Java NIO 群聊系统

服务器（selector实现）：

package com.ronghao.nio;

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

public class GroupChatServer {
    //定义属性
    private Selector selector;
    private ServerSocketChannel listenChannel;
    private static final int PORT = 9999;

    //初始化工作
    public GroupChatServer() {
        try {
            //选择器
            selector = Selector.open();
            //通道
            listenChannel = ServerSocketChannel.open();
            listenChannel.socket().bind(new InetSocketAddress(PORT));
            listenChannel.configureBlocking(false);
            listenChannel.register(selector, SelectionKey.OP_ACCEPT);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //监听
    public void listen() {
        try {
            //循环处理
            while (true) {
                int count = selector.select();
                if (count > 0) {//有事件处理

                    //遍历得到selectionKey集合
                    Iterator<SelectionKey> iterator = selector.selectedKeys().iterator();
                    while (iterator.hasNext()) {
                        //去除selectionkey
                        SelectionKey key = iterator.next();

                        //监听到accept
                        if (key.isAcceptable()) {
                            SocketChannel sc = listenChannel.accept();
                            //非阻塞
                            sc.configureBlocking(false);
                            //将该sc注册到selector上
                            sc.register(selector, SelectionKey.OP_READ);
                            //提示
                            System.out.println(sc.getRemoteAddress() + "上线");
                        }
                        if (key.isReadable()) {//通道发送read事件，即通道是可读的状态
                            //处理读
                            readData(key);
                        }
                        //当前key从集合中删除，防止重复处理。
                        iterator.remove();
                    }
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //读取客户端消息
    private void readData(SelectionKey key) {
        //定义一个SocketChannel
        SocketChannel channel = null;
        try {
            channel = channel = (SocketChannel) key.channel();

            ByteBuffer buffer = ByteBuffer.allocate(1024);
            int count = channel.read(buffer);
            if (count > 0) {
                //把缓冲区的数据转换成字符串
                String message = new String(buffer.array());
                //输出该消息
                System.out.println("from 客户端:" + message);
                //向其他客户端转发消息(去掉自己)，专门写一个方法来处理
                sendInfoToOtherClients(message, channel);
            }
        } catch (IOException e) {
            try {
                System.out.println(channel.getRemoteAddress() + " 离线了");
                //取消注册
                key.cancel();
                //关闭通道
                channel.close();

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

    //转发消息给其它客户（通道）
    private void sendInfoToOtherClients(String msg, SocketChannel self) throws IOException {
        //遍历所有注册到selector上的SocketChannel,并排除self
        for (SelectionKey key : selector.keys()) {

            //通过key取出对应的SocketChannel
            SelectableChannel targetChannel = key.channel();
            //排除自己
            if (targetChannel instanceof SocketChannel && targetChannel != self) {
                //转型
                SocketChannel dest = (SocketChannel) targetChannel;
                //将msg存储到buffer
                ByteBuffer buffer = ByteBuffer.wrap(msg.getBytes());
                //将buffer的数据写入通道；
                dest.write(buffer);
            }
        }
    }

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

客户端：

package com.ronghao.nio;

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

public class GroupChatClient {
    //定义相关属性
    private final String HOST = "127.0.0.1";//服务器的ip
    private final int PORT = 9999;//服务器端口
    private SocketChannel socketChannel;
    private String username;


    //初始化工作
    GroupChatClient() {
        try {
            //连接服务器
            socketChannel = SocketChannel.open(new InetSocketAddress(HOST, PORT));
            //非阻塞
            username = socketChannel.getLocalAddress().toString().substring(1);
            System.out.println(username + " is ok ...");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //发送数据
    public void sendInfo(String info) {
        try {
            info = username + " 说：" + info;
            socketChannel.write(ByteBuffer.wrap(info.getBytes()));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //读取从服务端回复的消息
    public void readInfo() {
        try {
            ByteBuffer buffer = ByteBuffer.allocate(1024);
            socketChannel.read(buffer);
            String msg = new String(buffer.array());
            System.out.println(msg.trim());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        //启动客户端
        GroupChatClient chatClient = new GroupChatClient();

        //启动一个线程，每隔3秒，读取从服务器发送数据
        new Thread(() -> {
            while (true) {
                chatClient.readInfo();
                try {
                    Thread.sleep(3000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }).start();

        //获取用户输入，发送到服务器
        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNextLine()) {
            String s = scanner.nextLine();
            chatClient.sendInfo(s);
        }
    }
}