基于NIO实现一个简单的群聊系统

server端代码

import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.*;
import java.util.Set;

public class Server {

    private static ServerSocketChannel serverSocketChannel;
    private static Selector selector;
    private static final Integer PORT = 8888;

    public Server() {
        try {
            serverSocketChannel = ServerSocketChannel.open().bind(new InetSocketAddress(PORT));
            selector = Selector.open();
            serverSocketChannel.configureBlocking(false);
            serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private void listen() {
        try {
            while (true) {
                int select = selector.select(3000);
                if (select <= 0) {
//                    System.out.println("无监听事件，继续下一次监听");
                    continue;
                }
                Set<SelectionKey> selectionKeys = selector.selectedKeys();
                for (SelectionKey selectionKey : selectionKeys) {
                    if (selectionKey.isAcceptable()) {
                        SocketChannel socketChannel = serverSocketChannel.accept();
                        socketChannel.configureBlocking(false);
                        socketChannel.register(selector, SelectionKey.OP_READ);
                        System.out.println(socketChannel.getRemoteAddress().toString() + "已经上线了");
                    }
                    if (selectionKey.isReadable()) {
                        SocketChannel socketChannel = (SocketChannel) selectionKey.channel();
                        ByteBuffer buffer = ByteBuffer.allocate(1024);
                        int read = 0;
                        try {
                            read = socketChannel.read(buffer);
                        }catch (Exception e){
                            System.out.println(socketChannel.getRemoteAddress() + "客戶端：离线了");
                            selectionKey.cancel();
                            socketChannel.close();
                            continue;
                        }
                        String msg = null;
                        if (read > 0) {
                            msg = new String(buffer.array());
                            System.out.println(socketChannel.getRemoteAddress() + "客户端：" + msg);
                        }
                        // 群发给其他的人
                        if (null != msg) {
                            sendInfoOtherPeople(msg, socketChannel);
                        }
                    }
                    // 防止重复消费
                    selectionKeys.remove(selectionKey);
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }

    }

    private void sendInfoOtherPeople(String msg, SocketChannel self) {
        try {
            Set<SelectionKey> keys = selector.keys();
            for (SelectionKey key : keys) {
                Channel socketChannel = key.channel();
                if (socketChannel instanceof SocketChannel && socketChannel != self) {
                    SocketChannel targetChannel = (SocketChannel) socketChannel;
                    targetChannel.write(ByteBuffer.wrap(msg.getBytes()));
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }


    public static void main(String[] args) {
        Server server = new Server();
        server.listen();
    }

}

client端代码

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.*;
import java.util.Scanner;
import java.util.Set;

public class Client {

    private SocketChannel socketChannel;
    private static final String HOST = "127.0.0.1";
    private static final Integer PORT = 8888;
    private Selector selector;
    private static java.lang.String userName;

    public Client() {
        try {
            socketChannel = socketChannel.open(new InetSocketAddress(HOST, PORT));
            socketChannel.configureBlocking(false);
            selector = Selector.open();
            socketChannel.register(selector, SelectionKey.OP_READ);
            userName = socketChannel.getLocalAddress().toString().substring(1);

        } catch (Exception e) {
            e.printStackTrace();
        }


    }

    private void listen() {
        try {
            int select = selector.select(3000);
            if (select <= 0) {
                return;
            }
            Set<SelectionKey> selectionKeys = selector.selectedKeys();
            for (SelectionKey selectionKey : selectionKeys) {
                if (selectionKey.isReadable()) {
                    SocketChannel socketChannel = (SocketChannel) selectionKey.channel();
                    ByteBuffer buffer = ByteBuffer.allocate(1024);
                    int read = socketChannel.read(buffer);
                    if (read > 0) {
                        System.out.println(new String(buffer.array()));
                    }
                }
                selectionKeys.remove(selectionKey);
            }

        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private void sendInfo(String msg) {
        try {
            socketChannel.write(ByteBuffer.wrap(msg.getBytes()));
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        Client client = new Client();
        new Thread(new Runnable() {
            @Override
            public void run() {
                while (true) {
                    client.listen();
                }
            }
        }).start();

        // 发送数据
        Scanner scanner = new Scanner(System.in);

        while (scanner.hasNextLine()) {
            String msg = scanner.next();
            client.sendInfo(msg);
        }

    }

}

总结：代码实现的比较简单，欢迎大家前来补充指正。