Java NIO示例：多人网络聊天室完整代码

服务端: 

package cn.zhangxueliang.herostory.chatroom;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.*;
import java.nio.charset.Charset;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

/**
 * @ProjectName herostory3
 * @ClassName ChatRoomServer
 * @Desicription TODO
 * @Author Zhang Xueliang
 * @Date 2019/12/11 13:58
 * @Version 1.0
 *
 *  * 网络多客户端聊天室
 *  * 功能1： 客户端通过Java NIO连接到服务端，支持多客户端的连接
 *  * 功能2：客户端初次连接时，服务端提示输入昵称，如果昵称已经有人使用，提示重新输入，如果昵称唯一，则登录成功，之后发送消息都需要按照规定格式带着昵称发送消息
 *  * 功能3：客户端登录后，发送已经设置好的欢迎信息和在线人数给客户端，并且通知其他客户端该客户端上线
 *  * 功能4：服务器收到已登录客户端输入内容，转发至其他登录客户端。
 *  *
 *  * TODO 客户端下线检测
 *
 **/
public class ChatRoomServer {


    private Selector selector=null;
    static final int port=9999;
    private Charset charset=Charset.forName("UTF-8");
    private static HashSet users = new HashSet<>();
    private static String USER_EXIST="system message : user exist, please change a name用户名已存在,请更换一个名称";
    private static String USER_CONTENT_SPLIT="#@#";
    private static boolean flag=false;
    
    public void init() throws Exception{
        selector=Selector.open();
        ServerSocketChannel server = ServerSocketChannel.open();
        server.bind(new InetSocketAddress(port));
        server.configureBlocking(false);
        server.register(selector, SelectionKey.OP_ACCEPT);
        System.out.println("Server is listening now...服务端正在监听中");
        while (true){
            int readyChannels = selector.select();
            if (readyChannels==0){
                continue;
            }
            Set selectionKeys = selector.selectedKeys(); //可以通过这个方法，知道可用通道的集合
            Iterator keyIterator = selectionKeys.iterator();
            while (keyIterator.hasNext()){
                SelectionKey sk = keyIterator.next();
                keyIterator.remove();
                dealWithSelectionKey(server,sk);
            }
        }
        
    }

    private void dealWithSelectionKey(ServerSocketChannel server, SelectionKey sk) throws IOException {
        if (sk.isAcceptable()){
            SocketChannel sc = server.accept();
            sc.configureBlocking(false);
            sc.register(selector,SelectionKey.OP_READ);
            sk.interestOps(SelectionKey.OP_ACCEPT);
            System.out.println("Server is listening fron client: "+sc.getRemoteAddress());
            sc.write(charset.encode("please input your name."));

        }
        if (sk.isReadable()){
            SocketChannel sc = (SocketChannel) sk.channel();
            ByteBuffer buff = ByteBuffer.allocate(1024);
            StringBuilder content = new StringBuilder();
            try{
                while (sc.read(buff)>0){
                    buff.flip();
                    content.append(charset.decode(buff));
                }
                System.out.println("Server is listening from client: "+sc.getRemoteAddress()+" data rev is: "+content);
                sk.interestOps(SelectionKey.OP_READ);
            }catch (IOException io){
                sk.cancel();
                if (sk.channel()!=null){
                    sk.channel().close();
                }
            }
            if (content.length()>0){
                String[] arrayContent = content.toString().split(USER_CONTENT_SPLIT);
                if (arrayContent!=null && arrayContent.length==1){
                    String name = arrayContent[0];
                    if (users.contains(name)){
                        sc.write(charset.encode(USER_EXIST));
                    }else {
                        users.add(name);
                        int num = OnlineNum(selector);
                        String message = "welcome "+name+" to char room! Online numbers is :"+num;
                        BroadCast(selector,null,message);
                    }
                }else if (arrayContent!=null && arrayContent.length>1){
                    String name = arrayContent[0];
                    String message = content.substring(name.length()+USER_CONTENT_SPLIT.length());
                    message=name+" say "+message;
                    if (users.contains(name)){
                        BroadCast(selector,sc,message);
                    }
                }


            }
        }
    }

    private void BroadCast(Selector selector, SocketChannel except, String content) throws IOException {
        for (SelectionKey key:selector.keys()){
            Channel targetchannel = key.channel();
            if (targetchannel instanceof SocketChannel && targetchannel!=except){
                SocketChannel dest = (SocketChannel) targetchannel;
                dest.write(charset.encode(content));
            }

        }

    }

    private int OnlineNum(Selector selector) {
        int res=0;
        for (SelectionKey key:selector.keys()){
            SelectableChannel targetChannel = key.channel();
            if (targetChannel instanceof SocketChannel){
                res++;
            }
        }

        return res;
    }

    public static void main(String[] args) throws Exception {
        new ChatRoomServer().init();
    }


}

客户端:

package cn.zhangxueliang.herostory.chatroom;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import java.nio.charset.Charset;
import java.util.Iterator;
import java.util.Scanner;
import java.util.Set;
import java.nio.ByteBuffer;
/**
 * @ProjectName herostory3
 * @ClassName ChatRoomClient
 * @Desicription TODO
 * @Author Zhang Xueliang
 * @Date 2019/12/11 14:33
 * @Version 1.0
 **/
public class ChatRoomClient {

    private Selector selector = null;
    static final int port = 9999;
    private Charset charset = Charset.forName("UTF-8");
    private SocketChannel sc = null;
    private String name = "";
    private static String USER_EXIST = "system message: user exist, please change a name";
    private static String USER_CONTENT_SPILIT = "#@#";

    public void init() throws IOException
    {
        selector = Selector.open();
        //连接远程主机的IP和端口
        sc = SocketChannel.open(new InetSocketAddress("127.0.0.1",port));
        sc.configureBlocking(false);
        sc.register(selector, SelectionKey.OP_READ);
        //开辟一个新线程来读取从服务器端的数据
        new Thread(new ClientThread()).start();
        //在主线程中 从键盘读取数据输入到服务器端
        Scanner scan = new Scanner(System.in);
        while(scan.hasNextLine())
        {
            String line = scan.nextLine();
            if("".equals(line)) continue; //不允许发空消息
            if("".equals(name)) {
                name = line;
                line = name+USER_CONTENT_SPILIT;
            } else {
                line = name+USER_CONTENT_SPILIT+line;
            }
            sc.write(charset.encode(line));//sc既能写也能读，这边是写
        }

    }
    private class ClientThread implements Runnable
    {
        public void run()
        {
            try
            {
                while(true) {
                    int readyChannels = selector.select();
                    if(readyChannels == 0) continue;
                    Set selectedKeys = selector.selectedKeys();  //可以通过这个方法，知道可用通道的集合
                    Iterator keyIterator = selectedKeys.iterator();
                    while(keyIterator.hasNext()) {
                        SelectionKey sk = (SelectionKey) keyIterator.next();
                        keyIterator.remove();
                        dealWithSelectionKey(sk);
                    }
                }
            }
            catch (IOException io)
            {}
        }

        private void dealWithSelectionKey(SelectionKey sk) throws IOException {
            if(sk.isReadable())
            {
                //使用 NIO 读取 Channel中的数据，这个和全局变量sc是一样的，因为只注册了一个SocketChannel
                //sc既能写也能读，这边是读
                SocketChannel sc = (SocketChannel)sk.channel();

                ByteBuffer buff = ByteBuffer.allocate(1024);
                String content = "";
                while(sc.read(buff) > 0)
                {
                    buff.flip();
                    content += charset.decode(buff);
                }
                //若系统发送通知名字已经存在，则需要换个昵称
                if(USER_EXIST.equals(content)) {
                    name = "";
                }
                System.out.println(content);
                sk.interestOps(SelectionKey.OP_READ);
            }
        }
    }



    public static void main(String[] args) throws IOException
    {
        new ChatRoomClient().init();
    }
}