBuffer);
                //  If there's data , Print out the data 
                if (len > 0) {
                    System.out.println(" Message received ：" + new String(byteBuffer.array()));
                } else if (len == -1) { //  If the client is disconnected , hold socket Remove... From the set 
                    iterator.remove();
                    System.out.println(" Client disconnected ");
                }
            }
        }
    }
}

  Open two telnet Try to link

 

It is found that both network connections are successfully linked , And not to BIO Also blocked in accept method .

But there is a big problem with this simple method , We are traversal chanel, If most links are not sent , But the link is not broken , We have a lot of useless links to traverse .

Here leads us NIO Multiplexer of .

Selector( multiplexer )：channel Will register to selector in ,selector Will listen channel Events in , Its essence is to call linux In the server Epoll function

Code up

package com.tuling.nio;

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 NioSelectorServer {

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

        //  establish NIO ServerSocketChannel
        ServerSocketChannel serverSocket = ServerSocketChannel.open();
        serverSocket.socket().bind(new InetSocketAddress(9000));
        //  Set up ServerSocketChannel Non blocking 
        serverSocket.configureBlocking(false);
        //  open Selector Handle Channel, creating epoll
        Selector selector = Selector.open();
        //  hold ServerSocketChannel Sign up to selector On , also selector Client side accept Connection operations are of interest 
        SelectionKey selectionKey = serverSocket.register(selector, SelectionKey.OP_ACCEPT);
        System.out.println(" Service started successfully ");

        while (true) {
            //  Blocking waits for events to be processed to occur 
            selector.select();

            //  obtain selector Of all events registered in  SelectionKey  example 
            Set<SelectionKey> selectionKeys = selector.selectedKeys();
            Iterator<SelectionKey> iterator = selectionKeys.iterator();

            //  Traverse SelectionKey Deal with the incident 
            while (iterator.hasNext()) {
                SelectionKey key = iterator.next();
                //  If it is OP_ACCEPT event , Then get the connection and register the event 
                if (key.isAcceptable()) {
                    ServerSocketChannel server = (ServerSocketChannel) key.channel();
                    SocketChannel socketChannel = server.accept();
                    socketChannel.configureBlocking(false);
                    //  Only read events are registered here , If you need to send data to the client, you can register write events 
                    SelectionKey selKey = socketChannel.register(selector, SelectionKey.OP_READ);
                    System.out.println(" Client connection successful ");
                } else if (key.isReadable()) {  //  If it is OP_READ event , Read and print 
                    SocketChannel socketChannel = (SocketChannel) key.channel();
                    ByteBuffer byteBuffer = ByteBuffer.allocateDirect(128);
                    int len = socketChannel.read(byteBuffer);
                    //  If there's data , Print out the data 
                    if (len > 0) {
                        System.out.println(" Message received ：" + new String(byteBuffer.array()));
                    } else if (len == -1) { //  If the client disconnects , close Socket
                        System.out.println(" Client disconnected ");
                        socketChannel.close();
                    }
                }
                // Delete this processed... From the event set key, Prevent next time select Reprocessing 
                iterator.remove();
            }
        }
    }
}