NIO舉例流程

代碼

package com.example.mybatis_demo.io;

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.nio.charset.Charset;
import java.util.Iterator;
import java.util.Set;

public class NIOServer {

    public static void main(String[] args) throws IOException {
        // 1. serverSelector負責輪詢是否有新的連接，服務端監測到新的連接之後，不再創建一個新的線程，
        // 而是直接將新連接綁定到clientSelector上，這樣就不用 IO 模型中 1w 個 while 循環在死等
        Selector serverSelector = Selector.open();
        // 2. clientSelector負責輪詢連接是否有數據可讀
        Selector clientSelector = Selector.open();
        new Thread(() -> {
            try {
                // 對應IO編程中服務端啓動
                ServerSocketChannel listenerChannel = ServerSocketChannel.open();
                listenerChannel.socket().bind(new InetSocketAddress(3333));
                listenerChannel.configureBlocking(false);
                listenerChannel.register(serverSelector, SelectionKey.OP_ACCEPT);
                while (true) {
                    // 監測是否有新的連接，這裏的1指的是阻塞的時間爲 1ms
                    if (serverSelector.select(1) > 0) {
                        Set<SelectionKey> set = serverSelector.selectedKeys();
                        Iterator<SelectionKey> keyIterator = set.iterator();
                        while (keyIterator.hasNext()) {
                            SelectionKey key = keyIterator.next();
                            if (key.isAcceptable()) {
                                try {
                                    // (1)
                                    // 每來一個新連接，不需要創建一個線程，而是直接註冊到clientSelector
                                    SocketChannel clientChannel = ((ServerSocketChannel) key.channel()).accept();
                                    clientChannel.configureBlocking(false);
                                    clientChannel.register(clientSelector, SelectionKey.OP_READ);
                                } finally {
                                    keyIterator.remove();
                                }
                            }
                        }
                    }
                }
            } catch (IOException ignored) {
            }
        }).start();
        new Thread(() -> {
            try {
                while (true) {
                    // (2) 批量輪詢是否有哪些連接有數據可讀，這裏的1指的是阻塞的時間爲 1ms
                    if (clientSelector.select(1) > 0) {
                        Set<SelectionKey> set = clientSelector.selectedKeys();
                        Iterator<SelectionKey> keyIterator = set.iterator();
                        while (keyIterator.hasNext()) {
                            SelectionKey key = keyIterator.next();
                            if (key.isReadable()) {
                                try {
                                    SocketChannel clientChannel = (SocketChannel) key.channel();
                                    ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
                                    // (3) 面向 Buffer
                                    clientChannel.read(byteBuffer);
                                    byteBuffer.flip();
                                    System.out.println(
                                            Charset.defaultCharset().newDecoder().decode(byteBuffer).toString());
                                } finally {
                                    keyIterator.remove();
                                    key.interestOps(SelectionKey.OP_READ);
                                }
                            }
                        }
                    }
                }
            } catch (IOException ignored) {
            }
        }).start();
    }
}

流程圖1

流程圖2